Z.K. Li

      International Rice Research Institute, P. 0. Box 933, 1099 Manila, Philippines

     Major advances have been made in DNA marker technology in rice during the last few years. A number of genes for resistance to diseases, insects and other agronomic traits such as photoperiod sensitivity, wide compatibility, aroma and male sterility, have been tagged with DNA markers. Marker assisted selection (MAS) is being explored as an important supplement to phenotypic selection in rice breeding. PCR based technology offers great potential to enhance the efficiency of MAS.

     Among various sources of cytoplasmic male sterility (CMS), WA (wild abortive) is the predominantly used CMS source in hybrid rice breeding. Two genes, Rf-1 and Rf-3 located on rice chromosomes 10 and 1 respectively are largely responsible for fertility restoration of all WA CMS lines. We developed PCR-based DNA markers for Rf-3 using RG14O which is closely linked to Rf-3 on chromosome 1 (Zhang et a!. 1997). Based on the sequence data (STS) of RG14O, two primer pairs were designed, including RG14OFL (GTA CAT AGT AGC ACC TGC TC)/RL (TCC CTA GTT TGT GCT ACT CC), and RG14OFIJRB (CCA GCC AGT ACG TAT GTC CT).

     PCR products were amplified with the two primer pairs from genomic DNA of a WA CMS line, Thenshan 97A (ZSA) and a restorer line, 1R24, which did not reveal polymorphism between ZSA and 1R24. However, digestion of the PCR products with restriction enzymes EcoRI, PvuII, and DraI, produced polymorphic codominant markers between the CMS line and restorer (Fig. 1). Progeny testing using 130 F2 plants from the cross between ZSA and 1R24 has demonstrated that selection for Rf-3 based on marker genotypes is highly accurate (Table 1). The potential use of the PCR based markers developed in this study was further confirmed by examining 8 1R24 near isogenic lines and 5 closely related breeding lines differing at the Rf-3 locus. In all these cases, amplification with RG14O primer pairs plus appropriate enzyme digestion(s) can clearly differentiate the lines with different alleles at the Rf-3 locus (data not shown). Thus, these two primer pairs can be used in future MAS of RF-3 in hybrid rice breeding programs.