Control of Dutch elm disease by the sterol biosynthesis inhibitors fenpropimorph and fenpropidin

Sterol biosynthesis inhibitors that inhibit the yeast-hyphae conversion inOphiostoma ulmi suppressed Dutch elm disease development in two elm clones. After curative treatment with fenpropimorph-sulphate of 27 Vegeta elms which had previously been inoculated withO. ulmi, 25 trees did not show disease symptoms by the end of the second season. All 41 control trees, inoculated withO. ulmi only, were clearly diseased. In an experiment with Commelin elms three fenpropimorph salts and thiabendazole were compared. Injection of the trees three weeks after inoculation withO. ulmi gave by the end of the second season no symptoms of Dutch elm disease in any of the trees injected with fenpropimorph-phosphate or thiabendazole, and in most trees injected with fenpropimorph-acetate or-sulphate. Similar treatments with the free base of fenpropimorph and fenpropidin-sulphate were less effective due to insufficient uptake of the fenpropimorph emulsion and phytotoxicity of fenpropidin-sulphate, respectively. Injection of fenpropimorph-sulphate or thiabendazole six weeks after inoculation withO. ulmi did not result in significant differences from the control group inoculated withO. ulmi only.Fenpropimorph-phosphate and-sulphate completely suppressed Dutch elm disease upon injection of only 7.5 or 10 g per tree (average tree diameter 28 cm). Residue analyses showed only a slow decrease in concentration of the fungicide over two growing seasons and an apparent transport into the new annual ring, other prerequisites for a possible future use for control of Dutch elm disease.Samenvatting De iepeziekte kan onderdrukt worden door sterolbiosyntheseremmers die de overgang vanOphiostoma ulmi van de gistvorm in de hyfevorm remmen. Aan het eind van het tweede seizoen na een curatieve behandeling van 27 Vegeta iepen met fenpropimorfsulfaat bleken 25 bomen geen symptomen van iepeziekte te vertonen. Alle controlebomen, die alleen metO. ulmi geïnoculeerd waren, waren duidelijk ziek. In een proef met Commelin iepen werden drie fenpropimorfzouten en thiabendazool vergeleken. De zouten werden drie weken na de inoculatie metO. ulmi geïnjecteerd. Aan het eind van het tweede seizoen vertoonden geen van de bomen die met fenpropimorffosfaat of thiabendazool geïnjecteerd waren en slechts enkele bomen die met fenpropimorfacetaat of-sulfaat geïnjecteerd waren iepeziektesymptomen. Behandelingen met fenpropimorf (vrije base) en fenpropidinsulfaat werkten minder goed door de slechte opname van de fenpropimorfemulsie en de fytotoxiciteit van fenpropidin. Injectie met fenpropimorfsulfaat of thiabendazool zes weken na inoculatie leidde niet tot significante verschillen met de controlegroep die alleen metO. ulmi geïnoculeerd was.Een dosis fenpropimorffosfaat of-sulfaat van 7.5 of 10 g per boom met een gemiddelde boomdiameter van 26 cm bleek de iepeziekte volledig te kunnen onderdrukken. Uit residue-onderzoek bleek dat de concentratie van het fungicide gedurende de twee groeiseizoenen slechts langzaam afnam en dat het middel naar de nieuwe jaarring werd getransporteerd, twee voorwaarden voor een toepassing op praktijkschaal van fenpropimorf voor de bestrijding van de iepeziekte.     

Pseudomonas for biological control of dutch elm disease. I. Labeling,detection and identification of pseudomonas isolates injected into elms; comparison of various methods

To understand the mechanisms involved in biological control of Dutch elm disease byPseudomonas, data were needed on the distribution of the introduced bacteria within elm and on the development of the bacterial population over a period of time.As traditional biochemical identification techniques are not suitable for distinguishment between individualPseudomonas isolates, three alternative approaches were compared.

