Recombinant inbred lines (RILs) derived from the cross between
Japonica variety Kinmaze and Indica variety DV85 were developed by single
seed decent method. Subsequently, we have developed chromosome segment
substitution lines by backcrossing RILs with recurrent parent Kinmaze.
During the process of backcrossing, segregation of short panicle and awn
were observed in the BC2F2 progeny from a selected
BC2F1 plant in which DV85 chromosome segment retained
in chromosomes 6, 7 and 8. For mapping, 71 BC2F2
plants were genotyped and their 71 BC2F3 lines (24 plants/line) were used
for trait investigation.
In the BC2F3 lines, short panicle plants with about
15 cm length were clearly differentiated from the normal (or long) panicle
plants with the length more than 20 cm (Fig. 1A). On the other hand, awn
plants were clearly differentiated from the awnless plants (Fig. 1B).
For short panicle, out of 71 BC2F3 lines there were
24 normal, 35 segregating and 12 short panicle lines
(chi2 for 1:2:1 = 4.1). Normal plants were predominant to
short panicle plants within the segregating lines. These results indicated
that this trait was controlled by a single recessive gene. In this manner,
awn also segregated with 1:2:1 ratio (chi2 for 1:2:1 = 1.4)
and awn plants were predominant within the segregating lines, indicating
that awn was dominant and was under monogenic control.
Linkage mapping of two traits was performed using RFLP markers on chromosomes
6, 7, and 8. The gene for short panicle was located between RFLP markers
R1440 and R1357 of chromosome 7, with genetic distance of
11.6 cM and 10.6 cM (Fig. 2 A). While, the gene for awn linked to G187
of chromosome 8 with 8.2 cM (Fig. 2 B). Since a short panicle gene sp
is identified on chromosome 11 (Yoshimura et al. 1997), the short
panicle gene newly identified on chromosome 7 in this study was designated
as sp2. So far, an awn gene An4 is reported to be located
on chromosome 8, but the map position of An4 on molecular map is
not available (Sato and Tsukasaki 1984). Although there is a possibility
that the gene for awn identified in this study is identical to An4,
it was tentatively designated as An6(t) to avoid the inevitable
confusion.
References
Harushima, Y., M. Yano, A. Shomura, M. Sato, T. Shimano, Y. Kuboki, T.
Yamamoto, S.Y. Lin, B.A. Antonio, A. Parco, H. Kajiya, N. Huang, K. Yamamoto,
Y. Nagamura, N. Kurata, G.S. Khush and T. Sasaki, 1998. A high-density
rice genetic linkage map with 2275 markers using a single F2
population. Genetics 148: 479-494.
Sato, S. and S. Tsukasaki, 1984. Genetical studies on awnedness gene An4
locating on the twelfth chromosome of rice plant. Japan. J. Breed. 34
(Suppl. 1): 288-289 (in Japanese).
Yoshimura, A., O. Ideta and N. Iwata, 1997. Linkage map of phenotype and
RFLP markers in rice. Plant Mol. Biol. 35: 49-60.
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