The reaction between the various hosts with Pisolithus tinctorius shows the broad host range of this fungal species showing different degrees of host compatibility. There is wide variation in both rate and extent of ECM formation by different isolates of Pisolithus tinctorius of different geographical regions within a species. Thus Pisolithus tinctorius displays much intraspecific heterogeneity of host specificity and interspecific compatibility. There are variable degrees of plant-fungal isolate compatibility, implying specificity, and this is an important factor influencing successful ectomycorrhiza formation and development. The molecular data also suggested that the Pisolithus tinctorius isolates analyzed from different geographical regions belong to distinct groups. Further studies are therefore warranted to elucidate the molecular, biochemical and physiological differences between the Pisolithus tinctorius isolates at the fungus-root interface of different plant species.