Effects of bacteria-free filtrate fromBacillus megateriumstrain L2 on the mycelium growth and spore germination ofAlternaria alternata

Strain L2 (a Bacillus megaterium species that was isolated from tobacco's rhizosphere) was applied to inhibit the pathogen Alternaria alternata in an attempt to reduce tobacco brown spot disease. This study focused on inhibition experiments, in which culture filtrate inhibited A. alternata’s mycelium growth, its spore germination rate and its spore output. The results indicated that an approximately 1.5%–20% concentration of the bacteria-free filtrate, could effectively inhibit hyphae growth. Additionally, bacterial suppression of germ tubes and mycelium growth was observed, rather than lysis. Furthermore, the filtrate caused some of the germinal tubes to undergo vacuolization and even rupturing. The inhibitory effect was associated with the change of the concentration: the greater the concentration, the greater the impact on A. alternata.