Abstract
The objective of this study in Rhoeo spathacea was the cytological identification of a trisomic plant which includes an acrocentric chromosome. The homology of the extra chromosome was not identified with certainty by karyotype analysis because of its lack of similarity with any other chromosome. Somatic metaphase analysis indicates that interchanges take place in terminal regions of Rhoeo chromosomes. The presence of the acrocentric also supports this idea. On the basis of behavior at MI, this extra chromosome seems to be homologous with one of the largest chromosome. MI was as expected for ring forming Rhoeo (Chains of 13, 45.7%; 12+1I, 15.7%; or 11+2I, 15%) and not as expected for a desynaptic. The extra chromosome was either associated by its long arm with its supposed homologue or free; when associated, its short arm was free. At AI the segregation was mostly 6:7, with microspores with n=5 to n=26, n=7, 34.4% and also producing SDR with n=13 (22.4%). When all the progeny is included in the observations, a possible apomictic mechanism of origin was postulated.
