华北大黑鳃金龟对20种植物源挥发物的电生理和行为反应

［目的］ 发掘能影响华北大黑鳃金龟行为反应的植物挥发性物质,以利用化学生态学技术调控华北大黑鳃金龟的行为,达到绿色防控的目的。［方法］ 采用触角电位（EAG）及Y型嗅觉仪行为测定技术,对20种植物挥发物进行筛选。［结果］ 在10 μg/μL浓度刺激下,顺2己烯醇、反2己烯醇、乙酸顺3己烯酯、辛醛和苯乙醇能引起华北大黑鳃金龟触角较强的电位反应,总体趋势雌虫反应大于雄虫。行为测试中,反2己烯醇、芳樟醇、乙酸顺3己烯酯、1己醇、邻氨基苯甲酸甲酯吸引能力都显著高于对照正己烷,但辛醛和苯乙醇对华北大黑鳃金龟的吸引作用低于对照正己烷,并呈极显著差异（p＜0.01）。［结论］ 华北大黑鳃金龟对本文所选的部分植物源挥发物对有显著的电生理和行为反应,该结果可为开发对其的田间引诱剂或驱避剂提供一定的理论依据。     

华北大黑鳃金龟植物源引诱剂配方筛选及引诱效果

为研制华北大黑鳃金龟Holotrichia oblita的植物源引诱剂,选取7种植物挥发物单体,筛选各单体最佳引诱浓度并据此设计35个三元配方,通过华北大黑鳃金龟成虫触角电位反应试验及进一步的趋势行为反应试验筛选出对华北大黑鳃金龟雌、雄成虫引诱作用较强的配方,并通过笼罩引诱试验测试所筛选配方对成虫的引诱效果。结果表明,趋势行为反应试验中配方5(邻苯二甲酸二丁酯+芳樟醇+苯甲醇)、配方14(肉桂醛+苯甲醇+顺-3-己烯基乙酸酯)、配方27(1-己醇+肉桂醛+苯甲醇)和配方35(1-己醇+顺-3-己烯基乙酸酯+顺-3-己烯基异丁酸酯)对雌成虫引诱效果较好,选择反应率分别为62.09%、62.79%、60.22%和85.13%;配方3(邻苯二甲酸二丁酯+肉桂醛+顺-3-己烯基乙酸酯)、配方6(邻苯二甲酸二丁酯+芳樟醇+顺-3-己烯基乙酸酯)和配方35对雄成虫引诱效果较好,选择反应率分别为69.12%、64.22%和89.05%。笼罩引诱试验结果表明,成虫对配方3、配方6和配方35的选择反应率分别为68.16%、60.24%和70.59%,均高于其它配方;配方3、配方6和配方35引诱的成虫数量分别为61、61和72头,均显著高于其对照引诱的成虫数量(29、40和30头)。表明配方3、配方6和配方35对华北大黑鳃金龟成虫具有显著引诱效果,可作为其引诱剂备选配方应用于生态防控。     

铜绿丽金龟对寄主植物挥发物的触角电生理及行为反应

为深入了解铜绿丽金龟的取食行为,探索开发安全高效的植物源引诱剂,应用昆虫触角电位反应仪和Y型嗅觉仪测试其对不同寄主植物挥发物的趋向行为差异,并根据室内行为结果配制诱剂进行大田试验。结果表明:铜绿丽金龟雄虫对水杨酸甲酯和(1,1’-联环戊基)-2-酮的触角电位反应(electroantennography,EAG)值显著高于其它试剂;石竹烯和水杨酸甲酯能引起雌虫触角较强的电位反应;乙酸顺式-3-己烯酯和石竹烯分别对雄虫和雌虫有较高的嗅觉选择反应率,分别达0.95和0.94。综合EAG和嗅觉试验结果,选择对雌、雄虫均有较好引诱效果的反式-2-己烯醛、乙酸顺式-3-己烯酯、石竹烯、(1,1’-联环戊基)-2-酮和水杨酸甲酯进行田间试验,最终筛选到铜绿丽金龟雄虫的最适引诱剂为每诱芯360 mg乙酸顺式-3-己烯酯,雌虫的最适引诱剂为每诱芯360 mg石竹烯,日诱虫量分别可达33.00±1.53头和29.33±1.45头。     

