Showing papers in "European Journal of Plant Pathology in 1990"

Fusarium head blight and mycotoxin contamination of wheat, a review.

Abstract: An infection of bread wheat by fusarium head blight contaminates the crop with mycotoxins, particularly deoxynivalenol (DON) and nivalenol (NIV). The toxicity and natural occurrence of these mycotoxins in wheat are reviewed. Based on 8 years data of fusarium head blight epidemics of wheat in the Netherlands, DON contamination of the grain was estimated. Fusarium head blight ratings averaged an infection of 1.7% of all spikelets; estimates for DON contamination averaged 0.9 mg kg−1. Taking a guideline level for DON in uncleaned bread wheat of 2 mg kg−1, in 1979 and 1982 a wheat crop was produced with estimated DON concentrations above the limit of tolerance. Human and animal exposure to mycotoxins in the Netherlands appears to be small but chronic. The information presented in this paper illustrates the need for an annual evaluation of the crop for fusarium head blight incidence and mycotoxin content, and the necessity of fusarium head blight resistant wheat cultivars. Aaraantasting van tarwe doorFusarium culmorum enFusarium graminearum leidt tot vorming van mycotoxinen in het graan, waarvan deoxynivalenol (DON) en nivalenol (NIV) de belangrijkste toxinen zijn. In dit artikel wordt een overzicht gegeven van de toxicologische aspecten, en het voorkomen van deze toxinen in tarwe. Informatie over DON en NIV in tarwe in West-Europa is schaars. Gebaseerd op gegevens vanFusarium epidemieen in de jaren 1979–1986 wordt een schatting gegeven van de concentratie DON in Nederlandse tarwe. Rekening houdend met de herkomst en verwerking van tarwe, blijken zowel in dierlijk als menselijk voedsel lage concentraties DON chronisch voor te komen. Op basis van een maximaal toelaatbare dagelijkse dosis DON van 3 μg kg−1 lichaamsgewicht is de schatting van de dagelijkse opname van DON in het jaar volgend op de oogst van 1982 net op de grens. Zowel een jaarlijkse inventarisatie vanFusarium aantasting en DON besmetting van het graan, als de ontwikkeling vanFusarium-resistente rassen zijn noodzakelijk.

Carbohydrate composition of apoplastic fluids isolated from tomato leaves inoculated with virulent or avirulent races of Cladosporium fulvum (syn. Fulvia fulva)

Abstract: Inoculation of tomato (Lycopersicon esculentum) with virulent races ofCladosporium fulvum (compatible interactions), resulted in substantial changes of the carbohydrate composition of apoplastic fluids isolated from the leaves, during the course of the infection process. In addition to a decrease in the concentration of the translocation sugar sucrose, a transient accumulation of the hexoses glucose and fructose and an accumulation of the polyol mannitol were observed. The latter coincided with a rising level of mannitol dehydrogenase, an enzyme that reduces fructose to mannitol. Only minor changes were detected in the carbohydrate composition of apoplastic fluids isolated from leaves of uninoculated control plants or plants inoculated with avirulent races ofC. fulvum (incompatible interactions). The fungal metabolite mannitol was not detected in apoplastic fluids isolated from the latter plants. These results suggest that, upon colonization of the intercellular spaces by virulent races ofC. fulvum, apoplastic sucrose is hydrolyzed by a host and/or fungal invertase and the resulting hexoses, glucose and fructose, are converted into mannitol by the fungus. In incompatible tomato-C. fulvum interactions a functional nutritional relationship between plant and fungus is prevented by plant defense responses, which might explain why in these interactions the carbohydrate composition of apoplastic fluids is similar to that of uninoculated control plants. Inoculatie van tomaat (Lycopersicon esculentum) met virulente fysio's vanC. fulvum (compatibele interacties), leidde tot aanzienlijke veranderingen in de koolhydraatsamenstelling van apoplastische vloeistoffen die uit de bladeren werden geisoleerd in de loop van het infectieproces. Naast een sterke daling van de concentratie van de transportsuiker saccharose, vond er ophoping van de hexoses glucose en fructose en de polyol mannitol plaats. De accumulatie van mannitol ging gepaard met een toename in de activiteit van mannitol dehydrogenase, een enzym dat fructose reduceert tot mannitol. In de koolhydraatsamenstelling van apoplastische vloeistoffen geisoleerd uit bladeren van niet geinoculeerde controleplanten, of planten geinoculeerd met avirulente fysio's vanC. fulvum (incompatibele interacties), werden slechts kleine veranderingen waargenomen. De schimmelmetaboliet mannitol kon niet worden aangetoond in de apoplastische vloeistoffen die uit deze planten werden geisoleerd. Deze resultaten suggereren dat bij de kolonisatie van de intercellulaire ruimtes door virulente fysio's vanC. fulvum, saccharose uit de apoplast wordt gehydrolyseerd door invertase afkomstig van de plant of de schimmel waarna de ontstane hexoses, glucose en fructose, door de schimmel worden omgezet in mannitol. Bij incompatibele tomaatC. fulvum interacties wordt een functionele voedingsrelatie tussen plant en schimmel voorkomen door het optreden van afweerreacties van de plant, hetgeen kan verklaren waarom in deze interacties de koolhydraatsamenstelling van apoplastische vloeistoffen vergelijkbaar is met die van niet geinoculeerde controleplanten.

