豇豆疫霉LAMP检测方法的建立

本研究以豇豆疫霉Phytophthora vignae Purss核糖体内转录间隔区(internal transcribed spacer,ITS)序列为靶标片段,设计4条特异性引物,建立了环介导等温扩增(LAMP)检测方法。特异性检测结果表明:8株不同地理来源的豇豆疫霉菌株LAMP检测均为阳性(绿色),扩增产物用2.0%琼脂糖凝胶电泳出现特有的梯形条带,而其他11种卵菌近缘种及12种常见病原真菌和细菌共42个菌株均未观察到这些现象。灵敏度分析显示:该方法检测灵敏度在DNA水平上可达到100fg/25μL。采用LAMP方法对福建建瓯和宁德采集的62份疑似豇豆疫病病株样本进行检测,并用组织分离方法进行验证。结果表明,LAMP和组织分离方法的检出率分别为67.7%(42/62)和61.3%(38/62)。综合以上结果,LAMP方法具有特异性强、灵敏度高、快速高效、操作简单的特点,适合基层部门用于田间豇豆疫霉快速检测。     

利用环介导等温扩增方法快速检测瓜类细菌性果斑病菌和番茄细菌性溃疡病菌

为建立简单、快速和灵敏地检测瓜类细菌性果斑病菌Acidovorax avenae subsp. citrulli(Aac)和番茄细菌性溃疡病菌Clavibacter michiganensis subsp. michiganensis(Cmm)的环介导等温扩增(loop-mediated isothermal amplification,LAMP)方法,以Aac的ugpB基因和Cmm的micA基因为靶标,分别设计、合成和筛选特异性引物,摸索和优化各项反应条件和反应体系,成功建立了以钙黄绿素颜色为指示且只需要金属浴恒温反应30～60 min的LAMP扩增体系。特异性分析表明该LAMP方法可以快速检出5株不同的Aac菌株和2株不同的Cmm菌株,其它对照菌株如燕麦嗜酸菌燕麦亚种A. avenae subsp. avenae、丁香假单胞菌Pseudomonas syringae、水稻黄单胞菌水稻致病变种Xanthomonas oryzae pv. oryzae和茄科雷尔氏菌Ralstonia solanacearum则呈现阴性反应;引物比目前报道的LAMP引物有更高的DNA样品检测灵敏度,Aac和Cmm的灵敏度分别为1.72×10~2fg/μL和1.26×10~2fg/μL。研究结果表明,所设计的Aac和Cmm引物特异性好、灵敏度高,更有利于从源头上控制这2种检疫性细菌病害的流行和传播。     

木薯细菌性萎蔫病菌的LAMP快速检测方法

建立了一种木薯细菌性萎蔫病菌的环介导恒温扩增快速检测方法,为木薯细菌性萎蔫病的快速检测提供有力的技术支持。针对木薯细菌性萎蔫病菌TAL效应器蛋白质(pthBXam)靶序列的6个位点设计4条特异性引物,并对反应温度和内引物浓度等参数进行了优化,设计的引物与试验中提供的其他黄单胞近缘种都没有扩增反应,表现了较好的特异性。LAMP方法对木薯细菌性萎蔫病菌菌株DNA的检测下限为1pg/μL,比常规PCR灵敏度高100倍。该方法采用SYBR Green I染料法对扩增产物闭管检测,裸眼观察颜色变化判断反应结果,能快速、准确地对田间样品进行检测,没有出现假阳性和假阴性。与其他检测方法相比,LAMP方法检测时间短,效率高,降低了设备投入,易于操作,适合木薯细菌性萎蔫病菌的现场检疫和大规模监测。     

