An apparatus for collecting total conidia of Blumeria graminis f.sp. hordei from leaf colonies using electrostatic attraction

Conidia from living conidiophores of barley powdery mildew ( Blumeria graminis f.sp. hordei ) on host leaves were collected consecutively using an electrostatic spore collector. The collector consisted of an electrical conductor plate linked to an electrostatic voltage generator and insulator plates placed abreast on a timed conveyer. The conductor plate was negatively charged by the potential supplied from the voltage generator. The negatively charged conductor plate caused dielectric polarization of the insulator plate, and the surface charge on the insulator plate attracted mature conidia abstricted from conidiophores on colonies growing on leaves placed 2 cm from the insulator plate. The surface charge on the insulator plate was proportional to the voltage applied to the conductor plate. Under optimized conditions, abstricted conidia were attracted to the electrostatically activated insulator plates without any detriment to their survival. During a colony's life span of c . 460 h, conidia were released throughout the day and c . 12 × 10⁴ conidia were collected during the lifetime of the colony. This is the first report on the direct quantification of progeny conidia produced by powdery mildew infecting host leaves.     

宁夏温室瓜菜白粉病菌鉴定及病害流行预测模型构建

为明确宁夏回族自治区温室瓜菜白粉病菌的分类地位,对采自该地区温室的南瓜、黄瓜和甜瓜上的白粉病菌基于ITS序列分析进行分子鉴定;利用孢子捕捉器对温室中甜瓜白粉病菌的孢子量进行监测,分析环境因子、孢子量和病情指数之间的关系,并采用逐步回归分析法构建温室甜瓜白粉病的流行预测模型。结果表明,基于ITS序列的分子鉴定结果,3种瓜菜白粉病的病原菌均为单囊壳白粉菌Podosphaera xanthii。发病期间,每日温室中甜瓜白粉病菌的孢子量在12:00—16:00时段最多,占24 h内总孢子量的34%~81%,20:00—08:00时段最少;白粉病菌孢子的释放与光照强度有关,相关系数为0.602。第t天的病情指数与标准累积温度、标准累积湿度、t-4 d前08:00—12:00时段的累积孢子量、第t-4天16:00—20:00时段的孢子量均具有显著的相关性,相关系数分别为0.935、0.938、0.956和0.921。以标准累积湿度和第t-4天16:00—20:00时段的孢子量为预测变量构建了温室甜瓜白粉病流行预测模型,决定系数为0.962,表明该模型具有较好的实际应用价值。     

A natural fungicide for the control of <Emphasis Type="Italic">Erysiphe betae</Emphasis> and <Emphasis Type="Italic">Erysiphe cichoracearum</Emphasis>

This study examines the effects of a vegetable fungicide on sugar beet powdery mildew (Erysiphe betae) and cucumber powdery mildew (Erysiphe cichoracearum). The formulations consisting of a dispersion of Brassicaceae meal in vegetable or mineral oils on infected leaves of sugar beet, reared in the greenhouse, and of musk melons cultivated under plastic tunnels, were tested in comparison to each oil taken separately. Both formulations containing Brassicaceae meals, caused 94% of conidia to be distorted while for the untreated group only 2% were distorted. Furthermore, the leaf area infected by E. betae was 56% for untreated plants and 2.7 and 9.9% respectively, for plants treated with meal containing mineral and vegetable oil. Vegetable oil considered separately or with Brassicaceae meals showed no phytotoxicity, while the formulations based on mineral oil showed a significantly lower fresh and dry weight on tomato plants. The low level or absence of phytotoxicity of plants treated with vegetable oil formulations suggests that to improve the efficacy of powdery mildew control, they could be used mixed with sulphur. The efficiency of the vegetable formulations in the powdery mildew control observed during these trials encourages further investigation on other parasitic fungi and foliar pathogens.     

