Host diversity can reduce potato late blight severity for focal and general patterns of primary inoculum

The use of host diversity as a tool for management of potato late blight ha s not been viewed as promising in the past. But the increasing importance o f late blight internationally has brought new consideration to all potentia l management tools. We studied the effect of host diversity on epidemics of potato late blight in Oregon, where there was little outside inoculum. The experimental system consisted of susceptible potato cv. Red LaSoda and a h ighly resistant breeding selection, inoculated with local isolates of US-X Phytophthora infestans. Potatoes were grown in single-genotype plots and al so in a mixture of 10 susceptible and 26 resistant potato plants. Half of t he plots received inoculation evenly throughout the plot (general inoculati on) and half received an equal quantity of inoculum in only one corner of t he plot (focal inoculation). The area under the disease progress curve (AUD PC) was greater in single genotype stands of susceptible cv. Red LaSoda ino culated throughout the plot than with stands inoculated in one focus. The h ost-diversity effect on foliar late blight was significant in both years of the investigation; the AUDPC was reduced by an average of 37% in 1997 and 36% in 1998, compared with the mean disease level for the potato genotypes grown separately. Though the evidence for influence of inoculum pattern on host-diversity effects was weak (P = 0.15), in both years there was a trend toward greater host-diversity effects for general inoculation. Statistical significance of host-diversity effects on tuber yield and blight were foun d only in one of the two years. In that year, tuber yield from both the res istant and susceptible cultivar was increased in mixtures compared with sin gle genotype stands and tuber blight was decreased in mixtures for suscepti ble cv. Red LaSoda.