Identification of microsatellite markers and their application to population genetics of Venturia inaequalis

Microsatellite markers of Venturia inaequalis were developed using genomic libraries of V. inaequalis enriched for the simple sequence repeats (TC)(n) and (AAC)(n). Seven markers, three with (TC)(n) repeats and four with (AAC)(n) repeats, were selected for the analyses of 350 isolates of V. inaequalis collected from 11 sites in Europe. Polymorphism in the (TC)(n) repeats was higher than in the (AAC)(n) repeats. Nei's expected genetic diversity (H-H) varied between 0.52 and 0.96 for the microsatellites containing (TC)(n) stretches and between 0.09 and 0.36 for the microsatellites containing (AAC)(n) stretches. Within-population diversity (H-S) was very high with values ranging from 0.28 to 0.49, whereas differentiation among all European populations (G(ST)) was low with an average of 0.07. In the population from Ahrensburg (northern Germany) where isolates were mainly collected from apple varieties carrying the Vf gene, usually resistant to V. inaequalis, we showed a bottleneck effect with reduced diversity and loss of alleles. The great advantages of microsatellite markers over random amplified polymorphic DNA and polymerase chain reaction-restriction fragment length polymorphism markers are their high specificity, high polymorphism, good reproducibility, and unambiguous scorability.