Morph physiological responses of Okra (Abelmoschus Esculentus (L.) Moench) genotypes to the effects of single and concurrent stress of drought and heat

Abstract

Drought and heat are abiotic stressors that often occur together, reducing crop productivity. While their individual effects on crops are well-studied, their combined impact is less researched. Okra, a vital vegetable in sub-Saharan Africa, supports rural and peri-urban livelihoods by providing employment and income. However, it remains under-researched and unimproved and is particularly sensitive to drought and heat stress, which severely affect its yield and productivity. This study used a quick, simple, and improvised climate chamber to evaluate the morphophysiological responses of 63 okra genotypes to stress due to heat, drought, and their combination. The genotypes showed considerable differences in their responses to heat and drought stress. Broad-sense heritability was high (>0.60) for all measured traits. Drought stress had a greater impact than heat stress alone, and the combined effect of heat and drought stress was more severe. A strong and positive relationship was observed between photosynthetic efficiency traits (Fv/Fm ratio, chlorophyll content, relative water index) and biomass traits (dry shoot weight). Genotypes considered tolerant to drought and heat, and hence climate resilient, maintained high internal water potential, possibly reducing osmotic and oxidative damage. The 63 okra genotypes were classified into three (3) distinct clusters, offering selection opportunities for future breeding efforts to build climate-resilient okra production. In a second experiment, ten genotypes were selected from different clusters to assess their yield responses to drought and biochar amendment. The drought effect was generally pronounced. It caused a reduction in fruit length, diameter, number of fruits per plant and total fruit yield in all genotypes relative to the control. However, there were differential genotypic responses. Some genotypes recorded higher biomass production under drought stress, translating into higher fruit yields. Biochar application mitigated the drought impact in all genotypes. There was increased biomass accumulation and increased fruit yields with increasing biochar rates. Genotypes GH172 and GH148 exhibited superior drought tolerance and biomass accumulation. They recorded the highest total fruit yield irrespective of the treatment, suggesting that these genotypes are reliable for further breeding.