Abstract
The antagonist bacterium Brevibacillus laterosporus ZQ2 with broad-spectrum antifungal activity was isolated from an apple rhizosphere at Mount Tai in China. The fermentation medium for the production of antifungal substances from ZQ2 was statistically optimized. In one-factor-at-a-time experiments, five components, including carbon sources, nitrogen sources, and inorganic salt, were selected. Two factors were determined as critical based on the Plackett-Burman design. Steepest ascent experiments were then used to determine the design space containing the optimum point, followed by application of the response surface methodology. A quadratic model fitting the actual production was established using a central composite design. The obtained optimum medium for the antifungal substances production consisted of the following (in g/L): glucose, 15.6; soybean meal, 8.2; starch, 20; ammonium sulfate, 2; and monopotassium phosphate, 1. Furthermore, the inhibition rate of the substances against Rhizoctonia solani increased by more than 132% compared with the control. B. laterosporus ZQ2 strongly inhibited the growth of many apple phytopathogens in vitro. The inhibition rates against different fungi ranged from 55.26 to 79.02%. As well, the strain significantly reduced the disease damage caused by R. solani in the in vivo tests. Maximum disease protection (46.89%) was recorded when the bacterium applied 3 days before pathogen inoculation. Key words: Brevibacillus laterosporus, antifungal activity, fermentation optimization.
Highlights
Rhizoctonia solani, Penicillium expansum, and Botrytis cinerea are common and destructive phytopathogenic fungi with a wide range of hosts and are major constraints to apple production (Sharma et al, 2009)
The antagonist bacterium Brevibacillus laterosporus ZQ2 with broad-spectrum antifungal activity was isolated from an apple rhizosphere at Mount Tai in China
The antifungal activities of ZQ2 were determined on a potato dextrose agar (PDA; 200 g of potato, 20 g of glucose, 10 g of beef extract, 2 g of ammonium sulfate, 1 g of sodium chloride, and 20 g of agar in 1 L distilled water) plate using R. solani as the fungal indicator (Dake et al, 2007)
Summary
Rhizoctonia solani, Penicillium expansum, and Botrytis cinerea are common and destructive phytopathogenic fungi with a wide range of hosts and are major constraints to apple production (Sharma et al, 2009). Chemical control remains the primary method for preventing the diseases caused by these fungi. Numerous synthetic chemicals comprise the majority of the market share of fungicides (Imre et al, 2009; Jönssson et al, 2010). Because of the increasing number of resistant mutants and environmental pollution, the demand for more effective and safer fungicides with novel modes of action is increasing (Zhenzhen et al, 2010). The use of antagonistic microorganisms for biological control is considered to be one such alternative method. Over the last few years, various antifungal bacteria
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