The dry bubble disease, caused by Lecanicillium fungicola, is an important fungal disease of white button mushroom in Iranian mushroom production farms. Twenty-three isolates of the pathogen collected in Iran and identified as L. fungicola var. fungicola, were compared for genetic polymorphism, diversity in growth rate and virulence. Ten Universal Rice Primers (URP) were used to evaluate the genetic diversity of L. fungicola var. fungicola. URP analysis showed that the genetic diversity of

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... an isolates was low (average 10 % over the 10 primers used) and that they were almost clonal. Relative correlations between geographical origins of isolates and molecular grouping were observed but there was no correlation between mycelial growth rate, virulence assays and URP patterns. Significant differences were observed between isolates based on mycelial growth rate and virulence assays. The high level of genetic homogeneity is attributed to the effect of fungicides used for control of the mushroom diseases which might have imposed a significant selection pressure on the fungal populations.