Screening and identification of an antagonistic bacterium against blackhead disease of Korla fragrant pear

Abstract:

[Background] Blackhead of Korla fragrant pear is a kind of fungal disease caused by Alternaria brassicicola XL2 reported in recent years, which led to huge economic losses. Due to high fruit decay rate, it has become one of the most important postharvest diseases for Korla fragrant pear. [Objective] This study aims to isolate and identify effective antifungal strains to control the Blackhead of Korla fragrant pear, and preliminary dissect the possible antifungal mechanism, thus providing potential biocontrol bacteria candidates. [Methods] Bacterial strains were isolated from the surface of different healthy fruits harvested in Xinjiang. Antagonistic bacteria were screened by plate confrontation method with pathogen A. brassicicola XL2. The identification of the antifungal bacterial strain was based on morphological, physiological, and biochemical characteristics as well as 16S rRNA gene sequence analysis. The inhibitory effect of bacterial cell-free filtrate on the colony extension of the pathogen was determined, and the influence of bacterial cell-free fermentation filtrate on the mycelial growth condition of the pathogen was examined microscopically. The inhibitory effect of bacterial cultures on the pathogen growth in Korla fragrant pear fruits was further evaluated. [Results] Among the isolated ninety bacterial strains, strain Y2 isolated from the surface of nectarines, which was identified as Bacillus subtilis Y2, had strong anatagonism capability against the pathogen A. brassicicola XL2. Cell-free fermentation filtrate of Y2 strain significantly inhibited the colony extension of A. brassicicola XL2. The inhibitory rate of 2% cell-free filtrate against A. brassicicola XL2 was 70.96%. Cell-free filtrate of Y2 strain also severely disrupted the mycelial growth of the pathogen, which showed distortion, increased branch of the hyphae and dense structure at the tip of the hyphae. In addition, both the fermentation broth and cell-free filtrate of Y2 strain significantly inhibited spore germination of the pathogen. The fermentation broth of Y2 strain also showed good inhibitory effect against the pathogen lesion inoculated on Korla fragrant pear fruits, the inhibition rate calculated with lesion diameter and lesion depth were 37.66% and 42.74%, respectively. [Conclusion] Bacillus subtilis Y2 showed a good antifungal capability against A. brassicicola XL2, which is a novel potential biological control strain for the blackhead disease of Korla fragrant pear.