Variation of ploidy level in inter-section hybrids obtained by reciprocal crosses between tetraploid Primula denticulata (2n=4x=44) and diploid P-rosea (2n=2x=22)

Inter-section hybrids were successfully obtained from reciprocal crosses between tetraploid Primula denticulata (section Denticulata) and diploid P rosea (section Oreophlomis) by applying ovary culture 4 weeks after pollination. Differences in ploidy levels were found in these hybrids by flow cytometric analysis and by counting chromosome numbers. When P denticulata was used as maternal parent, all the hybrids were triploid, with two genomes of R denticulata and one genome of P rosea. In contrast, when P rosea was used as maternal parent, two genome-type hybrids were obtained: one was a triploid hybrid, with the same genome combinations as those obtained when P denticulata was used as maternal parent, and the other type was a tetraploid hybrid with two genomes of each species. These results suggest that unreduced (2x) gametes were formed only in the female side of P rosea.