The resistance of peach cultivars to the most important diseases caused by fungi, bacteria, viruses and mycoplasms was studied in Romania over two working stages in the period between 1985-2005. The major diseases examined were: Cytospora cincta Sacc., Taphrina deformans (Berk) Tul., Moruluua laxa (Aderh. & Ruhl) Honey, Sphaerotheca pannosa var. persicae Woron., Stigmina carpophila (Lev) M.B.Ellis, Pseudomonas syringae pv. syringae, mycoplasm and plum pox potyvirus. Based on the obtained results, the studied cultivars were classified into resistance groups for the different diseases (very resistant, resistant, medium resistant, sensitive and very sensitive).Based on the results of our study, the following gene sources were chosen following the evaluation of the various genetic material in the peach germoplasm fund, in the climatic conditions of Romania: Cytospora cincta: Cullinan, Cardinal, Hamlet, NJF 3, Onakita Gold, Triumf, "Superba de Toamna", Anderson, Weinberger; Stigmina carpophila: Armgold, ARK 109, Stark Early Blaze, Cardinal, Congres; Taphrina deformans: Madeleine Pouyet, Cumberland, Harbelle, Indian Blood, Sulivan, Victoria, Zafrani, Pekin, Naradnji Ranhii; Spaherotheca pannosa var. persicae: Triumf; Congres; Victoria; Armking; Morton; Regina; Nectared 7; ARK 125; ARK 134; Regina.

In a two-year study, we aimed to determine the susceptibility of four plum cultivars to two fungal pathogens of plum (Stigmina carpophila and Polystigma rubrum) in two training systems with tree spacings of 4 x 1.5m and 6 x 3m. Results showed that shothole symptoms were not detected on cvs ’Bluefre’ and ’Stanley’ in August, 2016. Disease incidence was above 50% in the case of ’Čačanska lepotica’ in both training systems in 2016. There were no significant difference between the two training systems. Shot hole incidence was lower in the 6 x 3m spacings compared to the 4 x 1.5m spacings on cv ’President’ in 2016. Cultivar ’Čačanska lepotica’ showed the highest incidence of Stigmina carpophila in the 4 x 1.5m spacing in 2017. Disease incidence of Stigmina carpophila was significantly lower in the 6 x 3m spacing compared to the 4 x 1.5m spacing. Shothole incidences on cv ’President’ were similar to the values in 2016 ranging from 40% to 60%. Leaf disease incidence was higher in the 4 x 1.5m spacing compared to the 6 x 3m plot. Low disease incidence (below 10%) was observed on cv ’Stanley’ in 2017 and only in the 4 x 1.5m spacing. There were no visible symptoms of blackhorn dotty in 2016 due to inadequate weather conditions for the Polystigma rubrum fungus. However, all the four cultivars were infected by Polystigma rubrum in 2017. The most susceptible cultivar was cv ’Čačanska lepotica’ with the highest disease incidence in the 4 x 1.5m spacing. Disease incidence of this cultivar was lower in the 6 x 3m spacing which was significantly less than in the 4 x 1.5m spacing. The least susceptible cultivar was ’Bluefre’ and symptoms were observed only in the spacing of 4 x 1.5m. The disease incidence of cv ’President’ was similarly low to cv ’Stanley’ in both spacings.