SPATIAL AND TEMPORAL PATTERNS OF SPOTTED WILT EPIDEMICS IN PEANUT

The spatio-temporal patterns of spotted wilt disease in peanut, caused by thrips-vectored tomato spotted wilt tospovirus (TSWV), were analyz ed by several methods. The spatial distributions of symptomatic plants were mapped at 2-wk intervals during two consecutive years in fields of the susceptible peanut cultivar Florunner and in the resistant cult ivar Southern Runner. The disease frequency data were subjected to qua drat analyses, including indices of dispersion (variance/mean ratio an d the negative binomial k parameter), comparison of frequency distribu tions of symptomatic plants to expected distributions derived from sev eral models of spatial dispersion (binomial, Poisson, and negative bin omial), and two-dimensional distance class analysis at each sampling i nterval. Although significant spatial aggregation of diseased plants w as detected in most samples, random or nearly random clusters of infec ted plants that apparently arose from a continuous immigration of viru liferous vectors dominated spatial aspects of epidemic progress. Aside from smaller incidence of disease in the resistant compared to the su sceptible cultivar, no effect of cultivar was noted in relation to spa tial or temporal patterns of disease development in this pathosystem. Spotted wilt temporal progress was well described by monomolecular mod els of disease progress in each cultivar and year. The data and analys es were consistent with the hypothesis that most infections arise as a result of primary transmission and that there is limited secondary sp read of TSWV after it becomes established in the field.