Higher Stability in Leaf Water Status in Heat-Tolerant Cultivars of Greengram (Vigna radiata (L.) Wilczek)

Greengram is adapted to relatively warm, dry climatic conditions and temperatures during reproductive period of >40°C during the day result in yield reduction. Greengram cultivars SAMRAT and IPM 02-3, which were developed from Indian Institute of Pulses Research shows higher heat tolerance than other cultivars. For an effective breeding program understanding of the mechanism controlling the heat tolerance in heat tolerant cultivar is necessary. High temperature often coincides with intensive solar radiation, which causes excessive transpiration and temporal water deficit in plants in the mid-day and there was a cultivar difference in mid-day depression of leaf water status. In heat-tolerant cultivars, mid-day depression in leaf water status was smaller and stomatal conductance was higher than those in heat-sensitive cultivars, well reflecting stomatal conductance and growth. Chlorophyll stability index showed less reduction in heat tolerant cultivars than susceptible ones under heat stress environment. The results are discussed in terms of heat tolerance strategies in relation to changes in leaf water status and gas exchange in plants. We conclude that daily stability in leaf water status could be a reliable characteristic to estimate heat tolerance in greengram.