The hymenopteran parasitoids of some elm bark beetles in Serbia

The parasitoids of the elm bark beetlesScolytus ensifer, S. kirschi, S. multistriatus, S. pygmaeus andPteleobius vittatus were studied in ten localities in Serbia. Eleven species of parasitoids ofS. ensifer, 10 ofS. kirschi, 13 ofS. multistriatus, 12 ofS. pygmaeus, and four ofP. vittatus were found. The most abundant wereEcphylus silesiacus, Dendrosoter protuberans, Cheiropachus quadrum andRhaphitelus maculatus. Acrocormus semifasciatus, Cerocephala eccoptogastri, Mesopolobus typographi andDoryctes pomarius were found in some samples. http://www.phytoparasitica.org posting May 4, 2007     

Genetic evidence for natural hybridization between the Dutch elm disease pathogens Ophiostoma novo-ulmi ssp. novo-ulmi and O. novo-ulmi ssp. americana

The Dutch elm disease pathogen Ophiostoma novo-ulmi is separated into subspecies novo-ulmi , formerly known as the Eurasian (EAN) race, and subspecies americana , formerly known as the North American (NAN) race. Both subspecies occur in Europe, and hybrids between them are suspected to have emerged in parts of Europe where their ranges overlap. Authenticated isolates of both subspecies were examined in order to determine whether fixed mutations occur in the cerato-ulmin ( cu ) and in the colony type gene ( col1 ). One and six mutations were detected between subspp. novo-ulmi and americana in cu and col1 , respectively. The mutation in cu and one mutation in col1 proved to be located within restriction sites, and were used for PCR-RFLP. This method provides a quick and reliable diagnostic method to differentiate the two subspecies. Seven isolates of O. novo-ulmi from Austria were suspected to be hybrids between subspp. novo-ulmi and americana , and were tested by PCR-RFLP of their cu and col1 genes. Two of the suspected hybrids from Austria (isolates AT73 and AT146) had the cu PCR-RFLP profile of ssp. americana and the col1 PCR-RFLP profile of ssp. novo-ulmi . Furthermore, a ssp. novo-ulmi tester isolate from Poland (P150) showed a similar hybrid pattern. This is the first evidence revealing recombination between two genes and thus hybridization between the two subspecies of O. novo-ulmi in nature.     

Field evaluation of a supervised control system forBotrytis leaf blight in spring sown onions in the Netherlands

Between 1988 and 1992 two existing weather based advisory models to control leaf blight in onions, were evaluated in the Netherlands. The first model, BOTCAST, can be used to time the initial spray while the second model, SIV, can be used to advise on every subsequent spraying. The evaluation based on field trials showed that application of both BOTCAST and SIV can reduce the number of sprays by 54% compared to a weekly spraying program without any yield loss or a higher disease severity. There was no relation between yield losses of untreated plots and disease severity expressed as lesion counts or leaf dieback. Relative disease growth rate was significantly but not closely related to weather based model characteristics or the observed crop micro-climate using linear regression analysis. The model characteristics did not yield better regressions than the climatological characteristics. Two changes to improve BOTCAST are proposed. Introduction of a supervised control system based on BOTCAST and SIV seems only economically feasible when the system is used as a regional warning system.     

Assessment of Phaeotheca dimorphospora for biological control of the Dutch elm disease pathogens, Ophiostoma ulmi and O. novo-ulmi

The antagonistic fungus Phaeotheca dimorphospora was tested as a biocontrol agent against the Dutch elm disease pathogens, Ophiostoma ulmi and O. novo-ulmi , on Ulmus americana seedlings in the glasshouse. Curative inoculation of seedlings with P. dimorphospora had no significant effect on disease development. Conditioning inoculation of seedlings with the antagonist protected them against O. ulmi but not against the more aggressive O. novo-ulmi . In seedlings challenged with both the antagonist and either one of the pathogens, P. dimorphospora only spread locally around the inoculation point; however, the pathogens spread systemically throughout the whole plant. O. novo-ulmi survived in the region colonized by P. dimorphospora , whereas O. ulmi did not.     

