人参(Panax ginseng)根系分泌物成分对人参致病菌的化感效应

采用室内培养结合生物学测定的试验方法,研究了不同浓度人参(Panax ginseng)根系分泌物成分苯甲酸、邻苯二甲酸二异丁酯、十六酸和2,2-二(4-羟苯基)丙烷对人参立枯丝核菌(Rhizoctonia solani)、黑斑菌(Alternaria panax)、疫病菌(Phytophthora cactorum)、菌核菌(Sclerotinia schinseng)、锈腐菌(Cylindrocarpon destructans)和绿色木霉菌(Trichoderma viride)菌落生长及孢子萌发的化感效应.结果显示,不同浓度人参根系分泌物成分对人参致病菌及绿色木霉菌的化感效应存在显著差异.苯甲酸浓度与人参立枯丝核菌、菌核菌和锈腐菌菌落生长以及人参黑斑菌、锈腐菌孢子萌发呈负相关,与人参黑斑菌、绿色木霉菌菌落生长呈正相关;对人参疫病菌菌落生长的化感效应表现为低浓度和高浓度抑制,中浓度促进.邻苯二甲酸二异丁酯浓度与人参立枯丝核菌、黑斑菌、菌核菌和绿色木霉菌菌落生长以及人参黑斑菌孢子萌发呈负相关;对人参锈腐菌菌落生长和孢子萌发表现为低浓度和高浓度抑制,中浓度促进;对人参疫病菌菌落生长表现为低浓度和中浓度抑制,高浓度促进.2,2-二(4-羟苯基)丙烷浓度与人参立枯丝核菌、黑斑菌、疫病菌、绿色木霉菌菌落生长以及人参黑斑菌、锈腐菌孢子萌发呈负相关;对人参菌核菌、锈腐菌菌落生长表现中浓度促进,高浓度抑制.十六酸浓度与人参锈腐菌、疫病菌和绿色木霉菌菌落生长呈正相关,与人参锈腐菌孢子萌发呈负相关,对黑斑菌孢子萌发表现为中浓度抑制.4种根系分泌物的等量混合物浓度与人参致病菌及拮抗木霉菌菌落生长速率呈负相关.     

骏枣内生生防细菌的分离、筛选与鉴定

选择交城骏枣(Zizyphus jujube cv.Jiaocheng Junzao)作为分离内生细菌的材料,从中共分离到18株内生菌株,运用平板对峙法从中筛选出5株对大枣病原菌及部分植物病原菌有拮抗作用的内生细菌。抑菌试验结果表明:筛选出的5株细菌对刺盘胞菌Colletotrichum gloeosporides、链格孢菌Alternaria alternata、尖孢镰刀菌Fusarium oxysporium、烟草赤星病菌Alternarial longipes、稻瘟病菌Pyricularia oryzae、人参立枯病菌Rhizoctonia solani、人参菌核病菌Sclerotinia schinseng和小麦根腐病菌Bipolaris sorokiniana均有一定的抑菌活性。对这5株内生细菌进行了形态特征观察和生理生化鉴定。     

