Trichoderma harzianum produces nonanoic acid, an inhibitor of spore germination and mycelial growth of two cacao pathogens

An isolate of Trichoderma harzianum Rifai from an infected cacao pod produces and secretes nonanoic (pelargonic) acid into a liquid culture medium. Nonanoic acid (NA) was very inhibitory to spore germination and mycelial growth of two cacao pathogens, Crinipellis perniciosa Stahel and Moniliophthora roreri Cif. H.C. Evans. It was highly active causing 75% inhibition of spore germination in an in vitro assay at a rate as low as 0.09 μM for M. roreri and 0.92 μM for C. perniciosa. Mycelial growth was comparatively less sensitive to inhibition, but still there was a 75% reduction in growth with 0.62 μM in M. roreri and 151 μM NA in C. perniciosa. In contrast, NA did not affect Trichoderma mycelial growth or spore germination at concentrations that were inhibitory to the pathogens. 6-pentyl-α-pyrone was also produced and secreted into the medium by T. harzianum, however; it was not antagonistic to the cacao pathogens. Although a number of metabolites produced by Trichoderma spp. have been identified in the past, this is the first report of NA production and secretion by any Trichoderma. The results suggest that NA may play a role in the successful use of some Trichoderma spp. isolates in the biocontrol of fungal diseases of plants.     

生防菌XC-1的筛选、鉴定及其对马铃薯黑痣病的防效研究

从马铃薯根际土壤中分离筛选得到对立枯丝核菌有较强拮抗作用的菌株XC-1,对其进行鉴定及生防特性分析,并评价其对马铃薯黑痣病的生防效果.形态学、16S rDNA和gyrB基因序列分析以及生理生化检测结果表明,XC-1菌株为枯草芽孢杆菌(Bacillus subtilis).XC-1菌株具有产纤维素酶、蛋白酶及嗜铁素和HC...     

Quantification of the biocontrol agent Pseudomonas fluorescens Pf153 in soil using a quantitative competitive PCR assay unaffected by variability in cell lysis- and DNA-extraction efficiency

Although often neglected, variability in cell lysis efficiency and DNA extraction yield represents the major hurdles of any polymerase chain reaction (PCR)-based quantification protocol in soil and other natural environments. In this study we developed a technique that minimizes the effects of these constraints, providing at the same time a reliable internal control to distinguish between PCR-inhibition and negative results. We used Pseudomonas fluorescens Pf153, a root-colonizing bacterium that shows biocontrol activity against tobacco and cucumber black root rot, as the target organism for PCR quantification. Prior to DNA extraction, the genetically engineered, cognate reference strain P. fluorescens CHA0/c2 was inoculated in a reference soil. CHA0/c2 in the reference soil and Pf153 in the soil sample were lysed in parallel and afterward the lysates were mixed in known proportions. CHA0/c2 carries the plasmid pME6031-cmp2 that contains an allelic variant (competitor) of the Pf153 specific sequence Pf153_2. In a quantitative competitive PCR (QC-PCR) assay the competitor allows the quantification of the target strain down to 0.66 Pf153 CFU/mg soil. Processing the reference strain in the same way as Pf153 enables the exact quantification of the target strain in biocontrol assays performed in natural soil, overcoming differences in DNA extraction efficiency and PCR amplification from different soil environments. This technique is easily adaptable to other Pseudomonas strains simply by replacing the competitor used here with one derived from a SCAR-marker which is specific for the strain of choice.     

土壤拮抗链霉菌R15菌株发酵产物的抑菌作用

对一株土壤拮抗链霉菌(Streptomycespp.)R15菌株发酵液的抑菌效果、热稳定性和酸碱稳定性以及作用机制进行了初步研究。结果表明,拮抗链霉菌R15发酵液对棉花枯萎病菌分生孢子萌发抑制作用强,抑制率达98.37%。烟草赤星病菌孢子萌发后芽管顶端膨大成球形,芽管停止生长;烟草炭疽病菌孢子萌发后不能产生附着胞,且芽管顶端有突起。处理烟草黑胫病菌和辣椒疫霉病菌菌丝畸变、扭曲、菌丝壁消解;R15通过菌丝缠绕、穿透、紧贴的方式重寄生于烟草黑胫病菌菌丝上,致使菌丝断裂。链霉菌R15发酵液的热稳定性和酸碱稳定性较强,在20～55℃,pH3～9范围内都具有抑菌活性。     

