First Report of Soybean yellow mottle mosaic virus on Soybean (Glycine max) in India

Abstract

Soybean (Glycine max) is one of the most important crops as a source of high-quality protein and oil. In India, soybean area has expanded with the introduction of high-yielding varieties with wide adaptability, which also favored the development of new diseases with increased incidence. During 2016, 38 samples from initial varietal trials of soybean cultivars from India exhibiting symptoms such as mosaic, mottling, necrosis, and puckering were collected from the fields of the Indian Agricultural Research Institute, New Delhi, India, and tested for the presence of viruses, namely, Cowpea mild mottle virus, Groundnut bud necrosis virus, Soybean mosaic virus, Soybean vein necrosis virus, Soybean yellow mottle mosaic virus (SYMMV), and Tobacco streak virus. Crude sap from 3 of the 38 samples strongly reacted with the polyclonal antibodies raised against SYMMV in direct antibody coating ELISA (A₄₀₅ₙₘ= 1.2 to 1.8) (Sandra et al. 2015). To confirm the SYMMV infection, total RNA was extracted from the ELISA-positive soybean leaf samples showing mosaic and mottling symptoms using the SV Total RNA isolation system (Promega, Madison, WI) followed by reverse-transcription polymerase chain reaction (RT-PCR) with coat protein (CP) gene specific primers (forward, 5′-ATGAATTCATGAATGGAACAATGCTCACCGT-3′; reverse, 5′-CAAAGCTTAGTGTGTGGGTTTTAACTGGCGTTGTTA-3′) (Sandra et al. 2015). The RT-PCR product of 1,065 base pairs was cloned into TA cloning vector (Real Biotech Corporation), and the clones were sequenced in both orientations and deposited in GenBank (accession no. MG768974). Sequence analysis of the CP gene showed 98 to 100% identity with Indian isolates (KR260903, KR260902, and KP259608) followed by 82 and 92% similarity with Korean isolates of SYMMV at nucleotide and amino acid levels, respectively. Identity at the nucleotide and amino acid level of 29 to 42% and 16 to 25% was observed with the corresponding CP region of other carmoviruses. For further confirmation, French bean seedlings (cv. Pusa Parvati) were mechanically sap inoculated with an extract from an ELISA-positive soybean leaf sample, and these seedlings showed systemic chlorotic blotches after 10 to 12 days postinoculation, which were then confirmed by ELISA and RT-PCR as above. Previously, SYMMV was reported on soybean from South Korea and North America (Li et al. 2009; Nam et al. 2009). More recently, SYMMV was reported on mungbean and urdbean from India (Sandra et al. 2015). To our knowledge, this is the first report of natural infection of soybean by SYMMV in India and suggests that this newly identified SYMMV may be adapting to other leguminous host plant species.