基于环介导等温扩增技术检测由强雄腐霉引起的玉米茎腐病

为建立强雄腐霉Pythium arrhenomanes的快速分子检测技术,基于环介导等温扩增技术(loop-mediated isothermal amplification,LAMP)以β-tubulin基因为靶标序列,设计强雄腐霉的特异性引物,建立了一种准确快速的LAMP检测方法,并对该检测方法的特异性、灵敏度和实际应用效果进行评估。25μL LAMP最终反应体系为:10×ThermoPol Buffer 2.5μL、10 mmol/L dNTPs 3.5μL、6 mmol/L MgSO_4 2μL、5 mol/L甜菜碱4μL、40μmol/L FIP-1/BIP-1各1μL、5μmol/L F3-1和B3-1各1μL、40μmol/L LB-1 1μL、Bst DNA polymerase 1μL、2.5 mmol/L HNB 1.9μL、模板DNA 2μL、灭菌水3.1μL。LAMP体系在等温64℃条件下反应60 min,HNB显色反应显示天蓝色即为阳性反应;扩增产物经2%琼脂糖凝胶电泳验证为梯形条带,也可判定为阳性反应。特异性检测结果显示,LAMP体系能特异性地检测出强雄腐霉,而其它卵菌近缘种和常见植物病原真菌均未检测出。灵敏度检测结果显示,LAMP体系的最低检测灵敏度为10 pg/μL,是普通PCR反应灵敏度的1 000倍。在实际应用中,LAMP体系能够快速检测出人工接种和实际发病玉米组织中的病原菌。表明本研究建立的快速、准确、可视化的LAMP检测方法能在60 min内检测出强雄腐霉。     

玉蜀黍黑粉菌环介导等温扩增检测体系的建立及应用

 本文根据玉蜀黍黑粉菌(Ustilago maydis )的UmPep1、UmPit2和UmSee1基因各设计4套环介导等温扩增(LAMP)引物,从中筛选出1套引物对LAMP反应体系进行3因素(Bst DNA聚合酶浓度、Mg²⁺浓度、内外引物浓度比)3水平的优化试验。并对优化的U. maydis LAMP反应体系进行特异性、灵敏度及田间检测可行性试验。特异性试验表明,该方法能特异性检测U. maydis,而与其他病原菌的DNA没有交叉反应;灵敏度试验表明,该反应体系的最低检出限为44 fg·μL^-1 pEasy-Pep质粒DNA,制作的标准曲线可对U. maydis进行定量分析。该方法也适用于在U. maydis侵染前或侵染早期对田间样品进行检测,对现场采集的172份田间样品进行检测,其中140个样品显示为阳性。本研究所建立的LAMP体系具有特异性好、灵敏度高、重复性好的特点,并能在45 min内完成对田间样品的检测,是快速、定量检测U. maydis的有效手段。     

番石榴焦腐病菌LAMP检测方法的建立及应用

 以钙黄绿素（calcein）为指示剂,建立了番石榴焦腐病菌（Botryosphaeria rhodina）的环介导等温扩增（Loop mediated isothermal amplification, LAMP）可视化快速检测方法。在该方法中,以番石榴焦腐病菌特异的核糖体转录间隔区（Internal transcribed spacer, ITS）序列为目的DNA片段,设计4条引物（2条内引物、2条外引物）,优化LAMP反应条件和反应体系,并进行特异性和灵敏度验证。研究确定最佳反应温度为64℃,反应时间1 h;特异性检测结果显示,15株不同地理来源的番石榴焦腐病菌和10份番石榴焦腐病病果组织LAMP产物均为阳性（绿色）,而26株其它病原菌及10份健康番石榴果实组织LAMP产物均为阴性（橘黄色）;灵敏度验证结果显示,该方法的检测灵敏度在DNA水平上可达到10 pg。实验结果表明,快速、准确、灵敏的LAMP检测方法适合基层部门及田间检测番石榴焦腐病菌使用。     

