Surendra Kumar Meena

Mungbean ( Vigna radiata ) is a warm‐season legume crop and plays a crucial role in food and nutritional security in South and Southeast Asia. Being a legume crop, it also plays a role in ecosystem sustainability. However, crop cultivation is facing an imminent threat amid the recent rise in global temperature. The optimum temperature range for mungbean cultivation is 28–35°C, although some genotypes can grow well even up to 40°C of atmospheric temperature. Therefore, in this study, 1515 mungbean accessions were initially screened for heat‐responsive morphological and physiological traits to identify superior genotypes. From this preliminary screening, 75 diverse accessions were selected for a more comprehensive evaluation of heat‐responsive traits. Subsequently, 32 promising genotypes were chosen for an in‐depth analysis of enzymatic and nonenzymatic antioxidant activities under both heat‐stressed and non‐stressed conditions. Certain genotypes, namely IC76475, IC418452 and IC489062, were superior for multiple heat stress‐responsive traits. The phenotypic expression of these genotypes was further validated under controlled environmental conditions. Their heat stress tolerance was confirmed through RT‐PCR analysis of key candidate genes ( GmAKT2 , Cu / ZnSOD , APX1 and CAT1 ). The findings from this study will aid in developing mungbean cultivars with enhanced tolerance to heat stress.

Pulses are inherently climate-resilient crops by virtue of their special morphophysiological attributes, such as deep tap root system, higher water-use efficiency, nitrogen-fixing ability, ability to host beneficial microbes in the rhizosphere to solubilize phosphates, etc. Low water and nutrient requirements, nitrogen-fixation ability, and high proteins are the prominent features of pulses that discriminate them from other crops. Besides having the potential to increase soil fertility, the seeds of pulses are densely packed with nutrients. Being rainfed crops, pulses often experience terminal drought and heat stress at reproductive stages. The majority of the pulses are sensitive to high temperature above 35°C, leading to inhibition of photosynthesis and reduction of pollen fertility. Improving water relation characteristics could be one of the best strategies to addresses combined drought and heat tolerances. Deep root, osmotic adjustment, lower ¹³C/¹²C carbon isotope discrimination ratio, and lower stomatal aperture contribute significantly toward improving water-use efficiency, although cellular-level tolerance, including expression of antioxidative enzymes, heat shock proteins, acquired thermotolerance, membrane stability, and altered carbohydrate metabolizing enzymes, play important roles toward dual tolerance. However, the primary strategy of pulses to acquire tolerance could be by means of improved water relation characteristics. Faster biomass accumulation, early flowering, deep roots, and regulated transpiration water loss through modified stomatal morphology have direct ways of conserving moisture and cellular-level tolerance have further additive advantages toward combined tolerance. Pulses should be acquired with adequate photothermoinsensitivity and introgressed with cellular-level tolerance to stabilize yield. Based on precision phenotyping, such as chlorophyll fluorescence, antioxidative enzymes, photosynthesis, osmotic adjustment, root profile, acquired thermotolerance, and water-use efficiency, a number of pulse germplasms have been identified as tolerant to various abiotic stresses. Field-level screening, including thermal imaging, NDVI, and SPAD chlorophyll readings, are available at the first level of selection against drought or heat. Major pulses, such as chickpea, pigeonpea, lentil, and lathyrus, are relatively drought tolerant as compared to greengram, blackgram, and fieldpea. Wild species of these pulses are the house of many abiotic stress-tolerance genes. Genetic diversity of abiotic stress tolerance can be exploited by using precision phenotyping. Genomics, transcriptomics, epigenomics, proteomics, metabolomics, and phenomics tools have enabled speeding up breeding programs more precisely.

To understand the physiological basis of tolerance to combined stresses to low phosphorus (P) and drought in mungbean (Vignaradiata (L.) R. Wilczek), a diverse set of 100 accessions were evaluated in hydroponics at sufficient (250 μM) and low (3 μM) P and exposed to drought (dehydration) stress. The principal component analysis and ranking of accessions based on relative values revealed that IC280489, EC397142, IC76415, IC333090, IC507340, and IC121316 performed superior while IC119005, IC73401, IC488526, and IC325853 performed poorly in all treatments. Selected accessions were evaluated in soil under control (sufficient P, irrigated), low P (without P, irrigated), drought (sufficient P, withholding irrigation), and combined stress (low P, withholding irrigation). Under combined stress, a significant reduction in gas exchange traits (photosynthesis, stomatal conductance, transpiration, instantaneous water use efficiency) and P uptake in seed and shoot was observed under combined stress as compared to individual stresses. Among accessions, IC488526 was most sensitive while IC333090 and IC507340 exhibited tolerance to individual or combined stress. The water balance and low P adaptation traits like membrane stability index, relative water content, specific leaf weight, organic acid exudation, biomass, grain yield, and P uptake can be used as physiological markers to evaluate for agronomic performance. Accessions with considerable tolerance to low P and drought stress can be either used as ‘donors’ in Vigna breeding program or cultivated in areas with limited P and water availability or both.

To understand the physiological basis of tolerance to combined stresses to low phosphorus (P) and drought in mungbean (Vigna radiata (L.) R. Wilczek), a core set of 100 accessions were evaluated in hydroponics at sufficient (250 μM) and low (3 μM) P, and exposed to drought (dehydration) stress. The principal component analysis and ranking of accessions based on relative values revealed that IC280489, EC397142, IC76415, IC333090, IC507340 and IC121316 performed superior while IC119005, IC73401, IC488526 and IC325853 performed poorly in all treatments. Selected accessions were evaluated in soil under control (sufficient P, irrigated), low P (without P, irrigated), drought (sufficient P, withholding irrigation) and combined stress (low P, withholding irrigation). Under combined stress, a significant reduction in gas exchange traits (photosynthesis, stomatal conductance, transpiration, instantaneous water use efficiency), P uptake in seed and shoot was observed under combined stress as compared to individual stresses. Among accessions, IC488526 was most sensitive while IC333090 and IC507340 exhibited tolerance to individual or combined stress. The water balance and low P adaptation traits like membrane stability index, relative water content, specific leaf weight, organic acid exudation, biomass, grain yield and P uptake can be used as physiological markers to evaluate for agronomic performance. Accessions with considerable resilience to low P and drought stress can be either used as ‘donors’ in Vigna breeding program or cultivated in areas with limited P and water availability or both.

Genetic variability in carboxylate exudation capacity along with improved root traits was a key mechanism for P-efficient green gram genotype to cope with P-stress but it did not increase grain yield.