Improving upland rice variety NSIC Rc9 through in vitro mutation

Mature seeds of upland rice cv NSIC Rc9 were cultured in vitro and the resulting calli were irradiated with varying dose, viz., 10, 30, 50 and 70 Gy, of gamma rays from 60Co- of the 252 callus pieces irradiated in 2009 dry season (DS), 1.6% (50 Gy) to 20.6% (70 Gy) plant regeneration was obtained, constituting the first generation in vitro mutation (IVM1) induced plants. The regenerated 57 IVM1 plants yielded 181 IVM2 lines which were evaluated for agronomic traits and yield in 2010 DS. The maturity of 98 (54%) lines was 4 days to 13 days earlier compared with the wild type or the progenitor NSIC Rc9, which matured in 119 days after seeding. The yield of 130 (71.8%) lines was 0.301 t/ha to 3.651 t/ha higher than the progenitor with a yield of 5.799 t/ha. The IVM lines were evaluated for tolerance to herbicide and drought stress at seedling stage in 2010 WS resulting in the identification of 76 (41.9%) and 53 (65.4%) tolerant lines for herbicide and drought stress, respectively. In the same season, the grain quality, in terms of grain size and shape, and percent apparent amylose content (% AC), of the mutant lines was assessed and compared with the progenitor using the IVM3 seeds. Milled grain length of 81 (44.8%) was significantly increased by 0.9 mm to 1.7 mm shifting the classification of medium, for the progenitor, to long size, for the mutant lines. Likewise, the grain shape of the mutants was increased by 0.1 mm to 0.8 mm relative to that of the progenitor shifting the shape from intermediate to slender. On the other hand, the % AC of 127 (84.1%) lines was reduced significantly by 1.9% to 8.6% compared to the 25.8% AC of the progenitor. A total of 27 (14.9%) promising improved IVM lines derived from NSIC Rc9 were identified. These lines mature earlier, with higher yield of acceptable grains size and shape, and % AC and with tolerance to herbicide and drought stress. The results obtained from this study exhibited the effectiveness and efficiency of combined tissue culture and induced mutation also known as in vitro mutagenesis, in developing breeding lines with improved agronomic traits and grain quality, and tolerance to abiotic stresses.