水稻细菌性条斑病菌LAMP快速检测方法的建立

以SYBR Green I荧光染料为指示剂,针对水稻细菌性条斑病菌糖基转移酶,设计了4条普通LAMP引物,并在此基础上设计了2条LAMP环引物,建立了水稻细菌性条斑病菌的环介导等温扩增可视化快速检测方法。结果表明:水稻细菌性条斑病菌呈荧光的阳性反应,近缘菌株则呈橙色的阴性反应;检测灵敏度DNA为100 fg/μL,菌悬液为3×103 cfu/m L。LAMP技术的建立为现场检疫和大规模检测提供了新的方法。     

环介导等温扩增技术检测大丽轮枝菌

 本研究基于环介导等温扩增技术(loop-mediated isothermal amplification,LAMP),通过比对分析大丽轮枝菌(Verticillium dahliae)与其相近种不同靶标序列间的差异,选取Gpd(glyceraldehyde-3-phosphate dehydrogenase,甘油醛-3-磷酸脱氢酶)基因作为靶标基因,设计并筛选了四条特异性强、灵敏度高的LAMP引物和两条环引物,建立了一种基于颜色判定的简单、快速和灵敏的大丽轮枝菌的检测方法,并进行了特异性、灵敏度实验及田间发病组织的检测。该方法在62 ℃等温条件下进行核酸扩增反应70 min,扩增前加入染料HNB(羟基萘酚蓝),反应后根据染料颜色变化判定扩增结果。特异性试验中,仅含有大丽轮枝菌菌株DNA的反应管扩增后呈天蓝色的阳性反应,而其他供试菌株均呈紫色的阴性反应。该方法的最低检测限为100 pg·μL^-1,在土壤中检测的灵敏度为10个孢子/0.25g土壤。该技术能够检测出棉花发病组织中的目标菌,对采自江苏和山东的24份疑似病害样本进行检测,11份为阳性。该方法的建立为大丽轮枝菌的检测及其所致病害的诊断提供了新的技术。     

采用环介导等温扩增法(LAMP)快速检测苹果根结线虫

为高效、简便、快速地对我国进境植物检疫性有害生物名录中的非中国种—苹果根结线虫Meloidogyne mali进行检疫,通过比较Gen Bank中根结线虫相关序列,以苹果根结线虫28S r DNA非保守区域序列设计环介导等温扩增(loop-mediated isothermal amplification,LAMP)的特异性引物,并优化反应条件,建立一种可快速检测苹果根结线虫的LAMP检测体系。结果显示:d NTPs浓度为0.4 mmol/L、Mg~(2+)浓度为5.0 mmol/L、不添加甜菜碱、反应时间为60 min时,LAMP检测体系扩增效率最高;用琼脂糖凝胶电泳、SYBR Green I染色和LFD试纸均能检测到苹果根结线虫的扩增产物。所建立的LAMP检测体系能够从10种供试植物线虫种群中特异性地检测出苹果根结线虫,灵敏度为1/20 000条线虫DNA,比常规PCR灵敏度高10倍。表明所建立的苹果根结线虫LAMP快速检测体系可用于我国口岸进境植物中苹果根结线虫检疫。     

基于环介导等温扩增技术快速检测美澳型核果褐腐病菌

本文建立了美澳型核果褐腐病菌(Monilinia fructicola)环介导等温扩增技术,并利用此技术开展了M.fructicola的检测和鉴定。采用M.fructicola SCAR分子标记的MO368特异片段为靶标序列,设计并筛选出M.fructicola的特异性LAMP引物,建立了该病菌快速诊断方法。试验结果表明,仅M.fructicola的菌株DNA扩增后呈天蓝色的阳性反应,而在其他真菌的供试菌株中均呈紫色的阴性反应。检测灵敏度可达到100 pg/μL。利用该方法对无锡机场截获的7份疑似李子褐腐病样本进行检测,结果有3份样品呈LAMP阳性反应。本文建立的M.fructicola LAMP检测方法具有灵敏度高、特异性好,简便易行等优点,为美澳型核果褐腐病菌的快速检测提供了一种新技术。     

Epidemiology and simulation of population development of Sitobion avenae in winter wheat

