Reciprocal chromosome segment substitution series derived from Japonica and Indica cross of rice (Oryza sativa L.)

Chromosome substitution series are useful tools for precise mapping of quantitative trait loci (QTLs) and for the evaluation of gene action as a single factor or in the case of gene interactions. In this study, we produced reciprocal sets of chromosome segment substitution lines (CSSLs) between Asominori (Japonica) and IR24 (Indica) in cultivated rice, Oryza sativa L. A set of chromosome segment substitution lines carries a single or a few donor chromosome segments overlapping with neighboring segments in a uniform genetic background. Reciprocal sets were developed by repeated backcrossing to respective recurrent parents and DNA marker-assisted selections. The sets consisted of a series of 70 lines of Asominori CSSLs with IR24 genetic background (designated as 'IAS') and a series of 91 lines of IR24 CSSLs with Asominori genetic background (designated as 'AIS'). These substitution series represented most of the genome of the donor parents on the alien genetic backgrounds. Each of the substitution lines was nearly isogenic to the recurrent parent: the average proportions of recurrent parent's genome were 93% and 91% in the IAS and AIS, respectively. Consistent reciprocal QTL effects for heading date and grain size were observed in both IAS and AIS. The reciprocal substitution set appeared to be an efficient and systematic method for QTL precision analysis.