Lithium chloride and cucumber powdery mildew infection

Lithium chloride solutions (1 mM), supplied to cucumber plants via the root system, conferred protection against powdery mildew infection of the leaves by Sphaerotheca fuliginea. The development of infection structures was significantly inhibited by this treatment. Effective concentrations of the lithium salt increased the growth of shoots but resulted in some reduction of root growth, The incorporation of lithium by different parts of plants was assessed during a 20-day treatment period, The possible mode of action of lithium on this host-pathogen system is discussed.     

防治西葫芦和黄瓜白粉病的生物制剂的筛选

瓜类白粉病是蔬菜上的重要病害之一,为加大对该病害的生物防治力度,本研究采用课题组研发的1×109cfu/g玫瑰黄链霉菌水剂和10亿芽胞/g枯草芽胞杆菌悬浮剂以及市场上常用的枯草芽胞杆菌、哈茨木霉菌、寡雄腐霉、武夷菌素、多抗霉素等多种生物制剂进行田间药效试验,比较几种生物制剂的防治效果。结果表明,供试生物制剂对西葫芦白粉病的防效为57.65%~84.98%,其中3%多抗霉素水剂600倍液的防效最好,为84.98%,且具有明显的促生长作用,增产率达12.65%。其次为1 000亿芽胞/g枯草芽胞杆菌可湿性粉剂(武汉天惠)400倍液、2%武夷菌素水剂600倍液和3×108 cfu/g哈茨木霉菌可湿性粉剂300倍液,可作为西葫芦白粉病防治的选用药剂。1×109 cfu/g玫瑰黄链霉菌水剂对西葫芦和黄瓜白粉病均具有较好的防效,分别为78.68%和73.59%,具有开发和应用的市场价值。     

The isolation of haustoria from cucumber leaves infected with powdery mildew

A procedure is described for the isolation of haustoria from cucumber leaves infected with powdery mildew(Sphaerotheca fuliginea). It consists of a removal of the hyphae from the leaf surface and a release of the haustoria from the intact host cells by homogenization of the leaves, followed by purification of the haustoria by means of centrifugation of the leaf homogenate in glycerol and filtration through micro-mesh sieves of 15 and 5 µ with the use of ultrasonic vibration. Preliminary experiments showed that oxido-reduction processes still proceed in isolated haustoria.     

Germination of powdery mildew conidia in vitro on cellulose membranes

Conidia of several powdery mildews were found to germinate to a high and reproducible percentage on 25 m thick cellulose membranes, laid on modified Czapek Dox agar in Petri dishes. Germination on 45 m thick, uncoated cellulose, coated cellulose, cellulose acetate and collodion membranes always was lower and more irregular than on 25 m thick cellulose. Probably, the water permeability of the membranes is of importance in causing a humidity gradient favourable for germination of powdery mildew conidia.Samenvatting Bij incubatie van conidiën van echte meeldauwschimmels op 25 m dikke cellulosemembranen, gelegd op agar in Petri-schalen werden hoge kiemingspercentages verkregen. Kieming op 45 m dikke, ongecoate cellulose, gecoate cellulose, cellulose-acetaat- en collodionmembranen was altijd slechter en onregelmatiger dan op 25 m dikke cellulosemembranen. Waarschijnlijk is de waterdoorlaatbaarheid van de membranen van belang voor de kieming door de vorming van een vochtigheidsgradient.     

一体化智能孢子捕捉系统在黄瓜霜霉病和黄瓜白粉病预测上的应用

为探索国内研制的新型一体化智能孢子捕捉系统在黄瓜霜霉病和黄瓜白粉病预测预报上的应用,在田间自然发病情况下,通过对捕捉孢子的形态进行识别,优化一体化智能孢子捕捉系统主要工作参数如有/无空气切割头、空气采集口高度和空气采集时间;通过病害及孢子的动态监测分析大棚黄瓜霜霉病和黄瓜白粉病病情指数与孢子捕捉量的关系。结果表明,当不加装空气切割头、空气采集口高度为70 cm、孢子捕捉时间在10:00—10:30时段有利于孢子的捕捉。黄瓜霜霉病和黄瓜白粉病病情指数与连续7 d孢子捕捉总量具有强正相关性。连续多日监测到黄瓜霜霉病菌孢子囊且数量快速增加是黄瓜霜霉病发生或快速上升的一个预测指标。黄瓜白粉病发病之前没有监测到黄瓜白粉病菌分生孢子,且在病害盛发期分生孢子捕捉量仍较少。研究表明,一体化智能孢子捕捉系统适用于黄瓜霜霉病的预测,但在黄瓜白粉病的预测上尚存在一定问题。     

