Evaluation of promising plum (Prunus domestica L.) genotypes for resistance to causal agents of the most important diseases

Plum breeding at the Fruit Research Institute, Cacak, Republic of Serbia, has a decades-long tradition and significant results achieved. So far, 15 new plum cultivars have been recognized. Positive selection of promising hybrids obtained in continuous breeding programmes is based not only on biological, pomological and productive properties but also on their resistance or tolerance to the causal agents of economically the most important diseases. Reaction of promising plum hybrids 38/62/70, IV/63/81, 32/21/87, 34/41/87 and 22/17/87, and the cultivar 'Nada' to Plum pox virus - PPV and causal agents of red leaf spot [Polystigma rubrum (Pers.) DC], rust [Puccinia prunispinosae (Pers.: Pers.)] and blossom blight and brown rot [Monilinia laxa (Aderhold & Ruhland) Honey] were evaluated in the field under natural high infection pressure condition during a three-year period (2009-2011). Resistance to PPV was also examined by artificial inoculation with characterized PPV-M, PPV-D and PPV-Rec isolates in controlled conditions. The hybrids 32/21/87, 34/41/87 and 22/17/87 exhibited high levels of resistance to natural infections by PPV and causal agents of red leaf spot and rust. No typical symptoms of blossom blight and brown rot were found on the hybrids IV/63/81 and 32/21/87. The hybrids 32/21/87, 34/41/87 and 22/17/87 showed also resistance or high degree of tolerance to infection with certain PPV strains by artificial inoculation.