Detection and inheritance of stylar ribonucleases associated with incompatibility alleles in apricot

Stylar proteins were surveyed by non-equilibrium pH gradient electrofocusing to identify S-RNases associated with gametophytic self-incompatibility in nine apricot cultivars. RNase activities associated with the alleles of incompatibility S-1, S-2, S-5, and S-6 and with the allele of compatibility Sc were clearly identified. Two other bands that we considered related to the alleles S-3 and S-4 were unique to cultivars Sunglo and Harcot, respectively. Two generations of 17 seedlings from the cross Moniqui x Pepito and 38 from Gitano x Pepito were used to determine the inheritance of the S-RNases. Inheritance of these RNase bands followed the expected segregation ratios and the band combinations correlated perfectly with the known self-incompatibility status of the seedlings determined after self-pollination and observation of pollen tube growth. All evidence presented in this study strongly suggests that RNases are associated with gametophytic self-incompatibility of apricot and that RNases may be the S-gene products. This is the first report identifying S-RNases and describing the inheritance of these S-RNases in apricot.