Persistence of resistance to fungicides in Sphaerotheca fuliginea

Isolates ofSphaerotheca fuliginea collected in 1981–1983 in cucumber glasshouses in the Netherlands were tested for their sensitivity to benzimidazole fungicides, dimethirimol, dinocap and pyrazophos.Resistance to dinocap was not observed, although this fungicide has been used for over 30 years. Resistance to benzimidazole fungicides and dimethirimol has been persistent since these fungicides were withdrawn for control of cucumber powdery mildew more than 10 years ago. Although pyrazophos has only been used incidentally after 1977, the level of resistance has not decreased.Factors possibly involved in the persistence of resistance and implications for disease control in practice are discussed.Samenvatting De gevoeligheid voor twee benzimidazool-fungiciden en dimethirimol, dinocap en pyrazofos werd getoetst vanSphaerotheca fuliginea isolaten die in 1981–1983 verzameld waren in komkommerkassen in Nederland. Resistentie tegen dinocap werd niet waargenomen, ofschoon dit fungicide al meer dan 30 jaar wordt gebruikt.De resistentie tegen benzimidazool-fungiciden en dimethirimol, die meer dan 10 jaar geleden werden teruggetrokken voor de bestrijding vanS. fuliginea, was persistent. Hoewel pyrazofos slechts incidenteel gebruikt is sinds 1977, is het resistentieniveau niet teruggelopen. Factoren die mogelijk betrokken zijn bij de persistentie van resistentie en de gevolgen voor de ziektebestrijding worden besproken.     

大黄酚对黄瓜白粉病菌的抑制作用研究

 采用子叶喷雾法分别测定了大黄酚(chrysophanol)对黄瓜白粉病菌(Sphaerotheca fuliginea)的保护和治疗生物活性。结果表明,大黄酚能有效降低黄瓜白粉病的病情指数,其保护和治疗作用的EC₅₀分别为0.23μg/mL和25.88μg/mL,对照药剂50%硫磺悬浮剂保护作用的EC₅₀为59.75μg/mL,10%苯咪甲环唑可湿性水分散粒剂治疗作用的EC₅₀为13.55μg/mL。在此基础上,利用2.4μg/mL大黄酚溶液处理黄瓜子叶24h后接种白粉病菌,在不同时段对病组织进行透明染色观察白粉病菌的变化情况。结果发现,大黄酚可有效降低黄瓜白粉病菌分生孢子的萌发率和萌发芽管个数,并能抑制菌丝的生长以及降低新生分生孢子的个数。接菌后24h,清水对照萌发率为66.6%,而大黄酚处理后的孢子不萌发;接菌后48h,对照菌丝的平均长度为414.7μm,大黄酚处理的菌丝平均长度为40.1μm;接菌后144h,对照的新生分生孢子串最多为8个孢子,大部分为6-7个,而大黄酚处理后的新生分生孢子串孢子个数最多为2个,大部分为1个。接菌7d后对照的病情指数为72.2,大黄酚处理组的病情指数仅为2.1,其保护作用防治效果达到97.1%,远高于50%硫磺悬浮剂65.4%的防效。     

Occurrence of decreased sensitivity of Sphaerotheca fuliginea to ditalimfos

Samenvatting In proefvelden van een instituut voor gewasbescherming te Heraklion op Kreta, waar fungiciden op hun werking tegen komkommermeeldauw worden getoetst, bleek de werking van ditalimfos na toepassing in twee proeven reeds verminderd te zijn. Het optreden van resistentie werd bevestigd in proeven in een klimaatkamer. Voor drie isolaten uit de proefvelden was de ED₅₀ van het middel ongeveer 19 maal zo hoog als die voor zes willekeurige isolaten uit praktijkpercelen.De detalimfos-resistente isolaten waren wel gevoelig voor fenarimol en pyrazophos.In proefvelden, die niet met het fungicide werden behandeld, bleken de resistente isolaten zich temidden van gevoelige isolaten te handhaven gedurende tenminste negen maanden.     

