Breakdown of the Classical Meiotic System in Rhoeo spathacea (Commelinaceae)

抄録

The locally cultivated material of Rhoeo spathacea (=R. discolor) is totally pollen sterile, irrespective of the time of the year. Meiotic analyses of random samples have shown complete breakdown of the well known Rhoeo system. A fully opened-out ring of 12-chromosomes is not observed, and a chain of twelve occurred only rarely. The chiasmata are not confined only to the pairing segments, but also occur in the interstitial and differential segments which, very often leads to a break-up of the interchange complex into two to five groups. The orientation at metaphase I is basically non-disjunctional, and often unequal distribution occurs at anaphase I. Pollen mitoses revealed sub-haploid, hyper-haploid, diploid and tetraploid pollen. It is suggested that during its long history of cultivation through vegetative means, several mutations may have accumulated upsetting the genetic control on chromosome pairing limited only to the pairing segments. We suggest that most of the pollen sterility is segregational and recombinational in origin; and there is also the probability of the occurrence of mutations causing pollen sterility or the occurrence of some developmental block originating outside the pollen perhaps mediated by environmental factors, as yet unidentified.