BREEDING FOR SWEET AND SOUR CHERRY DISEASE RESISTANCE IN HUNGARY

The fungal pathogen, Cytospora leucostoma, has long been a serious disease of both sweet and sour cherry in Hungary. It readily infects trees via natural or man-made wounds during the course of orchard management, producing a toxin that that can kill entire trees within a few years. One strategy to prevent the disease would be to develop and plant varieties that are resistant or tolerant to C. leucostoma and C. rubescens. Using artificial infections in the laboratory with excised shoots, we screened 13 varieties each of sweet and sour cherry for Cytospora tolerance. Both Prunus species were more susceptible to C. rubescens than to C. leucostoma, and xylem symptoms were more severe than those in phloem tissues. The in vitro laboratory screening method proved to be quick and expedient for identifying potential differences in Cytospora susceptibility of the varieties and hybrids. Additionally, we screened 6 sour cherry varieties in the field using 2-year-old nursery trees, which confirmed the relative tolerance identified initially in the lab for `Újfehértói fürtös’ (‘Balaton’) and `Csengõdi’. Finally, we also evaluated susceptibility of sweet and sour cherry hybrids to Blumeriella jaapii, which revealed significant variability and suggested several genotypes that may be tolerant or resistant.