Biologia da polinização e reprodução de Cambessedeira hilariana (Kunth.)DC. (Melastomatacae)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The sexual reproduction mediated by a poliinator agent is one of the mechanisms by which the plants increase the genetic variability of its offspring. The majority of the Angiosperms has hermaphroditic flowers what, at the same time, optimises the transference and the withdrawal of pollen in an unique visit and increases the possibilities of self-pollination. Certain morphological characters, as hercogamy, and the recognition and rejection systems of the endogenous pollen are characteristics of the plants that, allied to the foraging behaviour of the pollinators, act as means to diminish the inbreeding taxes. The reproductive phenology, the pollination biology and the reproduction biology of Cambessedesia hilariana (Melastomataceae) have been studied in a population occurring in a rocky outcrop of a semideciduous forest pertaining to the IAG-USP in Vinhedo/SP, between January 2001 and November 2002. The Cambessedesia hilariana flowering period extends from August to the beginning of June, with a peak between October and November. The flowers are receptive and all with viable pollen during the anthesis period (ca. 60 hours). Controlled crossings in bagged flowers in the pre-anthesis suggest: (i) absence of apomixis (n=60) and spontaneous self-pollination (n=30); (ii) low taxes of fruit- set (12,5%) due to handmade self-pollination (n=350); (iii) high taxes of fruit-set (74%) due to cross-pollination (n=200), as well as in natural conditions (n=60). These data indicate the great importance and efficiency of the pollinators, since the formation of fruits is significantly higher in cross-pollinations. In pistils settled in FAA, 84 hours after manual treatments, the pollen tubes reach and penetrate the micropyl of the ovules in cross pollinations as well as in self pollinations. However, in self pollinations the fruits are aborted in different development stages. It can be suggested that these abortions are involved with pos-zygotic mechanisms, as inbreeding depression or self-incompatibility. The pollination is carried out by buzzing bees, being the most frequent, Centris sp. (50,65%), Xylocopa sp. (18,49%), Centris cf. nitens (12,26 Yo), Bombus morio (1O,91 Yo) and Eug/ossa cordata (3,66%). Aiming to recognize the contribution of each pollinator species in seed formation, some flowers received a controlled number of visits, being the percentage of seeds formed in one and two visits, respectively: Centris sp.: 20,34%/28,35%; Xylocopa sp.: 65,42%/72,87 Yo; Centris cf. nitens: 48,04%/75,55%; Bombus morio: 39,78%/58,20%; Euglossa cordata: 22,85%/45,12%. The frequency of visitors varied during the flowering period. There was also a variation in the frequencies of visits during the day, noting that some species were active during low temperature periods and others during the hottest period of the day. The bees rarely visit the same flower more than once and the formation of seeds varies between 20% and 78%. The most frequent bee species, Centris sp., little contributes in the formation of seeds as its foraging behaviour favours geitonogamy. The contribution of the other bees, specially Centris cf. nitens and Euglossa cordata, is significantly higher after two visits. The most but in only one visit carries enough pollen to the formation of seeds and in enough quantity frequent pollinator (Centris sp.) is the one that less contributes in the formation of seeds, to maintain the fruit. The contribution of each bee species in the plants reproductive success must be evaluated by the number of viable seeds and not only by the percentage of fruits developed

ASSUNTO(S)

polinização morfologia (biologia) reprodução

ACESSO AO ARTIGO

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