Modeling PWN-induced wilt expression: A mechanistic approach

Abstract

Pinewood nematode [PWN] (Bursaphelenchus xylophilus) is a saprophytic organism that usually exploits dead or dying trees. Adult feeding by its main distribution vector, longhorn beetles of the genus Monochamus, can introduce the organism into healthy trees, without any apparent effects on plant activity. Unusually, and in a number of geographical regions, PWN has been shown as the causal agent for the death of a mature host tree within a short time after introduction of the nematode to the vascular system of the tree. A body of evidence has demonstrated that, with significant seasonal variation in water availability combined with elevated temperatures during summer, the organism induces wilt expression in susceptible tree species. Under certain environmental conditions the severity of wilt expression can result in death of the host plant. This paper uses current understanding of plant-host interactions as the basis for assumptions incorporated into a mechanistic model describing relevant process dynamics. The model describes plant host physiological behaviour following PWN infestation that ultimately may result in death of the host plant. Several simulations are run for sites in the Iberian Peninsula, including those where fatal infestation of pines with PWN occur, indicate a high likelihood of host death, both immediately and in the year following infestation. Globally in regions where the nematode occurs and where environmental conditions do not result in significant tree stress, PWN does not result in wilting and host death. An ongoing observational experiment using PWN-infested trees, suggests a good correlation between simulated and observed results. It is proposed that, with further refinement and validation, the model may be suitable for developing a generic framework to predict the vulnerability of different hosts to the organism across a range of geographical regions. © 2008 Springer Science+Business Media B.V.