葡萄白腐病菌对抑霉唑的敏感基线及其与不同杀菌剂的交互抗性

为明确山东省胶东地区葡萄白腐病菌Coniella diplodiella对抑霉唑的敏感性及抑霉唑与常规杀菌剂之间的交互抗性,采用菌丝生长速率法测定葡萄白腐病菌对抑霉唑等杀菌剂的敏感性,并通过分析抑霉唑与戊唑醇、吡唑醚菌酯、福美双、多菌灵、代森锰锌毒力的相关性,判断抑霉唑与各药剂之间是否存在交互抗性。结果表明,供试69株葡萄白腐病菌菌株对抑霉唑的EC₅₀在0.13~55.53 μg/mL之间,最高值与最低值相差427.15倍;其频数分布图呈多峰曲线,第一主峰内EC₅₀平均值为6.34 μg/mL,可作为胶东地区葡萄白腐病菌对抑霉唑的敏感基线。与敏感基线相比,田间已出现抑霉唑低抗菌株,占检测总株数的8.70%,未检测到中、高抗菌株。选择3个抗性菌株连续继代培养10代后,其对抑霉唑的敏感性明显提高,说明其抗药性不能稳定遗传。抑霉唑EC₅₀对数值与戊唑醇、吡唑醚菌酯、福美双、多菌灵、代森锰锌的EC₅₀对数值之间的相关系数分别为0.799、-0.143、-0.089、-0.268和0.159,说明抑霉唑与戊唑醇存在一定的交互抗性,但与其他4种药剂之间不存在交互抗性。表明抑霉唑可用于胶东地区田间葡萄白腐病的有效防控。     

河南省小麦赤霉病菌对咯菌腈的敏感性

为明确河南省小麦赤霉病菌Fusarium graminearum对咯菌腈的敏感性,采用菌丝生长速率法测定了咯菌腈对从该省11个地市分离的95株菌株的毒力,通过方差分析法及聚类分析法对测定结果进行了分析,并研究了咯菌腈与多菌灵、戊唑醇对病菌毒力的相关性。结果显示：咯菌腈对小麦赤霉病菌菌丝生长的最低抑制浓度为0.1 μg/mL;咯菌腈对供试95株菌株的EC₅₀范围在0.003~0.088 μg/mL之间,平均EC₅₀为0.011 μg/mL;敏感性频率分布图显示,病菌群体中存在着对咯菌腈敏感性较低的亚群体,但67.4%供试菌株敏感性频率呈正态分布,将此部分菌株的EC₅₀平均值0.007 μg/mL作为小麦赤霉病菌对咯菌腈的敏感性基线。方差分析及聚类结果均显示,同一县市内的菌株对咯菌腈EC₅₀的最大值和最小值之比为1.1~8.3;除周口市沈丘县的菌株外,其余县市的菌株对咯菌腈敏感性差异不明显,咯菌腈EC₅₀平均值变化范围在0.005~0.028 g/mL之间,最大值是最小值的5.6倍;小麦赤霉病菌对咯菌腈的敏感性与其对多菌灵、戊唑醇的敏感性之间无明显相关性。表明河南省小麦赤霉病菌群体中尽管存在着敏感性较低的亚群体,但可通过药剂复配进行防控。     

