Effects of gamma radiation on agro-morphological characteristics of rice (Oryza sativa L. var. Azucena) mutants

Philippine traditional rice variety Azucena is known for its aromatic and good grain qualities, but is taller, produces fewer tillers, and matures longer than commonly preferred rice varieties. Induced mutation by gamma radiation was done to generate mutants with shorten stature and earlier maturity, aside from having good over-all plant quality. Seedling height, days to heading, tiller count and plant height of M1 mutants generated from irradiation at 150-300 GY doses using Cosup 60 were evaluated. Seedling height of M1 plants ranged from 187-319 mm with seedlings generated from irradiation in 300 GY showing significant difference from the non-irradiated Azucena and other mutants. In terms of plant height, M1 mutants ranged from 87-164 cm, as opposed to non-irradiated Azucena mean height of 136.13 cm. As for tiller number, the control plants had a mean of 9 tillers per plant, while the mutants developed 3-60 tillers per plant across irradiation doses. From the mutant population, selected promising M1 mutants showed fewer days to heading, shorter stature, more tillers and higher percent filled spikelets compared to the non-irradiated Azucena plants. Selected mutants had as much as 25.31% height reduction, which was observed at 300 GY. They also had 125.62-222.92% increase in the number of tillers, and 11.93-15.54% increase in the percentage of productive tillers. Percent filled spikelet was also higher by at least 11.93% in the selected mutants over the non-irradiated Azucena. Selected plants constituted the M2 population, which also underwent evaluation and selection. Selected M2 plants had 6% lower germination percentage than non-irradiated Azucena and with a number of chlorophyll mutants also noted among the mutant lines. M2 mutants were also observed to have shorter plant height (101-121 cm), more tillers (17-28 tillers per plant), acceptable percent productive tillers and earlier heading. This study shows the potential improvement of Azucena through mutation.