Relative efficiency of a number of aphid species in the transmission of potato virus YN in the Netherlands

Abstract: This paper reports the results of live-trapping winged aphids in an Ashby (1976) trap in potato crops in the Netherlands from 1983–1987. During this period, a total of 122 aphid species were trapped. Although only four of those species were able to colonise potato, 26 of them were able to transmit PVYN from potato to potato test plants. The transmission rates and relative efficiency factors (REF's) of those transmitters were determined.

Control of Fusarium wilt in carnation grown on rockwool by Pseudomonas sp. strain WCS417r and by Fe-EDDHA

Abstract: In carnations grown on rockwool disease incidence of fusarium wilt caused byFusarium oxysporum f.sp.dianthi (Fod) was reduced when Fe-EDDHA instead of Fe-DTPA was used as iron source in the nutrient solution. Addition ofPseudomonas sp. strain WSC417r intensified this reduction in the cultivar Pallas, moderately resistant to Fusarium, but not in the susceptible cultivar Lena. Treatment of plants with Fe-EDDHA instead of Fe-DTPA as iron source resulted in higher numbers and percentages on the roots, ofin vitro antagonistic fluorescent pseudomonads. However, differences were only significant at 56 days after planting for cv. Lena and at 14 and 28 days after planting for cv. Palas. Both chelators, at different concentrations, had no effect on root colonization by eitherPseudomonas sp. strain WCS417r orFod strain WCS816. However, when coinoculated, reduced numbers of propagules ofFusarium were found at concentrations of Fe-EDDHA lower than 10−5 M. Higher concentrations of the siderophore fusarine produced byFod strain WCS816 were demonstrated when Fe-EDDHA instead of Fe-DTPA was used as iron source in culture media. At equal concentrations, no such differences were found in the amount of siderophore produced by WCS417r. Germ tube length ofFod was less with Fe-EDDHA than with Fe-DTPA. The reduction of germ tube length was stronger when the purified siderophore of WCS417r was added in excess to the culture media with Fe-EDDHA than those with Fe-DTPA. Therefore, the observed reduction of germ tube growth can not completely be explained by iron deprivation. It appeared that EDDHA exhibited a toxic effect for conidia ofFod strain WCS816 as well. we conclude that the observed disease reduction by Fe-EDDHA is a consequence of a limitation of iron availability forFod. This limitation is possibly intensified by the increase in number or percentage of antagonistic fluorescent pseudomonads that strongly compete for iron. The additional effect after bacterization withPseudomonas strain WCS417r in Fe-EDDHA treated carnations of cv. Pallas is likely to be due, at least partly, to a direct competition for iron between the siderophores ofFod strain WCS816 and ofPesudomonas sp. strain WCS417r. Verwelkingsziekte in anjers op steenwol, veroorzaakt doorFusarium oxysporum f. sp.dianthi (Fod), werd gereduceerd indien het ijzer-chelaat Fe-EDDHA in plaats van Fe-DTPA werd toegevoegd aan de nutrientenvloeistof. Bacterisatie metPseudomonas sp. stam WCS417r had een additioneel effect bij de matig resistence cultivar Pallas maar niet bij de vatbare cultivar Lena. Toevoeging van Fe-EDDHA in plaats van Fe-DTPA aan planten als ijzerbron resulteerde op de wortels in hogere aantallen en percentages fluorescerende pseudomonaden, diein vitro antagonistisch waren ten opzichte vanFod. De verschillen waren echter alleen significant 56 dagen na planten voor de cultivar Lena en 14 en 28 dagen na planten voor de cultivar Pallas. Beide chelaten vertoonden bij verschillende concentraties geen effect op de kolonisatie van de wortel door beide microorganismen. Echter, wanneer beide micro-organismen gezamelijk werden toegevoegd nam de wortelkolonisatie doorFod stam WCS816 af bij concentraties lager dan 10−5 M Fe-EDDHA. Er werd meer van het siderofoor fusarine doorFod stam WCS816 geproduceerd bij concentraties lager dan 10−4 M Fe indien Fe-EDDHA in plaats van Fe-DTPA als ijzerbron aan het cultuurmedium was toegevoegd. Er werd geen effect van beide chelaten gevonden op de siderofoorproduktie door WCS417r. Indien een overmaat van het gezuiverde siderofoor van WCS417r werd toegevoegd aan Fe-EDDHA werden een sterkere afname van de kiembuislengte gevonden dan toevoeging aan Fe-DTPA. De reductie van de kiembuislengte bleek niet volledig verklaard te kunnen worden door een afname van de ijzerbeschikbaarheid. Het chelaat EDDHA heeft ook een toxisch effect op conidien van fusarium. Wij concluderen, dat de waargenomen reductie van de verwelkingziekte door Fe-EDDHA een gevolg is van de afname van de ijzerbeschikbaarheid voorFod. Dit wordt waarschijnlijk versterkt door de ontwikkeling van een antagonistische, fluorescerendePseudomonas-populatie die sterk concurreren om ijzer. Het additioneel effect dat door bacterisatie metPseudomonas sp. WCS417r van de met Fe-EDDHA behandelde matig resistante anjers (‘Pallas’) werd verkregen is voor een deel het gevolg van een directe concurrentie om ijzer tussen de sideroforen vanFod stam WCS816 en vanPseudomonas sp. stam WCS417r.

