Phenotypic Study and Response of Very High Tillering Rice Mutant to Nitrogen Fertilizer, Planting Density and Gibberellic Acid.

Several dwarf rice mutants have been identified and characterized but recently, a novel very high tillering and dwarf mutant was identified in an early generation of L202 x Saber cross. To characterize the new mutant, field phenotyping study of advanced lines and response of two mutant lines 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 condition were conducted. A separate study was done to determine the response of the two mutant lines to gibberellic acid (GA) application. In field condition, the mutant lines were 50-55 cm tall and produced 89-121 tillers per plant at harvest. The panicles were very short (12-13 cm) and had 25-30 typical long grains. It flowered in 95 days and matured in 121 days. The first tiller emerged at 4^th leaf stage and the tiller number was doubled every week till 7 weeks after emergence of seeds resulting to a final tiller number that was 6-8 times higher than conventional rice, Cocodrie. Majority of the tillers of the mutants followed the dn-type dwarf pattern based on Takeda’s classification but few plants have different dwarfing pattern not included in the classification. The tillering ability of mutants was affected by five different planting densities as well as three nitrogen levels.  Mutant produced more tillers both productive and non-productive tillers at lowest plant density. There was no significant differences observed among 179 and 202 kg ha^-1 for total tiller number. Variations in other agronomic traits were found not significant. The response of the mutant to GA application was similar to Cocodrie, thus was considered GA responsive.  Preliminary DNA data using SSR markers supported the origin of the mutants and the genetic analysis indicated one recessive gene controlling the dwarfing and very high tillering traits.