Taxa de cruzamento e sistema reprodutivo de uma população natural de Copaifera langsdorffii Desf. na região de Lavras (MG) por meio de isoenzimas

Abstract

-(Outcrossing rate and mating system of a natural population of Copaifera langsdorffii Desf. in the region of Lavras, MG, starting from isozyme). A natural population of the tree species Copaifera langsdorffii Desf., commonly found in Brazil, was investigated by isozyme electrophoresis, aiming to determine the outcrossing rate and mating system. The population sampled is located along a stretch of the river Capivari in an area of preservation (Riparian Forest), between the towns of Lavras and Itumirim, south of Minas Gerais State, Brazil. Samples of leaf tissue were taken from 20 adult individuals and from 400 progenies for isozyme analysis. Five enzymatic systems were evaluated in adults (24 alleles average) and progenies (29 total alleles). The mating system of this population was approached by the Hardy-Weinberg equilibrium test (HWE) where it was found that most loci of the adult individuals is in the ratios of the HWE and most loci of the progenies is out of the it. The estimate of the average multilocus ( m t ) and unilocus outcrossing rate ( S t ) was respectively 0.917 and 0.877, pointing out the existence of self-fertilization (8%) in the population studied. The results obtained by isozymes analyses indicated also that the species Copaifera langsdorffii is predominantly alogamous. The population has relatively high genetic variation making this population of C. langsdorffii a valuable source for genetic conservation. The minimum area size estimated for the in situ conservation was 5.0 ha. RESUMO -

Low levels of realized seed and pollen gene flow and strong spatial genetic structure in a small, isolated and fragmented population of the tropical tree Copaifera langsdorffii Desf

“…Similar results were reported for the tropical tree Neobalanocarpus heimii (Naito et al, 2005). Thus, the higher outcrossing rate we observed at the seedling stage compared with the rate observed by Oliveira et al (2002) for mature seeds very likely resulted from inbreeding depression. This is consistent with the excess homozygosity found in the population, as discussed above.…”

“…Our results suggest a very high realized outcrossing rate among the studied seedlings (t ¼ 0.9992). This value is higher than has been previously estimated for openpollinated seeds (t m ¼ 0.917, Oliveira et al, 2002). Both results confirm that most populations of the species reproduce predominantly by outcrossing.…”

“…Both results confirm that most populations of the species reproduce predominantly by outcrossing. However, the higher outcrossing rate detected herein is probably partly because of the fact that this was estimated at the seedling stage (realized outcrossing rate), whereas Oliveira et al (2002) analysed open-pollinated seeds (effective outcrossing rate). Studies of mating systems in tropical tree species have suggested that the outcrossing rate can change between fertilization and seedling establishment.…”

“…C. langsdorffii is a hermaphroditic tropical tree that is pollinated by insects (predominantly bees, Apis mellifera and Trigona spp. ; Carvalho, 2003) and reproduces in a mixed mating system (Oliveira et al, 2002). Trees can begin flowering at approximately 5 years of age, but the flowering and fruiting events are not annual.…”

Estrutura genética de populações de pindaíba (Xylopia brasiliensis Sprengel) por isoenzimas

“…Inúmeras investigações têm utilizado esta técnica para estimar os níveis de variabilidade genética de populações naturais, estudar o fluxo gênico entre populações, a dispersão de espécies, tamanho efetivo da população e taxas de cruzamento (Ferreira & Grattapaglia 1998, Lepsch-Cunha et al 1999. No Brasil, várias pesquisas utilizando marcadores isoenzimáticos foram realizadas com espécies arbóreas nativas (Lepsch-Cunha et al 1999, Oliveira et al 2002, Sebben et al 2003.…”