Panicle Characteristics in High-yielding japonica Rice lines carrying Ur1 (undulated rachis-1) Gene.

Abstract

Ur1 (Undulate Rachis -1), an incompletely dominant gene on chromosome 6, being characterized by undulation of primary and secondary branches at the lowest part of a panicle, has the principal effect of increasing number of secondary branches per primary branch, and additional effects of increasing both spikelet number per single secondary branch and number of primary branches per panicle. This genic effect can increase grain yield by enlarging sink size. We examined the panicle traits of two high-yielding Ur1-carrying lines (MR79 and MR53) and two commercial varieties (‘Hinohikari’ and ‘Nishihikari’). They were grown at high, middle and low fertilizer levels in a paddy field. In addition to the traits mentioned above, the numbers of differentiated (developed + degenerated) primary and secondary branches were measured. MR53 was outstandingly higher than the two commercial varieties in spikelet number per panicle, number of secondary branches per primary branch and number of differentiated secondary branches per primary branch. In each of these traits, MR79 was higher than the two commercial varieties, but lower than MR53 more or less. By number of differentiated secondary branches per primary branch, the spikelet twinning and the panicle opening in total, plants with the Ur1/Ur1 genotype could be selected in a segregating population like F2 in a process of breeding by the use of Ur1, even if undulation is little or absent like in MR79