福建省番茄灰霉病菌对氟啶胺敏感基线建立及与不同杀菌剂的交互抗性

为明确中国福建省番茄灰霉病菌对氟啶胺的敏感性及其与不同杀菌剂的交互抗性,采用菌丝生长速率法测定了106株采自福建省主要番茄产区的番茄灰霉病菌对氟啶胺的敏感性。结果表明,氟啶胺对福建省番茄灰霉病菌菌丝生长的EC50值在0.0037～0.0452 μg/mL之间,平均值为（0.0221 ±0.0098）μg/mL,其敏感性频率分布呈连续单峰曲线,符合正态分布,因此可将该EC50平均值（0.0221±0.0098）μg/mL作为福建省番茄灰霉病菌对氟啶胺的敏感基线,用于其田间抗药性监测。从106株菌株中选择15株对氟啶胺敏感性不同的菌株,测定了其对嘧霉胺、异菌脲、腐霉利和啶氧菌酯的敏感性。结果表明,供试5种杀菌剂对15株番茄灰霉病菌菌丝生长的平均抑制活性依次为氟啶胺 >异菌脲 >腐霉利 >啶氧菌酯 >嘧霉胺,氟啶胺与异菌脲、腐霉利、啶氧菌酯和嘧霉胺之间均不存在交互抗性。     

吉林省西瓜蔓枯病菌对吡唑醚菌酯的抗性监测及抗性风险评估

为明确吉林省西瓜蔓枯病菌Stagonosporopsis citrulli对吡唑醚菌酯的敏感基线和抗性风险,采用菌丝生长速率法测定吉林省151株西瓜蔓枯病菌菌株对吡唑醚菌酯的敏感性及吡唑醚菌酯对西瓜蔓枯病菌的最低抑制浓度,并监测375株西瓜蔓枯病菌菌株对吡唑醚菌酯的抗性水平。结果表明,供试的151株菌株对吡唑醚菌酯的敏感性频率分布呈连续的单峰曲线,接近正态分布,敏感基线为1.800 μg/mL;吡唑醚菌酯的最低抑制浓度MIC为80.000 μg/mL。抗性水平监测结果显示,375株菌株对吡唑醚菌酯的抗性频率为0。室内药剂驯化获得的抗性突变菌株T-LH3-1和T-XZC5-1在连续转接培养8代后的EC₅₀分别为16.139 μg/mL和31.782 μg/mL,抗性倍数分别为15和51,均为中抗水平,抗药性可以稳定遗传。抗性突变体及其亲本菌株生物学性状结果显示,抗性突变体生物适合度与其亲本菌株差异不显著。交互抗性结果表明,吡唑醚菌酯与醚菌酯之间存在正交互抗性,与戊唑醇、异菌脲、多菌灵和肟菌酯之间不存在交互抗性,可以交替使用以达到延缓抗药性的产生。     

福建省玉米小斑病菌对丙环唑、烯唑醇和咪鲜胺的敏感性

为明确玉米小斑病菌对丙环唑、烯唑醇和咪鲜胺的敏感性,采用菌丝生长速率法测定了自福建省15个市、县分离的185株玉米小斑病菌对3种药剂的敏感性。结果显示:供试菌株对丙环唑、烯唑醇和咪鲜胺的EC50值分别在0.0186~7.779、0.0416~22.32和0.0053~7.930μg/mL之间。敏感性频率分布图显示,玉米小斑病菌群体中已出现对丙环唑、烯唑醇和咪鲜胺敏感性降低的亚群体。以连续单峰频次分布的大多数菌株群体的EC50平均值(0.5199±0.0284)、(0.4079±0.0204)和(0.3818±0.0202)μg/mL分别作为玉米小斑病菌对丙环唑、烯唑醇和咪鲜胺的相对敏感基线,发现各有15.14%、20.00%和17.30%的菌株对丙环唑、烯唑醇和咪鲜胺产生了抗性,抗性倍数最高分别为14.96、54.71和20.77。玉米小斑病菌对3种杀菌剂之间具有显著的交互抗性,而丙环唑和烯唑醇之间的交互抗性相关系数最高,为0.8662。本研究结果可为田间玉米小斑病防控杀菌剂的合理使用提供理论依据。     

