Host responses in Norway spruce roots induced to the pathogen Ceratocystis polonica are evaded or suppressed by the ectomycorrhizal fungus Laccaria bicolor

Abstract

The outcome of a compatible mycorrhizal interaction is different from that in a compatible plant-pathogen interaction; however, it is not clear what mechanisms are used to evade or suppress the host defence. The aim of this work is to reveal differences between the interaction of Norway spruce roots to the pathogen Ceratocystis polonica and the ectomycorrhizal Laccaria bicolor, examine if L. bicolor is able to evade inducing host defence responses typically induced by pathogens, and test if prior inoculation with the ectomycorrhizal fungus affects the outcome of a later challenge with the pathogen. The pathogen was able to invade the roots and caused extensive necrosis, leading to seedling death, with or without prior inoculation with L. bicolor. The ectomycorrhizal L. bicolor colonised primary roots of the Norway spruce seedlings by partly covering, displacing and convoluting the cells of the outer root cortex, leaving the seedlings healthy. We detected increased total peroxidase activity, and staining indicating increased lignification in roots as a response to C. polonica. In L. bicolor inoculated roots there was no increase in total peroxidase activity, but an additional highly acidic peroxidase isoform appeared that was not present in healthy roots, or in roots invaded by the pathogen. Increased protease activity was detected in roots colonised by C. polonica, but little protease activity was detected in L. bicolor inoculated roots. These results suggest that the pathogen efficiently invades the roots despite the induced host defence responses, while L. bicolor suppresses or evades inducing such host responses in this experimental system.

Fertility‐related interplay between fungal guilds underlies plant richness–productivity relationships in natural grasslands

“…However, this appears to be a context‐dependent mechanism, because the significant association of potential plant pathogens with both plant components was observed at only the low‐nutrient site where significant negative interplay between mycorrhizal fungal and potential plant pathogen abundances occurred. Mycorrhizal fungi can confer protection to host plants against attack by plant pathogens (Wehner et al ., ; Nagy & Fossdal, ). The higher mycorrhizal fungal abundance at the low‐nutrient site relative to the high‐nutrient site might cause a more pronounced suppression effect by mycorrhizal fungi on potential plant pathogens along the plant richness gradient.…”

Extreme rainfall affects assembly of the root‐associated fungal community

“…(3) Increased diversity and relative abundance of root pathogens were associated with the rainfall event. Mycorrhizal fungi may play a vital role in protecting plants from attack by pathogens, and increased colonization by pathogens could be a consequence of reductions in the diversity and composition of ECM fungi (Nagy & Fossdal, ).…”

The role of locally adapted mycorrhizas and rhizobacteria in plant–soil feedback systems

“…But mycorrhizal benefits are not solely based on mineral nutrient acquisition and transfer (Newsham, Fitter & Watkinson 1995a). Both AM and EM fungi have been shown to reduce plant drought stress (Aug e 2001; Lehto & Zwiazek 2011), suppress plant pathogens (Schelkle & Peterson 1997;Sikes, Powell & Rillig 2010;Jung et al 2012;Nagy & Fossdal 2013) and either directly or indirectly influence intra-and interspecific plant competition (Rinaudo et al 2010;Hodge & Fitter 2013).…”

“…Both AM and EM fungi have been shown to reduce plant drought stress (Augé ; Lehto & Zwiazek ), suppress plant pathogens (Schelkle & Peterson ; Sikes, Powell & Rillig ; Jung et al . ; Nagy & Fossdal ) and either directly or indirectly influence intra‐ and interspecific plant competition (Rinaudo et al . ; Hodge & Fitter ).…”