Greenhouse trials of newBacillus thuringiensis isolates for control ofChilo partellus larvae in sorghum

Eight newBacillus thuringiensis Berliner (Bt) isolates originally recovered from different source materials and geographic locations in Kenya were tested againstChilo partellus (Swinhoe) on sorghum grown in a greenhouse. All isolates had been demonstrated previously to be toxic to this pest.Bt strains were cultured in a liquid growth medium and preserved as powders for experimental application. Three-week-old sorghum plants (4-6 leaves) were artificially infested with 20 neonateC. partellus and sprayed 24 h later withBt suspensions. Non-infested sorghum and infested non-treated sorghum served as the comparative checks within each experimental trial. Plant development and dead-heart formation were monitored up to harvest; at harvest, grain yield was recorded. In each replicate trial, all of theBt strains tested reduced plant damage consistently, compared with the infested, non-treated checks. Dead-heart formation was significantly reduced and grain yields were significantly higher. Three novel isolates, A-3, A-C-2 and M44-2, provided superior levels of protection throughout. Statistically, there was no difference among these threeBt treatments and the non-infested check in terms of the number of dead-hearts (i.e., non-yielding plants) that formed during the course of the experiment. In the infested, non-treated check plots, dead-hearts developed in 74.5±10.0% of the plants, compared with only 3.1±1.2% of the non-infested plants, and 3.1 ±1.5%, 6.2±2.0% and 6.2±2.0% of the plants treated with M44-2, A-3 and A-C-2, respectively. At harvest, the weight of grain obtained from the non-infested control plots was considered to be 100% of the potential yield for each experimental replicate. In the infested, non-treated controls, only 14±5.6% of the potential yield was realized. When isolates M44-2, A-3 and A-C-2 were applied, proportionate yields of 83±5.4%, 93±2.3% and 98±1.2%, respectively, were obtained. Results showed that theBt strains selected may have a strategic role to play in the management ofC. partellus, providing applications are timed to target young larvae feeding in the leaf whorl.     

Release and establishment ofCotesia flavipes for biological control of maize stemborers in Zimbabwe

Five populations of the crambid stemborerChilo partellus (Swinhoe) and one of the noctuid borerBusseola fusca (Fuller) from Zimbabwe were evaluated for their suitability for immature development of the exotic braconid larval parasitoidCotesia flavipes Cameron. Successful parasitoid development occurred only onC. partellus but parasitism as well as egg-to-adult development time did not vary among the five populations. Smallest parasitoid broods, and sex ratios as the proportion of female offspring, however, were produced withC. partellus from the Muzarabani area of Zimbabwe.Co. flavipes became successfully established in five out of eight locations, where it had been released in July 1999 and the 2004/05 summer season. Its spread and impact, however, still need to be assessed. http://www.phytoparasitica.org posting March 10, 2008.     

不同药剂和施药方法对韭蛆的田间防治效果

为筛选对韭菜迟眼蕈蚊Bradysia odoriphaga高效低毒的防治药剂、使用剂量及科学合理的施药方法,分别采用定点喷淋法、二次灌根法和常规灌根法对呋虫胺、噻虫嗪、虱螨脲、氟铃脲和灭蝇胺5种药剂的4个浓度进行田间药效试验。结果表明:不同药剂相同有效成分用量1.125 kg/hm~2下,第28天的防治效果依次为呋虫胺、噻虫嗪氟铃脲虱螨脲灭蝇胺,保株效果依次为呋虫胺、噻虫嗪、氟铃脲虱螨脲灭蝇胺,呋虫胺、噻虫嗪和氟铃脲的防治效果分别为100.00%、99.03%和96.82%,显著高于对照药剂40%辛硫磷乳油(3.600 kg/hm~2)的防治效果。与农药残留限定标准比较,所有韭菜样品的农药残留均未超标。另外,比较呋虫胺、噻虫嗪和氟铃脲在不同施药方法下对韭蛆的防治效果,二次灌根法定点喷淋法常规灌根法。因此,选择呋虫胺、噻虫嗪和氟铃脲的有效成分用量分别为1.125、0.900和0.900 kg/hm~2,并采用二次灌根法施药对韭蛆有良好的防治效果。     