天山大峡谷原始森林黏细菌的分离鉴定及其抗菌活性

【背景】黏细菌是一类具有多细胞群体行为特征的高等原核生物,其对植物病原真菌和细菌的捕食特性使其在植物病害防治方面具有重要的应用潜力。【目的】探究乌鲁木齐天山大峡谷原始森林可培养黏细菌的多样性并分析其抗菌活性,为发掘黏细菌生防菌株奠定基础。【方法】以天山大峡谷原始森林采集的土样和腐木为分离材料,采用兔粪诱导法和被捕食菌诱导法从中分离纯化黏细菌菌株,结合形态学观察、生理生化测定和16S rRNA基因序列分析确定其分类地位,并以6种植物病原真菌[大丽轮枝菌(Verticillium dahliae)、尖孢镰刀菌萎蔫专化型(Fusarium oxysporum f. sp. vasinfectum)、拟轮枝链孢霉(Fusarium verticillioides)、立枯丝核菌(Rhizoctonia solani)、黄色镰刀菌(Fusarium culmorum)、细极链格孢菌(Alternaria tenuissima)]和1种植物病原细菌[梨火疫病菌(Erwinia amylovora)]为靶标菌,通过平板对峙法和菌苔捕食法测定其抗菌活性。【结果】从采集的样品中分离出70株菌株,经纯化后获得36株黏细菌纯培养物。经鉴定隶属于4个属,黏球菌属(Myxococcus) 30株、孢囊杆菌属(Cystobacter) 3株、珊瑚球菌属(Corallococcus) 2株和原囊菌属(Archangium) 1株。抗菌活性分析显示,本研究获得的36株黏细菌至少对2种植物病原真菌有抗菌活性,表现出广谱的抗真菌活性,初步筛选出一株菌株NSE37-1兼具广谱和高效抗真菌活性;供试的15株黏细菌对梨火疫病菌均具有捕食活性,初步筛选出一株对梨火疫病菌具有较强捕食能力的黏细菌菌株NSE25。【结论】天山大峡谷可培养黏细菌资源比较丰富,黏球菌属是该地区可培养黏细菌菌群中的优势菌。分离纯化出的黏细菌菌株均表现出广谱的抗植物病原菌活性,具有进一步研究和开发的潜在价值。     

拮抗植物病原真菌的纤维素/木质素降解菌株的筛选及鉴定

【背景】秸秆还田在改善土壤肥力和丰富营养等方面有重要作用,但是也存在秸秆难以快速降解利用和病原真菌病害威胁的问题。【目的】为解决还田秸秆的降解和病原真菌病害问题,从长期秸秆还田地区采集样品,从中筛选出具有降解秸秆和抑菌功能的菌株。【方法】采用稀释分离法、苯胺蓝染色法和刚果红染色法等对秸秆高效降解菌株进行筛选,通过16S rRNA基因测序及构建系统发育树进行菌株鉴定。采用对峙培养法测定筛选到的秸秆降解菌株对玉米大斑病菌(Setostphaeria turcica)、梨黑斑病菌(Alternaria kikuchiana)、马铃薯早疫病菌(Alternaria solani)、链格孢属真菌(Alternaria alternata) ACCC38230和ACCC38231等5种供试植物病原真菌的抑制作用。以玉米大斑病菌(Setostphaeria turcica)为后期供试植物病原真菌,测定拮抗菌株代谢产物的抑菌能力;通过观察拮抗菌株粗提液对玉米大斑病菌分生孢子萌发和菌丝生长的影响,从而测定菌株对病原真菌的抑制作用。【结果】从秸秆还田土壤中分离筛选获得3株高效降解纤维素及木质素菌株并命名为JY122、ZY133和JY215。通过形态学观察和16S rRNA基因测序鉴定上述菌株全部为芽孢杆菌属(Bacillus)。通过系统发育树分析结果表明,JY122与蜡样芽孢杆菌(Bacillus cereus)相似性为99.4%,ZY133与枯草芽孢杆菌(Bacillus subtilis)相似性为100%,JY215与贝莱斯芽孢杆菌(Bacillus velezensis)相似性为99.1%。平板对峙实验结果显示,JY122、ZY133和JY215菌株对不同种属的植物病原真菌均有较强的抑制作用,抑制率高达43.74%-67.54%。此外,上述芽孢杆菌代谢产物具有抑菌活性及很强的热稳定性,经95℃处理后依然具有良好的抑菌效果。【结论】筛选获得的JY122、JY133和JY215菌株具有高效降解纤维素/木质素能力,抑制多种植物病原真菌生长,代谢产物抑菌能力强且热稳定性高。这为玉米秸秆还田提供菌株资源,也为进一步解决秸秆还田难点提供了新方法和思路。     

