بیماریهای فیزیولوژیک

winter ice damage in poorly drained areas of turf

Low-Temperature Effects

Tomato “catface,”

killing of young seeds in canola

potato freezing necrosis

subfreezing kill of winter wheat plants

Relative susceptibility of fresh vegetables to freezing injury

Symptoms of freezing injury

(A). Freezing injury of citrus. If a thawed fruit is pulled apart, the membranes between the segments appear water-soaked. Fruits that have been severely frozen may exhibit browning of peel or mushy breakdown.

(B). Freezing injury of peaches is characterized by a translucent, water-soaked appearance of the flesh. Severely frozen fruit tends to break down on thawing, the injured tissue becoming soft, brown and watery

A B

Citrus are tropical fruit that thrive in warm temperatures and generally have a low affinity for cold temperatures. Citrus trees are subject to frost damage and freezing when exposed to temperatures of -10C or lower

Freeze Damage

All species of palms are susceptible to cold temperature, but the temperature at which injury will occur is dependent on the species and the extent of its cold acclimation.

• Appear within a few days• Hard freeze canopy will dry

out & smell like hay• Can lead secondary bud rots

Freeze Damage palms

Chilling Injury

Some very tropical palms can be damaged by temperatures well above freezing

Northern Exposure

Evergreen Damage

Rhododendron Damage

Frost Injury Freeze Damage

Frost Injury

Late Frost InjuryFrost Damage

Chilling injury:If the plants grown in hot temperature are exposed to low temperature, they will be killed (or) severely injured. When the night temperature is below 15°C field crops may show yellowing symptoms (eg) Tropical annuals.

Freezing injury :When the plants are exposed to how temperature, water freezes into ice crystals in the intercellular spaces. (eg) Cell dehydration Temperate crops (potato, tea etc.,)

Suffocation: Formation of thick cover of ice/snow on the soil surface presents the entry of oxygen and crop suffers. This presents the respiration and lead to accumulation of harmful substances.

Frost damage:

(1) Advective frosts

Advective frosts are due to incursion of large masses of cold air over a region from the colder areas.

(2) Radiation frost:

Occur on clear calm nights when heat is freely radiated from all exposed objects.

گياهان روي نامطلوبسرما اثرات از جلوگيري: آيد بوجود منطقه هر در است ممکن سرما نوع دو

تشعشعي .  1 radiative freezingسرمازدگيهواي اينکه بدون محدود محيط و معين محدوده يک در و بوده اي منطقه کامال که سرمايي   . آرام و ساکت هاي درشب همواره سرما، نوع اين کند نفوذ منطقه به جاها ساير از سردي

کند بروز بهار اوايل يا زمستان اواخر اگردر و ميشود، ظاهر وباران برف و باد ابرو بدونميشود . محسوب خطرناک

اي.  2 جبهه advective freezingسرمازدگيموجب که آيد مي پيش منطقه از آن عبور و قطبي سرد جريان يک هجوم دراثر که سرماي . اين ميشود صفر زير درجه چندين به دما سقوط و حرارت درجه ناگهاني و شديد تقليلجاي ازيک همواره که است اين آنها کلي خاصيت و بوده آسماني نزوالت با توأم اغلب جريانيعني درختان، خواب دوران در بيشتر و نميباشند محلي و ميکنند ونفوذ منتقل منطقه به ديگرودوام مقاومت آن درمقابل زيادي حد تا سير سرد ميوه درختان که ميکنند بروز زمستانو. ميشود ديده خزان و بهار فصل اوايل در هايي سرما چنين ها سال بعضي در البته دارند

. ميگردد سنگين خسارات موجب

عمده دوبخش به عمدتا ازسرمازدگي هان گيا حفاظتشوند مي تقسيم

1 .    فعال حفاظت Active freeze protectionروشهايغيرفعال.  ) 2 حفاظت ي (Passive freeze protectionروشها

Plant management against frost damage: Frost free growing seasonAdjusting the sowing timeSelection of resistant varietiesSprinkler irrigation

Ice Nucleation Active (INA) Proteins

All proteins interact with water, but there are two classes of proteins in particular which

have a function relating to ice:

antifreeze proteins (AFPs) and ice-nucleation proteins (INPs). AFPs have particular structures known to inhibit formation of ice crystals by preventing ideal

alignment of water molecules for freezing into the crystal structure of ice.

INPs do just the opposite, and thus allow freezing to occur at warmer temperatures.

