Putative source of the invasive Sirex noctilio fungal symbiont, Amylostereum areolatum, in the eastern United States and its association with native siricid woodwasps

Two genotypes of the fungal symbiont Amylostereum areolatum are associated with the invasive woodwasp Sirex noctilio first found in North America in 2004. S. noctilio is native to Europe but has been introduced to Australasia, South America and Africa where it has caused enormous losses in pine plantations. Based on nucleotide sequence data from the intergenic spacer region (IGS) of the nuclear ribosomal DNA, the A. areolatum genotypes found in North America are most similar to genotypes found in Europe, and not to genotypes from the southern hemisphere. Although two IGS strains of A. areolatum were found in North America it cannot be stated whether A. areolatum was introduced to North America from Europe once or twice based on our study. Genetic groupings formed by sequencing data were in most cases supported by vegetative compatibility groups (VCGs). Other siricid woodwasp species in the genus Sirex are native to North America. The North American native Sirex edwardsii emerging from the same tree as S. noctilio carried the same strain of A. areolatum as S. noctilio. The North American native Sirex sp. ‘nitidus’ collected outside the geographical range of S. noctilio carried a unique strain within A. areolatum. Our findings of A. areolatum in the native North American species, S. sp. ‘nitidus’, contrast with the previous view that A. areolatum was not present in North America before the accidental invasion of S. noctilio.