Effect of Gamma Irradiation Combined with Multiple Shoot Induction on Change in some Agronomic Traits of Aromatic Rice (Oryza sativa L.) Variety Khao Dawk Mali 105

Abstract

Mutation induction of aromatic rice (Oryza sativa L.) was conducted after in vitro multiple shoot induction and gamma irradiation. Seeds of aromatic rice variety Khao Dawk Mali 105 (KDML 105) were irradiated by gamma radiation at the doses of 0, 4, 8, 12, 16, 20, 24, 28, 32, 36 and 40 krad. After irradiation, the multiple shoots were induced from the seeds. The shoots were rooted and the plantlets (M subscript 1 R subscript 1) were grown under greenhouse condition until maturity. It was found that at the lower doses the height of M₁ R₁ plants increased and subsequently reduced at the higher doses. The doses from 4 to 20 krad caused a reduction in the number of days to flowering compared with the other doses. Number of tillers and panicles per plant increased as the dose increased. At the doses of 8 and 12 krad the number of fertile panicles per plant increased and gradually decreased at the doses higher than 12 kard. The percentage of seed fertility decreased as the dose increased. The 1,000 grain weight varied depending on the dose. Chlorophyll variation was observed among M₁ R₁ plants derived from the cultures of non-irradiated and irradiated seeds. In M₂ R₂ generation, plant height, number of tillers, panicles and fertile panicles per plant varied depending on the doses (0 to 36 krad) compared to control which grown directly from seeds of KDML 105. However, the percentage of fertile seeds still decreased when the dose increased. Chlorophyll mutation was also found in M₂ R₂ progenies. It is of interest that the M₂ R₂ progenies derived from cultures of non-irradiated and irradiated seeds were photoperiod insensitive. They flowered when they reached the maximum vegetative growth stage without the influence of short daylength. On the contrary the control grown directly from seeds of the photoperiod sensitive KDML 105, flowered after stimulation of short daylength. The inheritance of photoperiod insensitive character in M₃ R₃ generation will be investigated later. If the photoperiod insensitive character expressed in the M₂ R₂ progenies is heritable, it will be useful for selection of pure line KDML 105 for photoperiod insensitivity.