Detection of Pseudomonas syringae pv. syringae on citrus in Tunisia. Pseudomonas syringae pv. syringae

Pseudomonas syringae pv. syringae (Pss) is the most polyphagous plant bacterium belonging to the P. syringae specie. In light of this, the aim of our study was to detect if Pss is the causal agent of the Tunisian citrus blast and citrus black pit disease. The emergence of this disease in the Tunisian citrus orchards was observed as early as the spring of 2011. A collection of Pss like-bacteria was obtained and characterized. Samples were collected mostly from fields located in the North of Tunisia where disease symptoms were expanding and less from the Center where the disease was absent through 2012-2015.Based on phenotypic tests (LOPAT and GATTa) and genetic studies (16SrRNA, rep-PCR, PCR-MP) the causal agent was confirmed to be Pss. As more recently MLSA was described a reliable technique for species delineation and strain identification in Pseudomonas, we used it for a better species classification in comparison to strains from various countries and hosts. Overall, fingerprinting techniques and housekeeping genes diversity analyses showed that citrus Pss strains are homogenous without any geographic distinction and they are closely related to the LMG5694 Pss strain isolated from Citrus sinensis from Greece in 1962.