Showing papers in "European Journal of Plant Pathology in 1989"

Book review: Experimental techniques in plant disease epidemiology, J. Kranz & J. Rotem (eds.). Springer-Verlag Berlin, 1989, 299 pp.

Abstract: Various textbooks have been written on the epidemiology of plant diseases. Most of them present theory of epidemiology, thus giving a description of epidemiological principles. Some of these are of a general nature, whereas others concentrate on specialized subjects, but there are no books on experimental techniques in epidemiology. This omission has been recognized and rectified by Kranz and Rotem. As mentioned in their preface they intended, by editing and publishing the book, 'to help in the development of a methodology able to provide a choice of adequate methods widely acceptable amongst epidemiologists for varying applications and objectives'. For this purpose, they invited 27 distinguished plant pathologists, a number of them from Kranz's 'stable', to participate, and to provide information from their own rich experience. There are 20 chapters spread over four sections. Section I (General techniques), deals with techniques and approaches used in experiments in the field and under controlled conditions. Advantages and disadvantages of such experiments and the relations between them are explained. In Section II (.Measurements and their analysis) disease assessment, crop development and estimation of spore production, dispersal, survival and infectiousness are treated. The analysis of spatial patterns of soil-borne pathogens {s discussed in a separate chapter, for soil-borne diseases have to be approached differently. This section is concluded with two chapters on the monitoring and analysis of environmental factors. Section III (Special topics) is a collection of items, such as the analysis of the effects of control measures, fungicide resistance, virulence in pathogen populations, components in yield loss, development of forecasters, aphid-borne epidemiology, quantitative nematology, geophytopathology and long-distance dispersal. As the editors explain, these are 'not necessarily connected with each other, but all dealing with definite objectives in epidemiological experimentation'. The reasoning for the addition of these topics to the contents is clear. Most are worth treatment, and each has specialized techniques and approaches. The reasoning for collecting them all together under 'Special topics' is a little unsatisfactory. A rather simple rearrangement and naming of the subjects could separate them into a couple of better defined chapters, which would have made the contents more accessible to the eager user. Section IV (The synopsis of experimental restilts) gives the reader a look into the methods in comparative epidemiology, and into the development and use of simulation models for root and foliar diseases. The limitations, necessarily imposed upon the authors, to prevent the publication of an unwieldy and ever more expensive handbook lead to the question whether the editors 'bit more than they could chew'. Especially the chapters on modeling and simulation suffer under these limitations. Most authors have achieved a fine work, though readers, familiar with the authors' publications, can 'taste' a bit of subject.ivity in the choice and approach of techniques and methods by some of them. The book might be a useful addition to the library of all those involved in experimental work in epidemiology, but particularly those called 'novices in epidemiology' in the preface. The editors may have had undergraduates and young postgraduates in mind, but this work might be useful for other epidemiologists too. It is a pity that the high price will hinder young scientists from purchasing the book, particularly those in developing countries.

Effects of temperature, relative humidity and age of conidia on the incidence of spotting on gerbera flowers caused by Botrytis cinerea

Abstract: In recent years, spotting of ray florets of gerbera flowers has become an important problem. This type of small necrotic lesions may occur before, but especially shortly after harvesting the flowers.Botrytis cinerea was easily isolated from such lesions.

New aspects on the infection mechanism of Botrytis cinerea Pers

Abstract: With the help of active types of oxygen, extracellular enzymes and mechanical processes,Botrytis cinerea is capable of infecting plant tissue. Whereas no clear correlation was found between the activities of protease, pectolytic or other cell wall degrading enzymes and virulence, a positive correlation between pathogenicity and the intensity of active types of oxygen released was apparent in some isolates. It is assumed that these toxins result from the activity of glucose or xylose oxidases. Antioxidants inhibited the infection. It is concluded from these results, that active types of oxygen play a decisive role in the infection process.

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

Abstract: 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, onlyOlpidium 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. Monsters van hevig aangetaste gewasresten werden aangebracht in composthopen (2.5–4.6 m3) van het Indore-type. De temperatuur liep op tot 50–70°C binnen 6 dagen na het opzetten van de hopen, afhankelijk van de aard van de gewasresten en de plaats in de hoop. De warmtefase duurde 2–3 weken en werd gevolgd door een rijpingsfase van c. 5 maanden. Van de 17 pathogenen die werden getoetst, overleefden alleenFusarium oxysporum enOlpidium brassicae het composteren, maar ook van deze schimmels was het inoculum drastisch afgenomen. Op plaatsen waar 58 °C werd bereikt, wasF. oxysporum f. sp.lilii volledig geinactiveerd. Proeven met inbrengen en wegnemen van monsters in verschillende stadia van het proces lieten zien datF. oxysporum f. sp.melonis, O. brassicae enPlasmodiophora brassicae werden geinactiveerd gedurende de korte warmtefase, maar de langdurige rijpingsfase overleefden, zonder enig verlies van activiteit. Er wordt op gewezen dat naast de warmte als belangrijkste factor fungitoxische omzettingsproducten en microbieel antagonisme betrokken kunnen zijn bij de inactivering. Het effect van deze twee factoren is echter moeilijk te kwantificeren. Om te voorspellen of compost veilig kan worden gebruikt is alleen de temperatuur een bruikbare factor als parameter voor de sanitatie. Aangezien de buitenste monsters op 10 cm diep waren aangebracht, kan geen uitspraak worden gedaan over de sanitatie aan de buitenkant van de composthoop. Voor een veilig gebruik wordt aangeraden de buitenste laag van 10 cm te verwijderen.

