LAUSR

Abstract Interspecific hybridization is often hindered by incompatibility reactions occurring at various stages of hybridization, from early pollination to initial growth and reproductive stages of the progeny. Characterization of reproductive barriers leads to further understanding of how each species recognizes its own identity and supports the development of methods to overcome the barrier and produce interspecific hybrids. We investigated interspecific cross-(in)compatibility among five species in Prunus (Rosaceae), namely P. armeniaca, P. avium, P. mume, P. persica and P. salicina. In vivo pollen tube growth tests showed the presence of a post-mating pre-zygotic barrier in many cross combinations. Irrespective of the crossing direction, reduced pollen tube growth was observed in interspecific hybridization with P. avium, a species phylogenetically remote from the other species. Different compatibility reactions in reciprocal crosses were observed in some interspecific hybridizations. P. persica as a pollen donor was compatible with P. mume and P. salicina, while the reciprocal cross was incompatible. Furthermore, P. salicina as a pistil parent accepted pollen from P. armeniaca, P. mume and P. persica, while P. salicina was cross-incompatible with those species in reciprocal crosses. These results suggest that not only the phylogenetic relationship but also other mechanisms may be involved in interspecific cross-(in)compatibility. Embryo rescue culture showed the presence of a post-zygotic barrier in the cross between P. mume as seed parent and P. persica as pollen parent. Factors affecting interspecific hybridization are discussed with special reference to genetic distance between parents and morphological characters such as pistil length.