甜瓜白粉病内生拮抗细菌的筛选鉴定及其防治效果的研究

［目的］从高抗白粉病的甜瓜品种植株内分离筛选出对甜瓜白粉病有较好防效的内生拮抗细菌菌株,为甜瓜白粉病生物防治探寻新途径。［方法］ 采用温室盆栽试验和叶盘漂浮法分离筛选有较好防效的内生拮抗菌,并对其进行形态学、生理生化和分子生物学鉴定。［结果］ 从高抗白粉病的甜瓜品种‘MR-1’植株内分离获得31株内生细菌,其中1株内生菌Mg15对甜瓜白粉病盆栽试验防效达到74.3%。在离体叶盘上,经Mg15发酵液处理12 h后白粉菌孢子萌发率仅为9.29%,14 d后产孢量与对照相比降低了60%。扫描电镜观察发现,Mg15发酵液处理后的病菌菌丝皱缩生长,甚至产生畸形。Mg15发酵原液温室防病效果达80.66%。［结论］ Mg15对甜瓜白粉病具有显著防治效果,经鉴定该菌株为枯草芽胞杆菌（Bacillus subtilis)。     

Nature of resistance of seven melon lines to Sphaerotheca fuliginea

The nature of resistance of Sphaerotheca fuliginea Poll. race 1 was investigated in leaves of susceptible, moderately resistant and resistant genotypes of Cucumis melo . For this purpose three different tests were carried out. The first one was designed to assess whether resistance was caused by pre- or post-infectional mechanisms, and the other two tests were focused to determine if any differences were present in the progression ratio of the disease, measured as the delaying time in conidiophore and conidia formation, among the different cultivars which were tested. The results showed that in the resistant controls ('PMR5' and 'PI 124111'), the resistant reaction was probably due to pre-infectional mechanisms, or at least very near to the moment of infection, while in the moderately resistant and resistant Spanish local cultivars it was clearly due to post-infectional mechanisms characterized by an important delay in the growth and development of the fungus when compared with the susceptible cultivars. Suggestions are made for the development of more successful breeding programmes.     

黄瓜白粉病菌在不同抗性黄瓜材料上的侵染过程

白粉病是黄瓜生产中发生普遍,危害严重的主要病害之一。pm5.1和PM5.2是黄瓜上的2个白粉病抗性位点,本文对7份不同抗病基因型的黄瓜自交系进行了黄瓜白粉病抗性鉴定,并开展了黄瓜白粉病菌侵染过程的研究,对侵染后12、24、72 h的萌发率、菌丝形成率及菌落形成率等进行了分析。结果表明,当基因型为PM5.1PM5.1 pm5.2pm5.2时,黄瓜病情指数最高,表现为高感白粉病;当基因型为PM5.1PM5.1PM5.2 PM5.2和pm5.1pm5.1pm5.2pm5.2时,表现为中感白粉病;当基因型为pm5.1pm5.1PM5.2PM5.2时黄瓜自交系病情指数最低,表现为抗白粉病。分生孢子在抗、感黄瓜自交系植株叶片上均能萌发,但只能在感病黄瓜材料上完成整个无性生长周期,产生分生孢子。此外,黄瓜白粉病菌分生孢子在感病材料上的萌发率、菌丝形成率及菌落形成率均高于抗病材料。     

Comparison of three biological control agents against cucumber powdery mildew (Sphaerotheca fuliginea) in semi-commercial-scale glasshouse trials

The effect of three reported biological control agents, Ampelomyces quisqualis, Verticillium lecanii and Sporothrix flocculosa, was tested against cucumber powdery mildew (Sphaerotheca fuliginea). Two glasshouse experiments, one in the summer and one in winter/spring were conducted on a semi-commercial scale. In both experiments, a susceptible and a partially resistant cultivar were used. In the second experiment, the additional effect of integration of biological control and silicon amendments to the nutrient solution was also assessed. In both experiments, A. quisqualis did not control the disease. V. lecanii had a small effect on powdery mildew in the first experiment but not in the second. S. flocculosa gave the best control of powdery mildew in both experiments. In the first experiment, weekly application of S. flocculosa reduced disease in the partially resistant cultivar to the same level as a treatment in which the fungicides bupirimate and imazalil were each applied once. Addition of silicon in the nutrient solution in a concentration of 0.75 mM reduced disease by 10–16%, averaged over all treatments. There was no interaction between silicon and the biocontrol agents. Yield was recorded in the second experiment and was significantly increased by the fungicide treatment compared to the control in the partially resistant cultivar. Yield in the treatment with S. flocculosa was not significantly different from the fungicide treatment in this cultivar. Silicon had no effect on yield in either cultivar.     

