ARS | Publication request: Resistance to Black Dot in Potato

Submitted to: Potato Progress
Publication Type: Popular Publication
Publication Acceptance Date: March 15, 2008
Publication Date: April 18, 2008
Citation: Nitzan, N., Cummingson, T., Johnson, D., Batchelor, D., Olsen, C., Brown, C.R. 2008. Resistance to Black Dot in Potato. Potato Progress. VIII (5) p 1-3.

Technical Abstract: Black dot fungus can colonize tubers on the surface, in the stolon end, or in a combination of both.On the surface the fungus is prevalent as sclerotia, and in the stolon end the fungus colonizes the vascular tissuesas hyphae. The fungus is introduced to non-infested soils mostly by infected potato tubers. It becomes soil-borneas infected plant debris carrying sclerotia (Fig.2) is left in the field. The disease develops from either the soil-borne or the tuber-borne inocula, which are the major sources of inoculum. Inoculum may also be air-borne as sclerotia disseminated by wind, or as spores splashed onto leaves o stems by irrigation water. Among the three inocula sources, soil-borne is the more aggressive causing higher disease severities than tuber or air-borne inocula. Infections of potato plants usually initiate on roots and stolons. The infection takes place relatively early in the season without evident symptoms of chlorosis or necrosis on the foliage. As potato plants enter the tuber bulking stage (growth stage 4) and the foliage starts to senesce the fungus spreads into the aboveground stems andcolonizes the plant. At the end of the season sclerotia become visually evident on roots, stolons, and stems, andblemishes may be present on tubers. A breeding program was initiated in 2006, screening potato selections (clones and commercial cultivars) for resistance to black dot. To evaluate disease, stem disks were removed from the aboveground stem at different heights, and a disease severity index was calculated. To standardize the screening Russet Burbank was chosen as the susceptible standard and all selections were contrasted to R. Burbank. Selections with disease severities lower than Russet Burbank were considered resistance. In 2006, thirty-six potato selections were tested for black dot resistance in a commercial field near Moses Lake. The plants were exposed to the natural inoculum that was present in the field. Nineteen selections were more resistant to black dot than Russet Burbank (Fig. 3). These selections progressed to the next season and were retested in 2007 in Moses Lake (Fig. 4). Summit Russet, PA98NM38-1, A00681-7 and A0012-5 were resistant to black dot both years (Figs. 3 & 4) indicating the presence of resistance to black dot in potato germplasm. Currently, the resistant selections are retested in Moses Lake the third year, and greenhouse studies are in progress in attempt to develop a rapid screening technique that would hopefully correlate with the results from the field.Resistance to Black Dot in Potato.