Randomly amplified polymorphic DNA markers are superior to somatic incompatibility tests for discriminating genotypes in natural populations of the ectomycorrhizal fungus Suillus granulatus.

Assessing genetic variation within populations and genetic exchange between populations requires an understanding of the distribution and abundance of individual genotypes within the population. Previous workers have used somatic incompatibility testing to distinguish clones or individuals in natural populations of ectomycorrhizal fungi. However, somatic incompatibility tests performed with isolates of Suillus granulatus from a natural population revealed a lack of transitiveness, which brought into question the validity of this method. Subsequent studies of genetic identity of these isolates, using randomly amplified polymorphic DNA (RAPD) markers, conclusively showed that somatically compatible isolates are not necessarily genetically identical. RAPD marker analysis is more reliable and provides higher resolution of genotype distribution in natural populations than does somatic incompatibility testing. This is of particular importance in populations of organisms such as ectomycorrhizal fungi in which the mating systems are incompletely known.