Contents Summary893I.Introduction894II.Induced defence mechanisms in trees894III.Systemic induction of resistance897IV.Defence signalling networks900V.Future prospects: what does IR offer for management of forest systems?902Acknowledegements904References904 Summary Tree resistance can be enhanced by a variety of biotic and abiotic inducers, including nonpathogenic and pathogenic microbes, and herbivores, resulting in enhanced protection against further biotic injury. Induced resistance (IR) could be a valuable tool in sustainable pest management. IR has been actively studied in herbaceous plant species, and, in recent years, in woody plant species, and is fast emerging as an intriguing, eco‐friendly concept for enhancing tree resistance. However, before application of IR becomes possible, there is a need to increase our knowledge of the mechanisms of defence in forest trees. A richer understanding of these phenomena will play a critical role in developing sustainable integrated pest management strategies. This review summarizes our current knowledge of IR in forest trees, focusing on inducible defence mechanisms, systemic induction of resistance and phytohormone signalling networks. We conclude by discussing the potential advantages and limitations of applying IR‐based management tools in forest systems.

Recent studies have investigated interspecific variation in resistance of ash (Fraxinus spp.) to the exotic wood-boring beetle, emerald ash borer (EAB, Agrilus planipennis). Manchurian ash (Fraxinus mandshurica) is an Asian species that has coevolved with EAB. It experiences little EAB-induced mortality compared to North American ashes. Host phloem chemistry, both constitutive and induced, might partly explain this interspecific variation in resistance. We analyzed the constitutive phloem chemistry of three ash species: Manchurian ash and North American white (Fraxinus americana) and green (Fraxinus pennsylvanica) ash. Analysis of the crude phloem extracts revealed the presence of an array of phenolic compounds including hydroxycoumarins, a monolignol, lignans, phenylethanoids, and secoiridoids. Both qualitative and quantitative differences were observed among the three ash species. Hydroxycoumarins and the phenylethanoids, calceloariosides A and B, were present only in the phloem of Manchurian ash and might represent a mechanism of resistance against EAB.

No abstract

Sequence-based markers were developed to study the genetic structure and reproductive biology of the ectomycorrhizal fungus Suillus pungens Thiers & Smith in a Bishop pine (Pinus muricata D. Don) forest. Six different basidiome genotypes were found in a 1200 m# area. Five of the six genotypes were represented by single basidiomes. The remaining genotype comprised 13 basidiomes and covered an area of at least 300 m#, with maximum measured dimensions of 40 m and 14 m. This is the largest genet of an ectomycorrhizal fungus described to date, and is likely the result of vegetative growth, because analysis of single spore isolates eliminates the possibility of genetic identity resulting from either apomixis or fortuitously indistinguishable recombinant genotypes. Genetic analysis also shows that although out-crossing appears to predominate in the population, at least a low percentage (1n4 %) of spores are secondarily homothallic.The combination of extensive vegetative growth and abundant fruiting suggests S. pungens utilizes more carbon than might be expected for a species which accounts for 3 % of the total ectomycorrhizal abundance at the site. Additional carbon might come from either more efficient host-fungus transfer, pooling of carbon from the roots of different host plants, or saprophytism.

No abstract