Moisture Stress Effects on the Relative Water Content, Stomatal Resistance, Transpiration Rate and the Yield of Mungbean at Different Growth Stages

Abstract

The effects of soil moisture stress on the relative water content (RWC), stomatal resistance (RS), transpiration rate (TR) and the yield of mungbean (cv. MI-6) were studied during the vegetative, flowering and pod-filling stages in the greenhouse of the Department of Botany, Eastern University, Sri Lanka. This experiment was layed out in a Completely Randomized Design (CRD) with four treatments and five replications. Moisture stress was imposed for a period of 12 days by withholding water completely at once. The control plants were regularly watered to field capacity at four days interval. The RWC, RS and TR were measured on the 12th day from the commencement of the stress at different growth stages. The RS was significantly (P<0.05) higher and the RWC and TR were significantly (P<0.05) lower in the stressed treatments than the control irrespective of the stages of growth. The increase in RS was due to stomatal closure resulted in decreased TR values. Decreased water content of the stressed plants would have reduced the RWC values. The relationship between RS and TR was assessed for the stressed and the control treatments on the 12th day from the commencement of the stress during the flowering stage. Large variations in the TR values for a narrow range of low RS values in the control treatment indicated the stress avoidance features of mungbean under well-watered condition. Persistence of low TR values for a wide range of high RS values in the water stressed treatment indicated the stress tolerance features of mungbean under water deficit situation. Hence, mungbean show stress avoidance and stress tolerance features under two different situations. Moisture stress significantly (P<0.05) reduced the yield of mungbean and the reduction was highest when the stress was imposed during the flowering stage. The next highest yield reduction was observed when the stress was given during the vegetative stage of the plants. The plants when subjected to moisture stress during the flowering stage would have lost large number of flowers. In addition, the size of the newly produced flowers also would have reduced. All these events would have contributed for the highest yield reduction during the flowering stage of these plants. A significantly high correlation (r =0.42*) was found between the RWC and the yield of mungbean. This indicated that the reduction in yield was attributed to reduced water content in these plants.