Efficient production of phialoconidia of Verticillium lecanii for biocontrol of cucumber powdery mildew,Sphaerotheca fuliginea

A method is described that yields over 3×10⁹ phialoconidia/ml ofVerticillium lecanii.     

黄瓜白粉病菌拮抗真菌鉴定及生防效果评价

本文对黄瓜白粉病菌Sphaerotheca fuliginea拮抗真菌进行了筛选和鉴定及防治效果的评价。结果表较高的拮抗活性。菌株JK-13发酵液处理白粉菌孢子48 h后,其对孢子萌发抑制率为89.93%;发酵液处理发病的离体叶片和盆栽幼苗7 d后,其防治效果分别为88.02%和76.34%。利用形态学和分子生物学技术鉴定该菌为腐皮镰刀菌Fusarium solani。     

The ultrastructure of powdery mildew,Sphaerotheca fuliginea,isolated from cucumber leaves

The fine structure of conidia, hyphae, and of isolated haustoria of cucumber mildew (Sphaerotheca fuliginea) was studied. Large vacuoles are present in the spores and hyphae. Rosette-shaped particles, presumably glycogen, occur in the spores. Certain haustoria were found which lack the protrusions of the central body of mature haustoria. Most probably these haustoria are young and not yet fully developed. Portion of the sheath membrane of these haustoria is in close contact with the central body wall. The observations suggest that the haustorial sheath membrane is formed as a specialized portion of the haustorial body wall. Presumably the formation of the sheath membrane precedes the formation of the sheath and that of the protrusions of the central body.Samenvatting Er werd een onderzoek verricht naar de submicroscopische structuur van conidia, hyphen en haustoriën, geïsoleerd uit komkommerbladeren die geïnfecteerd waren met echte meeldauw (Sphaerotheca fuliginea). Sporen en hyphen bevatten grote vacuolen. In de conidiën werden rozetachtige deeltjes, waarschijnlijk glycogeen, gevonden. Er werden ook haustoriën gevonden, waarbij de normaal voorkomende uitstulpingen van het centrale lichaam in volwassen haustoriën ontbraken. Bij deze waarschijnlijk jonge haustoriën is een gedeelte van de schedemembraan in nauw contact met de wand van het centrale lichaam. Deze resultaten doen vermoeden dat de schedemembraan gevormd wordt als een speciaal gedeelte van de wand van het centrale lichaam. Waarschijnlijk scheidt de membraan zich daarna van het centrale lichaam bij de vorming van de schede. Verondersteld wordt, dat de uitstulpingen van het centrale lichaam nà of tijdens de vorming van de schede ontstaan.The study has been carried out at the Laboratory of Phytopathology, State Agricultural University, Wageningen, in connection with the activities of TNO Research Unit for Internal Therapy of Plants.     

Changes during a three-year period in the sensitivity to ergosterol biosynthesis inhibitors of Sphaerotheca fuliginea in the Netherlands

