Hybrid rice varieties have higher yield potential over inbred varieties. This improvement is not always translated to the grain yield and its physiological causes are still unclear. In order to clarify it, two field experiments were conducted including two popular indica hybrids (BRRI hybrid dhan2 and Heera2) and one elite inbred (BRRI dhan45) rice varieties. Leaf area index, chlorophyll status, and photosynthetic rate of flag leaf, postheading crop growth rate, shoot reserve translocation, source-sink relation and yield, and its attributes of each variety were comprehensively analyzed. Both hybrid varieties outyielded the inbred. However, the hybrids and inbred varieties exhibited statistically identical yield in late planting. Both hybrids accumulated higher amount of biomass before heading and exhibited greater remobilization of assimilates to the grain in early plantings compared to the inbred variety. Filled grain (%) declined significantly at delayed planting in the hybrids compared to elite inbred due to increased temperature impaired-inefficient transport of assimilates. Flag leaf photosynthesis parameters were higher in the hybrid varieties than those of the inbred variety. Results suggest that greater remobilization of shoot reserves to the grain rendered higher yield of hybrid rice varieties.
Submergence stress at early vegetative stage is one of the most important constraints in the productivity of rice in Bangladesh. Submergence causes yield loss of rice at Aman season in Bangladesh and therefore, it is necessary to develop submergence tolerant rice cultivars. A pot experiment was conducted at the net house of Department of Crop Botany, Bangladesh Agricultural University, during Aman season from July to December, 2017 to evaluate the changes in root porosity and water soluble carbohydrates (WSCs) associated with submergence tolerance in rice. The experiment consisted of two factors—(i) Rice cultivars (Binadhan-11, Binadhan-12, BRRI dhan51 and BRRI dhan52 as tolerant and BRRI dhan49 as susceptible) and(ii) Submergence stress: Submergence for 14 days at vegetative stage and control. Submergence stress was imposed by dipping of pots into a water tank with about 90 cm depth of water while the control plants are maintained in the pot house of the field laboratory. The plants were sampled at seven days interval during submergence to determine the changes in root porosity and to examine the contribution of shoot reserves for their survival. The root porosity was measured by pycnometer method and water soluble carbohydrate was measured by the anthrone method. Tolerant cultivars showed greater root porosity development in both control and stress condition but the susceptible cultivar showed significantly lower root development in stress condition. Higher root porosity might help tolerant cultivars to survive in submergence stress more efficiently. Tolerant rice cultivars had high initial soluble carbohydrate than the susceptible one. Under submergedcondition, the tolerant cultivars showed slow depletion of water soluble carbohydrate compared to susceptible cultivar. Higher carbohydrate contents in tolerant cultivars might act as buffer stock during submergence for their better survival and growth. J Bangladesh Agril Univ 17(4): 539–544, 2019
Complete submergence up to 1-2 weeks of low land rice crops during flash floods occurs in large areas of South-East Asia including Bangladesh, resulting in increased mortality of plants as well as low productivity of rice crops. A pot experiment was conducted at the Net House, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, during Aman season from July 2017 to December 2017 to evaluate morphological and phenological traits associated with submergence tolerance in rice. The experiment consisted of two factors—Rice cultivars (Binadhan-11, Binadhan-12, BRRI dhan51 and BRRI dhan52 as tolerant and BRRI dhan49 as susceptible) and submergence stress for 14 days at vegetative stage and control. Submergence stress was imposed by dipping of pots into a water tank with about 90 cm depth of water. After desubmergence, the plants were grown with proper care till maturity. Control plants are maintained in the pot house of field laboratory. Leaf greenness was measured after desubmergence to physiological maturity. The tolerant cultivars maintain higher leaf greenness for a long time than the susceptible cultivar after desubmergence. Reduction of grain filling rate and yield was significantly higher in susceptible cultivar than the tolerant cultivars. Among the five cultivars, BRRI dhan51 contributed the highest yield under stress treatment. Submergence tolerant rice cultivars (Binadhan-11, Binadhan-12, BRRI Dhan51 and BRRI Dhan52) had maintained higher tiller number, 1000-grain weight and the higher number of grains per panicle during submergence, as compared to susceptible rice cultivar BRRI Dhan49. J Bangladesh Agril Univ 17(4): 545–550, 2019
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