Cytological Studies in Cultivated Species of Camellia : III. Tetraploid Species and Hybrids between Diploid Species and Hexaploid Species

Pairing between the homologous chromosomes in some cultivated clones of Camellia gralethamialea was found to be complete and normal at metaphase I. The comparative study of meiosis revealed the presence of some univalents, trivalents, or quadrivalents in a tetraploid cultivar of C. japoleica and 10 tetraploid hybrids between diploid species and hexaploid species. Majority of the hybrid combinations showed similar patterns of chromosome associations at metaphase I: the most common configuration was 30u, and the mean numbers of chiasmata per bivalent were quite high, 1.9-2. O. Thus, among 30 bivalents 15 suggested allosyndetic pairing between one genome from diploid parent and one genome from hexaploid parent. Metaphase chromosome pairing in meiosis I in the tetraploid hybrids of Camellia studied was not sufficient to assign distinct genome formulas for the properties of different chromosome sets in various species. The presence of sterility and partial sterility shown in a tetraploid cultivar of C. japonica and 10 tetraploid hybrids might be due to both genetic and unstable meiotic chro-mosome configurations at metaphase I as well as developing petaloidy.