粘虫雌蛾性信息素特征成分鉴定及其不同配比的室内引诱效果

为确定粘虫Mythimna separata(Walker)雌蛾的性信息素特征成分及其不同配比的室内引诱效果,采用气相色谱-质谱和气相色谱-触角电位联用技术检测了雌蛾性腺浸提液,并利用Y型嗅觉仪测定了粘虫雄蛾对不同配比性信息素特征成分的选择反应。结果显示,从粘虫的求偶雌蛾性腺浸提液中可分离到顺-11-十六碳烯醛、十六碳醛和顺-11-十六碳烯醇3种特征成分,在色谱柱中的保留时间依次为15.82、16.06和17.27 min,含量分别为3.37、1.83和0.10 ng,比例约为34∶18∶1。无论是天然存在于雌蛾性腺还是人工合成的顺-11-十六碳烯醛均能够激发雄蛾的电生理反应。顺-11-十六碳烯醛、十六碳醛和顺-11-十六碳烯醇不同配比对雄蛾表现出不同的引诱活性,最大引诱率达87%,极显著高于对照溶剂石蜡油对雄蛾的引诱率。表明顺-11-十六碳烯醛、十六碳醛和顺-11-十六碳烯醇为中国粘虫种群的雌蛾性信息素特征成分,且其不同配比对雄蛾有不同的引诱活性。     

双委夜蛾雌蛾性信息素组分及其室内活性测定

为明确双委夜蛾Athetis dissimilis雌蛾性信息素主要组分及其对雄蛾的引诱效果,利用气相色谱-质谱联用仪对双委夜蛾未交配雌蛾性腺提取物的活性组分进行鉴定,分析不同日龄雌蛾性腺活性组分滴度的变化,同时利用二项选择嗅觉仪测定未交配雄蛾对雌蛾性腺活性组分的选择反应。结果显示,从双委夜蛾未交配雌蛾性腺提取物中分离到顺-9-十四碳烯醇、顺-7-十六碳烯醛和顺-11-十四碳烯乙酸酯3个组分,其在色谱柱中的保留时间依次为21.940、26.312和26.844 min,各组分滴度分别为2.00、1.20和1.86 ng/雌,三者的比例约为3∶2∶3。这3种组分以不同体积比混合后对雄蛾的引诱活性不同,以1∶1∶1三元混合物的引诱效果最好,且在使用剂量为0.2μg时雄蛾对其的选择率最高,达80.77%。顺-9-十四碳烯醇和顺-11-十四碳烯乙酸酯在不同日龄雌蛾中的滴度变化基本一致,均为羽化后前3 d缓慢增加,第4天升至最高,此后又快速下降;顺-7-十六碳烯醛的滴度在羽化后前2 d差异不大,第3天显著升高,第4天略有下降,之后再度升高并于第6天达到最高。推测顺-9-十四碳烯醇、顺-7-十六碳烯...     

铜绿丽金龟对植物源挥发物的触角电位和行为反应

为筛选适宜的铜绿丽金龟植物源引诱剂,利用触角电位(EAG)和Y形嗅觉仪技术,测定了铜绿丽金龟雌、雄虫对20种植物源挥发物的电生理和行为反应。结果表明:在10μg/μL浓度下,铜绿丽金龟对甲基庚烯酮、顺-3-己烯乙酸酯、壬醛、1-辛烯-3-醇、芳樟醇和反-2-己烯醇具有较强的触角电位反应,且呈雌虫大于雄虫的趋势。Y形嗅觉仪行为测定中,雌虫对多数挥发物的敏感度高于雄虫。其中反-2-己烯醇、顺-3-己烯乙酸酯、甲基庚烯酮和1-辛烯-3-醇对铜绿丽金龟雌虫的吸引作用显著高于对照;而雄虫仅对顺-3-己烯乙酸酯有显著的趋向选择。本研究为开发有效的铜绿丽金龟田间引诱剂用于生态治理提供依据。     

