Abstract
Heat stress damages the photosynthetic capacity and ultimate crop yield; the genetic basis of which is scarcely known. Studies
were conducted during the years 2014 and 2015 to understand the physiological basis of heat tolerance in seven mungbean
[Vigna radiata (L.) Wilczek] varieties by monitoring changes in hydrogen peroxide (H2O2) and malondialdehyde (MDA)
contents, photosynthetic pigments and gas exchange attributes in the trifoliate leaf in proximity to the pods as well as nutrient
partitioning to the pods and developing seed by applying heat stress at the flowering stage. After 15 days of stress, the data for
physiological and biochemical attributes were recorded while the data for seed yield and quality were taken at maturity. Heat
stress caused a marked accumulation of H2O2 and MDA whilst decreasing net photosynthesis, stomatal conductance and water
use efficiency, chlorophyll a and b, and total chlorophylls in the sensitive varieties, while increased carotenoids contents in the
tolerant varieties. Seed yield per plant and 1000 seed weight were affected due to heat stress, leading to more reduced harvest
index in the sensitive varieties. Heat stress also hampered the partitioning of nutrients such as nitrogen, sulfur and calcium to
the developing seed. Interrelationships of different parameters revealed that heat stress damaged the leaf chlorophyll and leaf
gas exchange due to enhanced production of H2O2 and MDA, while tolerant varieties (NM-2011 and NM-2006) exhibited
better gas exchange properties and produced higher seed yield and harvest index in both the years. Seed yield was directly
correlated to the partitioning of nutrients especially nitrogen, sulfur and calcium under heat stress. In conclusion, despite
significant differences in the varieties, the yield loss in mungbean is associated to heat stress mediated oxidative stress on the
leaf photosynthesis and reduced assimilate partitioning to the pod development and seed filling. Thus, selection based on
greater rate of photosynthesis of the proximal leaf may be helpful for fetching better mungbean yield in relatively warmer
environments.