Survey of cereal diseases and petts in the Netherlands. 5. Occurrence of Septoria spp. in winter wheat

Data of the annual surveys of circa 100 commerical winter wheat fields were compiled to describe epidemics ofSeptoria spp. in the Netherlands during 1974–1986. In May, during the first node stage,S. tritici was dominant whileS. nodorum was virtually absent. In July, during ripening,S. tritici on average dominated overS. nodorum, though in the most continental districts of the countryS. nodorum predominated.In May between 1974 and 1984, on average 56% of the fields showed leaf infections bySeptoria spp., while in July between 1975 and 1986, on average 83% of the fields showed leaf infections. Prevalence ofSeptoria spp. has increased during the surveys. Annual intensity ofSeptoria spp. in winter wheat crops was positively correlated with precipitation and negatively with average monthly sunshine duration during the harvest-month August of the previous growing season. The correlation with sunshine during August could indicate that ascospores play a major role in subsequent epidemics; but whether it is a causal relation remains to be answered.Present address: Center for Agrobiological Research (CABO-DLO), PO Box 14, 6700 AA Wageningen, the Netherlands     

Occurrence of pepper yellow vein in the Netherlands

Samenvatting Het verschijnsel van geelnervigheid bij paprika (Capsicum annuum) kon door verenting en met de schimmelOlpidium brassicae worden overgebracht. Hierdoor bleek de ziekte identiek te zijn met een eerder in Engeland gemelde ziekte. Door inoculatie met zoösporen of rustsporen vanO. brassicae werden ook symptomen verkregen inC. baccatum, C. chacoense enC. frutescens. S. villosum bleek een waardplant te zijn voor het geelnervigheidsagens, waarbij zwakke nerfchlorosen werden waargenomen.Seconded to the Glasshouse Crops Research Station, P.O. Box 8, 2670 AA Naaldwijk, the Netherlands.     

Surveys of cereal diseases and pests in the Netherlands. 2. Stem-base diseases of winter wheat

In the period 1974–1986, ca. 100 commercial winter wheat fields were surveyed annually for stembase diseases. In these years, on average 6% of the tillers was infected with eyespot in spring at the first-second, node stage. Eyespot intensity in spring was high in years with high temperature during winter. Eyespot, intensity in the milky-ripe stage in July, averaged 13% of the culms and was high in years with high temperature in April and high precipitation in March, April and May. These data may improve forecasts.In the milky-ripe stage, 2% of the culms were infected with sharp eyespot, but its intensity has gradually increased during the survey years. No significant correlation of sharp eyespot intensity with dry periods in autumn, spring or summer was found.Symptoms of take-all were found on 0.2% of the stem-bases during ripening. Its intensity was low in years with high precipitation in March, April, May and June and high temperature in May and June.Samenvatting Een honderdtal percelen wintertarwe werd in 1974–86 jaarlijks op voetziekten geïnventariseerd. In het voorjaar, tijdens het, eerste en tweede knoopstadium van het gewas, was gemiddeld 6% van de spruiten aangetast door oogvlekkenziekte. De intensiteit van de ziekte was hoog in jaren met een hoge gemiddelde wintertemperatuur. Tijdens het melkrijpe stadium, in juli was gemiddeld 13% van de halmen aangetast door oogvlekkenziekte. De aantasting in juli was hoog in jaren met een hoge temperatuur in april en veel neerslag in de maanden maart, april en mei. Met deze gegevens kunnen adviessystemen worden verbeterd.Scherpe oogvlekkenziekte was op gemiddeld 2% van de halmen in juli aanwezig. De ziekte nam geleidelijk met de jaren toe. De jaarlijkse intensiteit was niet gecorreleerd met droge perioden in de herfst, voorjaar of zomer.Symptomen van halmdoder waren op gemiddeld 0.2% van de halmen aanwezig. De intensiteit van de ziekte was hoog in jaren met weinig neerslag in maart, april, mei en juni en met een lage temperatuur in mei en juni.     