辽宁省稻瘟病菌对稻瘟灵的抗性监测及其对稻瘟病的田间防治效果

为明确辽宁省水稻稻瘟病菌Magnaporthe oryzae对稻瘟灵的抗性水平及变化动态,本研究于2017—2019年自辽宁省6个市的6个稻区采集并分离获得187株稻瘟病菌,利用菌丝生长速率法测定这187株稻瘟病菌菌株对稻瘟灵的敏感性及抗性,并采用茎叶喷雾法测定稻瘟灵对水稻稻瘟病的田间防治效果以及该药剂与其它药剂的交互抗性。结果表明：供试187株稻瘟病菌菌株对稻瘟灵的EC₅₀范围为0.94~34.96 μg/mL,左侧正态分布峰内EC₅₀平均值为5.05 μg/mL,稻瘟病菌对稻瘟灵的敏感性分布频率不符合正态分布,表明菌群中已经出现对稻瘟灵敏感性下降的亚群体。187株稻瘟病菌菌株对稻瘟灵的平均抗性倍数为3.70,抗性菌株出现频率为55.61%,平均抗性指数为0.40,抗性水平呈逐年增加趋势。2017—2019年稻瘟灵对水稻叶瘟病的防治效果分别为82.97%、78.86%和81.36%,对水稻穗颈瘟的防治效果分别为79.81%、77.68%和80.20%,说明在现有防控手段下未产生高水平抗性群体。稻瘟灵与肟菌酯、戊唑醇之间无交互抗性。与不同药剂轮换使用的前提下,稻瘟灵仍可作为主要药剂防治稻瘟病。     

番茄叶霉病菌对氟硅唑敏感基线及抗药性风险研究

从辽宁省不同地区未使用过氟硅唑的保护地中采集番茄叶霉病叶,经单孢分离获得43株叶霉病菌。采用茵丝生长速率法测定其对氟硅唑的敏感性。结果表明,菌株间存在较大差异,EC50值最低为0.151 9μg／mL,最高达4.647 5 μg／mL。所有菌株的EC₅₀总平均值为1.253 1μg/mL,可作为番茄叶霉病菌对氟硅唑的敏感基线。野生菌株经紫外线照射,获得两个抗药性突变菌株,其抗药性倍数分别为6.0和7.6。突变菌株的菌丝生长速率及产孢能力显著低于原野生菌株。     

辣椒疫霉对双炔酰菌胺敏感性及对其它杀菌剂的交互抗性

采用菌丝生长速率法测定了不同地区115个辣椒疫霉菌株对双炔酰菌胺的敏感性,同时测定了紫外诱导和药剂驯化的10个抗性突变体及其4个亲本菌株对双炔酰菌胺、烯酰吗啉、甲霜灵、嘧菌酯和霜脲氰的敏感性。山东青州、寿光和河北定兴、藁城4地辣椒疫霉菌株均对双炔酰菌胺较敏感,且敏感性差异不显著。不同抗性水平菌株对5种药剂的敏感性测定和相关性分析结果显示,双炔酰菌胺与其它几类药剂之间均不存在交互抗性。10个抗性突变体继代培养11代后,8个抗性突变体抗药性不能稳定遗传;2个抗性突变体抗药性不仅能够稳定遗传,且EC₅₀值维持在很高水平,分别为1 429.524 μg/mL和6 872.476 μg/mL,因此,双炔酰菌胺的连续使用有利于抗药群体的发展。     

黑龙江省和吉林省马铃薯晚疫病菌对氟啶胺和甲霜灵的敏感性变化

2006-2008年在黑龙江省和吉林省共分离获得61株马铃薯晚疫病菌,测定了这些菌株对交配型、氟啶胺和甲霜灵的敏感性。交配型测定结果显示所有菌株都显示A1交配型。甲霜灵测定结果显示10个菌株(16.4%)显示为敏感性,11个菌株(18.0%)显示为中抗,40个菌株(65.6%)显示为抗性。这说明吉林省和黑龙江省发生的晚疫病菌已对甲霜灵产生抗性。氟啶胺敏感性测定结果表明,不同地区、不同年份分离的马铃薯晚疫病菌对氟啶胺的敏感性无显著差异, 其敏感性呈连续的单峰曲线分布, EC50在0.203 3~0.783 7 μg/mL之间, 最不敏感菌株是最敏感菌株的3.85倍, 平均值为(0.4781±0.0163)μg/mL, 未出现敏感性下降的抗药性群体, 因此可作为马铃薯晚疫病菌对氟啶胺的敏感性基线;83.6%的供试菌株对甲霜灵的敏感性下降, 甲霜灵与氟啶胺之间不存在交互抗药性。测定氟啶胺对马铃薯晚疫病的盆栽防治试验结果表明,氟啶胺可湿性粉剂、氟啶胺悬浮剂和烯酰吗啉能很好地控制晚疫病,防治效果分别为85.71%、87.00%、82.19%,而甲霜灵的为23.92%。     

