Susceptibility of Serbian plum cultivars to indigenous bacterial and Monilinia laxa isolates

The susceptibility of Serbian plum cultivars to pathogens originating from their phyllosphere was evaluated by inoculating detached young leaves and mature fruits. The virulence of indigenous isolates of the bacteria Pseudomonas syringae, Pseudomonas congelans, Erwinia persicina, Clavibacter michiganensis and Rhizobium nepotum was tested on detached leaves of four Serbian plum cultivars (Ranka, Pozegaca, Cacanska lepotica and Cacanska rodna). The Pseudomonas syringae isolates formed intense symptoms within 48 hours on all tested cultivars with severity index values in the range of 41 - 47%. The other isolates had significantly lower severity values or no symptoms were developed. This study demonstrates for the first time pathogenicity of Pseudomonas congelans on plum, with symptom intensity not significantly different from P. syringae after 96 h of incubation. Virulence of Monilinia laxa isolates was tested on mature fruit of the Cacanska rodna and Pozegaca cultivars and was detected in both of them. Higher susceptibility to M. laxa was recorded for the Pozegaca cultivar, with a fruit infection rate between 43 and 66%. In the case of the Rodna cultivar, no statistically significant difference in the fruit infection rate was detected between the four tested M. laxa isolates. These data indicate significant susceptibility of Serbian plum cultivars to indigenous P. syringae and M. laxa isolates.