Comparison of immunofluorescence colony-staining in media, selective isolation on pectate medium, ELISA and immunofluorescence cell staining for detection of Erwinia carotovora subsp. atroseptica and E. chrysanthemi in cattle manure slurry

Abstract: Various isolation and serological techniques were compared for the detection ofErwinia carotovora subsp.atroseptica (Eca) andE. chrysanthemi (Ech) in cattle manure slurry containing c. 108 colony forming units (cfu) per ml. The slurry samples could be preserved at −80°C for 8 months without reduction in the number of bacteria but not at −20°C. Samples stored at −80°C were inoculated with concentrations of the target bacterium ranging from 102 to 108 per ml. Only immunofluorescence colony-staining (IFC) in combination with selective media was able to detect the target organism at a concentration of 100 cells per ml. No IFC-positive colonies were found in pour plates of the non-inoculated cattle slurry. The recovery of the target bacterium from slurry inoculated with 102 cfu of Ech per ml was 64% in PT medium (containing polygalacturonic acid) and 19% in crystal violet pectate medium (CVP). Recoveries of Eca were 32% and 82%, respectively. Ech and Eca could be detected at levels of 103 cfu per ml of slurry by isolation on CVP. Crude filtration procedures were necessary for analysis of slurry samples with immunosorbent immunofluorescence (ISIF) cell staining. The detection level of ISIF for Ech was 105 cells per ml of slurry. IF-positive cells were incidentally observed in the non-inoculated slurry. Detection of Ech and Eca with ELISA was only possible in slurry inoculated with 108 cells of the target bacterium per ml.

Assessment of the inoculum potential of Polymyxa betae and beet necrotic yellow vein virus (BNYVV) in soil using the most probable number method

Abstract: Application of a bioassay on serial dilutions of rhizomania-infested soil provided adequate information on the level of infestation withPolymyxa betae and beet necrotic yellow vein virus (BNYVV). Different combinations of dilution ratios ratios and numbers of replicates (N) that had the same average precision were compared. A most probable number (MPN) computer programme was written to enable the comparison, because MPN tables available in literature are limited to certain dilution ratios and values of N. Most probable numbers of infective units per ml soil assessed for infested soil from the Noordoostpolder and from Tholen (the Netherlands) were 48 forP. betae with 7.1 for BNYVV and 16 forP. betae with 1.6 for BNYVV, respectively. So in these soils 10–15% of the infective population ofP. betae was viruliferous. The inoculum potential of stored soil samples was not affected by conditions during storage for 28 months (dry and warm or wet and cool). Toepassing van de verdunningsmethode en de ‘MPN’-berekening op de biotoets voor rhizomanie resulteerde in kwantitatieve gegevens over de mate van besmetting van de grond, zowel voorP. betae als voor BNYVV. De besmettingsgraad van bewaarde grondmonsters werd niet beinvloed door de bewaaromstandigheden gedurende 28 maanden (droog en warm of vochtig en koud). Mogelijkheden voor praktische toepassing van de methodiek worden besproken.

A selective medium for botrytis cinerea to be used in a spore trap

Abstract: A selective medium has been developed for the use in spore-traps to study the dispersion ofB. cinerea on gerbera grown in glasshouses. Een selectief medium voorB. cinerea is, ontwikkeld voor het gebruik in sporevangers. Deze sporevangers werden gebruikt bij het bestuderen van de ontwikkeling vanB. cinerea in gerbera geteeld onder glas.

Identification of resistance genes to Puccinia striiformis in seedlings of Ethiopian and CIMMYT bread wheat varieties and lines

Abstract: In a controlled environment, the reaction was observed of 42 bread wheat varieties and lines inoculated with 19 isolates of yellow rust differing in their virulence to 20 differential varieties. Five varieties and lines showed resistance to all isolates. The remaining ones appeared to have the genes Yr2, Yr3, Yr4, Yr6, Yr7, Yr9 and YrA, either singly or in combination. Yr9 derived from rye was present in 67% of the varieties and lines. Yr4 is the only effective gene in that material as, in Eastern and Central Africa, yellow rust has virulence to the other Yr genes. Recognition of virulence to Yr genes is enhanced by the use of a supplemental set of differential varieties supposedly carrying a single gene. Additional keywords: yellow (stripe) rust races, Triticum aestivum, Yr genes.

Photosynthesis is not impaired in healthy tissue of blighted potato plants.

