Abstract
From numerous pollinations of Helianthus laciniatus A. Gray sect. Ciliares by H. annuus L. sect. Helianthus (each with n = 17), a single hybrid was grown to maturity. The hybrid was vigorous but only 2.24% pollen-fertile compared to greater than 96% fertility in the parents. Backcrossing to the parental species was unsuccessful, so the possibility of gene flow between the species in nature is remote. Chromosome pairing in the parental plants was normal, but the hybrid was heterozygous for at least one paracentric inversion and numerous translocations. Chiasma frequencies of the parental genotypes were significantly different. The hybrid was significantly different from H. laciniatus and from the midparent value but not from H. annuus. These differences in chiasma frequencies were tested by the way chiasmata were allocated among the different meiotic configurations. Methods of converting multivalents to bivalent equivalents for comparison of chiasmata distribution among species and hybrids are demonstrated.
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