RESPONSE OF TRANSPLANTED AMAN RICE VARIETIES TO DIFFERENT SOIL MOISTURE LEVELS

Abstract

Due to irregular rainfall during aman season between July and November rice suffers from drought. Sometimes the farmers do not afford to provide irrigation in boro rice field; where providing irrigation in the aman rice field seldom happens leaving the best option to cultivate drought tolerant rice varieties in aman season. Considering the above conditions three pot culture experiments were carried out at Sher-e-Bangla Agricultural University, Dhaka, Bangladesh during the period from July 2012 to November 2014 to study the performance of four transplanted aman rice genotypes (BRRI dhan56, BRRI dhan57, Binadhan-7 & BRRI dhan49) under three different soil moisture levels (100% field capacity moisture content or control, 70% of the control moisture and 40% of the control moisture). Another experiment under different PEG induced water stress conditions, was conducted to justify whether a lower soil moisture condition affects rice growth. The experiment was laid out in two factors Randomized Complete Block Design with four replications. The results indicated that plant height, tiller number, life duration, effective tiller, leaf area and total dry matter decreased under water stress. Increased dry matter investment to root in BRRI dhan49 helped to uptake more water under water stress. Relative water content, stomatal conductance and transpiration rate were found the highest at 100%FC condition and the lowest at 40%FC condition; but the reduction was comparatively lower in BRRI dhan56 and BRRI dhan49. BRRI dhan56 and BRRI dhan49 also performed comparatively better in PEG treatment. The grain yield and harvest index decreased with decreasing soil moisture in all the genotypes; BRRI dhan49 produced more than 90% relative grain yield under 70%FC treatment. Increased proline content in BRRI dhan56 and BRRI dhan49 helped them to give better yield under low soil moisture condition. The relative injury, chlorophyll content, soluble sugar content, starch content decreased with increasing water stress. The lower drought susceptible index (DSI) in BRRI dhan49 and BRRI dhan56 and higher in BRRI dhan57 and Binadhan-7 indicated that BRRI dhan49 and BRRI dhan56 were tolerant and BRRI dhan57 and Binadhan-7 were susceptible to water stress.