Interactive effects of drought and pathogens in forest trees

Abstract

-This review synthesizes the available knowledge on drought-disease interactions in forest trees with a focus on (1) evidence and patterns of drought-disease interactions, (2) current understanding of processes and mechanisms, and (3) three well documented cases studies. The first part is based on the analysis of a database of slightly more than one hundred studies, obtained by keyword searches combining drought, diseases or pathogens, and forest trees. A large majority of published studies referred to a positive association between drought and disease, i.e. disease favoured by drought or drought and disease acting synergistically on tree health status, with a predominance of canker/dieback diseases, caused by pathogens like Botryosphaeria, Sphaeropsis, Cytospora and Biscognauxia (Hypoxylon). The type of disease-related variables (incidence vs. severity) and the intensity and timing of water stress were shown to be significant factors affecting the drought-infection interaction. Interactions with other abiotic stresses and species-specific and genetic effects, related to host or pathogen, have also been reported. Direct effects of drought on pathogens are generally negative, although most fungal pathogens exhibit an important plasticity and can grow at water potentials well below the minimum for growth of their host plants. Studies on indirect effects of drought on pathogens through other community interactions are still relatively scarce. Positive drought-infection effects can mostly be explained by indirect effects of drought on host physiology. The predisposition and the multiple stress hypotheses are presented, as well as recent developments in the study of the molecular basis of abiotic and biotic stress, and their interactions. Sphaeropsis sapinea on pines, Biscognauxia mediterranea on oaks and root pathogens in declines associated with drought provide illustrative examples, treated as case studies, of pathogens of current significance associated with drought. The conclusion highlights some knowledge gaps, e.g. the role of latent parasites and the shift to a pathogenic stage, or the genetics of some fungal groups. The need for prevention of pathogen dispersal, especially crucial in the case of latent pathogens, is emphasized. drought / water stress / pathogenic fungi / predisposition / forest trees Résumé -Interactions entre sécheresse et agents pathogènes chez les arbres forestiers. Cette revue synthétise les connaissances actuelles sur les interactions entre sécheresse et maladies chez les arbres forestiers, avec trois grandes parties : (1) description des types d'interaction ; (2) connaissances acquises sur les mécanismes impliqués ; (3) trois études de cas bien étudiées. La première partie est basée sur l'analyse d'une base de données d'une centaine d'études, sélectionnées par recherche sur mots clés. La plupart de ces études se rapportent à des maladies favorisées par la sécheresse ou à un effet synergique entre sécheresse et maladie sur l'état sanitaire des arbres, avec une prédominance de m...

Comparative study of genome-wide plant biomass-degrading CAZymes in white rot, brown rot and soft rot fungi

“…CO27-5 v1.0 (Wu et al 2017), Neurospora crassa OR74A v2.0 (Galagan et al 2003), Lecythophora sp. AK0013 v1.0 (Damm et al 2010; U’Ren et al 2012), Botryosphaeria dothidea (Slippers et al 2004; Desprez-Loustau et al 2006; Schoch et al 2006; Slippers and Wingfield 2007; Piškur et al 2011), Fusarium oxysporum sp. lycopersici 4287 v2 (Ma et al 2010) with available annotated genomes were retrieved from the JGI (Joint Genome Institute) MycoCosm database.…”

Monoterpene responses to interacting effects of drought stress and infection by the fungus Heterobasidion parviporum in two clones of Norway spruce (Picea abies)

“…In temperate zones, drought is associated with enhancement of disease development in several tree species by many pathogens that may affect both the tree crown and the root system (Madar et al, 1989). Indeed, the heat wave and the severe drought that Western Europe experienced in 2003 had serious consequences for forest health (Desprez-Loustau et al, 2006).…”

The contribution of remote sensing to the assessment of drought effects in forest ecosystems

“…-the development of digital analysis tools adapted to the assessment of scattered damage on very fine resolution data; -the development of strategies for a spatial assessment of damages including the use of remote sensing data; -developments in a number of water stress issues, such as the identification of potential risk areas [12], its interactions with biotic factors [26] and its impact on biodiversity [4];…”