Effects of Drought and Flooding Stresses on Growth and Photosynthetic Activity of Mungbean,, Vigna radiata (L.) Wiilczek, Cultivars

The responses to drought and nooding stresses and the recovery from stress-induced damages were compared between three mungbean cultivars, Chinese (CN), and newly released cultivars in Myanmar, VC2991-112B-1B (VC) and KPS2 (KP). Growih, gas exchange rate and chlorophyll fluorescence quenching of these cultivars were investigated. The results were as follows: (1) CN was sensitive to both drought and flooding treatments compared to the other cultivars. VC and KP were less sensitive to drought and flooding, respectively. (2) The photosynthetic rate (PN) and stomatal conductance (G.) in VC were less affected by drought, with a quick recovery by re-watering. On the other hand, both parameters in KP were strongly depressed by drought, but less by nooding. (3) VC showed a higher value for the quantum yield of photosystem H (<~.) and a lower value for the photorespiration ratio (P,?lTc) than the other cultivars in the drought treatment. KP had a higher ~)* and lower PR/Tc in the flooding treatment. (4) The stomatal behavior was closely related to the stress-tolerance of mungbean cultivars. A partial retainment of gas exchange under the stress conditions was essential to sustain electron transport in the photosystems and prevent functional damages caused by excessive accumulation of energy in leaves