Japonica background of rice

     T. KUBO, K. NAKAMURA and A. Yoshimura

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

     Chromosome introgression or substitution series are useful for mapping quantitative trait loci (QTLs) precisely and evaluation of the action and interaction of QTLs. We have attempted to produce the reciprocal sets of chromosome segment substitution lines (CSSLs) between Indica and Japonica rice using backcrossing and marker assisted selection (MAS). As the first product, the series of Japonica CSSLs in Indica genetic background have already been reported (Aida et al. 1997). This paper describes the development of a series of Indica CSSLs in Japonica genetic background.

     To develop Indica CSSLs, recombinant inbred lines derived from the cross between Japonica variety Asominon and Indica variety [R24 (Tsunematsu eta!. 1996), were crossed and backcrossed with Asominori. The breeding scheme for developing the Indica CSSLs is shown in Fig. 1. The promising plants for CSSLs were selected based on wide coverage of IR24 genome, restoration for Asominori genetic background and duplication of substituted region. Sixty-six promising plants were selected from 268 BC3FL plants by a whole genome survey at 116 RFLP loci. To obtain the homozygous substituted segments, out of about 400 BC3F2 plants from 66 BC3F2 lines, 91 plants were selected as the final candidates for CSSLS. The graphical genotypes of a minimum required 57 lines are shown in Fig. 2. These CSSLs represented whole IR24 genome except for a part of chromosome 3.

     The breeding schemes for developing the reciprocal two CSSLs were different. In the Japonica CSSLs, MAS was carried out from earlier generation (BC1F1), while in the Indica CSSLs, backcrossing were advanced to BC3F1 generation without MAS. However, genomic components of these sets were not so different. The average restoration ratios of recurrent genome were 93 % in the Japonica CSSLs and 91% in the Indica CSSLs.