Molecular characterization of Pseudomonas syringae isolates from fruit trees and raspberry in Serbia

Infection of fruit trees by Pseudomonas syringae is a potentially serious problem that may limit the establishment and sustained productivity of pome and stone fruit orchards in Serbia. To estimate possible diversity of Pseudomonas syringae fruit trees strains, we collected a set of strains in several areas of Serbia. The samples were taken from infected orchards with raspberry, plum, cherry, sour cherry, peach, pear and apple trees. Genetic diversity of P. syringae strains isolated from fruit trees was determined by using SpeI macrorestriction analysis of genomic DNAs by pulsed-field gel electrophoresis (PFGE) and REP-PCR. Molecular analysis showed that most of isolates had unique profiles, with the exception of isolates from plum and cherry that displayed profiles identical to each other and similar to P. syringae pv. morsprunorum. The study presented here clearly demonstrates the discriminative power of molecular techniques in enabling a detailed analysis of the genetic variations between strains of P. syringae from different pome and stone fruit hosts in Serbia

Sorbus sp - New host of Erwinia amylovora in Serbia

In 1989 Erwinia amylovora was confirmed to be a pathogen of pear and quince in Serbia. Subsequently, apple, firethorn, hawthorn, Mespilus spp., Cotoneaster horisontalis and Cheanotneles spp. were confirmed as hosts of the pathogen. During the summer 2005, fire blight symptoms were observed on Sorbus spp. for the first time in the south-eastern Serbia, near Nis. Disease symptoms included leaf and shoot blight and cankers with purple-brown colouration of necrotic tissue on mature branches. The diseased tissue was macerated and the suspension was streaked on nutrient sucrose agar (NAS) and King's medium B. Typical light grey, levan-positive colonies developed on NAS medium after two day incubation at 25 degrees C. Colonies on King's medium B were white and nonfluorescent. The results of physiological and biochemical tests of the bacterium were as follows: gram negative, oxidative and fermentative metabolism of glucose; oxidase negative, gelatin hydrolysis positive, aesculin hydrolysis negative and acid produced from most carbon sources. In pathogenicity tests, all isolates induced HR in tobacco leaves and necrosis on artificially inoculated pear fruits followed by appearence of bacterial ooze. After inoculation of petioles and shoots of the host plant (Sorbus spp.) initial symptoms were dark green, watersoaked, eliptical spots on inoculated tissues. Leaf and shoot blight resembling the natural infection appeared five to six days after inoculation. The investigated strains reacted positively with antisera specific to E. amylovora in DASI ELISA test. Identity of isolated strains also was confirmed by polymerase chain reaction (PCR). According to the biochemical and physiological characteristics, pathogenicity tests, results of PCR analyses and ELISA test, strains isolated from Sorbus spp. plants were identified as E. amylovora. This is the first report of E. amylovora on Sorbus spp. plants in Serbia

Characterization of Gnomoniopsis idaeicola, the Causal Agent of Canker and Wilting of Blackberry in Serbia

Blackberry cane diseases with the symptoms of necrosis, canker, and wilting are caused by several fungi worldwide. Surveys conducted from 2013 to 2016 in Serbia revealed the occurrence of Gnomoniopsis idaeicola, the causal agent of cane canker and wilting, which was found to be distributed in almost half of the surveyed orchards, in three blackberry cultivars, and with disease incidence of up to 80%. Wide distribution and high disease incidence suggest that G. idaeicola has been present in Serbia for some time. Out of 427 samples, a total of 65 G. idaeicola isolates were obtained (isolation rate of 34.19%). Reference isolates, originating from different localities, were conventionally and molecularly identified and characterized. G. idaeicola was detected in single and mixed infections with fungi from genera Paraconiothyrium, Colletotrichum, Diaporthe, Botryosphaeria, Botrytis, Septoria, Neofusicoccum, and Discostroma, and no diagnostically specific symptoms could be related directly to the G. idaeicola infection. In orchards solely infected with G. idaeicola, blackberry plant mortality was up to 40%, and yield loses were estimated at 50%. G. idaeicola isolates included in this study demonstrated intraspecies diversity in morphological, biological, pathogenic, and molecular features, which indicates that population in Serbia may be of different origin. This is the first record of a massive outbreak of G. idaeicola infection, illustrating its capability of harmful influence on blackberry production. This study represents the initial step in studying G. idaeicola as a new blackberry pathogen in Serbia, aiming at developing efficient control measures