Cytogenetics of Cultivated Bougainvilleas. IX. Precocious Centromere Division and Origin of Polyploid Taxa

Precocious centromere division at metaphase I leading to diploid gamete formation has been observed in three cultivars. Some of the PMC's are characterized only by rod bivalents whose centromeres split at metaphase I. After passing to respective poles, the already divided centromeres fall apart at telophase I, with the result that each pole has unreduced number of 34 chromosomes. There is no second division and such cells form dyads which give rise to diploid pollen grains. Such unreduced pollen are 100 per cent fertile because of reduced (or no) recombination between hamoeolugous genomes and the presence of two sets of chromosomes. Thus, triploids or even tetraploids can arise when such pollen grains are involved in tertilization with reduced or unreduced egg of other cultivars.