Abstract: The net photosynthetic rates of green leaf tissue of potato plants of different cultivars were measured in the field and in a controlled environment after infection of the plants byPhytophthora infestans Infection had no significant effect on the net photosynthetic rate at light saturation, the efficiency of light use at low light intensities, or dark respiration The reported effect ofP infestans on tuber yield seems to be caused solely by a reduction in the green leaf area Therefore, a high rate of photosynthesis in green leaf tissue of infected plants is not a good selection criterion for potato genotypes Bepalingen van netto fotosynthesesnelheden, bij verschillende aardappelrassen, werden uitgevoerd in het veld en onder geconditioneerde omstandigheden De metingen werden gedaan aan groen blad van planten die in verschillende mate waren aangetast doorPhytophthora infestans Infectie had geen significante invloed op de netto fotosynthesesnelheid bij lichtverzadiging, de efficientie van lichtbenutting bij lage lichtintensiteit, of de donkerademhaling Het effect vanP infestans op de knolopbrengst van aardappelrassen lijkt uitsluitend veroorzaakt te zijn door een vermindering van groen bladoppervlak Daarom is selectie van aardappelgenotypen met superieure handhaving van fotosynthetische activiteit bij aantasting, geen kansrijk veredelingsdoel

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

Abstract: 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. Een honderdtal percelen wintertarwe werd in 1974–86 jaarlijks op voetziekten geinventariseerd. 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.

Fluorescent Pseudomonas isolate E11.3 as biocontrol agent for Pythium root rot in tulips

Abstract: FluorescentPseudomonas isolates were obtained from Pythium-diseased tulip roots or rhizospheres A selection of these isolates was tested for root rot-suppressing capabilities, using tulip cultivar Paul Richter (ice-tulip) as host andPythium ultimum P17 as pathogen With isolate E113 root rot suppression was consistently found, but the extent of the effects varied from experiment to experiment Beneficial effects were obtained after introduction of the bacteria either by mixing them through the soil or by dipping the bulbs in a bacterial suspension, immediately before planting Application of bacteria in methylcellulose also reduced disease, but is of no practical value as methylcellulose by itself increased disease In steamed soil, disease was more severe than in natural soil In both circumstances, however, beneficial effects of bacterization with E113 were observed Fluorescerende pseudomonaden werden geisoleerd van tulpewortels of uit de rhizosfeer daarvan Een aantal van deze isolaten is getoetst op wortelrot-onderdrukkend vermogen in een experimenteel systeem met tulpecultivar Paul Richter (vriestulp) als waardplant enPythium ultimum isolaat P17 als pathogeen Wortelrotonderdrukking werd consequent waargenomen na bacterisatie metPseudomonas isolaat E113; de mate waarin rotonderdrukking optrad verschilde echter van experiment tot experiment Bacterisatie vond plaats of door de bacterien door de grond te mengen of door de bollen vlak voor het planten in een bacteriesuspensie te dompelen Met beide methoden werden positieve resultaten bereikt Toedienen van bacterien in methylcellulose leidde ook tot reductie van de ziekte, maar heeft geen practische betekenis aangezien methylcellulose op zich de ziekte doet toenemen Wortelrot was ernstiger in gestoomde dan in nietgestoomde grond, maar in beide omstandigheden werkte E113 wortelrotonderdrukkend

Stepwise development of laboratory resistance to DMI-fungicides in Penicillium italicum.

Abstract: Isolates ofPenicillium italicum with differential levels of resistance to imazalil were obtained via step-wise mass selection of conidia of the fenarimol-resistant isolate E300-3 on imazalilamended PDA. Three out of five selection steps were successful. The resistance level to imazalil of isolates acquired after the two last selection steps was on average 122 and 197. The differential level of resistance was also apparent in decay control on oranges by imazalil inoculated with the various isolates. The isolates showed a similar cross-resistance pattern to other fungicides which inhibit C-14 demethylation of sterols (DMIs), although the level of resistance to these fungicides was significantly higher. All isolates displayed negatively-correlated cross-resistance to tridemorph and dodine. Most isolates had a normal virulence on oranges. In competition experiments with mixed-inocula of the wild-type and a resistant isolate, the proportion of the wild-type increased in successive generations on untreated oranges and the proportion of the resistant isolate increased on imazalil-treated oranges. The lower competitive ability of the resistant isolate on untreated oranges may be due to a decrease in spore production as compared with the wild-type.

Localization of phytoalexin accumulation and determination of changes in lignin and carbohydrate composition in carnation (Dianthus caryophyllus L.) xylem as a consequence of infection with Fusarium oxysporum f. sp. dianthi, by pyrolysis-mass spectrometry

Abstract: Minute pieces of xylem and other tissues from stems of healthy and fungus-infected plants of two carnation cultivars Novada and Lena were investigated for lignification (lignin/polysaccharide ratios) and lignin composition by means of pyrolysis mass spectrometry and pyrolysis gas chromatography mass spectrometry. This technique proved also very effective for the localization of dianthramide phytoalexins which accumulate in carnation after infection withFusarium oxysporum f.sp.dianthi. The composition of healthy tissues from both cultivars was practically the same. In the resistant cultivar Novada, infection induced a change from guaiacyl-syringyl lignin into a mainly guaiacyl lignin in the gum-occluded parts of the xylem. Considerable amounts of the phenolic amide dianthalexin and of other dianthramide phytoalexins were present in occluded xylem, but not in adjacent phloem, medulla or unoccluded xylem. Xylem from susceptible ‘Lena’ suffering degradation was characterized by a loss of syringyl groups from the lignin and by demethylation of pectin in an early stage of infection. Small quantities of dianthalexin and other dianthramide phytoalexins were found in ‘Lena’ when local defense responses (particularly occlusion) had occurred. In both cultivars evidence for degradation of hemicellulose was found.

