Physiological and biochemical studies in cluster bean (Cyamopsis tetragonoloba (L.) Taub) as influenced by light and moisture stress

Abstract

The programme entitled “Physiological and biochemical studies in cluster bean [Cyamopsistetragonoloba(L.) Taub.] as influenced by light and moisture stress” was carried out at the Department of Plant Physiology, College of Agriculture, Vellayani, during 2019-2020. The objective of the programme was to study the light and moisture stress induced physiological and biochemical changes in cluster bean. A field study was carried out with the cluster bean variety ‘KAU Suruchi’ in Factorial Randomized Block Design (FRBD). It involved a combination of three levels of light stress (different shade levels) and three levels of moisture stress (different field capacity levels) which is inclusive of a control also, with four replications .The observations were taken at three different critical stages of the crop viz.vegetative stage, flowering stage and pod filling stage. Different shade levels were provided by using high-density polyethylene nets with differential light transmission to maintain 50 % and 25% shade and no shade net for open condition. Whereas for imposing moisture stress, three irrigation regimes based on gravimetric estimations were followed to maintain the field capacity levels of 100%, 75% and 50%.The treatment ( open condition + 100% field capacity) served as the control (T7) for the experiment. Different growth parameters such as plant height, number of primary branches per plant, root dry weight, shoot dry weight, root: shoot ratio, crop growth rate and relative growth rate were studied. It was found that only root dry weight and root: shoot ratio increased under combined light and moisture stress in comparison to control . However, plant height was found to increase under the treatments T1 (50% shade + 100% field capacity), T4 (25% shade + 100% field capacity), T5 (25% shade + 75% field capacity) and T6 (25% shade + 50% field capacity) compared to the control. The physiological parameters studied viz. transpiration rate and photosynthetic rate were found to decrease under the influence of both light and moisture stress conditions compared to the control. Among the biochemical parameters studied, total chlorophyll content was found to increase under the influence of both the stresses with the highest value (1.747 mg g-1, 1.947 mg g-1 and 2.141 mg g-1) across the three growth stages except that of treatment T9 (open + 50% field capacity).The chlorophyll ‘a’content was found to increase across all the treatments compared to the control. However chlorophyll ‘b’ content was found higher under shaded condition. But the chlorophyll a: b ratio was found to be higher only under open conditions. The total soluble protein content showed a decrease under the combined abiotic stresses. Overall it was observed that under the combined influence of light and moisture stress, physiological parameters such as plant height(T1,T4,T5 and T6), root weight and root: shoot ratio were up regulated whereas number of primary branches per plant, shoot weight, crop growth rate, relative growth rate, photosynthetic rate and transpiration rate were down regulated. As far as biochemical characters are concerned chlorophyll ‘a’, chlorophyll ‘b’ (T1 to T6), chlorophyll a: b ratio (T8 and T9) and total chlorophyll content (T1 to T8) improved, whereas the total soluble protein was found to decrease across all treatments compared to control. Considering the physiological, and biochemical characters, treatment T6 (25% shade + 50% field capacity) is favourable for the tolerance of cluster bean to the light and moisture stress, in view of the enhancement of plant height and chlorophyll content and the comparatively better performance than other stress combinations in comprehending the stress combination. However, the severest stress combination of treatment T3 (50% shade + 50% field capacity) enhanced the root: shoot ratio and lowered the transpiration rate the most, which is a positive aspect in terms of stress tolerance. In short, cluster bean is capable of tolerating light and moisture stress levels up to 50% shade and 50% field capacity respectively.