Interactions among a soil-borne pathogen, mycorrhizal fungi and rhizobacteria

Wheat crops are known to be devastated by infections of soil-borne pathogens, especially the fungus Gaeumannomyces graminis var. tritici (Ggt) that causes ‘take-all’. Plant growth promoting rhizobacteria (PGPR) such as Pseudomonas fluorescens have received much attention as biocontrol agents against Ggt, mainly due to their ability to produce antibiotics. The polycetide secondary antimicrobial metabolite 2,4-diacetylphloroglucinol (DAPG) is produced by a number of fluorescent pseudomonad strains and is known to suppress Ggt. Another soil microbial group which have been under investigation for their biocontrol potential against Ggt, are arbuscular mycorrhizal (AM) fungi which have the potential to out-compete Ggt and improve host plant nutrition and vigour. In this thesis, I report results from experiments that investigate interactions among AM fungi, Ggt, and DAPG-producing bacteria. A central hypothesis is that carbon flow from plants and AM fungi stimulates DAPG production. I therefore focus on interactions among AM fungi, Ggt and bacteria in vivo with wheat plants and in vitro with only fungal exudates. The synergistic co-operation of pseudomonads and AM fungi against Ggt was demonstrated and the fungal exudates (from AM and Ggt) produced both in vitro and in vivo increased DAPG production by P. fluorescens. The ecology and functioning of beneficial AM fungi was found not to be influenced by the presence of either Ggt or DAPG, highlighting the potential sustainable suppression of “take all” in wheat rhizosphere.EThOS - Electronic Theses Online ServiceGBUnited Kingdo