W. S. Tsai,
S. L. Shih,
L. M. Lee, and
J. T. Wang, AVRDC – The World Vegetable Center, Shanhua, Tainan, 74151 Taiwan;
U. Duangsong, Research and Development in Agriculture Program, Kasetsart University, Nakhon Pathom 73140 Thailand; and
L. Kenyon, AVRDC – The World Vegetable Center, Shanhua, Tainan, 74151 Taiwan
A disease of okra (Abelmoschus esculentus) causing yellowing veins and mosaic on leaves and fruit has emerged in Thailand. Incidences of 50 to 100% diseased plants were observed in fields in Kanchanaburi and Nakhon Pathom provinces in 2009 and 2010, respectively. Leaf samples were collected from three and four diseased plants in Kanchanaburi and Nakhon Pathom, respectively. All seven samples tested positive for begomovirus by PCR using universal primer pair PAL1v1978B/PAR1c715H (3). One sample from Kanchanaburi also tested positive by ELISA using Okra mosaic virus (Genus Tymovirus) antiserum (DSMZ, Braunschweig, Germany). When the nucleotide sequences of the 1.5 kb begomovirus PCR products were compared they were found to share 99.1 to 99.5% identity with each other, and 97.5 to 97.7% identity to Bhendi yellow vein mosaic virus Okra isolate from India (GenBank Accession No. GU112057; BYVMV-[IN: Kai:OY: 06]). The complete DNA-A sequence for a Kanchanaburi isolate (JX678967) was obtained using abutting primers WTHOK6FL-V/-C (WTHOK6FL-V: 5′-GCGAAGCTTAGATAACGCTCCTT-3′; WTHOK6FL-C: 5′-TCCAAGCTTTGAGTCTGCAACGT-3′), while that of a Nakhon Pathom isolate (JX678966) was obtained with primers WTHOK6FLV/WTHOK2FL-C (WTHOK2FL-C: 5′-TCCAAGCTTTGAGTCTGCATCGT-3′). The DNA-A sequences of both isolates are 2,740 nucleotides in length and share 99.6% identity. Each has the geminivirus conserved sequence (TAATATTAC), two open reading frames (ORFs) in the virus sense (V1 and V2) and four in the complementary sense (C1 to C4). Based on BLASTn searching GenBank and sequence analysis using MegAlign (DNASTAR), both DNA-A sequences have greatest nucleotide identity (96.2 to 96.4%) with BYVMV-[IN: Kai:OY: 06] from India. Also, BYVMV-associated betasatellite DNA (1.4 kb) was detected in all begomovirus-positive samples, except one sample from Nakhon Pathom (1). However, no virus DNA-B was detected in any of the samples using either general detection primer pair DNABLC1/DNABLV2 or DNABLC2/DNABLV2 (2). Okra infected with BYVMV has been reported in South Asia in Bangladesh, India, and Pakistan. To the best of our knowledge, this is the first report of BYVMV associated with Okra Yellow Vein Mosaic Disease in Southeast Asia. Since fruits with symptoms are regarded as low quality and have little market value, even low incidence of the disease is likely to cause significant reductions in marketable yield. Strategies for managing BYVMV in okra in South and Southeast Asia should be sought, including the breeding and selecting of resistant varieties.
References: (1) R. W. Briddon et al. Mol. Biotechnol. 20:315, 2002. (2) S. K. Green et al. Plant Dis. 85:1286, 2001. (3) W. S. Tsai et al. Plant Pathol. 60:787, 2011.