Water Deficit at the Anthesis Stage Induces Early Leaf Senescence and Affects Dry Matter Accumulation and Remobilization Efficiency in Black Gram (P. mungo, L.)

To investigate the effects of two levels of irrigation regimes (full irrigation [FI], i.e., normal water supply; and limited irrigation [LI], i.e., limited water supply) on growth and grain yield of two varieties of Phaseolus mungo (PU 19 and Type 9), a greenhouse experiment with three replicates was conducted from February to May in 2005. Results showed that pots in which water-deficit stress was introduced at the anthesis stage induced early senescence in both varieties (PU 19 and Type 9). Leaf chlorophyll content declined more quickly as leaves approached maturity for LI plants than for FI plants. The experiment demonstrated that var. PU 19 was a superior variety under both normal and limited irrigation conditions, compared with Type 9. It maintained high relative water content (RWCL) and net assimilation rate (NARL) in leaves under LI. PU 19 had the highest amount of remobilized dry matter (ARDM), remobilization efficiency (REE), remobilization efficiency percentage (REP), seed weight and grain yield (GY) under LI. We therefore conclude that senescence and remobilization are apparently promoted by a limited water supply or drought stress, and they are coupled processes. Studying RWC, NAR and leaf senescence can be used as indirect selection criteria for grain yield. This would be a beneficial for understanding of the many physiological mechanisms that confer water-deficit tolerance, leading to the development of leguminous plant species better adapted to such environments.