Abstract:
Rice scientists have long argued that the SUB1 QTL on chromosome 9, and particularly its SUB1A-1 allele, is the single most tractable target for improving submergence tolerance in lowland rice through marker-assisted selection. This research tested that position by introgressing SUB1 from Swarna-Sub1 into Swarna, BR11, and BRRI dhan52, three widely grown Bangladeshi lowland varieties, through a BC3F2 marker-assisted backcross scheme. Six SSR and gene-specific markers (ART5, SC3, AEX1, GnS2, Sub1A-173, SRR38) were used for foreground and background selection across 2020-2023. Of 182 BC3F2 plants evaluated, 124 (68.1%) carried homozygous SUB1A-1 by Sub1A-173 marker. Under 14-day complete submergence in concrete tanks, homozygous SUB1 plants showed 82.4% survival versus 9.7% in null plants and 6.2% in the IR42 susceptible check. Field performance of advanced MAS-derived lines in flash-flood conditions produced 4.12-4.48 t ha⁻¹ grain yield against 1.34 t ha⁻¹ for the recurrent parent under the same conditions. Background recovery through recurrent-parent markers reached 93.6-96.1% in the best MAS lines. The data confirm MAS efficiency for SUB1 introgression and suggest release-grade candidates emerging from the Swarna genetic background.
