Characterization and genetic analysis of a very high tillering and dwarf rice (Oryza sativa L.) mutant
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This study focused on characterizing and determining the inheritance pattern of very high tillering and dwarf traits of a rice mutant. To characterize the new mutant, field phenotyping studies, and response of two mutant lines (M-13662 & M-13684) to three levels of nitrogen (179, 202, 224 kg ha-1) and five planting densities (1, 2, 3, 4, 5 plants hill-1) in greenhouse conditions were conducted. A separate study was carried out to determine the response of the two mutant lines to gibberellic acid (GA) application. The mutants were 50-55 cm tall and produced 89-121 tillers plant-1 at harvest. Dwarfness of the mutants was due to average shortening of the top four internodes as well as compression of 2-3 basal internodes. The first tiller emerged at the 4th leaf stage whereas no tiller was observed in semi-dwarf rice cultivar, Cocodrie. Results showed that the production of high tiller numbers was the result of the release of axillary buds from a dormant stage rather than the initiation of additional axillary buds. The mutants were late maturing than controls (Cocodrie & Zhe733). The panicles were very short (10-12 cm) and had 25-30 small grains. The majority of tillers of the mutants followed the dn-type dwarf pattern based on Takeda?s classification, but a few plants had a different dwarfing pattern not included in the classification. Both mutant lines were found to have similar agronomic traits but were significantly different from controls. The tillering ability of the mutants was affected by the five different planting densities as well as the three nitrogen levels. Mutants produced more tillers, both productive and non-productive, at the lowest plant density. The longest and shortest panicles were observed at 202 kg ha-1 and 179 kg ha-1, respectively. Variations in other agronomic traits were found not significant. The response of the mutant to GA application was similar to Cocodrie, and thus was considered GA responsive. Preliminary DNA data using SSR markers supported the presumed origin of the mutants and the genetic analysis indicated that one recessive gene controlled both the dwarfing and very high tillering traits.