Bacillus megaterium shows potential for the biocontrol of septoria tritici blotch of wheat

Control of septoria tritici blotch (STB) of wheat caused by the fungal pathogen Mycosphaerella graminicola is heavily reliant on fungicide application. Rapid emergence of fungal isolates resistant to Quoine outside Inhibitors (QoI) and with reduced sensitivity to triazole-based fungicides necessitates the development and adoption of alternative control strategies. A collection of bacteria originating from barley leaves and grain, oat chaff and wheat rhizospheres and leaves were screened for their ability to control STB. A total of seven bacteria were further assessed under controlled environmental conditions and these inhibited STB development by up to 92%. Three of these bacteria [Pseudomonas fluorescens (strains MKB21 and MKB91) and a Bacillus megaterium (strain MKB135)] were assessed for their abilities to control STB on adult wheat plants in small-scale field trials, conducted both in 2004 and 2006. In these trials only B. megaterium (strain MKB135) consistently retarded STB development (by up to 80%). Additional in vitro seedling studies showed that both B. megaterium cell wall components and its culture filtrate and P. fluorescens strain MKB91 culture filtrate were capable of inhibiting disease development (by 62, 36 and 52%, respectively). While none of the three bacteria directly inhibited fungal growth in dual culture plate assays, in dual liquid culture assays volatiles produced by these bacteria reduced fungal biomass production by ⩾43%. Thus the ability of the most promising bacterium, B. megaterium strain MKB135, to reduce STB severity may be the result of a combination of different mechanisms.