Sporulation of Phytophthora fragariae shows greater stimulation by exudates of non-mycorrhizal than by mycorrhizal strawberry roots

Arbuscular mycorrhizal fungi (AMF) show significant potential for biocontro l of Phytophthora spp., but there is little evidence for the mechanisms inv olved in the process. This study establishes that microorganism free exudat es from roots colonised by AMF result in significantly less sporulation of P. fragariae than those from uncolonised plants. Experiments in vitro showe d that after 48 h in the presence of exudates from strawberry roots colonis ed by Glomus etunicatum and G. monosporum, sporulation of P. fragariae was reduced by ca 67% and 64% relative to sporulation in the presence of uncolo nised roots. After 72 h sporulation was reduced by 83% and 89% respectively . These data were then confirmed in an in vivo system in which Phytophthora fragariae was inoculated into the mycorrhizosphere of either uncolonised s trawberry plants or those colonised by G. etunicatum. A similar h end was o bserved, with a 69% reduction in sporulation of P. fragariae after 72 h in the mycorrhizosphere of colonised plants relative to sporulation in the myc orrhizosphere of uncolonised plants.