http://www.ibiblio.org/pub/academic/agriculture/sustainable_agriculture/faqs/fungi-faq.html#4. Mycorrhizae and their significance said:The ectomycorrhizal fungi have the added advantage of being able to produce antib iotic substances that inhibit the fungal pathogens. Prior colonization by mycorrhizal fungi may also stimulate the root to produce natural defensive wall structures and chemicals (chitinases and phytoalexins) that protect the root from attack by pathogens. The mycorrhizosphere (or area on and aroun d the root of mycorrhizal roots) also contains communities of helpful microorganisms including fungi and bacteria that are anta onistic to pathogens and that solubilize nutrients such as rock phosphate.
http://www.mycorrhiza.com/index.php?cid=22 said:Some specific mycorrhizal fungi like Glomus mosseae (Figure 10) and Glomus intraradices are particularly effective in preventing fusarium, pythium, and phytophora infections (St-Arnauld et al 1995; Sitaramaiah and Sikora 1981; Baghel and Bhatti 1990))