柑橘内生真菌的分离鉴定及其发酵产物对柑橘溃疡病菌的抑制活性

本研究从柑橘抗病品种的健康植株不同组织中分离纯化和鉴定内生真菌,并测定其发酵产物对柑橘溃疡病菌的抑制活性,以明确柑橘抗病品种中内生真菌的组成及其产抗柑橘溃疡病菌活性代谢产物的潜力,为柑橘溃疡病抗菌剂的开发奠定基础。该研究通过组织培养法分离内生真菌,采用形态学和分子生物学方法对其进行鉴定; 基于前期的拮抗预试验结果,选取代表性菌株进行发酵培养,通过乙酸乙酯浸提、真空抽滤、旋转蒸发浓缩制备粗提物; 采用带毒平板涂布法测定不同菌株发酵产物乙酸乙酯提取物对柑橘溃疡病菌的抑制活性。结果表明:(1)共分离得到72株内生真菌,归为2门(Ascomycota、Basidiomycota)、14个属,其中优势属为刺盘孢属(Colletotrichum)、球座菌属(Guignardia)、链格孢属(Alternaria)和镰刀菌属(Fusarium)。(2)不同柑橘品种中内生真菌多样性指数为温州蜜柑(桂林)>沙糖桔(桂林)>沙糖桔(梧州)。(3)不同组织中内生真菌多样性变化因地理位置差异而有所不同,采自桂林的温州蜜柑和沙糖桔均为叶片中的内生真菌的多样性高于枝条,而采自梧州的沙糖桔为叶片中的多样性低于枝条,并且采自梧州的柑橘样品与采自桂林的柑橘样品中的内生真菌相似性低。(4)测定了30株内生真菌乙酸乙酯提取物对柑橘溃疡病菌的抑制活性,其中29株菌株表现出不同程度抑制活性。不同柑橘品种中的优势属的MIC介于0.312 5～10 mg·mL^-1之间,特有属的MIC介于0.156～5 mg·mL^-1,共有属镰刀菌属的MIC介于0.312 5～2.5 mg·mL^-1之间。研究结果表明柑橘抗病品种中内生真菌具有丰富多样性,并且其发酵提取物普遍对柑橘溃疡病菌具有抑制作用。特有属抑菌活性总体优于优势属,共有属镰刀菌属在不同柑橘抗病品种中均具有显著抑菌效果。     

金荞麦和苦荞麦抗菌活性内生真菌的筛选及鉴定

从药用植物金荞麦和苦荞麦的根、茎、叶、花中分离到62株内生真菌,并以金黄色葡萄球菌(Staphylococcus aureus)、大肠杆菌(Escherichia coli)、枯草芽孢杆菌(Bacillus subtilis)[CMCC(B)63501]、小麦赤霉病菌(Fusarium graminearum)、黄瓜枯萎病菌(Fusarium oxysporum f.sp.cu-cumerinum)和绵腐病菌(Pythium aphanidermatum)6种微生物为指示菌对分离到的内生真菌进行抗菌活性检测。结果发现,分离的内生真菌菌株KQH-01、KQH-02和JQY-1的发酵醇提取物具有较好的抑菌活性。形态学特征和分子鉴定确定菌株KQH-01为炭角菌属(Xylaria sp.)真菌,菌株KQH-02为球毛壳菌(Chaetomium globosum),菌株JQY-1为葡萄座腔菌(Botryosphaeria dothidea)。     

库尔勒香梨黑斑病菌拮抗菌筛选及其抑菌机理

【背景】由互隔交链孢(Alternaria alternata)引起的黑斑病是库尔勒香梨采后贮期的主要病害之一,严重影响果实品质,造成巨大的经济损失。【目的】筛选对梨黑斑病菌具有高拮抗活性的菌株并探究其可能的抑菌机制,为香梨采后保鲜提供理论依据。【方法】从库尔勒香梨园健康植株根际采集土壤样品,采用稀释涂布法分离细菌并进行纯化,通过平板对峙法和琼脂打孔法筛选对梨黑斑病菌具有显著拮抗作用的菌株,结合形态学观察和16S rRNA基因序列分析进行初步鉴定;通过平板对峙法对拮抗菌抑菌谱进行测定;采用特异性平板定性检测拮抗菌产酶活性,采用3,5-二硝基水杨酸比色法法及福林-酚法定量酶活;通过孢子萌发抑制试验和扫描电镜观察,测定拮抗菌对梨黑斑病菌的拮抗作用。【结果】筛选得到2株对梨黑斑病菌有较强抑制活性的菌株JE53和JE56,经分析鉴定为多粘类芽孢杆菌(Paenibacillus polymyxa)及枯草芽孢杆菌(Bacillus subtilis),其发酵上清液对梨黑斑病菌的抑菌圈直径分别为22.49 mm和22.40 mm。抑菌谱测定结果表明,菌株JE53和JE56对马铃薯黑痣病菌等9种植物病原菌均有不同程度的抑制作用。胞外酶测定结果显示这2株菌可产生4种胞外酶;其发酵上清液能够显著抑制病原菌孢子萌发,抑制率分别为70.30%和88.87%;扫描电镜发现这2株菌可导致病原菌菌丝表面粗糙、扭曲变形。【结论】JE53和JE56对梨黑斑病菌有较好的抑制效果,具有进一步开发和应用的潜力。     

