Genetic studies on an awnness gene An-4 on chromosome 8 in rice, Oryza sativa L.

Abstract

An awnness gene which was isolated through breeding of an isogenic line of an awnless cultivar Taichung 65 with interchange chromosomes 4-8, was independently introduced into Taichung 65 (T65) after ten backcrossings. The mode of inheritance for the awn trait was examined on the basis of two measurements, the percentage of awned spikelets per panicle and average awn length of ten spikelets, using breeding materials in the B8F2, B9F1 and B10F1 generations. Experimental results showed that the trait was controlled by an incomplete dominant gene and that recessive homozygotes produced completely awnless spikelets, while dominant homozygotes produced long-awned spikelets in a high percentage of awned spikelets per panicle, while heterozygotes produced short-awned ones in a low percentage. The awnness gene was found to be located on chromosome 8 based on linkage analysis with the use of 13 awnless isogenic interchange homozygotes of T65 involving chromosome 4 and/or chromosome 8. Although three awnness genes had been reported, it was estimated that the awnness gene occupied a different locus from these three genes, because they were located on different chromosomes from the eighth. The present gene was, thus, designated as An-4. Through linkage analysis with the use of isogenic interchange homozygotes, some distorted segregations for the An-4 were observed. Pleiotropic effects of the An-4 gene on other traits were examined, also. The gene did not affect heading time, tiller number, and culm, internode, leaf blade and leaf sheath lengths, while it affected panicle traits; the primary branches were elongated, the number of secondary branches and the number of spikelets per panicle were increased. It was, thus, considered that the An-4 gene could be used for improving the sink size.