The Genetic Structure of Cypress Canker Fungus in Italy Using RAPD and Minisatellite Markers

Abstract

Over the past half century a destructive blight of Cupressus spp., caused by Seiridium cardinale, has spread worldwide from North America, devastating forests, plantations, and ornamental cypresses. The epidemic has been particularly severe in the Mediterranean region, on C. sempervirens. Seventy-seven isolates of Seiridium cardinale have been collected for the genetic characterization of the North-Italian populations of the fungus. Five Seiridium spp. isolates from different countries and different hosts growing in different parts of the world were used for comparison. The structure of the population has been analysed by means of Random Amplified Polymorphic DNAs (RAPDs) and Direct Amplification of Minisatellite-Region DNA (DAMD) PCR marker techniques by using the M13 core sequence. The results indicated a very high level of homogeneity in the North-Italian population of the fungus, whereas a certain variability was recognized in isolates from other hosts and other species. The isolates belonged to the North-Italian population appear to be very similar from the molecular comparison with both type of markers. The isolate from Greece was included in the same group of the Italian isolates. Only the S. cardinale from Chile was clustered at significant distance from the other S. cardinale isolates from Italy and Greece. The genetic homogeneity of the fungus in Italy suggests that this population has gone through a recent genetic bottleneck, perhaps from the introduction in Europe of few genotypes of the fungus. This supports the hypothesis that the pathogen was introduced to Europe during World War II on infected wood material from the United States. The results are discussed in relation to the introduction and spread of the fungus in Europe.