Characterization and monitoring of copper tolerance of Pseudomonas syringae pv. tomato strains from tomato plants in Turkey

Tomato is grown in a wide range of climatic conditions and is one of the most important vegetable crops in the world. In this study, we have collected symptomatic leaves of tomato bacterial speck caused by Pseudomonas syringae pv. tomato ( Pst ) in different districts of Turkey (mainly Mediterranean region) during 2010–2023. The putative causal agent was identified based on the basis of phenotypic, biochemical, genotypic, and pathogenicity tests. All tested strains were pathogenic on tomato, but not on lemon fruit, were confirmed by LOPAT 1a (+ –− +), and produced 650 bp band size in PCR. The genotypic test for differentiation of coronatine-producing bacteria by PCR and pathogenicity tests on lemon fruit allowed clear differentiation of the 78 Pst strains from Pseudomonas syringae pv. syringae ( Pss ). Among the 78 strains tested using in vitro assay, no copper-sensitive strains were detected, and all strains ( n = 77) except one strain (S Pst 2) were resistant with minimum inhibition concentration (MIC) values 1.80–2.60 mM of copper sulfate. Four out of 78 Pst strains (YA-568, S Pst 30, S Pst 46 and S Pst 50) obtained from different tomato cultivars in Turkey possessed the CusCBA genes. All types of copper-based compounds controlled the disease symptoms on tomato plants, and thus, they were considered to be effective to some extent in bacterial speck management. To the best of our knowledge, this is the first study indicating that cusCBA genes responsible for copper resistance are present in Pst strains from tomato cultivars in Turkey.