Changes in carbohydrate composition of cucumber leaves during the development of powdery mildew infection

Within 3 days after inoculation, greater rates of decrease of hexoses, and of increases in inositol and α-glucans, were detected in leaves of cucumber leaves infected with Sphaerotheca fuliginea (now reclassified as Podosphaera xanthii ) than in healthy leaves, together with synthesis of fungal mannitol, arabitol and trehalose. With the onset of sporulation (5 days after inoculation, dai), glucose, polyols, trehalose and glycogen content, as well as fresh and dry weight of leaf tissue, increased more rapidly than in healthy plants, while sucrose, raffinose and starch declined. Starch, glycogen and other α-glucans, extracted from ethanol-insoluble tissue fractions of different water-solubility from healthy and infected leaves, were quantified after amyloglucosidase treatment. Infection-induced alterations in partitioning of photosynthate during a 14 h photoperiod at 7 dai, including a close correspondence in patterns of synthesis of glucose, polyols and glycogen, further clarified the process of diversion of host assimilate to the pathogen. The presence of glucose, but only traces of sucrose in spores, supported evidence from other powdery mildew infections for photosynthate being transferred to S. fuliginea as glucose.     

The impermeability of powdery mildew conidia and their germination in arid environments

Conidia of Erysiphe graminis formed germ hyphae while floating on aqueous solutions of glutaraldehyde (0.25 M), formaldehyde (1 M), NaF (0.1 M), HgCl (0.05 M) and HgCl₂. (0.1 M). Inhibition of germination ranged from 60.1% (NaF) to 88.8% (HgCl₂). In an atmosphere of HCN gas (5 mM) inhibition was 72.8%. The detergents Triton X-100. sodium dodecylsulphate and cetyl trimethylammonium bromide at 10 g 1^-1 caused approximately 90% inhibition but at lower concentrations Triton X-100 was the most inhibitory, both to germination and germ hypha elongation. Results of simultaneous treatment with HCN and Triton X-100 suggested that their actions were independent but comparisons of LD 50 for glutaraldehyde and Triton X-100 used separately and together indicated antagonism.     

四氟醚唑对黄瓜的安全性及其对黄瓜白粉病的防治效果

为明确四氟醚唑对黄瓜植株的安全性,采用浸种及茎叶喷雾处理的方法测定其对不同生长时期黄瓜植株的影响,采用子叶保湿培养法测定白粉病菌对其敏感性,并在田间进行防治白粉病的药效试验,综合评价了四氟醚唑对黄瓜白粉病的效果。浸种处理后,黄瓜子叶上白粉病发病率明显降低,对黄瓜株高和根长的抑制率、茎周增长率及叶绿素含量增加率与己唑醇相比均较低;发芽期及幼苗期的黄瓜植株使用四氟醚唑处理,新生节间均出现轻微的抑制伸长现象;4％四氟醚唑水乳剂对黄瓜白粉病菌的EC50为0．8146mg／L,敏感毒力高于50％醚菌酯水分散粒剂;田间间隔期10天喷雾,在末次药后7天对黄瓜白粉病的防治效果为76．02％～85．77％,与5％己唑醇水乳剂防效相当,明显高于50％醚菌酯水分散粒剂的防效。表明四氟醚唑对黄瓜生长安全且用药间隔期长,是防治白粉病的高效轮换药剂。     

Electron microscopic observations on haustoria isolated from cucumber leaves infected with powdery mildew

The fine structure of haustoria isolated from cucumber leaves infected with powdery mildew (Sphaerotheca fuliginea) was studied. Electron microscopy showed a haustorial body of 5–7 which contains many mitochondria and is surrounded by an electron lucent sheath of up to 4 in thickness. The sheath is limited by a heavily invaginated membrane of about 0.03 . The central body is connected with the sheath membrane by fingerlike convoluting protrusions.Samenvatting Er werd elektronenmicroscopisch onderzoek verricht aan haustoriën, geïsoleerd uit komkommerbladen geïnfecteerd met echte meeldauw (Sphaerotheca fuliginea).De haustoriën bevatten een centraal lichaam van 5 to 7 met veel mitochondriën dat omgeven is door een schede van maximaal 4 die de elektronenbundel gemakkelijk doorlaat. De schede wordt begrensd door een geïnvagineerde membraan van ongeveer 0,03 .Het centrale lichaam is via kronkelend verlopende uitstulpingen verbonden met de schedemembraan.The study has been carried out at the Laboratory of Phytopathology, State Agricultural University, Wageningen, in connection with the activities of T.N.O. Research Unit for Internal Therapy of Plants.     

