Chromosome Pairing in Natural First and Advanced Generation Liatris Hybrids

Chromosome pairing was analyzed in natural F1 and advanced generation hybrids of crosses between Liatris aspera and L. spicata, and L. aspera and L. cylindracea. The status of the hybrids was determined on the basis of morphological and chromatographic criteria. The F1 hybrids of L. aspera × L. spicata contained pairing irregularities in 30% of their PMC's as compared to 10% in the hybrid segregates. Notably, translocation figures appeared in 7% of the F1 PMC's as compared to 0.6% in the segregate PMC's. The F1 hybrids of L. aspera × L. cylindracea contained irregularities in 19% of their PMC's as compared to 7% in the segregates. Translocation figures occurred in 6% of the F1 PMC's, but only in 0.7% of the segregate PMC's. The incidence of pairing and level of structural heterozygosity was far lower in the hybrid segregates than was anticipated on the basis of F1 pairing relationships. Thus it would appear that there is selection for structural homozygosity in the hybrid segregates.