Tospoviruses are emerging as serious pathogens in India negatively impacting the cultivation of numerous field and horticultural crops. The type species of the genus,
GBNV has a wide host range affecting several important crops. The virus was shown to be the causal agent of soybean bud blight, tomato bud blight, potato stem necrosis and necrosis in cowpea and mungbean. WBNV was identified as the causal agent of bud necrosis disease of watermelon seriously affecting watermelon production. Association of WBNV was also observed with necrosis disease in cucumber and other cucurbits. An outbreak of IYSV in onion crops in Maharashtra was recently reported. The geographic distribution of these viruses in India varies: GBNV is endemic in many states including Andhra Pradesh, Gujarat, Karnataka, Kerala, Madhya Pradesh, Orissa, Rajasthan, Tamil Nadu and Uttar Pradesh whereas, WBNVthough recently reported from Uttar Pradesh is largely confined to southern parts of India including Andhra Pradesh, Karnataka and Tamil Nadu. IYSV has been reported from Maharashtra while its presence in other states cannot be ruled out. Genetic diversity studies on tospoviruses in India have been largely based on nucleocapsid protein (N) and movement protein (NSm) genes. GBNV isolates from various hosts and locations were indistinguishable as both N (96–99% amino acid identity) and NSm (98–100% amino acid identity) genes were highly conserved. Similarly N gene was highly conserved (95–100% amino acid identity) within WBNV isolates. Other ORFs such as non structural protein (NSs) and glycoprotein precursor (Gn/Gc) were also indistinguishable. Major differences were observed in the length of intergenic regions (IGRs) of M RNA segments. The M IGR of GBNV (Mungbean isolate) (422nt) was 15-nucleotide longer than that of the GBNV (type isolate) (408nt). The size of M IGR of another GBNV isolate from tomato was also different (347nt), 75 nucleotides smaller than that of mungbean isolate. The secondary structure of IGRs was also different in the three isolates. Comparision of size, sequence identity and secondary structure of M IGRs revealed that mungbean and type isolates originating from leguminous hosts were more similar as compared to GBNV (tomato isolate) originating from solanaceous hosts, suggesting thst the IGRs might have some role in host specificity of various isolates. Some differences were also observed in the topology of Gn-Gc protein of mungbean and type isolates. The two isolates differed in the N – and O – glycosylation sites and these differences might play important role in virus transmission by thrips, as insect transmission and specificity are mainly determined by tospoviral envelope glycoproteins.
