First report of Sweet potato virus G in sweet potato in Italy

Abstract

Sweet potato (Ipomoea batatas) is the sixth most important food crop in terms of production globally. In Italy, sweet potato is mainly cultivated in Veneto province (northeast Italy), and to a lesser extent in Lazio and Apulia provinces, on a total area of about 400 hectares. Among the sweet potato pests, viruses are the second most important constraint next to sweet potato weevil (Barkessa, 2018). In 2020, tubers of six different genotypes, with uncertain geographical origins, were sent by a grower from Veneto province to IPSP-CNR, with the aim of ascertaining their phytosanitary status. Two tubers of each genotype were grown in an insect-proof greenhouse (26/22°C, day/night) under natural light conditions and transplanted in 25 cm diameter pots containing peat bog-moss as a substrate. After about one month, leaves of only one genotype (identified as DP/578) showed light diffuse chlorotic symptoms (Figures 1, 2). Sap extracts from both plants of each of the six genotypes were tested with ELISA using broad-spectrum potyvirus antibodies (Bioreba, Switzerland). Only the symptomatic genotype DP/578 tested positive to potyvirus antibodies. Total RNA was extracted from the leaves of the two plants of DP/578 and from a healthy plant, with the Plant RNA Kit (Omega Bio-Tek, USA), and subjected to RT-PCR using the universal Potyviridae forward primer (5'-GGBAAYAAYAGYGGDCARCC-3'; Gibbs & Mackenzie, 1997) and the reverse primer SPFMV-Rv (5'-TTGCACACCCCTCATTCCYAAG-3'; Parrella et al., 2006). An amplification product of approximately 1700 bp was produced only from samples with symptoms but not from the healthy control. Sequences obtained from the two symptomatic plants were identical (GenBank Accession No. MW456564) and showed highest identity (98.2%) with the CH2-32-1 isolate of Sweet potato virus G (SPVG) from China (MK778832). SPVG alone is not considered a real threat to sweet potato production since infected plants rarely display symptoms (Rännäli et al., 2008). Significant yield losses have been recorded only when SPVG co-infects sweet potato with other potyviruses such as Sweet potato feathery mottle virus (SPFMV) (Clark & Hoy, 2006). Previously, outbreaks of SPFMV were reported in sweet potato cultivation in central Italy (Parrella et al., 2006). In the current study, attempts to amplify other sweet potato closely related potyviruses were unsuccessful using RT-PCR developed by Li et al. (2012). Based on our observation and results (symptoms recorded and serological detection of SPVG), the yield effects of SPVG may have been overlooked in sweet potato. Considering the number of existing SPVG strains and of sweet potato landraces/varieties, further investigation would be desirable to understand the real incidence of SPVG in individual sweet potato crops and its effects on production.