Soybean mosaic virus (SMV) causes systemic infections in soybean plants, leading to chlorotic mosaic and producing significant yield losses. The virus is widely distributed in all soybean production areas in the world. In Argentina, three geographical isolates were identified: Marcos Juarez (MJ), Manfredi (M), and North Western Argentina (NOA), and another isolate named "Planta Vinosa" (PV), which causes severe necrosis symptoms in some cultivars. Here, the biological, molecular and physiological characterization of these isolates was performed for the first time. Three of the four isolates showed a low genetic divergence in the evaluated genes (P1, CI and CP). Although SMV-NOA and SMV-PV had high homology at the sequence level, they showed wide differences in pathogenicity, seed mottling and the ability of transmission by seeds or aphids, as well as in physiological effects. SMV-NOA caused early alterations (before symptom appearance, BS) in quenching of PSII and MDA content in leaves with respect to the other isolates. After the appearance of macroscopic symptoms (late symptoms, LS), SMV-M caused a significant increase in the content of MDA, total soluble sugars, and starch with respect to the other isolates. Thus, early alterations of quenching of PSII and soluble sugars might have an impact on late viral symptoms. Likewise, SMV-MJ developed more severe symptoms in the susceptible Davis cultivar than in DM 4800. Therefore, our results show differences in genome, biological properties and physiological effects among SMV isolates as well as different interactions of SMV-MJ with two soybean cultivars.

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.