Twenty four hybrid rice varieties of diverse origin were studied for genetic variability, correlation and path analysis under medium high land of Gazipur. The PCV values were greater than GCV, revealing little influence of environment in character expression. High values of heritability along with moderate genetic advance were observed for panicle/m 2 , days to 50% flowering and plant height. Grain yield showed positive significant association with number of effective tillers/hill, panicle/m 2 , spikelet fertility and thousand grain weight at both genotypic and phenotypic levels. Same traits had highest significant positive effect on yield.

One hundred and sixty rice varieties from the tidal and flood prone areas of south and south East Asian countries were analyzed. Samples sizes were: 50 varieties from Bangladesh (deepwater, tidal and flood prone rice and modern varieties), 14 varieties from India (flood prone rice), 16 varieties from Sri Lanka (flood prone rice), 7 varieties from Vietnam (tidal varieties), 69 varieties from Indonesia (tidal varieties) and 4 check varieties from IRRI. All 30 primer pairs created polymorphic bands among the 160 rice varieties from flood and tidal prone areas, which indicated that the microsatellites used were suitable for diversity analysis. A total of 337 alleles were detected with an average of 11 alleles per locus and the number of alleles per locus varied from 4 to 21. The highest PIC values were observed for the primer of RM474 (0.91), followed by RM5 (0.82), RM484 (0.81), RM214 (0.81), and RM19 (0.79). Cluster analysis divided the genotypes into four main clusters and six sub-clusters based on geographical origins and ecotypes. Microsatellite clustering (over 30 polymorphic loci) and submergence screening data indicated greater genetic diversity among 160 genotypes for molecular loci and for submergence tolerance. Tolerant genotypes in Cluster-1 are expected to have different tolerance genes. Finding relationship between tolerance and country of origin, highly tolerant varieties (FR13A and FR43B) were found from east India. Genetic diversity analysis among flood prone rice will be useful for identifying the varieties having maximum diversity with submergence tolerance and selected varieties will be useful for further studies.

No abstract

Deep water rice ecosystem represents the flood-prone rice ecosystem where rice plant requires elongation ability to reach the surface with a certain amount of plant height to withstand in stagnant flood water condition. Low yield potentiality of locally adapted deep water cultivars limits the total rice production in the country. In present study, efforts were made to evaluate the suitability and adaptability of newly developed high yielding deep water breeding line BR10230-15-27-7B and control variety Fulkori under semi deep water ecosystem of farmer’s field condition in three consecutive years. At six locations, water depth varied from 60 to 140 cm under semi deep water ecosystem. In 2016 and 2017, mean yield of the line ranged between 2.9 to 3.1 t ha-1 while 1.7 t ha-1 for the local control variety Fulkori. However, around 1.0 t/ha yield advantage was found for the newly developed breeding line. Thus, the higher yield potentiality of the breeding line under 140 cm water depth conditions suggested its suitability under shallow flooded environments. During final evaluation in 2018, larger variation was observed in terms of grain yield ranging from 1.1 to 3.8 t ha-1 for the line while 0.4 to 1.7 t ha-1 for the control variety when evaluated under actual deep water areas. This result also supported that this line have greater potentiality under shallow flooded condition. In addition, the breeding line exhibited similar plant height with at least six days earliness compared to the control variety. Finally, National Seed Board (NSB) approved this line as variety and designated as BRRI dhan91 for broadcast Aman (B. Aman) season. In future, this new rice variety could help the local rice growers to cultivate modern high yielding rice variety in shallow flooded environments. BRRI dhan91 also showed better performance for tallness with lodging tolerance, submergence tolerance and moderate elongation ability under shallow flooded conditions. Bangladesh Rice j. 2019, 23(1): 57-63

A cluster of three ethylene response factor (ERF) like genes at the Sub1 locus has been identified from rice variety FR13A that confers tolerance to submergence for about 14 days. Restriction digestion-based haplotype variations among 11 rice accessions were analyzed to generate polymorphisms at Sub1C and Sub1A loci. Considering different combinations of SNPs (haplotype), four haplotypes: A1C1, A1C2, A2C2 and A0C2 were detected. Further, using semi-quantitative RT-PCR-Sub1A and Sub1C transcripts in different haplotypes were interpreted in respect with stem elongation and survival for understanding mechanism of submergence tolerance. Expression variations in Sub1 genes in relation with duration of submergence, haplotype diversity and an interaction of loci were found. Differential expression of Sub1A and Sub1C affected the stem elongation and survival of different haplotypes differentially. In tolerant varieties (A1C1 haplotype, IR40931), the highest expressed gene was Sub1A; while expression of Sub1C was lower. Over-expression of Sub1A gene in tolerant varieties, suppressed the stem elongation under submergence, which improved the level of submergence tolerance. In susceptible cultivar (Fulkari), the highest-expressed gene was Sub1C, while the Sub1A was not expressed which showed higher susceptibility. In moderately tolerant varieties (Kottamali), both Sub1A and Sub1C gene transcripts were up-regulated by submergence and higher level of both Sub1A and Sub1C genes transcripts. The varieties in A2C2 haplotype showed moderate level of tolerance without the Sub1A1 allele and a distinct novel mechanism favored the expression of both the Sub1A and Sub1C alleles that confer higher tolerance under complete submergence.