Further identification of races of Cladosporium fulvum (Fulvia fulva) on tomato originating from The Netherlands, France and Poland

Abstract: Races ofCladosporium fulvum, which can overcome the resistance of the genes Cf2, Cf4, Cf5, Cf8, Cf9 and Cf11 have appeared in the Netherlands, France and Poland. Known isolates from the Netherlands and France and three new isolates from Poland have been investigated for the presence of virulence genes using a set of genotypes carrying resistance genes Cf2 to Cf11.Several Dutch isolates of races, earlier designated as 2.4, 2.4.5 and 2.4.5.9, were found to break down the resistance gene Cf11. These races must therefore be designated as 2.4.11, 2.4.5.11 and 2.4.5.9.11 respectively. In the new Polish isolates virulence genes, overcoming the resistance genes Cf2, Cf4, Cf8, Cf9 and Cf11 were found. Since all races able to grow on genotypes with Cf4, could also grow on genotypes carrying Cf8, it was impossible to discriminate between the genes Cf4 and Cf8. These Polish isolates were designated as races 4.11, 2.4.11 and 2.4.9.11. The consequences of the occurrence of these races for tomato breeding are discussed. Fysio's vanCladosporium fulvum, die de resistentie-genen Cf2, Cf4, Cf5, Cf8, Cf9 en Cf11 kunnen doorbreken, zijn in Nederland, Frankrijk en Polen opgetreden. Met behulp van een groep genotypen, die de resistentie genen Cf2 tot en met Cf11 dragen, zijn Nederlandse, Franse en enkele nieuwe Poolse isolaten onderzocht op de aanwezigheid van virulentiegenen. Enkele Nederlandse isolaten, eerder aangeduid met 2.4, 2.4.5. en 2.4.5.9, bleken het resistentie-gen Cf11 te kunnen doorbreken. Deze moeten daarom aangeduid worden als respectievelijk 2.4.11, 2.4.5.11 en 2.4.5.9.11. In de nieuwe Poolse isolaten werd virulentie gevonden voor Cf2, Cf4, Cf8, Cf9 en Cf11. Alle fysio's die op genotypen met Cf4 konden groeien, groeiden ook op genotypen met Cf8. Daarom kon geen ondersheid gemaakt worden tussen Cf4 en Cf8. De Poolse isolaten behoren tot de fysio's 4.11, 2.4.11 en 2.4.9.11. De gevolgen van het voorkomen van deze fysio's voor de tomateveredeling worden besproken.

Nine years of practical experience with phenylamide resistance in Phytophthora infestans in the Netherlands

Abstract: Resistance to phenylamide fungicides in thePhytophthora infestans population in the Netherlands decreased from a level of 77% of the samples containing resistant strains in 1980 to 0% in 1986 with decreasing use of metalaxyl, the only phenylamide fungicide registered for use against late blight in this country. Use of metalaxyl decreased because the fungicide alone and combinations of metalaxyl with preventive late blight fungicides were not commercially available from 1981 through the first part of the potato growing season of 1984. When metalaxyl was made available again in August 1984 in a mixture with mancozeb and from 1985 in a mixture with almost full rates of maneb and fentinacetate its use remained limited because growers were advised to apply the combination only two times per season in critical situations only to control the severe late blight epidemics of 1984 and 1985. Moreover application on seed potato crops was not allowed. In 1986 the combination was hardly used because the mild epidemic was easily controlled by preventive compounds only. In 1987 and 1988 phenylamide resistance increased to 16 and 42%, respectively, inherent to a general use of the combination in both years in most potato growing regions of up to two applications to combat a very severe epidemic. In lots of seed potatoes harvested in 1988 the percentage of blighted tubers yielding resistant isolates significantly differed from 13% for regions where seed potatoes are predominantly grown for table and processing crops to 41% for a region where predominantly starch potatoes are grown, both as seed and production crops. The more intensive use of metalaxyl combinations in the latter area through the years as compared to the other areas is assumed to be responsible for the higher incidence of resistance. In most years application of the combination induced a significant shift in the population to resistance as is indicated by the higher frequency at which resistant isolates were present in leaf samples taken from treated fields or tuber samples from the harvested crop. The strategy adopted by Dutch potato growers to combat phenylamide resistance in late blight, involving limited use of metalaxyl mixtures to a maximum of two times in critical situations only, has kept up to now resistance in the population at a level at which metalaxyl still significantly contributes to the efficacy of the combination in controlling the disease. Never-theless the observed increase in resistance in the population of 1988 after two consecutive late blight years indicates that this may change if severe epidemics occur each year. Resistentie tegen fenylamiden in dePhytophthora infestans populatie in Nederland nam af van een niveau van 77% van het aantal monsters met resistente stammen in 1980 tot 0% in 1986 in relatie tot een verminderd gebruik van metalaxyl, het enige fungicide uit de groep van fenylamiden, dat tot nu toe in dit land voor de bestrijding van de aardappelziekte is toegelaten. Het gebruik van metalaxyl nam af omdat het als afzonderlijk fungicide en in een mengsel met preventieve fungiciden ter bestrijding van de aardappelziekte commercieel niet beschikbaar was vanaf 1981 tot het midden van het groeiseizoen van 1984. Toen het fungicide weer beschikbaar kwam in combinatie met mancozeb in augustus 1984 en in 1985 in een combinatieprodukt met maneb en fentinacetaat, gebruikten de telers het in deze jaren slechts tweemaal per seizoen en alleen wanneer van preventieve middelen onvoldoende resultaat werd verwacht vanwege de aanwezigheid van de ziekte in het gewas bij kritieke weersomstandigheden. In 1986 werd het combinatieprodukt nauwelijks gebruikt vanwege de lage ziektedruk. In 1987 en 1988 werden in respectievelijk 16% en 42% van het aantal monsters resistente stammen aangetroffen. Een op grote schaal tweemalig gebruik van het combinatieprodukt in alle aardappelteeltgebieden ter bestrijding van een hevige epidemie wordt hiervoor verantwoordelijk geacht. In partijen pootgoed die in 1988 waren geoogst varieerde het percentage zieke knollen waaruit een resistente stam kon worden geisoleerd van 13% voor de gebieden waar het pootgoed voornamelijk wordt geteeld voor consumptieaardappelen en aardappelen voor de verwerkende industrie tot 41% voor het teeltgebied van fabrieksaardappelen. Het, gedurende meerdere jaren, intensievere gebruik van het combinatieprodukt in dit gebied waar de pootgoedteelt vaak op het eigen bedrijf plaats vindt, is hiervoor waarschijnlijk verantwoordelijk. Toepassing van het combinatieprodukt leidde in de meeste jaren tot een verschuiving in de populatie naar meer resistentie, gezien de hogere frequentie waarmee resistente stammen werden aangetroffen in blad- of knolmonsters van behandelde percelen. De strategie die door de Nederlandse aardappeltelers wordt gevolgd voor het tegengaan van fenylamide resistentie inP. infestans inhoudende een beperkt gebruik van maximaal twee keer onder kritische omstandigheden, heeft tot nu de resistentie op een zodanig niveau weten te houden dat van metalaxyl nog een bijdrage kan worden verwacht aan de effectiviteit van het combinatieprodukt. De Toename in resistentie in 1988 na twee seizoenen met een zware epidemie geeft evenwel aan dat de werkzaamheid van metalaxyl zal verminderen indien elk jaar de aardappelziekte in hevige mate voorkomt en dezelfde strategie wordt gevolgd ten aanzien van het gebruik van fenylamide combinatie produkten.

