High intercontinental migration rates and population admixture in the sapstain fungus Ophiostoma ips.

Ophiostoma ips is a common fungal associate of various conifer-infesting bark beetles in their native ranges and has been introduced into non-native pine plantations in the Southern Hemisphere. In this study, we used 10 microsatellite markers to investigate the population biology of O. ips in native (Cuba, France, Morocco and USA) and non-native (Australia, Chile and South Africa) areas to characterize host specificity, reproductive behaviour, and the potential origin as well as patterns of spread of the fungus and its insect vectors. The markers resolved a total of 41 alleles and 75 haplotypes. Higher genetic diversity was found in the native populations than in the introduced populations. Based on the origin of the insect vectors, the populations of O. ips in Australia would be expected to reflect a North American origin, and those in Chile and South Africa to reflect a European origin. However, most alleles observed in the native European population were also found in the native North American population; only the allele frequencies among the populations varied. This admixture made it impossible to confirm the origin of the introduced Southern Hemisphere (SH) populations of O. ips. There was also no evidence for specificity of the fungus to particular bark beetle vectors or hosts. Although O. ips is thought to be mainly self-fertilizing, evidence for recombination was found in the four native populations surveyed. The higher genetic diversity in the North American than in the European population suggests that North America could be the possible source region of O. ips.

Characterisation of Ophiostoma species associated with pine bark beetles from Mexico, including O. pulvinisporum sp. nov.

Bark beetles (Coleoptera: Scolytidae) are common vectors of Ophiostoma species. These fungi include primary tree pathogens and important sapstain agents. In Mexico, Ips calligraphus and Dendroctonus mexicanus occur on many species of pine. Pinus maximinoi and P. pseudostrobus are the hosts of both species of insects. Little research has been done on ophiostomatoid fungi associated with pine bark beetles in Mexico. We recently obtained specimens of these bark beetles and their galleries from Mexico. The aim of the study was to isolate and identify Ophiostoma species associated with the two beetle species. In total, six ophiostomatoid species were found to be associated with them. These included Ceratocystiopsis minuta, Ophiostoma pluriannulatum, an O. galeiformis-like species, two unidentified Sporothrix spp., as well as a new species similar to O. adjuncti, O. ips, and O. montium, that we name as O. pulvinisporum sp. nov.

The Ophiostoma piceae complex in the Southern Hemisphere: a phylogenetic study.

The Ophiostoma piceae species complex incorporates several economically important species, including serious tree pathogens and agents of bluestain. The species in the complex are morphologically similar, but can be distinguished from each other based on morphology, biology, mating type studies and molecular data. At present, all the species in the complex are considered to be native to the Northern Hemisphere, most of them with a very wide distribution. Only a few sporadic reports of members of the complex are available from the Southern Hemisphere, where they are believed to have been introduced, including New Zealand, Australia, Chile, Brazil and Uruguay. This study aims to confirm the identity of isolates resembling O. piceae originating from three Southern Hemisphere countries, using mating compatibility and rDNA sequencing. Our results show that O. quercus is widely distributed throughout South Africa on both native and exotic hardwoods. O. quercus is also reported for the first time from Brazil, again from a native host. O. floccosum is reported for the first time from South Africa, but from an exotic Pinus sp. These results suggest that species of the O. piceae complex are common in the Southern Hemisphere, and that current views on the origins of especially O. quercus need to be reconsidered.