Trang_De cuong NC

8/7/2019 Trang_De cuong NC

1/43

TRNG I HC VINHKHOA NNG LM NG

===

===

CNG NGHIN CU LUN VN TT NGHIP

Chuyn ngnh: Trng trt

Tn ti:

NH GI KH NNG CHU HN CA MT S MU GING LANNG VNG PHA TY NGH AN

Cn b hng dn:PGS.TS. V Vn Lit

Ngi nghin cu: L Th TrangC s o to:Khoa Nng Lm Ng - i hc Vinh

VINH - 2010


2/43

I. TNH CP THIT CA VIC NGHIN CU TI1.1. t vn

La go l mt trong ba loi cy lng thc hng u , cung cp ti 23% nnglng , 16% protein dng tiu cho con ngi, ngoi ra n cn cung cp cc chtkhong v cc vitamin cng nh cc hydratcacbon.

Vit Nam, din tch canh tc la khong 4,36 triu ha, trong c 2,2triu ha l t thm canh, ch ng ti tiu nc, cn li hn 2,1 triu ha l tcanh tc la trong iu kin kh khn. Trong 2,1 triu ha c khong 0,5 triu hala cn, khong 0,8 triu ha nu ma to v tp trung hay b ngp ng v cn likhong 0,8 triu ha l t bp bnh nc. (V Tuyn Hong, 1995). Theo s liuthng k (nm 2002), trong nhng nm gn y din tch gieo trng la hngnm c khong 7,3-7,5 triu ha, th c ti 1,5-1,8 triu ha thng b thiu ncv c t 1,5-2,0 triu ha cn phi c s u t chng ng khi gp ma to vtp trung. Trong iu kin t ma, thiu nc ti s ko theo s bc mn v

phn nhng vng ven bin [T].Ngun ti nguyn nc phc v cho nng nghip ngy cng hn ch

c bo ng trong nhiu Hi ngh khoa hc ca th gii gn y. Cc nhkhoa hc u khng nh, kh hn nh hng nghim trng n an ton lngthc ca nhn loi v ti nguyn nc phc v cho nng nghip khng phi l vtn. Bn cnh , p lc dn s km theo s pht trin ca cc th lm giatng nhu cu nc phc v dn sinh v cc ngnh cng nghip. Chnh v vy,thiu nc ti trong sn xut nng nghip l vn ang c d bo cp thittrn qui m ton cu. Vi tm quan trng nh vy, ngi ta hoch nh mtth t u tin cho u t nghin cu tnh chng chu kh hn, chu mn v chungp ng trong lnh vc ci tin ging cy trng trn ton th gii [B].

Trong sn xut, mun t c 1kg thc, cn cung cp 5.000 lt nc.Nhiu quc gia nh Ai Cp, Nht Bn, c c gng ci tin nhm nng caohiu qu s dng nc, gim xung 1,3 m3/kg thc. Ti Trung Quc, cc nhchn ging ang th nghim m hnh cy la canh tc trn t thong kh, vithut ng aerobic rice. B r la s pht trin nh cy trng cn vi ch ti ci tin, nhm tit kim nc ti a [B].

Nng sut v sn lng la ca nc ta trong nhng nm gn y khng

ngng c nng ln mt cch vng chc. Nm 1996, nng sut la trung bnhca c nc t 37,7 t/ha, n nm 2000-t 42,4 t/ha v nm 2002-t 45,5t/ha. Trong , nng sut la vng cn t rt thp, t 10-18 t/ha. nhngvng t cn, kh khn v nc ti, thng s dng cc ging la a phng,c nng sut thp, thi gian sinh trng di, nhng c kh nng chu hn tt vcht lng go ngon. i vi nhng vng bp bnh v nc, th ngoi cc gingla a phng cn s dng mt s ging la thm canh, nhng kh nng chuhn km, hoc s dng mt s ging chu hn ci tin nhng cht lng cha

ph hp vi th hiu ngi dn a phng [H].


3/43

Vit Nam nm trong vng nhit i gi ma. Lng ma trung bnh 1900-2000 mm/nm, phn b khng u theo vng, theo thng trong nm, tp trung80-85% vo cc thng ma ma. Ch ma trn gy ngp ng, kh hn thtthng. Do , vic s dng cc ging la ci tin c kh nng thch nghi, chng

chu c vi hn hn, cho nng sut cao v n nh l mt bin php tit kimchi ph hu hiu nht. Ngoi ra, cc ging la mang gen chu hn cng cn thiti vi nhng vng trng la khc, bi tnh trng thiu nc c th xy ra huht cc vng trng la hoc s ri vo mt vi giai on sinh trng ca ca cyla [B].

Vic y mnh nng sut la cc vng thm canh v vng kh khn lunl phng hng chin lc v mc tiu c th cho cng tc chn to v phttrin ging la. c bit trong thi gian ti, nhng d bo v kh hu tri t ckh nng thay i, ngun nc ti trong nng nghip c th gim i, din tcht cn hoc thiu nc c th tng ln. Do vy, vic nghin cu v pht trincc ging la cho vng kh hn, thiu nc l ht sc quan trng, gp phn m

bo an ninh lng thc v xo i gim ngho cho ngi nng dn nhng vngc iu kin kh khn.

Theo hng ny, vic nghin cu nh gi ngun gen cc ging la cnthuc cc vng cao, vng kh hn c xem l cng vic khi u v cn tinhnh thng xuyn cho nhng chng trnh chn ging chu hn. Thnh cngca cng tc chn to ging ph thuc rt nhiu vo s lng v cht lng cavt liu khi u. Vt liu khi u cng nhiu v cht lng cng tt c hi to ra ging mi cng nhanh v thu c kt qu mong mun. Gp phn vomc tiu trn, chng ti thc hin ti nghin cu: nh gi kh nng chiuhn ca mt s mu ging la nng vng ni pha Ty Ngh An.1.2. Mc tiu1.2.1. Mc tiu chung

nh gi kh nng chu hn ca cc mu ging la nng ry c thu thp tivng ni pha Ty Ngh An.1.2.2. Mc tiu c th

Xc nh 5 7 mu ging la nng c kh nng chu hn phc v cho mc tiuchn to ging canh tc nh nc tri.1.3. Yu cu

nh gi kh nng chu hn ca cc mu ging giai on ny mmnh gi kh nng chu hn ca cc mu ging giai on cy m 3 lnh gi kh nng chu hn ca cc mu ging cc giai on sinh trng v

pht trin ngoi ng rung.2. TNG QUAN TI LIU2.1.C s khoa hc ca ti

Tnh a dng ca t nhin, s phong ph v a hnh, t ai, kh hu thitit v s phn b ca lng ma; cng vi s a dng ca cc bin d v ditruyn thng qua qu trnh chn lc t nhin to nn s phong ph ca ngungen cy trng [Thp]. Cy la l mt tp hp ngun gen qu tng ng vi nhiu

h sinh thi la khc nhau v hnh thnh h sinh thi la cn, la nc, la nc

3


4/43

su, la ni, la mn... Do cc vng sinh thi rt c th v khc bit m cyla cn a phng l ngun gen qu cho cng tc lai to, chn lc, b sung cctnh trng c trng nh tnh chu hn, chu rt v chng chu su bnh... cho cyla [Thp]. Xy dng chng trnh nghin cu c th tin hnh ci tin ging

la cn ph hp vi cc iu kin sinh thi c trng v s m t r rt cc ctnh mi ging, mi loi mi trng khc nhau l tiu chun chn lc c hiuqu.

Chin lc s dng ng ngun vt liu bn a v ngun bn ngoi(exotic) trong qui m qun th hi giao ci tin (advanced backcross) ang ckhuyn khch i vi cy trng, c bit l nhng tnh trng s lng c tngtc vi mi trng v cng phc tp (nh tnh chng chu kh hn, chng chumn, chng chu thiu ln,...). Chn to ging la thch nghi vi k thut canhtc tit kim nc (dng hnh aerobic), hoc tht s chng chu kh hn. Bncnh , cc vt liu lm nhim v bc cu vi kh nng kt hp (compatibility)cao cn c xc nh trong trng hp lai xa, lai khc loi, khc sub-species(di loi), hoc khai thc tnh trng thm ngon t cy c truyn, nng sut thpvo cy trng cao sn [B].

Nhm khc phc tnh trng thiu ht nc trong tng lai v gim thiuc nhng thit hi v nng sut do hn hn gy ra, trc ht cn thng qua conng hp tc, trao i, tranh th khai thc ngun gen qu ca cc ging la a

phng cng nh ging nhp ni; nghin cu su hn v di truyn tnh chngchu hn v hot ng ca cc gen chng chu.2.1.1. Khi nim v la cn v la chu hn

Hin nay, trn th gii c nhiu nh ngha ca cc nh khoa hc v cyla cn, la chu hn.

Theo Chang T.T v Bardenas (1965) [44] hay Surajit K. De Datta (1975)[56] u cho rng: La cn l loi la hon ton c gieo ht trn t kh, tkhng c b, n sng tu thuc vo m do lng ma cung cp (nh nctri).

Theo Gio s Micenr ti hi tho La ry Cao Bng-Vit Nam,t 9-11/3/1994 v theo nh ngha ti hi tho Bouake-B Bin Ng: La cnl la c trng trong iu kin ma t nhin t thot nc, khng c s tchnc trn b mt, khng c cung cp nc v khng c b [31].

Theo Khush G.S. (1984) v Trn Vn t (1986) [21]): La cn ctrng trong ma ma, trn chn t cao, t thot nc t nhin trn nhng chnrung khng c b hoc c p b v khng c nc d tr thng xuyn trn

b mt. La cn c hnh thnh v pht trin t la nc thch nghi vinhng vng trng la thng gp hn.

Cc nh chn ging Vit Nam cng quan nim v la cn tng t nhtrn. Chng hn, theo tc gi Bi Huy p (1978), La cn c hiu l loi lagieo trng trn t cao, nh l cc loi hoa mu trng cn khc, khng tch nctrong rung v hu nh khng bao gi c ti thm. Nc cho la ch yu donc ma cung cp v c gi li trong t [7].

Theo Nguyn Gia Quc (1994) [26] th la cn c chia lm 2 dng:

4


5/43

- La cn thc s (la ry, Dry rice hoc Upland rice): l loi la thngc trng trn cc trin dc ca i, ni khng c b ngn v lun lun khngc nc. Cy la hon ton s dng lng nc ma ngm trong t sinhtrng v pht trin.

- La cn khng hon ton (la nc tri, Rainfed rice): l loi la trng trin thp, khng c h thng ti tiu ch ng, cy la sng hon ton bngnc ma ti ch, nc ma c th d tr trn b mt rung cung cp cho cyla.

V Tuyn Hong v Trng Vn Knh, ... [7, Thp 2-3] nh ngha vphn vng cy la cn v chu hn theo loi hnh t trng nc ta nh sau:

- t ry (trng la ry, Upland rice hay Dry rice): nm cc vng trungdu, min ni pha Bc, min Trung, Ty Nguyn v mt phn ca ng Nam B.

- t la thiu nc hoc bp bnh v nc (loi hnh cy la nh nctri Rainfed rice): nm ri rc cc vng ng bng, trung du, ng bng ven

bin ng v Nam B, k c ng bng sng Hng, ng bng sng Cu Long.K c din tch t bng phng nhng khng c h thng thu nng hay h thngthu nng cha hon chnh vn nh nc tri hoc c mt phn t nc ti,rung v tr cao thng xuyn mt nc.

Do iu kin mi trng sng thng xuyn b hn hoc thiu nc nnnhiu ging la cn c kh nng chu hn tt. Tuy nhin, mt s ging la nccng c kh nng chu hn mt s giai on ca chng.2.1.2. Khi nim v hn v phn loi hn2.1.2.1. Khi nim v hn

Theo J.H Hulse (1989) [39], t hn, ting Anh l drought, xut pht tngn ng Anglo-Saxon c ngha l t kh (dryland).

Hin nay cha c mt nh ngha tng hp hon chnh v hn, song tugc nghin cu m c nhng khi nim khc nhau.

Dere C.Hsiao (1980) [T] nh ngha: Hn l s mt cn bng nc cathc vt th hin trong s lin quan hu c gia t-thc vt-kh quyn.

Mt cch tng qut, Gio s Nguyn c Ng (2002) [25] nh ngha:Hn hn l hin tng lng ma thiu ht nghim trng, ko di, lm gimhm lng m trong khng kh v hm lng nc trong t, lm suy kit dngchy sng sui, h thp mc nc ao h, mc nc trong cc tng cha ncdi t gy nh hng xu n sinh trng v pht dc ca cy trng, lm mamng tht bt, mi trng suy thoi, gy ra i ngho v dch bnh.

Theo Gibbs (1975), hn hay ng hn l s thiu ht nc cy trng l smt cn bng gia vic cung cp nc v nhu cu nc. Cn Mather (1986), hintng hn trong sn xut nng nghip thc cht l do thiu s cung cp mcho s sinh trng ti a ca cy trng t lng ma hoc t lng nc d trtrong t [39].2.1.2.2. Phn loi hn

Khi nghin cu v nguyn nhn gy nn hn, cc tc gi u cho rng victhiu nc ma thng xuyn l nguyn nhn chnh gy nn hn hn. Vn v

5


6/43

thi gian ma, khong cch thi gian gia cc ln ma quyt nh ti tnh chthn cc b hay hn khc lit [72, Thp]

Theo Gulialep v ctv; L Kh K, o Th Tun v ctv, chia hn thnh4 loi chnh sau ([Thp]:

- Hn khng kh: Do m khng kh thp 10-20% gy nn s ho tm thicho cy, v khi nhit khng kh cao gy nn m khng kh gim, lm lngnc bc hi dn n cc b phn non ca cy b thiu nc. Nu hn ko di dlm cho nguyn sinh cht b ng kt v cy nhanh chng b cht cn gi l cmnng. Tc hi nht l gi kh. Hn khng kh din ra trong thi gian di s dnti hn t.

- Hn t: Gy nn hn lu di, cy thiu nc, khng c nc ht,m cy b kh i nhiu v s sinh trng tr ln rt kh khn; hn t lun gynn s gim thu hoch, nu hn sm c th dn n mt trng, khng cho thuhoch.

- Hn kt hp: Khi c s kt hp c hn t v hn khng kh thng gynn hn trm trng, nu ko di c th lm tn hi ln n cy trng.

- Hn sinh l: Khi c y nc m cy vn khng ht c nc c thdo: nhit qu thp, hoc phn xung quanh r c qu nhiu cht gy c cho rhoc nng dinh dng xung quanh vng r l qu cao.

Theo s liu tng lng ma nhiu nm, thi gian phn b ma v m cc thng ca nc ta so snh vi bng phn loi hn ca D.P.Garrity 1984 thhn Vit Nam ch yu l hn t, hn khng kh i khi cng xy ra nhng cc

b min Trung v cc vng khc din ra trong thi gian ngn.2.1.3.Khi nim v c ch ca tnh chng, n (trn), trnh, chu hn v khnng phc hi sau hn2.1.3.1. Khi nim ca tnh chng, n (trn), trnh, chu hn v kh nng

phc hi sau hnTheo Gupta (1986), phn ln cc nh chn ging s dng nm thut ng

sau y khi ni n kh nng chng chu hn [36]:- Chng hn: l kh nng sng st, sinh trng v vn cho nng sut mong

mun ca mt loi thc vt trong iu kin b gii hn v nhu cu nc hay bthiu ht nc tng giai on no .

