Physiological and Biochemical Characterization of Waterlogging Tolerance in Pigeon pea (Cajanus cajan L.) Genotypes
Abstract
Background: Waterlogging is a major abiotic constraint limiting pigeon pea productivity, particularly in regions receiving high rainfall during early growth stages or in crop lands with poor drainage. Exposure to prolonged soil saturation during the early vegetative stage disrupts normal physiological processes, resulting in reduced plant growth, impaired metabolism, and yield losses. Deciphering of the adaptive responses associated with waterlogging stress is crucial for devising crop breeding and selection strategy for developing waterlogging-resilient pigeon pea cultivars. Methods: Thirty pigeon pea genotypes, comprised test genotypes as well as tolerant and susceptible checks, were evaluated under controlled waterlogging conditions during two consecutive growing seasons. Waterlogging stress was imposed for 24, 48 and 72 hours at 30 days after sowing while a parallel set of plants was maintained under normal conditions. Morphological responses, survival percentage, adventitious root formation and aerenchyma development were recorded. Physiological parameters viz. photosynthetic rate, stomatal conductance, transpiration rate, chlorophyll content, nitrogen balance index, flavonols content, anthocyanin content and NDVI were recorded using standard analytical procedures. The biochemical parameters namely, antioxidant activity of enzymes and soluble sugar concentration were also estimated using standard protocol to assess biochemical responses associated with waterlogging stress. Result: Considerable variation in waterlogging tolerance was observed among the evaluated genotypes. IPAC-79, ICPL-87091, ICPL-20241, ICP-2376, IPAC-212, IPAWL-22-7 and IPAWL-22-8 consistently exhibited superior tolerance by maintaining higher survival, improved photosynthetic performance, greater chlorophyll retention and enhanced antioxidant activity under stress. These genotypes also developed abundant adventitious roots and well-defined aerenchyma tissues, facilitating adaptation to oxygen-deficient conditions. Moderately tolerant genotypes displayed intermediate responses, whereas susceptible genotypes exhibited severe chlorosis, wilting, poor survival and substantial reductions in physiological and biochemical traits in response to prolonged waterlogging stress.