The study aims at identifying some submergence-tolerant rice genotypes through morphological and molecular characterization and their genetic variability analysis. Ten rice genotypes including two submergence-tolerant checks, two susceptible varieties and six advanced lines were evaluated for submergence tolerance in the laboratory and in the field during January-December 2015. The experiment was conducted in the field following randomized complete block design in a two-factor arrangement using five replications. Ten characters, viz. days to flowering, plant height, tiller number plant, effective tiller plant, and yield plant etc. were studied for four treatments. A significant genotype×environment interaction was observed for all traits studied in this experiment. The yield was reduced for all genotypes at a different level of submergence stress compared to control. Binadhan-11, Binadhan-12, RC 249 and RC 251 showed tolerance, whereas RC 192, RC 193 and RC 225 showed moderate tolerance in submerged condition. The phenotypic coefficient of variance (PCV) was higher than the genotypic coefficient of variance (GCV) in all the studies traits. High heritability (75-97%) was found for all traits. High heritability along with high genetic advance was found for days to flowering (45.55) and plant height (40.05). Molecular characterization of the used genotypes was done with three SSR markers viz. RM 24, and submergence specific SC3 and SUB1. SC3 was found reliable for detection of submergence tolerant genotypes due to the highest gene diversity (0.840) compared to others. The banding pattern of the submergence specific markers SC3 and SUB1 identified in Binadhan-11, Binadhan-12, RC 192, RC 193, RC 225, RC 227, RC 249, and RC 251, which possess the SUB1 gene. Finally, clustering also separates the tolerant genotypes from the susceptible by dividing them into different clusters. The identified genotypes might be useful for the breeding programme for the development of submergence tolerant as well as resistant rice variety in Bangladesh.

A considerable progress in plant breeding for higher yield is attained mainly through selection of morpho-physiological attributes in rice. The field experiments were conducted at three different locations under sub-tropical conditions with four early maturing rice varieties viz., Binadhan-7, Binadhan-17, BRRI dhan33, and BRRI dhan39 during kharif-2 rice season (Aman; July-October) of 2016 to find out the natural variation in the morpho-physiological attributes contributing to  higher grain yield in rice. Morphological parameters on plant height, root structure, tillering ontogeny, internode elongation pattern, flag leaf length, flag leaf width, flag leaf angle, number of primary & secondary rachis, branches and also physiological traits on chlorophyll content, photosynthesis rate, total dry mass, growth rate, number of vascular bundles,  harvest index with yield and yield contributing characters were studied. Results indicated that plants having rapid growth and development at early growth stages showed  higher chlorophyll content, photosynthesis rate, long flag leaf, number of vascular bundles in 1st internode and also exhibited the increase in the number of grains per panicle resulting higher grain yield. Among the test varieties, Binadhan-17 showed superiority in the most morpho-physiological criteria and higher number of vascular bundles manifesting in higher grain yield. This information may help breeders to identity and develop high yielding rice variety.