Effects of a Major Gene Ur1 Characterized by Undulation of Rachis Branches on Yield and its Related Traits in Rice
An incompletely dominant gene Ur1 is characterized by undulation of primary and secondary rachis branches. The gene increases spikelet number per panicle owing to increase of secondary branches. The Ur1/Ur1, Ur1/+ and +/+ genotypes with sd1 (denoted by u, h and d, respectively, viz. three dwarfs) and those without sd1 (U, H and T, respectively, viz. three talls) were produced under the common genetic background of a japonica variety Taichung 65. The six genotypes were grown in 2000. Yield and
... s related traits were measured. Analysis of variance on yield indicated that the effect of Ur1 was significant whereas the effects of sd1 and the Ur1 × sd1 interaction were nonsignificant. Genotypes u and h had significantly higher yields than d; h showed the highest yield of all genotypes. The three talls had yields in the order of H ≥ U ≥ T (H > T). Regarding spikelet number per panicle, the genotypes were in the order of u = U > h ≥ H > T > d, reflecting the principal effect of Ur1. Regarding panicle number per m 2 , the effect of Ur1 was not significant. The ripened-grain percentages of the six genotypes were almost in the reverse order of spikelet number per panicle. The 1000 grain weight of the genotypes was in the order of U ≅ u ≤ h ≤ H ≤ d < T. Sink size-2 (single grain weight × fertilized-spikelet number per m 2 ) showed a high positive correlation with yield. As for LAI, there were no significant differences among the six genotypes. The total weight per m 2 at maturity for the three dwarf genotypes were in the order of h ≥ u ≥ d (h > d). As for harvest index, u and h were higher than d. Similar results were obtained for the three dwarf genotypes under three fertilizer levels in 1998. Thus, Ur1 enlarged sink size through increase of spikelet number per m 2 resulting in higher yield. Consequently, Ur1 may be utilized for developing high yielding inbred varieties and F 1 varieties at the Ur1/+ genotype.