我国棉蚜对吡虫啉和氟啶虫胺腈抗性水平监测与交互抗性分析

为了解我国不同地区棉蚜Aphis gossypii对吡虫啉和氟啶虫胺腈的抗性现状,对代表性棉区棉蚜田间种群进行抗药性监测,同时通过构建具有R81T及V62I单突变和R81T-V62I共同突变的棉蚜烟碱型乙酰胆碱受体（nicotinic acetylcholine receptor,nAChR）蛋白模型,与吡虫啉和氟啶虫胺腈进行分子对接,分析这些突变在吡虫啉和氟啶虫胺腈抗性中的作用,并分析吡虫啉和氟啶虫胺腈之间是否存在交互抗性。结果显示,不同地区棉蚜对吡虫啉产生了高水平抗性,抗性倍数为174.70~56 409.18,对氟啶虫胺腈产生了低至中等水平抗性,抗性倍数为7.35~44.63,说明不同地区的棉蚜对氟啶虫胺腈的敏感度高于吡虫啉,且吡虫啉抗性和氟啶虫胺腈抗性间不存在相关性。R81T、V62I单突变和R81T-V62I共同突变导致吡虫啉与棉蚜nAChR的亲和力降低,对氟啶虫胺腈与棉蚜nAChR的结合无明显影响。R81T及V62I单突变和R81T-V62I共同突变导致棉蚜对吡虫啉产生靶标抗性,但是对氟啶虫胺腈的抗性无明显影响,这些突变不会导致吡虫啉与氟啶虫胺腈产生靶标突变的交互抗性。     

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.     

Plant Viruses Transmitted by Whiteflies

One-hundred and fourteen virus species are transmitted by whiteflies (family Aleyrodidae). Bemisia tabaci transmits 111 of these species while Trialeurodes vaporariorum and T. abutilonia transmit three species each. B. tabaci and T. vaporariorum are present in the European–Mediterranean region, though the former is restricted in its distribution. Of the whitefly-transmitted virus species, 90% belong to the Begomovirus genus, 6% to the Crinivirus genus and the remaining 4% are in the Closterovirus, Ipomovirus or Carlavirus genera. Other named, whitefly-transmitted viruses that have not yet been ranked as species are also documented. The names, abbreviations and synonyms of the whitefly-transmitted viruses are presented in tabulated form together with details of their whitefly vectors, natural hosts and distribution. Entries are also annotated with references. Whitefly-transmitted viruses affecting plants in the European–Mediterranean region have been highlighted in the text.     

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.     

Relationships of <Emphasis Type="Italic">Barley yellow dwarf virus</Emphasis>-PAV and <Emphasis Type="Italic">Cereal yellow dwarf virus</Emphasis>-RPV from Iran with viruses of the family <Emphasis Type="Italic">Luteoviridae</Emphasis>