Effect of seventeen fungicolous fungi on sporulation of cucumber powdery mildew.

Abstract: Nineteen isolates of 17 different fungal species thriving upon other fungi were tested for their ability to control sporulation of cucumber powdery mildew,Sphaerotheca fuliginea. More than half of the fungi reduced the number of healthy conidiophores to less than 10%.Tilletiopsis albescens was superior toAmpelomyces quisqualis. Three species, viz.A. quisqualis, Aphanocladium album andT. albescens, were selected for further greenhouse experiments.

Book review: Control of plant diseases: costs and benefits, B.C. Clifford & E. Lester (eds.).

Abstract: Clark, M.E & Adams, A.N., 1977. Characteristics of the microplate method of enzyme-linked immunosorbent assay for the detection of plant viruses. Journal of General Virology 34: 475-483. Duffus, J.E., Whitney, E.D., Larsen, R.C., Liu, H.Y. & Lewellen, R.T., 1983. First report in western hemisphere of rhizomania of sugar beet necrotic yellow vein virus. Plant Disease 68: 251. H~ini, A., 1983. Rhizomania Eine Krankheit an Zuckerrfiben. Mitteilungen Schweizerische Landwirtschaft 31: 225-229. Hess, W., 1984. Ueberdauerung, Verbreitung und Bek~impfung des Aderngelbfleckigkeitsvirus (BNYVV) tier Zuckerrfibe. Dissertation. Giessen: 1-60. Heijbroek, W., 1984. Distribution of BNYVV in the Netherlands, Proceedings 1st International Conference of Sugar-beet Virologists, Colmar: 95-96. Nie, L.H. de & Poel, P.W. van de, 1986. In: Uniform methods for sampling and analysis of sugarbeets in the Netherlands: 760-763. Published by the Dutch Sugar Industry. Mfiller, H.J., 1983. Virusbefall in Verhalten von Inhaltstoffen auch in abh/ingigkeit von Vorfrfichten im Jahre 1982 in Oesterreich. Zuckerindustrie 108: 760-763. Pollach, G., 1984. Versuche zur Verbesserung einer Rizomania-Diagnose auf Basis konventioneller Rfibenanalysen. Zuckerindustrie 109: 849-853. Putz, C. & Richard Molard, M., 1984. La rhizomanie de la betterave une maladie/t virus, qui a pris une grande extension en France en 1983. Comptes Rendus hebdomadaires des S6ances de l'Acad6mie d'Agriculture de France 70: 370-378. Sch/iufele, W., 1983. Die vir6se Wurzelbartigkeit (Rhizomania, eine ernste Gefahr ffir die Rfibenanbau). Gesunde Pflanzen 35: 269-274. Walter, B., Kuszala, J. & Vuittenez, A., 1979. Diagnostic s6rologique par les tests PALLAS et ELISA. Application aux virus de la rhizomanie de la betterave et du court-nou6 de la vigne. Abstract 16e Colloqui6 de la Soci6t6 Fran~aise de Phytopathologie, 22 juin 1979. Wieninger, L. & R6ssner, G., 1983. Zum Verhalten rizomania-gesch~idigter Rfiben in der Saftreinigung. Zuckerindustrie 108: 758-760.

