During the development of a series of Oryza glumaepatula introgression
lines obtained from crosses of O. sativa L. (cv. Taichung 65) with
O. glumaepatula Steud. (Acc. IRGC105688) and continuous backcrossing
with Taichung 65 as the recurrent pollen parent (Sobrizal 1999), a locus
for F1 pollen semi-sterility was found.
A BC4F2 population 231 was used for analysis of
the F1 pollen semi-sterility. The parental BC4F1
plant of the BC4F2 population 231 was found to have
retained O. glumaepatula chromosomal segments on chromosomes 1,
2, 7, 9 and 10 when the BC4F1 generation of O.
glumaepatula introgression lines was genotyped using 106 RFLP markers
scattered on 12 chromosomes (Sobrizal 1999). The BC4F2
population 231 showed clear-cut bimodal distribution for pollen fertility
when classified into normal and semisterile plants (Fig. 1). There were
32 normal and 36 semi-sterile segregants. Semi-sterile plants showed approximately
50% pollen fertility and normal spikelet fertility.
Segregation analysis between semi-sterility and RFLP markers on chromosomes
1, 2, 7, 9 and 10 revealed that the pollen semi-sterility was associated
with the RFLP marker S910 on chromosome 2 in the BC4F2
population 231 (Table 1). At S910 locus, the 32 plants showing
normal pollen fertility were homozygous for Taichung 65 alleles and the
other 36 plants showing pollen semi-sterility were heterozygous. The observed
segregation ratio agreed with the expected 1:1 ratio, and we assume that
the gametes carrying the allele of O. glumaepatula and Taichung
65 are equally transmitted through female side but only the gametes with
the allele of Taichung 65 are transmitted through male side. In fact,
no plant homozygous for O. glumaepatula alleles at S910
was observed in the BC4F2 population 231, suggesting
that the pollen grains carrying O. glumaepatula allele aborted.
results demonstrated that the pollen semi-sterility was under monogenic
control and the locus was tightly linked with RFLP marker S910
on the short arm of chromosome 2 (Fig. 2).
Sano (1994) also found S12, a gene for pollen sterility, in the
backcross progeny of O. sativa and O. glumaepatula. In case
of S12, the pollen grains carrying O. sativa allele aborted.
Since no other gene for pollen semi-sterility or hybrid sterility on chromosome
2 has been reported, the new gene for pollen sterility was designated
The S22(t) causing male gamete abortion in the heterozygous condition
is responsible for one of the reproductive barriers. Hence, it limits
the utilization of O. glumaepatula specific traits in improving
rice varieties. Understanding the nature of this gene as well as the other
genes for reproductive barriers between O. sativa and O. glumaepatula
is useful for using the O. glumaepatula genome for improving rice
This study was supported in part by Bio-oriented Technology Research Advancement
Institution (BRAIN), Japan.
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