杜仲内生球毛壳菌的抗氧化活性研究

本文研究了分离自杜仲叶片的内生真菌球毛壳菌菌株No.173发酵液提取物的抗氧化活性,采用铁氰化钾还原力测定法、β-胡萝卜素/亚油酸模型和光照核黄素体系评价了发酵液提取物的抗氧化作用,并采用Folin-Ciocalteu法测定杜仲内生球毛壳菌发酵液提取物总多酚含量。结果表明,其抗氧化能力与Vc基本相当;清除超氧阴离子的能力优于芦丁;多酚含量为255.53±1.38mg/g,是其主要的抗氧化活性成分。     

高寒草地珠芽蓼内生拮抗固氮菌Z19的鉴定及其固氮功能

【目的】从东祁连山高寒草地珠芽蓼内生细菌中筛选和鉴定具有固氮能力和拮抗能力的内生细菌。【方法】采用16S rRNA基因序列同源性分析和生理生化指标测定方法对该菌株进行鉴定。【结果】从珠芽蓼中分离获得的21株内生细菌中6株内生菌具有固氮能力,76.2%具有抑菌能力,其中5株内生细菌对5种以上的病原菌有抑制作用;菌株Z19具有较强固氮能力和分解纤维素的能力,其纤维素溶解圈直径与菌落直径比达3.33,产生的纤维素酶活性为0.31 U,且对辣椒立枯丝核病菌(Rhizoctonia solani)、油菜菌核病菌(Sclerotinia sclerotiorum)、番茄灰霉病菌(Botrytis cinerea)、小麦根腐病菌(Bipolaris sorokiniana)和番茄早疫病菌(Alternaria solani)具有较强拮抗能力;经PCR扩增和测序,获得了菌株Z19的固氮基因(nifH)序列和16S rRNA基因序列,在GenBank中的登录号分别为EU693340和EU236746;菌株Z19呈革兰氏阳性,杆状,产芽孢。【结论】结合生理生化特征及16S rRNA基因序列同源性比较,鉴定其为枯草芽孢杆菌(Bacillus subtilis)。     

药用植物二色补血草内生真菌分离及其抑菌活性初步研究

对药用植物二色补血草内生真菌进行分离,以番茄灰霉病菌、黄瓜枯萎病菌、枸杞黑果病菌、黄瓜立枯病菌、小麦全蚀病菌、枯草芽孢杆菌、大肠杆菌、金黄色葡萄球菌和铜绿假单胞菌为靶标菌,采用对峙法和改进的菌块法进行抗菌活性初步筛选。结果表明:(1)从二色补血草根、茎、叶组织器官中分离出18株内生真菌,其中以叶部最多,根部和茎部次之;经形态学初步鉴定归于2目,2科,4属。(2)有10株内生真菌对2种或多种植物病原真菌有不同程度的抑制作用,占分离菌株总数的55.6%;8株内生真菌对1种或多种供试细菌具有不同程度的抑制作用,占分离菌株总数的44.4%;菌株LBEFL001和LBEFL006分别对5种供试真菌具有明显抑制作用,属于曲霉属和青霉属;菌株LBEFR006、LBEFS002分别对金黄色葡萄球菌和铜绿假单胞菌2种供试细菌具有明显抑制作用,属于梭孢霉属;菌株LBEFL004对枯草芽胞杆菌和金黄色葡萄球菌2种供试细菌具有明显抑制作用,属于曲霉属。研究发现,二色补血草具有较为丰富的内生真菌资源,对植物病原真菌具有明显的抑菌活性,且抑菌范围较宽;对病原细菌抑制作用具有一定的选择性,总体上对金黄色葡萄球菌抑制作用明显。     