Histology of roots of resistant and susceptible carnation cultivars from soil infested with fusarium oxysporum f.sp. dianthi

Abstract: Fusarium wilt-resistant ‘Novada’ and wilt-susceptible ‘Early Sam’ carnations were planted in soil infested withFusarium oxysporum f.sp.dianthi, and their roots studied after five and ten weeks. Both in ‘Novada’ and ‘Early Sam’, the extravascular tissue of undamaged young root parts were scarsely colonized. In roots of ‘Novada’, infected xylem vessels were usually occluded with gums and surrounded by phellem tissue. In mature parts of roots, the phellem surrounding occluded vessels often merged with the external phellem surrounding the vascular cylinder, after which the occluded vessels were shed from the roots. The phellem at the root surface appeared to be a strong barrier to fungal invasion. In roots of ‘Early Sam’ carnations, as well as in a few roots of ‘Novada’ carnations, the defence responses did not result in compartmentation of the fungus, and colonization and degradation of the vascular tissues followed. Diseased roots finally healthy. Shoots of ‘Early Sam’ carnations, and eventually a few shoots of ‘Novada’ carnations, were colonized and developed wilt symptoms. Resistente ‘Novada’ en vatbare ‘Early Sam’ anjers werden geplant in grond besmet metFusarium oxysporum f.sp.dianthi. Na vijf en tien weken werden de wortels van de planten bestudeerd. De extravasculaire delen van onbeschadigde jonge wortelgedeelten waren in beide cultivars nauwelijks gekoloniseerd. In de wortels van ‘Novada’ waren geinfecteerde houtvaten meestal verstopt door gommen en omgeven door kurkweefsel. In oudere wortelgedeelten sloot het kurkweefsel rond verstopte vaten vaak aan op het kurkweefsel aan de buitenkant van het vaatweefsel, waarna de aangetaste vaten werden uitgestoten uit de wortel. Het kurkweefsel aan het worteloppervlak leek een belangrijke barriere te vormen tegen het binnendringen van de schimmel. In de wortels van ‘Early Sam’ en in enkele wortels van ‘Novada’ mislukte het afweerproces, en werd het vaatweefsel door de schimmel gekoloniseerd en vervolgens afgebroken. Aangetaste wortels werden na afloop van tijd hol. De bovengrondse delen van de meeste ‘Novada’ anjers werden niet gekoloniseerd en bleven gezond. De bovengrondse delen van de ‘Early Sam’ anjers, en op den duur die van enkele ‘Novada’ anjers, werden gekoloniseerd en verwelkten.

Effects of triazole fungicides on sterol biosynthesis during spore germination of Botrytis cinerea, Venturia inaequalis and Puccinia graminis f. sp. tritici

Abstract: With three plant pathogens,Botrytis cinerea, Venturia inaequalis and Puccinia graminis f. sp.tritici, the time course of sterol biosynthesis during spore germination was examined by labeling experiments along with the question whether this pathway could be inhibited by triazole fungicides. Conidia ofB. cinerea andV. inaequalis are able to synthesize sterols immediately after the beginning of the germination process when the germ tubes have not yet emerged. On the contrary uredospores ofP. graminis start sterol biosynthesis after 6 to 8 h germination time almost at the end of the germ tube phase, indicating that sterol reserves of the spores are likely to be used for the germ tube growth.

The Elegans fusaria causing wilt disease of carnation. II. Distinction of vegetative compatibility groups.

Abstract: The vegetative compatibility patterns among isolates ofElegans fusaria causing wilt disease of carnation were investigated. Nitrate non-utilizing mutants were generated from 16 isolates labelledF. redolens, nine of which came from carnation, and from 33 isolates labelledF. oxysporum, 19 of which came from carnation. Pairings of the mutants revealed five vegetative compatibility groups among the isolates from carnation, corresponding withF. oxysporum f.sp.dianthi race 1 (VCG1), race 2 (VCG2) and race 4 (VCG3),F. redolens f.sp.dianthi (VCG4) andF. redolens isolates from foot rot-diseased carnations (VCG5). Besides three isolates typical ofF. redolens, VCG4 comprised a now slightly deviating subculture of the type isolate ofF. redolens f.sp.dianthi of which the cultural characteristics correspond toF. oxysporum instead ofF. redolens. This observation may be taken to support previous conclusions that the distinction between both taxa is not justified. Otherwise, the compatibility patterns did not provide decisive evidence to accept or reject conspecificity of both taxa. Isolates from carnation did not form heterokaryons with other formae speciales ofF. oxysporum.

Check-list for scientific names of common parasitic fungi. Series 3b: Fungi on bulbs: Amaryllidaceae and Iridaceae

Abstract: This list is a continuation of Series 3a (Neth. J. Pl. Path. 94 (1988), Supplement 1), an account of the nomenclature of common parasitic fungi on bulbs as used in official publications of the Netherlands Society of Plant Pathology and the Netherlands Ministry of Agriculture and Fisheries. The selected names include one new species,Curvularia gladioli Boerema & Hamers, one new pathogenic form,Fusarium oxysporum f.sp.croci Boerema & Hamers, and one new combination,Sclerotium narcissi (Sacc.) Boerema & Hamers.

Effect of culture filtrates of seventeen fungicolous fungi on sporulation of cucumber powdery mildew

Abstract: Cultuurfiltraten van 17 mycoparasitaire schimmelsoorten, die waren geisoleerd van andere schimmels, werden getoetst op hun werkzaamheid tegen komkommermeeldauw, Spaerotheca fuliginea. De beste biologische bestrijding werd verkregen met Calcarisporium arbuscula

Effect of propiconazole on growth and sterol biosynthesis by Sclerotium rolfsii

Abstract: Germination of sclerotia ofSclerotium rolfsii on agar nutrient medium was delayed or slightly inhibited by concentrations of propiconazole between 0.4 and 4.0 μg ml−1, but was strongly inhibited by 8 μg ml−1 and completely inhibited by 16 μg ml−1. On the other hand, growth of hyphae from the germinated sclerotia was strongly inhibited by propiconazole at 1 μg ml−1 or greater. Hyphal growth from agar discs on agar medium was about 8 times less sensitive than hyphal growth from the sclerotia or from hyphal inoculum in liquid media. Propiconazole at 0.25 and 1.0 μg ml−1 strongly inhibited ergosterol biosynthesis, but this was not associated with large accumulations of C-14 methyl sterols. The ratio of eburicol to ergosterol in hyphae grown in the presence of 0.25 μg ml−1 propiconazole for 16, 30 or 45 h was 0.11, 0.13 and 0.04, respectively, for the three intervals while for hyphae grown in the presence of 1 μg ml−1, the ratios were 0.29, 0.36 and 0.30, respectively, for the same intervals. In view of a ratio of 23.5 for14C-acetate incorporation into the two sterols during the initial 6 h growth period in the presence of propiconazole, it is believed that the lack of large accumulation of C-14 methyl sterols is due to the feedback inhibition by eburicol or to cell lysis when the content of ergosterol becomes too low in the actively growing cells.

