RESUMO
Stem necrosis disease caused by Tobacco streak virus (TSV), first recognized in 2000, has emerged as a potential threat to peanut (Arachis hypogaea) in southern states of India. The virus induces severe necrosis of shoots leading to death of the plant, and plants that survive are malformed, with severe reduction in pod yield. All the currently grown peanut cultivars in India are highly susceptible to the virus. Therefore, wild relatives of peanut were evaluated to identify potential sources of resistance to TSV infection. In all, 56 germplasm accessions from 20 wild Arachis spp. in four sections (Arachis, Erectoides, Procumbente, and Rhizomatosae), along with susceptible peanut cultivars (JL 24 and K 1375), were evaluated for resistance to TSV under greenhouse conditions using mechanical sap inoculations. Systemic virus infection, determined by enzyme-linked immunosorbent assay (ELISA), in the test accessions ranged between 0 and 100%. Twenty-four accessions in section Arachis that had 0 to 35% systemically infected plants were retested, and systemic infection was not detected in eight of these accessions in repeated trials in the greenhouse. These are International Crops Research Institute for the Semi-Arid Tropics groundnut (ICG) accession nos. 8139, 8195, 8200, 8203, 8205, and 11550 belonging to A. duranensis; ICG 8144 belonging to A. villosa; and ICG 13210 belonging to A. stenosperma. Even though the resistant accessions had 0 to 100% TSV infection in inoculated leaves, TSV was not detected in the subsequently emerged leaves. This is the first report of TSV resistance in Arachis spp. The eight TSV resistant accessions are cross compatible with A. hypogaea for utilization in breeding for stem necrosis disease resistance.
RESUMO
Safflower, Carthamus tinctorius L. (Asteraceae), is extensively cultivated in India, China, and other parts of Asia for edible oil, dyeing agent, and its medicinal value. In 2003, safflower entry (NARI-6) in the All-India Coordinated Research Project on Oilseeds (Safflower) grown in the experimental fields of M/s Syngenta India Ltd., Aurangabad (Maharashtra State, India) exhibited symptoms of veinal and leaf necrosis, necrotic streaks on the stem, necrosis of the terminal bud, and ultimately plant death. The disease was attributed to Tobacco streak virus (TSV) because sunflower growing adjacent to safflower showed similar symptoms caused by TSV (1). Mechanical inoculations of sap from symptomatic safflower leaves caused typical symptoms of TSV (local, irregular, necrotic rings, veinal necrosis, and systemic veinal necrosis) on Vigna unguiculata (L.) Walp. cv. C-152 and Phaseolus vulgaris (L.) cv. Topcrop, and symptoms of local, necrotic lesions, veinal necrosis, and systemic necrosis of leaf and growing bud on Arachis hypogaea L. cv. JL-24. Sap-inoculated safflower cv. Manjeera showed chlorotic and necrotic local lesions followed by systemic leaf necrosis, leading to necrosis and death of the terminal bud. Safflower cvs. A-1, BIP-2, Co-1, and Bheema (10 plants of each cultivar) inoculated with sap from safflower plants showing typical TSV symptoms did not show any visible symptoms except stunting, but six to nine plants of each cultivar tested positive for TSV using enzyme-linked immunosorbent assay (ELISA) tests. In direct antigen coating-ELISA, the virus reacted positively with antiserum produced to an isolate of TSV from peanut (2) and to antiserum to TSV (ATCC-PVAS 276 for Datura stramonium), but did not react to peanut bud necrosis tospovirus antiserum. Examination of leaf extracts using leaf-dips and immunosorbent electron microscopy with the antiserum of TSV-peanut isolate showed isometric particles resembling those in the genus Ilarvirus. To our knowledge, this is the first report of an isolate of Tobacco streak virus infecting safflower. References: (1) R. D. V. J. Prasada Rao et al. J. Oilseeds Res. 17:400, 2000. (2) A. S. Reddy et al. Plant Dis. 86:173, 2002.
RESUMO
A virus disease of peanut (groundnut, Arachis hypogaea L.), characterized by necrosis of the stem and terminal leaflets followed by death, caused severe crop losses in Andhra Pradesh, India during the rainy season of the year 2000. The disease was referred to as peanut stem necrosis disease (PSND). Cowpea (Vigna unguiculata, cv. C-152) and Phaseolus vulgaris (cv. Topcrop) were found to be suitable for propagating the virus. In laboratory inoculation tests, the virus was found to infect a large number of plants. In laboratory tests, the virus was transmitted by the thrips Frankliniella schultzei. Virus particles were purified by differential centrifugation and sucrose density gradient centrifugation from infected cowpea plants and were used to elicit the production of a rabbit polyclonal antiserum with high titer. Extracts of infected plants reacted with antiserum to Tobacco streak virus (TSV). Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from purified virus particles showed them to contain a major protein of 28 kDa and a minor, though prominent, protein of 57 kDa. Gel electrophoresis of RNA extracted from virus particles resolved it into four species with estimated sizes of 3.7, 3.1, 2.2, and 0.9 kb. Complementary DNA (cDNA) was made using as template a sample of the 2.2-kb RNA 3 and as primer an oligonucleotide complementary to sequence in RNA 3 of TSV. Following second strand synthesis, the cDNA was cloned in pBluescript and the nucleotide sequence was obtained for 868 nt of the cDNA. The sequence was 88.4% identical to the sequence in RNA 3 of TSV (strain WC). The results indicate that the causal agent of PSND is TSV. The same virus also was found to cause sunflower necrosis, an economically important disease in India. Studies on the epidemiology of PSND and the identification of virus-resistant peanut genotypes have been initiated to devise strategies to control PSND.