Dynamics of the sweetpotato potyvirus aphid pathosystem in Louisiana

Sweetpotato potyviruses [Sweet potato feathery mottle virus (SPFMV), Sweet potato virus G (SPVG) and Sweet potato virus 2 (SPV2)] commonly infect sweetpotato and weedy morning glories in the USA. These viruses are transmitted in a non-persistent manner by various aphid species and cause up to 15% yield loss. Sweetpotato is vegetatively propagated, and in the USA growers are supplied with virus tested propagation material to minimize impact of viruses. However the rapid re-infection of these materials with viruses warranted further studies to determine factors that influence the epidemiology of these viruses. The objectives of this study were: (i) to determine if differences in acquisition hosts, aphid species and infection status influenced transmission of SPFMV; (ii) to determine how aphid abundance, aphid species diversity and virus titers relate to the spread of potyviruses in Louisiana sweetpotato fields; to determine the effects of virus infection on the population dynamics of aphids on sweetpotato and morning glories; and (iv) to determine the effects of virus infection on stylet penetration behaviors of aphids. SPFMV was transmitted at a greater rate from morning glories which also had greater virus titers compared with sweetpotato and from mixed infection sources than from singly infected sources, and Aphis gossypii was the most efficient vector. Aphids were captured in fields during the entire crop cycle, and A.gossypii and Rhopalosiphum padi, were the most abundant species occurring throughout the growing season. Virus infection of sentinel plants occurred mainly during the months of June to August when virus titers were high in sweetpotato plants. SPFMV was more commonly detected than SPVG or SPV2 in sentinel plants. Myzus persicae had a significantly greater reproduction on sweetpotato cvs. Beauregard and Evangeline with mixed virus infection compared with non-infected plants. Stylet penetration behaviors were variable depending on host and virus infection status. Differences in virus transmission rates depending on host plant, aphid species, virus species and virus titers,and pattern of spread in sweetpotato fields suggest the dissemination of sweetpotato potyviruses is influenced by the source of inoculum, the quantity of inoculum, virus species and aphid species vectors.