Assessment of the profile of powdery mildew and its damage function at low disease intensities in field experiments with winter wheat.

Abstract: Damage by mildew to winter wheat was studied in 11 field experiments in the Netherlands. Damage is described by the simple function: −0.013 (SE=0.003) kg are−1 per pustule-day of mildew per leaf, from second node stage to early dough at yield levels of 70 to 90 kg are−1, in diseasefree plots. No deviations from linearity at disease stresses from zero to two thousand pustuledays per leaf were observed. Years, cultivars or soil types did not affect the damage function significantly. The effects of mildew on some yield components were suggested. Mildew profiles in untreated plots could be described by the equation: CM=CLAb, in which CM and CLA are the cumulative pustule number and the cumulative leaf area, respectively, calculated both from top to bottom of the canopy, and totals standardized at unity. Estimates of the gradient parameter b aveaged 3.4 (SE=0.9). Observed differences in steepness of the profiles did not affect the damage function significantly. Opbrengstderving van wintertarwe door meeldauw werd bestudeerd in 11 veldproeven in Nederland. De schade bedroeg gemiddeld 0.013 (SE=0.003) kg are−1 per puistdag meeldauw per blad, vanaf het tweede-knoop stadium tot begin deegrijp bij opbrengstniveaus van 70 tot 90 kg are−1, in de blanco. Bij een ziektestress van 0 tot 2000 puistdagen meeldauw per blad werd geen afwijking van een rechtlijnig verband gevonden. De schaderelatie werd niet significant beinvloed door de verschillende jaren, rassen of grondsoorten. Het effect van meeldauw op enkele opbrengstcomponenten werd aangetoond. Meeldauwprofielen in de onbehandelde veldjes konden worden beschreven met de vergelijking: CM=CLAb, waarin CM het cumulatieve aantal puistjes is en CLA het cumulatieve bladoppervlak, beide berekend van bovenin het bladerdek naar beneden, de totalen gestandaardiseerd op een. De gradient parameter b bedroeg gemiddeld 3.4 (SE=0.9). Waargenomen verschillen in steilte van de meeldauwprofielen beinvloedde de schaderelatie niet aantoonbaar.

The significance of VA-Mycorrhiza to future arable farming in the Netherlands

Abstract: Present conditions of high inputs and narrow rotations render the importance of vesicular-arbuscular mycorrhiza (VAM) in arable farming in the Netherlands rather low. Changes expected in the near future under the influence of economic pressures and environmental problems may change this situation. This is discussed in the light of some such expected changes in Dutch arable farming.

Factors affecting build-up of fungicide resistance in powdery mildew in spring barley

Abstract: In replicate-plot field experiments done in the UK, at one site in Avon for 3 years and another in Warwickshire for 2 years, application of ethirimol or triadimenol sprays or seed treatments was followed by decreases in sensitivity of mildew samples to the particular fungicide applied. Application of ethirimol-triadimenol or tridemorph-triadimenol mixtures caused smaller or no decreases in sensitivity. Differences between isolates in responses to ethirimol and to triadimenol treatment were usually negatively correlated. Early-season inoculum differed in fungicide sensitivity between sites. At one site sensitivity shifted markedly from one season to another. No clear interactions between cultivar, mildew pathotype and shifts in fungicide response could be discerned. There were no major differences in resistance build-up between seed or spray treatments.

Broad bean mottle virus: Identification, host range, serology, and occurrence on faba bean (Vicia faba) in West Asia and North Africa

Abstract: One of the faba bean viruses found in West Asia and North Africa was identified as broad bean mottle virus (BBMV) by host reactions, particle morphology and size, serology, and granular, often vesiculated cytoplasmic inclusions. Detailed research on four isolates, one each from Morocco, Tunisia, Sudan and Syria, provided new information on the virus.

A highly mutable major gene for triadimenol resistance in Nectria haematococca var. cucurbitae

Abstract: Mutants ofNectria haematococca var.cucurbitae with high resistance to triadimenol could be isolated at high frequency. Resistance of 30 such mutants studied, was due to a mutation at thetri-1 locus, that maps in linkage group I, 10 cross-over units from the mating type locus. Thetri-1 mutation has no obvious effects on growth and sporulation on media without fungicide and on virulence for squash seedlings and mature fruit. In addition, a resistant mutant killed all of artificially inoculated seedlings in the presence of triadimenol at a concentration which gave 100% protection against the original wild type strain. Thetri-1 mutants were crossresistant at various levels to triadimefon, bitertanol, and propiconazol, but not to non-triazole SBIs. Their sensitivity to three imidazole derivatives was even higher than that of the wild type strains. This is believed to be the first report of a major gene for resistance to an SBI fungicide.

Aphanomyces euteiches as a component of the complex of foot and root pathogens of peas in Dutch soils.