Further characterization of melon necrotic spot virus causing severe disease in glasshouse cucumbers in the Netherlands and its control

A severe leaf necrosis, observed since 1978 in glasshouse cucumbers grown on rockwool and later also in crops on soil, is described. A virus could be isolated and the disease be reproduced in cucumber and melon. The virus could be transmitted by leaf inoculation with expressed sap and by pouring rockwool leakage water onto sterilized soil containing cucumber seedlings. Infectivity steeply declined in expressed sap between dilutions 10 and 100 (dilution endpoint ca 10⁶), at temperatures between 55 and 65°C (thermal inactivation point 75°C) and during storage between 1 and 1 1/2 month at room temperature.Out of 40 plant species tested only three species, viz. cucumber, melon and watermelon, were susceptible. All 21 cucumber cultivars and all 8 melon cultivars tested reacted severely with local lesions and some with systemic necrosis, but systemic infection and reaction were erratic under experimental conditions.Purified virus sedimented in sucrose and CsCl gradients and during analytical ultracentrifugation in a single peak. Thes ₂₀ was 134S and buoyant density in CsCl was 1.33 g.cm^–3. Virus particles in crude sap and purified suspensions were spherical and ca 30 nm in diameter. They contained one type of protein with a relative molecular mass of 46 000 and one RNA species. An antiserum with a titre of 1024 did not react with cucumber and tobacco necrosis viruses, nor did their antisera react with our cucumber virus. Serologically and in physicochemical properties the virus is similar to if not identical with the melon necrotic spot virus incompletely described in Japan.Disease control may be through improved hygiene, including steam sterilization of rockwool, soil disinfection by steam sterilization or with methyl bromide, and addition of a surfactant to nutrient solutions, and prevention may be by grafting cucumber ontoCucubita ficifolia rootstocks, immune to the virus.Samenvatting Sinds 1978 komt in de op steenwol en in grond geteelde kaskomkommer een ernstige bladnecrose voor, die vooral in het najaar tot afsterving van planten kan leiden en in wel 45% van de planten van een aangetast gewas is geconstateerd. Uit zieke planten kon een virus worden geïsoleerd dat gemakkelijk overging door sap-inoculatie en in lekvocht uit besmette steewol (waarschijnlijk door tussenkomst van eenOlpidium-soort), nadat dit werd gegoten op gesteriliseerde grond waarin komkommerzaailingen groeiden. Met dit virus konden de symptomen van de ziekte worden greproduceerd.Het infectivermogen van ruw platesap nam snel af bij verdunning tussen 10 en 100× (verdunningseindpunt ca 1 millioen), en bij warmtebehandelingen tussen 55 en 65°C (inactiveringstemperatuur 75°C) en bij bewaring bij kamertemperatuur tussen 1 en 1 1/2 maand.Slechts 3 van de 40 getoetste plantesoorten bleken vatbaar voor het virus, te weten komkommer, meloen en watermeloen. Alle 21 getoetste komkommercultivars en alle 8 getoetste meloenerassen reageerden hevig met lokale lesies en enkele, onder de heersende proeformastandigheden onvoorspelbaar, met systemische necrose. De wel als onderstam gebruikteCucurbita ficifolia is onvatbaar.Gezuiverd virus sedimenteerde in suiker- en CsCl-gradiënten en bij analytische ultracentrifugering in één piek. Des ₂₀ was 134S en de zweefdichtheid in CsCl 1.33 g.cm^–3. In ruw sap en gezuiverde suspensies deden de virusdeeltjes zich voor als bolletjes met een diameter van ongeveer 30 nm. Ze bevatten slechts éé soort eiwit met een relatieve moleculaire massa van 46 000 en één RNA-soort. Een antiserum met titer 1024 werd bereid. Het reageerde niet met komkommernecrosevirus en tabaksnecrosevirus. Wel reageerde het virus met een uit Japan ontvangen antiserum tegen het daar sinds 1966 bekende melon necrotic spot virus, terwijl het Japanse virus reageerde met het Nederlandse antiserum. Serologisch, zowel als in biologische en fysisch-chemische eigenschappen lijken de Nederlandse en Japanse isolaten identiek. Voor het virus wordt daarom de Nederlandse namm meloenenecrosevirus voorgesteld. Het verschilt van drie andere, onlangs min of meer gelijktijdig in Oost-Duitsland, op Kreta en in Libanese grond aangetroffen, via de bodem overgaande komkommervirussen, die evenals tabaks- en komkommernecrosevirus ook andere plantesoorten dan cucurbitaceeën kunnen infecteren.Waarschijnlijk is meloenencerosevirys al sinds 1967 bekend in Frankrijk als verwekker van criblure du melon. Het is ook nauw verwant aan de verwekker van een in een veredelingsprogramma van meloen in Californië opgedoken necrosevirus, waarvan echter wordt beweerd dat het overgaat met zaad van meloen en wordt overgebracht door bladkevertjes,Diabrotica-soorten. Het meloenenecrosevirus is in ons land voor het eerst geconstateerd als ziekteverwekker van kaskommer. Ook in England is het daarin onlangs aangetroffen. De ziekte kan op verschillende manieren bestreden, respectievelijk voorkomen worden. De grond dient gestoomd te worden of begast met methylbromide. Steenwolmatten kunnen bij hergebruik gestoomd worden, terwijl aan de voedingsoplossing uitloeier (Agral) toegediend kan worden. Zowel bij grond- als steenwolteelten is de ziekte te voorkomen door komkommerplante te enten op de onvatbare onderstamCucurbita ficifolia.     

