NEW RECORDS OF Pseudomonas syringae IN YOUNG SWEET CHERRY PLANTATIONS

Abstract

Bacterial canker caused by Pseudomonas syringae pathovars is one of the most serious cherry diseases worldwide. Nowadays in Serbia, sweet cherry production significantly increased and the new plantations, mainly based from imported planting material are being raised every year. In general, bacterial canker is mostly distributed in young sweet cherry plantations worldwide and in Serbia also. During spring, in May 2018 and 2019, occurrence of bacterial canker symptoms was observed on a newly planted sweet cherry plantations on two localities, Žitorađa and Karavukovo. Therefore the aim of this work was to determine causal agent of the disease using conventional and molecular tools. Typical P. syringae colonies were isolated on Nutrient Sucrose Agar from all collected sweet cherry samples with expressed bacterial canker or leaf spot symptoms. All isolates were Gram negative, catalase positive, produced fluorescent pigment on King B medium under UV light and showed oxidative metabolism of glucose. Results of the LOPAT test (+---+) determined isolates to belong to fluorescent Pseudomonas Group Ia, while in G+A+T Ta- showed characteristics described for pv. syringae. Pathogenicity was confirmed on immature fruits of sweet and sour cherry where all isolates caused typical symptoms in form of black, sunken lesions, characteristics for pv. syringae. Selected bacterial isolates were further identified by DNA sequencing using gyrB housekeeping gene. All tested isolates were identified as P. syringae pv. syringae using NCBI BLAST. Isolate RE05, isolated from sweet cherry stem (Karavukovo) showed 99.51% homology with P. syringae pv. syringae strain CFBP4215 (sweet cherry, France). Isolates RE3 and RE4 (Žitorađa) originated from branch and leaf, respectively, showed 99.19% homology with P. syringae pv. syringae strain Pss9097 (sweet cherry, UK) and CFBP2118 (sweet cherry, France). Phylogenetic analysis grouped isolates from Žitorađa (RE3 and RE4) in one tree cluster, separate from the isolate RE05, showing presence of two genetically diverse groups of P. syringae pv. syringae isolates, obtained from two geographically distinct localities in Serbia. Considering that during last few years P. syringae continuously occurs mainly in young sweet cherry plantations, where imported material is used for raising, health status check needs to be included as obligatory measure when nursery materials is used from import.