Biologia reprodutiva de espécies de Bignoniaceae ocorrentes no Cerrado e variações no sistema de autoincompatibilidade

Abstract

Bignoniaceae present mainly self-incompatibility system and diploid chromosome number, although some self-fertile, apomictic and polyploid species have been reported. The Cerrado flora seems to concentrate a high number of polyploid angiosperm species and the herbaceous-shrub layer presents species predominantly self-fertile, which contrasts with the mostly self-sterile trees species. Such features led us to investigate if the sub-shrub species of Bignoniaceae occurring in the Cerrado present changes on ploidy level or on breeding system which would conform to those general trends. Furthermore, we analyzed in detail these groups to understand the possible causes of such changes. In this sense, we determined the chromosome number and occurrence of polyembryony in populations of 23 species of Bignoniaceae and detailed the floral biology and breeding systems of seven sub-shrub species. We also did breeding system studies in tree species of Handroanthus. Histological analyses were carried out in order to confirm the somatic origin of the extranumerary embryos in Anemopaegma acutifolium. Our data showed that changes in life-form from trees or lianas into sub-shrub Cerrado species did not imply in breeding system changes, indicating the species were able to adapt to the new habitat and life-form maintaining self-sterility and diploid chromosome number. However, Anemopaegma sub-shrub species from the Cerrado were confirmed as self-fertile and polyploidy. Polyploid agamic complexes were observed only in the genera Anemopaegma and Handroanthus, which presented sporophytic apomixis and self-fertility. Gene flow among citotypes was viable for the species of Handroanthus, indicating that sexual reproduction was preserved in this agamic complex, concurring to maintain a high genetic variability. The observed changes on the breeding systems of the studied species of Bignoniaceae may have different causes, polyploidization being probably the most effective. The self-fertility associated with polyploidy is present mostly in species possibly of hybrid origin, without apparent links with the different life forms in the Bignoniaceae. However, the hybridization did not lead necessarily to the rise of agamic complexes, since the evidences of hybridization in Adenocalymma were detected in selfsterile and diploid populations.