Investigation of S-incompatibility breakdown in 'Karina' sweet cherry

The paper presents results of a two-year study of self-(in)compatibility in 'Karina', previously reported as a self-incompatible sweet cherry cultivar. After emasculation and bagging, pistils of 'Karina' were selfed and pollinated with the nominally cross-incompatible cultivars 'Germersdorfer 1' and 'Lambert' at the beginning of full flowering. In the same way, the pollen of 'Karina' was used to pollinate 'Germersdorfer 1' and 'Lambert'. PCR analysis to determine S-genotypes of 'Karina', 'Germersdorfer 1' and 'Lambert' using consensus and allele-specific primers for S-RNase resulted in patterns consistent with S3S4 genotype. After selfing, 'Karina' behaved as self-compatible, since its pollen tubes reached the base of the style and ovary, penetrating the nucellus and fruit set was recorded in both years. Pollen tubes penetrating the nucellus and fruit set were also recorded after pollination with 'Germersdorfer 1' and 'Lambert'. In contrast, 'Germersdorfer 1' and 'Lambert' did not set any fruit when pollinated with 'Karina'. Microscopic observation showed pollen tubes ending the growth in the upper and middle third of the style. The behaviour of 'Karina' after selfing, as well as its behaviour as the pollen donor/recipient in pollination with cultivars of the same S-allele constitution requires further molecular and genetic analysis