Benomyl-resistant Fusarium-isolates in ecological studies on the biological control of fusarium wilt in carnation

Ecological properties and stability of benomyl resistance of three benomyl-resistant mutants of nonpathogenicFusarium-isolates antagonistic to fusarium wilt in carnation, and three benomyl-resistant mutants of a pathogenic isolate ofFusarium oxysporum f.sp.dianthi were evaluatedin vitro and in glasshouse experiments. The benomyl resistance of the nonpathogenic mutants was stable under all conditions tested, also after a 1000-fold increase of the population in sterilized soil. Mutants of the pathogen were stable during allin vitro tests, but after proliferation in carnation stems only part of the population was benomyl resistant.Compared to the wild type, mutants of the pathogen were less pathogenic, also if thein vitro propeties were similar. Colonization of carnation by benomyl-resistant nonpathogenicFusarium in the presence of the pathogen showed that the antagonistic effect correlated with the presence of the nonpathogenic isolates within the carnation stem. The wild types and two of the mutant nonpathogenicFusarium-isolates controlled fusarium wilt in the susceptible cultivar Lena for 50% or more.UV-induced benomyl resistance appeared to be a valuable marker to distinguish between differentFusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prerequisite since alterations in antagonism and pathogenicity can occur.     

Possibilities of biological and chemical control of Verticillium wilt in pepper

In pathogen populations in Serbia, the incidence, pathogenic and morphological characters ofVerticillium spp. were studied. Biological and chemical control ofVerticillium was investigated in pepper plants (Capsicum annuum L. cv. ‘Soroksari’) with the biofungicide Polyversum^® (Pythium oligandrum) and the conventional fungicides benomyl and propamocarb-hydrochloride. On the basis of macroscopic and microscopic characters of the isolates originating from eight localities in Serbia, it was established that they apparently belong to the speciesVerticillum dahliae. The isolates differed in their pathogenic characters. However, all of them caused marked wilting symptoms on pepper plants 40 days after inoculation, conducted when there were more than nine fully developed leaves on the primary stem. The fungicides were applied either before or after inoculation. Benomyl was the most efficient fungicide in wilt control (88.2% when applied after inoculation and 94.6% when applied before inoculation). Polyversum proved more efficient (66.6%) when applied before rather than after inoculation. Propamocarb-hydrochloride provided sufficient Verticillium wilt control; its efficacy and that of Polyversum were similar, and less efficient than benomyl, but still significantly different from the disease control.     

