Genetic analysis of stunted growth by nuclear-cytoplasmic interaction in interspecific hybrids of Capsicum by using RAPD markers

When eight cultivars of Capsicum annuum were used as female parents in interspecific crosses with two accessions of C. chinense, dwarfism occurred in hybrids originating from 10 out of 16 combinations, while hybrids of the remaining 6 combinations grew normally. In contrast, when C. chinense was used as female parent, all of the hybrids showed severely stunted growth as if affected by a virus. These results suggested that the stunted growth expressed in the cross of C. chinense x C. annuum is caused by an interaction between nuclear gene(s) from C. annuum and the cytoplasm of C. chinense. To examine the number of nuclear gene(s) which cause(s) the stunted growth, we backcrossed F₁ hybrids of C. annuum x C. chinense to C. chinense. About one-quarter of the progeny in the backcrossed hybrids of C. chinense x (C. annuum x C. chinense) showed the same stunted growth shown by the f₁ hybrids of C. chinense x C. annuum, suggesting that two complementary genes of C. annuum cause the stunted growth. However, the higher abortion rates of ovules and lower germination percentage of seeds in C. chinense x C. annuum than in the selfed C. chinense implied that the genetic ratio of the stunted type would have been higher than that observed in the C. chinense x (C. annuum x C. chinense) progeny. We then attempted a linkage analysis between the stunted growth and randomly amplified polymorphic DNA (RAPD) of C. chinense x (C. annuum x C. chinense) progeny. A RAPD marker that associated with 94% of the stunted plants but not with 94% of the normal one was identified. This confirmed that a single nuclear gene of C. annuum which is linked to the RAPD marker with a recombination value of 6% causes the stunted growth in an interaction with the cytoplasm of C. chinense.