Breakdown of the classical meiotic system in Rhoeo spathacea (Commelinaceae).

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Abstract
The locally cultivated material of R. spathacea (= R. discolor) is totally pollen sterile, irrespective of the time of year. Meiotic analyses of random samples showed complete breakdown of the Rhoeo system. A fully opened-out ring of 12-chromosomes was not observed and a chain of 12 occurred only rarely. The chiasmata are not confined to the pairing segments; they also occur in the interstitial and differential segments which often leads to a break-up of the interchange complex into 2-5 groups. The orientation at metaphase I is basically non-disjunctional and unequal distribution often occurs at anaphase I. Pollen mitoses revealed sub-haploid, hyper-haploid, diploid and tetraploid pollen. During its long history of cultivation through vegetative means, several mutations probably accumulated, upsetting the genetic control on chromosome pairing limited to the pairing segments. Most of the pollen sterility is probably segregational and recombinational in origin; 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.