Oryza glaberrima is a valuable source of genes for O. sativa
improvement (Jones et al. 1997). However, a series of genetic loci
that induce interspecific hybrid sterility between these cultivated species
has been identified in O. glaberrima. The series includes gamete
eliminator S1 and pollen killers S3, S18, S19,
S20 and S21(Doi et al. 1998, 1999; Sano et al.
1983, 1986; Taguchi et al. 1999). These loci are major obstructions
to the introgression of favorable gene/traits from O. glaberrima
into O. sativa. An understanding of these and other sterility genes
is necessary to be able to overcome crossing barriers and thus open the
door for mining useful genes from O. glaberrima. In this study,
we identified a new pollen killer S29(t)
and mapped it on chromosome 2 by SSR markers.
A near-isogenic line WAB450-6, derived from interspecific hybrid of O.
sativa and O. glaberrima, induced frequent abortion of pollen
grains but gave completely fertile spikelets when hybridized with its
recurrent parent, WAB56-104, an upland japonica from WARDA (Tao
et al. 2002). Semi-sterile individuals were backcrossed as female
parents to WAB56-104, and a semi-sterile individual of BC2F1
was selected to produce a BC2F2 population with
142 plants in the winter crop season (November-April) in Hainan, China,
in 2004. The population showed a clear-cut bimodal distribution for pollen
fertility (Fig. 1), indicating a single gene controlling sterility. This
BC2F2 population was employed in segregation analysis
for the sterility gene and 216 SSR markers distributed among the 12 chromosomes.
The sterility gene was linked with the SSR marker RM7033 on chromosome
2. Thus, a molecular linkage map in this region was constructed for mapping
the male sterile gene from WAB450-6, and this gene was mapped to the interval
between markers RM423 (1.3 cM) and RM7033 (1.1 cM) on chromosome 2 (Fig.
2). The fact that none of the sterility genes previously reported from
O. glaberrima was on chromosome 2 suggests that this gene is a
new pollen killer, tentatively designated as S29(t). Fine mapping
of this gene using a bigger advanced backcross population is ongoing.
This study was supported by grants from Yunnan Natural Science Foundation
of China (2002C0009Z).
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