The predictability of the Rf-phenotype by the CRF-S870 marker was 100%, as this marker was developed for Rf locus conditioning fertility restoration of Peterson’s cytoplasm, which is the only known male sterile AJ 76 in commercial use ( Kumar et al., 2009). In a recent study, the CRF-S870 marker was compared with cleaved amplified polymorphic sequences (CAPS) and a high resolution melting (HRM) marker linked with the Rf-phenotype and was found to be the most useful one, with 89% correct prediction of the Rf-phenotype (Jo et al., 2010). In contrast, previously developed RAPD markers presumably associated with the Rf phenotype ( Zhang et al., 2000) could not be validated in an array of restorer and maintainer lines (Kumar et al., 2007).
3.4. CRF-S870 marker-assisted backcrossing
After the validation of CRF-S870 marker i.e. its co-segregation with the Rf-phenotype, CRF-S870 was successfully used to identify restorer plants (Rfrf) in each backcross generation at seedling stage i.e. well before the plants reached the flowering stage. These putative restorer plants with CRF-S870 were backcrossed to the respective sweet pepper recurrent parents (Fig. 1). The use of CRF-S870 in MAB was very effective and facilitated rapid generation advancement. Conventional selection of restorer plants requires two steps. First, the candidate restorer line is phototrophs crossed as male parent to a CMS plant as female parent (first season) and then evaluation of test crosses (second season) are performed to determine whether the involved male plant was a restorer (test cross is male fertile) or maintainer (test cross is male sterile). In contrast, the CRF-S870 marker allows for selection of Rf-genotypes at the seedling stage of the first season.