Abstract
BackgroundUnderstanding pathways of genetic information transfer from one generation to another is particularly important when open-pollinated seeds are collected for reforestation or for enrichment of native forests. Nothofagus alpina (Poepp. & Endl.) Oerst. is native to temperate forests of southern Chile and Argentina. However, lack of knowledge of its reproductive biology has hampered its management in forest plantations and conservation of natural populations. Therefore, a clonal seed orchard of N. alpina in southern Chile was used to analyse the mating system and to estimate the number of pollen donors in this species.MethodsThe mating system was investigated using manual pollination tests on six clones, open-pollinated seeds were collected from four other clones to study gene flow and paternity analysis was done on progenies using microsatellite genetic markers. Pollen donors were inferred for 194 offspring of four adult trees using five microsatellite loci and an exclusion process.ResultsThis species is exogamous and largely self-incompatible. The effective number of pollen donors found was 5, which was less than the 19 expected theoretically. Results indicated that pollen flow in the seed orchard is deficient. This could be a result of limitations in the wind-pollination system, coupled with phenological dissynchrony among clones present.ConclusionsN. alpina is an exogamous, highly self-incompatible species. It does not reproduce through agamospermy, since there was no seed formation in the absence of pollen. Only a few trees contributed to the paternity of the progeny evaluated. This finding indicates that there exists a limited gene flow within the orchard due to reproductive isolation among genotypes.
Highlights
Understanding pathways of genetic information transfer from one generation to another is important when open-pollinated seeds are collected for reforestation or for enrichment of native forests
The production of full seeds from manual cross-pollination varied among different trees evaluated, ranging from 0.31 to 0.49 full seeds per flower, whereas the range obtained in individuals that were manually self-pollinated was less than or equal to 5.1% (Table 2)
The effective number of fathers of progeny from the given mothers evaluated here varied between two and three
Summary
Understanding pathways of genetic information transfer from one generation to another is important when open-pollinated seeds are collected for reforestation or for enrichment of native forests. A clonal seed orchard of N. alpina in southern Chile was used to analyse the mating system and to estimate the number of pollen donors in this species. Mating system and gene flow are two mechanisms that allow a population of a species to maintain genetic variation. Such mechanisms facilitate adaptation to potentially changing environmental conditions, both in time and space (Boshier 2000). These mechanisms define the mode of genetic transmission between generations and govern the distribution of genetic variation within and. Genetic factors include genes that control self-incompatibility, sexual presentation system, reproductive maturity and endogamy depression while environmental factors influence flowering phenology and behaviour of pollinators.
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