Stylet penetration behaviors of Myzus persicae (Hemiptera: Aphididae) on four Ipomoea spp. infected or noninfected with sweet potato potyviruses

Myzus persicae (Sulzer) is an efficient vector of potyviruses in sweet potato, Ipomoea batatas (L.). These potyviruses also infect members of the morning glory family Ipomoea cordatotriloba Dennstedt and Ipomoea hederacea Jacqin commonly found within or around sweet potato fields. Infection of sweet potato with potyviruses increases the intrinsic rate of increase of M. persicae. Thus, from the epidemiological stand point, virus infection can modify vector population dynamics, and therefore increase virus spread. To better understand this, stylet penetration behaviors of M. persicae on virus infected and noninfected sweet potato cvs. 'Beauregard' and 'Evangeline', as well as morning glory plants I. cordatotriloba and I. hederacea were monitored. Stylet penetration behaviors associated with nonpersistent virus transmission such as time to first intracellular puncture (potential drop), number of potential drops, duration of potential drop, duration of potential drop subphase II-3, and number of potential drops with subphase II-3 pulses were significantly increased on virus-infected compared with noninfected Beauregard, but greatly reduced on virus-infected compared with noninfected I. hederacea plants. Stylet penetration behaviors associated with host acceptance such as reduced nonprobing duration and nonprobing events were greater on virus-infected compared with noninfected Beauregard plants. In contrast, on Evangeline, I. cordatotriloba and I. hederacea stylet penetration behaviors by M. persicae indicate it had less preference for virus-infected compared with noninfected plants.

Epidemiology of soybean vein necrosis-associated virus

Soybean vein necrosis-associated virus has been linked to an emerging soybean disease in the United States and Canada. Virus distribution and population structure in major growing areas were evaluated. Data were employed to design and develop sensitive detection protocols, able to detect all virus isolates available in databases. The host range for the virus was assessed and several species were found to sustain virus replication, including ivyleaf morning glory, a common weed species in soybean-growing areas in the United States. Koch's postulates were fulfilled using soybean thrips and transmission efficiency was determined. This article provides significant insight into the biology of the most widespread soybean virus in the United States.

Population dynamics of three aphid species (Hemiptera: Aphididae) on four Ipomoea spp. infected or noninfected with sweetpotato potyviruses

Three aphid species, Aphis gossypii Glover and Myzus persicae (Sulzer) (efficient sweetpotato potyvirus vectors) and Rhopalosiphum padi (L.) (an inefficient vector), are commonly found in sweet potato, Ipomoea batatas (L.), in Louisiana. Field-grown sweet potatoes are naturally infected with several potyviruses: Sweet potato feathery mottle virus, Sweet potato virus G, and Sweet potato virus 2. Thus, these aphids commonly encounter virus-infected hosts. What is not known is how each of these aphids responds to sweet potato, either infected or virus-free. The objectives of this study were to 1) determine if these aphid species can colonize mixed virus-infected sweet potato 'Beauregard', and if so, 2) determine the effects of virus infection on the population dynamics of each aphid. A. gossypii failed to larviposit and R. padi deposited a single nymph that died within a day on mixed virus-infected Beauregard. M. persicae larviposited and colonized Beauregard and further life-table analyses were warranted. M. persicae had a significantly greater reproduction on sweet potato cultivars Beauregard and 'Evangeline' with mixed virus infection compared with noninfected plants. On morning glory species, Ipomoea cordatotriloba (Dennestedt) and Ipomoea hederacea (Jacquin), M. persicae had a significantly lower reproduction on Sweet potato feathery mottle virus-infected compared with noninfected plants.

Sweepoviruses cause disease in sweet potato and related Ipomoea spp.: fulfilling Koch's postulates for a divergent group in the genus begomovirus

Sweet potato (Ipomoea batatas) and related Ipomoea species are frequently infected by monopartite begomoviruses (genus Begomovirus, family Geminiviridae), known as sweepoviruses. Unlike other geminiviruses, the genomes of sweepoviruses have been recalcitrant to rendering infectious clones to date. Thus, Koch's postulates have not been fullfilled for any of the viruses in this group. Three novel species of sweepoviruses have recently been described in Spain: Sweet potato leaf curl Lanzarote virus (SPLCLaV), Sweet potato leaf curl Spain virus (SPLCSV) and Sweet potato leaf curl Canary virus (SPLCCaV). Here we describe the generation of the first infectious clone of an isolate (ES:MAL:BG30:06) of SPLCLaV. The clone consisted of a complete tandem dimeric viral genome in a binary vector. Successful infection by agroinoculation of several species of Ipomoea (including sweet potato) and Nicotiana benthamiana was confirmed by PCR, dot blot and Southern blot hybridization. Symptoms observed in infected plants consisted of leaf curl, yellowing, growth reduction and vein yellowing. Two varieties of sweet potato, 'Beauregard' and 'Promesa', were infected by agroinoculation, and symptoms of leaf curl and interveinal loss of purple colouration were observed, respectively. The virus present in agroinfected plants was readily transmitted by the whitefly Bemisia tabaci to I. setosa plants. The progeny virus population present in agroinfected I. setosa and sweet potato plants was isolated and identity to the original isolate was confirmed by sequencing. Therefore, Koch's postulates were fulfilled for the first time for a sweepovirus.