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Materials and Methods
Prior to initiating this study, the Chinese Spring (CS) monosomic
series (kindly provided by Dr. E.R. Sears) was identified using the
modified C-banding technique of Endo (1986). The seedlings of CS
monosomic series were planted in autumn 1994. Three to five monosomic
plants in each monosomic line were selected by cytological
examination of root-tip cells, and were pollinated by the common
wheat oligo-culms line, "88F2185" (provided by X.L. Zhang,
agronomist in Xianyang Agricultural Institute, China). Three disomic
CS plants were crossed reciprocally with "88F2185". Data
on culm number per plant were recorded and evaluated in the following
analysis:
(1) test-cross analysis: F1 seeds of reciprocal crosses
between CS (euploid line) and "88F2185" were planted in
Markang city for summer propagation. A part of reciprocal
F1 plants backcross to CS to obtain BC1 seeds. Other
F1 hybrids were selfed to obtain F2 seeds. On 3
Nov. 1995, seeds of "88F2185", euploid CS, BC1
and the reciprocal F1 and F2 were sowed
separately in the same experimental field in Dujiangyang city. The
distances between plants were kept 10cm apart.
(2) F2 monosomic analysis: 24 different populations
comprising 21 F2 populations that derived from
F1 plants monosomic for different chromosomes, the
F2 population that derived from disomic F1
plants and the two euploid parental lines were analyzed. In all, 128
seeds of each population were planted in four randomized double rows,
1.5m long each. The distances between plants were kept 10cm apart in
every rows, and the rows were spaced 30cm apart. The sowing date was
3 Nov. 1995.
Some F2 populations that derived from F1
monosomic plants needed grouping according to whether they were
monosomic or disomic. So, seeds of plants in these F2
populations were individually harvested, and chromosome counts of
five F3 seeds was carried out at mitosis. The
F2 plant was considered as disomic if all the five
F3 seeds that derived from it had 42 chromosomes, or as
monosomic if one or more seeds possessed 41 chromosomes in somatic
cell.
In 1996, the culm number per plant and the final plant height were
investigated at harvest. The total tiller number was investigated at
jointing stage, when the tiller number per plant reached the maximum
for the materials in the present experiment. The F2
population derived from F1disomic plants was taken as
cheek population in F2 monosomic analysis. The
significance of differences between the mean values were detected by
t-test, and F-test was adopted to detect the significance of the
differences between the variances.
Results and discussion
Test-cross analysis:
The F1 population of the cross (88F2185 x CS)
showed 4.15 culms per plant, whereas the Fi1population of cross (CS x
88F2185) showed 4.18 culms per plant. However, statistic
analysis showed the difference of culm number per plant between the
reciprocal F1 populations was not significant (P=0.912).
In addition, two F2 populations that derived from the
reciprocal F1 hybrids segregated for culm number per
plant, with mean culm number per plant of 5.90 and 5.96 respectively.
Statistic analysis of the two reciprocal F2 populations
indicated homogeneity in culm number per plant (P=0.874). These
results indicated that cytoplasmic differences for the oligo-culms
was absent, and that data from reciprocal crosses could be
pooled.
The result of test-cross was shown in Fig.
1.
F1 progeny showed similar culm number to
"88F2185". This result means that the oligo-culms is a
dominant character. So, the suggestion of Richards that a recessive
gene inhibit the tillering capacity is not valid for the present
experiment.
The BC1 frequency distribution figure of culm number per
plant could be divided into two parts. One part comprised 133 (52.4%)
plants with 1-6 culms, the other comprised 121 (47.6%) plants with
7-13 culms. If we arbitrate the plants with 1-6 culms per plant as
oligo-culms plants, and the others as regular ones, the segregation
of BC1 population was fitted to the ratio of 1: 1
(chi2=0.476, P=0.493). Therefore, the BC1
frequency distribution of culm number per plant could be interpreted
as one gene segregation.
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