An incompletely dominant gene
Ur1 (Undulate rachis -1) increases spikelet number per panicle, and can enhance grain yield by enlarging sink size. The yield-increasing effect of
Ur1 was examined on five different genetic backgrounds. The
Ur1 isogenic line of ‘Nishihikari’ (N
U) has been developed by successive backcrossing. ‘Nishihikari’ (N) has the highest lodging-resistance in southern Japan. This isogenic line, N and their F
1 possessing the
Ur1/+ genotype (N
H) were grown in 2000. The yield of the three genotypes was in the order N
U > N
H > N, though the difference between N
U and N
H was not significant.
Ur1 increased spikelet number per panicle by 29 and 24%, respectively, in N
U and N
H, whereas
Ur1 decreased panicle number per m
2, ripened-grain percentage and 1000 grain weight by the ranges of 4 to 8% and 4 to 6%, respectively, in N
U and N
H. From the F
1 of N × the isogenic line of ‘Taichung 65’ carrying both
Ur1 and
sd1-d, four isogenic-line pairs (e.g. 27
U and 27
+) were developed after maintaining the heterozygosity (
Ur1/+) to F
8 or F
9 generation. These four number-named isogenic-line pairs, N
U and N were planted under a field condition in 2001. Analysis of variance indicated that the effects of
Ur1, genetic background and the interaction were significant in yield. The five
Ur1-carrying isogenic lines had a varying yield from 752 (N
U) to 542 (30
U) g/m
2. The yield increase by
Ur1 ranged from 250 g/m
2 (61%) to 75 g/m
2 (16%). In spikelet number per panicle, the increase by
Ur1 ranged from 62.1 to 39.2, while the percentage increase varied from 90 to 42%. The spikelet-increasing effect of
Ur1 was greater on a small-panicled genetic background than on a large-panicled genetic background.
Ur1 decreased ripened-grain percentage by 17% in 30
U, relative to 30
+, whereas no significant decreases were noticed in the other four
Ur1-carrying isogenic lines.
Ur1 increased culm length in 27
U, 52
U and 74
U, whereas no increase was noticed in N
U and 30
U. It is concluded that N
U could be a prospective material for developing high-yielding
japonica varieties carrying
Ur1, from the viewpoint of lodging tolerance as well as yield.
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