Characteristics and host range of tomato powdery mildew

The anamorphic state of a powdery mildew, which first appeared on tomato in the UK in 1987, currently listed as Erysiphe orontii (anamorph Oidium violae ), was examined microscopically on both tomato and alternative hosts. Host range studies were also carried out. In 1993–95, species and cultivars of plants from 26 of the 30 families listed as hosts of E. orontii were inoculated with tomato powdery mildew in the glasshouse and assessed for susceptibility on a 0–3 scale based on degree of sporulation and growth. Thirteen families contained species or varieties that were susceptible and a total of 80 varieties, including many economically important Cucurbitaceae and Solanaceae, supported sporulation to some extent (susceptibility score 1–3). Necrosis was not a constant feature of plants exhibiting resistance, as it could accompany sporulation on some susceptible varieties. Microscopic measurements showed that conidial size, conidiophore length, conidiophore foot-cell length and width, and the number of cells distal to the foot-cell were remarkably constant between samples of powdery mildew taken from tomato each year and from the various alternative hosts. Based on the production of conidia singly, the presence of nipple-shaped to moderately lobed appressoria, and occurrence of straight conidiophores, it is concluded that this fungus on tomato should more correctly be named Oidium lycopersicum until the sexual stage is discovered. The highly polyphagous nature of this powdery mildew would suggest that it represents a potential risk to UK agriculture and horticulture, but the failure to recover any powdery mildew from 120 samples of potato, including varieties Cara and Maris Piper, on which the tomato powdery mildew could sporulate in the glasshouse, suggests that environmental factors may play a key role in preventing establishment of this powdery mildew on alternative hosts on a commercial scale in the field.     

Morphological and molecular characterization for a Japanese isolate of tomato powdery mildew Oidium neolycopersici and its host range

 A single conidium of tomato powdery mildew was isolated from heavily infected leaves of tomato (cv. Moneymaker) grown in the greenhouse of Kinki University, Nara Prefecture, Japan. It was successively multiplied so the morphological and taxonomic characteristics of the pathogen and its host range under high humidity conditions could be analyzed. The isolate KTP-01 of the tomato powdery mildew optimally developed infection structures at 25°C under continuous illumination of 3500 lx. More than 90% of the conidia germinated and developed moderately lobed appressoria. After forming haustoria, the pathogen elongated secondary hyphae from both appressoria and conidia. The hyphae attached to leaf surfaces by several pairs of appressoria and produced conidiophores with noncatenated conidia. In addition to its morphological similarity to Oidium neolycopersici, the phylogenetic analysis (based on the sequence of internal transcribed spacer regions of rDNA) revealed that KTP-01 could be classified into the same cluster group as O. neolycopersici. In host range studies, KTP-01 produced abundant conidia on the foliage of all tomato cultivars tested and tobacco (Nicotiana tabacum), and it developed faint colonies accompanied by necrosis on leaves of potato (Solanum tuberosum), red pepper (Capsicum annuum), petunia (Petunia × hybrida), and eggplant (S. melongena). The pathogen did not infect other plant species including Cucurubitaceae plants, which have been reported to be susceptible to some foreign isolates. Thus, the present isolate of the tomato powdery mildew was assigned as O. neolycopersici, a pathotype different from foreign isolates of the pathogen. Received: December 5, 2002 / Accepted: December 26, 2002 Acknowledgments This work was supported in part by a Grant-in-Aid (12660050) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. We express our deepest thanks to professor Dr. Y. Sato, Toyama Prefectural University, for his kind and valuable suggestion on taxonomic analysis of the powdery mildew pathogen described in the present study.     

黑龙江省番茄白粉病病原鉴定

通过收集东北农业大学日光温室中的番茄白粉菌,并对其进行形态和分子鉴定及分析,明确了该白粉病的病原种类及其分类地位。根据分生孢子的显微形态观察初步确定为新番茄粉孢菌（Oidiumneolycopersici L. Kiss）。进一步根据真菌rDNA-ITS序列检测分析后发现该病原菌与新番茄粉孢菌（O. neolycopersici）的相似性为100%,并对与其相似性较高的序列构建进化树分析发现,本试验研究的白粉菌与其他国家和地区的白粉菌相似性不高,这可能是由于哈尔滨地区白粉菌自身小种进化的原因。     

Sporenverteilung des Echten Mehltaus im Hopfen ausgehend von Infektionsherden und Abhängigkeit vom Vegetationsstadium