生防细菌复配对苹果主要病原真菌抑菌活性筛选及其稳定性

采用生长速率法测定4种生防细菌及其复配对5种苹果主要病原菌的抑制效果,并将筛选出的最佳复配生防细菌发酵液进行稳定性测定。结果表明,单一生防细菌发酵液中多粘类芽孢杆菌FS-1206对苹果树腐烂病菌的抑菌效果最好,为78.19%;当多粘类芽孢杆菌FS-1206与解淀粉芽孢杆菌TS-1203复配比例为2∶1时,其对苹果树腐烂病菌的抑菌率高达86.64%,抑菌效果显著优于单一生防细菌发酵液。稳定性测定结果表明,复配生防细菌(FS-1206∶TS-1203=2∶1)发酵液在紫外照射、高温和强酸强碱环境条件下,其抑菌活性均具有良好的稳定性。     

普城沙雷氏菌BU09的分离鉴定及其对疮痂链霉菌的防治效果

[目的]筛选马铃薯疮痂病的生防菌。[方法]从马铃薯疮痂病发病土壤中取样,经过稀释培养和二次划线纯化获得单克隆菌株,通过抑菌试验最终得到1株对马铃薯疮痂病具有较好抑制效果的细菌BU09,通过16S r DNA测序和系统进化分析对该菌株进行分子鉴定。[结果]细菌BU09属于普城沙雷氏菌,对马铃薯疮痂病具有较好的防治效果。[结论]试验结果为马铃薯疮痂病的田间防治提供了参考。     

木霉拮抗烟草赤星病菌菌株的筛选及其生防机制

 利用诱捕法从土壤中分离得到18株木霉(Trichoderma spp.)菌株,采用对峙法从中测定、筛选出一株对烟草赤星病菌(Alternaria alternata)具有极强拮抗作用的菌株(Tv－1),光学显微镜及透射电镜观察结果表明,Tv－1菌株的生防机制主要为生长竞争、重寄生作用以及产生生物活性类物质使病菌菌丝消解的直接抗菌作用,表现为Tv－1菌株菌丝生长迅速;能附着、缠绕于病菌菌丝上,并产生吸器侵入菌丝;同时还能分泌使病菌菌丝原生质浓缩、断裂、消解的物质。     

地黄枯萎病拮抗菌生防机制的初步研究

[目的]对地黄枯萎病拮抗菌的生防机制进行初步研究。[方法]对9株生防菌株的竞争作用、重寄生作用、抗生作用和对地黄土壤和根际微生物数量的影响进行研究。[结果]木霉T4、T3的生防机制较为复杂,具有拮抗作用和对营养和空间的竞争作用;放线菌S72、S15、S52和细菌B21、B6主要是对枯萎病病菌有拮抗作用;不同生防菌处理均对地黄土壤和根际微生物的数量有一定的影响。[结论]该试验为地黄枯萎病防治机理的研究提供了依据。     

6种放线菌抗药性标记及其在植株体内定殖能力测定

用抗药性标记法对6种生防放线菌进行标记,并测定其在黄瓜、小麦、大麦以及大豆体内的定殖能力,发现15—3可以在黄瓜、小麦以及大麦的根部定殖,在黄瓜根部的定殖能力强于在其它两种作物根部的定殖能力。6种生防菌对黄瓜、小麦、大麦以及大豆种子萌发或苗期生长没有明显抑制作用;菌株15—3对大麦、黄瓜以及大豆具有不同程度的促生作用;菌株SE2和A4发酵液对黄瓜的生长有抑制作用。     

放线菌153菌株的定殖和促生效果研究

研究放线菌菌株153对番茄和茄子的促生效果、基本促生机制以及在植株体内的定殖规律。结果表明,不同菌液浓度的153发酵菌液对种子萌发和芽的生长均具有促进作用,且对植株的生长性状有明显的影响,对植株鲜质量和干质量的影响最显著,鲜质量和干质量分别比对照增加114.69%、99.75%和124.06%、96.60%。放线菌菌株153在番茄、茄子根际及体内都可稳定定殖;14~30 d之间,153在植株根内及茎内的定殖数量随时间推移基本不变,菌量分别保持在104和103cfu/g。放线菌153可通过定殖提高植株体内的叶绿素含量以及根系还原强度而促进番茄和茄子的生长。