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Title: Field Resistance to Potato Stem Colonization by the Black Dot Pathogen Colletotrichum coccodes

item NITZAN, NADAV - Washington State University
item EVANS, MARC - Washington State University
item CUMMINGS, TOM - Washington State University
item JOHNSON, DENNIS - Washington State University
item BATCHELOR, DALLAS - Con Agra Foods, Inc
item OLSEN, CHRIS - Lj Olsen, Inc
item Haynes, Kathleen
item Brown, Charles - Chuck

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2009
Publication Date: 11/1/2009
Citation: Nitzan, N., Evans, M.A., Cummings, T.F., Johnson, D.A., Batchelor, D.L., Olsen, C., Brown, C.R. 2009. Field Resistance to Potato Stem Colonization by the Black Dot Pathogen Colletotrichum coccodes. Plant Disease. 93(11):1116-1122.

Interpretive Summary: Black dot is serious fungal disease of potato. It has emerged as a major limitation on yield in the Columbia Basin of the Northwest in the last ten years. There are no good chemical controls for it. Much of the seed that is planted these days is contaminated with black dot. This means that isolation and quarantine has ceased to be an effective control measure. The fungus is harbored in the potato plant largely in a symptomless status until the potato plant flowers and starts to get old. The fungus mobilizes spreading throughout the tissue at the crown of the plant and moves up the stem. Breeding varieites that are resistant to black dot is the best solution. We found a number of clones in our breeding program that resisted the spread of black dot up the stem and resisted rot of the crown of the plant. These clones all have a common ancestor, the variety Summit Russet. Although this variety has not had commercial success, it is good parent for black dot resistance. Deploying new varieties with black dot resistance could increase the yield by fifteen percent adding 25 million dollars to the net receipts.

Technical Abstract: Forty six potato selections (experimental clones and commercial cultivars) were tested for resistance to black dot, caused by the fungal pathogen Colletotrichum coccodes, in three field trials from 2006 to 2008. Resistance was determined by comparing disease severity on aboveground stem to the average disease severity of the three industry susceptible standard cultivars Russet Burbank, Ranger Russet and Umatilla Russet. Selections with less (P<0.05) disease than the standards were regarded resistant; those with notably (0.05=P=0.1) less disease than the standards were considered moderately-resistant. Four selections, PA95B2-4, PA98NM38-1, PO94A009-7 and POR00HG5-1 that were tested all years demonstrated resistance to black dot. These four selections also possess resistance to root galling, caused by the powdery scab pathogen Spongospora subterranea f.s. subterranea. The three potato selections PA95B2-4, PA98NM38-1 and PO94009-7 also have two other factors in common: (i) they were derived from an introgression program to incorporate resistance to the Columbia root-knot nematode Meloidogyne chitwoodi from the Mexican wild species Solanum bulbocastanum; and (ii) they have the commercial cultivar Summit Russet appearing more than once in their ancestry. The last selection POR00HG5-1 is a progeny of a cross with the wild species Solanum hougasii. These four selections are promising steps towards a sustainable management of black dot and powdery scab and will be further tested and used in our breeding program.