Barley yellow dwarf disease is one of the most important problems confronting cereal production in Iran. Barley yellow dwarf virus-PAV (BYDV-PAV) and Cereal yellow dwarf virus-RPV (CYDV-RPV) are the predominant viruses associated with the disease. One isolate of BYDV-PAV from wheat (PAV-IR) and one isolate of CYDV-RPV from barley (RPV-IR) were selected for molecular characterisations. A genome segment of each isolate was amplified by PCR. The PAV-IR fragment (1264 nt) covered a region containing partial genes for coat protein (CP), read through protein (RTP) and movement protein (MP). PAV-IR showed a high sequence identity to PAV isolates from USA, France and Japan (96–97%). In a phylogenetic analysis it was placed into PAV group I together with PAV isolates from barley and oats. The fragment of RPV-IR (719 nt) contained partial genes for CP, RTP and MP. The sequence information confirmed its identity as CYDV. However, RPV-IR showed 90–91% identity with both RPV and Cereal yellow dwarf virus-RPS (CYDV-RPS). Phylogenetic analyses suggested that it was more closely related to RPS. These data comprise the first attempt to characterise BYD-causing viruses in Iran and southwest Asia. The nucleotide sequence data reported appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession numbers AY450425 and AY450454     

Broad bean mottle virus in Morocco; curculionid vectors,and natural occurrence in food legumes other than faba bean (Vicia faba)

Broad bean mottle virus (BBMV) was transmitted from infected to healthy faba-bean plants by the curculionid weevilsApion radiolus Kirby,Hypera variabilis Herbst,Pachytychius strumarius Gyll,Smicronyx cyaneus Gyll, andSitona lineatus L. The latter appeared to be an efficient vector: acquisition and inoculation occurred at the first bite, the rate of transmission was c. 41%, and virus retention lasted for at least seven days.S. lineatus transmitted the virus from faba bean to lentil and pea, but not to the three genotypes of chickpea tested. This is the first report on the generaHypera, Pachytychius, andSmicronyx as virus vectors, and onA. radiolus, H. variabilis, P. strumarius, andS. cyaneus as vectors of BBMV.Out of 351 samples of food legumes with symptoms suggestive of virus infection, 16, 11, 19, and 17% of the samples of chickpea, lentil, pea, and common bean, respectively, were found infected when tested for BBMV in DAS-ELISA. This is the first report on the natural occurrence of BBMV in chickpea, lentil, pea, and common bean. The virus should be regarded as a food-legume virus rather than a faba-bean virus solely, and is considered an actual threat to food legume improvement programmes.     

Identification,incidence and characterization of <Emphasis Type="Italic">Fusarium proliferatum</Emphasis>on ornamental palms in Spain

During a survey conducted from 1998 to 2002, Fusarium proliferatum was found associated with young and adult palms belonging to the genera Chamaerops, Phoenix, Trachycarpus and Washingtonia showing symptoms of wilt and dieback. The fertility and toxicological profile of 36 strains representing different locations and hosts were studied. All of them except two, which were infertile, belonged to mating population D. Both mating types (MATD-1 and MATD-2) were isolated from the same host species, showing a high potential of genetic recombination in the field. Additionally, eight strains were fertile once crossed as female. Toxin analysis showed differences in the ability of strains to produce fumonisin B₁, moniliformin, beauvericin, fusaric acid and fusaproliferin. Only 17 of them produced all the toxins analyzed. Pathogenicity tests were conducted on Phoenix dactylifera and P. canariensis using nine F. proliferatum Spanish strains and two reference strains from Saudi Arabia. Eight months after inoculation all strains caused disease, with palms showing lesions on the bases of leaves and development of wilt symptoms similar to those originally observed in affected plants. This is the first report on the occurrence of F. proliferatum on P. dactylifera in Spain and also the first report of this pathogen on C. humilis, P. canariensis, P. reclinata, T. fortunei, W. filifera and W. robusta.     

