Effect of waterlogging stress on yield and yield components and photosynthetic characteristics of two Mung bean cultivars in Ahvaz conditions

Mung bean (Vigna radiata L.) is one of the most important legumes in the world. This nitrogen-stabilizing plant has rapid growth and a short growth period, leading to improved soil fertility. Mung bean is widely cultivated in tropical and subtropical regions of Asia due to its high adaptation range. Plants are obligate aerobic organisms and thus depend on O2 to grow and compete successfully with neighbouring plants in natural environments. Waterlogging stress is one of the most important factors limiting the planting of mungbean under Ahvaz conditions.

In order to study the effects of waterlogging stress on some agronomic and physiological characteristics of two Mung bean cultivars, a pot experiment was conducted as split-plot factorial in a completely randomized block design with three replications in the field. The main plots were different growth stages consisted of: vegetative growth stage, the beginning of flowering, grain filling stage, and three growth stages. The combination of stress levels (control and waterlogging stress) and two Mung bean cultivars (Hindi and Omrani) were as sub plots.

Waterlogging was caused to decrease significantly dry matter and grain yield in both cultivars at each growth stages, In Hindi cultivar, the highest grain yield reduction was observed at flowering stage and the least difference was observed in waterlogging stress at all three growth stages. In Omrani cultivar, the highest grain yield reduction was observed in waterlogging stress at all three growth stages, and the least grain yield decrease at flowering stage Overall, the reductions in dry weight and grain yield were higher in Omrani than Hindi cultivar at three growth stages. Therefore, in stress-prone areas such as Ahvaz where summer plants such as Mung bean are exposed to waterlogging stress at different growth stages, Hindi cultivar is suggested for cultivation. Waterlogging stress did not show a significant effect on grain weight and grain number per pod, but significantly reduced the number of pods per plant. The number of pods per plant was significantly more important in determining yield and had a positive and significant correlation (r = 0.846 **) with grain yield.

The reason of difference between two cultivars was the better physiological compatibility of Hindi cultivar under stress conditions, including higher levels of photosynthesis and photosynthetic pigments contents. When plants were treated only with water logging stress in one growth stage, the Omrani cultivar could compensate some damages due to its infinite growth and phenological flexibility, as the period of pod formation was longer in this cultivar. SPAD number had the highest correlation with grain yield (r = 0.707 **) compared to other photosynthesis-related traits and could be used as a marker trait for selection of tolerant cultivars because of its ease, speed, cheapness and the possibility to measure this trait in the field.