Better cultivars faster - identification of interspecific blueberry hybrids using SSR markers

Blueberry accessions available in New Zealand are highly heterogeneous with respect to species and are hence a potentially valuable resource of parental germplasm. However, they are not readily available for use in routine breeding, as hybridisation between different species and different ploidy levels does not produce viable seed. We have investigated in vitro ovule culture as a way of producing interspecific hybrids to increase genetic variability, as well as to introgress desired traits from different species into our blueberry breeding programme. When ovules from 24 crosses designed to create interspecific, interploidy blueberry progeny were cultured aseptically, more than 200 plants regenerated within 8-10 weeks, and all were confirmed as true hybrids by simple sequence repeat (SSR) analysis. The use of SSRs was of particular value for identifying back-cross hybrids generated from existing pentaploid interspecific hybrids and for which flow cytometry was unable to discriminate reliably between the pentaploid parent and the new back-cross hybrids. Our study has demonstrated that in vitro ovule culture and embryo rescue are useful in overcoming post-zygotic barriers to interspecific hybridisation among Vaccinium species with differing ploidy, and that SSR marker analysis is a useful and efficient tool to confirm hybridity at a very early phase of in vitro plantlet growth.