Cytogenetic study of Helianthus laevigatus and its F1 and BC1F1 hybrids with cultivated sunflower, Helianthus annuus

Although the wild sunflower species Helianthus laevigatus has not been extensively studied, it may be considered for sunflower breeding as a potential source of desirable genes for Sclerotinia stalk rot resistance and high contents of proteins and linoleic acid in the seed. A set of six H. laevigatus populations was crossed to cultivated sunflower lines and produced nine F-1 (2-14 plants) and 66 BC1F1 hybrid combinations (1-13 plants). Male sterility occurred in F-1 and BC1F1 hybrid combinations and pollen viability was lower in the progenies than in the parents (51.6-77.2% in F-1 and 4.8-34.0% in BC1F1). Meiosis was normal in the H. laevigatus populations. It was found that this tetraploid species also occurred in a hexaploid form. Numerous irregularities were observed in the meiosis of the F-1 interspecific hybrids. During diakinesis, quadrivalents and hexavalents were recorded in addition to bivalents. Dislocated chromosomes and chromosome bridges were present in the other phases. The chromosome number in F-1 was 68 (tetraploid). Irregularities in chromosome pairing were observed in the interspecific hybrids at BC1F1. There were many univalents, and trivalents, quadrivalents and hexavalents were also present. The chromosome number in the BC1F1 generation ranged from 34 to 60. The occurrence of meiotic irregularities in the F-1 and BC1F1 interspecific hybrids indicates that H. laevigatus and the cultivated sunflower differ in genome constitution.