Improving agronomic and grain quality of upland rice variety NSIC Rc9 through seed mutation

Seeds of NSIC Rc9, a drought tolerant upland rice variety, with intermediate maturity and plant height, medium-intermediate grain size and shape, with purple apiculus, high % amylose content (%AC), and above average % chalky grains were irradiated with 250Gy and 300Gy y-rays from sup 60 Co. The M1 and M2 populations, established plant to a row in 2008 wet season (WS), and 2009 dry season (DS) and WS generated 946 plants with reduced plant height, improved grain size and shape and apiculus color. In 2010 DS, the M3 lines were evaluated for field drought tolerance resulting in the selection of mutants with comparable recovery rate from drought stress as the wild type or the progenitor NSIC Rc9. The 54 mutant line selections comprising the M4 population were advanced to observational nursery for agronomic and grain quality trait evaluation in 2010 WS. Maturity of the mutants ranged from 110 to 119 days after sowing (DAS), with 27 (50.0%) and 14 (25.9%) mutants matured earlier and later, respectively, compared with the progenitor which matured in 114 DAS. Plant height was reduced, from 88cm to 111cm, as compared with 121cm of the progenitor. The mutant lines generated 12 to 21 productive tillers while the progenitor had 12 productive tillers. The mutant lines yielded 3.925t/ha to 7.193t/ha, with 18 (33.3%) yielding 0.012t/ha to 1.365t/ha higher than the progenitor, with 5.828t/ha yield. The milling potentials of most lines are within the recommended values, viz., 75.0% and above % brown rice, 65.1% and above % total milled rice, and 48.0% and above % head rice. Milled grain length of 32 (59.3%) mutant lines were significantly increased by 0.6mm to 1.3mm, shifting the shape from medium to long size, and grain shape by 0.8 to 1.2, shifting the shape from intermediate to slender. The apparent % AC of the 31 (38.9%) lines reduced significantly by 1.2 to 4.2%. The chalky grain of 47 (87.0%) lines was likewise, reduced significantly by 3.3% to 11.5%. The mutant lines will be evaluated further for biotic and abiotic stress tolerance. The results of this study exhibited the effectiveness of mutation breeding for improving agronomic and grain quality traits in rice.