Marker-assisted trait enhancement for drought tolerance and bacterial leaf blight resistance in rice cultivar HUR-917

Moisture stress and bacterial blight (BB) are major constraints limiting rice productivity in irrigated and rainfed shallow lowland ecosystems. Despite the identification of several drought-yield quantitative trait loci (QTLs) and BB resistance genes, their combined deployment in aromatic short-grain rice cultivars remains limited. The popular aromatic cultivar HUR-917, a restorer line HUR-917, a restorer line to reproductive-stage drought and BB, highlighting the need for developing climate-resilient and disease-resistant versions without compromising yield and grain quality. The present study aimed to improve HUR-917 through marker-assisted introgression of drought-yield QTLs qDTY2.2 and qDTY4 .1 along with BB resistance genes xa5, xa13 , and Xa21 . DRR Dhan-42 was used as the donor for drought QTLs, while improved HUR-917 (HUR-917-15-2-2-1) served as the donor for BB resistance genes, with HUR-917 used as the recurrent parent (RP). Marker-assisted backcross breeding (MABB) was employed for precise introgression of target loci and accelerated recovery of the RP genome (RPG) using gene-linked markers and 98 polymorphic SSR markers. A total of 16 BC 3 F 4 near-isogenic lines (NILs) carrying the target QTLs and BB resistance genes were developed, with more than 90% RPG while retaining the product profile of HUR-917. Among them, NILs HR-12-1-4-87-5-2-4, HR-12-1-4-87-5-2-8, HR-12-1-4-87-5-2-32, HR-12-1-4-87-295-4-19, HR-12-70-9-258-169-1-8, and HR-12-70-9-258-223-5–12 exhibited stable performance under both drought stress and irrigated conditions. Under moisture stress, the NILs showed comparatively lower reductions in plant height, spikelet fertility, and grain yield than the RP, primarily due to improved spikelet fertility and higher grain number per panicle. Importantly, no yield penalty was observed under non-stress conditions. The improved NILs also retained desirable grain quality attributes, including aroma, amylose content (AC), and head rice recovery (HRR). Physiological analyses further confirmed enhanced drought tolerance, as the NILs maintained higher chlorophyll content and accumulated substantially greater proline levels (average, 77.06 mg g - ¹) compared with the RP. Overall, the combined introgression of qDTY2 .2, qDTY4 .1, xa5, xa13 , and Xa21 successfully enhanced drought tolerance, BB resistance, and yield stability without adversely affecting grain quality. The developed multi-stress-tolerant NILs constitute valuable genetic resources for breeding climate-resilient aromatic rice cultivars suited to the Indo-Gangetic Plains.