Screening and characterization of endophytic fungi of Panax ginseng Meyer for biocontrol activity against ginseng pathogens

Forty endophytic fungi isolated from ginseng plants were screened to identify metabolites that had antifungal activity against ginseng microbial pathogens. The metabolites from the fungi were extracted from the liquid culture filtrates using ethyl acetate and then evaluated in vitro for antimicrobial activity against ginseng pathogens (Alternaria panax, Botrytis cinerea, Colletotrichum panacicola, Cylindrocarpon destructans, Rhizoctonia solani, and Phytophthora cactorum). Six of the fungi (Colletotrichum pisi, Fusarium oxysporum, Fusarium solani, Phoma terrestris, unknown 1 and 2) showed effective antimicrobial activity against all or some of the ginseng pathogens, with the extract of P. terrestris showing the strongest antimicrobial activity. The extract also showed inhibitory activity against spore germination of the pathogens. Gas chromatography–mass spectrometry (GC–MS) analysis of P. terrestris extract revealed that forty-one compounds were present in metabolites containing mainly N-amino-3-hydroxy-6-methoxyphthalimide (32% of the total metabolites) and 5H-dibenz [B, F] azepine (7%). Treatment with P. terrestris extract also caused morphological changes and reduced expression of the genes involved in mycelial growth and virulence. Treatment also induced defense-related genes in detached Arabidopsis leaves that were inoculated with the pathogens. These results indicate the antimicrobial potential for use of metabolites extracted from the ginseng endophytic fungi as alternatives to chemicals for biocontrol.     

Decomposition of cellulose strips in relation to climate,litterfall nitrogen,phosphorus and C/N ratio in natural boreal forests

Isolates of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Penicillium sp., Rhizoctonia solani, Stemphylium sp., Thielaviopsis basicola, and Verticillium dahliae were cultured on potato–dextrose agar (PDA), barley-sand and alfalfa-sand substrates in petri-dish or in column microcosms. N-mineralization by fungi and fungal-feeding nematodes in combination or fungi alone was assessed. Numbers of Aphelenchus avenae or Aphelenchoides composticola supported by the fungi were measured every 7 days. Times for full colonization of the substrates by fungi ranged from 5 to 15 days. Rhizoctonia solani and B. cinerea on PDA supported the largest A. avenae and A. composticola populations, respectively. Penicillium sp. was a nonhost for A. composticola and A. avenae. Rhizoctonia solani, B. cinerea, V. dahliae, and F. oxysporum supported significantly more nematodes than the other four fungal species. The ranked order of fungi based on the amount of N mineralized in columns free of nematodes was A. alternata (with a rate of 0.052 μg N/g-sand per day), Stemphylium sp., V. dahliae, T. basicola, B. cinerea, F. oxysporum, R. solani, and Penicillium sp. (with a rate of 0.0045 μg N/g-sand perday). The presence of A. avenae resulted in significant increases in mineral N, compared to nematode-free columns colonized by F. oxysporum, R. solani, and T. basicola alone. The presence of A. composticola resulted in significant increases in mineral N, compared to nematode-free columns colonized by A. alternata, B. cinerea, F. oxysporum, and R. solani alone. There was more mineral N incolumns in the presence of A. composticola than A. avenae in most cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Induced proteome of Trichoderma harzianum by Botrytis cinerea

As a notable biocontrol agent, Trichoderma harzianum can antagonize a diverse array of phytopathogenic fungi, including Botrytis cinerea, Rhizoctonia solani and Fusarium oxysporum. Elucidating the biocontrol mechanism of T. harzianum in response to the pathogens enables it to be exploited in the control of plant diseases. Two-dimensional gel electrophoresis (2-DE) was performed to obtain secreted protein patterns of T. harzianum ETS 323, grown in media that contained glucose, a mixture of glucose and deactivated B. cinerea mycelia, deactivated B. cinerea mycelia or deactivated T. harzianum mycelia. Selected protein spots were identified using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Ninety one out of 100 excised protein spots were analyzed and some proteins were sequence identified. Of these, one l-amino acid oxidase (LAAO) and two endochitinases were uniquely induced in the media that contained deactivated B. cinerea mycelia as the sole carbon source. Activities of the cell wall-degrading enzymes (CWDEs), including β-1,3-glucanases, β-1,6-glucanases, chitinases, proteases and xylanases, were significantly higher in media with deactivated B. cinerea mycelia than in other media. This finding suggests that the cell wall of B. cinerea is indeed the primary target of T. harzianum ETS 323 in the biocontrol mechanism. The possible roles of LAAO and xylanase were also discussed.     