In order to assess the potential of infection of hop powdery mildew it is important to know the spore dissemination coming from different sources. Overwintering via cleitothecia is not provable in experiments. So wild hops, not correctly cleared cultural hops and non-cultivation hops are potential carriers of powdery mildew which is overwintering via mycel. In 2007 we found a source which has infected an area of about 30?ha cultural hops. By the observation of infections in these hop gardens we found that half of the amount of conidia is in a distance of 9,55?m away from the source. In a smaller dimension we counted the amount of conidia around one single plant in a commercial hop garden by a special spore trap. In the single plant the amount of spores is lower than outside, while it is decreasing in a higher distance from the single plant. Analysing the micro spore dissemination in a single plant there was a big diversity of the amount of spores because of the complex architecture of the hop plants. Further studies showed that the susceptibility of hop is much higher in May than later in the year. Thus, statistically a lower amount of conidia is needed for one complete infection. However, a lower amount of conidia can easily be transported for long distances by wind. As a result a source of powdery mildew in a long distance from the cultural hops is a serious danger for the commercial hop gardens early in the year. Later each source of conidia looses its influence nearly completely.     

番茄白粉病的病原菌鉴定

 作者在吉林省长春市温室中发现了番茄白粉病,对其病原菌进行了形态学和分子生物学鉴定。根据分生孢子形态和萌发特性将该菌鉴定为新番茄粉孢菌(Oidium neolycopersici Kiss)。分生孢子椭圆形,无色,单生于分生孢子梗顶端。分生孢子梗直立,简单不分枝,无色,脚胞圆柱形,有时略弯曲,上面通常有1~2个细胞。分生孢子侧面萌发,芽管末端产生裂片状或直筒状附着胞。附着胞乳突状或浅裂片状。未发现有闭囊壳。采用分子生物学方法,对该病原菌rDNAITS区进行了PCR扩增和序列测定,测得序列与O. neolycopersici同源性为100%。由O. neolycopersici引起的番茄白粉病国内未见报道。     

Occurrence of New Powdery Mildew on Greenhouse Tomato Cultivars

During a year-round survey on the occurrence of powdery mildew on greenhouse-cultivated tomato plants, the disease was most severe in June and July. All tomato plants (45 commercial cultivars and 11 breeding lines) tested were infected with the pathogen but had different degrees of susceptibility. The pathogen was epiphytic and produced white, round pustules mainly on leaves of tomato plants. The pathogen produced conidia singly on conidiophores and forked appressoria on inoculated tomato leaves and seemed to be an Oidium sp. of Erysiphe polygoni type. Received 18 December 2000/ Accepted in revised form 22 July 2001     

Cytological events in tomato leaves inoculated with conidia of <Emphasis Type="Italic">Blumeria graminis</Emphasis> f. sp. <Emphasis Type="Italic">hordei</Emphasis> and <Emphasis Type="Italic">Oidium neolycopersici</Emphasis> KTP-01

Leaves of tomato and barley were inoculated with conidia of Blumeria graminis f. sp. hordei race 1 (R1) or Oidium neolycopersici (KTP-01) to observe cytological responses in search of resistance to powdery mildew. Both conidia formed appressoria at similar rates on tomato or barley leaves, indicating that no resistance was expressed during the prepenetration stage of these fungi. On R1-inoculated tomato leaves, appressoria penetrated the papillae, but subsequent haustorium formation was inhibited by hypersensitive necrosis in the invaded epidermal cells. On the other hand, KTP-01 (pathogenic to tomato leaves) successfully developed functional haustoria in epidermal cells to elongate secondary hyphae, although the hyphal elongation from some conidia was later suppressed by delayed hypersensitive necrosis in some haustorium-harboring epidermal cells. Thus, the present study indicated that the resistance of tomato to powdery mildew fungi was associated with a hypersensitive response in invaded epidermal cells but not the prevention of fungal penetration through host papilla.     

