Chromosomal Differentiation among the Annual Helianthus Species

Abstract

The chromosomal relationships of the 11 annual diploid species in Helianthus sect. Helianthus were investigated by analyzing meiotic abnormalities in the interspecific hybrids. Hy- brids were secured from 40 of the 55 interspecific cross combinations via embryo culture or con- ventional hybridization techniques. Species differed from each other by 0-6 translocations and 0- 8 paracentric inversions. Intraspecific variation in chromosome structure was found in some species but was not as complex as the interspecific variation. Pollen stainability for the different hybrids was 1% to over 75%, mainly reflecting the meiotic abnormalities of the hybrids. Chromosome end arrangements consistent with the observed hybrid multivalent configurations are presented for all but two of the species. A phylogenetic diagram based on translocation differences is presented. The chromosome end arrangement of H. debilis is considered ancestral, while those of H. neglectus and H. annuus are the most differentiated from the ancestral arrangement.