First Report of Groundnut Ringspot Virus Infecting Mungbean in Argentina

Mungbean (Vigna radiata) is a plant species native to India and widely cultivated worldwide. In recent decades, its production and consumption outside Asia have increased significantly, mainly due to its high protein content. In Argentina, it has been incorporated into production systems to diversify summer crops in the northwest of the country (Vizgarra et al. 2014). Orthotospoviruses cause severe damage to economically important crops in many parts of the world, causing significant losses in yield and product quality (Pappu et al. 2009). In Argentina, groundnut ringspot virus (GRSV, a member of the species Orthotospovirus arachianuli) has been identified as a pathogen affecting several crops. However, there have been no reports of GRSV infecting mungbean, either in Argentina or globally. Mungbean plants with virus-like symptoms including distorted leaves, mosaic and chlorotic ringspots (Figure 1) were collected during the 2023/24 growing season in Córdoba and Santiago del Estero provinces. A total of 121 samples were analysed by PTA-ELISA using antisera raised against alfalfa mosaic virus (IPAVE, Córdoba, Argentina), and potyviruses (Agdia, USA) and by DAS-ELISA with cucumber mosaic virus antiserum (BIOREBA, Switzerland). Furthermore, a polyclonal antiserum raised against the GRSV nucleocapsid (N) protein, which was heterologously expressed in Escherichia coli, was employed to differentiate infections caused by GRSV and tomato spotted wilt virus (TSWV) by DAS-ELISA (Williams et al. 2001). Among the samples tested, five yielded positive results for GRSV, exhibiting an average OD405 value of 0.95. In comparison, negative controls showed an average OD405 value of 0.030 and the positive controls for GRSV and TSWV had OD405 values of 1.25 and 0.006, respectively. No positive results were obtained for the other viruses tested. Total RNA was extracted from three of the GRSV-positive samples using the CTAB method. Reverse transcription reactions were performed using the M-MLV reverse transcriptase enzyme (Epicentre, USA) and the reverse primer NGRSVR (Boari et al. 2002), according to manufacturer's instructions. PCR reactions were performed using Pegasus Taq polymerase (Bio-Logical Products, Argentina) and the specific primers NGRSVR and NGRSVF (Boari et al. 2002). The reaction consisted of 30 cycles with the following steps: 95°C for 1 min, 57°C for 2 min and 72°C for 1 min, with a final extension at 72°C for 7 min. A DNA fragment of approximately 800 base pairs, corresponding to the N gene was amplified. The amplicon was purified and Sanger sequenced (Genomics Unit of the Institute of Biotechnology of INTA Castelar). The obtained sequence (670 bp; GenBank Accession No. PQ699789) had >97% nucleotide identity (Figure 2) with sequences of other Argentinian GRSV isolates, all obtained from peanut. This is the first report of GRSV infecting mungbean in Argentina and globally. Understanding the host range of the virus is an important step in developing effective management strategies. This work was funded by the Instituto Nacional de Tecnología Agropecuaria (INTA), Grant/Award Number: PD084.