3种金龟甲对寄主植物的行为反应研究

选取不同寄主植物叶片对暗黑鳃金龟、铜绿丽金龟、大黑鳃金龟的雌雄虫进行室内嗅觉试验,结果表明不同植物叶片对上述几种金龟甲的引诱作用差异较显著。大黑鳃金龟雌虫对榆树的选择反应率和选择系数最高,分别为81%和0.61; 雄虫对沟叶结缕草趋向较强,选择反应率和选择系数为93%和0.85。榆树对暗黑鳃金龟雌虫的引诱效果显著,其选择反应率和选择系数达到80%和0.59; 雄虫对桑树有强趋性,选择反应率和选择系数分别高达87%和0.74。女贞对铜绿丽金龟雌雄虫均有好的引诱活性,雌虫选择反应率和选择系数达到79%和0.58,雄虫分别为72%和0.44。以上寄主植物对金龟甲诱集作用的研究不仅对现阶段农田防治金龟甲有重要指导意义,而且还可为金龟甲生防植物的选择及食诱剂的研制和开发提供知识储备。     

7种林木植物对华北大黑鳃金龟取食和繁殖的影响

为明确华北大黑鳃金龟Holotrichia oblita(Faldermann)的嗜食植物,优化其室内人工饲养技术及为诱虫植物提供候选材料,以花生叶片为对照,研究了7种林木植物叶片对华北大黑鳃金龟取食和繁殖的影响。结果表明,华北大黑鳃金龟对8种植物日均取食量由高到低依次为金叶女贞、刺槐、核桃、榆树、花生、柳树、香椿、毛白杨,其中金叶女贞、香椿和毛白杨与花生间有极显著差异,金叶女贞与刺槐、核桃、榆树间无显著差异;单雌产卵量由高到低依次为金叶女贞、柳树、核桃、香椿、花生、榆树、毛白杨、刺槐,其中金叶女贞、柳树、核桃、刺槐与花生间有极显著差异,而金叶女贞与柳树间无显著差异。研究表明,饲养华北大黑鳃金龟成虫适宜饲料植物为金叶女贞,日均取食量最高为4.70 g,产卵期最长为56.00 d,单雌产卵量最多为58.88个,其次为核桃和柳树。     

烟粉虱MED隐种对13种植物挥发性物质的行为反应

为明确烟粉虱Bemisia tabaci MED隐种对不同植物挥发性物质的行为选择,采用Y型嗅觉仪测定了烟粉虱雌、雄成虫对13种植物挥发性物质的趋向行为反应。结果显示,烟粉虱MED隐种雌、雄成虫对不同浓度植物挥发性物质的选择性存在明显差异。1、0.01和0.0001μL/μL浓度的芳樟醇、反-2-己烯醛和桉树脑对烟粉虱MED隐种雌、雄虫校正反应率均为正值,具显著吸引效果;而p-伞花烃、月桂烯、3-蒈烯、α-蒎烯和顺-3-己烯-1-醇对雌、雄成虫的校正反应率均为负值,说明其对烟粉虱MED隐种雌、雄虫具有不同程度的趋避性。雌烟粉虱对0.0001μL/μL浓度桉树脑的选择率达最大值70.30%,与对照差异显著,具显著吸引作用。雌、雄烟粉虱对0.01μL/μL浓度的顺-3-己烯-1-醇的选择率最小,仅为24.75%和27.03%,具显著驱避作用。因此,烟粉虱MED隐种雌、雄成虫对不同浓度植物挥发性物质趋性反应不同,可能是烟粉虱环境适应性的表现。     

