Author : Ngwe Sin Moe Satt

Summary : This study aimed to enhance submergence tolerance in rice by introgressing qSUB2, located on chromosome 2, into the genetic background of FARO 66 (qSUB1). Phenotyping and genotyping were conducted across BC2F2, BC2F3 and BC3F1 populations derived from FARO 66 x ART 280 to combine complementary tolerance mechanisms. Evaluation under complete submergence revealed wide variation in survival (0-100%) and plant height traits, confirming segregation and recombination of tolerance alleles. Several line including FARO 66//ART 280-164-1-1/FARO 66-26-154 and -10-94 exhibited higher survival than FARO 66, demonstrating additive effects between qSUB1 and qSUB2. High heritability (79-96%) indicated strong genetic control and potential for selection. Molecular genotyping identified 2,962 polymorphic SNPs (19.62%), providing sufficient genome coverage. Most BC2F2 lines recover 80% of recurrent genome while BC3F1 lines reached up to 96% recovery, confirming effective background selection. Some genotypes exhibited lower percentage of similarity of FARO 66 due to transmission of undesirable loci from donor parent. QTL mapping revealed multiple loci associated with submergence tolerance on chromosomes 1, 2, 3, 4, 6, 9, 10, and 12. The significant loci on chromosome 2 aligned with qSUB2, contributing moderate effects to improved survival recovery. The integration of qSUB1 and qSUB2 enhanced tolerance by moderating elongation, conserving energy, and stabilizing growth during and after submergence. The best performing line (FARO 66//ART280-164-1-1/FARO 66-10- 94) combined high survival desirable agronomic traits and high genome recovery, demonstrating that pyramiding qSUB1 and qSUB2 broadens and stabilizes submergence tolerance in rice. Therefore, it could be used for generation advancement and to develop as an improved variety to farmers in rice growing flooded areas.