Sustainable agriculture by development of Brevibacillus brevis biocontrol methods for grey mould (Botrytis cinerea) of greenhouse crops
Lettuce and tomato field trials were performed in an unheated polytunnel in Aberdeenshire to investigate the efficacy and mode of activity of Brevibacillus brevis against grey mould disease (Botrytis cinerea). This was achieved by means of treating plants with whole cultures of B. brevis WT (containing gramicidin S and biosurfactant) and B. brevis E1 (containing biosurfactant only) and also with supernatant and spore fractions of such cultures so that the effects of treatments containing one, both or neither of the potentially active components, gramicidin S (bound to the bacterial spore) and biosurfactant (released into the culture medium) could be assessed. In winter lettuce, WT and E1 reduced grey mould by up to 79% (p=0.05) with no significant disease (p=0.05) between efficacy of these treatments. WT reduced disease by 59% in spring lettuce but at low significance (p=0.2) although marketable yields were significantly improved (p=0.05). The biocontrol treatments WT, E1, SWT and SE1 reduced (p=0.05) grey mould by up to 48% in tomato leaves and 73% of WT treated plants had no stem lesions, significantly more (p=0.05) than lesion-free control plants (17%). These results suggest that both the biosurfactant and gramicidin S play a role in disease reduction. The biosurfactant appears to be responsible for disease reduction on aerial plant surfaces with large surface areas whilst Gramicidin S reduces disease in regions of higher humidity, such as the base of lettuce plants and on tomato stems.