POR06V12-3

PA00V6-3

PA92A8-17

Rysto MPI61.510/53

PVY resistance

4x hybrid

Lemhi Russet

S. chacoense

(4x)

S. chacoense (2x) RPLRV

Leafroll resistance

Gem Russet

PA01N22-2

PA97B3-6

CRS resistance

A8469-5

A77715-6

Lemhi Russet

S. vernei

PI 407415

(CIP 800291)

Summit Russet

Field Selection of Resistance to Corky Ringspot Disease

INTRODUCTION: “Spraing” is a descriptor used world wide for an internal disease symptom (brown or rust colored concentric arcs or rings, spot and flecks) in potatoes. Spraing is associated with two viruses Tobacco Rattle Virus (TRV) and Potato Mop Top Virus (PMTV). The first report of Corky Ringspot Disease (CRS) was in 1946 by Arthur Eddins in Hastings, Florida. CRS is the common term used for the visuals associated with TRV and is vectored by the Stubby Root nematode (Paratrichodorus allius). PMTV is vectored by Powdery Scab (Spongospora subterranea). It is extremely unusual for either of these soil-borne viruses to show foliar symptoms. Most recently it has been shown that the tuber symptomology of these diseases overlap extensively and cannot be definitively determined without specific molecular testing procedures. Additionally, it is possible to have mixed infections. A duplex reverse transcription polymerase chain reaction (RT-PCR) is performed to accurately determine which viruses are present.

FIELD EVALUATIONS: A dedicated two acre field of viruliferous Stubby Root nematode has been maintained for decades by rotating Sordan and test plots. This provides a very intense disease pressure to challenge new breeding lines. Screening data shows the combined percent with internal defects and the Disease Severity Incidence (DSI) associated with Tobacco Rattle Virus and Corky Ringspot Disease.

2013 2014 2015 Russet Clones % w/int Avg DSI % w/int Avg DSI % w/int Avg DSI

POR06V12-3 0.00 0.00 0.36 0.05 10.00 2.60 OR05039-4 0.83 0.42 3.23 1.04 23.33 8.65 AO03123-2 12.39 5.18 0.00 0.00 30.83 11.98 A03921-2 36.19 21.87 58.02 29.55 60.00 28.13 A03141-6 38.68 21.18 26.25 14.03 32.68 12.14 AO01114-4 39.00 30.66 20.51 29.05 65.26 46.96 Russet Norkotah 40.66 34.67 88.68 73.99 66.08 41.91 Ranger Russet 43.24 38.20 76.56 51.35 77.50 56.63 AOR06070-1KF 45.45 30.61 41.41 26.37 6.67 2.40 A06021-1T 55.24 41.18 60.71 67.17 49.05 31.07 Shepody 61.80 41.42 46.67 23.25 62.47 35.15 Russet Burbank 65.52 53.47 62.96 58.34 73.27 54.33

C. Brown R. Quick L. Hamlin J. Whitworth R. Novy

USDA-ARS

V. Sathuvalli B. Charlton S. Yilma C. Shock Oregon State University

H. Mojtahedi M. Pavek R. Knowles Washington State University

TRV

PMTV

Foliar TRV and infected tubers showing a range of symptoms of TRV; POR06V12-3 is immune.

Foliar PMTV and infected tubers showing a range of symptoms of PMTV; POR06V12-3 is symptomless.

Evaluation Procedure: 1) Visual readings taken for 'internal defects' - tubers cut lengthwise, quartered and scored (0-8) based on the number of sides of the wedges that were affected

2) Disease Severity Index (DSI) was calculated for each replication by summing the scores (S) of each tuber evaluated (T) and dividing that number by the number of tubers evaluated times the worst possible score (8) and multiplying by 100

DSI = (∑ S)/(T*8)*100

010203040506070

POR06V12-3

Payette

Pomerelle

Classic Russet

Teton Russet

Mountain GemTarghee

RussetNorkotah

Ranger Russet

Shepody

Russet Burbank% w/int

Avg DSI

2013 – 2014 Combined Averages

PEDIGREE:

STATEGIES FOR CONTENDING WITH CRS:

Provide a product with conventional breeding that provides a sound agronomical solution for the grower, processor and consumer.

Knowledge is power: 1) Soil-borne pests 2) Can be persistent for years 3) Certified seed is not the solution for TRV.

Proactive machinery and field management to avoid spread of contaminated soil.

Crop rotation with non-viral hosts, such as mint or alfalfa.

CRS, depending on how it is measured, is charged to the grower at harvest. It is not until the product arrives to the packer or processor that it is determined the level of internal damage.

How do we determine disease resistance within the breeding program?

Should a CRS infectious nursery servicing the PNW breeding be maintained?

Reported in 1965 that TRV is vectored by the Stubby Root nematode (Paratrichodorus allius) nematode (Harrison, Hoff, Jensen 1965). Detection of the virus targets the coat protein by using RT-PCR in research laboratories.

IN CONCLUSION: It is unlikely that TRV appears in fields through seed. Fields with a historical outbreak are likely to have epidemics if not fumigated, even if no Stubby Root nematode is detected in soil samples. Fumigation easily costs 10% of the total production expense. Breeding for resistance is the best strategy. Research questions include: 1) How much resistance is enough? 2) Are there DNA markers that will aid in selection? 3) What is the priority of breeding CRS resistance? Through conventional breeding, over numerous years, POR06V12-3 has been developed and has ancestry from the three wild species S. chacoense, S. stoloniferum and S. vernei contributing resistances to Potato Leaf Roll Virus (PLRV), Potato Virus Y (PVY) and TRV, respectively. The moderate resistance to PMTV remains unknown. It is an advanced russeted potato cultivar in the Western Regional Trials. The multiple virus resistances can cut production costs and improve harvest quality, through reduction in fumigation and pesticide applications giving the grower and the processor the opportunity to have a more economically sound cultivar, which ultimately benefits the consumer.