Abstract: The occurrence ofAphanomyces euteiches Drechs. in Dutch soils is reported for the first time. Isolates of the pathogen were obtained from peas (Pisum sativum L.). A bioassay was used that baited the pathogen from soil into the cortex of stem and root of seedlings of a highly susceptible pea cultivar. The pathogen could subsequently be isolated on a semi-selective medium. Screening of soil samples from 13 fields known to be infested with fungi causing foot and root rot demonstrated the presence ofA. euteiches in 10 cases. In a second screening on soil samples from 43 fields, the pathogen was present in 16 cases. A positive correlation was found between the disease severity caused byA. euteiches in the seedling bioassay and the disease severity caused by the complex of foot and root pathogens in the same soils as evidenced by a mature plant bioassay. It is considered probable thatA. euteiches has since long been a common component of the foot and root rot complex in Dutch soils but has not been detected previously due to inadequate sampling and isolation techniques.

Influence of spray schedules on fungicide resistant populations of Botrytis cinerea Pers. on grapevine

Abstract: Treatments with dicarboximide fungicides provided only 20 to 40% control of grey mould on grape (cv. Moscato d'Asti) in vineyards where benzimidazole and dicarboximide resistant strains ofBotrytis cinerea Pers. constituted about 50% of the fungal population and a high disease pressure existed. The percentage of dicarboximide resistant strains increased after treatment. Fungicide combinations of a benzimidazole with diethofencarb, sprayed twice per season or once alternated with a dicarboximide, provided satisfactory control of grey mould and decreased the percetage of benzimidazole resistant strains. A combination of thiram and procymidone controlled grey mould, but increased dicarboximide resistance in the population.

Effect of phytotoxic compounds produced by Clavibacter michiganensis subsp. michiganensis on resistant and susceptible tomato plants

Abstract: A phytotoxic fraction of high molecular weight was isolated from the culture filtrate ofClavibacter michiganensis subsp.michiganensis, the causal agent of bacterial canker of tomato, and partly purified. This high molecular weight fraction consists of sugars and a minor protein moiety and is therefore probably of similar nature to that of the toxin fromC. michiganensis subsp.michiganensis reported earlier in literature. The high molecular weight fraction was albe to induce wilting, the predominant symptom of the disease, as shown in a bioassay with tomato cuttings. However, this wilting reaction turned out to be non-specific in the bioassay, since (partially) resistant and susceptible genotypes responded similarly. No correlation could be found between the degree of virulence of fiveC. michiganensis subsp.michiganensis strains and the amount of the phytotoxic high molecular weight fraction produced in vitro. As the isolated high molecular weight fraction showed a phytotoxic effect on tomato plants it is worthwhile to test its potential for use as a selective agent in in vitro selection. Een fytotoxische fractie werd geisoleerd uit cultuurfiltraat vanClavibacter michiganensis subsp.michiganensis, de veroorzaker van de bacterieverwelkingsziekte bij tomaat. Een eerste karakterisering toonde aan dat deze toxische fractie hoog-moleculaire component(en) bevat, bestaande uit polysacchariden en een gering percentage eiwit. Dit is in overeenstemming met toxines vanC. michiganensis subsp.michiganensis die al eerder beschreven zijn. Deze hoogmoleculaire toxische fractie was in staat verwelking te induceren van stengeltoppen van verschillendeLycopersicon esculentum enL. peruvianum genotypen in een bioassay. Gewichtsverandering van de stengeltoppen, uitgedrukt als percentage ten opzichte van het begingewicht, werd gebruikt als parameter voor verwelking. De toxische fractie reageerde niet-specifiek in de bioassay, want er werd geen verschil gevonden in respons van (partieel) resistente en gevoelige genotypen. Er bleek geen correlatie te zijn tussen de mate van virulentie van verschillende isolaten vanC. michiganensis subsp.michiganensis en de hoeveelheid van de toxische fractie geproduceerd in vitro. Het mogelijke gebruik van deze hoogmoleculaire toxische fractie als selectief agens bij in vitro selectie zal nader onderzocht worden.

Elimination of tomato mosaic virus by composting tomato residues

Abstract: Tomato plants infected by tomato mosaic virus (ToMV) were composted Although the temperature in the stack of tomato residues did not exceed 47°C during composting, ToMV was not detected in samples during composting Moreover, tomato seedlings grown in pots containing a mixture of Russian peat and the composted material did not become infected Because ToMV was detected in samples stored in an incubator at 47°C up to the 75th day of the incubation, it was concluded that the biological degradation of ToMV seems to play a more important role than the heat inactivation of the virus Met tomatemozaiekvirus (ToMV) geinfecteerde tomateplanten werden gecomposteerd Hoewel de temperatuur in de composthoop tijdens de compostering niet hoger werd dan 47°C, kon ToMV niet worden geisoleerd uit monsters, die tijdens de compostering werden genomen Bovendien werden tomatezaailingen, die in een mengsel van potgrond met gecomposteerd materiaal waren opgegroeid, niet met het virus geinfecteerd Omdat ToMV tot 75 dagen na het begin van de incubatie bij 47°C in de monsters kon worden aangetoond, kan worden geconcludeerd, dat de biologische afbraak van ToMV een belangrijker rol speelt dan de inactivering ten gevolge van de warmteontwikkeling

A possible role in pathogenesis for the swelling of extracellular slime of Erwinia amylovora at increasing water potential

Abstract: The volume of the cells ofErwinia amylovora (Burrill) Winslow et al. hardly changes with changing water potential, but its extracellular slime swells strongly with increasing water potential. When bacterial slime has accumulated in intercellular spaces of the host plant and the water potential rises, the slime will swell. If this slime cannot escape, it will exert a pressure on the surrounding plant cells. This ‘swelling pressure’ can rise to Δψ, being the change in water potential (up to 3 MPa). The pressure may lead to compression of soft host cells and to formation of large slime-filled holes in the plant tissue. Moreover, the swelling slime may force its way to the outside of the plant (exudation) or to healthy parts. Cork barriers, being formed by the plant after infection, may be breached if the mechanical pressure is high and the cork barrier is incomplete or not yet fully developed. Then, the resistance reaction of the plant, the attempt to seal off, is not effective. The swelling pressure would explain how the extracellular slime may function as a virulence factor.

