Abstract
Urdbean (Vigna mungo L. Hepper) is one of the important pulse crops. Its cultivation is not so popular during summer seasons because this crop is unable to withstand excessive heat stress beside lack of humidity in the atmosphere. Therefore, a panel of 97 urdbean diverse genotypes was assessed for yield under stress and non-stress conditions with an aim to identify heat tolerant genotypes. This study identified 8 highly heat tolerant and 35 highly heat sensitive genotypes based on heat susceptibility index. Further, physiological and biochemical traits-based characterization of a group of six highly heat sensitive and seven highly heat tolerant urdbean genotypes showed genotypic variability for leaf nitrogen balance index (NBI), chlorophyll (SPAD), epidermal flavnols, and anthocyanin contents under 42/25°C max/min temperature. Our results showed higher membrane stability index among heat tolerant genotypes compared to sensitive genotypes. Significant differences among genotypes for ETR at different levels of PAR irradiances and PAR × genotypes interactions indicated high photosynthetic ability of a few genotypes under heat stress. Further, the most highly sensitive genotype PKGU-1 showed a decrease in different fluorescence parameters indicating distortion of PS II. Consequently, reduction in the quantum yield of PS II was observed in a sensitive one as compared to a tolerant genotype. Fluorescence kinetics showed the delayed and fast quenching of Fm in highly heat sensitive (PKGU 1) and tolerant (UPU 85-86) genotypes, respectively. Moreover, tolerant genotype (UPU 85-86) had high antioxidant activities explaining their role for scavenging superoxide radicals (ROS) protecting delicate membranes from oxidative damage. Molecular characterization further pinpointed genetic differences between heat tolerant (UPU 85-86) and heat sensitive genotypes (PKGU 1). These findings will contribute to the breeding toward the development of heat tolerant cultivars in urdbean.
Highlights
The Kanpur location is situated in the northern part of India (26.28◦N and 80.21◦E) where early sown genotypes experienced heat stress with a rise of temperature (>40◦C) coinciding with the reproductive stage, whereas late sown genotypes received moderate temperature (
The heat sensitive and tolerant genotypes were identified at a preliminary stage based on the heat susceptibility index (HSI) under a field trial conducted in two contrasting environments
Sensitive genotypes were characterized with an Heat susceptibility index (HSI) ranging from 0.08 to 3.19 at the Kanpur location and from 0.37 to 13.75 at the Vambam location, while HSI varied from -0.01 to -20.48 at Kanpur and -0.03 to –62.29 at Vambam among tolerant genotypes (Table 3)
Summary
India is the largest producer and consumer of urdbean. It produces about 3.36 million tons of urdbean (Project Coordinator’s Report, 2019-2020) and imports another 0.5 million tons from other urdbean growing countries, from Myanmar. Urdbean is dense with protein (21-28%), dietary fiber (161-187 g/kg), iron (16-255 mg/kg), zinc (5134 mg/kg), and other micronutrients like other pulses (Chitra et al, 1996; Sen Gupta et al, 2020). Its nutrient-dense profile has encouraged an introduction to many developed countries including the United States, Russia, and European nations as a potential pulse crop (Sen Gupta et al, 2020)
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