The epidemiology ofSitobion avenae and its natural enemies in winter wheat was studied in 1975, 1976 and 1977. Immigration was important until the end of flowering. The alate immigrants had apterous offspring. These became the driving force in population growth. Their offspring were mostly alatae which usually left the field. A model of the epidemic was developed. Quantitative relations between the aphids and their environment were obtained from literature or established in laboratory trials. The model simulated population development and population composition from the beginning of June till the population peak at the end of June or early in July. Because quantitative data on relations between aphids and their natural enemies and pathogens are scarce, and since the knowledge on wing formation is still limited, the population collapse could not be predicted. In the future, prognosis over a period of three weeks seems possible.Samenvatting De toenemende betekenis van graanbladluizen (vooralSitobion avenae) gepaard gaande met een sterke toename van het gebruik van insecticiden op granen maakte verbetering van de prognose over het schadelijk optreden wenselijk. Door gedetailleerde tellingen in het veld (Fig. 1–7) werden gegevens verkregen over het verloop van de epidemie en het optreden van natuurlijke vijanden in 1975, 1976 en 1977.Een immigratieperiode tot in de bloei kon worden vastgesteld. Daarna lijkt de aantrekkelijkheid van het gewas voor alate luizen te verminderen. De alate immigranten krijgen aptere nakomelingen. Deze vormen de stuwende kracht van de populatiegroei. De nakomelingen van apteren zijn merendeels alaat. Zij verlaten het gewas.Een model van de populatieontwikkeling gedurende de epidemie werd opgesteld. De relatiediagrammen Fig. 9 en 10 laten groei en ontwikkeling vanS. avenae en een predator (Syrphus corollae) zien. Kwantificering van de betrekkingen werd mogelijk door literatuurgegevens en laboratoriumexperimenten.Met het model kon de populatieontwikkeling vanS. avenae vanaf begin juni tot aan de populatiepiek in 1975, 1976 en 1977 vrij goed worden gesimuleerd (Fig. 12). Ook de populatieopbouw kon worden gesimuleerd (Fig. 14). De teruggang van de populatiedichtheid blijkt moeilijker te voorspellen door het ontbreken van gegevens over natuurlijke vijanden.Het lijkt waarschijnlijk dat in de toekomst met het model een prognose over de piek van de bladluispopulatie circa 3 weken tevoren mogelijk zal zijn.     

Tumours of Begonia and some other ornamentals,induced by Corynebacterium fascians

In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten.     

Nematicidal Activity of Chrysanthemum coronarium

Organic amendments and green manure are potential alternatives to the harmful chemical control means currently used against plant-parasitic nematodes. In this work, Chrysanthemum coronarium was applied to the soil as a green manure to control the root-knot nematodes Meloidogyne incognita and M. javanica. Chrysanthemum coronarium significantly reduced nematode infection of tomato roots and improved plant-top fresh weight, both in the greenhouse and in microplots. Other green manures, derived from Anthemis pseudocotula, wild chickpea (Cicer pinnatifidum), Geranium spp. and wheat, were not as effective as C. coronarium. Chrysanthemum coronarium, retained its nematicidal activity even when applied as a dried material. Only mature C. coronarium plants, in their flowering stage, exhibited nematode control activity, but the green plant parts were more effective than the flowers. An aqueous extract of C. coronarium exhibited in vitro, nematostatic activity towards M. incognita and M. javanica second-stage juveniles and inhibited their hatching from eggs and egg-masses; its nematostatic activity was expressed also against other phytonematode species such as Heterodera avenae and Pratylenchus mediterraneus, but did not affect the beneficial entomopathogenic nematode Steinernema feltiae.     

