Within-crop spread of sweet potato virus disease and the population dynamics of its whitefly and aphid vectors

Abstract

Sweet potato virus disease (SPVD) is the most damaging disease of sweet potato ( Ipomoea batatas (L) Lam) in Uganda and results from dual infections of Sweet potato feathery mottle virus (SPFMV), vectored by aphids, and Sweet potato chlorotic stunt virus (SPCSV), vectored by whiteflies. For three cropping cycles, whiteflies ( Bemisia tabaci), aphids ( Myzus persicae and Aphis gossypii) and the spread of SPVD were monitored within and outside the sweet potato crop containing a central plot of SPVD-infected plants. There were similar catches of whiteflies on sticky traps placed on poles within the crop at different distances and directions around the infected plot. Outside the crop, there were also similar catches of whiteflies near (15 m) and far away (100 m) from the sweet potato crop. However, more whiteflies were trapped within than outside the crop. Most whiteflies were trapped close to the canopy. Aphids were rarely found on sweet potato plants, although they were commonly found on the traps. The number of aphids trapped inside the crop did not differ significantly from those trapped outside the crop. Consistently, a higher proportion of plants developed SPVD symptoms in the inner square than plants located further away from the infected plot. Number of infected plants correlated with trap catches of whiteflies only for the first season.