Naturally occurring allelic variation is a new resource for the functional analysis of plant genes. Several permanent mapping populations, such as chromosome segment substitution lines (CSSLs) and backcross inbred lines (BILs), were developed for the analysis of naturally occurring allelic variation underlying complex traits in rice (Yano 2001).

We have constructed a library of single segment substitution lines (SSSLs) in rice. To construct the library, we selected Hua-jing-xian 74, an elite indica variety from south China, as recipient and 24 varieties including 14 indica and 10 japonica varieties collected worldwide as donors (He et al. 2003). Twenty-four crosses were made using Hua-jing-xian 74 as female parent and 24 donors as male parents, respectively. Hua-jing-xian 74 was then used as recur-

rent parent in the successive backcrossing. To select the SSSLs, whole genome survey was conducted from BC₂F₁ generation using 574 SSR markers with an average marker density of 2.7 cM. Some of the markers were selected from the SSR maps (Temnykh et al. 2001, McCouch et al. 2002) and others were developed by our lab to make the markers having an evenly spaced coverage in rice genome.

In the BC₃ to BC₅ generations, a total of 1123 SSSLs were developed from the 24 crosses. On the average, each donor derived 46.8 SSSLs, from 14 in IR66897B to 88 in IAPAR 9. The substituted segments in the SSSLs distribute on 12 chromosomes, from 53 on chromosome 12 to 202 on chromosome 6 (Table 1). Each of the SSSLs contains only one substituted segment from a donor in Hua-jing-xian 74 genetic background. The size of substituted segments in the SSSLs is from 0.15 to 109.7 cM with an average of 19.3 cM (Fig. 1). The total length of substituted segments in the SSSL library is 21,674 cM, which is the size of about 14 times of rice genome. The library provides complete coverage of the genome with overlapping substituted segments of each line.

The SSSL library collected a large number of the naturally occurring allelic variation in rice genome. It will be a powerful tool for functional genomics and molecular breeding in rice.

Acknowledgement

This research was supported in part by the key project (30330370) from National Natural Science Foundation of China and in part by the team project (20003023) from Natural Science Foundation of Guangdong Province, China.

References

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