Inactivation of soil-borne plant pathogens during small-scale composting of crop residues

Samples of heavily infested crop residues were incorporated in static compost heaps (2.5–4.6 m³) of the Indore type. Temperature increased to 50–70°C within 6 days depending on the type of crop residues used and the location within the heap. The heat phase (>40 °C) lasted 2–3 weeks and was followed by a c. 5-months maturation phase (<40 °c).=" among=" the=" 17=" pathogens=" tested,=">Olpidium brassicae and one of the four formae speciales ofFusarium oxysporum that were tested survived composting, but also their inoculum was greatly reduced.Survival during specific phases of composting was studied by incorporation and retrieval of samples at various stages of the process.F. oxysporum f. sp.melonis was completely inactivated andO. brassicae andPlasmodiophora brassicae were almost completely inactivated during the short heat phase. The three pathogens survived the long-lasting maturation phase without loss of viability. Heat evolved during composting was found to be the most important factor involved with sanitation of crop residues. The possible involvement of fungitoxic conversion products and microbial antagonism is discussed.     

Effects of the saprophytic leaf mycoflora on growth and productivity of winter wheat

The effects of the saprophytic mycoflora and its interference with cereal aphids on growth and yield of winter and spring wheat was studied in field experiments in 1980, 1981 and 1982.Yields varied between 5000 and 8000 kg dry matter of kernels per ha. The effect of the saprophytic mycoflora on yield was determined in different treatments: A) no control measures against cereal aphids and saprophytic and necrotrophic fungi, B) no control of cereal aphids, control of saprophytic and necrotrophic fungi, C) control of cereal aphids and control of saprophytic and necrotrophic fungi, D) control of cereal aphids and stimulation of saprophytic mycoflora and E) control of cereal aphids, no control of saprophytic and necrotrophic fungi nor stimulation of saprophytic mycoflora.Considerable differences in top densities of saprophytic mycoflora (10 times as large in A and D as in B and C) were determined. The consequences of these differences for the growth and productivity of wheat were minor. A negative effect of saprophytic mycoflora on the yield could not be detected in 1981 and 1982, whereas a small positive significant effect was found in 1980. This stimulation may have been due to competition between necrotrophic fungal pathogens and saprophytic mycoflora. As a result of favourable weather conditions necrotrophic fungal pathogens were very numerous in 1980 and could form an important yield reducing factor. Yield levels may effect the importance of the necrotrophic and saprophytic mycoflora as yield reducing factors. Additionally, in the presence of aphid honeydew captafol was found to be relatively ineffective against saprophytic fungi.     

浅黄恩蚜小蜂和丽蚜小蜂对温室白粉虱的寄生潜能分析

浅黄恩蚜小蜂Encarsia sophia GiraultDodd和丽蚜小蜂Encarsia formosa Gahan是防治粉虱类害虫的优势寄生蜂,通过生命表技术方法分析了2种寄生蜂对温室白粉虱Trialeurodes vaporariorum(Westwood)的防治潜能。结果表明,丽蚜小蜂在羽化第3天和第10天出现2次寄生高峰,占其总寄生量的13.7%和8.0%,在2次高峰之间逐日寄生粉虱数量比较平稳,单雌逐日平均产雌数保持在10.6~13.4头,10 d后寄生量呈明显的下降趋势;而浅黄恩蚜小蜂羽化10 d内逐日寄生粉虱量变化不大,单雌逐日产雌数稳定在4.2~5.4头,羽化14 d后寄生量呈明显下降趋势。丽蚜小蜂和浅黄恩蚜小蜂的R0、T、rm、λ值分别为171.5、18.0、0.2854、1.3303和61.6、16.2、0.2544、1.2897;粉虱若虫充足时,丽蚜小蜂平均单雌寄生若虫数是浅黄恩蚜小蜂的2.7倍,而后者平均单雌取食若虫数为60.6头,明显高于前者42.7头,总的来看,丽蚜小蜂通过寄生和取食杀死粉虱总量220.8头,明显高于浅黄恩蚜小蜂的127.9头。表明在应用寄生蜂防治温室白粉虱时,单独释放丽蚜小蜂比浅黄恩蚜小蜂显示出更好的防治潜能。     

