Finding the fighters. Maturity-adjusted resistance of potato cultivars to Verticillium wilt

Authors: Simko, Ivan; Haynes, Kathleen

Submitted to: Potato Grower
Publication Type: Trade Journal
Publication Acceptance Date: 8/10/2017
Publication Date: 8/28/2017
Publication URL: http://handle.nal.usda.gov/10113/5755710
Citation: Simko, I., Haynes, K.G. 2017. Finding the fighters. Maturity-adjusted resistance of potato cultivars to Verticillium wilt. Potato Grower. 46:38-39.

Interpretive Summary: Verticillium wilt, also known as potato early dying, is a soil-borne fungal pathogen of potato. Early maturing cultivars are generally more susceptible to the disease than later maturing cultivars, however, there is some variation in this relationship. This study showed that maturity rating explains part of the resistance but is not the sole source of resistance. After adjusting disease ratings for maturity, some resistant cultivars were rated more susceptible and some susceptible cultivars were rated more resistant. This study will benefit potato breeders looking to identify sources of resistance to early dying that are less dependent on plant maturity and enable them to develop early maturing, Verticillium wilt resistant cultivars in the future.

Technical Abstract: Verticillium wilt of potato, also known as early dying disease, is caused by two soil-borne fungi of Verticillium: V. dahliae and V. albo-atrum. Of the two, V. dahliae is found in most of the U.S., whereas, V. albo-atrum is found primarily in the northern U.S. and southern Canada. The fungus is capable of long-term survival in the soil and infects plants through the root system and from there spreads to the vascular tissue where it interferes with water and nutrient transport. Disease symptoms on potato leaves include wilting, chlorosis, and eventually necrosis. Stems of infected plants show vascular discoloration and tubers develop necrosis in the vascular tissue which substantially reduces their quality. Verticillium wilt can also markedly decrease yield. Soil fumigation with methyl bromide can control Verticillium wilt but this fungicide is being phased out because it depletes the ozone layer. Breeding for improved resistance to Verticillium wilt is highly desirable. No potato cultivars are completely resistant but some show a fairly high level of partial resistance. Potato growers need more information about partial resistance to identify cultivars suitable for production. Potato breeders need such information to select parental materials to develop resistant cultivars. Cultivar variations in plant maturity can make it difficult to separate out symptoms of the disease from natural senescence. Early maturing cultivars are generally more susceptible to the disease than late maturing cultivars. In our study, we evaluated 274 cultivars for their reaction to infection with V. dahliae by inoculating the soil around two-week old potted plants growing in the greenhouse. We also evaluated the same 274 cultivars for maturity based on the development of buds and flowering in the greenhouse. The experiment was repeated a second year. There was a moderate correlation between resistance and maturity in both years, indicating, as expected, that early maturing cultivars were generally more susceptible to Verticillium wilt than later maturing cultivars. The most resistant cultivars were Abnaki, Cariboo, Houma, Navajo, Reddale and Russette. The most susceptible cultivars were Irish Cobbler, Pungo and Russet Norkotah. These results indicate that plant maturity should be taken into consideration when evaluating potato resistance to Verticillium wilt. Snowden and Ranger Russet are just two examples of cultivars rated with a higher level of resistance when resistance is not adjusted for by maturity. Kennebec and Russet Legend are just two examples of cultivars rated with a lower level of resistance when resistance is not adjusted for by maturity. A maturity-adjusted resistance rating was calculated from residuals of the regression between resistance and maturity. The maturity-adjusted resistance rating minimizes the effect of maturity on the rating for resistance. However, even after adjusting resistance ratings for maturity, there were still significant differences among the cultivars, indicating that a large part of the resistance cannot be explained by maturity alone. With maturity-adjusted resistance, both short-season and long-season cultivars with partial resistance to Verticillium wilt can be identified. This information will benefit growers in choosing cultivars for their particular growing environment and also enable breeders to select cultivars for use as parents with resistance less influenced by maturity.