Polyphasic Characterization of Acidovorax citrulli Strains Originating from Serbia

Nevena Zlatković,Nemanja Kuzmanović,Anđelka Prokić,Aleksa Obradović,Katarina Gašić,Milan Ivanović,Svetlana Živković

doi:10.3390/agronomy12020235

Abstract

Acidovorax citrulli, the causal agent of bacterial fruit blotch (BFB), is an economically important pathogen of watermelon and related plant species worldwide. In the period 2014–2018, several outbreaks of BFB were observed in major watermelon production regions in Serbia. A total of 43 strains, isolated from symptomatic watermelon tissue, were analyzed by biochemical, pathogenic and molecular tests. Based on the phenotypic characteristics, PCR assay, and 16S rRNA gene sequence analysis, all strains were identified as A. citrulli. A multilocus sequence analysis of the four housekeeping (adk, gyrB, pilT and gltA) and three virulence genes (Aave_1548, avrRx01 and luxR) revealed that studied A. citrulli strains represent the homogeneous population and they clustered together with group II reference strain AAC00-1. Strain affiliation to group II was confirmed by PCR based on the putative type III secretion effector gene and by duplex PCR test. High homogeneity of studied strains was also confirmed by BOX-PCR. Differences were observed for two strains in their pathogenicity as well as susceptibility to copper compounds. Moreover, six major watermelon varieties grown in Serbia showed high sensitivity to the pathogen, while cross inoculation assay revealed that the strains were able to infect other species within the Cucurbitaceae family.

Highlights

Cucurbit cultivation contributes significantly to vegetable production in Serbia
During August 2014, typical bacterial fruit blotch (BFB) symptoms were noted on mature watermelon (Citrullus lanatus) fruits originating from fields in the north of Serbia (Srem district)
The strains isolated from watermelon in Serbia belong to A. citrulli [27]

Summary

Introduction

Cucurbit cultivation contributes significantly to vegetable production in Serbia. Cucumber, watermelon, melon, pumpkin and muskmelon represent some of the most important species used for fresh consumption, and for processing and the pharmaceutical industry. Until 1996, A. citrulli was largely studied as a pathogen of watermelon. Assouline et al [14] stated that the pathogen was detected in several shipments of tomato seeds imported from India, as well as in eggplant seedlings grown from imported seed [15]. This was the first detection of BFB pathogen outside the family Cucurbitaceae. A group of authors from Israel confirmed previous reports by isolating A. citrulli strains from symptomatic eggplants and tomato [16]. Malliarakis et al [17] reported the disease occurrence on tomato seedlings in Greece. Serious losses in the production were recorded

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Results

Conclusion