库尔勒香梨黑头病拮抗菌的筛选和鉴定

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

摘要:

【背景】库尔勒香梨黑头病是近年来发现的一种由芸薹生链格孢菌(Alternaria brassicicola) XL2引起的采后病症，由于其高侵染率和高腐烂率造成了极大的经济损失，目前已成为库尔勒香梨采后储运的主要防治病症之一。【目的】发掘高效的库尔勒香梨黑头病拮抗菌，探索拮抗菌株的抑菌作用，为其生物防治提供潜在资源菌。【方法】从采后健康果蔬表面分离不同微生物，采用平板对峙法，以A. brassicicola XL2为靶标菌筛选具有拮抗作用的菌株，结合形态学观察、生理生化检测和16S rRNA基因序列分析鉴定拮抗菌株分类地位；检测拮抗菌无菌滤液对A. brassicicola XL2的抑制效应，显微观察拮抗菌对A. brassicicola XL2菌丝生长的影响；验证拮抗菌发酵液在库尔勒香梨果实上的抑菌活性。【结果】从新疆油桃表面分离获得90株菌，其中菌株Y2对A. brassicicola XL2有较强拮抗作用，经鉴定其为枯草芽孢杆菌(Bacillus subtilis)。菌株Y2的无菌滤液对A. brassicicola XL2菌落生长具有明显抑制作用，2%的无菌滤液抑菌率达到70.96%；Y2无菌滤液造成A. brassicicola XL2菌丝扭曲变形、分枝增加、尖端出现致密结构等异常现象；Y2发酵液和无菌滤液明显抑制A. brassicicola XL2的孢子萌发；Y2发酵液在库尔勒香梨果实上具有较高抑菌活性，对库尔勒香梨病斑直径抑制率达到37.66%，深度抑制率达到42.74%。【结论】枯草芽孢杆菌(B. subtilis) Y2能有效抑制A. brassicicola XL2的生长，对库尔勒香梨黑头病具有显著的生物防治效果。

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.