AFLP Analysis of Intraspecific Variation Between Monilinia laxa Isolates from Different Hosts

We analyzed with an amplified fragment length polymorphism (AFLP) marker system the genetic diversity and relationships among 67 Monilinia laxa isolates obtained from different host plants. From a total of 1,089 amplified bands scored using 20 primer combinations with two selective nucleotides, 354 were polymorphic and further used in genetic diversity analysis. Genetic relationships among isolates were assessed with different phenetic approaches, including unweighted pair group method with arithmetic mean clustering and principal coordinate analysis; the population's differentiation estimate was analyzed by molecular variance; and model-based clustering was employed to infer population structure. All four analyses clearly showed significant differences between isolates from apple trees and isolates from other host plants. No further grouping according to any other host plant was observed. The results indicate host specialization of apple isolates and support the taxonomic grouping of apple isolates.