Cytogenetics and cytotaxonomy of Brazilian species of Senna Mill. (Cassieae - Caesalpinioideae - Leguminosae).

摘要

Chromosome numbers, meiotic behaviour, meiotic indexes and pollen fertility are reported for 17 Senna Mill. species occurring in Southern Brazil. Haploid numbers were n=11, 12, 13, 14 and 28. No intraspecific variability was detected; n=14 predominated. The only accession of S. rugosa showed to be tetraploid, in contrast to the a previous reference for this species. Meiotic behaviour was generally regular for all species and accessions, but some irregularities such as uni and multivalents and unequal segregation were occasionally observed. Meiotic indexes were high, over 95 %. Mean pollen fertility was over 81 % for all species, but in some taxa much lower values were found in some accessions. All species had prolate-spheroidal pollen grains. No relation between grain size, taxonomic position and chromosome number could be established. Our results, together with literature data, suggest that x=14 is the basic number for the genus, probably a secondary number derived from the x=7 suggested for all Caesalpinioideae, and that the other numbers in the genus represent a disploid series. A broader cytogenetic survey of a more representative number of species, along the geographic distribution of the genus, should be done addressing questions such as the extent of intra and inter-specific variability in chromosome number, occurrence of polyploidy and the real role of disploidy in Senna evolution.