Understanding how geographical and environmental features affect genetic variation at both the population and individual levels is crucial in biology, especially in the case of pathogens. However, distinguishing between these factors and the effects of historical range expansion on spatial genetic structure remains challenging. In the present study, we investigated the case of Mycosphaerella fijiensis-a plant pathogenic fungus that has recently colonized an agricultural landscape characterized by the presence of potential barriers to gene flow, including several commercial plantations in which disease control practises such as the use of fungicides are applied frequently, and low host density areas. We first genotyped 300 isolates sampled at a global scale on untreated plants in 2 dimensions over a 50x80 Km area. Using two different clustering algorithms, no genetic structure was detected in the studied area, suggesting expansion of large populations and/or no influ ence of potential barriers. Second, we investigated the potential effect of disease control practises on M. fijiensis diversity by comparing populations sampled in commercial vs. food-crop plantations. At this local scale, we detected significantly higher allelic richness inside commercial plantations compared to the surrounding food-crop plantation populations. Analysis of molecular variance (AMOVA) indicated that 99% of the total genetic variance occurred within populations. We discuss the suggestion that high population size and/or high migration rate between populations might be responsible for the absence of any effect of disease control practises on genetic diversity and differentiation.

Individual GenotypesThis file contains genotypes (i.e allele sizes) of all the stains used in the publication HDY-12-OR0095R. The file include two sheets for the two different data sets (see Fig 1 of the manuscript). NA indicates a missing data.