Population biology of the forest pathogen Heterbasidion annosum:implications for forest management

Abstract

Heterobasidion annosumranks as one of the most destructive pathogens in North American coniferous forests. Understanding the popula­tion biology of this fungus may facilitate un­derstanding not only the basic biology of the organism, but also the general patterns of disease development, modes of host-pathogen interactions, effect of management practices on the dynamics of dispersal, establishment, and evo­lution of the pathogen and/or the host. In turn, this information allows for a more profound understanding of the general health of an eco­system, leading to more refined and targeted management practices. In the case of H. anno­sum, previous research has elucidated aspects of the etiology and spread of disease for host species such as European pines and spruces. In these instances, primary stump infection and root-to-root secondary contagion appear to be major avenues of disease development. No in­formation is available on the true fir/H. anno­sum pathosystem for Western North America, although the pathogen is increasingly affecting this tree species. Because of the different hosts involved, of the different biogeographic region, and of the significant genetic divergence among groups of H. annosum characterized by different host preferences, it is not possible to extrapolate results from other regions of the world to Western North America, and in par­ticular to California. Two genetically distinct intersterility groups (ISGs) of the fungus are present in California: the S ISG mostly infects true firs, hemlocks, Douglas-firs, and sequoias, while the P ISG is found mostly on pines, in­cense cedars, and junipers. These two ISGs are known to mate in the laboratory, but evidence of mating in nature has been gathered only recently. Still, there is no understanding of the frequency of mating and gene flow between the two groups. In these last years the authors? research effort has been to elucidate the dynamics of fungal estab­lishment and spread in California mixed coni­fer forests with a predominance of true fir. The scale of analyses has ranged from small scale studies designed to understand the ge­netic structure of pathogen populations in indi­vidual mortality centers to larger analysis at the broader regional level; the latter analyses have been designed to shed light on medium to long distance gene flow between demes of one ISG and even potentially be­tween ISGs. One focus of the authors has been to re­late the genetic structure of this organism to forest stand characteristics in the attempt to un­derstand the impact of forest to understand the impact of forest management on the population biology of this organism, on the epidemiology of the disease, and on the sever­ity of the mortality associated with this pathogen.

Citation

Garbelotto, M.; Otrosina, W.J.; Cobb, F.W.; Bruns, T.D. 1998. Population biology of the forest pathogen Heterbasidion annosum:implications for forest management. In: Proceedings of the 46th annual meeting; California Forest Pest Council; 1997 November 12-13; Sacramento, CA. [Place of publication unknown]: [Publisher unknown]: p. 24-35.