Characterization and management of watermelon bud necrosis virus infecting watermelon in India

Abstract

Bud necrosis disease is an emerging threat for watermelon cultivation in India. It is characterized by necrotic spots and patches on leaves, bud and fruits with characteristic chlorotic ring spots as documented in Coimbatore and Villupuram districts of Tamil Nadu, India. The causative agent of this disease was identified as watermelon bud necrosis virus (WBNV) by reverse-transcription polymerase chain reaction (RT-PCR) followed by sequence analysis of amplified fragment using Orthotospovirus universal degenerate primer pair. Upon mechanical inoculation, the virus produced circular chlorotic local lesions on leaves of cowpea and Chenopodium amaranticolor, necrotic local lesions on Trianthema portulacastrum and bottle gourd, systemic vein clearing on Luffa aegyptiaca, whereas both local and systemic symptoms were observed on Nicotiana tabacum and watermelon. The complete nucleotide sequences of the coat protein (NP), movement protein (MP), replicase (RdRp) and NSs protein genes from WBNV genome of Coimbatore isolate (TN KTP WM1) had a maximum identity of 97% with the genome of the WBNV-JT strain from Southern India. WBNV infection causes significant reduction in nutritional parameters such as carbohydrate, protein, crude fibre, calorific value, total sugar, reducing sugar and vitamin A in infected fruits when compared to the healthy ones. For the management of WBNV in watermelon, an Integrated Pest Management (IPM) module has been devised which reduced the thrips population and WBNV incidence to a great extent besides increasing the fruit yield.