Endophytic Bacillus subtilis ZZ120 and its potential application in control of replant diseases

An endophytic bacterial strain ZZ120 that was isolated from healthy stems of Prunus mume (family: Rosaceae) was identified as Bacillus subtilis based on biochemical and physiological assays and 16s rRNA, rpoB and tetB-yyaO / yyaR genes analysis. Both the culture filtrate and the n-butanol extract of strain ZZ120 showed strong growth inhibition activity in vitro against the replant disease phytopathogens Fusarium graminearum, Alternaria alternata, Rhizoctonia solani, Cryphonectria parasitica and Glomerella glycines. The active metabolite in the filtrate was found to be produced 24 h after inoculation and the concentration remained at a high level until 66 h and was quite thermally stable with more than 75% of the antifungal activity even after being held at 121°C for 30 min. In addition, the antifungal activity of the filtrate remained almost unchanged when the culture was exposed to a pH ranging from 1 to 8, but significantly reduced after the filtrate had been exposed to alkali conditions (pH 9 to 14) for 30 min. The antifungal compounds were isolated from n-butanol extract as a mixture of iturins. The strong antifungal activity suggested that the endophytic B. subtilis ZZ120 and its bioactive components might provide an alternative agent for the biocontrol of replant diseases.