Evaluation of some pathogenicity and virulence factors in Xanthomonas arboricola pv. pruni strains from Khorasan-Razavi Province

Xanthomonas arboricola pv. pruni (Xap) is a causal agent of leaf, fruit spot, and branch bacterial canker in warm and humid conditions on stone fruit trees. Herein, the pathogenicity of 18 Xap strains from Khorasan-Razavi Province, Iran was evaluated in greenhouse trials on Santha-Rosa plum saplings. Some pathogenicity factors including pXap41, T3SS effectors, and virulence features such as motility, biofilm, xanthan and biosurfactant production, cell wall degrading enzymes and their possible correlation with pathogenicity rate were investigated. The studied strains were divided into two severe and weak pathogenicity groups based on percentage of necrotic lesions. All 18 strains besides ICMP7485, had pXap41, xopE3 and xopA effector genes. In some cases, there was a direct correlation between disease severity and factors involving in virulence. For example, two strains, ShL45 and NB28k, showed the highest percentage of necrosis spots (62.5%), produced high levels of biosurfactant and biofilm that indicated significant differences with other strains at 5% probability levels. It seems that xanthan has no significant effective role in Xap virulence. The rate of swarming in 92.3 % of strains belonging to the severe pathogenicity group was more than the swimming (P≤ 0.05). All strains were also capable of secreting different amounts of enzymes, including protease, cellulase, polygalactronase, and pectatelyase. However, the rate of secretion in all them was not entirely consistent with virulence. It is suggested that more Xap strains from different regions of the country, along with other X. arboricola pathovars, should be tested to get results that are more accurate.