昆虫病原线虫泰山1号防治花生地蛴螬的方法及其效果

结果表明,用昆虫病原线虫泰山1号,在花生地防治华北大黑鳃金龟及暗黑鳃金龟幼虫的方法,使每666.7m~2花生地蛴螬的残虫量由8083头控制到167头,花生的损失率由原来的38.7%降至0.2%。线虫防治与施药区比较,每亩可增收花生150kg 以上,较空白对照区可增收花生237.5kg。充分显示了用该线虫取代农药防治的可行性,为控制历年严重为害花生的华北大黑鳃金龟及暗黑鳃金龟找到了新的途径。     

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.     

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。     

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.     

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.     

Detection of the phytotoxin coronatine by ELISA and localization in infected plant tissue

Several pathovars of Pseudomonas syringae produce the phytotoxin coronatine (COR)in vitro, and the availability of purified toxin has facilitated development of immunological detection methods. A modified, indirect competitive ELISA using the COR-specific monoclonal antibody 11B8 was developed to detect COR in various host plants infected by P. syringae. The estimated detection limit for COR was 50 pg per well, and COR could be reliably quantified from 5 to 40 ng ml⁻¹. The subcellular localization of COR within infected tomato tissue was investigated using the COR-specific antibody MAb 8H3G2. Immunofluorescence microscopy and immunogold labelling showed that COR was present inside tomato cells and was associated with chloroplasts and particles of proteinase inhibitor I. Localization studies indicated that COR is mobile in infected plant tissue and can be detected in healthy tissue adjacent to the bacterial lesions.     

Influence of humidity on incidence of Didymella bryoniae on cucumber leaves and growing tips under controlled environmental conditions

The influence of relative humidity, leaf wetting, mechanical injury and inoculum concentration on the incidence ofDidymella bryoniae on growing tips and young and older leaves of cucumber was studied in growth chambers.Infection was rare at 60% r.h. It increased at 95% r.h. and was most serious if the leaves were kept wet. A period of 1 hour of free water was sufficient for the initial stage of infection. For further expansion of the disease, leaf wetness was required.A high relative humidity did not predispose leaves to infection byD. bryoniae. Wounding was essential for infection of older leaves, but not for infection of young plant tissue.A higher conidial concentration increased infection. Without keeping, the leaves wet at 95% r.h. a tenfold conidial concentration was needed to get equal infection as with leaf wetting.To control the disease by means of the climate, it is of major importance to prevent the presence of free water on plant parts.Samenvatting De invloed van de relatieve luchtvochtigheid, het bevochtigen van het blad, mechanische beschadiging en inoculumconcentratie op het optreden vanDidymella bryoniae op groeipunten en jonge en oudere bladeren van komkommer is in klimaatkasten onderzocht.Aantasting kwam zelden voor bij 60% R.V., nam toe bij 95% R.V. en was het ernstigst als de bladeren nat werden gehouden. Voor de eerste fase van infective was de aanwezigheid van vrij water gedurende 1 à 2 uur voldoende. Voor een verdere uitbreiding van de aantasting moest het blad nat zijn.Een hoge relatieve luchtvochtigheid had geen predispositie-effect of de infectie van bladeren doorD. bryoniae.Voor de infectie van oudere bladeren was verwonding nodig, voor die van jong planteweefsel niet.Een hogere concentratie van conidiën verhoogde de aantasting. Zonder het blad nat te houden, was een tienvoudige concentratie van conidiën nodig om een gelijke infectie te verkrijgen als met bladbevochtiging.Voor de bestrijding van de ziekte via het klimaat is het tegengaan van de aanwezigheid van vrij water op plantedelen van het grootste belang.Seconded to the Glasshouse Crops Research and Experiment Station, Zuidweg 38, 2671 MN Naaldwijk, the Netherlands.