9. RFLP mapping of genes for long kernel and awn on chromosome 3 in rice

Plant Breeding Laboratory, Faculty of Agriculture, Graduate School, Kyushu University, Fukuoka, 812-8581 Japan

Some QTLs for grain length were identified using recombinant inbred (RI) lines derived from a cross between Asominori and IR24 (Tsunematsu et al. 1995). A major QTL was located between C1677 and R19 on chromosome 3. The IR24 chromosome segment substituion lines (CSSLs) with genetic backgrounds of Asominori were developed by crossing the RI lines with Asominori and subsequent backcrossing (Kubo et al. 1999). In BC3F1 generation, we selected the BC3F1 plant that was heterozygous around the region between C1677 and R19 on chromosome 3. A BC3F2 population was used for RFLP mapping.

The segregation for grain length was apparent in BC3F2 population, and showed bimodal distribution. BC3F2 population consisting of 48 plants was divided into two groups: normal kernel group which are 7.5 -8.3 mm long corresponding to Asominori and long kernel group which are 8.4 -9.0 mm long corresponding to IR24. There were 37 normal kernel group plants and 11 long kernel group plants, indicating that the observed ratio fitted the monogenic segregation ratio. The results demonstrated that long kernel was controlled by one recessive gene. The gene was tentatively designated as lk3 (t) (long kernel 3). Linkage analysis was carried out using RFLP markers located on chromosome 3. The result suggested that lk3(t)

was located between RFLP makers C1677 and G1316 with map distance of 2.4cM and 2.2cM, respectively (Fig.1).

Ten out of 11 plants with long kernels showed long awns at the tip of each panicle; 37 plants with normal kernel showed short awns or no awns, indicating that a gene for awnness was linked to lk3(t). The gene was tentatively designated as An5(t) (Awn 5). Linkage analysis demonstrated that An5(t) was located between lk3(t) and RFLP marker R19, and co-segregated with G1316 (Fig. 1).

The long kernel gene Lkf (Takeda and Saito 1980) and the awned gene An3 (Takamure et al 1991) were mapped on chromosome 3, and Lkf was linked to An3 with the recombination value of 11.3%. lk3 (t) and An5(t) might be the same locus as Lkf and An3, respectively.

This study was supported in part by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan.


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