Inductive response of protective enzymes in coconut (Cocos nucifera L.) subjected to stress

The coconut hybrids WCT x four exotic Talls viz., Philippines Ordinary (PHOT), Fiji (FIJT), Cochin China (CCNT), Strait Settlement Green (SSGT) as well as one indigenous tall-Kappadam (KPDT) were screened for tolerance to drought by using stomatal resistance and transpiration rate in the field as well as by the activities of the stress sensitive enzymes viz., malic dehydrogenase, peroxidase, super oxide dismutase and catalase under induced stress condition. Leaf water potential (Ψ leaf) was determined both in situ and induced stress conditions. Differences in the parameters studied did not give any significant variations among the hybrid combinations during non-stress or stress periods and significant variations were observed only between the two periods under in situ conditions. However, under induced stress condition, the hybrids behaved differentially in activities of the enzymes in response to the decreased Ψ leaf. Based on the increase or decrease in the water relation components as well as stress related enzyme activities as compared with the normal level the hybrids were ranked for tolerance to drought. Ranking of the hybrids based on y leaf under induced stress condition as well as under field stress conditions gave similar results. Among the T x T combinations, WCT x SSGT was found to have relative tolerance to drought in terms of water relation components and enzyme activities. The results further established that rapid screening techniques can be employed with ease for screening large number of coconut cultivars/hybrids for tolerance to drought.