Selection for Resistance to Yellow Vein Mosaic Virus Disease of Okra by Induced Mutation

Yellow vein mosaic virus disease (YVMD) caused by a begomovirus is the most serious factor affecting okra (Abelmochus esculentus) production for both exporting and domestic consumption in Thailand. Seeds of two okra varieties, Annie and Okura, were irradiated with Gammarays at doses of 400 and 600Gy. Screening of YVMD resistant plants was conducted for M 3 and M 4 plants under field conditions in Petchaburi and Phichit provinces, and greenhouse conditions using whitefly transmission in Bangkok. One M 4 plant of Okura (B-21) irradiated at 400Gy was found to be highly resistant, but none of Annie. M 5 plants of B-21 were screened further for YVMD resistance under both greenhouse and field conditions. Ten resistant lines obtained by screening for YVMD resistance up to the M 7 generation were selected for yield trial observations at Phichit Horticultural Research Center (PHRC) and Chiengmai Horticultural Research Station (CHRS), both located in the northern Thailand. Three of the mutant lines were further tested at Kanchanaburi Horticultural Research Center (KHRC) in Kanchanaburi province, an okra growing area in the west of central Thailand where YVMD was seriously widespread. At the KHRC, all tested mutant lines showed resistance up to a month, when the susceptible check variety already showed symptoms of the disease. However, only a small portion of the plants of the mutant lines appeared to be resistant throughout the whole growth duration; others eventually exhibited the yellow vein symptom. Plants were further screened in two growers’ fields. Growers were satisfied with the plant stature and fruit shape of the mutants and their delayed disease development, and further screening is underway to select uniformly YVMD resistant lines for okra production in Kanchanaburi.