Characterization of Pseudomonas syringae pv. actinidiae (Psa) isolated from France and assignment of Psa biovar 4 to a de novo pathovar: Pseudomonas syringae pv. actinidifoliorum pv. nov.

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Inglés. <p>Since 2008, bacterial canker of kiwifruit (Actinidia deliciosa and A. chinensis) caused by Pseudomonas syringae pv.<br />actinidiae (Psa) has resulted in severe economic losses worldwide. Four biovars of Psa can be distinguished based on<br />their biochemical, pathogenicity and molecular characteristics. Using a range of biochemical, molecular and pathogenicity<br />assays, strains collected in France since the beginning of the outbreak in 2010 were found to be genotypically<br />and phenotypically diverse, and to belong to biovar 3 or biovar 4. This is the first time that strains of biovar 4 have<br />been isolated outside New Zealand or Australia. A multilocus sequence analysis based on four housekeeping genes<br />(gapA, gltA, gyrB and rpoD) was performed on 72 strains representative of the French outbreak. All the strains fell<br />into two phylogenetic groups: one clonal corresponding to biovar 3, and the other corresponding to biovar 4. This second<br />phylogenetic group was polymorphic and could be divided into four lineages. A clonal genealogy performed with<br />a coalescent approach did not reveal any common ancestor for the 72 Psa strains. Strains of biovar 4 are substantially<br />different from those of the other biovars: they are less aggressive and cause only leaf spots whereas Psa biovars 1, 2<br />and 3 also cause canker and shoot die-back. Because of these pathogenic differences, which were supported by phenotypic,<br />genetic and phylogenetic differences, it is proposed that Psa biovar 4 be renamed Pseudomonas syringae pv. actinidifoliorum<br />pv. nov. Strain CFBP 8039 is designated as the pathotype strain</p>