Microbial conversion and in vitro and in vivo antifungal assessment of bioconverted docosahexaenoic acid (bDHA) used against agricultural plant pathogenic fungi

Microbial modification of polyunsaturated fatty acids can often lead to special changes in their structure and in biological potential. Therefore, the aim of this study was to develop potential antifungal agents through the microbial conversion of docosahexaenoic acid (DHA). Bioconverted oil extract of docosahexaenoic acid (bDHA), obtained from the microbial conversion of docosahexaenoic acid (DHA) by Pseudomonas aeruginosa PR3, was assessed for its in vitro and in vivo antifungal potential. Mycelial growth inhibition of test plant pathogens, such as Botrytis cinerea, Colletotrichum capsici, Fusarium oxysporum, Fusarium solani, Phytophthora capsici, Rhizoctonia solani and Sclerotinia sclerotiorum, was measured in vitro. bDHA (5 μl disc⁻¹) inhibited 55.30–65.90% fungal mycelium radial growth of all the tested plant pathogens. Minimum inhibitory concentrations (MICs) of bDHA against the tested plant pathogens were found in the range of 125–500 μg ml⁻¹. Also, bDHA had a strong detrimental effect on spore germination for all the tested plant pathogens. Further, three plant pathogenic fungi, namely C. capsici, F. oxysporum and P. capsici, were subjected to an in vivo antifungal screening. bDHA at higher concentrations revealed a promising antifungal effect in vivo as compared to the positive control oligochitosan. Furthermore, elaborative study of GC-MS analysis was conducted on bioconverted oil extract of DHA to identify the transformation products present in bDHA. The results of this study indicate that the oil extract of bDHA has potential value of industrial significance to control plant pathogenic fungi.     

Molecular characterization of fungal endophytes from Calotropis procera plants in Taif region (Saudi Arabia) and their antifungal activities

Fungal endophytes were isolated from the leaves of Calotropis procera (Apocynaceae) collected from Taif region (Saudi Arabia). Thirty-three different taxa were recovered. The overall foliar colonization rate was 35.1%. A total of 161 isolates were obtained and identified into 33 distinct operational taxonomic units based on the sequencing of the internal transcribed spacer regions of the rRNA gene. The most prevalent fungi were Aspergillus flavus, Chaetomium globosum, Cochliobolus lunatus, Fusarium dimerum, F. oxysporum, and Penicillium chrysogenum. A total of 161 isolates were tested for antifungal activities against four plant pathogenic fungi (Alternaria alternata, Fusarium oxysporum, Botrytis cinerea, and Pythium ultimum), of which 33 isolates showed antifungal activity against at least one plant pathogenic fungi. Four isolates of Chaetomium globosum and three isolates of Myrothecium verrucaria showed the strongest antifungal activity. This study reported the occurrence of a much wider spectrum of fungi, when compared with previous work. Also, it confirmed the variation of different isolates from the same species in terms of antifungal activity.     

The synthetic strigolactone GR24 influences the growth pattern of phytopathogenic fungi

Strigolactones that are released by plant roots to the rhizosphere are involved in both plant symbiosis with arbuscular mycorrhizal fungi and in plant infection by root parasitic plants. In this paper, we describe the response of various phytopathogenic fungi to the synthetic strigolactone GR24. When GR24 was embedded in the growth medium, it inhibited the growth of the root pathogens Fusarium oxysporum f. sp. melonis, Fusarium solani f. sp. mango, Sclerotinia sclerotiorum and Macrophomina phaseolina, and of the foliar pathogens Alternaria alternata, Colletotrichum acutatum and Botrytis cinerea. In the presence of this synthetic strigolactone, intense branching activity was exhibited by S. sclerotiorum, C. acutatum and F. oxysporum f. sp. melonis. Slightly increased hyphal branching was observed for A. alternata, F. solani f. sp. mango and B. cinerea, whereas suppression of hyphal branching by GR24 was observed in M. phaseolina. These results suggest that strigolactones not only affect mycorrhizal fungi and parasitic plants, but they also have a more general effect on phytopathogenic fungi.     