Isolates ofSphaerotheca fuliginea colleeted in 1981–1984 in cucumber giasshouses in the Netherlands were tested for their sensitivity to the ergosterol biosynthesis inhibitors (EBIs) fenarimol and imazalil.The data collected in the 1981 survey indicated that sensitivity to EBIs was lower than that of reference isolates. In the 1982 and 1983 surveys, sensitivity to EBIs continued to decrease. In 1984, data were collected until July; no significant difference in sensitivity with the 1983 level was apparent.Isolates collected in the district of Limburg, where EBIs were applied less frequently than in the district of Pijnacker, showed a significantly higher sensitivity to EBIs than isolates collected in Pijnacker.Besides differences in sensitivity to EBIs between years, differences within years were noticed. In 1983, the sensitivity to fenarimol and imazalil was significantly higher in the beginning of the growing season, before any fungicides were applied, than later in the growing season.Generally, changes in sensitivity to EBIs did not result in full failure of control. In most cases, a change to shorter spray intervals has been sufficient to compensate for the decrease in sensitivity and to achieve proper control by fenarimol and imazalil. The results once more emphasize the necessity of designing strategies to prevent resistance to EBIs.Samenvatting Uit komkommerkassen in Nederland werden gedurende de periode 1981–1984 isolaten vanSphaerotheca fuliginea verzameld. De gevoeligheid van deze isolaten voor fenarimol en imazalil, twee ergosterolbiosyntheseremmers (EBR's), werd getest. De gegevens verzameld in 1981 wijzen erop dat de gevoeligheid voor EBR's lager was dan die van referentie-isolaten. In 1982 en 1983 daalde de gevoeligheid voor EBR's nog verder. In 1984 werden gegevens verzameld tot en met juli. Er werd geen significant verschil in gevoeligheid waargenomen met het niveau van 1983.Isolaten verzameld in Limburg, waar EBR's minder vaak toegepast worden dan in Pijnacker, hadden een significant hogere gevoeligheid voor EBR's dan isolaten uit Pijnacker.Naast verschillen in gevoeligheid voor EBR's tussen jaren, werden ook verschillen binnen de jaren waargenomen. In het begin van het groeiseizoen in 1983, voordat fungiciden waren gebruikt, was de gevoeligheid voor fenarimol en imazalil hoger dan later in het groeiseizoen. In het algemeen hadden de veranderingen in gevoeligheid voor EBR's geen volledig falen van de bestrijding tot gevolg. In de meeste gevallen was een verkorting van de intervallen tussen de toepassingen van fenarimol en imazalil voldoende om te compenseren voor de verminderde gevoeligheid en om een goede bestrijding te verkrijgen. De resultaten benadrukken nogmaals de noodzaak om strategieën te ontwerpen die resistentie tegen EBR's voorkomen.     

Suppression of powdery mildew (Sphaerotheca fuliginea) in cucumber by the detergent Zohar LQ-215

The effect of the detergent Zohar LQ-215 alone or combined with the fungicide fenarimol (Rubigan) on cucumber powdery mildew (caused bySphaerotheca fuliginea) was examined under controlled environmental conditions and in the field. In laboratory tests conducted on leaf disks, the efficacy of fenarimol was 30 times greater than that of Zohar LQ-215 as indicated by the ED₅₀ values of the compounds (0.012% and 0.356%, respectively). Zohar LQ-215 did not reduce spore germination or germ-tube elongation, but inhibited the later stages of the disease cycle (i.e., mycelial growth and sporulation). Although the detergent was degraded relatively quickly, its effect on the polycyclic development of the disease lasted for up to 24 days after spraying. Low disease severity (2.4% compared with 27% in the control) was maintained following three applications of the detergent at 5 days intervals. In a greenhouse trial, a mixture of Zohar LQ-215 and fenarimol at half rate did not improve disease suppression beyond the effect of fenarimol applied alone at half rate. However, the effects of the two compounds were additive when applied in the field as a mixture.     

Virulence variation and DNA polymorphism in Sphaerotheca fuliginea, causal agent of powdery mildew of cucurbits

