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Materials and methods
Four sets of F6: F9 near-isogenic lines
(NILs) were developed from Chugoku 81/5* Nugaines. The sets
represented three semidwarf genotypes (Rht1 Rht1 Rht2 Rht2, Rht1
Rht1 rht2 rht2, rht1 rht1 Rht2 Rht2) and the nonsemidwarf
genotype (rht1 rht1 rht2 rht2). Sets comprised 3 to 10 lines
each. The genotype of Nugaines is rht1 rht1 Rht2 Rht2 and the
genotype of Chugoku 81 must be Rht1 Rht1 rht2 rht2 because
progeny with nonsemidwarf and two-gene semidwarf phenotypes were
obtained from this population. Seed of Chugoku. 81 was obtained from
Byung Hee Hong, Korea University, Seoul, Korea. Chugoku 81 is an
early maturing selection having facultative growth habit developed at
the Chugoku. National Agricultural Experiment Station, Fukuyama,
Japan (Takashi Nagamine, personal communication).
The genotypes of NILs having plant heights similar to Chugoku 81 and
Nugaines were determined by test crossing to Nugaines (Rht2
tester) and Stephens (Rht1 tester). The lines were tested
in 7 replicated trials at 3 eastern Washington locations during 1991
to 1993. Individual plots were 2.97m2. Locations
represented irrigated, summer fallow and annual crop management
systems.
Agronormic data were obtained for the tine traits shown in Table
1. Analyses of variance were performed for each trait and trial.
Combined analyses across trials were also performed and these
statistics are given in Table 1.
Results and discussion
Means and ranges of nine agronomic traits for NILs representing
the four plant height genotypes appear in Table
1. Except for spike number, significant (P =< 0.05 ) mean
trait differences occurred among the plant height genotypes.
Comparisons between the Rht1 (Rht1 Rht1 rht2
rht2) and Rht2 (rht1 rht1 Rht2 Rht2) NILs
were of main interest. The Rht1 NILs had higher overall mean
grain yields, kernel weights, and plant heights than Rht2 NILs
while the Rht2 NILs had heavier test weights than Rht1
NILs (Table 1). An earlier study (Allan
1989) found no differences in grain yield or kernel weight between
Rht1 and Rht2 NILs, while NILs with Rht1 had
heavier test weights than Rht2 sibs in some populations. The
current and earlier study showed the Rht1 NILs were slightly
taller than their Rht2 sibs. The grain yield advantage of the
Rht1 and Rht2 genes in the Nugaines genetic background
was generally greater than that obtained when these genes were.
transferred into genetic backgrounds of nonsemidwarf wheat varieties.
In the Nugaines genetic background Rht1 and Rht2 NILs
yielded 36 and 28%, respectively, greater than their nonsemidwarf
rht1 rht1 rht2 rht2 sibs while in three nonsemidwarf genetic
backgrounds the yield increases associated with Rht1 and
Rht2 averaged only 16% greater than their rht1 rht2
sibs (Allan 1989).
Yield component differences
between Nugaines Rht1 NILs vs rht1 rht2 NILs were
similar to results obtained in the earlier study. In both studies the
Rht1 gene was associated with reduced test weight and kernel
weight but increased kernels/spike; it was neutral for spike number.
In the case of Rht2 vs rht1 rht2 NILs, the two studies
differed. Unlike the earlier study, with Nugaines, the Rht2
gene was neutral for test weight, kernels per spike and spike
number. In the earlier study, the Rht2 gene was associated
with enhanced spike number and kernels/spike but with reduced test
weights among all nonsemidwarf genetic backgrounds.
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