Utilization of doubled haploid breeding approach in introgression of QTL/gene(s) for parental line improvement of hybrid rice.

Abstract

This study aimed to improve the restorer line IR 42266-29-3R (A42) for multiple stress tolerance using integrated marker-assisted backcross breeding (MABB) and the doubled haploid (DH) approach. The primary objective was to introduce the abiotic stress tolerant QTL (qDTY1.1 and qHTSF4.1) into the background IR 42266-29-3R, which already harbors three bacterial blight (BB) resistance genes (xa5, xa13, and Xa21). The BC₁F₁ population was derived from crosses between IR 42266-29-3R and N22, leading to the development of 113 true DHs. Efficient callus induction (29.64%) was achieved using N6 medium supplemented with 2.0 mg/l 2,4-D, 0.5 mg/l BAP, and 3% maltose. Green plant regeneration rates were notably high on the MS medium supplemented with 0.5 mg/l NAA, 0.5 mg/l Kn, 2.0 mg/l BAP, and 3% sucrose, reaching 68.6% and 61.9% on the 2nd and 7th days, respectively. From the 113 DHs, 24 were selected based on superior morpho-agronomic traits and maximum gene combinations. These DHs underwent phenotypic evaluation during the reproductive stage for drought and heat stress responses, alongside assessment for BB resistance. Among them, CS65 showed a genetic profile encompassing xa13, Xa21, qDTY1.1, and qHTSF4.1, while six others exhibited xa5, Xa21, qDTY1.1, and qHTSF4.1. Notably, CS1, CS3, CS37, CS64, and CS65 demonstrated low susceptibility to heat and drought stresses, coupled with yields comparable to the recurrent parent and moderate to high resistance against bacterial blight. CS65 emerged as the most promising genotype due to its robust tolerance to multiple stresses and improved yield potential. Moreover, eight out of the 24 DHs tested positive for both Rf3 and Rf4 genes, displaying spikelet fertility rates exceeding 75%. These selected restorer lines will serve as foundational material for developing superior hybrid rice lines, while the non-restorer lines will contribute to the broader pool of rice varieties in future breeding programs.