Mating system and gene flow of Nothofagus alpina (Poepp. & Endl.) Oerst. in a clonal seed orchard

Abstract

Background: Understanding 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. Methods: The 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. Results: This 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. Conclusions: N. 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.