- Thot hn: l kh nng chn sm ca mt loi thc vt trc khi vn khng hong nc tr thnh mt nhn t hn ch nng sut nghim trng.

- Trnh hn: l kh nng duy tr trng thi trng nc cao ca mt loithc vt trong sut thi k hn.

- Chu hn: l kh nng chu ng s thiu ht nc ca mt loi thc vtkhi c o bng mc v khong cch thi gian ca s gim tim nng nc thc vt.

- Phc hi: l kh nng phc hi li s sinh trng v cho nng sut camt loi thc vt sau khi xy ra khng hong nc, nhng thit hi do s thiunc gy ra l khng ng k.

Kh nng chng hn thc vt c th l mt trong bn kh nng: thot hn,

trnh hn, chu hn v phc hi hoc l s kt hp ca c bn kh nng trn.

6


7/43

2.1.3.2. C ch ca tnh chng, n (trn), trnh, chu hn v kh nng phchi sau hn

Trn th gii c rt nhiu cng trnh nghin cu ca cc nh khoa hc vc ch chng hn trn cc loi cy trng cn nh la m, la mch, cao lng,

ng v c cy la go...Theo M.A Arraudeau (1989) [36], c mt vi c ch chu hn v cc c

tnh lin quan c cc nh chn ging cy trng s dng trong cng tc chnging la:2.1.3.2.1. C ch n (thot) hn (Escape)

Theo Tunner (1979) [31], thc vt nhm ny thng l cc loi c thigian sinh trng ngn, l cc cy on sinh, thng sng cc vng sa mc.Chng nhanh chng hon thnh vng i v kt ht trc khi xy ra hn. cim ca loi thc vt ny l s sinh trng v pht trin nhanh, c tnh mmdo.

Ngi ta s dng 4 c tnh c bn sau nghin cu c ch n hn [39].(i) Tnh chn sm (early maturity) l mt c tnh chung nht v d nht

chn ging. S chn sm dn n kh nng cho thu hoch trc khi hn hn tncng.

(ii) Tnh cm ng nh sng: lin quan n giai on sinh thc m trngkhp vi thi k c trin vng ma nhiu.

(iii) Tnh tr hon s hnh thnh hoa sm.(iv) Ri lon s hnh thnh chi (s nhnh la).

2.1.3.2.2. C ch trnh hn (Avoidance)y l nhng hot ng thc vt lm hn ch s mt hi nc v tng

cng s cung cp nc khi gp hn. gim s mt nc c th thng qua vic iu chnh ng m kh khng, hay

l t cun li hoc iu chnh din tch l. Cn tng cng cung cp nc thnh vo b r n su, n rng v s lng r nhiu, to... [31], [39], [h].

Mt s c tnh lin quan n c ch trnh hn l:(i) Mt h thng r n su s lm tng tng lng nc hu hiu trong cy.

B r n su ca ging la cn ch ra ging c kh nng chu hn tt. B r vh thng mch dn xylem ln trong r v trong thn r m bo cho s ht nc,dn nc tt hn.

(ii) Lp ph cutin c coi l hng ro ngn cn s mt nc khng quakh khng.

(iii) Hot ng ca kh khng: khi kh khng ng kn l triu chng rrng v tnh trng gim st nc trong cy. N ch xy ra khi cc t bo thc vtang b mt sc trng. Thc vt ng kh khng trong sut thi k hn. Khi ,cc l kh khng l mt c im thch nghi. (iv) Din tch l: khuynh hnggim din tch l hn ch ti a s mt nc thng qua vic gim qu trnhthot hi nc. Din tch l ln cc ging la cn, chu hn c truyn l mtdu hiu phi quan tm trong vic s dng c tnh lin quan n din tch lny.

7


8/43

(v) S cun l: tuy khng phi l c ch bo v nhng l bng chng vtnh trng gim st nc trong cy.2.1.3.2.3 C ch chu hn (Tolerance)

Theo Tunner (1979) [31], y l hot ng ca cy trng nhm duy tr chc

nng sinh l ca m t bo v kh nng ca thc vt thng qua vic iu chnh psut thm thu, tng nht ca cht nguyn sinh, lm t bo chu c s mtnc. C ch ny biu hin 3 c tnh sau [39]:

(i) S vn chuyn, tch lu cc cht ng ho l s di chuyn ca cc chtng ho t thn l vo ht cy la cn cy la cn. Theo nhiu tc ginghin cu c ch ca gen chu hn, chnh hot ng tng tch lu hydrat cacbon,c bit l cc axit amin, cc loi ng... lm tng tnh chu hn cy trng vcy la.

(ii) S iu chnh p sut thm thu v tnh thm ca t bo: n c th trhon v gp phn lm gim s cht cc m t bo khi b mt nc. Mt phn tnha dng di truyn cy la ghi nhn vn ny (OToole, 1982).

(iii) S co dn t bo: kch thc t bo c th thay i theo s tng hocgim ca lng nc tn ti.2.1.3.2.4. C ch phc hi (Recovery)

(i) Lp r n nng gp phn thc y nhanh s ht nc khi c ma xy rasau mt thi k hn.

(ii) Phn ng siu cm: t bo thc vt phn ng mt cch nhanh chngbng vic ng ngh khi c s thiu nc xy ra v cng ngay lp tc phc hihiu qu lm vic ca chng khi c nc tr li [39].2.1.3.2.5. C ch chng hn (Resistance)

Thc vt c c ch chng chu hn c th hin tt c cc c tnh vkh nng ht nc, gi nc v s dng tit kim nc [39].

(i) Gim s bc hi nc thng qua kh nng ng m kh khng, gimdin tch l, gc l hp v s vn ng ca b l c hng song song vi nhsng mt tri, hoc l cun li gim s bc hi nc qua b mt.

(ii) duy tr s cung cp nc thng c mt b r cc pht trin, n su,rng vi s lng r v mt r cao. Cc r to mp, c h thng mch dn(xylem) ln vic vn chuyn nc tr nn d dng.

(iii) Kh nng iu chnh tnh thm cao, tng kh nng tch lu cht ngho gim th thm thu, gip cho vic iu chnh p sut thm thu v tngsc trng m t bo, c kh nng duy tr nguyn vn v cu trc cng nh ccchc nng sinh l ca mng t bo v cc c quan t, m bo nht ca chtnguyn sinh lm cho cht nguyn sinh chu c s mt nc cao.

Ngoi cc c ch trn, mt s tc gi khc cn a ra kin sau:- Theo Ebleringer (1976), s ph lng t hay s mc lng c coi l mt

c im thch ng vi vic thiu nc.- Gc l: cc ging la m c gc l lng lo, xo cho nng sut cao hn v

n nh hn cc vng a phng sm xy ra hn.- S nhnh: s nhnh nhiu l bt li i vi cy la go v la m khi c

hn xy ra trc tr.

8


9/43

- Ru ht: gp phn kh quan trng cy la m quang hp, c coi nhl mt nhn t quyt nh n nng sut khi c khng hong m trm trng.

C rt nhiu cc c tnh k trn c cc nh chn ging s dng khi tinhnh cng tc chn ging la chu hn. Th nhng n s ko theo cc thay i

sau qu trnh chn lc hay cn gi l cc hiu ng pleiotropic, tm dch lhiu ng a hng ca tnh trng. Mt c tnh no lm tng hiu qu sdng nc thng i km vi hiu ng pleiotropic. Ngoi ra, tng kh nngchu hn s nhn c kt qu l gim nng sut [36].2.1.4. c tnh chng chu hn ca thc vt v cy la

Nhiu cng trnh khoa hc ca cc nh khoa hc nh Kaul (1967), Sanchez(1979), Jones (1979), Blum (1980) trn la m; Blum, Stout v Simpson (1978),OToole v Cruz (1979) trn la min; Boyer (1980) trn u tng; OToole vMoya (1978) trn la go... u ghi nhn vai tr ca gen chng chu hn ca cytrng cn (trch dn qua [31], [42], [43], [h]. Nhng nghin cu v di truyn tnhchng chu hn cng ch ra rng: kh nng chng chu hn biu hin qua cc cim vt hu hc, sinh vt hc, sinh l hc... thc vt ni chung v cy la ldo nhiu gen (a gen) kim sot v rt phc tp. Cc gen kim sot tnh chngchu c th trng lp nhau vi nhng stress khc nhau. Trong genome ca la mv la mch, ngi ta nhn thy cc nh hng di truyn kim sot s phn ngca cy i vi kh hn, mn v lnh nm trn cng bn di truyn nhim scth tng ng. C t nht 10 tnh trng s lng (QTLs) c tm thy i vitng tnh trng chng chu ny v chng nm chng nn nhau ti mt s vngnhim sc th [2].

Theo Nguyn Vn Hin (2000) [9], nguyn nhn ca tnh chu hn cytrng l nh vo cc yu t sau:

- c tnh gii phu hnh thi ca thc vt gim bc hi (mt khkhng, chiu dy tng cutin, chiu dy l).

- c tnh chng chu sinh l ca t bo cht i vi vic mt nc, nhit cao, nng mui (kh nng iu chnh tnh thm).

- c tnh sinh vt hc ca s sinh trng v pht trin cc ging (c bitl tnh chn sm).

- Tnh chu hn ca thc vt lin quan vi tnh thch ng sinh thi ca ccging. V d: ging la m chu hn cha nhiu lng nc lin kt hn ccging khng chu hn.

Bit c bn cht tnh chu hn cy trng cho php cc nh chn gingc th y nhanh tin ci tin ging chng chu v cng vic to ging lachng chu dng nh s l kh thi hn.

* Cy la phn ng vi hn nh th no?- C s l thuytMt s lng ln cc cng trnh nghin cu v qu trnh, c ch v cc

tnh trng phc tp quyt nh nng sut la trong iu kin nc ti hn ch(Fukai and Cooper, 2001) ch ra 3 c ch ln nh hng n nng sut l phthuc vo mc nghim trng ca hn; kh nng d on hn ca mi trng

9


10/43

mc tiu v tim nng sut, hnh thc trnh hn v chu hn. Mi quan h gia 3thnh phn ny vi cc iu kin hn khc nhau c trnh by trong hnh 1.

Hnh 1: S ca 3 thnh phn di iu kin mi trng hn (Timnng nng sut, kiu hnh v tnh trng chng chu hn) v mi quan h gianng sut vi cc hnh thc hn khc nhau la canh tc nh nc tri.

Khi khng gp hn th tim nng nng sut quyt nh bi nng sut ht.T bn tri sang phi ca s hn c xu hng nghim trng hn khi trnhn hoc chu hn tr thnh quan trng. Nu theo chiu ng t di ln hn cth d on c th la chn kiu hnh (chn sm) hoc thi gian gieo trng lla chn tt, nhng hn khng d on c th tnh trng chu hn l la chnduy nht (Fukai and Cooper 2001)

Hnh 1 cho thy rng khi mc hn trung bnh nng sut gim nh hn 50%, timnng nng sut l mt c ch quan trng trong TPE (target population ofenvironment). mc nghim trng hn, yu cu l chng chu hn, nu hnnghim trng nhng c th d on c vo giai on sinh trng cui th cch trnh hn l hiu qu vi cc ging chn sm. Hn xy ra gia v v khngtheo quy lut yu cu ci tin ging c kh nng chng chu hn. Tim nng nngsut l vt qua hn ch ca nng sut khng b p lc ca nc, dinh dng vsu bnh. Xc nh tim nng, nng sut nh sau (Monteith, 1977; Bnziger vcs., 2000; Mitchell v cs., 1998):

Nng sut ht l chc nng ca:RAD = Bc x ti trn ngy (15 20 MUm-2 iu kin nhit i)%RI = Phn bc x l xanh nhn (khong 95% ti thi im cy khp tn, nhng

ch 45% trong ton b chu k sng)GLD = Thi gian l xanh, hoc ngy s l duy tr mu xanh (120 ngy vi cc

ging ci tin v 140 ngy tr ln vi cc ging truyn thng)RUE = Hiu qu s dng bc x (khong 2,0 g sinh khi cht kh di iu kinkhng hn chHI = H s thu hoch ( 0,5 vi ging ci tin v 0,3 vi ging a phng)

10


11/43

Cc nh chn ging cy trng ci tin tim nng nng sut ch yu bngnng cao ch s thu hoch (thp cy, chn sm, nhnh nhiu), cy gn, thigian xanh ca l (GLD) thng qua din tch l ln hn trong thi k di.

Nh nng hc mong mun tng s dng hiu qu bc x RUE

(Radiation-use efficency) v GLD thng qua s dng dinh dng tt hn, thpcy, nhnh khe ng v chu phn bn.

Cc ging c tim nng nng sut cao nhn chung tin b hn cc gingc tim nng nng sut thp ngay c di iu kin hn trung bnh. C kh nngxy ra hiu qu trn ca tim nng nng sut (khng c bt thun hn) n btthun hn trung bnh c th c lng bng tng quan di truyn (rG) ca nngsut hai mi trng (khng hn v hn trung bnh). Hiu qu trn c th mongi khi (rG) gi tr dng c ngha.

Nng sut di iu kin nc hn ch c xc nh bng cc nhn tnh:

DM = T x WUEY = DM x HI

Trong : DM sinh khi cht kh, T l lng thot hi nc ca cy (0,6vi la cn v 0,3 vi la c ti), WUE l hiu qu s dng nc Y lnng sut, HI l h s thu hoch.

Sn lng cht kh (DM) ph thuc vo lng s thot hi nc ca cyv hiu qu s dng nc. Nng sut ht sau ph thuc vo h s thu hoch(HI) la quan trng nht ca cc thnh phn ny l HI, hn xay ra xung quanhthi k tr nh hng mnh nht ln t l u ht v HI ( th 2)

Hnh 2: Nng sut ca cng mt ging la IR36 trng 16 ngy khc nhau, btthun nc xy ra cc ngy khc nhau ca thi k ra hoa v bt thun ti a

11


12/43

ngy 2/5 cho thy nh hng mnh ca bt thun nc trong thi k ra hoa(T.C. Hsiao, O.P. Namuco, 1980)

Do vy cch tip cn chnh cho chn ging cho mi trng hn

(i) Ci tin tim nng nng sut, ty thuc vo kiu hn, chn lc thigian chn ph hp trnh hn

(ii) Chn lc chu hn trong tt c cc thi k sinh trng, trong thi k rahoa trnh nhng dng ging cn s dng qu nhiu nc giai on ny (to rakhi lng cht kh DM ln) v tho ht nc thi k tr khng khong nc.Vi la cn v cy trng a kh khc c th c c hi tng s lng nc thothi qua h thng r khe.

