Biologia reprodutiva e hibridação em especies sintopicas de Ludwigia (Onagraceae) no sudeste do Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

The family Onagraceae Juss. is considered a natural family and particularly interesting to study breeding systems because its moderate size and relatively abundant morphological, systematic, molecular and chemical information. Ludwigia L. is a distinct genus in the family, the only member of the tribe Jussiaeeae, comprises more than 80 species distributed mainly in South America. The purposes of this research were to study the breeding systems of 12 populations ITom 10 sympatric species growing together in wet habitats (Centro Experimental de Campinas - Instituto Agronômico, Campinas, SP), examining the relationships among phenology, floral density, seeds size, germination and habits. Different species living together are interesting to also determine the significance of hybridization natural barriers, external and internal. The phenology was analysed by limited sample areas. Flowering and ftuiting peakes and the floral density (DF) were calculated monthly for each population. AlI species have one day lasting yellow flowers and flowering occurs mainly in autumn and ftuiting ITom the middle of autumn to the end of winter (drought season). The maximum small DF was found to annual species (0.4 to L. octovalvis population-OCTO until .9 to L. leptocarpa). Among self-incompatible erect shrub species were found the highest DFs: L. sericea = 3,5 and L. nervosa = 7. Little flowers that were open each day would increase cross pollination and avoid floral herbivory by coleoptera, observed in section Myrtocarpus. The flowering season was concentrated during the beginning of drought season when pollinators, oligoletic bees were active. The capsules usually open with dormant seeds or the germination is delayed until the next spring, when there is more rainfall and increased daylight hours. The seeds are dispersed by water, because could be afloat, such as the seedlings, wind or secondarily by animal surface. The seeds were stored, weighed and germinated ( controlled environrnental chambers at 25°C and 12: 12h light-dark photoperiod). The smallest seeds were found in the herbaceous annual L. decurrens, L. erecta and L. hyssopifolia (about 0,01 mg) and the biggest mass was found in the perennial population of L. octovalvis (0,082 mg). Comparing two different storage periods, L. octovalvis and L. erecta germinated more copiously in the small period, while the other species, mainly L. decurrens, L. hyssopifolia and L. elegans, germinated more after the longer storage time. This indicated that Ludwigia species could lost viability or the dormancy period is variable. The annual species with small seeds tend to have smaller germination rates (1 %.; to 60%) while the perennials, with bigger seeds, germinated trom 14 to 86%. The period to germination was trom 7 days until maximum 133 days (L. sericea). The highest seedlings growth rate, after 5 months, were exhibited by the shrubby L. sericea and L. nervosa. Ludwigia species series show a variety ofhabits and reproductive biology, trom autogamous annual herbs until selfincompatible perennials erect shrubs. Agamospermy was not detected. The inhibition of zincompatible pollen tubes was in the upper part of the style, following a pattem, which is different trom the other Onagraceae. The self-compatible species increase pollen grains dispersal among individuals by the small number of open flower each day and distance between the anthers and stigma. From field studies each biology reproductive treatment: spontaneous pollination, manual self-pollination and cross-pollination were collected ftuits. Samples were weighed and the germination samples were monitored and seedlings were growth and weighed 5 months after. The cross- pollination seeds appear reduce the dormancy and increase the germination rate among Ludwigia herbaceous annual species, while among shrubby species, the most visible stage is the fastest initial development of seedlings. Experimental hybridization among studied species revealed that also among South - American Ludwigia species, such as the other sections in this genera, the hybridisation barriers could be broken. There was not reciprocity in the ftuits and seeds developing between interspecific crosses and the self-incompatibility system appear no interfere in the pollen tube growth between species. The detected barriers would be a sum of external and internal barriers: different flowering peak associated with pollination behaviour that prevail intraspecific visits, slow pollen tube velocity and ginoecium dimension, abnormally dehiscent capsules, viable seeds production. These barriers do not act alone, but together, such as an overlid filters system

ASSUNTO(S)

hibridação biologia - reprodução

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