Effects of a Major Gene Ur1 Characterized by Undulation of Rachis Branches on Yield and its Related Traits in Rice.

Abstract

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 its 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.

Effects of sd1 and Ur1 (Undulate rachis -1) on Lodging Resistance and Related Traits in Rice

“…The six genotypes by combining Ur1 and the sd1 originating from 'Dee-geo-woo-gen', which were used in the previous study (Murai et al 2002b), were also used in the present study. Taichung 65 (T) is a tall Taiwanese japonica variety and the common recurrent parent of all the isogenic lines described below.…”

“…This genic effect increased grain yield in both Ur1/Ur1 and Ur1/+ genotypes by enlarging sink size on the genetic background of a japonica variety Taichung 65, despite the reduction in ripened-grain percentage, and the extents of yield increase in the Ur1/Ur1 and Ur1/+ genotypes were similar to each other (Murai et al 1997 and2002b). Thus, Ur1 is expected to be a useful tool for developing high-yielding inbred varieties.…”

“…Moreover, other dwarfing allele(s) at the sd1 locus, having origins different from that of 'Dee-geo-woo-gen', were contributing to develop elite japonica varieties in both the Northeastern districts and Kyushu districts of Japan as well as in California USA (Futsuhara 1968, Mackill and Rutger 1979, Kikuchi et al 1985, Mckenzie et al 1994, Takadate et al 1997, Murai and Yamamoto 2001. When rearranging the results of the experiments using isogenic lines (Murai et al 1995(Murai et al , 2002a(Murai et al and 2002b, the culm reduction by the sd1 of 'Dee-geo-woo-gen' ranged from 20 to 37 cm (27 to 38 %) on the two genetic backgrounds of 'Taichung 65' and 'Shiokari' (japonica varieties) under various cultivated conditions at several sites from southern Japan to Hokkaido. It is known empirically that improved varieties carrying the dwarfing alleles are more lodging-resistant than old and tall varieties.…”

“…Nevertheless, Ur1 increases culm length, and the long culms Communicated by K. Takeda Received February 4, 2004. Accepted May 19, 2004 below the large panicles are ready to lodge (Murai et al 1997(Murai et al , 2002b(Murai et al and 2003a. In fact, the complete lodging at maturity was observed in the Ur1/Ur1 and Ur1/+ genotypes in contrast to no lodging in the recurrent parent Taichung 65 under a field condition (Murai et al 2002b).…”

“…The Ur1/Ur1, Ur1/+ and +/+ genotypes with sd1 (three dwarfs) and those without sd1 (three talls) (Murai et al 2002b) were used in the present study. These six genotypes including the common recurrent parent Taichung 65 were grown under a paddy field condition, and the index of lodging, traits related to lodging and lengths of culm and internodes were measured.…”