Microsatellite and mating type markers reveal unexpected patterns of genetic diversity in the pine root‐infecting fungusGrosmannia alacris

Abstract

Grosmannia alacrisis a fungus commonly associated with root‐infesting bark beetles occurring onPinusspp. The fungus has been recorded in South Africa, theUSA, France, Portugal and Spain and importantly, has been associated with pine root diseases in South Africa and theUSA. Nothing is known regarding the population genetics or origin ofG. alacris, although its association with root‐infesting beetles native to Europe suggests that it is an invasive alien in South Africa. In this study, microsatellite markers together with newly developed mating type markers were used to characterize a total of 170 isolates ofG. alacrisfrom South Africa and theUSA. The results showed that the genotypic diversity of the South African population ofG. alacriswas very high when compared to theUSApopulations. Two mating types were also present in South African isolates and theMAT1‐1/MAT1‐2ratio did not differ from 1:1 (χ2 = 1·39,P = 0·24). This suggests that sexual reproduction most probably occurs in the fungus in South Africa, although a sexual state has never been seen in nature. In contrast, the large collection ofUSAisolates harboured only a single mating type. The results suggest that multiple introductions, followed by random mating, have influenced the population structure in South Africa. In contrast, limited introductions of probably a single mating type (MAT1‐2) may best explain the clonality ofUSApopulations.