INPs are able to promote ice formation in raising the nucleation temperature,

ice-nucleating bacteria

Species Gene

Pseudomonas syringae inaZ

″ inaK

″ inaV

″ inaQ

″ 728a

Pseudomonas fluorescens inaW

Pseudomonas putida Not sequenced

Pseudomonas trivialis Not sequenced

Pseudomonas viridiflava Not sequenced

Pantoea ananatis inaA

″ inaU

Pantoea agglomerans inaE

Pantoea uredovora Not sequenced

Xanthomonas campestris inaX

Ice-nucleating bacteria trigger freezingsprayed with deionised water, then held at -4.0°C for 2 h

sprayed with IN+ P. syringae, then held at -4.0°C for 2 h

Ice-nucleating bacteria trigger freezing

How do they do it?

Kajava and Lindow. 1993. A model of the three-dimensional structure of ice nucleation proteins. J. Mol. Biol., 232, 709-717.

3 proteins stuck together

Enlargement of ice-nucleating protein

Kajava and Lindow. 1993. A model of the three-dimensional structure of ice nucleation proteins. J. Mol. Biol., 232, 709-717.

3 proteins stuck together

Enlargement of ice-nucleating protein

Water

Water

Ice

Antifreeze proteins (AFPs) or ice structuring proteins (ISPs) refer to a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria that permit their survival in subzero environments

common epiphytic ice nucleation active (INA) bacteria Pseudomonas syringae and Erwinia herbicola are sufficient to incite frost injury to sensitive plants at -5C. Bacterial ice nucleation on leaves can be detected at about -2°C, whereas the leaves themselves, ie. without INA bacteria, contain nuclei active only at much lower temperatures.

This product is freeze resistant and lowers the freezing point so it helps to increase the plants resistance to cold injuries.

CROPAIDNatural Plant Antifreeze

Made from a mixture of minerals and Thiobacillus’ bacteria (T. Ferrooxidant; T. Thiooxidant; T. Thioparus )

MOISTURE EFFECTSLow Soil Moisture Effects

(A) Wilting of pepper plants due to water stress.(B) Reduced growth, leaf scorching, and dieback of twigs of ornamental shrub due to prolonged water stress.

Wilting leaves due to water stress

Water Stress

Oldest leaves palm are usually the first to show symptoms

Failed maize crop after severe drought

Milwaukee Tree drought damage to a Norway Maple

drought damage to a Norway Maple tree causes leaves to brown

Leaf scorch can result from a single dry spell. If drought continues, the entire leaf will die.

Long-term drought can cause dieback in the upper branches of a tree

drought of maple

Tomato plants can develop several abiotic disorders that distort plants and blemish fruits. Abiotic disorders are not caused by a living pathogen, but rather are the result of cultural practices or environmental conditions. Generally, good cultural practices that ensure consistent plant growth will reduce the occurrence of abiotic disorders.Tomato varieties also differ in susceptibility to these disorders. By trial and error you can find the best varieties for your location. In addition, seed catalogs often give varietal information that may help avoid problems.

Disorders of Tomato

Disorders Physiologic Leaf RollBlossom-end RotSunscaldGrowth CracksCatfaceHerbicide Injury

Leaf roll is a physiological disorder of tomatoes that is most commonly associated with hot dry weather, but can occur in response to other stresses like fast growth, high production, and pruning. Leaf margins roll upward until they touch or overlap in an almost tube like fashion. Affected leaves are firm and leathery to the touch. This disorder is believed to be a strategy to conserve moisture. Lower leaves are commonly affected first. Once leaves roll, they will not unroll even if weather conditions become cool and wet. In severe conditions the entire plant may exhibit leaf roll. Leaf roll does not noticeably reduce plant growth or yield. Some varieties exhibit leaf roll more easily than others.

Physiologic Leaf Roll

Sunscald Sunscald occurs on tomato fruit that have been exposed to too much sun. This is common in plants that are suffering leaf loss from a leaf spot disease or insect feeding, but can also occur on plants that are over pruned or on fruit that are otherwise exposed to the sun. Sunscald results in a pale yellow to white spot on the side of the fruit facing the sun. This area may become a flattened, grayish-white spot. The surface may dry out to a paper like texture. Sunscald spots are frequently invaded by decay-causing fungi and bacteria that further rot the fruit. The best way to avoid sunscald is to maintain a healthy tomato plant through management of insect and disease pests that defoliate tomatoes.

