Sweet potato yellow curling (YC), the most severe disease of sweet potato detected in Argentina, causes symptoms and damage to sweet potato crops in all cultivated regions. Since 2010/11, the presence of four viruses has been detected in symptomatic cv. Arapey INIA: two potyviruses non-persistently transmitted by Myzus persicae (sweet potato feathery mottle virus, SPFMV and sweet potato virus G, SPVG); a closterovirus, sweet potato chlorotic stunt virus (SPCSV) and a geminivirus, sweet potato leaf curl virus (SPLCV), both transmitted by Bemisia tabaci in a semi-persistent and persistent manner, respectively. All the plants were collected from fields in Colonia Caroya, Córdoba province, Argentina. The objectives of the present work are to isolate and identify the virus or viruses involved in YC disease of sweet potato, and to elucidate the viral combination that reproduces YC symptoms. The most severe YC symptoms for this genotype in the field were only reproduced by a combination of the four viruses. The symptoms include chlorosis, stunting, mosaic, blistering, leaf curling, chlorotic spots, chlorotic patterns, leaf area reduction and distortion, and upward curling of leaf edges. The presence of each virus was detected by serological (DAS, NCM and TAS-ELISA) and molecular (PCR) tests. It is concluded that the interaction of SPFMV, SPVG, SPCSV and SPLCV is needed for the development of YC symptoms. Highlights Four viruses involved in yellow curling disease, SPFMV, SPVG, SPCSV and SPLCV were isolated and identified. The first antiserum produced in Argentina allows the fast, safe and efficient diagnosis of SPVG. The interaction of SPFMV, SPVG, SPCSV and SPLCV is needed for the manifestation of yellow curling in Argentina.

ABSTRACT Sweet potato, in Argentina, is affected by the “encrespamiento amarillo”, a viral disease in which seven viruses are involved, among them two potyvirus (sweet potato feathery mottle virus - SPFMV and sweet potato virus G - SPVG) and a crinivirus (sweet potato chlorotic stunt virus - SPCSV). This research aimed to study the interaction between SPFMV and SPVG with SPCSV in sweet potato. Two sweet potato cultivars (Gem and Arapey INIA) and Ipomoea setosa as an indicator susceptible plant were tested as single (SPFMV or SPVG), double (SPFMV + SPVG, SPFMV + SPCSV or SPVG + SPCSV) or triple (SPFMV + SPVG + SPCSV) grafts. Both potyviruses were purified and the viral concentrations in the plant tissues were quantified by the DAS-Elisa method. The viruses and their severities were evaluated at 7, 15, 21, 30 and 35 days post-inoculation. A synergistic effect was observed with the three viruses in the indicator plant. The viral concentration increase was 50 times for SPFMV (day 35) and two times for SPVG (day 21) in the Gem cultivar, and 1.89 times for SPFMV (day 35) and three times for SPVG (day 7) in the Arapey INIA. For multiple infections, the indicator plant and the Gem cultivar exhibited synergistic symptoms and increase in the viral titers, with a higher severity and variability of the symptoms. Co-infections such as SPFMV + SPVG showed characteristic potyvirus symptoms, without increasing the viral concentrations; triple co-infections exhibited viral complex symptoms, with increase in the potyvirus titers; and the symptoms were mild or imperceptible in the simple infections.