Genetic variation in partial resistance to leaf rust in winter wheat: disease progress, foliage senescence and yield reduction.

Abstract: Relations between leaf rust progress, foliage senescence and yield reduction were studied for seven winter wheat genotypes, differing in their partial resistance to leaf rust. Leaf rust accelerated leaf and ear senescence. Photosynthesis measurements showed, however, that the photosynthetic capacity of the remaining green surface was not affected. Differences between genotypes in yield reduction were largely explained by differences in leaf senescence and, therefore, in cumulative light interception (r=0.83) and crop photosynthesis. Reduction in cumulative light interception was closely related to the area under the disease-progress-curve (r=0.85), which was also closely associated with yield reduction (r=0.88). However, the time taken to reach a 50% reduction of green leaf area and the pustule density on 1 July (i.e. halfway through the epidemic) were just as good predictors of yield reduction as cumulative light interception and area under disease-progress-curve, suggesting that the former are useful criteria in the selection for partial resistance to leaf rust. De relatie stussen de epidemiologie van bruine roest, bladveroudering en oprengstderving werden bestudeerd bij zeven wintertarwegenotypen die verschilden in partiele resistentie tegen bruine roest. Bruine roest versnelde de veroudering van blad en aar. Fotosynthesemetingen wezen echter uit dat de fotosynthesecapaciteit van het resterende groene oppervlak niet werd beinvloed. Verschillen tussen de genotypen in opbrengstderving werden voornamelijk veroorzaakt door verschillen in bladveroudering en daarmee in cumulatieve lichtinterceptie (r=0.83) en gewasfotosynthese. De reductie in cumulatieve lichtinterceptie was nauw gerelateerd aan de cumulatieve ziektedruk (in puistdagen) (r=0.85), welke ook nauw was geassocieerd met de opbrengstderving (r=0.88). De opbrengstreductie werd echter even goed voorspeld door de tijdsduur tot 50% reductie van het groene bladoppervlak en de puistdichtheid halverwege de epidemie als door cumulatieve lichtinterceptie en cumulatieve ziektedruk, waardoor beide eerste criteria gebruikt kunnen worden in de selectie voor partiele resistentie tegen bruine roest.

Broad bean wilt virus: Host range, purification, serology, transmission characteristics, and occurrence in faba bean in West Asia and North Africa

Abstract: A virus affecting faba bean in West Asia and Norht Africa was identified as broad bean wilt virus (BBWV) by host reactions, particle morphology and size, serology and transmission characteristics. An isolate from Syria (SV3-88) and one from Egypt (EV319-86) were found to be serologically identical and of serotype I. In host-range studies, the Syrian isolate infected systemically 59 out of 87 plant species tested. The virus was transmitted non-persistently by four aphid species naturally prevalent in Syria, but most efficiently byMyzus persicae. Inoculation of faba bean with SV3-88 14 weeks (pre-flowering) and 6 weeks after sowing (flowering) led to 25.8 and 1.8% yield loss and seed-transmission rates of 0.6 and 0.4%, respectively. The isolate SV3-88 was purified from systemically infected faba bean and yield 1.5–2 mg of partially purified virus per 100 g of leaves. When samples, with symptoms suggestive of virus infection, were collected during 1985–1989 from a number of countries in West Asia and North Africa and tested by ELISA, the virus was detected in 8 out of 127 samples tested (8/127) from Egypt, 0/44 from Lebanon, 1/23 from Morocco, 38/485 from the Sudan, 38/385 from Syria and 23/138 from Tunisia.

The influence of Verticillium dahliae and drought on potato crop growth. 1. effects on gas exchange and stomatal behaviour of individual leaves and crop canopies

