Revisiting the S-allele Nomenclature in Sweet Cherry (Prunus avium) Using RFLP Profiles

Correct assignment of self-incompatibility alleles ( S -alleles) in sweet cherry ( Prunus avium L.) is important to assure fruit set in field plantings and breeding crosses. Until recently, only six S -alleles had been assigned. With the determination that the stylar product of the S -locus is a ribonuclease (RNase) and subsequent cloning of the S -RNases, it has been possible to use isoenzyme and DNA analysis to genotype S -alleles. As a result, numerous additional S -alleles have been identified; however, since different groups used different strategies for genotype analysis and different cultivars, the nomenclature contained inconsistencies and redundancies. In this study restriction fragment-length polymorphism (RFLP) profiles are presented using Hin dIII, Eco RI, Dra I, or Xba I restriction digests of the S -alleles present in 22 sweet cherry cultivars which were chosen based upon their unique S -allele designations and/or their importance to the United States sweet cherry breeding community. Twelve previously published alleles ( S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 9 , S 10 , S 11 , S 12 , and S 13 ) could be differentiated by their RFLP profiles for each of the four restriction enzymes. Two new putative S -alleles, both found in `NY1625', are reported, bringing the total to 14 differentiable alleles. We propose the adoption of a standard nomenclature in which the sweet cherry cultivars `Hedelfingen' and `Burlat' are S 3 S 5 and S 3 S 9 , respectively. Fragment sizes for each S -allele/restriction enzyme combination are presented for reference in future S -allele discovery projects.