Germination and appressorium formation of wheat leaf rust on susceptible, partially resistant and resistant wheat seedlings and on seedlings of other Gramineae

Abstract: Germination and appressorium formation of wheat leaf rust urediospores were studied in two experiments. No consistent differences could be detected between 11 genotypes of wheat (Triticum aestivum), two of barley, one ofTriticum dicoccum, one ofT. dicoccoides, one ofT. boeoticum and one ofAegilops squarrosa. Host genotypes and non-hosts gave similar results, suggesting that the phases before penetration of the host leaf are not affected by the resistance mechanisms operating in hosts and non-host genotypes.

Survey and biological differentiation of viruses of wild and cultivated umbelliferae in the Netherlands

Abstract: Biological testing of 974 leaf samples of wild and cultivated Umbelliferae in the Netherlands yielded 569 virus isolates; 550 could be classified into 19 viruses, two of them with two strains each. Viruses frequently occurred in mixtures, and infection often was symptomless. Anthriscus carlavirus and caraway latent virus are tentatively described as new viruses. Incomplete descriptions of carrot yellow leaf virus, celery yellow spot virus, cow parsnip mosaic virus, parsnip mottle virus and HV4 from cow parsnip, now named parsnip leafcurl virus, are supplemented. These viruses are new to the Netherlands. Parsnip mottle virus, with two strains differing in transmissibility byAcyrthosiphon pisum, resembles parsnip yellow fleck virus, but differs in not requiringAnthriscus yellows virus as a helper for transmission byCavariella spp. In the Netherlands virus infection is prevalent in the wild Umbelliferae cow parsley, cow parsnip and parsnip. Wide distribution and incidence of these species, their preponderantly biennial or perennial nature, prevalent (symptomless) virus infection, and role as intermediate hosts for migratingCavariella spp. make them important sources of virus infection of umbelliferous crops. TheAnthriscus strain of parsnip yellow fleck virus is spread to other crops than the parsnip strain of the virus and some other viruses, indicating the involvement of differentCavariella spp. The ecology of some of the virus diseases is further complicated by the involvement of viruses required as a helper for aphid transmission. Vanaf 1971 werden in totaal 974 bladmonsters van geteelde en wilde schermbloemigen (Tabel 2) onderzocht op virusinfectie. Behalve selderijmozaiekvirus (CeMV: mozaiek van knolselderij), peenroodbladvirus (CRLV: peenroodbladigheid), pastinakegeelvlekvirus (PYFV-fluitekruidstam: virusinsterving van peen), latent selderijvirus (CeLV) en latent peterselievirus (PlLV), waarover reeds eerder is gepubliceerd, werden ook andere virussen aangetroffen. Met het oog op de geringe kennis van veel van deze virussen was het nodig de monsters overwegend door overdracht met sap en bladluizen te toetsen op een uitgebreide reeks van indicatorplanten (Tabel 4). Op deze wijze werd het mogelijk 550 virusisolaten te identificeren en daarbij 19 virussen te onderscheiden (Tabel 1 en 3) en van twee ervan elk twee stammen (Tabel 5).Anthriscus-carlavirus (ACV) en latent karwijvirus (CwLV) bleken geheel nieuw. Van het eveneens geisoleerde pastinakevlekkenvirus (PMotV), peengeelbladvirus (CYLV), selderijgeelspatvirus (CeYSV) en het eenmaal eerder in Schotland gevonden virus HV4 uit bereklauw, nu pastinakebladkrulvirus (PLcV) genoemd, konden de tot dusver zeer onvolledige beschrijvingen verder worden aangevuld. Twee in overdracht metAcyrthosiphon pisum te onderscheiden stammen van pastinakevlekkenvirus lijken op pastinakegeelvlek virus (PYFV), maar verschillen er vooral van doordat ze voor overdracht doorCavariella-soorten niet afhankelijk zijn van hetAnthriscus-vergelingsvirus (AYV) als helper (Tabel 5). Naast PYFV zijn ook CYLV en CeYSV voor-bladluisoverdracht afhankelijk van een helpervirus. Naast ACV, CwLV, CYLV, CeYSV, PLcV en PMotV is ook het bereklauwmozaiekvirus (CPMV) voor Nederland nieuw. Veel van deze virussen werden verrassend veel aangetroffen in bereklauw, fluitekruid en wilde pastinaak, vaak zonder duidelijke symptomen. Vanwege het algemene voorkomen van deze wilde schermbloemigen, hun twee- of meerjarige leefwijze en rol als tussenwaard voor de van wilg naar eenjarige schermbloemigen migrerendeCavariella-soorten, zijn ze potentieel belangrijke bronnen van virusinfectie, voor schermbloemige gewassen. Uit de overeenkomsten tussen de natuurlijke waardplanten en nietwaardplanten van virus(stam) (Tabel 3) en bladluissoort is af te leiden dat de fluitekruidstam van pastinakegeelvelkvirus (PYFV-A) waarschijnlijk doorC. aegopodii woodt verspreid, terwijl de pastinakestam van hetzelfde virus (PYFV-P), bereklauwmozaiekvirus (CPMV) en pastinakevlekkenvirus (PMotV-C) waarschijnlijk doorC. pastinacae en/ofc. theobaldi worden verspreid. Dit kan verklaren waarom uitsluitend de eerstgenoemde virusstam (PYFV-A) in fluitekruid een bedreiging vormt voor peen (Tabel 3). Uit experimenteel waardplantonderzoek bleek dat de andere virusstam (PYFV-P) en bereklauwmozaiekvirus en pastinakevlekkenvirus zeer virulent zijn voor een aantal vlinderbloemigen zoals erwt (Tabel 4).

