Problems associated with the use of Heliantbus species for the breeding of the cultivated sunflower: Ploidy level or phylogenetic distance?

Abstract

Of the 49 species that comprise the genus Helianthus, 42 are present in the wild species collection at the Institute of Field and Vegetable Crops. This is a rich bank of desirable genes for sunflower breeders. However, numerous problems are associated with the use of inter specific hybridization. The wild sunflower species are either di-, tetra- or hexaploid, while the cultivated sun­flower is diploid. Consequences of differences in chromosome number and structure are incom­patibility at crossing and the occurrence of sterility, reduced fertility and meiotic irregularities in inter specific hybrids. Long-term studies on the cross ability of wild species and the cultivated form and cytogenetic analyses of wild species and F1 inter specific hybrids have shown that phylogenetic differences pose larger problems to the use of wild species in sunflower breeding than the differences in the number of chromosomes. This hypothesis was confirmed by the full cross-incompatibility observed between several diploid perennial species (H. maximiliani, H. giganteus...) and the cultivated sunflower and high percentages of successful crosses between the cultivated sunflower and some tetra- and hexaploid species (H.decapetalus, H.hirsutus, H.tuberosus, H.rigidus, H.resinosus...). The phylogenesis of the genus Heliantbus classifies the species into different sections, i.e., series within the genus.

Keywords

• sunflower
• wild species
• interspecific hybridization
• ploidy
• phylogenesis