Response of russet-skinned potato cultivars to increasing soil populations of Verticillium dahliae

Verticillium wilt, mainly caused by the soil-borne fungal pathogen Verticillium dahliae, is a major disease of potato that affects yield and quality of potatoes worldwide. While several russet-skinned cultivars with high levels of resistance are commercially available, the preferred cultivars by processors are susceptible to Verticillium wilt. Hence, a better understanding of the relationship between soil infestation level and variation in the reaction of potato cultivars with differing levels of disease susceptibility is important for management decisions. In this study, we evaluated disease development, pathogen colonization, yield, and tuber vascular discoloration of russet-skinned potato cultivars with Verticillium wilt reaction ranging from resistant to susceptible when challenged with a range of soil infestation levels. Results indicated that Verticillium wilt severity of susceptible cultivar Russet Norkotah was higher than all other cultivars, regardless of the infestation level. Significant differences in wilt were not observed across resistant cultivars Dakota Trailblazer, Bannock Russet, and Premier Russet, or the moderately resistant cultivar Ranger Russet. Stem colonization, measured by qPCR, increased significantly with higher infestation levels across cultivars in greenhouse trials. In field trials, stem colonization remained low in resistant cultivars. Significant increases in stem colonization were observed across infestation rates with moderately susceptible Russet Burbank in one year and susceptible Russet Norkotah in both years. In field trials, total yield and tuber vascular discoloration were unaffected by increasing levels of soil infestation. Additionally, multiple regression analysis indicated that wilt incidence and tuber discoloration could be significant predictors of the yield with the exception of Russet Norkotah. These results demonstrate that genetic resistance in cultivars did not break down under increasing soil pathogen levels, further highlighting the importance of planting resistant cultivars as an essential management practice of V. dahliae to minimize wilt development, yield losses, and to avoid pathogen buildup in the soil.