Mixed Mating System of an Annatto (Bixa orellana) Population Determined with Microsatellite Markers

Knowledge of the mating system of crop plants is important for plant breeding and conservation. Using 12 microsatellite loci, progenies from a Bixa orellana population from the Tocantins River basin, in the State of Pará, Brazil, were evaluated to determine the mating system. This population, collected in a field of a local variety of annatto, was represented by 20 progenies with 15 individuals each. Microsatellite fingerprints were obtained with an ABI Prism 3130xl capillary sequencer using GeneScan 500 Rox-labelled size standard. Mating system analysis was based on the mixed mating and correlated mating models using the multilocus mating system program MLTR. Multilocus outcrossing rate was 0.532 (±0.047), indicating a mixed mating system for this B. orellana population. Biparental inbreeding (0.081) contributed to the selfing rate in this population. The paternity correlation was high (0.253), indicating that more than 25 % of the outcrossing occurred between related individuals. The parental fixation index (F) was estimated at 0.033, indicating the presence of inbreeding. As a result of selfing and high paternity correlation, the coancestry coefficient within families (0.313) was higher than expected in half sib progenies (0.125). The estimated effective number of pollen donors in this population was 3.8, meaning that approximately 4 males crossed to each of the 20 females. In conclusion, due to this mixed mating system, the collection of open-pollinated seeds for plant breeding or conservation purposes should include at least 100 trees in order to ensure a representative sample.

Financial support: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP – nº 2012/08307-5; nº 2013/08884-5; nº 2015/26837-0)