Paecilomyces farinosus destroys powdery mildew colonies in detached leaf cultures but not on whole plants

Since 2001, several isolates of Blumeria graminis, the causal agent of cereal powdery mildew, maintained on detached leaves at the John Innes Centre, Norwich, UK, have spontaneously become infected with an unknown filamentous fungus whose mycelia have quickly overgrown the powdery mildew colonies and destroyed them completely. A total of five isolates of the contaminant were obtained and identified as Paecilomyces farinosus based on morphological characteristics and rDNA ITS sequence data. To determine whether these P. farinosus isolates can be considered as biocontrol agents (BCAs) of powdery mildews, we studied the interactions between P. farinosus and the following four powdery mildew species: B. graminis f.sp. hordei infecting barley, Oidium neolycopersici infecting tomato, Golovinomyces orontii infecting tobacco and Podosphaera fusca infecting cucumber. The powdery mildew colonies of all these four powdery mildew species were quickly destroyed by P. farinosus in leaf cultures but neither conidial suspensions nor cell-free culture filtrates of P. farinosus isolates could suppress the spread of powdery mildew infections on diseased barley, tomato, tobacco or cucumber plants in the greenhouse. It is concluded that P. farinosus cannot be considered as a promising BCA of powdery mildew infections although it can destroy powdery mildew colonies in detached leaf cultures and can be a menace during the maintenance of such cultures of cereal, apple, cucurbit and tomato powdery mildew isolates.     

Effects of light quality on conidiophore formation of the melon powdery mildew pathogen <Emphasis Type="Italic">Podosphaera xanthii</Emphasis>

The lengths of conidiophores in fungal colonies of the melon powdery mildew pathogen Podosphaera xanthii Pollacci KMP-6 N cultured under greenhouse (natural) conditions differed markedly from those cultured in a growth chamber. We hypothesized that light wavelength was responsible for the differences in conidiophore length. In this study, we examined the effects of light-emitting diode (LED) irradiation (purple, blue, green, orange, and red light) and white light on colony development and conidiophore formation in KMP-6 N using a stereomicroscope and a high-fidelity digital microscope. Colonies on leaves were flat under greenhouse conditions and under red LED light irradiation but were stacked under growth chamber conditions and under purple, blue, green, and orange LED light irradiation. In addition, KMP-6 N formed catenated conidia comprising six conidia per conidiophore under greenhouse conditions and red light but more than seven conidia per conidiophore under growth chamber conditions and purple, blue, green, and orange light. Furthermore, almost none of the conidia on top of the conidiophores grown under blue light were fully constricted. Therefore, these fungi could not scatter their conidia and spread infection. This is the first report of the effects of LED lights on conidiophore formation in the melon powdery mildew fungus P. xanthii. The results provide insight into the mechanisms underlying the responses of conidiophores to light of specific wavelengths and conidial scatter from conidiophores of melon powdery mildew fungi.     

What types of powdery mildew can infect wheat-barley introgression lines?

This work is a detailed study of the infection of fungal biotrophic pathogens causing powdery mildew diseases on introgression lines originating from the intergeneric hybridisation between wheat and barley (Triticum aestivum L. × Hordeum vulgare L.). Powdery mildew fungi are among the most widespread biotrophic pathogens of plants also and infect dicot and monocot species. Most powdery mildew species are strictly host specific. They colonize only a narrow range of species or one particular host species. The intergeneric hybridisation between wheat and barley could result in expansions of host ranges of the barley powdery mildew. Our experiments covered natural infections in the field and artificial infections under greenhouse conditions. Formae speciales of powdery mildew were identified on the basis of the sequencing results of ribosomal internal transcribed spacer sequences (rDNA-ITS). We identified Blumeria graminis f.sp. tritici isolate 14 (HM484334) on the wheat parent and all wheat-barley introgression lines and B. g. f. sp. hordei isolate MUMH1723 (AB 273556) on the barley parent, respectively. The wheat-barley introgression lines were inoculated with barley powdery mildew under greenhouse conditions. According to our results the added barley chromosomes (or segments) do not cause host range expansion of barley powdery mildew.     

Conditions for development of powdery mildew of tomato caused by Oidium neolycopersici

