Cytogenetical Studies in Rhoeo spathacea (Commelinaceae). IV. Ring-Forming Diploid and Desynaptic Tetraploid Sibs

Abstract

By selfing a desynaptic-SDR mutant of Rhoeo spathacea (GAVA 1.1) 123 plants were obtained, 90 of those exhibited a diploid chromosomes number, 29 resulted in diplandrogynous autotetraploids and 4 presented an hyperploid condition (2n=13, 2n=25). A sample of 10 diploid and 10 tetraploid plants was studied. In diploids, desynapsis reverts to ring-forming and 56.76% of 2884 PMC analyzed presented a ring of 12 chromosomes while the remaining PMC presented one or two chains. No more than one univalent/PMC was observed. At AI 61.95% PMC presented a 6 : 6 disjunction. Pollen fertility ranged from 0% (in a male sterile plant) to 62.90%. The male sterile mutant is the first recorded in R. spathacea and it is here identified as ms₁. In diplandrogynous autotetraploid plants desynapsis was observed in 100% of 942 PMC, with 8 to 24 univalent/PMC. Twenty four univalents were observed in 37.09% of PMC analyzed and 59.9% PMC exhibited a range of 14-22 univalents/cell. At AI a 12 : 12 disjunction was observed in 37.89% of PMC. Pollen stainability of 48.02% was the observed average in tetraploid plants. These results confirm the hypothesis that in the rings observed at TI pairing occurs and therefore interchange of chromosome segments affecting the desynaptic gene is possible. As a result of this pairing at TI only diploid parts of the progeny revert desynapsis to ring-forming. Otherwise only one allele should be present.