Drought tolerance screening of okra genotypes in relation to growth and physio-biochemical traits at the vegetative stage

Evaluation of the genotypes of an agronomic or horticultural crop for their drought tolerance ability is of utmost importance to ensure sustainable production and food security. Although a number of okra [Abelmoschus esculentus (L.) Moench] genotypes are commonly grown in Thailand, most of which have not been evaluated for their drought tolerance ability. The present study evaluated 17 of the most popular okra genotypes for their drought tolerance ability where plants were subjected to two water regimes of well-watered (WW) and water-deficit (WD; withholding irrigation for 10 days) at the vegetative stage. A significant variation among genotypes was observed in terms of growth and physio-biochemical response (15-70% reduction in shoot dry matter at WD compared with WW for different genotypes, 45% average reduction in membrane stability index for all genotypes, 62-89% reduction in net photosynthetic rate at WD compared with WW for different genotypes, and 7-146% increase in crop water stress index at WD compared with WW for different genotypes). Based on Ward's multivariate cluster analyses of growth and physio-biochemical traits, the tested genotypes were classified into drought tolerant, moderately drought tolerant, and drought sensitive ones. Among the 17 tested genotypes, five genotypes (Four Compass 443, Green Nam Tao, Dark Green Okra No.5, Maejo 70, and Jusco) were found drought tolerant, six genotypes (Dow Morakot, King Star, Queen Star, Hisao, Bhalsar, and Maejo 49) were found moderately drought tolerant, while the remaining six genotypes (Best Green 5, TVRC 064, River Green No.1, Taratip, Lucky Five 473, and Chia Tai) were found drought sensitive. This study provides a base for okra growers to select the most feasible genotype for their areas based on the condition of irrigation water availability. The findings will also serve as firsthand information for the plant breeders to screen the newly-released genotypes for their drought tolerance ability.