Overcoming two post-fertilization genetic barriers in interspecific hybridization between Capsicum annuum and C. baccatum for introgression of anthracnose resistance

Abstract

Interspecific hybridization is essential to introgress resistance genes from Capsicum baccatum, a related species of cultivated pepper (C. annuum), since reliable genetic resources resistant to anthracnose have recently been identified within the C. baccatum germplasm. In conventional interspecific hybridization between the two species, hybrids could not be generated due to embryo abortion, which has been known to be a post-fertilization genetic barrier. Some partially compatible cross combinations, determined through observations of embryo development after pollination, were identified using a large number of accessions of C. annuum as pistillate parents. Embryo rescue technique was successfully employed to produce hybrids in these partially compatible crosses. Immature seeds bearing torpedo or early cotyledonary embryos, developed 35-40 days after pollination, were excised and the embryos were cultured on MS medium with sucrose and plant growth regulators. Hybridity was confirmed by observation of corolla yellow spot as a dominant species-specific trait of C. baccatum and using random amplified polymorphic DNA (RAPD) marker analysis. All the hybrid plants displayed vigorous growth but complete pollen sterility. The hybrid sterility was overcome through intensive backcrossing using C. annuum as the pollen parent. Consequently, hundreds of interspecific BC1F1 progenies were raised, and introgression of anthracnose resistance was confirmed in this segregating population.