RESUMO
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.
RESUMO
Leaf curl and yellowing symptoms on tomato, and yellow mosaic symptoms on eggplant, are frequently observed in Kanchanaburi Province, Thailand. DNA was extracted from leaves of 13 symptomatic tomato and six symptomatic eggplant samples by the method of Gilbertson et al (1). Viral DNA was amplified by polymerase chain reaction (PCR) using the begomovirus-specific degenerate primer pair PAL1v1978/PAR1c715 (3), which amplified a 1.4-kb fragment of DNA-A. All samples, except one eggplant sample, yielded the expected product. The 1.4-kb PCR products of one tomato and one eggplant sample were cloned and sequenced. Both begomoviruses from tomato and eggplant contained a DNA-B component, amplified using two degenerate primer pairs, DNABLC1/DNABLV2 and DNABLC2/DNABLV2 (2). Based on sequences of the DNA products amplified by the degenerate primer pairs, specific primers were designed to complete the DNA-A and DNA-B sequences. Computer-assisted sequence comparisons were performed with geminivirus sequences available in the laboratory at the Asian Vegetable Research and Development Center, Taiwan and in the GenBank sequence database. Both tomato (GenBank Accession Nos. AF511529 and AF511528) and eggplant (GenBank Accession Nos. AF511530 and AF511527) virus isolates contain the conserved geminivirus sequence-TAATATTAC on the DNA-A and B. Based on the high sequence identities of 99% DNA-A and 98% DNA-B, these two virus isolates are considered to be the same species. Although the genome organization of these two isolates was the same as Tomato yellow leaf curl virus Thailand (TYLCTHV; GenBank Accession Nos. X63015 and X63016), including six open reading frames (ORFs) on the DNA-A (AV1, AV2, AC1, AC2, AC3, and AC4) and two ORFs on the DNA-B (BV1 and BC1), sequence comparisons showed highest DNA-A sequence identity (73%) with Ageratum yellow vein virus from Singapore (GenBank Accession No. X74516) and highest DNA-B identity (77%) with the TYLCTHV (X63016). To our knowledge, these tomato- and eggplant-infecting viruses from Thailand constitute a distinctly novel bipartite Begomovirus species. References: (1) R. L. Gilbertson et al. J. Gen. Virol. 72:2843, 1991. (2) S. K. Green et al. Plant Dis. 85:1286, 2001. (3) M. R. Rojas et al. Plant Dis. 77:340, 1993.