Development of submergence tolerance introgression lines (ILs)-F 5 using major Sub1QTL on chro9 from BRRI dhan52 in rice (Oryza sativa L.) through Marker-Assisted Selection (MAS)

Rice is a highly polymorphic crop species with a wide geographical distribution. Molecular markers are important tools for breeding selection, genotype detection, and studying the organization and evolution of plant genomes. The main objective of this study was to introgress Sub1 QTL into high yielding rice cultivars for developing submergence tolerance with Sub1 gene fix in selected lines. The band corresponded to an allele for F₁ confirmation from the susceptible parent Binadhan-17 and the tolerant one BRRI dhan52, as 159 bp and 169 bp bands, respectively, at locus SC32/RM23668. The lowest survival% (32.75 %) was recorded in F₂-6 and the highest (68.25 %) in F₂-12 plant numbers from Binadhan-17 x BRRI dhan52. In F₃ generation, the highest survival rate (%) at vegetative stage was obtained from Binadhan-17 x BRRI dhan52 (F₃) 94.25% in F₃-15, then the other crosses were 93.25% in F₃-11 from Binadhan-7 x BRRI dhan52 (F₃) and Guti swarna x BRRI dhan52 (F₃) in F3-10 of 85.25%. All F₁ confirmation plants with Sub1 introgression had significantly lower survival rates than the original parent and survival rates and Sub1 gene expression were significantly higher with homozygous tolerant selected lines than heterozygote plants. The introgressed lines of the crosses at F₄ generations were designated as BPRLs BPR21 (P7 = BPR21-1-S, P9 = BPR21-2-S, P11 = BPR21-S-S, P12 = BPR21-S-M), BPR22 (P12 = BPR22-1-S, P13 = BPR22-2-S, P15 = BPR22-S-S) and BPR17 (P2 = BPR17-S-M, P10 = BPR17-S-17) showed homozygous amplification of Sub1 gene. As the tolerant allele at Sub1C on chromosome 9 was fixed as Sub1C173 and ERF3 in this selected population, additional QTL responsible for submergence tolerance were expected to be revealed. The antioxidants such as SOD, POD, CAT, APX and GPX activities increased under submergence stress compared to respective controls. BPR17-S-M, BPR21-S-M and BPR22-S-S showed higher antioxidant activity compared to the control. Higher SOD, POD, CAT, APX and GPX enzyme activities indicate greater mitigating levels of O₂•- and H₂O₂ under submergence stress. Importantly, under stress conditions, three breeding lines, BPR21-S-M (19.33 g), BPR22-S-S (20.23 g) and BPR17-S-M (15.26 g), produced the most grain yield per plant, which was significantly higher than the donor parent of BRRI dhan52 (12.71 g) and also was found to be 3.00 g to 8.00 g more than the parent and 20 g to 25 g less than the non-flooded condition. However, three Sub1 lines; BPR21-S-M, BPR22-S-S and BPR17-S-M showed better yield contributor with very good recovery ability after submergence stress under field conditions. It could be concluded that these three newly developed promising Sub1 lines will be used to develop high yielding submergence tolerant (21 days) cultivars for flood prone areas in Bangladesh. It will be ensured the food security of the nation by continuing rice production cold prone areas in Bangladesh