* Nhng thi im hn nh hng mnh n nng sut la- Hn u v:Trong giai on sinh trng sinh dng, s lng nc s dng tng

ng vi lng thot hi nc v sn phm cht kh to ra. Din tch l pht trinnhanh hn do c tng s nhnh v din tch l. Thot hi nc v s dng nchu hiu nhanh hn, khi khp tn thot hi nc xc nh ch yu bng dnnc thng qua kh khng. Khi kh khng ng thot nc thng qua lpcutin ca l. Khi kh khng m c hai qu trnh quang tng hp v thot hi ncu mc cao.

Ti mt s giai on sinh trng, m t s bt u gim v phn nghiu qu nht ca cy l gim thot hi nc. S sinh trng ca l v ko dithn rt nhy cm vi tnh trng nc v s nh hng t ngay qu trnh u.Hu ht cc cy trng qu trnh trao i kh khng b nh hng khi m tvn t khong 30%, nhng la th bt u gim khi m t 70%, iu nych ra rng la rt mn cm vi hn (Lilley and Fukai 1994). Mt biu hin khit gim m l l la cun li gim bc x ln mt l trnh thot hi nc,s cun l l hnh thc biu hin n gin ca s ho (mt sc trng) ca l.Mt hnh thc khc l s ng kh khng, phn ng ny gip cy gim thot hinc, bo ton nc v trnh thiu ht. Mc d vy, cy la c th gim mtnc thng qua ng kh khng nhng vn mt nc qua b mt l. La c lpcutin thp, lp sp bo v hn ch, cc kiu gen c lp sp cutin thp c th hosm hn bnh thng khi gp bt thun hn.

Nu hn xy ra rt sm th c th li thi gian cy trnh hn, nhng mc th gi dn n nng sut thp. Kiu gen khc nhau nh hng ca m gi nnng sut khc nhau, nhng c ch ny cha c hiu bit nhiu, mt schng trnh nghin cu cy tui m khc nhau nghin cu tp on c cckiu gen phn ng khc nhau khi tr hon cy.

Nu hn xy ra mun hn khi bt u nhnh: kh nng chu hn datrn din tch l cn xanh v kh nng nhnh ca chng sau khi hn, iu nychng minh v kh nng phc hi khc nhau ca cc ging ti giai on u sinhtrng ca cy (Lilley and Fukai 1994) [Breed].

- Hn gia v khng lin tc

12


13/43

Khi hn khng lin tc xy ra xung quanh thi im tr, nng sut ht bnh hng r rt. Hu ht cc nghin cu u cho thy kh nng kt ht rt mncm vi tnh trng nc, thi gian hn trong cc giai on pht trin ca cy cnh hng rt ln n kh nng u ht. Cc ging c thi gian tr khc nhau ch

vi ngy phn ng cng rt khc nhau. iu ny to cho vic so snh cc kiugen khc nhau thi gian chn l rt kh. Hn gia v khng lin tc xy ra ti btk mt giai on pht trin no, do vy ch c th p dng c khi chn nhngging ngn ngy trnh hn nh i vi kiu hn u v (hoc iu chnh ngycy).

Thi gian tr thng b tr hon 2-3 tun di iu kin hn, trong mt strng hp khng hnh thnh ht. S tr thot lin quan n sc trng v s trhon tr tng quan nghch vi tim nng nc ca cy (Pantuwan v cs., 2002).S tr hon pht trin ca hoa ci (ru ng) v hoa c (c ng) thng qua biuhin chnh lch tr c phun ru (ASI) do nh hng ca hn ng v s dngtnh trng ny rt hiu qu chn ging ng chu hn (Edmeades v cs., 1999).S dng s tr hon ra hoa nh mt tnh trng chn lc ging la chu hn.

- Hn cui vTrong iu kin hn xy ra cui v, tt c nc hu hiu vng r c

s dng cho thot hi nc. Cy s ho mi v cht. Nng sut ph thuc vo strnh nh hng ca hn xung quanh thi gian mn cm l thi gian tr v khnng s dng nc cc tng t khc nhau.

Nu din bin ca hn c th d on trc c th hng tt nht citin nng sut l trnh hn. Tuy nhin thi gian ra hoa vn b tr hon nu hncui v bt u trc khi ra hoa, sau ht hn; nhng mc tiu l nhn bit kiugen chn sm di iu kin khng hn v tr hon tr ti thiu nht khi gp hn.

Di iu kin hn cui v, s ht nc ca b r v hiu qu s dngnc quyt nh lng sn phm cht kh to ra (nng sut ht), cng nh cccy trng khc kh nng ht nc ph thuc vo chiu di r v mt r(OToole 1982, Lilley v Fukai 1994). Di iu kin nc v t bnh thngr la c tng chiu di cao hn ng nh minh ha trong bng sau:Bng 1. Tng s chiu di r (mm) ca la v ng di nhiu iu kin t

v nc khc nhauiu kin t/nc La t thp

canh tc nhnc tri

Lacn

Ng Tham kho

Trung bnh trn 8 aphng

8.880 Pantuwan vCS,1997

Hn trung bnh 1 aphng

6.980 3.495 Kondo v CS,1999

Hn nng ti 1 a phng 2.277 3.306 Kondo v CS,1999

Mc d vy, c nhng chng minh rng di iu kin hn nng, la cnthiu kh nng duy tr sinh trng b r. Mt so snh la cn v ng, tng

13


14/43

chiu di r gim 66% vi la v 8% vi ng, ngay c nhng ging la c b rtt hn trong iu kin hn trung bnh (Kondo v cs., 1999).

Phn b ca b r trong t i khi c phn khc nhau i vi la hn lcc cy khc. La t cao khong 70% chiu di r lp t mt 10 cm, nhng

ng ch 50% (Kondo v cs., 1999). La t thp canh tc nh nc tri n 85%l lp t trn, tri ngc vi cc cy trng khc nh ng, la ht nc cclp t su km hiu qu hn (Pantuwan v cs., 1997). V vy tng chiu di r lp t su vn l mt tnh trng cn quan tm i vi la cn.

C nhng chng minh la canh tc nh nc tri c kh nng xuyn suqua cc lp tng rn vi nhng kiu gen khc nhau (Samson v cs., 2002). Vncn cn chng minh mt r thp ti lp t su nh l mt kt qu tng khnng xuyn, c th ht nc v tng nng sut ht (Samson v Wade 1998).S tri ngc gia iu kin t hn v thi gian t ngp nc ym kh l thchthc i vi ci tin nng sut la thng qua ci tin h thng r la t thpcanh tc nh nc tri.

Cc cy duy tr hoc gi nc nhiu hn trong thi k chc ht s duy trb l xanh di hn, s kh l xy ra t hn, cc l s mt hn do thot hi nc.

Hiu qu s dng nc c xc nh bi cc bon c ng ha doquang hp trn mt n v thot hi nc, mt s cy trng bin d kiu gen c ngha trong s dng nc hiu qu (WUE) v hng n s dng nhng bin dny trong chng trnh to ging. la m thng s WUE l hu ch trong chnlc nng sut cao di cc iu kin nc hn l chn nng sut di iukin hn. la rt t ti liu cp bin d v kiu gen s dng nc ng gphnh thnh nng sut di iu kin hn, do vy cha tho lun thng s WUEcho chn ging la chu hn ti thi im ny.

Sc trng ca t bo c xc nh mt phn bng tim nng thm thu,cy c th iu chnh tim nng thm thu duy tr sc trng di iu kin

bt thun. iu chnh thm thu (Osmotic adjustment-OA) c th c mi quan hcao vi mt s gng (indica), n 1,5 MPa (mega pascal) khi o 70% lngnc lin kt (RWC-relative water content) (Babu v cs., 1999). Gi tr ny cth so snh vi k, mt loi cy trng chu hn. ng thi ci tin p sut thmthu k gi rng nng sut c th tng ln 5% di iu kin hn c th(Hammer v cs., 1999). Mc d vy khng c nghin cu no cng b v miquan h gia p sut thm thu vi nng sut ca la t thp canh tc nh nctri di iu kin hn (Fukai v cs 1999).

Theo kin ca Courtois v Lafitte th tri ngc vi la t thp, la cnt hoc khng c iu chnh p xut thm thu. vt qua vn ny v xcnh ng gp ca p sut thm thu n nng sut ht trong iu kin t caonhiu nh khoa hc c gng chuyn gen iu chnh p sut thm thu vongun gen la cn.2.1.5. nh hng ca hn n sn xut nng nghip v sinh trng ca cyla

Kh hn l yu t quan trng bc nht nh hng n an ton lng thc

ca nhn loi v iu ny nhiu ln xy ra trong qu kh trn nhng phm vi

14


15/43

rng hp khc nhau. Hn hn lm gim nng sut cy trng, lm gim din tchgieo trng v sau lm gim sn lng cy trng m ch yu l sn lnglng thc. Khi hn xy ra, con ngi y mnh thu li v cc u t khc,ng ngha vi tng chi ph sn xut nng nghip, do lm gim thu nhp ca

ngi lao ng nng nghip, ng thi ko theo mt lot cc hu qu kinh t xhi nghim trng nh bnh tt v i ngho...

Vit Nam l nc sn xut nng nghip chu nh hng nhiu ca yu tthi tit kh hu. Hn lun l mi nguy ln, e do v gy ra nhiu thit hi choi sng v sn xut nng nghip. Theo Cc Thy li, t nm 1960-2005 hnhn nng lm nh hng n v ng xun cc nm 1959, 1961, 1970, 1984,1986, 1993, nh hng ti v ma cc nm 1960, 1961, 1963, 1964, 1983, 1987,1988, 1990, 1992, 1993. Tuy nhin, nm c nh gi hn nng nht trongvng 45 nm qua l nm 1998 lm thit hi trn 5.000 t ng. Nguyn nhn hnch yu do ma ma kt thc sm hn mi nm khong mt thng nn lngma ch t 50-70% so vi trung bnh nhiu nm. Cng vi vic thiu ht lngnc ma, nhit cc thng u nm cng cao hn trung bnh nhiu nm t 1-30C. Tnh trng ny khin 898.962 ha la (chim 12% din tch c nc) bhn, trong c 122.081 ha b mt trng (Nguyn nh Ninh, 2005).

i vi cy la, hn vo lc cy ang sinh trng mnh ( nhnh) th chnh hng n sinh trng. Nhng nu hn vo giai on lm ng n tr thrt c hi v ngn tr s pht trin ca cc b phn hoa, gy nh hng r rt nnng sut v phm cht la. Theo Sasato (1968) v nhiu tc gi khc, cc giaion sinh trng khc nhau, cy la cn chu tc ng ca s thiu ht nctrong t rt khc nhau:

- Nu hn vo thi k cy la hi xanh th lm chm qu trnh hi xanh hoccht cy do sc chng hn yu. Thi k nhnh, cy la chu hn kh hnnhng cng b gim kh nng nhnh, chiu cao cy v din tch l. Thi kngm ng m gp hn th rt c hi, nht l giai on t bo sinh sn phn bogim nhim, lm thoi ho hoa, cn tr qu trnh hnh thnh gi v ht.

- Thi gian 11 ngy n 3 ngy trc tr, ch cn hn 3 ngy lm gimnng sut rt nghim trng, gy nght ng, cc b phn hoa b tn thngmnh, mm hoa b cht, dn n s bt th hoc qu trnh phi mu th tinh khkhn v hnh thnh nhiu ht lp.

- Khi ht lp, cy khng c cch no b nng sut na. Hn vo thi kchn sa lm gim trng lng ht, t l bc bng cao v b gim s tch lu

protein vo ni nh.Nhn chung, d thiu nc bt k giai on sinh trng no ca cy la

cng c th gy gim nng sut [27], [28], [59], [h].2.1.6.Nhng bin php nhm nng cao nng sut v kh nng chng chuhn ca cy la

tng nng sut la trong iu kin thiu nc, cc nh chn gingng thi phi tin hnh hai cng vic: ci tin cc c im nng hc v cc

bin php k thut canh tc; chn to cc ging c kh nng thch ng tt hn

vi iu kin hn [39], [51], [h].

15


16/43

Theo Trn Nguyn Thp (2001) [31], nhng bin php k thut kh hiuqu c th p dng l k thut ti luyn ht ging trc khi gieo trng, bn

phn vi lng tng kh nng chng chu, bn ln v kali hp l nhng bnm thn trng kt hp vi vic xi xo t v che ph mt rung... Tuy nhin,

bin php s dng ging chng chu l bin php tch cc, lu di v hiu qucao nht. Vi qui m ca mt vng sn xut ln, cn c k hoch qun l khaithc ngun nc v k thut ti nc tit kim; nghin cu s dng ging,chuyn dch ma v, thay i c cu cy trng ph hp vi tnh trng thiunc [12]2.2.Tnh hnh nghin cu, sn xut la cn trong v ngoi nc2.2.1.Ngun gc v s phn b ca cy la cn2.2.1.1. Ngun gc ca cy la cn

Theo Nguyn Vn Hin v Trn Th Nhn (1982) [10], la cn c phttrin t la nc thch ng c hn hn. La cn c pht trin theo hngrt ngn thi gian sinh trng, gieo sm v chu c hn, c bit l hn cuiv. Nhng trc c thuyt cho rng: la cn ch l do s t bin sinh thi dnti, qu trnh chn lc m ra (cn gi l thuyt chn lc). Watt (1891) chia ccging la di n ra 3 loi: Oryza granulata, Ness; Oryza officinalis, Wall;Oryza sativa, Linn. Theo ng, chi Oryza granulata pht sinh t loi t kh hnv trn ni cao, cn gi l mc r (wood rice), c th l thu t ca cy la cn.Thm ch, mt s tc gi c quan im la cn v la nc l khng cng ngungc (trch dn qua [27]).

Kato v ctv., (1982) [27], dng phn ng huyt thanh v c tnh c khnng kt ht nghin cu quan h xa gn gia cc loi la. ng xc nh giala cn v la nc khng c s phn bit v quan h thn thuc, ngha l chngc cng ngun gc. Ngoi ra, nm 1935, Hamada cng lm cc th nghimlin quan v chng minh rng quan im ca Kato l ng.2.2.1.2. S phn b ca cy la cn trn th gii v Vit Nam

Theo Surajit K. De Datta (1975) [56], la cn c trng ch yu trn balc a l chu , chu Phi v chu M La-tinh.

Theo Trn Vn t (1984) [21], mi trng trng la cn trn th gii cchia thnh 4 loi:

- Vng t cao, mu m, ma ma ko di (k hiu LF) ng v TyNam n , In--n-sia, Phi-lip-pin, Bng-la-t, Bra-xin, C-lm-bia...

- Vng t cao, km mu m, ma di (LU) Thi Lan, Mi-an-ma, Lo,Cm-pu-chia, vng ng Bc n , Vit Nam, B-li-via, M-xi-c...

- Vng t cao, mu m, ma ngn (SF)- Vng t cao, km mu m, ma ngn (SU) mt s nc Ty Phi.

Vit Nam, V Tuyn Hong, Trng Vn Knh v ctv., (1995) [15, 16,17, 18, 19], phn vng cy la cn v la chu hn theo loi hnh t trng nc ta nh sau:

- t ry (trng la ry): nm cc vng Trung du, min ni pha Bc,min Trung, Ty Nguyn v mt phn ca ng Nam B.