Oidium neolycopersici causes severe powdery mildew on all aerial parts of tomato, excluding the fruit. The objective of the present work was to examine factors that influence the development of O. neolycopersici on tomato and to identify potential methods for managing tomato powdery mildew. Under controlled conditions, the highest rates of conidial germination were observed at 25 degrees C, 99% relative humidity (RH) and minimal light, and the lowest on leaves adjacent to fruits. Optimal conditions for appressoria formation were 25 degrees C, RH ranging from 33 to 99%, and 1,750 lux light intensity. More conidia were formed at 20 degrees C, 70 to 85% RH, and 5,150 lux light intensity than at 16 and 26 degrees C, 99% RH, and 480 to 1,750 lux, respectively. Conidia survived and remained capable of germination for over four months when initially incubated at lower temperatures and higher RH, as compared with their fast decline under more extreme summer shade conditions. In growth chamber experiments, disease did not develop at 28 degrees C. Within the range of 70 to 99% RH, disease was less severe under the higher RH than the drier conditions. Disease was also less severe at lower light intensities. Data collected in three commercial-like greenhouse experiments involving various climate regimes were used to draw correlations regarding the effects of temperature and RH on the development of epidemics. Severity of powdery mildew was positively correlated with the duration of the range 15 to 25 degrees C, 1 to 4 weeks before disease evaluation (BDE), RH levels of 60 to 90% at 2 to 4 weeks BDE, and RH of 50 to 60% during the week BDE. Conversely, disease was negatively correlated with the duration of temperatures in the low and high ranges (5 to 15 degrees C and 35 to 40 degrees C) at 1 to 4 weeks BDE, with the duration of RH levels of 40% and below at 1 to 4 weeks BDE, and with 50 to 60% RH during the third week BDE. High (90 to 100%) RH was also negatively correlated with disease severity. These results suggest that the combination of high temperatures and low RH may help reduce O. neolycopersici powdery mildew severity in greenhouse tomatoes.     

新型杀菌剂氯苯肟唑对蔬菜主要病原菌的抑制作用及田间防病效果

对新化合物氯苯肟唑作为农用杀菌剂的效果进行了评价。分别采用孢子萌发法、含毒介质法、离体叶片法和盆栽试验法,测试了氯苯肟唑对不同蔬菜病原真菌的抑制作用;此外,还进行了20%氯苯肟唑水乳剂防治黄瓜白粉病和黑星病的田间药效试验。室内毒力测定结果显示,氯苯肟唑对供试的几种病原菌均具有较高的杀菌活性,其中500 mg/L的处理对番茄枯萎病菌、辣椒疫病菌、黄瓜黑星病菌的活性与对照药剂相当,对菜豆菌核病菌、黄瓜灰霉病菌和黄瓜白粉病菌的抑制率虽然低于对照药剂,但抑菌效果均在80%以上。田间试验中20%氯苯肟唑水乳剂40 mg/L药液对黄瓜白粉病和黄瓜黑星病的防效可分别达80％和84％。室内生物活性测定结果与田间试验结果一致。     

Morphological and molecular characterization of <Emphasis Type="Italic">Oidium</Emphasis> subgenus <Emphasis Type="Italic">Reticuloidium</Emphasis> (powdery mildew) newly occurred on cucumber in Japan

In 2002, a powdery mildew with catenate conidia lacking fibrosin bodies was found on cucumber in a greenhouse in Kanagawa Prefecture, Japan. Morphological observation revealed that the fungus belongs to Oidium subgenus Reticuloidium, anamorph of the genus Golovinomyces. Molecular phylogenetic analyses of the nucleotide sequences of the rDNA ITS regions and D1/D2 domains of the 28S rDNA indicated that the fungus belongs to the clade of G. orontii with other Golovinomyces fungi from a wide range of host plants, suggesting that the fungus was newly transported from abroad. Because there has been no prior report of cucumber powdery mildew caused by Reticuloidium, further research on the physiology, epidemiology, control and resistant cucumber varieties is required.     

Microcyclic conidiogenesis in powdery mildews and its association with intracellular parasitism by <Emphasis Type="Italic">Ampelomyces</Emphasis>

Microcyclic conidiogenesis (MC), a process defined as the production of conidia on a spore without any, or only a minimal, involvement of hyphal growth, has recently been reported in a little known powdery mildew species, Oidium longipes. To investigate whether this was an isolated case or it is a more general phenomenon in powdery mildew fungi, germinating conidia of eight species of the Erysiphales were examined using light microscopy. The following species were included in this work: Erysiphe necator on grapevine, Blumeria graminis f. sp. hordei on barley, Podosphaera xanthii on cucumber, Erysiphe sp. on Ligustrum vulgare, O. longipes on Petunia x grandiflora, O. neolycopersici on tomato, Golovinomyces cichoracearum on Rudbeckia laciniata and Sawadaea sp. on Acer negundo. In all these species, up to 4% of the germinated conidia exhibited MC. Moreover, when colonies of E. necator and O. neolycopersici, on detached grapevine and tomato leaves, respectively, were treated with a conidial suspension of Ampelomyces, the intracellular pycnidia of these mycoparasites appeared in microcyclic conidiophores. This represents a yet undescribed method of accelerating asexual reproduction in this mycoparasite. In the life cycle of powdery mildews, the importance of MC is still not clear but it should be taken into consideration when conidial germination is studied on the host surface for purposes such as epidemiology or species identification.     