Surveys of cereal diseases and pests in the Netherlands. 4. Occurrence of powdery mildew and rusts in winter wheat

Results of annual surveys of winter wheat fields from 1974 to 1986 were compiled to describe epidemics of powdery mildew and rusts in relation to weather and cultivar resistance.An average of 29 and 70% of fields were infected by powdery mildew in May and July, respectively. Mildew prevalence in May was positively correlated with average temperature in October and with average temperature over the months December, January, February and March. In addition, it was correlated negatively with the average grade of mildew resistance of the cultivars sown each year. Prevalence of mildew in July did not show consistent correlations with weather characteristics nor with mildew prevalence in May.Yellow rust was usually not detected in May and on average 18% of the fields was infected in July. The occurrence of yellow rust decreased after 1977, when the farmers adopted cultivars resistant or moderately resistant to yellow rust.Brown rust was usually not detected in May, while in July on average 48% of the fields was infected. Brown rust intensity in July was high in years with a high March temperature and high precipitation during April and May.Black rust was rare in the Netherlands, with 3 and 1% of the fields infected in July 1977 and 1981, respectively.     

加州新小绥螨对苹果全爪螨各螨态的捕食作用

为明确加州新小绥螨Neoseiulus californicus对苹果全爪螨Panonychus ulmi的控制潜力,在实验室条件下测定加州新小绥螨对苹果全爪螨各螨态的捕食功能反应、捕食选择性及加州新小绥螨自身密度对其捕食的干扰效应。结果表明:在25℃时,加州新小绥螨对苹果全爪螨各螨态的功能反应均属于HollingⅡ型圆盘方程;加州新小绥螨对苹果全爪螨卵的捕食能力最强,为40.3,对幼螨、第1若螨、第2若螨和雌成螨次之,捕食能力分别为36.9、17.3、15.2、3.6;加州新小绥螨对苹果全爪螨卵、幼螨、第1若螨、第2若螨和雌成螨的日最大捕食量分别为34.5粒、26.3、13.5、12.2和3.0头;加州新小绥螨对苹果全爪螨卵、幼螨和第1若螨有较强的嗜食性,选择系数分别为1.4、1.5、1.1,对第2若螨和雌成螨没有嗜食性,选择系数分别为0.9和0;加州新小绥螨对苹果全爪螨的总捕食量随自身密度增大而增大,但单头捕食量和捕食作用率随着自身密度增大而下降,其捕食作用率E与自身密度P的关系模型为E=0.050P-0.544。表明加州新小绥螨对苹果全爪螨各螨态尤其是卵、幼螨和第1若螨均有较强的控制潜力。     

Soil receptivity toFusarium solani f. sp.pisi and biological control of root rot of pea

Potential antagonists ofFusarium solani f. sp.pisi (Fsp) were selected from soil samples with varying degrees of receptivity to this pathogen. They were tested against Fsp isolate 48 (Fs48), in increasingly complex systems. Most species testedin vitro were able to antagonize Fs48. No relation could be establishedin vitro between the receptivity of the soil from which an isolate originated and its antagonism to Fs48. In soils naturally infested with pea root rot pathogens, which were stored humid at 4°C for a period longer than a year, various isolates ofFusarium, Gliocladium andPenicillium spp. were able to reduce root rot. After sterilization of these soils, onlyGliocladium roseum isolates, added at 10⁵ conidia g^–1 dry soil, significantly reduced disease severity and prevented root weight losses caused by Fs48 at 10⁴ conidia g^–1 dry soil. In soils in which the biota were activated by growing peas before the assays, doses of 10⁶ and 10⁷ ofG. roseum were required to reduce root rot. In these soils, the antagonistic effects of fluorescent pseudomonad strains from soil of low receptivity to Fsp were variable. Some strains of fluorescent pseudomonads, from soil moderately receptive to Fsp and from highly infested soils, were also able to reduce root rot. Disease suppression by pseudomonad strains was more evident in the absence than in the presence ofAphanomyces euteiches in the root rot pathogen complex. The role of receptiveness of the soil with regard to potential antagonists is discussed.     

