CHROMOSOME PAIRING IN NATURAL FIRST AND ADVANCED GENERATION LIATRIS HYBRIDS

Chromosome pairing was analyzed in natural F 1 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 F 1 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 F 1 PMC's as compared to 0.6% in the segregate PMC's. The F 1 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 F 1 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 F 1 pairing relationships. Thus it would appear that there is selection for structural homozygosity in the hybrid segregates.