Abstract: Potato (Solanum tuberosum L.) plants cv.Saturna were subjected to infection withVerticillium dahliae and drought stress. At the early stages of growth, stomatal conductance, transpiration and net photosynthesis were measured at light saturation (PAR>300 m−2) on individual leaves and with mobile field equipment with the aid of field enclosures. No significant changes in stomatal conductance and gas exchange characteristics occurred as a result ofV. dahliae instomatal conductance, transpiration and and photosynthetic rates, especially on older leaves and on plants exposed to direct sunlight for a longer period of time. In combination with drought,V. dahliae only occasionally showed interaction; their effects being less than additive. High values of coefficients of variatoon necessitated a high number of measurements per treatment; the more so in the inoculated plants which shows thatV. dahliae seems to affect certain leaves while not affecting others early in growth. Crop photosynthesis was less reduced byV. dahliae than individual leaf photosynthesis due to the levelling effect of integration over the whole canopy and possibly through a stimulation of the top leaves. The upper non-affected leaves are responsible for the bulk of photosynthetic crop activity. The results indicate that following an infection withV. dahliae photosynthesis is reduced early in growth as a result of drought stress in the leaves. Aardappelplanten (Solanum tuberosum L.) cv.Saturna werden onderworpen aan stress als gevolg vanVerticillium dahliae en droogte. In vroege stadia van de groei werden stomataire geleiding, transpiratie en netto fotosynthese bij lichtverzadiging (PAR>300 W m−2) gemeten aan individuele bladeren en met een mobiel instrumentarium met behulp van gewaskappen. Er werden geen significante verschillen gevonden in de waarden van de stomataire geleiding en de gasuitwisslingskarakteristieken als gevolg vanV. dahliae-besmetting tot een maand na opkomst. Daarna leidde infectie metV. dahliae tot een afname van de stomataire geleiding, transpiratie en netto fotosynthese, speciaal bij oudere bladeren en bij planten die meer aan zonlicht waren blootgesteld. Soms vertoondeV. dahliae interactie met droogte en bleken beide effecten minder dan optelbaar. De hoge waarden van de variatiecoefficienten maakten een groot aantal metingen per behandeling noodzakelijk; dit was vooral het geval bij metV. dahliae geinfecteerde planten hetgeen aantoont datV. dahliae vooral in het begin van de groei niet alle bladeren in gelijke mate aantast. Door de matigende invloed van de integratie van alle bladlagen en mogelijk doordat de bovenste bladeren werden gestimuleerd, werd de totale gewasfotosynthese in mindere mate beinvloed doorV. dahliae dan de individuele bladfotosynthese. De bovenste niet geinfecteerde bladeren bleken verantwoordelijk voor het grootste gedeelte van de gewas-fotosynthese. De resultaten tonen aan, dat volgend op een infectie metV. dahliae, de fotosynthese reeds in een vroeg stadium van de groei wordt verminderd als een gevolg van droogtestress in de bladeren.

Comparison of five stem inoculation methods with respect to phytoalexin accumulation and Fusarium wilt development in carnation

Abstract: Five methods of stem inoculation of carnations with conidial suspensions ofFusarium oxysporum f.sp.dianthi were compared for uptake of the suspension, induction of phytoalexin accumulation and wilt development. Inoculation was performed by incision of the stem across droplets of inoculum placed on leaves, or by injection of droplets into the stem. With both methods, higher inoculum dosages led to higher wilting rates and higher phytoalexin concentrations. Injection was more effective than incision since a lower inoculum dosage was required to obtain the same phytoalexin levels. Injection therefore appears the most promising technique for the development of routine screening methods for resistance based on phytoalexin accumulation.

Simulation of damage in winter wheat caused by the grain aphid Sitobion avenae. 1. Quantification of the effects of honeydew on gas exchange of leaves and aphid populations of different size on crop growth

Abstract: Damage in winter wheat caused by the grain aphidSitobion avenae F., was studied in the laboratory and at field level.

Effect of volatile and unstable exudates from underground potato plant parts on sclerotium formation by Rhizoctonia solani AG-3 before and after haulm destruction

Abstract: The acceleration of black scurf development after haulm destruction was mainly due to changes in the exudation of volatiles from tubers. Volatile products from decomposing potato roots and stolons and, probably, unstable substances in the tuber exudate as well, further promoted sclerotium formation.

Simulation of yield reduction by leaf rust in winter wheat, applied to the analysis of genetic variation in partial resistance.

Abstract: Differences in yield reduction among seven winter wheat genotypes due to leaf rust, as observed in a field experiment, were analysed using a simulation model. In this model, the effects of the disease on crop growth and yield were described on the basis of light interception, photosynthesis, respiration and assimilate partitioning. The model properly described the observed yield difference between the genotypes, both in the absence and in the presence of leaf rust. According to the model, 66% of total yield reduction was due to an accelerated decrease in green leaf area and 18% was due to light capture by dead leaf tissue at the top of the canopy. Genetic variation in yield reduction was, therefore, mainly explained by variation in leaf senescence. Leaf rust did not affect the photosynthetic rate of the remaining green leaf area. Opportunities of selection for individual damage components were assessed from their simulated effect on grain yield, together with their estimated genetic and environmental variance. Verschillen tussen zeven wintertarwegenotypen in opbrengstderving door bruine roest, zoals waargenomen in een veldexperiment, werden geanalyseerd met een simulatiemodel. In dit model werd het effect van de ziekte op gewasgroei en opbrengst beschreven op basis van lichtinterceptie, fotosynthese, ademhaling en assimilatenverdeling. Het model gaf een goede beschrijving van de waargenomen opbrengstverschillen tussen de genotypen, zowel bij aanwezigheid als bij afwezigheid van bruine roest. Van de totale opbrengstreductie werd, volgens modelberekeningen, 66% veroorzaakt door versnelde afname van groen bladoppervlak en 18% door het wegvangen van licht door dood bladweefsel boven in het gewas. De genetische variatie in opbrengstreductie werd zodoende vooral verklaard uit de waargenomen verschillen in bladveroudering tussen de genotypen. De fotosynthese per eenheid resterend groen bladoppervlak werd niet beinvloed door bruine roest. Respectieven voor selectie op afzonderlijke schadecomponenten werden geevalueerd op basis van hun gesimuleerde effect op korrelopbrengst, in combinatie met hun genetische en toevalsvariatie.