Strains of Sphaerotheca fuliginea, one of the causal agents of powdery mildew of cucurbits, were examined for differences in virulence, mating type and DNA polymorphism. The 28 strains were chosen to be diverse according to host and geographic origin. Characterization of virulence phenotypes was based on the expression of symptoms on 4 species of cucurbits and 6 cultivars of melon. Two pathotypes, capable of attacking either cucumber cv. Marketer and melon cv. IranH and squash cv. Diamant or cucumber cv. Marketer and melon cv. IranH were observed. Tests on melon cultivars revealed 3 races. In tests of sexual compatibility with reference strains, heterothallism was observed for all isolates. Frequency of the two mating types differed significantly in the population. DNA polymorphism was determined both by restriction fragment length polymorphism (RFLP) of the ribosomal internal transcribed spacers (ITS) and 5.8S DNA amplified by the polymerase chain reaction and by random amplified polymorphic DNA (RAPD). For any one of the 11 restriction enzymes tested all strains presented an identical pattern of ITS RFLP. RAPD analysis, using 22 primers which provided reproducible patterns, revealed a relatively low degree of polymorphism. Furthermore, cluster analysis based on RAPD data (152 markers) did not separate groups within the species S. fuliginea. No association could be found between virulence, mating type, geographical and host origin and RAPD patterns. The lack of association between phenotypic and molecular markers and the close fit to linkage equilibrium for the characters examined suggest that recombination may play a role in populations of S. fuliginea.     

诱导剂处理及白粉菌接种对甜瓜叶片叶绿素荧光参数的影响

以抗病品种Tam Dew和感病品种卡拉克赛为材料,研究了BTH、SA处理及白粉菌接种对甜瓜叶片叶绿素荧光参数的影响。结果发现:BTH和SA处理使甜瓜叶片光系统Ⅱ(PSⅡ)最大光化学效率(Fv/Fm)、PSⅡ光合电子传递效率(ΦPSⅡ)、天线转化效率(Fv'/Fm')显著提高,热耗散速率(Drate)显著降低。白粉菌接种使甜瓜叶片Drate显著升高,Fv/Fm、ΦPSⅡ、Fv'/Fm'显著降低。以上结果表明,BTH和SA处理能缓解因自然衰老和白粉菌侵染引起的甜瓜叶片光系统反应中心活性下降。     

Fitness of isolates of Sphaerotheca fuliginea resistant or sensitive to fungicides which inhibit ergosterol biosynthesis

Isolates ofSphaerotheca fuliginea resistant to fungicides which inhibit ergosterol biosynthesis (EBIs: bitertanol, fenarimol, imazalil) had been collected from glasshouses in the Netherlands. Fitness of these isolates was compared to that of isolates with a wild-type sensitivity to EBIs. Fitness parameters studied were germination of conidia, growth of germ tubes and mycelium, penetration, sporulation and competitive ability.In an experiment in which 10 EBI-resistant isolates were compared to 7 wild-type isolates, one or more values of fitness parameters for EBI-resistant isolates were slightly lower than those for the wild-type isolates. However, within the group of resistant isolates no relation existed between the degree of resistance to EBIs and the degree of fitness. In an experiment with fewer isolates but with more replicates, differences in fitness between EBI-resistant and wild-type isolates were not detected over a three-month period.In competition experiments in which no crowding was present, resistant isolates competed well with the wild-type isolate.It is concluded that the hypothesis that resistance to EBIs is unlikely to develop under practical conditions because of decreased fitness of EBI-resistant strains, does not seem to hold forS. fuliginea.Samenvatting Uit kassen in Nederland waren isolaten vanSphaerotheca fuliginea verzameld, die resistent waren tegen fungiciden die de ergosterol-biosynthese remmen (EBR's: bitertanol, fenarimol, imazalil). De fitness van deze isolaten werd vergeleken met die van isolaten met een wild-type gevoeligheid voor EBR's. De volgende fitness-parameters werden bestudeerd: sporekieming, groei van kiembuizen en mycelium, penetratie, sporulatie en competitievermogen.In een proef, waarin 10 EBR-resistente isolaten werden vergeleken met 7 wild-type isolaten, waren één of meer fitness-parameters iets lager dan die van de wild-type isolaten. Binnen de groep van de resistente isolaten bestond geen relatie tussen de mate van resistentie tegen EBR's en de waarden van de fitness-parameters. In een proef met iets minder isolaten maar met meer herhalingen in de tijd, werden geen verschillen in fitness waargenomen tussen de EBR-resistente en wild-type isolaten. In competitieproeven waarin een epidemie zich kon ontwikkelen, concurreerden de resistente isolaten goed met het wild-type isolaat.Er wordt geconcludeerd dat de hypothese dat resistentie tegen EBR's in de praktijk waarschijnlijk niet zou optreden vanwege een verminderde fitness van de EBR-resistente isolaten, niet van toepassing is opS. fuliginea.     

