CORRELATION OF STYLAR RIBONUCLEASE ZYMOGRAMS WITH INCOMPATIBILITY ALLELES IN SWEET CHERRY

Protein stylar extracts of 16 cultivars of sweet cherry (Prunus avium) , from the 10 different incompatibility groups to which incompatibilit y alleles have been assigned, were separated on acrylamide gels using isoelectric focusing (IEF) and were stained for ribonuclease activity. When two cultivars from the same incompatibility group were analyzed they gave identical zymograms and the cultivars of the 10 different in compatibility groups gave in all eight distinct zymograms. The ribonuc lease polymorphism could be correlated with the reported S allele cons titutions of the cultivars. Three ribonuclease bands were identified t hat each consistently corresponded to one of the six known incompatibi lity alleles (S-1, S-2 and S-6), a fourth band apparently corresponded to S-3 and to the combination of S-4 and S-5, and a fifth band to S-4 and S-5 in other combinations. Thus, it seems that S alleles of cherr y have ribonuclease activity and that IEF is useful for distinguishing S allele constitutions. The ribonuclease pattern of 'Summit', a culti var of unknown incompatibility group, indicated its incompatibility ge notype to be S1S2, and this was confirmed by controlled pollination. T he same band corresponded to S-4 and S-4', the mutant allele in self-c ompatible cultivars. IEF and ribonuclease staining promise to be usefu l tools for exploring the incompatibility relationships of cherry cult ivars and perhaps of other self-incompatible Prunus crops.