Estudos sobre a biologia reprodutiva de especies de melastomataceae de cerrado em Itirapina, SP

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

This study was set up to investigate some aspects of the reproductive biology of 11 species of Melastomataceae growing in cerrado vegetation, in Itirapina, SP, Brazil. These were: Leandra lacunosa Cogn., Miconia albicans (Sw.) Triana, M. fallax DC., M. langsdorffii Cogn., M. ligustroides (DC.) Naud., M. minutiflora (Bonpl.) DC., M. pepericarpa Mart. ex DC., M. pohliana Cogn., M. rubiginosa (Bonpl.) DC., M. stenostachya Schr. &Mart. ex DC. e Tibouchina stenocarpa (Schr. &Mart. ex DC.) Cogn. Each species was studied using standard pollination techniques and pollen-grain staining procedures. Flower and fruit phenology were followed for about 2 years. For some species pollen tube growth was observed, and an attempt was made to analyze meiosis and other cytological aspects in two species. Seven species produced apomictic fruits: L. lacunosa, M. albicans, M. fallax, M. ligustroides, M. pohliana, M. rubiginosa e M. stenostachya. Ali of thern produced viable seeds, except for M. pohliana, which was not tested. Within the four non-apomicitic species, M. langsdorffii and M. pepericarpa appear to be obligatory xenogamous. In these cases, pollen tube growth halted in the upper part of the style in self-pollinations, suggesting a gametophytic incompatibility system. Miconia minutiflora appear to be self-compatible, as is T. stenocarpa. Nevertheless, the former presented automatic self-pollination mechanisms, while the latter did not. Two of the sexual species, T. stenocarpa and M. pepericarpa, presented pollen-grain fertility means up to 80%. The other two, M. langsdorffii and M. minutiflora, revealed means close to 60%. All the agamospermous species showed means of under 40% fertile grains, while M. albicans presented completely sterile pollen. In spite of that, the means obtained for M. langsdorffii and M. minutiflora did not differ statistically from those obtained for some agamospermous species like L. lacunosa, M. fallax and M. rubiginosa. This rneans that it is not always possible to deduce the existence of agamospermy from pollen fertility evidence, although a high degree of sterility is almost always accompanied by agamospermy. Besides, for some species an enormous variation between individuals in the population, and between flowers in the same individual was found. It suggests that different levels of sterility may coexist inside a population, and sometimes this sterility may be due to some environmental factor, i.e., in M. langsdorffii. Thus. any pollen fertility analysis must be based on thorough sampling, which includes several individuals and different flowers in the same individual. In spite of the difficulties found during meiosis observations for M. fallax and M. stenostachya. the cytological studies showed that both species regularly produce meiotic imperfections. For these species, and perhaps for other apomicts, the low pollen fertility may be a result of these meiotic problems. The phenological data seem not to show any clear pattern of clustering or displacement, in both flower and fruit production. The flowering strategies varied from "multiple bang" in M. albicans, M. ligustroides, M. minutiflora, M. rubiginosa and M. stenostachya to "cornucopia" in L. lacunosa, M. fallax, M. langsdorffii, M. pepericarpa and T. stenocarpa. The seven apomictic species are members of the tribe Miconieae, as are almost 85°_ of the reported agamospermous Melastomataceae. These species are scattered throughout a great diversity of tropical habitats, which lead us to believe that the occurrence of apomixis in this group is due to phylogenetic (and therefor taxonomic) constraint, rather than environmental or habit factors. It seems that apomixis is a rare phenomenon in the cerrado flora, in species which do not belong to Melastomataceae and Poaceae

ASSUNTO(S)

melastomataceae plantas - reprodução

ACESSO AO ARTIGO

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