Virulence of, and interactions among, mountain pine beetle associated blue-stain fungi on two pine species and their hybrids in Alberta

Abstract

Mountain pine beetle (MPB) is the most serious pest of lodgepole pine in western Canada, and it is predicted to spread into boreal jack pine within the next few years. Colonization of host trees by MPB-associated blue-stain fungi appears to be required for successful beetle reproduction. Three species of blue-stain fungi, Grosmannia clavigera (Robinson-Jeffery and Davidson) Zipfel, de Beer, and Wingfield (≡ Ophiostoma clavigerum (Robinson-Jeffery and Davidson) Harrington), Ophiostoma montium (Rumbold) von Arx, and Leptographium longiclavatum Lee, Kim, and Breuil, are associated with MPB in Alberta. In inoculation experiments, all three fungi caused lesions on lodgepole pine, jack pine, and their hybrids. On average, lesions were longer on jack pine and hybrids than on lodgepole pine, suggesting that fungal development will not be a barrier to MPB success in these trees. Differences in lesion length caused by the three fungal species were minimal, with significant differences observed only on hybrid pine and between O. montium and the other fungal treatments. On average, lesions caused by combinations of the three fungi (pair-wise and all together) did not differ significantly in length from those caused by the fungi singly, and none of the fungal species competitively excluded any of the others. These observations suggest that all three species are pathogenic to boreal pines and that the virulence of all three species is comparable.

The Role of Phytopathogenicity in Bark Beetle–Fungus Symbioses: A Challenge to the Classic Paradigm

“…Studies employing low numbers of inoculations to living trees have been used to assess the length of lesions that result from fungal colonization of the phloem. Under the tree killing hypothesis, lesion length is used as a proxy for virulence and longer lesions are assumed to be produced by more virulent associates (64,65,80,82). In this context, lesion length is used to assess the relative value of each fungus to the bark beetle.…”

Bark beetle-associated fungi in Fennoscandia with special emphasis on species of Ophiostoma and Grosmannia

“…Christiansen 1985, Solheim et al 1993, Yamaoka et al 1995, Krokene and Solheim 1998, Kirisits 1998. The lesion length caused by the fungal infestation has been used as a measure to study the virulence of a fungus (Matsuya et al 2003, Rice et al 2007. Under the tree killing hypothesis, the most virulent fungal associates are believed to be the most effective in killing the tree, and therefore the most useful for bark beetles (Yamaoka et al 1990, Solheim andSafranyik 1997).…”

Evolving symbioses between insects and fungi that kill trees in Canada: new threats associated with invasive organisms

“…Another hypothesis is that interspecific competition between the fungal associates based on fungal virulence to pine is a mechanism that may explain the differences in the abundance of the fungal associates; G. clavigera was found to be more virulent on lodgepole pine and lodgepole pine × jack pine hybrids than O. montium but there was no difference between the two fungi on jack pine (Rice et al 2007a). A second inoculation study that included all three ophiostomatalean fungi found comparable virulence between all fungi and that lodgepole pine was less susceptible to the fungi than the hybrids with jack pine and pure jack pine, as assessed by lesion length (Rice et al 2007b).…”