Hyperparasites of Rhizoctonia solani in Dutch potato fields

Gliocladium roseum was found to be the most common and probably the most effective mycoparasite in potato fields in the northern parts of the Netherlands. It is able to parasitize and kill living hyphae at temperatures of 12°C and higher. Sclerotia ofR. solani are often infected and killed by this fungus under suitable conditions, i.e. at temperatures of 16°C and more. Killing of sclerotia by other antagonistic organisms was also observed. It is also shown by not parasitic fungi and is caused by toxins produced by the antagonist.The development of theG. roseum population was studied during the growth of a potato crop in two soils. In both soils its initial level was very low. In both a slightly acid sandy soil and a neutral sandy loam, suppression ofR. solani can occur;G. roseum accumulated in the former mainly under continuous potato crops,Colletotrichum coccodes was the main antagonist in the latter.Samenvatting In de meeste Nederlandse aardappelakkers komen schimmels voor dieRhizoctonia solani kunnen aantasten en doden. De meest algemene, en waarschijnlijk ook de meest belangrijke, die we tot nu toe vonden, isGliocladium roseum (Tabel 1). Het is bekend, dat deze schimmel stoffen produceert die voorR. solani giftig zijn. Met behulp hiervan kanG. roseum, evenals andere antibiotisch actieve micro-organismen, ook de sclerotiën doden (Tabel 2). Voor doding doorG. roseum is de temperatuur een factor van belang. Hyfen worden nog gedood bij een temperatuur van 12°C, waarbij de sclerotiën niet meer aangetast kunnen worden. Gedurende het winterseizoen worden sclerotiën door deze schimmel naar alle waarschijnlijkheid niet gedood.De ontwikkeling van de populatie vanG. roseum en andere antagonisten vanR. solani werd gevolgd in aardappelvelden op een licht zure zandgrond en op een neutrale zware zavel. Op de zandgrond werden twee proefplekken bemonsterd: één waarop voor het vierde achtereenvolgende jaar aardappelen werden geteeld en één met een vruchtwisselingsschema van graan, bieten en aardappelen.In de zandgrond nam in het groeiseizoen de populatie vanG. roseum toe. Op de proefplek waar voor het vierde jaar achtereen aardappelen stonden werdR. solani vanaf half augustus onderdrukt, evenwel niet volledig. Ook in het vruchtwisselingsstuk breiddeG. roseum zich flink uit, doch een onderdrukking vanR. solani werd niet bereikt.In de zware zavel nam de populatie vanG. roseum niet toe. Hier werdR. solani — uit besmet pootgoed — onderdrukt doorColletotrichum coccodes (zelf een pathogeen van stolonen) en antagonistische bacteriën. De resultaten zijn vermeld in Tabel 3.De besmetting van de geoogste knollen met sclerotiën, zoals die voorkwam op de zandgrond, is in Tabel 4 vermeld. Op de zavel leverde schoon pootgoed een bijna schone oogst (2% van de knollen was zeer licht bezet met sclerotiën). Besmet pootgoed leverde een oogst met 58% schone knollen, 35% met een zeer lichte en 7% met een iets zwaardere sclerotiënbezetting. Hoewel uit 100% besmet pootgoed een veel schonere oogst werd verkregen, was eerder toch een beschadiging van het gewas opgetreden. Pas tegen het eind van het groeiseizoen werdR. solani flink onderdrukt.