1Mahyco Research Center, Jalna-Aurangabad Road, Dawalwadi, Jalna-431203, Maharashtra.
2Virology Department, S.V.University, Tirupati, Andhra Pradesh.
Bud necrosis disease in watermelon (Citrullus lanatus (Thunb.) Matsun and Nakai is caused by Watermelon bud necrosis virus (WBNV) belonging to the genus Tospovirus family Buniyaviridae. During 2004–2005, surveys were conducted for the occurrence of bud necrosis in Maharashtra and recorded up to 40% disease incidence. The disease symptoms were characterized by chlorosis and mosaic mottling in young leaves, and necrotic streaks on veins, stems and growing buds resulting in dieback. The fruits from the infected plants were malformed with chlorotic rings on the surface. The virus suspected field isolates were detected by DAC and TAS-ELISA using polyclonal (PBNV) and monoclonal antibodies (WBNV). ELISA studies confirmed that the WBNV isolate from Maharashtra was belonging to Tospovirus Serogroup IV. The host range studies with the representative virus isolate produced local (chlorotic or necrotic lesion) and systemic (mosaic mottling & necrosis) symptoms on an experimental host plants under green house conditions. In RT-PCR analysis, amplified ~830 bp fragment of NP gene from the symptomatic leaves of watermelon bud necrosis isolates and absent in the corresponding healthy. The cloned NP gene nucleotide sequence analysis shared 92% and 84% homology with the reference WBNV and PBNV sequences, respectively. Based on the symptomatology, host-range, serology and nucleotide sequence analysis, the causal agent of watermelon bud necrosis disease from Maharashtra was characterized as a strain of WBNV from India.
