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 fields in southeastern Idaho were surveyed for soil variables, severity of Verticillium wilt, soil inoculum density ofVerticillium dahliae andColletotrichum coccodes, colonization of stems, root, and tubers byV. dahliae andC. coccodes, and tuber yield, size, and quality. As a generalization, factors related to soil integrity (organic matter, organic nitrogen, and increased nutrient availability) were most closely related to wilt suppression and higher tuber yields, whereas factors related to loss of soil integrity (sodium and reduced nutrient availability) were related to increased wilt and lower tuber yields. In a multiple regression analysis, three independent variables, feeder-root infections byV. dahliae, sodium content in soil, and soil organic content, were significant predictors of tuber yield. With these three factors, this model accounted for 49%, 53%, and 62% of the field variability related to total yield in 1994, 1995, and 1996, respectively. Throughout this investigation,V. dahliae root infections had the most direct effect on tuber yield, which emphasizes the importance of quantifying root infections in epidemiological studies of Verticillium wilt. Based on these results, organic matter may be one factor that can be manipulated for suppression of Verticillium wilt without reducing soil populations of the pathogen.