Interspecific hybridization between sunflower and wild perennial Helianthus species via embryo rescue

Interspecific crosses were made between the cultivated sunflower inbred line HA89 and accessions of five wild perennial Helianthus species (H. giganteus L., H. laevigatus T. & G., H. resinosus Small, H. pauciflorus Nutt. and H. decapetalus L.) resistant to broomrape ( Orobanche cernua Loefl.). Using the genetic male-sterile isogenic version of that line as female, successful reciprocal crosses were also obtained with all these wild species except with H. decapetalus. Five-day-old hybrid embryos were excised and cultured in vitro. In all cases, few mature plants were obtained from embryos in early developmental stages (early heart and globular) but up to 28% mature plants were obtained from embryos in later stages of development. Very immature embryos were difficult to excise without damage. Hybrid embryos and mature plants were obtained from all five wild species. Interspecific hybrid embryos from different wild species showed distinct developmental potentials, the proportion of hybrid embryos in different developmental stages varying among species. Differences in the proportion of hybrid embryos at the several developmental stages were also obtained for the reciprocal crosses (cultivated × wild), which showed higher proportion of fully developed embryos. Hybrids involving H. giganteus and cultivated sunflower were difficult to obtain without the use of embryo culture. Embryo culture proved to be an useful tool to overcome post-zygotic hybrid incompatibility in different Helianthus spp., and facilitated interspecific transfer of resistance to O. cernua.