Abstract:
This study focused on the high temperature tolerance of mungbean varieties using plexiglass canopy to increase the prevailing high temperature. The plant measurements were made for heat induced changes growth, photosynthetic pigments, gas exchange, osmolytes accumulation, oxidative stress and antioxidative response, shoot, root and seed nutrient and yield attributes at different growth stages. Data revealed that heat tolerance in mungbean was variable at three prime foliation and flowering stages. The varieties exhibiting prolific root system and leaf area (e.g., NM-2011 and NM-2006) were more tolerance to heat stress. Heat stress caused the loss of chlorophyll and inhibition of the leaf gas exchange. The tolerant varieties incurred a minimum loss of photosynthetic pigments; more importantly increased carotenoids contents were closely associated to heat tolerance. Among the studied osmolytes, the accumulation of soluble sugars and GB at flowering stage contribute greatly to heat tolerance in the studied varieties. Due to high temperature, the production of hydrogen peroxide (as reactive oxygen species) and malondialdehyde was seen, but the tolerant varieties produced minimum amounts of these oxidative stress metabolites, while the accumulation of phenolics, anthocyanin, and ascorbic acid were able to possibly protect the membrane especially in the tolerant varieties. The success of the tolerant varieties in displaying greater pod growth and seed yield characters appeared to be due maintenance of greater nutrient contents both in the shoot and root tissues especially under excessive high temperature stress. In conclusion, mungbean showed a large genetic variability for tolerance to heat stress at flowering and maturity stages. This implied that the varieties with a tendency to maintain greater nutrient contents was better able to withstand heat stress conditions. Among the studied attributes, the heat stress induced oxidative stress appeared to be a main reason for mungbean susceptibility to high temperature. Future studies will further our understanding on heat tolerance mechanisms and mungbean improvement programs for better growth in warmer areas.
