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First Report of Natural Infection of Luffa acutangula by Watermelon bud necrosis virus in India

In August 2002, ridge gourd (Luffa acutangula) plant samples exhibiting yellowing of leaves were collected from the experimental farm of Tamil Nadu Agricultural University, Coimbatore, India. Mechanical inoculations of ridge gourd seedlings using the above samples resulted in chlorotic spots on inoculated leaves and vein clearing followed by chlorotic rings and yellow netting along veins of newly developed leaves. The virus was reisolated from the chlorotic spots of the seedlings. Extracts from the field samples as well as mechanically inoculated seedlings reacted with antiserum to Watermelon silver mottle virus (WSMoV) in direct antigen coating enzyme-linked immunosorbent assay, suggesting the association of a tospovirus belonging to WSMoV serogroup (2). Symptomatic leaves from the second mechanical passage exhibiting yellow netting along the veins were subjected to reverse transcription-polymerase chain reaction (1) to identify the genus Tospovirus. Using the primer pair (5′TCTGTCCT(C/T) TTGAA (G/T) GTCCA3′ and 5′AGAGCAATCGAGGCGCT3′) derived from the conserved sequences of Groundnut bud necrosis virus (GBNV) and WSMoV, part of the nucleocapsid (N) protein gene and the complete noncoding region upstream of the N gene's coding sequence were cloned and sequenced. Comparative sequence analysis of 291-bp region of the N gene revealed that the genus Tospovirus infecting ridge gourd shared maximum identity both at nucleotide (94%) and amino acid (97%) levels with the corresponding region of Watermelon bud necrosis virus (WBNV), which is a distinct species of WSMoV serogroup infecting watermelon in India (1). In contrast, only 76 to 81% and 82% identity at nucleotide and amino acid levels, respectively, was observed with the corresponding region of the N genes of GBNV and WSMoV. Natural infection of WBNV in cucurbits except watermelon in India is not known. To our knowledge, this is the first report of natural infection of ridge gourd by WBNV.

References: (1) R. K. Jain et al. Arch. Virol. 143:1637, 1998. (2) J. W. Moyer. Tospoviruses (Bunyaviridae). Pages 1803--1807 in: Encyclopedia of Virology. A. Granoff and R. G. Webster, eds. Academic Press, New York, 1999.