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.
