The effect of high temperature on physiological and metabolic parameters and reproductive tissues of okra (Abelmoschus esculentus (L.) Moench)

Abstract

Okra is an important summer vegetable crop and high temperature has been shown to lower its growth and yield. In this study, 119 okra genotypes were initially screened for their response to a short period of heat shock (45°C for 4h and 6h) in a controlled environment facility by assessing chlorophyll fluorescence (Fv/Fm and Fv’/Fm’), photosynthesis (A), stomatal conductance (gs) and electrolyte leakage (EL) in control and heat. Additionally, DNA of fresh green leaf of okra was isolated by a modified CTAB method with additional PVP and RNase and amplified by 8 polymorphic SSR markers to generate a dendrogram. This preliminary screening identified 8 polymorphic genotypes with less than 50% genetic similarity, reduced Fv’/Fm’ in the heat with varying responses in gs, A and EL. These 8 genotypes were studied for their response in a long-term heat stress environment in two adjacent plastic tunnel houses, with 10°C warmer average temperatures in the hot tunnel house. After 15 weeks, high temperature had no significant effect on Fv’/Fm’ and A, while gs and EL increased significantly and yield decreased due to significant reduction in pollen germination. The tunnel house experiment was repeated (with 4 genotypes) assessing physiological, biochemical and histological parameters at flowering and bud initiation stages and monitored every 2 weeks for a total of 6 weeks. Okra demonstrated a physiological acclimation response however yield decreased severely due to heat damage in reproductive tissue. In the heat, plants produced lower anther numbers and pollen germination. The shape and structure of male tissues was altered in the early stage of bud development which may have resulted from alteration in carbohydrate content in the leaves. The results of this study suggest that okra is more vulnerable in the early stages of growth and development.