Occurrence and molecular characterization of strobilurin resistance in cucumber powdery mildew and downy mildew

ABSTRACT Between 1998 and 1999, control failure of powdery mildew (Podosphaera fusca) and downy mildew (Pseudoperonospora cubensis) by the strobilurin fungicides azoxystrobin and kresoxim-methyl was observed in cucumber-growing areas of Japan. Results from inoculation tests carried out on intact cucumber plants and leaf disks clearly showed the distribution of pathogen isolates highly resistant to azoxystrobin and kresoximmethyl. Fragments of the fungicide-targeted mitochondrial cytochrome b gene were polymerase chain reaction amplified from total pathogen DNA and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochrome b gene, resulting in substitution of glycine by alanine at position 143, was found in resistant isolates of downy mildew. This substitution in cytochrome b seemed to result in high resistance to strobilurins in this pathogen. The same mutation was found in some but not all resistant isolates of powdery mildew. This study suggests that a mutation at position 143 in the target-encoding gene, resulting in an amino acid substitution, was probably a major cause of the rapid development of high strobilurin resistance in these two pathogens.     

Biological control mechanisms of D-pinitol against powdery mildew in cucumber

D-pinitol is an effective agent for controlling powdery mildew (Podosphaera xanthii) in cucumber. In this study, we determined the mechanisms of D-pinitol in controlling powdery mildew in cucumber plants. We compared P. xanthii development on cucumber leaf surface treated with D-pinitol or water (2 mg ml⁻¹) at different time points after inoculation. The germinating conidia, hyphae, and conidiophores of the pathogen were severely damaged by D-pinitol at any time of application tested. The highest level of suppression of fungal development was obtained at 3 days after inoculation. The contents of chlorophyll, total phenolics, flavonoid, and gallic acid and its derivatives (GAD); the activities of phenylalanine ammonialyase (PAL), polyphenoloxidase (PPO), peroxidase (POX), and superoxide dismutase (SOD); and the expression of the genes encoding for PR-1, peroxidase (POX), lipoxygenase (LOX1), chitinase (Chit1) were higher in the cucumber leaves treated with D-pinitol and inoculated than in the leaves either treated with D-pinitol or inoculated with the pathogen. These results suggest that D-pinitol triggers several plant defense responses in cucumber leading to pathogen suppression and resistance to powdery mildew.     

Decreased sensitivity to pyrazophos of cucumber and gherkin powdery mildew

In some cucumber and gherkin greenhouses in the Netherlands, where Curamil (a.i. pyrazophos) had been used for control of powdery mildew, unsatisfactory disease control was obtained in recent years. Laboratory tests revealed a decreased sensitivity of the pathogen to the fungicide. The fitness and the competitive ability of pyrazophos resistant strains in absence of the fungicide appeared to be somewhat lower than that of the normal, sensitive strains. The implications with respect to disease control in practice are discussed.Samenvatting In enkele kassen, waar Curamil (a.i. pyrazofos) in 1977 aangewend werd ter bestrijding van meeldauw op komkommers en augurken, werd onvoldoende effekt met dit middel tegen deze ziekte verkregen. Toetsing in het laboratorium bracht een verminderde gevoeligheid van het pathogeen voor het fungicide aan het licht (Tabel 1). Bij afwezigheid van pyrazofos bleek het competitief vermogen (Tabel 2) en de vitaliteit (Tabel 3) van de pyrazofos resistente isolaten wat lager te zijn dan die van het normale, gevoelige pathogeen. De betekenis hiervan met betrekking tot de ziektebestrijding wordt besproken.     

电解水对黄瓜白粉病的防效以及对黄瓜生长和品质的影响

利用电解水喷施大棚黄瓜,研究其对黄瓜白粉病的防治效果,以及对植株生长指标、果实品质及产量的影响。结果表明,施用农药、先喷酸性电解水后喷碱性电解水、酸性电解水、及先喷碱性电解水后喷酸性电解水4个处理后黄瓜叶面病情指数显著降低,最终防治效果分别为88.5%、75.1%、72.8%、57.6%,碱性电解水处理防效为15.5%。电解水除对黄瓜植株具有一定的促徒长作用外,对黄瓜果实品质和产量未见不利影响,且酸性电解水和先喷酸性电解水后喷碱性电解水可增加植株根部、地上部分干重,促进黄瓜叶面生长。     

Light quality affects incidence of powdery mildew,expression of defence-related genes and associated metabolism in cucumber plants