16


17/43

- t la thiu nc hoc bp bnh v nc (trng la nh nc tri):nm ri rc cc vng ng bng, trung du, ng bng ven bin ng v NamB, k c ng bng sng Hng, ng bng sng Cu Long. K c din tch t

bng phng nhng khng c h thng thu nng hay h thng thu nng cha

hon chnh vn nh nc tri hoc c mt phn t nc ti, rung v tr caothng xuyn mt nc.2.2.2.Tnh hnh sn xut la cn, la chu hn2.2.2.1. Sn xut la cn trn th gii

La l cy lng thc ng th 2 ca th gii v din tch gieo trng vtng sn lng. Song l cy lng thc hng u cc nc chu , nht lvng ng Nam Chu . Theo s liu FAO (1993), din tch canh tc ca thgii 148 triu hecta (chu 133,3 triu hecta chim 90,07%), c 67,83 triuhecta (chim 45,83%) thng b thin tai e do. Trong , c 55,53 triu hectathng b thiu nc (chim 37,39%), trong s ny 19,16 triu hecta l t cn(la ry-upland rice), 36,37 triu hecta t hon ton nh nc tri (rainfed rice);t ngp nc chim 12,5 triu hecta. Nng sut la vng t kh khn t 0,8-1,7 tn/ha, ch bng 20-40% nng sut la ca vng ch ng nc. Cc gingla gieo cy trn vng ny phn ln l ging a phng: di ngy, cao cy,chng km, nng sut thp, nhng cht lng go ngon.

Hin nay th gii c 114 nc sn xut la phn b trn tt c cc Chulc nhng tp trung ln nht l chu vi 30 nc trng la v din tch chim89,7% din tch la ton th gii. Theo s liu thng k 2001 din tch trng latrn th gii t nm 1998 n 2001 khong trn 151 triu ha.

Bng 2. Din tch, nng sut la trn th gii v cc Chu lcNm

Chu Lc

1999 2000 2001DT

(triu ha)NS

(tn/ha)DT

(triu ha)NS

(tn/ha)DT

(triu ha)NS

(tn/ha)

Ton Th gii 156,891 3,90 153,783 3,89 151,624 3,93Chu Phi 7,662 2,28 7,696 2,25 7,680 2,13Bc Trung M 2,030 5,73 1,879 5,82 1,957 6,08Nam M 6,017 3,67 5,705 3,62 5,150 3,84Chu 140,430 3,96 137,760 3,96 136,077 3,99

Chu i Dng 0,159 8,86 0,140 8,00 0,194 9,17Chu u 0,593 5,23 0,603 5,22 0,566 5,59Ngun: Thng k ca FAO, 2001

Chu Phi c 41 quc gia trng la, nc c din tch trng la ln nhtchu lc ny l Nigeria 2,207 triu ha, nc din tch la nh nht l Reunion chc 40 ha. Nng sut la cao nht Chu lc ny l Ai Cp t 9,283 tn/ha. BcTrung M c 14 nc trng la, nc sn xut la ln nht l M 1,341 triu hav cng l nc t nng sut la cao nht 7,21 tn/ha, nc c din tch t nhtl Jamaica ch c 24 ha, nng sut thp nht l Haiti 2,012 tn/ha. Nam M c 13nc trng la, Brazin c din tch ln nht 3,142 triu ha, nhng nng sut cao

nht l Peru t 6,74 tn/ha v nng sut thp nht l Bolivia 1,92 tn/ha. Chu

17


18/43

c 30 nc trng la, nc trng la ln nht Chu lc ny v cng l ln nhtth gii l n 44,790 triu ha, thp nht l Brunei ch c 230 ha. Nng sutla cao nht chu l Hn Quc t 6,88 tn/ha, sau l Nht Bn 6,64 tn/hav Trung Quc t 6,20 tn/ha thp nht l Iraq ch t 0,9 tn/ha. Chu i

Dng l Chu lc c t nc trng la nht ch c 5 quc gia trng la, din tchln nht l c 186.100 ha v cng l nc t nng sut cao nht 9,45 tn/ha.

Nc c din tch nh nht l Micronesia ch c 80 ha v cng c nng sut thpt 1,13 tn/ha. Chu u c 11 nc trng la. Nc trng la ln nht l Italia217.622 ha v thp nht l Rumani ch c 1.155 ha, Ty Ban Nha l nc tnng sut la cao nht chu u l 7,84 tn/ha v Rumani cng c nng sut lathp nht chu u 1,261 tn/ha.

Theo Nin gim thng k v cy la 1997 [58], tng din tch trng latrn th gii l 148 triu ha. La cn chim 18.960.000 ha v la nc tri chim36.370.000 ha, phn b ch yu ba chu lc , Phi v M Latin. Tuy nhin,nng sut cn rt thp [46], [56].

Trn th gii la c trng 5 h thng chnh l: Vng ch ng ti tiu,t thp chu nc tri, t cao, vng ngp nc, t ngp do thy triu. Ckhong 80 triu ha chim 55% t trng la ca th gii c ti tiu ch ngtrong sut v gieo trng. Ngi ta c tnh khong 75% sn lng ca th giithu c t cc vng c ti tiu ny. m bo an ninh lng thc, hn ch cc tc ng bt li ca cc iukin kh khn FAO a ra khuyn co: tng cng cng tc nghin cu to racc ging la mi ph hp vi tng vng sinh thi, hon thin k thut canh tcti cc vng sinh thi . ng thi ch r: y l qu trnh khng ngng ngh, vch c nh vy mi c th y i ngho, lc hu.

La cn l mt b phn cu thnh trong sn xut la, c trng bi ccnng h nh, sinh sng cc vng ngho nht trn th gii trong h thng canhtc nh nc tri nhng ni khng th cung cp nc ch ng hoc hn hn l

ph bin. Tuy nng sut khng cao nhng la cn vn l loi cy trng khng ththay th nhng vng cao, vng kh khn v nc ti; ng thi l nguncung cp lng thc ti ch quan trng ca ngi dn tc thiu s.

chu , khong 50% t trng la l canh tc nh nc tri v mc dnng sut la nhng vng c ti tng gp 2 n 3 ln 30 nm trc y,nhng vng canh tc nh nc tri nng sut tng ln mc rt nh, bi vnhng vng ny s dng ging la ci tin rt kh khn do mi trng khngng nht v bin ng. Mt phn bi v to ging chu hn cn rt t [].

Nng sut la cn c th c ci tin hn trong iu kin thm canh vchm sc tt. Vi iu kin l tng cc trm tri th nghim, ngi ta thuc nng sut 7 tn/ha Philippine (De Datta v Beachell, 1972), Peru l 7,2tn/ha (Kawano, 1972) v 5,4 tn/ha Nigieria (Abifarin, 1972) [37], [56].

Hin nay, cc phng thc canh tc la cn trn th gii rt phong ph, baogm t du canh Malaysia, Philippine, Ty Phi v Peru... n hnh thc canh tcc trang b c gii hin i mt s nc M Latin nh Braxin, Colombia...

18


19/43

Nm 1997, ton chu M Latin c hn 3,5 triu ha trng la cn v lanc tri. Theo CIAT (1973), nng sut la cn trung bnh t 1,3 tn/ha. Braxinc din tch trng la cn ln nht, 3,5 triu ha trn 5,4 triu ha din tch trngla. Nng sut t t 1,2-1,5 tn/ha (De Datta v Beachell, 1972) [56], [57].

2.2.2.2. Sn xut la cn Vit NamTheo tc gi Bi Huy p (1978) [7], canh tc la cn Vit Nam bao

gm: h thng du canh theo cng thc sn xut nguyn thu, n gin nht trncc loi t dc nn nng sut thp; v h thng trng la nh canh trn cc loit cao, nng nh canh hay trn cc loi t mu cao ven sng, dc bin hoc cc khu vc ng bng, khng c kh nng ti nc nhng c u t chm bnnn nng sut c cao hn.

Vit nam, din tch canh tc la khong 4,36 triu ha, trong c 2,2triu ha l t thm canh, ch ng ti tiu nc, cn li hn 2,1 triu ha l tcanh tc la c nhng kh khn. Trong 2,1 triu ha c khong 0,5 triu ha la cnv 0,8 triu ha nu gp ma to, tp trung s b ngp ng v cn li 0,8 triu ha lt bp bnh nc (V Tuyn Hong, 1995). Nng sut la cn, la nng haynng sut la cc vng bp bnh nc ti rt thp, ch t trn di 10-12t/ha, bng 30-50% nng sut bnh qun ca c nc.

Trong 30 nm tr li y, cng tc nghin cu, chn to cc ging lacn, la chu hn ang l mt mc tiu quan trng ca nhiu Vin, Trung tmnghin cu quc t cng nh trong cc chng trnh chn to ging quc gia [].

Theo kt qu thng k ca Cc Khuyn nng-Khuyn lm nm 2001, hinc nc c khong 199.921 ha la cn, ch yu phn b cc tnh min ni phaBc (54,3%); Ty Nguyn (25,3%) cn li l vng ni thuc cc tnh Bc Trung

b (6,0%); Duyn hi min Trung (9,3%)... Theo bo co ca cc a phng,sn lng la cn ton quc nm 2001 t khong 241 nghn tn. Tuy chim mtdin tch khng ln so vi din tch la nc nhng la cn l cy trng truynthng, l phng thc gii quyt lng thc ti ch i vi ng bo cc dn tct ngi vng ni. Pht trin la cn gp phn n nh i sng, hn ch du canhdu c t nng lm ry, gi gn, bo v mi trng sinh thi, nht l i vi cctnh c t l la cn cao so vi tng din tch la ca tnh nh: Lai Chu:52,83%, Sn La: 48,35%, Lo Cai: 27,08%... Tuy c vai tr quan trng song snxut la cn hin cn rt nhiu hn ch. Cc ging la cn hin nay ch yu lcc ging a phng (99%) cao cy, nng sut thp, bp bnh (trn di 10t/ha) v c xu hng gim dn. Nguyn nhn ch yu l do la cn c trngtheo phng thc qung canh, t b khai thc cn kit, khng c bn phn bsung. Phn ln t trng la cn l t dc, hng nm b ra tri mnh, ph t

b gim nhanh chng lm cho ngun dinh dng t nhin b cn kit [].Theo s liu thng k, trong nhng nm cui Th k XX, din tch gieo

trng la hng nm bin thin t 6,77 triu ha nm 1995 n 7,67 triu ha nm2000, trong c 1,5-1,8 triu ha thng b thiu nc v 1,5-2,0 triu ha cn cs u t chng ng khi gp ma to v tp trung. Trong iu kin t ma,thiu nc ti ko theo nh hng ca mn v phn nhng vng ng bng

ven bin.

19


20/43

Nm 1995, nng sut la bnh qun t 36,9 t/ha v sn lng t 24,96triu tn; n nm 2000 nng sut t 42,4 t/ha v sn lng t 32,53 triu tn(Tng cc thng k, 2001). Mc d c s gia tng r rt v nng sut v snlng la, nhng s gia tng khng ng u gia cc vng. Ngoi 2 vng

trng la trng im l ng bng sng Hng (BSH) v ng bng sng Culong (BSCL), cn cc vng khc nh: Ty Nguyn (TN), Ty Bc (TB), BcTrung b (BTB), ng Bc b (BB), ng Nam b (NB) v Duyn hi NamTrung b (DHNTB) th nng sut la ch bng 62,3 n 95,6% nng sut bnhqun chung c nm ca ton quc. Nu so snh vi vng thm canh ch ngnc th nng sut la vng sinh thi kh khn ch bng 64,2-79,7%.2.2.3. Tnh hnh nghin cu la cn, la chu hn trong v ngoi nc2.2.3.1. Tnh hnh nghin cu la cn, la chu hn trn th gii

Trong vng 30 nm tr li y, cng tc nghin cu, chn to cc ging lacn, la chu hn ang l mt mc tiu quan trng nhiu vin, trung tm nghincu quc t cng nh cc chng trnh chn to ging quc gia.

Nm 1970, Vin nghin cu la quc t (IRRI) thnh lp ngnh la cn doTin s T.T. Chang ng u [55].

Nm 1973, IRRI bt u a ra Chng trnh nh gi v ng dng ditruyn (GEU). Mt trong nhng mc tiu chnh ca chng trnh ny l thu thpngun gen, nghin cu vt liu v chn ging la chng chu hn. y l mtchng trnh ln, c s ng gp ca nhiu chng trnh nghin cu la ccnc sn xut la go, c bit l cc nc chu . Chu Phi v M Latin cngthnh lp nhng trung tm quc t nghin cu v la cn, la chu hn nhIRAT, IITA, WARDA v CIAT [54].

Do yu cu v an ton lng thc, vo nm 1983, UREDCO, l tn gi caban iu hnh ca cc trung tm nghin cu la cn, c thnh lp. T y, ccchng trnh nghin cu la cn cc nc c m rng [21], [30]. Mt lotnhng thnh tu nghin cu v la cn t c nh sau:2.2.3.1.1. Nhu cu nc v kh nng chu hn ca cy la

S tin ho ca cy la nh l mt cy lng thc quan trng trn c stng v phn b ca lng ma(Huke, 1976). Nh vy nhu cu nc v cngquan trng i vi la. Nhu cu ny khc nhau gia cc nhm nh la nc, lacn, la chu nc su hay la ni. Nhu cu nc ca la cng khc nhau giacc thi k sinh trng, pht trin ca cy nh nu thiu nc giai on sinhtrng sinh thc c th nh hng nghim trng n nng sut la ca c la cnv la c ti. Hn nh hng n sinh trng pht trin ca cy nu qu giihn s lm cht cy. Nhng ging la cn c th phc hi khi ti nc hay cma, nhng nhng ging la c ti kh nng phc hi km hay khng th phchi.

Ma u v cung cp nc cho gieo ht, lng ma thp hoc cao unh hng n t l ny mm i vi la canh tc nh nc tri, nhng khngnh hng ln i vi vng trng la c nc ti. Giai on nhnh lacn lng nc ln hn v gim dn n khi chn. Giai on nhnh thiu

nc hay tha nc (nc qu su) cng hn ch kh nng nhnh ca la.

20


21/43

Giai on tr thiu nc dn n hin tng nghn ng khng tr thot, t llp cao. Giai on vo chc thiu nc cng dn n t l lp cao gim nngsut.

Nc bn cnh vic cung cp cho cc hot ng trao i cht ca cy cn

c tc dng iu ho tiu kh hu qun th rung la, hn ch c di, su bnh,cung cp oxy cho b r la pht trin. Ngun nc cung cp cho sinh trng cala v cng quan trng l ma, nu nc ti nhng khng c ma sinhtrng pht trin ca la cng km hn.