Association of three RNA molecules with potato mop-top virus

Abstract: Potato mop-top virus particles, purified from systemically infectedNicotiana benthamiana plants and then disrupted by heating with sodium dodecyl sulphate and 2-mercaptoethanol, contained only a single polypeptide of Mr 19 100 detectable by polyacrylamide gel electrophoresis. Single-stranded RNA preparations from virus particles, when subjected to electrophoresis in an agarose gel containing methylmercuric hydroxide as a denaturant, were shown to contain approximately equal proportions of three RNAs of 6.5, 3.2 and 2.5 kb. Double-stranded RNA preparations extracted from systemically infectedN. benthamiana leaves or from locally infectedN. debneyi leaves, was shown by polyacrylamide gel electrophoresis to contain a major species of 3.2 kbp and two minor species of 6.5 and 2.4 kbp.

Epidemiology of Fusarium wilt in cyclamen in an ebb and flow system

Abstract: Introduction ofFusarium oxysporum f. sp.cyclaminis either into the nutrient solution or into the potting soil, did not result in noticeable spread of disease in a cyclamen crop grown in pots on tables of an ebb and flow system. Immediately after its introduction, only a small amount of the inoculum was detected in the soil in the pots and in the nutrient solution flowing onto the tables.

Sexual compatibility types of Bremia lactucae isolates originating from Lactuca serriola

Abstract: Results are given on the occurrence of sexual compatibility types of seven isolates ofBremia lactucae originating fromLactuca serriola (prickly lettuce). It is concluded that the isolates studied are heterothallic. Both compatibility types (B1 en B2) were determined, but type B2 was prevalent. Sexual recombination ofB. lactucae isolates originating from wild and cultivated lettuce may occur. Zeven isolaten vanBremia lactucae, afkomstig vanLactuca serriola in Tsjechoslowakije, zijn onderzocht op hun sexuele compatibiliteitstype door ze te combineren met Nederlandse fysio's vanB. lactucae, afkomstig van cultuursla (L. sativa), waarvan het compatibiliteitstype (B1 of B2) bekend is. Alle isolaten vanL. serriola bleken heterothallisch te zijn, waarbij type B2 meer werd aangetroffen dan type B1. Sexuele recombinatie vanBremia-isolaten van wildeLactuca-soorten en cultuursla blijkt goed mogelijk te zijn.

Seed treatment of peas with fosetyl-Al against Aphanomyces euteiches.

Abstract: In 1983, seed dressing of peas with fosetyl-Al (Aliette) compared favourably with all other treatments on a field heavily contaminated with foot and root rot pathogens. Experiments carried out in 1983 and 1984 could not establish the reason for this phenomenon. Artificial inoculation with the most frequently isolated pathogens (Fusarium oxysporum, Phoma medicaginis var.pinodella, Pythium ultimum andFusarium solani f.sp.pisi) of sterilized soil before planting treated seeds did not reproduce the field observations, but glasshouse experiments using soil from the experimental field did. Glasshouse experiments in 1989, afterAphanomyces euteiches had been identified as a frequently occurring pea pathogen in the Netherlands, confirmed the favourable effect of fosetyl-Al as a seed treatment whenA. euteiches was in the pathogen flora.

Acute ozone exposure predispose Phaseolus vulgaris beans to botrytis cinerea

Abstract: The impact of ozone in predisposingPhaseolus vulgaris toBotrytis cinerea has been investigated. One day after 8 h exposures to 0, 120, 180 and 270 μg ozone m−3, primary and trifoliate leaves of four bean cultivars were detached and inoculated with conidia suspended in water or in an inorganic phosphate (Pi) solution. Visible ozone injury increased with increasing ozone concentrations in all cultivars. Primary leaves were more sensitive than trifoliate leaves. Conidia suspended in Pi solution caused lesions on healthy leaves, whereas conidia in water did not. Ozone-injured leaves of all cultivars showed lesions byB. cinerea after inoculations in water. The number of lesions was significantly correlated with ozone injury for primary leaves. After Pi inoculations, the number of lesions on the ozone-sensitive cultivars also increased with increasing ozone concentrations. However, the ozone-tolerant cultivar Groffy showed first a decrease in the Pistimulated infection at the lowest ozone dosages. The trifoliate leaves of all cultivars were less predisposed to the fungus than the primary leaves. The results indicate that realistic concentrations of ozone enhance the predisposition of bean leaves toB. cinerea. The rate of enhancement depends on the level of ozone-induced injury which was influenced by cultivar, leaf and ozone concentrations.