Evidence for an Osmotic Mechanism in the Control of Powdery Mildew Disease of Wheat by Foliar-applied Potassium Chloride

The mechanism by which foliar application of potassium chloride solution reduces symptoms of powdery mildew disease (Erysiphe graminis f.sp. tritici) of wheat was investigated. The hypothesis that potassium chloride reduces mildew by an osmotic effect on spore germination was tested in three glasshouse experiments. Either potassium chloride solution or the osmoticum polyethylene glycol 200 was sprayed on wheat at the three- or four-leaf stage. The plants were inoculated with spores and spore germination and leaf area affected by mildew were assessed. Leaf water potential was determined as a measure of the osmotic effect of the treatments. Spore germination and leaf area affected by mildew were related to leaf water potential using regression analysis in groups on the data averaged over the three experiments. Both spore germination on the leaf and leaf area affected by mildew were reduced as leaf water potential decreased. There was no difference between potassium chloride or polyethylene glycol in the relationship between spore germination and leaf water potential, but polyethylene glycol was slightly less effective at reducing mildew symptoms at any given leaf water potential. The results are compatible with the hypothesis that potassium chloride reduces symptoms of powdery mildew by an osmotic effect on spore germination.     

Laboratory and greenhouse evaluation of a new systemic fungicide,N,N'-bis-(1-formamido-2,2,2-trichloroethyl)-piperazine (CELA W 524)

The new systemic fungicide N,N'-bis-(1-formamido-2,2,2-trichloroethyl)-piperazine (CELA W 524) was shown to display a moderate to distinct fungitoxic activity in vitro towards several pathogenic and non-pathogenic fungi. Depending on the inert ingredients present², the available formulations proved to be either rather phytotoxic or virtually non-phytotoxic. Pre-infectional spraying with the non-phytotoxic formulation provided complete protection of barley, bean, cucumber, pea and tomato plants against barley powdery mildew, bean rust, cucumber powdery mildew and cucumber scab, pea powdery mildew and tomato leaf mould, respectively. some suppression of disease symptoms —although only at high concentrations of CELA W 524 — was observed in the case of leaf spot in pea plants. Upon post-infectional treatment disease control was less pronounced, although powdery mildew diseases and tomato leaf mould were effectively suppressed. When applied via the roots CELA W 524 proved to be systemically active, successfully protecting barley plants against powdery mildew, and cucumber plants against powdery mildew and cucumber scab.Samenvatting Het nieuwe systemische fungicide CELA W 524 (C. H. Boehringer Sohn, Ingelheim am Rhein, Duitsland) bleek een matige tot duidelijke fungitoxische werking in vitro te vertonen tegenover verschillende pathogene en niet-pathogene schimmels. Eén van de beschikbare formuleringen bleek vrij sterk fytotoxisch, de andere was nagenoeg niet fytotoxisch. Bespuiting vóór inoculatie met de niet-fytotoxische formulering resulteerde in volledige bescherming van gerst, bonen, komkommers, erwten en tomaten tegen respectievelijk gerstemeeldauw, boneroest, komkommermeeldauw en vruchtvuur, erwtemeeldauw en bladvlekkenziekte bij tomaat. Enige onderdrukking van ziektesymptomen trad ook op bij erwten, geïnoculeerd metAscochyta pisi, tenminste, wanneer hoge concentraties van CELA W 524 werden gebruikt. Bij bespuiting na inoculatie was het effect geringer, hoewel meeldauwziekten en bladvlekkenziekte bij tomaat toch doeltreffend bestreden werden. Toegediend via de wortels bleek CELA W 524 systemisch actief; het beschermde aldus gerst tegen meeldauw en komkommers tegen meeldauw en vruchtvuur.