Nc c nh hng n ton b i sng ca cy la v l yu t quytnh n sn xut la. Phn b lng ma l yu t quan trng hn ch nng sutca la canh tc nh nc tri. Loi hnh canh tc ny chim khong 80% dintch trng la Nam v ng Nam chu . Vng ny bin ng ca lng matrong thng v trong nm mnh hn bin ng ca nhit . Hu ht cc ncng Nam chu nh Brunei, Cambodia, Indonesia, Philippine v Vit Nam clng ma khong 2000 mm/nm. iu ny c ngha l nhng vng canh tcnh nc tri ch trng c mt v la trong mt nm vo ma ma, ngay cnhng ni c lng ma thp 1200 mm n 1500 mm cng trng c. Nhngvng canh tc nh nc tri ch yu l la nng (la ry) min ni pha Bc,Bc Trung B v Ty Nguyn. La nng khng th sinh trng pht trin cnu lng ma hng thng thp hn 200 mm (Brown,1969). Phn b lng ma200 mm nhng tp trung vo 2-3 ngy, sau 20 ngy khng c ma khng tt

bng lng ma phn b u (D. Datta,1981).2.2.3.1.2. Nghin cu v c trng hnh thi v sinh trng

Hesagawa (1963) [56], tng hp s liu t nhiu ngun khc nhau v rt rakt lun: trong giai on ny mm, ht la cn c khuynh hng ht nc nhanhhn cc ging la nc. Theo Chang v Bardenas (1965) [44], cc ging la cnvng nhit i ny mm rt nhanh sau khi ht c gieo vo t v sc ny mmca ht ging cng kho nn gip chng cnh tranh tt vi c di.

Theo T.T. Chang v ctv., (1972) [56], hu ht cc ging la cn aphng thng c thn to v dy, b gi ci nhanh chng khi la chn nn chngd ng vo giai on chn.

Mt nghin cu v chiu cao cy ca 252 ging la cn trong ma ma chothy: chiu cao cy dao ng t 80 cm cc ging la cn Nht Bn n 175 cm mt vi ging la nng Thi Lan. Cc ging la cn chu Phi v Philippinenhn chung cao trn 150 cm khi trng trong iu kin rung cn [56].

Cc th nghim ca IRRI v kh nng nhnh giai on 60 ngy saugieo (Chang v Bardenas 1965; Ono 1971; Chang 1972; De Datta v Beachell1972; Kawano 1972; Krupp 1972) [56], [31], [44], [h], u cho thy cc gingla cn nhnh t hn so vi cc ging la nc. Theo Chang, T.T. (1972) [45],kh nng nhnh km v bin ng cc ging la cn lm hn ch nng sutca chng ngay trong iu kin canh tc ph hp. Ngoi ra, Hasegawa (1963)[56], thy rng nhnh cp 1 u tin ca cc ging la cn thng xut hin nch l tht u tin. Trong khi cc ging la nc, n xut hin nch l tht

th hai.

21


22/43

Theo Chang v Benito S. Vergara (1975) [39], phn ln cc ging la cnnhit i c b l mu xanh nht, thng i km vi c im l di v r xung.Cc ging la cn chu Phi v Philippine c gc l ln, thng gp i gc lca cc ging bn ln. Tuy nhin, mt vi ging la a phng, v d ging

Jappeni Tunkungo, li c b l di, ng v xanh thm. Ngoi ra, Chang (1972)[45] nhn thy cc ging la cn a phng c din tch l ln hn cc ging la

bn ln, nhng ng thi tng trng v s l ca cc ging la cn li km hnla nc.

Hasegawa (1963) [56], lm th nghim v b r la cn Nht Bn thy rng:hai ging la cn c b r n su hn 20 cm trong khi ch c mt vi r ca 2ging la nc tham gia th nghim t ti su ny.

Cc nghin cu IRRI (1971) v nhiu tc gi khc khng nh: r ca mts ging la cn s pht trin di hn v dy hn khi xy ra khng hong v m. Nhng nghin cu la giai on sinh thc trong iu kin trng cn chothy: b r ca cc ging la cn (nh OS4 hay Palawan) va di, va to mp,cn cc ging la bn ln (IR8 hay IR20) li c s r t v nh [31], [37], [43],[44], [45], [48], [53], [54], [55].

Theo Loresto v Chang (1972) [45], s t hp ca hai hoc nhiu hn ccc trng b r di y hnh thnh nn cc ging la cn chu hn tt nh: tl cc r to cao, b r di v to, h thng r dy c v h thng r nhnh, r ph

pht trin ng u xung quanh cc r chnh.IRRI (1974) [55] so snh b r ca 25 ging la vi b r ca ng v la

min, l hai loi cy trng c kh nng chu hn kh hn la. T l r/thn l cang (146 mg/g) v la min (209 mg/g) cao hn nhiu so vi cc ging la. Tuynhin, ging la khc nhau th t l ny cng khc nhau. Chng hn, ging lamn cm vi hn IR20 c t l r/thn l rt thp (49 mg/g) trong khi phn lncc ging la cn chu hn (OS4, E425, Palawa, Dular, M1-48...) c t l ny gntng ng vi ng (101-120 mg/g). Theo Chang (1972); Kobata v cvt.,(1996) [56], [31], t l r/thn l ca cc ging la cn cao hn la nc v ngtin cy c hai iu kin nc v hn.

Bashar, Chang v cng s (1989) [31], nghin cu v di truyn tnh trngchu hn cho rng: cc c im ca b r c lin quan n kh nng chu hn cc ging la cn v la nng ry l kch thc b r ln, s mch dn trong rnhiu. Cn Namuco v ctv., (1993) [31], khi nghin cu v tng quan giang knh b r vi tnh chu hn kt lun: ng knh r ln nht ccging chu kh v nh nht cc ging mn cm. dy c ca r cng ctng quan cao vi tnh chng chu hn. Kt qu phn tch phng sai ch rarng mt r v s mch dn trc tip iu chnh p tnh chng chu hn.

Yu L.X., Ray, OToole v Nguyn H.T. (1995) [31], tin hnh th nghimv kh nng m xuyn qua mng sp nhn to ca r la nhn xt: r la chuhn c kh nng m xuyn qua mng ln hn la nc c v s lng v chiudi r.

Nghin cu thi gian sinh trng ca 284 ging la cn chu hn IRRI

thy c s bin ng t 80 n hn 170 ngy trong ma ma. V d ging la

22


23/43

cn Rikuto Norin 21 c thi gian sinh trng 95 ngy cn C22 l 125 ngy. Vinhng ging khng phn ng nh sng, thi gian sinh trng bin ng t 90-145 ngy trong ma kh. Theo Chang T.T. v Benito S.V. (1975), la cn thngtr mun 1-15 ngy trong iu kin rung cn [56].

Theo Chang v Benito (1975) [56], phn ln cc ging la cn c kiu bngto, di v khoe bng, c kh nng chng chu vi tc nhn gy hi. Theo cc tcgi ny, y l c tnh mong mun ca bt k ging la trng cn no. Nhnchung, ht la cn thng trn v to nn khi lng 1000 ht cao. Mc d vyvn c loi ht thon di.

Theo Jana v De Datta (1971); Chang (1974) [56], mt c im rt dnhn bit la cn l kh nng tp trung to ra cc bng hu hiu vi cc hthon ton y chc. Chnh iu ny gp phn lm cho nng sut cc ging lacn chu hn n nh, cho d khng cao.

Hm lng Amylose trong phn ln cc ging la cn chu Phi v ngNam l cao trung bnh, t 22-26%. Nhit ho h bin ng t thp n caonhng hu ht l trung bnh. Ring cc ging la cn Nht Bn c hm lngAmylose thp (15%) (IRRI, 1974) [31], [56].

V tim nng nng sut v tnh n nh ca cc ging la cn, nhngnghin cu ca Jana v De Datta (1971); IRRI (1971, 1972, 1973) [56], [31] ucho thy: khi xy ra hn nghim trng, nng sut ca tt c cc ging la uthp cho d c y dinh dng kt hp vi tr c hiu qu. Do vy, nng sutht thun ch phn nh mc trnh hn hn l tnh chu hn, c bit nu lac thu hoch trc khi thi k hn kt thc (Levitt, 1972). Nhng nu hn ktthc trc khi thu hoch th nng sut ht li ph thuc nhiu hn vo kh nng

phc hi ca ging la [39], [56].Kt qu th nghim ca IRRI (1971); Jana v De Datta (1971); Abifarin

(1972); Chang (1972); De Datta v Beachell (1972); Kawano (1972), u chorng: kh nng nhnh thp ca phn ln cc ging la cn l tr ngi chnhcho nng sut. Ngoi ra, Ono (1971) nhn thy nng sut ca cc ging la cnthp l do kiu cy cao v d ca chng. Mt nguyn nhn khc phi k n l tnh mn cm cao vi bnh bc l, kh vn, v bnh virus, mc d chng ckh nng chng bnh o n. Nhng b li, nng sut la cn vn tng i nnh do chng c kh nng to ra cc bng hu hiu to v ht chc ngay trongiu kin hn [37], [56].

T kt qu nghin cu tp on 4000 ging la cn a phng, cc nhkhoa hc IRRI tng kt: cc ging la cn a phng thng cao cy; b r nsu v phn b dy c; kh nng nhnh km v khng tp trung; b l muxanh nht, l di, rng bn v r xung, ch s din tch l khng cao; bng to vdi; hu nh khng phn ng vi nh sng. Thi gian sinh trng t 95-140ngy. Ht to, trn, hm lng tinh bt t thp n cao trung bnh (18-25%); nhit ho h trung bnh. T l lp thp. Chng chu gii vi hn, bnh o n; mncm vi ry v bnh virus. Chng chu vi iu kin t thiu ln, tha nhm vmangan. Chu phn km, c bit l phn m. Nng sut rt thp nhng n nh

[7], [56], [31], [44], [45], [48].

23


24/43

2.2.3.1.3. Nghin cu v cu to gii phu v hot ng sinh l chng chu hnTheo John C. OToole (1982) [39] vai tr lp sp cutin nh l mt hng ro

ngn cn s mt nc khng qua con ng kh khng, mc d cha c mi linh r rng vi kh nng trnh hn cy la.

Nhiu tc gi cho rng, s ng kh khng thc vt khi xy ra hn l mtc im thch ng. Henzell (1975) v Kaul (1971) li nhn thy cc dng la mv la mch chng hn nht c t bo kh khng khng mn cm. Nhng nghincu ca Ludlow (1980) khng nh thm rng: phn ln cc gen khng mt nckhng lm ng kh khng. Theo tc gi, y c s iu chnh p sut thmthu ca t bo kh khng trong iu kin hn [31].

Cc nh sinh l cho rng, p sut thm thu ng vai tr quan trng, to nnkh nng chng chu hn cy trng. Trong iu kin hn, cy trng c p sutthm thu cao lun duy tr c lng nc trong t bo, s m ca kh khng,ng thi duy tr qu trnh h hp v quang hp [6], [29], [34], [39], [40], [41].

Theo F.W.G. Baker (1989) [39], vai tr ca p sut thm thu lin quan mc c ngha vi nng sut la m trng trong iu kin thiu nc v hn.

Nhng nghin cu gn y khng nh: p sut thm thu cng lin quan n tl ny mm v ngh c th s dng xc nh nhng kiu gen c p sutthm thu cao.

Morgan (1999) [6] kt lun: ngm ht phn vo dung dch PEG(polyethylen glycol) 50% cng vi 10 m KCL, nhng ging la m c p sutthm thu thp th s co th tch t bo ht phn xy ra c ngha; ging c psut thm thu cao th kch thc ht phn khng co li, thm ch c chiu hngtng. p sut thm thu ca t bo ht phn c xc nh lm c s trong chnto ging la m chu hn. Nhng ging la m chu hn s c p sut thm thucao v ngc li.

Mt trong nhng c ch to nn tnh chng hn ca thc vt l qu trnhhnh thnh v tch lu proline. Nhiu tc gi nh Singh (1973); Blum v Ebercon(1976); Withers v King (1979); Hanson (1980); Stewart v Hanson (1980);Rajagopal v Sinha (1980) [42], [32], [49], [61], [62], [64], [66] nghin cuv chng minh vai tr ca proline trong vic cn bng nc v gi nc ccm t bo. Bernand (1989) xy dng c phng php xc nh c hmlng proline trong l la [40]. y, c th ni rng proline nh l mt yu tchng li s mt nc cy trng trong giai on thiu nc, biu hin:

- Khi b l b stress nc th khi m t bo c s xm nhp ca prolineiu khin gi li hm lng nc cao hn v l c cng ln.

- Proline kch thch hot ng ca phn ng nitrat ho, bo v v km hmhot ng ca enzim trong sut giai on hn thiu nc.

- Proline to iu kin thun li cho qu trnh trao i cht gii hn mtnc nht nh.

Theo nhng nghin cu ca Perrier (1961); Gates (1968); Blum (1980)[31], [39]... trn cy la m, c mt b l hp v xu hng gim din tch l l sthch nghi vi tnh trng thiu nc ca cy, lm hn ch ti a nhu cu s dng

nc.

24


25/43

Bewley (1979) [41] cho rng, mng t bo to thnh v tr trung tm choqu trnh trao i cht, v vy tnh chng chu s mt nc ca mng t bo rtquan trng.

Sullivan (1972) [65] tin hnh nghin cu v pht trin phng php

nh gi t l tn hi ca mng t bo cy la min bi s mt nc thng qua odn in Invitro t a l b stress nc. Phng php ny c nhiu nhkhoa hc (Blum, Ebercon...) p dng cho cc loi cy trng khc, trong c cyla.

Hin nay, ngi ta bit rng: nghin cu sinh l hc tm ra 3 hp phnchnh ng gp vo s kin chng chu kh hn ca cy la (Nguyn v ctv.,1997):

(i) Kh nng n su ca r xung tng t pha di;(ii) Kh nng iu tit p sut thm thu (c ch chng chu), gip cy bo

v sinh m khng b tn hi do mt nc;(iii) Kh nng kim sot s mt nc bn ngoi kh khng ca l.

2.2.3.1.4. Nghin cu v di truyn tnh chu hnKh hn l yu t chnh lm gim nng sut ca la (Oryza sativa L.), di

iu kin canh tc nc tri (rainfed) v tnh trng thiu nc ti ngy cngnghim trng hn vng c nc ti cng nh vng la ry. Ngi ta tp trungs ch vo i tng kh hn v mn, hai dng gy stress phi sinh hc quantrng i vi sn xut la, v t ra mc tiu hng ti ci tin ging la trnqui m ton cu. Kh hn s l yu t quan trng bc nht nh hng n an ninhlng thc ca th gii, n c th lm gim 70% nng sut cy trng ni chung(Bray v ctv. 2000). S khan him v nc ti phc v cho nng nghip c bo ng trong nhiu hi ngh khoa hc ca th gii gn y. Sn xut lanc Vit Nam khng phi l ngoi l.

