Paternity analysis in a 'Rainier' open pollination population using S-alleles and microsatellite genotyping

Fruit breeding programs usually use controlled hand pollination among cultivars and advanced selections for obtaining segregating populations to select new cultivars. In sweet cherries, however, sometimes in controlled pollination few hybrids are obtained. Caging whole trees with bees and flowers of the pollinating cultivar is sometimes used to obtain larger hybrid populations. To generate large segregating populations for the Chilean Sweet Cherry Breeding Program (run by the Consortium of BioFrutales S.A. and Instituto de Investigaciones Agropecuarias), the initial strategy was to harvest seeds from open pollinated self-incompatible cultivars maintained at the germplasm collection orchard of Univiveros, one of the leading fruit tree nurseries in Chile. While the female parent is known, the male parent is unknown. The pollen source will depend on the cultivars present in the area, the flowering time and the compatibility of the cultivars involved. In order to identify pollinators of the self-incompatible 'Rainier', which is surrounded by several other cultivars in the collection, a group of them were proposed as the most possible pollen donors considering their flowering time and location within the orchard. An initial screening using S-allele genotyping of 675 one-year-old seedlings from 'Rainier' open-pollination allowed for the identification of several S-genotypes, which suggested putative pollinators. These analyses identified two main putative pollen donors: 'Rivedel' (232 individuals, 34% of total) and 'Vanda' (101 individuals, 15% of the total). The paternity of these cultivars was confirmed or rejected after additional analysis with at least five highly informative microsatellite markers. The segregating population resulting from the cross 'Rainier' × 'Rivedel' (n=232) is currently being analyzed with microsatellite markers in order to build a linkage map for sweet cherry. In this population, parents exhibit contrasting phenotypes for skin and flesh color and berry firmness, among other agronomically important traits, making this population very interesting for future genetic studies.