Blossom-End Rot Blossom-end rot is one of the most common tomato disorders. Affected fruit have a tan to black flattened spot at the blossom end of the fruit. Secondary fungi and bacteria can enter the blossom end rot area, resulting in further decay of the fruit. Blossom end rot can appear on fruit in any stage of development, but it is most common when fruit are one-third to one-half grown. The first fruit produced by the plant are often most severely affected. Fruit that develop later in the season on the same plant can be unaffected.Blossom-end rot is caused by a calcium deficiency in the tomato plant. Although blossom end rot means that the plant does not have enough calcium with in the developing fruit, it does not mean that there is a lack of calcium in the soil. Often blossom end rot occurs as a result of several cultural or environmental factors that affect the plants ability to take up calcium. Fluctuations in soil moisture, heavy applications of nitrogen fertilizer, and injury roots can all predispose tomato plants to blossom end rot. The amount of calcium salt available to the plant decreases rapidly in the presence of excessive salts such as potassium, magnesium, ammonium, and sodium. Extreme fluctuation in moisture can also reduce the availability of calcium salts needed by the plant. Heavy applications of nitrogen fertilizers and abundant rain cause rapid and luxuriant plant growth and predispose the fruit to blossom-end rot, especially during periods of dry, hot weather. Blossom-end rot can be minimized by maintaining a uniform supply of moisture through regular watering and soil mulches, applying fertilizer according to the results of a soil test, and avoiding root injury by not cultivating within 1 foot of the base of the plant.

Blossom-end rot

Blossom-end rot

Blossom-End Rot (BER) - Characterized by a large, leathery brown or black spot on the bottom of the fruit. In some cases, internal BER can occur within fruit. It generally occurs on the first fruit cluster. BER is caused by a lack of calcium in the fruit which causes the fruit to die back creating the characteristic spot. What can you do to prevent it? Have your soil tested to make sure calcium is present in adequate amounts. Chances are the calcium level will be fine but if it is not, add limestone (for acid soils with a pH below 6), or gypsum when the soil pH is in the 6 to 7 range. If calcium levels are okay, the next most important control is to maintain optimum soil moisture. When tomatoes experience the slightest bit of drought, BER may result. Using mulches will usually significantly decrease BER as excessive evaporation from soil is reduced. If growing on bare ground, avoid cultivating too close to plants to prevent root damage and the need to maintain deep root development. Varieties will vary in their susceptibility so if you have a problem with a particular variety, choose a new one next year. When side-dressing plants, using a nitrate type fertilizer like calcium nitrate is preferable to ammonium based ones like urea. Finally, don't bother to use calcium sprays. They are worthless in combating the problem. The same problem can occur on pepper and eggplant.

Growth cracks result from extremely rapid fruit growth. This may be brought on by periods of abundant rain and high temperatures, or can occur when water is suddenly available to the plant through rain or irrigation after a period of drought. Cracks may radiate from the stem end of the fruit or may encircle the fruit. Cracks are often invaded by secondary fungi and bacteria that further rot the fruit. Maintaining even moisture by watering regularly and mulching the soil around the tomato plant can help reduce growth cracks. Varieties differ in susceptibility to cracking, and variety descriptions may be helpful in choosing a plant less likely to crack.

Fruit Cracking - This is due to rapid uptake of water by the fruit, as a result of heavy rain or heavy watering. The water can move to the fruit through the roots and also directly into the fruit around the stem scar. Cracks may be concentric (around the stem). (Fig. 6 a, b) , or radial (radiating out from the stem). (Fig. 7). To overcome the problem, choose crack resistant varieties like Mountain Pride or Mountain Delight and maintain uniform soil moisture by mulching and steady watering.

Catface Catface is a condition involving malformation and scarring of fruits, particularly at the blossom end. Affected fruit are often somewhat flat with a corky brown scar covering the base of the fruit. Catfaced fruit can have cavities extending deep into the flesh The causes of catfacing are not definitely known, but it is generally agreed that any disturbance to flowers or flower buds can lead to abnormally shaped fruits. Cold temperatures and contact with hormone-type herbicide sprays are commonly believed to be responsible for catface. Large fruited tomatoes are more susceptible to catface than small fruited tomatoes. In addition some varieties are particularly prone to catface and should be avoided if catface has been a problem in the past.

Catface. - Seen as severe scarring on the blossom end of the fruit, usually more severe on the first fruit harvested in the summer and on very large fruited varieties. Extended periods with temperatures of 60-65F during the day and 50-60F at night cause the problem. The temperatures do not directly affect the fruit but instead the flowers when they are very small. Protection of some kind (row covers, wall of waters, hot caps, etc.) will minimize the problem as will changing varieties. Although we normally think of the early fruit being affected, cool nights extended over the mid-season could cause the problem in later plantings.