Surveys of cereal diseases and pests in the Netherlands. 1. Weather and winter wheat cropping during 1974–1986

Abstract: During 1974–86, systematic annual surveys of diseases and pests in winter wheat were conducted. In a series of papers the occurrence of diseases and pests will be reported in relation to weather and cropping practices. In this paper, an introduction to the series of papers, the weather and the the changing winter wheat cropping practices are described. Grain yields and pesticide use in the surveyed fields are reported. Wintertarwe werd systematisch geinventariseerd op ziekten en plagen in de jaren 1974–86. In een serie artikelen zal het optreden van ziekten en plagen worden besproken in relatie tot het weer en cultuurmaatregelen. Dit artikel is daarop een inleiding. Het jaarlijkse weer werd gekarakteriseerd door de gemiddelde maandtemperaturen en de totale hoeveelheid neerslag in een maand. De teelt van wintertarwe gedurende 1974–86 wordt kort besproken. De behaalde opbrengsten en het gebruik van chemische bestrijdingsmiddelen in de geinventariseerde percelen wordt gerapporteerd.

Effects of powdery mildew and weather on winter wheat yield. 2. Effects of mildew epidemics

Abstract: Wheat yield losses caused by powdery mildew were computed based on effects of the disease on leaf photosynthesis. Powdery mildew was introduced in a crop model of wheat by quantification of five parameters, taking the vertical and horizontal distribution of mildew in the crop into account. The most important parameters were those of the mildew intensity, the distribution of mildew in the crop, and the effect of mildew on assimilation at light saturation. Measured mildew epidemics in field experiments in three different years, were used to compute yield losses. Computed losses were compared to measured losses. On average, computed yield loss approached measured, but measured yield loss was underestimated, especially in early mildew epidemics due to the computation of partitioning and reallocation of assimilates. Other processes which may cause an underestimation are described. The use of crop models as a method to upgrade disease management systems is discussed. Opbrengstderving van wintertarwe werd berekend aan de hand van het effect dat meeldauw heeft op de blad-fotosynthese. Een rekenmodel voor de gewasgroei van tarwe werd uitgebreid met meeldauw. Met inachtneming van de vertikale en horizontale verdeling van meeldauw in het gewas, werd meeldauw in het model gekwantificeerd door vijf parameters. De belangrijkste parameters waren die van de meeldauwintensiteit, de verdeling van meeldauw in het gewas en het effect van meeldauw op de assimilatie bij een overvloed aan licht. Epidemieen van meeldauw, gemeten in veldproeven in drie verschillende jaren, werden gebruikt om opbrengstdervingen te berekenen. Gemiddeld kwam deze redelijk overeen met de in de veldproeven gemeten opbrengstderving. De gemeten opbrengstderving werd echter onderschat, vooral bij vroege epidemieen van meeldauw door de wijze waarop de (her)verdeling van assimilaten wordt berekend. Andere mechanismen, die een onderschatting van opbrengstderving kunnen veroorzaken worden besproken. Of deze modellen als methode gebruikt kunnen worden om systemen voor de geleide bestrijding van ziekten te verbeteren wordt bediscussieerd.

Detection of squash mosaic virus in seeds of melon (Cucumis melo) by enzyme-linked immunosorbent assay (ELISA)

Abstract: Squash mosaic virus (SqMV, comovirus) is seed-transmitted in severalCucurbitaceae. Therefore, the use of virus-free seed is important to prevent establishment of this virus in the Netherlands and to avoid spread to other countries.

Symptomatological and histopathological observations on oil palms from Brazil and Ecuador affected by fatal yellowing

Abstract: Fatal yellowing in oil palms from Brazil and Ecuador is characterized by a chlorosis of the young unfolded leaves and a decay of spear leaves. Contrary to healthy-looking palms, diseased palms do not have roots with soft and white tips.

Check-list for scientific names of common parasitic fungi. Series 3c; fungi on bulbs: 'additional crops' belonging to the Araceae, Begoniaceae, Compositae, Oxalidaceae and Ranunculaceae.

Abstract: This list is a continuation and also the ending of Series 3a and 3b [Neth. J. Pl. Path. 94 (1988), Supplement 1 and 95 (1989), Supplement 3], an account of the nomenclature of parasitic fungi on bulbs as used in official publications of the Netherlands Society of Plant Pathology and the Netherlands Ministry of Agriculture, Nature Management and Fisheries. The ‘additional crops’ subject to this Series 3c do not refer to bulbs in the common sense, but come within the present Dutch definition of ‘Bolgewassen’. The selected names include one new species (anamorph):Entylomella dahliae Ciferri ex Boerema & Hamers. Dit is een vervolg op Serie 3a en Serie 3b (Boerema en Hamers, 1988, 1989), waarin de naamgeving werd behandeld van de parasitaire schimmels bij de bekende bloem-bollen-en bolbloementeeltgewassen, behorende tot respectievelijk de Liliaceae, Amaryllidaceae en Iridaceae. De bijgoedgewassen waarvan nu in dit slotdeeltje de parasitaire schimmel-naamgeving wordt besproken, zijn geselecteerd uitgaande van het door het Laboratorium voor Bloembollenonderzoek te Lisse gepubliceerde handboek ‘Ziekten en afwijkingen bij bolgewassen’, deel 2, 1978. Tot de geselecteerde namen behoort een nieuwe soort (anamorf):Entylomella dahliae Ciferri ex Boerema & Hamers. In de officiele publikaties van de Nederlandse Planteziektenkundige Vereniging en het Ministerie van Landbouw, Natuurbeheer en Visserij zullen de namen van de ‘check-list’-serie worden gebruikt.