Genetic improvement for blast resistance in high-yielding cold-tolerant rice ( Oryza sativa L.) cultivar Himalaya 741 by marker-assisted backcross breeding

Blast disease and cold stress are two major yield-limiting factors for rice under temperate climates. Marker-assisted backcross breeding approach (MABB) was employed for the improvement of blast resistance in a popular cold-tolerant variety ‘Himalaya741’ by introgressing a broad-spectrum resistance locus Pi9 from a Basmati donor PB1637. A combined use of phenotypic selection and marker-based genotypic selection ensured speedy reconstitution of the recurrent parent genome (RPG) in backcross progenies; RPG recovery in most of the progenies was > 96% with three progenies namely, HPU-1-33, -38 and -49 showing complete recovery of recurrent parent genome. Notwithstanding a very higher recovery rate of RPG in introgression lines, the lines still inherited a large linkage block > 13.3 Mb with Pi9 from the donor line PB1637. The donor chromosome segments co-inherited with Pi9 gene, however, did not have any adverse effect on the agronomic performance of the Pi9 introgression lines. Of the eight genetically superior Pi9 introgression lines identified, two exhibited resemblance to Himalaya 741 for most of the agronomic traits in addition to having superior grain length and tiller number. The introgression line HPU-1–81 displayed 44% yield superiority over recurrent parent, primarily due to improvement in yield-contributing traits, namely, tiller number, panicle length, thousand-seed-weight and grain length. All the Pi9 introgression lines displayed a high level of resistance comparable to PB1637 against two highly virulent blast races, which collectively displayed compatibility to 15 different major resistance genes. The introgression lines also possessed reproductive stage cold tolerance similar to recurrent parent under prevailing cold stress conditions. The agronomically superior Pi9 introgression lines developed herein are expected to provide a comparable or better substitute to blast susceptible variety Himalaya 741 for extenuating losses due to cold stress and blast disease.