Variability in the reaction of squash (Cucurbita pepo) to inoculation with Sphaerotheca fuliginea and methodology of breeding for resistance

Reaction to inoculation with powdery mildew caused by Sphaerotheca fuliginea was observed on leaf discs and young plants of eleven representatives of seven edible cultivar groups of Cucurbita pepo. Disease intensity (i.e. number of infections per leaf) was highly correlated ( r ²=0·863, P <0·0001) with spore yield per leaf. Spore yield per leaf and frequency of sporulation on leaf disks were moderately ( r ²=0·505), but significantly correlated ( P <0·01), suggesting that frequency of sporulation can be used for initial screening against susceptibility in a breeding programme. Spore yield per leaf and spore yield per artificially inoculated leaf disc were highly correlated ( r ²=0·87, P <0·0001); this suggests that counting of spores on leaf discs, a laborious but accurate procedure, could be used on the remaining plants as a second step in selection for resistance of the variation in the response of edible C. pepo to the pathogen, 85·8% was attributed to differences between the edible groups and only 14·2% to individual cultivars within a group. Cultivars of the cocozelle and vegetable marrow groups were the most susceptible, whereas relatively resistant cultivars were found in the scallop and straightneck groups.     

Suppression of cucumber powdery mildew (Sphaerotheca fuliginea) by foliar sprays of pbospbate and potassium salts

Powdery mildew, caused by Sphaerotheca fuliginea , was significantly controlled by a single spray of aqueous solutions (25 mm) containing various phosphates and potassium salts. Phosphates were suppressive when applied alone; however, treatments in combination with Tween-20 were more effective in causing the disappearance of powdery mildew pustules from diseased foliage. Efficiency of control, as expressed by the disappearance of 99% of pustules, was recorded 1 or 2 days after application of single sprays of phosphate and potassium salt solutions. Treatment was effective for up to 12 or 15 days, respectively, following application to small or large greenhouse-grown plants with established mildew infection. Treatments also markedly reduced (> 99%) the production of eonidia from colonies. A further application of these salts to the same plants resulted in the elimination of about 50% of mildew colonies present prior to the application. Further spray application inhibited disease development compared with water-sprayed plants, but did not reduce the number of existing lesions. Phosphate was more effective than the systemic fungicide pyrifenox and reduced established powdery mildew infection up to 11 days after application, but the converse was true when assessments were made after 15 days. These properties of phosphates and potassium salts make them appropriate for use as foliar fertilizers with a potential beneficial influence on disease control.     

Effects of cucumber genotype on the induction of resistance to powdery mildew, Sphaerotheca fuliginea, by 2, 6-dichloroisonicotinic acid

Conspicuous differences in inducibility of resistance to powdery mildew between susceptible and partially resistant cucumber cultivars were found when 2, 6-dichloroisonicotinic acid (INA) was used as a model substance. In the partially resistant cv. Flamingo, EC₅₀ was approximately 0·25 mg/1. In the susceptible cvs Corona and Lange Groene Gigant it was approximately 6mg/1. In greenhouse experiments with cv. Flamingo, powdery mildew could be well controlled with fortnightly applications in doses as low as 0·5 mg/1. The effect was highly cumulative.     

白粉病菌侵染对黄瓜叶片光合电子传递及其PSⅡ功能蛋白D1表达的影响

 本文研究了黄瓜(Cucumis sativus L.)感染黄瓜白粉病后,植物叶绿素含量、光合电子传递速率和光化学反应中心D1蛋白的变化。被感染的黄瓜叶片叶绿素含量降低,而且Chlb比Chla敏感。全链电子传递速率受到抑制,PSⅡ电子传递速率的变化与全链电子传递速率的变化趋势相似,但PSⅠ电子传递速率却未受到抑制。由于PSⅡ的光合反应中心D1蛋白含量变化与PSⅡ电子传递速率的变化类似,推测D1蛋白的表达量变化是引起电子传递活性波动的主要因素。