Glyphosate treatments for weed control affect early stages of root colonization byTuber melanosporumbut not secondary colonization

Abstract

The cultivation of the ectomycorrhizal fungusTuber melanosporumhas considerably spread in recent years throughout the world. During the first years of truffle cultivation, weed control is a key practice to improve the establishment of host trees and the proliferation of the fungus in the soil. Glyphosate is nowadays the most commonly used herbicide in Spanish truffle orchards. We explored the effect of glyphosate on the proliferation ofT. melanosporummycorrhizae, on extraradical mycelium and on the inoculum potential ofT. melanosporumspores in greenhouse experiments usingQuercus ilexseedlings as host plants. No detrimental effect on the secondary infection ofT. melanosporumwas found after three sequential glyphosate applications in young seedlings during one vegetative period. Instead, a change in the distribution of fine roots andT. melanosporummycorrhizae along soil depth was observed. On the other hand, results indicate that high application rates of glyphosate hinder the infectivity ofT. melanosporumspore inoculum, without apparent impact on the host performance. Our results suggest that glyphosate has the potential to jeopardise the role of the soil spore bank as inoculum source for the colonisation of new roots, also raising the question of whether glyphosate could hinder the presumed role of spores in sexual mating.