Chn ging truyn thng chng chu kh hn l cch tip cn rt c bntrong mt thi gian di, mt vi thnh cng c ghi nhn trn cy ng(Hoisington v ctv. 1996), cy la (Zhang v ctv. 2006), cy la m (Zhao vctv.2000). Tuy nhin, mt l hng ln gia cc mc chng chu hn vn chac xc nh trong hu ht cc loi cy trng. c bit l s n nh v nngsut v cng nhy cm vi s thiu nc (Xiao v ctv., 2007). p ng li hintng stress do kh hn, cy trng c mt c ch rt tin b t vic nhn tn hiun truyn n i vo h thng tinh vi ca t bo, kch thch hot ng ca genmc tiu (Thomashow 1999; Xiong v ctv. 2002). Chng chu kh hn l tnhtrng cc k phc tp, b nh hng bi s th hin ng thi c mt h thnggen mc tiu (Thomashow 1999; Xiong v ctv., 2002) v b nh hng bi ccyu t v mi trng, vt l, ha hc (Soltis v Soltis 2003). iu ny lm chonhng tin b nht nh v ci bin di truyn tnh chng chu kh hn xy ra rtchm chp. S pht trin nhanh chng ca ngnh genome hc chc nng v cngngh sinh hc trong thi gian gn y cung cp cho cc nh khoa hc c himi ci tin tnh trng chng chu kh hn. Chin lc c hiu qu cghi nhn l lm gia tng lng ng d ha tan, cc hp cht cn thit thng

qua tip cn vi k thut chuyn np gen. Nhng hp cht l: proline,

25


26/43

trehalose, betaine v mannitol, ng vai tr nh nhng th bo v thm thu(osmoprotestants); trong vi trng hp, chng n nh c cc phn t chcnng di iu kin b stress (Kishor v ctv., 1995; Hayashi v ctv., 1997; Shenv ctv., 1997; Garg v ctv., 2002). Protein LEA (late embryogenesis abundant)

cng c ch trong iu kin b stress do thiu nc (Xu v ctv., 1996;Maqbool v ctv., 2002; Goyal v ctv., 2005). Protein LEA c phn chia thnh5 nhm chnh trn c s chui trnh t amino acid ca n (Bake v ctv., 1988;Dure v ctv., 1989) v chng c xt nghim li thng qua cng c tin sinh hc(Wise 2003). Nhng protein nh vy ng gp phn no vo s tin ha canhm protein c tn gi l hydrophilins khi chng p ng vi iu kin thmthu cc trng (hyperosmotic) (Garay-Arroyo v ctv., 2000). Vai tr chnh ca

protein LEA l hot ha nhng amino acid a nc v np nng lng. S thhin ca cc gen LEA thng xy ra di dng abscisic acid c lp. N khngnhng ch c pht hin trong ht m cn trong cc m tng trng khi cy bstress do thiu nc, do mn, v do lnh (Ingram v Bartels 1996; Thomashow1998; Cuming 1996; Grelet v ctv., 2005). S th hin ca protein LEA v cim cu trc i phn t ca n cho thy vai tr bo v cy chng chu s kinmt nc (Ingram v Bartels 1996). Mc d chng ta c nhiu s liu v cu trcv s th hin ca protein ny, nhng rt t cng trnh cp n thao tc ca ccgen LEA nhm ci tin tnh chng chu kh hn trong iu kin ng rung(Raynal v ctv., 1999; Ndong v ctv., 2002; Grelet v ctv., 2005, Xiao v ctv.,2007). Th d, gen HVA1 m ha nhm protein 3 LAE ca cy la mch(Hordeum vulgare L.). Ngi ta chuyn np gen ny thnh cng vo cy la tng cng tnh chng chu kh hn v chng chu mn, ch trong iu kin nh li (Xu v ctv., 1996). Mt clone cDNA c di phn t y cha genLEA nhy cm vi stress do mn v gen OsLEA3-1 th hin tnh chng chukh hn trong iu kin ng rung, nh promoter HVA1-like v promoter kintrc CaMV35S (Xiao v ctv., 2007). y c th ni l s kin ni bt trong thigian gn y, nh kt qu ca th nghim ng rung mang li. Hu ht ccnghin cu v marker phn t u quan tm n nhng thnh phn rt c bittrong s kin chng chu kh hn, l:

- Kh nng ca r cy pht trin su xung tng t bn di,- Hin tng tr bng v tung phn vi thi gian cch qung c xc

nh (ASI = anthesis to silking interval)- S iu tit p sut thm thu (OA = osmotic adjustment)- Hin tng bin dng ABA (abscisic acid)- Hin tng nng hc WUE (water use efficiency c ngha l hiu qu s

dng nc)Mc tiu c bn ca bn QTL l tm hiu c s di truyn ca nhng

tnh trng s lng bng cch xc nh s lng, cc v tr, nhng nh hng cagen, v hot ng ca nhng loci bao gm tng tc gen (epistasis) v tng tcQTL x E (mi trng). Mt mc ch khc ca bn QTL l xc nh nhngmarker mang tnh chn on i vi nhng kiu hnh c th no , sao cho

vic p dng MAS tr nn c hiu qu, phc v yu cu chn dng (ging)

26


27/43

chng chu kh hn, chng chu mn, v.v.. Mc tiu lu di ca th nghim vbn QTL l cloning cc gen iu khin tnh trng s lng v cng phctp, thng qua tip cn k thut map-based cloning (Li 1999).

S QTL c tm thy i vi tnh trng chng chu kh hn thng thay

i t 1 n 4 i vi mt tnh trng thuc thnh phn trong s kin chng chuhn, v nhng QTL ny thng tri rng trn ton b genome vi nhiu nhmlin kt gen. Th d, tnh trng WUE (hiu qu s dng nc) c tm thy virt t QTL, t 4 n 5 trong genome cy u nnh (Milan v ctv., 1998).

Trong mt vi trng hp, c nhng QTL nh v trn cng mt nhmlin kt gen, iu khin nhiu tnh trng quan trng nh kh nng iu tit psut thm thu (OA), kh nng chng chu s thy phn, chng lin kt vi tnhtrng hnh thi hc ca r la (Lilley v ctv., 1996). Bin thin kiu hnh i vitng tnh trng xt trn mi v tr QTL xoay quanh gi tr 10%. Trong trng hpngoi l, QTL i vi tnh trng chiu di r giai on 28 ngy tui bin thin30% (Price v Tomas 1997).

Mi quan h gia nng sut v QTL thng cho kt qa m tnh trong vitrng hp, nhng i vi tnh trng ASI, kt qa chng chu hn khng ikhng vi nng sut (Ribaut v ctv., 1996). Nhng QTL i vi tnh trng ASIc tnh n nh nhiu nm, trong iu kin mc stress khc nhau, s c xem nh l nhng ng c vin trong chin lc pdng MAS.

H thng r pht trin tt l mt tnh trng v cng quan trng gip cytrng chng chu kh hn (c ch thot hn = drought avoidance mechanism).

Ngi ta s dng qun th n bi kp (DH) ca cp lai IR64 x Azucena tiVin La Quc T (IRRI). Sau Shen v ctv. (1999) pht trin qun th gnnh ng gen (NIL) ca IR64 c du nhp vi nhng QTL ch lc. Cc tc gi ghi nhn bn on trn nhim sc th s 1, 2, 7 v 9 l ni nh v cc QTLch lc trong phn tch chn lc tng QTL mc tiu.

Ngi ta thc hin nhiu cp lai gia cc cy BC3F2 mang nhng onmc tiu ca vt liu cho gen iu khin r la pht trin tt, loi tr nhhng di truyn theo kiu genetic drag v nh hng cc QTL mc tiu khcnhau chng lp theo hnh thp (Shen v ctv., 1999).

Thnh tu ca cng ngh sinh hc trong vic thc hin xy dng bn di truyn phn t cho php chng ta xem xt nhng tnh trng di truyn phc tpnh tnh chng chu kh hn v nng sut (Zhang v ctv., 1999). Ti i hcTexas Tech, nhm tc gi ny thc hin bn di truyn QTL i vi 2 tnhtrng quan trng lin quan n s kin chng chu kh hn, l: kh nng iutit p sut thm thu (OA), v nhng tnh trng hnh thi ca r la.

Hin tng iu tit p sut thm thu (OA) l mt hp phn quan trngtrong s kin chng chu kh hn. Kh nng OA ca cy gip n tch ly chtho tan mt cch ch ng trong t bo, khi cy b kh hn. Tnh trng OA kthp vi tnh trng nng sut n nh trong iu kin b stress do kh hn cquan st la m v cao lng, nhng hin tng ny khng c ghi nhn trn

cy la (Zhang v ctv., 2001).

27


28/43

Qun th la c s dng trc y lp bn QTL tnh trng OAl: Qun th cn giao ti t hp (RIL) ca t hp lai CO39/Moroberekan, vi 1QTL (Lilley v ctv., 1996). Qun th n bi kp (DH) ca t hp laiCT9993/IR62266, vi 4 QTL (Zhang v ctv., 1999). Qun th cn giao ti t hp

(RIL) ca t hp lai CO39/Moroberekan, vi 5 QTL (Lilley v ctv., (1996).Qun th la c s dng lp bn QTL tnh trng tch ly ABA

l: qun th F2 ca t hp lai IR20/63-83, vi 10 QTL (Quarrie v ctv., 1997)Zhikang Li v ctv., (CAAS, IRRI) s dng 260 vt liu (trong c

OM1723 ca Vit Nam) t 15 quc gia thc hin hi giao vi IR64 vTeqing. H thanh lc tnh chng chu kh hn ca 215 qun th BC1F1, v 4.677dng lai cn giao (Ils) nghin cu s bin thin di truyn cha c bit(CGV: cryptic genetic variation) ca gen chng chu kh hn thng qua phn tchQTL (Bi Ch Bu 2005).

Purwantomo v ctv., khai thc vai tr ca cc gen c tnh chthomeobox pht trin ging la chng chu kh hn. Trong khi , nhmnghin cu ca CIRAD, Php, tp trung nghin cu c tnh ca r la thch nghivi s pht trin (E Guiderdoni). S pht trin h thng r la tng thch vistress c nghin cu v so snh vi cy Arabidopsis thaliana. Mt dy biuth clone c qui m 22K i vi p sut thm thu v stress do mn (SSH), mtreceptor c bit v mt oligo ng vai tr chuyn m c xc nh. H phthin ra gen mc tiu c lin quan n r la trong iu kin b stress.

Bng vic s dng marker tr gip chn lc (MAS), cc vng gen linquan n cc tnh trng ny c nh v trn nhim sc th s 1, 2, 3, 4, 5, 9 v11 ca cy la [67]. Mt vng gen trn nhim sc th s 4 c xc nh l chacc locus tnh trng s lng chnh quyt nh chiu cao cy, nng sut ht, sht trn bng trong iu kin thiu nc.

Bn cnh , bng vic so snh s trng khp ngu nhin ca cc locus tnhtrng s lng vi mt s tnh trng c bit khc, ngi ta phn tch k milin h t nhin gia tnh trng b r v kh nng iu chnh tnh thm vi tnhtrng nng sut trong iu kin hn. Nghin cu ny chng minh vng gen khiu RG939-RG476-RG214 trn nhim sc th s 4 quyt nh quan h ca b rvi tnh trng chu hn (Babu, 2003) [38].

Yinong Yang v Lizhong Xiang (2003) [47], [69] cng b gen MAPK5(Mitogen-activated protein kinase 5) c vai tr tng cng sc chng chu cacy la vi cc khng hong mi trng trong c hn.

Theo Ray Wu v Ajay Garg (2003) [68] thuc trng i hc Cornell(M), hp cht c kh nng ci tin tnh chng chu hn, chu mn v nhit thp cy la l mt loi ng n, gi l trehalose. Trehalose c th hot ngnh nc thay th trn b mt ca cc protein lp mng t bo khi xy ra thiuht nc trm trng, ngn chn s kt tinh hay bin cht cc protein, gi cho cchot ng sinh ho, sinh l din ra bnh thng. Cc gen m ho enzyme tnghp trehalose l trehalose-6-phosphate synthase (TPS) v trehalose-6-phosphate

phosphatase (TPP).

28


29/43

Ngoi trehalose, Robert Locy v Narendra Singh (1996) thuc trng ihc Auburn (M) cho rng, cn nhiu hp cht ho hc khc c vai tr tng ttrehalose trong vic bo v cy trng chng li hn nh: cc axit amin (proline),

polyamine, protein, glycine betaine, sorbitol, marnitol... Cc loi thc vt khc

nhau th s dng loi ho cht khc nhau [63].Tuy nhin, cc nh khoa hc cha hiu r yu t no chi phi hin tng

v ng gp tch cc nht vo tnh chng chu kh hn thc vt. Hin nay, tin ci tin ging chng chu hn chm nhng kh thi. Tr ngi chnh l tnhtrng nng sut cao v tnh trng chng chu c kh nng tng hp nht. Mtcu hi ang c cc nh khoa hc t ra: Liu c s i khng gia nng sutv tnh trng chng chu hay khng?

Gio S Ray Wu, H Cornell, M, pht trin 3 dng la chuyn gen:(1) gen tng hp proline p5cs, (2) gen choline oxidase COX, (3) dung hp c haigen TPS v TPP trong tng hp trehalose. Gorantla v ctv., nghin cu ph thhin cc gen iu khin tnh chng chu kh hn vi nhiu gen mc tiu c

pht hin (Bi Ch Bu 2005). Toojinda v ctv., thc hin bn QTL iukhin tnh trng chng chu kh hn ti Thi Lan, vi cc tnh trng mc tiu:nng sut ht, sinh khi, ch s thu hoch HI, s ht chc v lp, s ht/bng, t l

bt th, trng lng 1000 ht, s bng, s nhnh, chiu cao, s ngy t gieo ntr,v.v.. QTL nh v trn cc nhim sc th 1, 2, 3, 4, 7, 8, 9 c phn tch,trn c s qun th DH ca t hp lai IR62266/CT9993 ti 3 a im khc nhautrong 3 nm lin tc. c bit ch nhim sc th s 3 v s 5, n tp hp nhiuQTL c lin quan n tnh chng chu kh hn (Bi Ch Bu 2005)

Hin tng nng hc WUE trong cy la c Karaba v ctv., (2007)nghin cu kh h thng vi s th hin ca gen HRD chuyn np tArabidopsis. Cy la chng hn tiu th nc t biu th s kin sinh khi r tngln trong iu kin c ti tr li. Gen HDR vi yu t chuyn m AP2/ERF,c phn lp trong dng t bin ca Arabidopsis (theo kiu gn thm chcnng) hrd-D, iu khin tnh trng sc mnh ca r, s phn nhnh, t bo biu

b, dy ca l vi t l lc lp tng cao trong t bo mesophyll, lm thc yhin tng ng ha quang hp v hiu sut quang hp (Karaba v ctv., 2007)

Trong cy cao lng, kh hn xy ra trc v sau khi tr bng gy ra hintng chn sm trong tnh trng mc ha gi ca l (senescence). Cy mtmu xanh nhanh chng, ng, v tht thu nng sut. Hn 80% cao lng u thlai c trng ti M di iu kin khng c nc ti, nhng hu ht ccging ny u c kh nng khng hn giai on trc khi tr bng, hin tngnh vy c gi vi thut ng l stay-green trait (tm dch l tnh trng biuhin mu xanh, tnh trng ko di thi gian ha gi, vit tt l SGT). Tnh trngnh vy l mt c ch khng hn gip cho cy cao lng chng li s lo hasm di iu kin khc nghit ca m t hn ch trong sut qu trnh saukhi tr (Subudhi v ctv., 1999).

