1887

Abstract

pv. avellanae (synonym: , Pav) is the causal agent of hazelnut decline in Greece and Italy. The population structure and evolutionary relationships of 22 strains from these two countries were examined by multilocus sequence typing (MLST) of four housekeeping genes (, , and ). Neighbour-joining and maximum-likelihood phylogenetic analysis revealed that Greek strains isolated from the original 1976 outbreak of hazelnut decline through 1990 were very similar to Italian strains isolated from 2002 through 2004. Other Italian strains that were isolated during the 1990s were very homogeneous and clustered in a clade that was quite distinct from the Greek isolates and Italian isolates from the 2000s. A split decomposition analysis found evidence for recombination between these two highly divergent clades in two of the four MLST housekeeping genes. Incorporating these data into a broad MLST analysis of the species complex showed that the Pav Greek and Italian strains from the 2000s clustered with phylogroup 1, which is predominantly composed of pathogens of tomato and hosts, while the Pav Italian strains from the 1990s clustered in phylogroup 2 and are most closely related to pea ( L.) pathogens. These results clearly indicate that the ability to infect hazelnuts has arisen twice. This evolutionary process may be due to adaptation to hazelnut by local strains (such as the colonizers of crops), or the result of genetic exchange from the original Greek Pav clonal group into a phylogroup 2 strain. The latter explanation is intriguing since there is no exchange of hazelnut propagative material between Italy and Greece, which would be a likely vector for the movement of these pathogens.

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2007-07-01
2019-10-18
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