Separate Origins and Pathogenic Convergence in Pseudomonas avellanae Lineages
Pseudomonas avellanae is the causal agent of hazelnut (Corylus avellana L.) decline both in northern Greece and central Italy, and two lineages related to the geographic origin of the pathogen have previously been pointed out. In order to verify the possible correlation between the genetic diversity and the geographic distance, forty representative strains, obtained from all the areas where the disease was so far observed, were analysed by combining the data obtained from repetitivesequence PCR using ERIC and BOX primer sets and IS50-PCR, and statistical methods revealing the genetic diversity among the populations. The Mantel test performed with ERIC-PCR, BOX-PCR and IS50-PCR data revealed that the P. avellanae populations that are spatially distant from each other are also genetically dissimilar. The gene flow estimates confirm such data. Virulence tests were carried out on hazelnut trees trained in soils with different pHs. The highest virulence of P. avellanae strains was observed when they were inoculated on twigs of trees grown in subacidic soils (pH 4.8). Such data are in agreement with the more severe occurrence of the hazelnut decline both in Greece and Italy in orchards characterized by subacidic soils. The sudden occurrence of hazelnut decline in different geographic areas could represent a case of pathogenic convergence in locally adapted phytopathogenic pseudomonads.
KeywordsCorylus avellana acidic soils Mantel test
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