Peanut stripe virus in Indonesia

Abstract: During a survey of groundnut in 1986 and 1987 in South Sulawesi, West and East Java and West Sumatra a disease was frequently observed which is characterized by the presence of green blotches. These blotches were either randomly distributed over the entire leaflets or concentrated along the veins; sometimes they were surrounded by light green rings. On the basis of test plant studies, serology and electron microscopy it was concluded that the causal agent of the disease is peanut stripe virus (PStV). This virus has been described for the first time in the USA in 1984. Some potyviruses described earlier in Indonesia, viz. groundnut mottle-y and peanut mottle virus (PMV) probably are also PStV. The similarity of symptoms caused by PStV and peanut mottle virus was the reason why blotching on groundnut in Indonesia was ascribed for many years to PMV. As PStV causes severe yield losses, further research is being done on the epidemiology of the virus, on yield loss assesment and on testing breeding lines of groundnut for resistance. Tijdens een inspectie in 1986 en 1987 in Zuid Sulawesi, West en Oost Java en West Sumatra werd in aardnoot (Arachis hypogaea) veelvuldig een ziekte aangetroffen, die opviel door donkergroene vlekkerigheid. De vlekken waren onregelmatig over de bladeren verspreid of kwamen voornamelijk voor rond de nerven. Soms waren de vlekken omgeven door een lichtgroene ring. Op grond van symptomen op toetsplanten, serologische verwantschap en elektronenmicroscopische eigenschappen werd geconcludeerd, dat deze ziekte veroorzaakt wordt door het ‘peanut stripe virus’. Dit virus is voor het eerst beschreven in 1984 in Amerika. Dit is de eerste officiele melding van het virus in Indonesie. Enkele eerder beschreven potyvirussen van aardnoot in Indonesie, ‘groundnut mottle-y’ en ‘peanut mottle virus’ (PMV) zijn waarschijnlijk ook PStV. De gelijkenis van de door PStV and ‘peanut mottle virus’ veroorzaakte symptomen heeft ervoor gezorgd dat de vlekkerigheid op aardnoot in Indonesie jarenlang aan PMV werd toegeschreven. Aangezien PStV veel schade veroorzaakt, wordt verder onderzoek gedaan aan de epidemiologie van dit virus, aan het oogstverlies en aan het toetsen van aardnootlijnen op resistentie.

Alternaria alternata in cotton (Gossypium hirsutum) cv. Acala: effects on gas exchange, yield components and yield accumulation

Abstract: The effect ofAlternaria alternata on gas exchange proceses, on total yield and on yield components in cottonGossypium hirsutum cv. Acala SJ-2, was examined under field conditions. Variations in disease severity levels were achieved by using three fungicide treatments (Fentin Acetate). Disease developed more rapidly on the upper canopy layer (>661 cm height) than on lower ones. Infections were not accompanied by leaf shedding. The main effect of the disease was a reduction on bolls' number. A significant increase in seedcotton and lint yield, as compared to the untreated control, was achieved by applying fungicides. It was found that omitting early and late applications was not followed by significant yield reduction. Alternaria leaf spot reduced photosynthetic rate more and transpiration rate less, than could be explained by the extent of infected leaf area alone. Het effect vanAlternaria alternata op fotosynthese en transpiratie, opbrengstcomponenten en totale opbrengst bij katoen (Gossypium hirsutum L.) werd onderzocht onder veldomstandigheden. Verschillen in aantastingsniveaus werden verkregen door fungicide (fentin acetaat) behandelingen. De ziekte ontwikkelde zich het snelst boven in het gewas (> 60 cm). Infectie ging niet gepaard met bladval. Het belangrijkste effect van de ziekte vormde een afname van het aantal vruchtdozen (‘bolls’). Een significante toename van zaadkatoen (‘seedcottton’) en van vezels (‘lint’) ten opzichte van de onbehandelde controle werd verkregen door toediening van fungiciden. Achterwege laten van vroege en late bestrijdingen had geen significante opbrenstverlaging tot gevolg.A. alternata verlaagde de fotosynthesesnelheid meer en de transpiratiesnelheid minder dan verklaard kon worden uit de geinfecteerde oppervlakte van het blad.

Experimental inundative releases of different strains of the egg parasite Trichogramma in Brussels sprouts

Abstract: The effectiveness of inundative releases of four strains of the egg parasiteTrichogramma (Hymenoptera, Trichogrammatidae) to control five lepidopterous species infesting Brussels sprouts crops in the Netherlands was examined in small-scale field experiments in 1982–1985. Strains were selected on the basis of behavioural characteristics investigated in laboratory experiments, i.e. parasitization activity at low temperature and host-species preference.Mamestra brassicae (Noctuidae) was the most abundant host species. Its density usually averaged between 0.5 and 2.0 eggs/plant throughout most of the season (June–September). A very high peak density of 12 eggs/plant occurred in 1982. In other years the peak was below 2.5 eggs/plant.

In vitro selection of sterol biosynthesis inhibitor sbi resistant mutants in monilinia fructicola wint. honey

Abstract: The inherent resistance risk forMonilinia fructicola against sterol-biosynthesis inhibitors (SBIs) was estimated inin vitro andin vivo laboratory studies. Several mutant strains were selected on media amended with the triazole fungicides penconazole, etaconazole or the morpholine fungicide fenpropimorph.