Sweet cherry (Prunus avium) is a member of the Rosaceae family, with a gametophytic self-incompatibility system that strongly affects pollination and fruit set. Alleles at the S-locus control this system, and fertilization does not occur if the S-allele of a haploid pollen gamete matches either S-allele of the diploid maternal pistil. To produce fruit, self-incompatible cherry trees require nearby cross-compatible trees with synchronous flowering. In cherry orchards, two or more cross-compatible pollinizer cultivars are therefore usually inter-planted with the main cultivar. Fortunately, self-compatibility exists, the result of a mutation of one of the alleles at the S-locus, permitting the breeding of self-compatible cultivars that do not require pollinizer trees. The Washington State University (WSU) sweet cherry breeding program seeks to produce self-compatible cultivars (in addition to superior fruit quality and other trait improvements) and desires an early detection system for self-compatible seedlings. PCR-based S-genotyping that included primers for detecting self-compatibility was conducted for 243 seedlings from crosses made in 2004 that initiated this modern breeding program. While self-compatible seedlings were identified, a large proportion of seedlings resulted from unintended parentage, with implications for future breeding strategies.
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