Interaction of cruciferous phytoanticipins with plant fungal pathogens: indole glucosinolates are not metabolized but the corresponding desulfo-derivatives and nitriles are

Glucosinolates represent a large group of plant natural products long known for diverse and fascinating physiological functions and activities. Despite the relevance and huge interest on the roles of indole glucosinolates in plant defense, little is known about their direct interaction with microbial plant pathogens. Toward this end, the metabolism of indolyl glucosinolates, their corresponding desulfo-derivatives, and derived metabolites, by three fungal species pathogenic on crucifers was investigated. While glucobrassicin, 1-methoxyglucobrassicin, 4-methoxyglucobrassicin were not metabolized by the pathogenic fungi Alternaria brassicicola, Rhizoctonia solani and Sclerotinia sclerotiorum, the corresponding desulfo-derivatives were metabolized to indolyl-3-acetonitrile, caulilexin C (1-methoxyindolyl-3-acetonitrile) and arvelexin (4-methoxyindolyl-3-acetonitrile) by R. solani and S. sclerotiorum, but not by A. brassicicola. That is, desulfo-glucosinolates were metabolized by two non-host-selective pathogens, but not by a host-selective. Indolyl-3-acetonitrile, caulilexin C and arvelexin were metabolized to the corresponding indole-3-carboxylic acids. Indolyl-3-acetonitriles displayed higher inhibitory activity than indole desulfo-glucosinolates. Indolyl-3-methanol displayed antifungal activity and was metabolized by A. brassicicola and R. solani to the less antifungal compounds indole-3-carboxaldehyde and indole-3-carboxylic acid. Diindolyl-3-methane was strongly antifungal and stable in fungal cultures, but ascorbigen was not stable in solution and displayed low antifungal activity; neither compound appeared to be metabolized by any of the three fungal species. The cell-free extracts of mycelia of A. brassicicola displayed low myrosinase activity using glucobrassicin as substrate, but myrosinase activity was not detectable in mycelia of either R. solani or S. sclerotiorum.     

In vitro antagonism of cotton seedlings fungi and characterization of chitinase isozyme activities in Trichoderma harzianum

The antagonistic fungus Trichoderma harzianum is widely recognized as a potential biocontrol agent against several soil-borne plant pathogens. T. harzinum is rich source of chitinoltic enzymes. In vitro screening of 5 isolates of T. harzinum, one isolate of Chaetomium globosum and one isolate of Conetherium mentance, revealed that all of them had reduced growth area of Macrophomina phaseolina, Fusarium solaniand Rhizoctonia solani on PDA medium, significantly. The inhibition percentage ranged from 77.9 % to 55.9% for M. phaseolina and 59.2% to 40.4% for R. solani by T. harzinum and C. mentance, respectively. Inhibition for F. solani ranged from 76.5% to 55.7% by T. harzinum and C. globosum, respectively. Isozyme gel electrophoresis was used to assess chitinase activity secreted by selected isolates of T. harzinum under different pH degrees and temperatures. Obtained results indicated that activity of chitinase isozyme produced at 30 °C was higher than 15–20 °C for all tested isolates and activity of chitinase produced by isolates No. 4 and 5 of T. harzinum at pH (7–7.5) was higher than at pH 6, respectively.     

Impact of salinity stress on soil-borne fungi of sugarbeet

The pathogenicity of Egyptian and German isolates of soil-borne root rotting fungi to seedlings of three cultivars of sugarbeet in presence or absence of different concentrations of either NaCl or CaCl₂ were studied under greenhouse conditions. In the absence of salt treatments Egyptian isolates ofRhizoctonia solani were most virulent on all sugarbeet cultivars followed bySclerotium rolfsii andFusarium oxysporum f. sp.betae, the latter proved to be a weak pathogen. The results also revealed that the German isolates ofSclerotinia sclerotiorum were pathogenic to all sugarbeet cultivars studied, whileBotrytis cinerea was only a weak pathogen. However, the presence of salts, NaCl or CaCl₂, in different concentrations seemed to cause alterations in such pathogenicity.