Take-all disease is systemically reduced in roots of mycorrhizal barley plants

The systemic effect of root colonization by the arbuscular mycorrhizal fungus Glomus mosseae on infection of barley by Gaeumannomyces graminis var. tritici (Ggt) was studied. In split-root systems of barley one side was inoculated with G. mosseae and the other side was inoculated with Ggt.Root infection by Ggt was systemically reduced when barley plants showed high degrees of mycorrhizal root colonization, whereas a low mycorrhizal root colonization exhibited no effect on Ggt infection. Our results show a clear systemic bioprotectional effect depending on the degree of root colonization by the mycorrhizal fungus. At a higher mycorrhizal colonization rate the concentration of salicylic acid (SA) was increased in roots colonized by the mycorrhizal fungus but no systemic increase of SA could be measured in non-mycorrhizal roots of mycorrhizal plants, indicating that the systemic bioprotectional effect against Ggt is not mediated by salicylic acid.