Recent observations on leafy gall in Liliaceae and some other families

Corynebacterium fascians, which causes leafy gall, has been shown to be responsible for the unusual symptoms recently found in lilies. The symptoms are described and the different bacterial isolates compared by biochemical, serological and pathogenicity experiments. No evidence could be found for the existence of specialized strains even though considerable variation in virulence could be demonstrated. Although the role of variation in susceptibility of the different lily cultivars should not be underestimated, it would appear that high inoculum levels ofC. fascians in the soil may be largely responsible for these outbreaks.Also included in this study are the results of biochemical, serological and pathogenicity experiments ofC. fascians which has been isolated fromKalanchoe, Euphorbia, Brodiaea, Hebe andVerbascum.Samenvatting Reeds een aantal jaren was in lelies een woekering in stengelbollen bekend, die echter sporadisch voorkwam en economisch van weinig betekenis was. Tijdens de zomer van 1977 echter trad de ziekte op één enkel perceel zo ernstig op dat zeer aanzienlijke oogstderving het gevolg was. Behalve de stengelbol kan ook de hoofdbol misvormd zijn. Bovendien kunnen misvormde stengelbollen lange spruiten vormen, zgn. sabeltandvorming. Soms is het wortelstelsel gereduceerd; in de kas zijn verdikte stengels waargenomen. De ziekte staat nu bekend onder de naam woekerziekte.Door de PD te Wageningen en het LBO te Lisse werd de bacterieCorynebacterium fascians (Tilford) Dows. uit het zieke materiaal geïsoleerd. In gezamenlijk onderzoek werd nagegaan of de bacterie de veroorzaker is van bovengenoemde symptomen en of hier sprake is van een op lelie gespecialiseerde stam.Biochemische en serologische vergelijkingen tussen isolaten vanC. fascians uit lelie,Kalanchoe, Euphorbia, Brodiaeea, Hebe enVerbascum laten zien dat er zeer weinig verschillen bestaan. Alle isolaten reageren op een standaard antiserum met titers variërend tussen 1: 640–1: 5120.Een oriënterende inoculatieproef werd uitgevoerd op het LBO in 1977. Daarna werden op de PD 10 van de 25 isolaten uit lelie en 8 uit andere waardplanten getoetst op lelie, chrysant en lathyrus. Uit de inoculatieproeven blijkt, dat de bacterie de veroorzaker is van de waargenomen symptomen. Tussen de isolaten blijkt een groot verschil in pathogeniteit te bestaan (12–100% aantasting), zonder dat dit aan herkomst gebonden is. Het voorkomen van op lelie of andere waardplanten gespecialiseerde stammen is daarom niet aan te nemen.In hoeverre de hevige aantasting een gevolg is van een opbouw van de bacterie-populatie door een te nauwe vruchtwisseling en mechanische rooimethoden moet worden nagegaan.     

A new <Emphasis Type="Italic">Rhizoctonia</Emphasis> sp. closely related to <Emphasis Type="Italic">Waitea circinata</Emphasis> causes a new disease of creeping bentgrass

Isolates of an unidentified Rhizoctonia sp. (UR isolates) were obtained from creeping bentgrass and Kentucky bluegrass with reddish brown sheath and foliar rots. Because the UR isolates anastomosed with isolates of three varieties of Waitea circinata (var. oryzae, var. zeae, and var. circinata), colony morphology, hyphal growth rate at different temperatures, pathogenicity, sequence analysis of the internal transcribed spacers (ITS) region of ribosomal RNA genes (rDNA) were compared. The colony color of mature UR isolates was distinct from isolates of the other three varieties of W. circinata. In pathogenicity tests on creeping bentgrass, the severity of the disease caused by UR isolates was significantly higher than that caused by the three varieties of W. circinata. Sequence similarities of the rDNA-ITS region between UR isolates and between isolates within each variety were high (97–100%), but they were lower among isolates from UR and the varieties of W. circinata (88–94%). In a phylogenetic tree based on the rDNA-ITS sequences, UR isolates formed a cluster separate from each of the clusters formed by the three varieties of W. circinata. These results indicate that the UR isolates clearly differ from the three varieties of W. circinata. We therefore propose that the UR isolates be classified as new Rhizoctonia sp. that are closely related to W. circinata and that the disease on creeping bentgrass should be called Waitea reddish-brown patch disease (Sekikasshoku-hagusare-byo in Japanese).     

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.     

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.