To determine whether light quality affects the incidence of disease, we exposed cucumber (Cucumis sativus L. cv. Jinyan No. 4) plants at the 4-leaf stage to white and other monochromatic lights and tested the effects on plant response to Sphaerotheca fuliginea, defence-related gene expression and metabolic changes. Exposure to red light resulted in higher levels of H₂O₂ and salicylic acid (SA), and stronger expression of defence genes such as PR-1 than exposure to white or other monochromatic lights. In comparison, plants grown under purple and blue light had higher activities of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO) and higher level of flavonoids than plants grown under other lights. Furthermore, plants grown under red light were more resistant whilst plants grown under other monochromatic lights were less resistant to Sphaerotheca fuliginea than plants grown under white light. These results suggest a role of red light in light-enhanced resistance, which correlates with enhanced SA-dependent signaling pathway.     

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.     

Biological control of cucumber powdery mildew with Tilletiopsis minor under greenhouse conditions

In growth cabinet and greenhouse experiments the efficacy ofTilletiopsis minor in controlling cucumber powdery mildew decreased as humidity was lowered. This effect could be counteracted by formulation of the mycoparasite with lipophilic substances, like Hora Oleo 11E and lipids from milk. These formulations, without the mycoparasite, were also found to be deleterious to powdery mildew development. In the long run, however, formulations withT. minor gave better biological control of cucumber powdery mildew than formulations alone.     

8种植物提取物对小麦白粉病病菌抑制活性研究

采用室内盆栽法,测定8种植物提取物对小麦白粉病的抑菌活性。结果表明,香樟叶、黄杨和刺槐提取物对小麦白粉病病菌(Blumeria graminis f.sp.tritici)有良好的抑制活性。其粗提物干质量浓度为40 mg/m L时,对白粉菌抑菌效果依次为57.68%,38.67%,42.39%;香樟叶粗提物对小麦白粉的室内预防和治疗作用的EC50分别为10.39 mg/m L和30.43 mg/m L,其预防效果显著优于治疗效果;测定香樟叶4种萃取物对小麦白粉病的预防效果,发现石油醚萃取物抑菌效果最好,EC50为8.71 mg/m L。说明其抑菌活性物质主要存在石油醚相中。     

A pattern in the appearance of cucumber powdery mildew in Dutch glasshouses

An inquiry was held in 1982, 1983 and 1984 to collect information on the survival and dispersal of cucumber powdery mildew. Growers who planted a crop in December, January or February were asked when they observed mildew for the first time in their crop. A gradual increase in the number of infected crops was observed from planting until May. The earliest observations of infected crops were immediately after planting. The weeks of the first observation of mildew, the disease-free periods and the apparent rates of increase of infected crops are presented for various districts. In the districts with the highest crop density (Pijnacker), mildew was generally observed early in the growing season, while the apparent rate of increase of infected crops was higher than in other districts. In the district with the lowest crop density (Northern Netherlands), mildew was observed late in the growing season and the apparent rate of increase of infected crops was low. Possible means of survival and dispersal of inoculum are discussed. It is suggested that overwintering of inoculum is possible because cucumber plants are grown all year round. Dispersal of cucumber powdery mildew is suggested to take place by transportation of infected planting stock, visitors and wind.     

Effect of temperature on infection and development of powdery mildew on cucumber

Podosphaera xanthii and Golovinomyces orontii are the causal agents of cucurbit powdery mildew. The effect of temperature on conidial germination, infection and sporulation was studied under controlled conditions. Conidia were inoculated on cucumber leaf discs, and incubated at six constant temperatures (from 10 to 35 °C in 5 °C steps) for 3 to 72 h to evaluate conidial germination and infection, and for 6–15 days to evaluate sporulation intensity. Germination took place at all tested temperatures, but was close to zero at 35 °C. The longest germ tubes measured in this experiment were 141.74 μm for the secondary germ tube of P. xanthii at 20 °C after 48 h of incubation, and 67.92 μm for G. orontii for the primary germ tube at 20 °C after 48 h of incubation. The optimal temperatures for conidial germination, infection and sporulation were 24.4, 25.7 and 22.3 °C, respectively, for P. xanthii, and 17.9, 17.3 and 14.9 °C, respectively, for G. orontii. Equations were developed to describe conidial germination with a coefficient of determination (R²) of 0.85 and 0.90 for P. xanthii and G. orontii, respectively. Infection equations resulted in R² of 0.94 and 0.93 for P. xanthii and G. orontii, respectively; and for sporulation, R² of 0.75 and 0.76 for P. xanthii and G. orontii respectively, as a function of temperature. These results can be used to develop models for the risk of cucurbit powdery mildew under field conditions.