Cc tnh trng s lng ca cy la giai on m: tng s r, th tch r, schi, t l r/chi, chiu di r ti a, im chng chu kh hn (1-5), b dy ca

29


30/43

r, chiu cao cy m, trng lng r kh, cun li ca l la, c thit lpbn QTL (Shashidhar v ctv., 1999).

Cc tc gi cn ghi nhn 21 QTL i vi nhng tnh trng khc trong iukin b stress do kh hn. Mc d c 2 QTL i vi tnh trng chiu cao nh v

nhim th s 1 v 3, kh ph bin, nhng khng c mt loci no i vi tnhtrng hnh thi hc ca r c ghi nhn ph bin gia hai giai on pht trin.S khng c mt ca nhng QTL ph bin i vi tnh trng hnh thi ca rgia hai giai on pht trin (65 ngy u c nc, v t ngy 65 n ngy 85:kh hn) cho thy s hin din ca nhng c ch di truyn cng tn ti songsong, cng khi ng cc giai on tng trng khc nhau, di iu kinnc ti khc nhau (Shashidhar v ctv., 1999). Th tch r v tng s r trnmt cy gim c ngha v mt thng k di iu kin b stress do kh hn,trong khi chiu di r ti a v chiu cao cy khc bit khng c ngha.

c bit, Wang v ctv., (2007) so snh s th hin gen gia ging lanc v ging la cn trong iu kin b stress do kh hn, s dng phng tincDNA microarray. Ging la cn IRAT109, Haogelao, Han 297 v ging lanc Zhongzuo 93, Yuefu, Nipponbare c s dng. Sau khi c chui trnht DNA, c 64 unique ESTs th hin mc cao ging la cn v 79 gingla nc. Tc gi d on s th hin ca cc gen mc tiu mc cao trongla cn c th ci tin c kh nng chng chu stress do kh hn trong lanc v nhng loi cy trng c lin quan gn v huyt thng (Wang v ctv.,2007).

Guenzi v ctv., (2003) ti i Hc Oklohama thnh cng trong chuynnp gen mannitol-1-phosphate dehydrogenase (gen mtlD) trong cy la mchng chu kh hn v mn. Gen ny c tnh cht b sung b gen vn c trong tnhin, nhm kch hot cy trng chng chu tt hn kh hn (ngun truy cp thttp://www.isaaa.org/kc).

Trong l cy b kh hn v trong r cy b stress do mn, nhng k thuttheo di s thay i v mc a dng ca protein, thay i v v tr ca proteinc bit v cha c bit l mt phng php rt ng ch . Nhng proteinl sn phm ca qu trnh quang tng hp, s ko di t bo, qu trnh bindng hp cht chng oxi ha (antioxidant) v qu trnh lignin ha c quantm trong nghin cu. Do , ngnh hc mi c thut ng proteomics s lcng c hu hiu, gip cho nh chn ging tm kim nhng kiu gen thch hpcho mc tiu ci tin tnh trng chng chu kh hn.

Cc tnh trng chng chu vi kh hn, mn hay lnh... l cc tnh trng slng (QTLs-Quantitative Traits Loci). Do vy, phi tin hnh xy dng bn tnh trng s lng (QTLs mapping). Ngi ta quan st ton b genome vinhng marker bao ph ton b cc nhim sc th, mt trung bnh 10 cM giahai marker. Thng qua , ngi ta xc nh nhng khu vc gi nh c cha ccgen iu khin tnh trng s lng m ta cn nghin cu, da vo s bin ngca tnh trng kt hp vi s thay i ca cc marker tng ng. Nhng v trc xc nh nh vy v cng cn thit cho chng trnh chn ging nh

marker tr gip (MAS) i vi tnh trng chng chu v rt cn thit cho k thut

30


31/43

cloning trn c s bn di truyn ca nhng gen thuc v tnh trng s lng.i vi cy la, thun li ln nht trong ng dng marker l bn genome can c bn c gii m.

Cc marker c ng dng trong chn ging cy trng phi c lin kt

cht vi gen mc tiu, trn c s bn phn tch di truyn. Hin nay, markerhiu qu ng tin cy l microsatellite (SSR). Ngi ta cng chun b a vos dng rng ri marker SNP (Single Nucleotid Polymorphisms) trong vi nmti. Theo Goff v nhiu tc gi khc (2002), chui k t SSR v SNP hin cthit k c khong 40.000 marker, k c cc phn t mt on hay xen on.Theo Gale (2002) y l nhng chui m ng nht mc 1%, mt 24 cMtrn mi gen [2].

Nh nghin cu ng dng k thut bn gen, nhiu nh khoa hc xcnh c v tr v vai tr ca mt s vng gen lin quan n kh nng chngchu hn. Cc c trng nh b r kho, n su; kh nng iu chnh p sutthm thu, kh nng duy tr th nc l trong iu kin kh hn... u quytnh quan trng n kh nng chu hn cy trng [2], [4], [38], [67].

nh gi v chn ging chu hn, theo M.A. Arraudeau (1989) [39], cth p dng k thut nui cy m, dng cc bin th soma v tnh chn lctheo hng chng chu hn. i vi la, ngi ta s dng k thut ny chn ging chng chu hn. Mt bng chng c th hn, ngi ta cng b sthnh cng trong vic chn ging yn mch chu mn thng qua nui cy m(Nabors, 1983).2.2.3.1.5. Nghin cu chn to ging la cn v la chu hn

nhng vng cao thiu nc hay vng c hn hn xy ra thng xuyn rtkh c th khc phc bng thu li v cc bin php k thut thng thng. Vn s dng ging chng chu hn tr thnh s la chn ti u cc vng trngla thiu nc.

Nm 1958, Vin nghin cu quc gia Ibazan ca Nigieria chn cging Agbele t t hp lai 15/56 FAR03, c kh nng chng chu hn kh v chonng sut cao [31].

Nhng nm 50-60, ti Philippine tin hnh thu thp, so snh v lai tocc ging la cn a phng. Ti nm 1970, cc ging la nh C22, UPLRi3,UPLRi5 c to ra vi chiu cao cy va phi, nhnh trung bnh, nhngnng sut kh v cht lng go tt. Tip theo l ging UPLRi6 c tim nngnng sut kh, thp cy, kh nng phc hi tt [31].

Ti Indonesia, cng tc lai to, tuyn chn phi hp vi nhp ni cng ctin hnh v a ra hai ging l Gata, Gatifu phc v sn xut t hiu qu.

u nhng nm 50, Thi Lan tin hnh chng trnh thu thp v lm thuncc ging a phng, chn lc v ph bin min Nam c hai ging la tl Muang huang v Dowk payon, c tim nng nng sut 20 t/ha; mt ging lanp l Sew maejan ph bin min Bc vi nng sut 28 t/ha.

Nm 1966, Trm nghin cu la Yagambi thuc Vin quc gia pht trinCng-g (nay l INEAL, Zaire) gii thiu ging R66 v OS6, cho nng sut cao

31


32/43

v chng chu hn kh hn Agbele (Jacquot, 1978). Ging OS6 c trng rngri Ty Phi [31].

Cng vo nm 1966, Vin IRAT, IITA v WARDA ng thi a ra ccging nh TOX 86-1-3-1; TOX 356-1-1; TOX 718-1 v TOX 78-2 (Dasgusta,

1983). Nhng ging ny c kh nng chng chu bnh tt [31].Trong sut ma kh nm 1974, hn 2000 ging v cc dng la tuyn chn

t chu ; chu Phi v M Latin c b tr lm th nghim trn ng rung caIRRI v kh nng chng chu hn. Mt t l ln nht cc ging la chu hn c tm thy trong s cc ging la cn a phng nhp t chu Phi, tip theol t Nam M v cc ging la c trng trn i dc Lo. Mt vi ging lachn sm, chng chu hn tt, c my cao c a vo sn xut l N22,Cartuna, Padi Tatakin, Rikuto Norin 21... Ngoi ra, con lai OS4 ca php lai giala cn chu Phi vi la nc c kh nng chng hn nh b m chng (nh ccging la cn chu Phi) [53].

Nm 1980, Trung tm Nng nghip Ibaraki, Nht Bn chn to cging la np cn Sakitamochi, c kh nng chng , chng chu su bnh,nng sut cao v cht lng tt. Nm 1991, chn c ging Kantomochi 168cht lng nu n ni ting v chu hn tt. Nm 1992, chn c gingKantomochi 172 cho nng sut rt cao [31].

Nm 1976, chng trnh hp tc thnh cng ca CIAT (Trung tm nngnghip nhit i quc t) vi ICA (Vin Nng nghip Colombia) a ra gingCICA-9, khng ch c trng nh l mt ging la nc Colombia m cnc trng nh mt ging la cn Costa Rica v Panama. Ging ny c timnng nng sut cao v chng bnh gii hn cc ging trng trc [54],[57].

pht trin din tch trng la cn Brazin, Vin Nng nghip Campinas(IAC) to ra mt lot cc ging la cao cy nhng chu hn rt tt nh:IAC1246; IAC47; IAC25. Ging IAC25 c thi gian sinh trng ngn hn 10ngy so vi hai ging trc v thot c thi k hn, a phng cn c

bit vi tn gi l Veranico [55], [57].Trong thi gian t 1972-1980, IRRI tin hnh 3839 cp lai chn

ging. Trong nm 1982, c trn 4000 dng, ging c IRRI gi ti th nghimti cc nc cho vic nh gi, chn lc ph hp vi tng vng sinh thi hn[31].

Thng qua chng trnh th nghim quc t c tn l INGER, cc t thnghim c tin hnh hng nm c tn: IRLYN-M; IURYN-E; IURYN-M;IURON; IRDTN din ra nhiu v tr thuc cc nc nh: n , Mianma,

Nepal, Nigieria, Philippine, Thi Lan, Brazin, B Bin Ng, Vit Nam... v ngayti IRRI. c bit m rng qui m ln t nm 1990 [31].2.2.3.2. Tnh hnh nghin cu la cn, la chu hn ti Vit Nam

nc ta, cng tc chn to ging la cho vng kh khn (hn, ng,mn...) c tin hnh t cui nhng nm ca thp nin 1970. Cho n nm2000, c nhiu ti cp Nh nc v la kh khn c thc hin; c

hng chc ging la chu hn, chu mn v chu ngp ng c chn to v a

32


33/43

vo sn xut, gp phn nng cao nng sut v sn lng la ca c nc. Tuynhin, trong thi gian qua, cng tc nghin cu chn to v pht trin cc gingla cho cc vng kh khn cn c mt s hn ch. Mt mt, cc ging la mito ra cn cha p ng y yu cu ca sn xut, nh: tnh chng chu vi

iu kin bt thun cn cha cao; thi gian sinh trng ca cc ging la cndi; phm cht go cha cao v nng sut cha n nh. Mt khc, cn thiunhng nghin cu v bin php k thut ph hp nhm nng cao nng sut ivi cc ging la mi nhng vng kh khn.

Cng tc bo tn ngun gen cy la min Nam cng c tng cngv ch trng nhng nm cui th k XX. Theo ti liu ca Bi Ch Bu v

Nguyn Th Lang, (2001) cho thy, n nay c trn 1.800 mu ging la aphng v 160 qun th la hoang c su tm v bo qun ti Vin la ngbng sng Cu Long. Ngoi ra Vin cn bo qun mt s ngun gen cy trngc nhp ni vo Vit Nam nhm s dng lm ngun vt liu phc v cho cngtc lai to.

Ngun ti nguyn di truyn cy la nc ta rt phong ph, a dng. Tngun vt liu ny chng ta to ra nhiu t hp lai, nhiu ging tt, c tnhchng chu cao vi su bnh v iu kin sinh thi bt thun c ph bintrong sn xut.

T nm 1978, Vin Cy lng thc v cy thc phm tin hnh chn toging la chu hn, thi gian sinh trng ngn, chng chu su bnh, t nngsut cao hn cc ging la chu hn, la cn a phng ang trng. Trong giaion t 1986-1990, c 3 ging thuc dng CH c cng nhn ging Nhnc l CH2, CH3, CH133 v hng lot cc dng, ging chu hn c trin vng(V Tuyn Hong v cng s, 1995) [13-19].

T nm 1986, Vin Cy lng th phi hp vi trng Trung cp nngnghip Vit Yn, H Bc (nay l Trng cao ng Nng lm Vit Yn, BcGiang) tin hnh mt lot cc th nghim so snh ging v nghin cu cc ctnh nng sinh hc ca cc ging la CH, c bit l cc c tnh lin quan nkh nng chu hn. Tip theo, xy dng thnh cng quy trnh k thut thm canhcc ging la cn, p dng cho nhng vng trng la cn v trng cc ging chuhn trn chn t khng ch ng nc. Kt qu th nghim v so snh nng sutch ra rng, nng sut ca cc ging CH u cao hn cc ging la cn C22, CK136, la thm a phng H Bc t 5-9 t/ha, trung bnh tng 20%. Ngoi ra,chng c kh nng chu hn v phc hi sau hn tt. Trong iu kin vng hncho nng sut 35-45 t/ha, c th t 50-60 t/ha trong iu kin c ti 60-70% lng nc ca lu nc. Nh vy, chng thuc loi hnh tit kim nc[15].

Nghin cu ca Nguyn Ngc Ngn (1993) [24] v c im v k thutcanh tc mt s ging CH trn vng t cn Vit Yn, Bc Giang v Hi Dngcho thy: cc ging CH c thi gian sinh trng 120-130 ngy; thn cng, lng, thng v dy; kh nng nhnh trung bnh; v c b r pht trin c vchiu rng v chiu su.

33


34/43

Theo V Tuyn Hong v cng s (1995) [13], hm lng nc ccging CH cao hn cc ging i chng, cng thot hi nc ca cc gingCH t 548-697 mg nc/dm2/h. c im ny gip cho cc ging CH c khnng chu hn tt hn. Hn th, cc ging CH c ng knh r t 62-65 cm,

tng ng vi chng nhng n su hn (t su 57,9-61,0 cm).Trong giai on 1995-1997, V Tuyn Hong, Trng Vn Knh v cng s [19] cng b thm 3 ging la mang nhng c tnh tt: cho nng sut cao, chngchu hn kh, d thch ng vi vng t ngho dinh dng b hn v thiu ncti. l cc ging CH5, CH7 v ging CH132. Nm 2002, ging CH5 ccng nhn l ging quc gia vi nhng u im v kh nng chng chu hn, su

bnh v cho nng sut cao c gieo trng rng ri nhiu vng kh khn vnc. Hin nay, Vin vn ang y mnh nghin cu v chn to cc ging lacn, la chu hn mi, trong s c mt s dng trin vng v ang ctin hnh th nghim v cho kt qu tng i kh quan nh CH207, CH208,CH209, CH210 v CH216[ ].

Cng tc thu thp nh gi v chn lc bi dc ngun vt liu ging aphng phc v chn to ging la cho vng canh tc nh nc tri ti vng nity Bc Vit Nam ca trng i hc Nng Nghip H Ni vi phng phpiu tra, thu thp, phn loi ging a phng v chn lc c th theo chu k lm vt liu di truyn lai to ging; kt qu thu thp c 60 mu ging a

phng v tin hnh nh gi chn lc c mt s dng trin vng nh G4, G6,G10, G13, G14, G19, G22, G24 (V Vn Lit v cs., 2004) [Hi ngh la go].

