Verticillium wilt of potato: A model of key factors related to disease severity and tuber yield in southeastern Idaho

In three years (1994, 1995, and 1996), a total of 100 commercial potato fie lds in southeastern Idaho were surveyed for soil variables, severity of Ver ticillium wilt, soil inoculum density of Verticillium dahliae and Colletotr ichum coccodes, colonization of stems, root, and tubers by V. dahliae and C . coccodes, and tuber yield, size, and quality. As a generalization, factor s related to soil integrity (organic matter, organic nitrogen, and increase d nutrient availability) were most closely related to wilt suppression and higher tuber yields, whereas factors related to loss of soil integrity (sod ium and reduced nutrient availability) were related to increased wilt and l ower tuber yields. In a multiple regression analysis, three independent var iables, feeder-root infections by V. dahliae, sodium content in soil, and s oil organic content, were significant predictors of tuber yield. With these three factors, this model accounted for 49%, 53%, and 62% of the field var iability related to total yield in 1994, 1995, and 1996, respectively. Thro ughout this investigation, V. dahliae root infections had the most direct e ffect on tuber yield, which emphasizes the importance of quantifying root i nfections in epidemiological studies of Verticillium wilt. Based on these r esults, organic matter may be one factor that can be manipulated for suppre ssion of Verticillium wilt without reducing soil populations of the pathoge n.