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Results and discussion
First, the segregation for chromosomal constitution, fertility, and
sterility in the hybrid progeny from a series of four crosses was
examined starting with a cross of an euploid male-sterile plant to
the aneuploids of group 5 chromosomes to determine if the putative
new Ms gene was the same as Ms3 gene that is closely
linked with centromere in the short-arm of chromosome 5A (Maan et al.
1987). The results are described below (Table1
).
A cross of an euploid male-sterile plant to dDt 5A produced 20
fertile and 15 male-sterile F1's (a 1: 1 ratio; P=0.398),
and a cross of a male-sterile F1 (2n=43; 20"+t1t''' 5A) to
nulli 5A-tetra 5D produced 20 fertile and 19 male-sterile plants (a
1: 1 ratio; P=0.875), including 7 fertile and 7 male-sterile
segregants with 19"+1"'+1' having maternal chromosome 5A and 11
fertile and 7 male-sterile plants with 19"+1'''+2t'5A having maternal
telocentrics. Similarly, a cross of a male-sterile plant with
19"+1'''+2t'5A to CS produced 38 fertile and 43 sterile plants (a 1:
1 ratio; P=0.575), including 14 fertile and 18 sterile plants with
19"+1'''+1' and 15 fertile and 10 sterile plants with 20"+1'. These
results indicated that the Ms gene was not located on
chromosome 5A of the original euploid male-sterile plant used in this
study . If Ms was located on chromosome 5A or was transferred
to one of the 5A telocentics by recombination the expected ratios
would be 3 fertile to 1 sterile plants, because the unpaired
univalent chromosome with Ms should be transmitted through 25%
of the female gametes (Sears 1954) but instead was transmitted to 50%
of the progeny (Table 1).
The results from another cross of a male-sterile plant having
20"+t1t''' 5A to CS confirmed the above conclusion. This cross
produced 16 fertile and 21 male-sterile plants (1:1 ratio; P=0.411),
including 9 fertile and 8 sterile plants with 21" and 5 fertile and
13 sterile plants with 20"+t1t'''. These results indicated a more
frequent occurrence of recombination between Ms and the
centromere than was expected of Ms3 because of close linkage
to the centromere on chromosome 5A (Maan et al, 1987). Therefore, the
new Ms gene is not located on chromosome 5A and is not the
same as Ms3.
Next, the segregation for chromosomal constitution, fertility, and
sterility was observed in progeny from a series of five crosses
starting with crosses of an euploid male-sterile plant to the
aneuploids of group 4 chromosomes. This was to determine if the
Ms gene in this study is the same gene as Ms2 located
on the short-arm of chromosome 4D, 31.16 crossover units from the
centromere (Liu and Deng 1986a, b; Deng and Huang 1988). The results
are described below (Table 2).
A cross between a euploid male-sterile plant and nulli 4D-tetra 4A
produced 12 fertile and 10 male-sterile tri 4A-mono 4D
F1's (2n=43; 19"+ 1'''4A+1'4D) (Table
2). A cross of a tri 4A-mono 4D male-sterile (2n=19"+1''' +1'4D)
F1 to dDt 4D produced 91 fertile plants in which maternal
4D was absent and 20 male-sterile plants in which maternal 4D was
present (3:1 ratio; P=0.089). These results indicated that the new
Ms gene was located on chromosome 4D. Of the 20 male-sterile
plants, 15 had 20"+t1t''' and 5 had 19"+1''' +1t" or 20"+ tS'. A
male- sterile plant with 20"+1t4D" was used in the cross described
below.
The progeny from- a cross between a male-sterile plant 20"+ t1"4DL
and CS produced 21 male sterile plants with 21" and 21 fertile plants
with 20+t1"4DL (Table 2). The absence of
fertile recombinant(s) with 21" and sterile recombinant(s) with
20+t1" indicated that the Ms gene was located on the short-arm
of chromosome 4D.
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