Cc nghin cu ca Nguyn Duy Bo, Nguyn Hu Ngha v T Minh Sn[31], khi nh gi kh nng chu nng; nghin cu h thng r v xc lp mitng quan gia kh nng chng hn vi sinh trng thn l v b r ca 20ging la thuc 3 nhm chu hn gii, kh v km nhn xt:

+ C th s dng phng php nh n nhit 380C trong thi gian 3gi cho php nh gi kh nng chu nng ca cc ging la cn.

+ C 3 ging c kh nng chu nng tt v chu hn kh c xc nh lX11, MW-10, OS6.

+ Gia la cn c truyn v la cn ci tin giai on 20 ngy khng cs sai khc v chiu cao cy, v chiu di r; giai on 60 ngy th c s khc

bit c ngha.+ Gia la cn v la nc giai on 20 ngy khng c s sai khc v

chiu cao cy nhng c s sai khc ngha v chiu di r, nn c th coi y lch tiu chn ging.

+ Chiu cao cy c tng quan nghch vi kh nng mn cm hn. Chiucao cy cng thp th nhim hn tng v ngc li.

Cc tc gi trn cng nghin cu nh hng ca 2 iu kin mi trng (nc v hn) n sinh trng ca la nc v la cn trong mt th nghim vi35 ging la cn v 35 ging la nc. Kt qu l, khi thay i iu kin trung nc sang rung cn v ngc li, cc ging la cn khng bin ngnhiu v chiu cao cy v thi gian sinh trng nhng cc ging la nc bin

ng rt ln. Thi gian sinh trng khi gieo kh ca la cn ngn hn gieo nc

34


35/43

2-6 ngy; ca la nc di hn gieo nc 4-20 ngy. Chiu cao cy (gieo kh)ca la nc thp hn cc gieo nc 30 cm nhng la cn t bin ng.

Nm 1994, Nguyn Th Lm tin hnh nghin cu nh hng ca m nkh nng sinh trng, pht trin v nng sut ca mt s ging la cn [21].

Theo tc gi, h thng r la cn pht trin mnh nht t giai on nhnh nlm ng v tr bng. m c nh hng n s pht trin b r la gieo trngcn. Khi lng m tng, dy v v s b mch ca r tng, to iu kin ttcho qu trnh vn chuyn v tch lu. Khi bn 60 kg N/ha i vi la cn a

phng, nng sut cao v hiu sut s dng ln (13-14 kg thc/kg N). Nhngnu vt qu ngng m thch hp, cc ch tiu trn khng tng. Mt khc, tcgi cho rng nn hn ch bn m khi gp hn.

Vo nm 1991, Nguyn Hu Ngha v cng s tuyn chn c bging la H3 t b quan st la cn ca Vin Nghin cu la quc t, l dng BR4290-3-35 c chn t t hp lai C22/IR9752-136-2. y l mt ging chuhn ngn ngy (63-70 ngy), gieo c nhiu v, thch hp trn t ngho dinhdng, hon ton nh nc tri, nng sut khong 34 t/ha, [16], [17].

Theo Gio s Nguyn Hu Ngha [31], n nm 1994, Vit Nam nhnc 270 b ging th nghim ca INGER c ngun gc t 41 nc v 5 trungtm nghin cu la quc t. T 1975 n 1994, Vit Nam xc nh v a vosn xut 42 ging la v nhiu dng trin vng, c bit l c mt ngun gen

phong ph cho chng trnh lai to. Ging la cn C22 c ngun gc tPhilippine chn lc c t ngun INGER v ph bin trong sn xut Vit

Nam nm 1985.Nm 1993, cng t b ging la ca INGER, Vin Khoa hc Nng nghio

min Nam chn c cc ging la cn a phng v chu hn tt nh:LC88-66; LC88-67-1; LC90-14; LC90-12; LC90-4; LC90-5... y l nhngging la ang c pht trin mnh cao nguyn, min ng Nam b v mts tnh min ni v trung du Bc b [19], [30], [31].

Theo Gio s V Tng Xun (1995) [35], ti Ty Nguyn, cc ging LC88-66; LC89-27; LC90-5; IRAT1444 c trng v t nng sut 28-30 t/ha.

Trn Nguyn Thp (2001) [31] tin hnh nghin cu nhng c trng cbn ca cc ging la chu hn nhm xy dng ch tiu chn ging. Qua kt quthu c, tc gi xut mt m hnh chn ging la chu hn. Vi th nghimnh gi kh nng chng chu hn nhn to ca cy la trong phng, tc gikhuyn co nn chn nng mui KClO3 3% hoc nng ng Saccarin0,8-1,0% x l ht.

Trn Nguyn Thp, Nguyn Trng Khanh, V Tuyn Hong, Nguyn TnHinh, Trng Vn Knh (2002) [32] cng b vai tr ca gen chng hn trong siu chnh hm lng proline trong l la trong iu kin mi trng thay i.Trong iu kin khng hong nc, hm lng proline c s khc nhau gia ccging la cn v la nc. Cc ging chu hn tt c biu th bi hm lng

proline trong l cao, c im chu hn v mc suy gim nng sut thp. S khcnhau v hm lng proline ca cc ging la cn v la nc lm sng t vai tr

ca gen i vi c ch chng li s mt nc iu kin gieo trng cn.

35


36/43

Nguyn Vn Dong (2002) [6] tin hnh nghin cu ng dng phngphp xc nh p sut thm thu ca ht phn bng dung dch Polyethylen glycol(PEG) trong chn to ging la m chu hn. Theo tc gi, phng php ny gip

phn bit cc ging c p sut thm thu cao v thp. M nhng ging la m

chu hn c p sut cao v ngc li. Mt khc, phng php kim tra ny rt dthc hin, khng i hi nhiu trang thit b my mc t tin v cho kt qu tt.V vy, ngh th nghim phng php ngm ht phn trong dung dch PEG nh gi kh nng chu hn vi la.2.2.3.3. Phng php tip cn v phng hng chn to ging la chu hn2.2.3.3.1. Phng php tip cn chn to ging la chu hn

Kh hn v mn l hai yu t c bn lm hn ch s tng trng v nngsut cy trng. Mc d chng ta c kh nhiu cng trnh nghin cu tnh trngchng chu kh hn ca cy trng, trong sut hai thp nin 1980 v 1990, nhngthnh tu c th v chn to ging chng chu kh hn vn cha mang li ngha ln lao (Reddy v ctv., 1999).

(i) Phng php tip cn th nht l phng php phn tch s ng gpca cc tnh trng c lin quan, vi m hnh QTL (quantitative trait loci). Phng

php tip cn ny ph hp vi hu ht cc loi cy trng ch yu nh cy la,nh bn di truyn vi nhiu marker phn t DNA ph kn trn nhim sc th.Hu ht cc nghin cu v tnh trng chng chu kh hn u quan tm nh gicc tnh trng c lin quan vi n s sng v pht trin ca. Cy trng trongiu kin kh hn. Phng php phn tch di truyn phn t gip cho ni dungy t hiu qa cao hn, trong khi thc hin trn tng tnh trng, trc khi chngta xem xt s sng v pht trin ca cy. Vic nh gi kiu hnh ca nhng tnhtrng ring bit y l v cng quan trng, ging nh vic nh gi kiu hnh cas p ng cy trng trong iu kin c kim sot nh li hay phng thnghim, trc khi chng ta nh gi ngoi ng rung. Mt s lin kt v cngcht ch c chng minh, l thc hin cc bc trong qui trnh MAS(chn ging nh marker phn t).

(ii) Phng php tip cn th hai l sng to ra mt kiu bin d mi cchc nng c hiu bit cn k trong phn ng ca cy trng khi b stress dokh hn, thng qua k thut chuyn np gen. Phng php chuyn np gen chothy l phng tin nhiu tim nng gn vo cy mc tiu mt ph rt rngca cc gen vi kh nng iu tit mt cch linh hot v tr up hoc downtrong qu trnh bin dng kt hp vi hin tng p ng khi cy b stress dokh hn. Nhng phng php chuyn np vi mt gen hay mt nhm gen trongmt l trnh c bit no c th khng thch ng trong iu kin chng chukh hn, bi v cc sn phm di truyn iu khin tnh chng chu kh hn xut

pht t rt nhiu l trnh khc nhau (Ingram v Bartels 1996). Thng thng,nhiu protein hoc nhng phn t osmolyte c trng lng phn t thp, ngvai tr iu tit p sut thm thu, s c tch t trong khi b stress do kh hn.

Ngi ta cha hiu r: yu t no chi phi hin tng thay i rt nhiu v nggp tch cc vo tnh chng chu kh hn. Phng php chuyn np gen c

xem nh rt c ch nhng n vn cha cho chng ta bit cc thng tin ng gi.

36


37/43

(iii) Phng php tip cn th ba l xc nh cc gen ng c vin(candidate genes) i vi tnh chng chu stress do kh hn, hoc mn, vi nhng

pht trin khng ngng ca k thut chuyn np gen, bn cnh nhng thnh tuv cng ngh phn lp gen (gene isolation) v thao tc gen (gene manipulation).

2.2.3.3.2. Phng hng chn to ging la chu hnTheo P.C. Gupta v J.C. OToole, 1986 [31], tiu chun chn ging la

chu hn l:(i) Nng sut cao, n nh, c nhiu dng hnh phong ph, tnh thch ng

cao, chiu cao cy t 110-130 cm, kh nng nhnh kh v chng tt.(ii) Chuyn t dng bng to sang dng nhiu bng, khi gp iu kin

thun li th vn cho nng sut cao.(iii) C b r dy, kho v n su. Mc kho, c kh nng cnh tranh vi c

di.(iv) Chn tp trung, t l lp thp. Cht lng cao.(v) Chu hn gii, chu phn m trung bnh. Chng chu vi su bnh nh

o n, kh vn, m nu, ry nu, su c thn... Chu c loi t ngho dinhdng, thiu ln, tha nhm va chua.

Theo T.T Chang (1986) [31], mc tiu chung cho cc nh chn ging lacn l:

(i) Nng cao tim nng nng sut bng cch pht trin cc kiu hnh cchiu cao cy trung bnh, nhnh kh thay th cc ging c truyn cao cy,thn yu. Mc tiu t 20 t/ha cho vng kh khn, 40 t/ha cho vng thun lihn v nc ti. Kiu cy cho vng kh khn l chiu cao va phi, l di trung

bnh, l pha trn thng, l pha di r xung ln t c di.(ii) Gi c c ch chng hoc chu hn, kh nng phc hi nhanh sau cc

t hn.(iii) To cc ging c thi gian sinh trng khc nhau thch ng vi cc

vng sinh thi, t mn cm vi quang chu k.(iv) Gi c cc c tnh nng sinh hc tt nh bng di, phi mu tt, ht

khng h, phm cht ht tt, n nh v mt di truyn, cm mm.(v) Nng cao tnh chng chu su bnh t cc vt liu ci tin (ch yu l

bn ln) ni bt l: chng chu bnh o n, kh vn, m nu, su c thn, rylng trng, su cun l v tuyn trng...

(vi) Duy tr v nng cao tnh chng chu vi cc yu t bt li ca t nhthiu ln, tha nhm, mangan...

Cc yu t c tnh cht a phng nh chu nhit thp cc vng nicao, ht go thm ngon, ni nh do... c thay i theo tng vng. Do s bini mi trng sinh thi trng la cn gia ni ny vi ni khc, cn xy dngchng trnh nghin cu c th ci tin ging la cn ph hp vi cc iukin sinh thi c trng. S m t r rt cc c tnh mi loi ging, mi loimi trng khc nhau l tiu chun chn lc c hiu qu.2.2.4.Tng lai ca cy la cn v la chu hn

37


38/43

Tuy xut hin sau la nc nhng hnh thc trng la cn nh du mtbc pht trin ca ngh trng la. Vi nng sut v cng thp, v sao la cnvn tip tc c trng? l cu hi m nhiu ngi t ra.

Thc t cho thy, sn xut la cn vn cn quan trng v l ngun cung cp

lng thc ch yu ca nhn dn vng cao. Theo s liu sn xut lng thckhu vc Ty Bc nm 1989, sn lng la cn (la nng, ry) ng gp212,8 nghn tn trn tng s 388,1 nghn tn la, chim 66,2%. C vng, snlng la nng ry chim 30-40% tng sn lng lng thc. Hn th so vimt s ging cy trng khc, cy la cn c u th trong vic s dng tt nhtlng nc tri, kh nng mt trng t xy ra. ng thi, vic thay th cy lacn bng h thng cy trng khc cha lm c do nhiu iu kin kinh t, thtrng v tp qun x hi chi phi [3], [26], [21].

Bn cnh , vic pht trin cc ging la chu hn lun l mt mc tiuchn ging c bn v lu di nc ta. Cc ging la chu hn c nng sut cao,cht lng tt ngay trong iu kin kh hn v thiu nc s thay th cho ccging la cn c truyn nng sut thp. Thm ch thay th cho c cc ging lanc khng c kh nng chu hn. iu gip chng ta tit kim lng ncdng trong sn xut la, mt iu rt c ngha trong tnh hnh ngy mt khanhim ngun nc nh hin nay v trong tng lai. t nht, cc ging la mi s

phi c c tnh chu hn kh [16], [17].Mt l do khc cho thy s cn thit ca cng tc chn to ging la chu

hn l cng tc thu li. Nu trng la trong iu kin ti tiu ch ng lrt tt. Tuy nhin, h thng thu li ca nc ta ang lm vic di cng sutthit k v chng ta ang tht bi trong vic phng chng l lt cng nh hnhn [60]. Theo Gio s Nguyn Vn Lut (2001) [22], ngay ti ng bng sngCu Long mt khu vc c kh nhiu cng trnh thu li, vi 2 triu ha trng lam din tch ti tiu c lng ch t 700.000 ha nn thng thiu nc ngtv b mn xm ln vo ma kh. R rng, h thng thu li ca nc ta cn qunhiu bt cp, hot ng km hiu qu v chi ph tn km [5], [11], [17], [60].Trong hon cnh nh vy, cc loi la chu hn hay loi s dng nc tit kims rt hu ch trong sn xut la.2.5.Nhng kt lun rt ra t tng quan nghin cu.

La cn l mt b phn cu thnh trong sn xut la, c trng bi ccnng h nh, sinh sng cc vng ngho nht trn th gii. Tuy nng sut khngcao song la cn vn l loi cy trng khng th thay th nhng vng cao haynhng vng kh khn v nc ti, ng thi l ngun cung cp lng thc tich quan trng ca cc dn tc thiu s. Do cc vng sinh thi rt c th vkhc bit, la cn a phng l ngun gen qu cho cng tc lai to, chn lc, bsung cc tnh trng c trng nh tnh chu rt, chng chu su bnh v chngchu hn... cho cy la.

Cc nh khoa hc trn th gii v Vit Nam c rt nhiu ngh

Documents

Trang_De cuong NC