Aetiology and causal agents of mango sudden decline disease in the Sultanate of Oman

Mango sudden decline is a recently introduced, economically serious disease in Oman. Affected mango trees have wilting symptoms that usually begin on one side and later spread to involve the entire tree. Trees exude amber-coloured gum from the bark of their trunks or branches and vascular tissues are discoloured. Having entered Oman in the recent past, survey data is presented that shows the disease to have spread throughout the northern part of the country. Evidence is presented that the vascular wilt pathogen Ceratocystis fimbriata causes mango sudden decline disease in Oman, possibly in concert with Lasiodiplodia theobromae and the recently described Ceratocystis omanensis. Isolates of these fungi from affected trees, cause infection and can be recovered from inoculated seedlings. Bark beetles (Hypocryphalus mangiferae) are shown to carry C. fimbriata and L. theobromae and are presumably responsible for transmitting both pathogens to healthy mango trees. Acting as a wounding agent and vector, the bark beetle is likely to have assisted the rapid spread of the disease across Oman.     

Identification and pathogenicity of Pythium species causing damping-off of kidney bean

Five Pythium species (Pythium irregulare, P. mamillatum, P. myriotylum, P. spinosum and P. ultimum var. ultimum) were isolated from the hypocotyls and roots of kidney bean plants with damping-off from a commercial field and from experimental plots that have undergone either continuous cropping with kidney bean or rotational cropping with arable crops. In inoculation tests, all five Pythium species were pathogenic to kidney bean. This is the first report of damping-off of kidney bean caused by Pythium species; we named this disease damping-off of kidney bean. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB291811, AB291944 and AB291945.     

Pathogenic fungi involved in root rot of peas in the Netherlands and their physiological specialization

Research on root rot pathogens of peas in the Netherlands has confirmed the prevalence ofFusarium solani, F. oxysporum, Pythium spp.,Mycosphaerella pinodes andPhoma medicaginis var.pinodella. Aphanomyces euteiches andThielaviopsis basicola were identified for the first time as pea pathogens in the Netherlands. Other pathogens such asRhizoctonia solani andCylindrocarpon destructans were also found on diseased parts of roots. F. solani existed in different degrees of pathogenicity, and was sometimes highly specific to pea, dwarf bean of field bean, depending on the cropping history of the field.A. euteiches was specific to peas, whereasT. basicola showed some degree of physiological specialization.     

Relationship Between Production of the Phytotoxin Prehelminthosporol and Virulence in Isolates of the Plant Pathogenic Fungus Bipolaris sorokiniana

A gas chromatographic method was developed to quantify the phytotoxin prehelminthosporol, which is a sesquiterpene metabolite of the plant pathogen Bipolaris sorokiniana. The toxin was extracted from mycelium or culture filtrates, pre-cleaned using solid phase extraction, and analyzed by gas chromatography as a trimethylsilyl-derivative. The detection limit of the method was 5ngl^–1 (signal to noise ratio 4:1) which corresponds to ca. 15ng prehelminthosporol per mg dry weight of mycelium or 15ng prehelminthosporol per ml culture filtrate. The total amount of prehelminthosporol (mycelium plus culture filtrate) increased with cultivation time when examined in six isolates of B. sorokiniana after 6, 9, 12 and 15 days of incubation. The screening experiment of 17 isolates for prehelminthosporol production after 8 days of incubation revealed significant differences in the toxin production between the isolates. The isolates with low toxin production had lower virulence towards barley roots compared to those with higher production of the toxin. However, the virulence did not increase with prehelminthosporol level among the high producing isolates. Prehelminthosporol was also analyzed in a number of related Bipolaris and Drechslera species. In addition to B. sorokiniana, three out of six Bipolaris species (B. setariae, B. zeicola, B. victoriae) produced prehelminthosporol, which indicates that ability to produce prehelminthosporol is conserved among closely-related Bipolaris species.