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.     

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。     

Isolation of genes expressed during compatible interactions between powdery mildew (Blumeria graminis) and wheat

Powdery mildew of wheat is an important disease caused by the obligately biotrophic fungus Blumeria graminis. In compatible interactions, the powdery mildew fungus undergoes a series of developmental stages to form haustoria within host cells through which nutrients are obtained. In this study, we utilized the cDNA-AFLP technique to isolate wheat genes expressed at 5 days' post-inoculation. The expression patterns of several sequences identified in the cDNA-AFLP profiling were further investigated by Northern hybridization and RT-PCR analyses. Genes with sequence similarity to GenBank accessions AAR91119, P20076, BT009372, ABA99697, BAD81963 or AAO72574 showed greater expression in susceptible rather than resistant or mock-inoculated leaves. In addition, several sequences with similarity to CAD27894, XM_466672, AAT79487 or AAM64566 were expressed only in the compatible interactions. Possible involvement of these genes in susceptibility of host wheat upon powdery mildew infection is further discussed.     

Consecutive monitoring for conidiogenesis by Oidium neolycopersici on tomato leaves with a high-fidelity digital microscope

Conidiogenesis by Oidium neolycopersici KTP-01 on tomato leaves was vitally monitored with a high-fidelity digital microscope. Conidiophores were initially formed 3 days after inoculation and then elongated to a maximum length within at least 12h. The apical part was split into two cells after two successive septations, accompanied by apical expansion. These cells subsequently developed into primary and secondary conidia. An additional septation at the stem portion of the conidiophores produced a generative and a foot cell. Subsequent conidiation occurred during repeated cycles of splitting of the generative cell, maturation of the apical cell into a conidium, and abstriction of the conidium. To our knowledge, this report is the first on the developmental process of conidiogenesis by powdery mildew on host leaves as revealed with the digital microscope.     

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。     

Effects of temperature and leaf age on conidial germination and disease development of powdery mildew on rubber tree

Powdery mildew is an important disease of rubber trees worldwide. To assess the effects of temperature and leaf age on conidial germination and disease development, conidia were inoculated onto rubber tree seedlings with leaves at three phenological stages (copper bronze, colour-changing, and light green) and then incubated at six constant temperatures (10, 15, 20, 25, 30, and 35°C). Leaf age did not affect conidial germination (p = .296) whilst temperature did (p < .0001), although conidia were able to germinate at all tested temperatures. The estimated optimal temperature for conidial germination was 23.2°C. Leaf age, temperature, and their interactions had significant effects on conidial infection and hypha number (p < .0001). At 10 and 35°C, more than 2 and 4 days were needed for infection to complete, respectively, compared to <2, 1, 0.5, and 0.5 days for 15, 20, 25, and 35°C, respectively. Sporulation and mildew symptoms were only observed on those inoculated leaves of all stages at 20 and 25°C, and at the copper bronze stage only at 15°C. The latent period on the copper bronze leaves at 15°C was longer (9 days) than at 20 and 25°C (4 days). The latent period at 20 and 25°C increased from 4 to 7 days as the leaf development stage increased from copper bronze to light green. Therefore, temperature affected germination and postgermination growth of rubber tree powdery mildew, whereas leaf age primarily affected postgermination growth of the pathogen.     

A new spore precipitator with polarized dielectric insulators for physical control of tomato powdery mildew

ABSTRACT In an attempt to physically protect greenhouse tomato plants from the powdery mildew fungus Oidium neolycopersici, we developed a new electrostatic spore precipitator in which a copper wire conductor is linked to an electrostatic generator and covered with a transparent acrylic cylinder (insulator). The conductor was negatively charged by the generator, and the electrostatic field created by the conductor was used to dielectrically polarize the insulator cylinder. The dielectrically polarized cylinder also produced an electrostatic force without a spark discharge. This force was directly proportional to the potential applied to the conductor and was used to attract conidia of the pathogen. The efficacy of this spore precipitator in protecting hydroponically cultured tomato plants from powdery mildew was evaluated in the greenhouse. The hydroponic culture troughs were covered with a cubic frame installed with the spore precipitator, and the disease progress on precipitator-guarded and unguarded seedlings was traced after the conidia were disseminated mechanically from inoculum on tomato plants. Seedlings in the guarded troughs remained uninfected during the entire experiment, in spite of rapid spread of the disease to all leaves of the unguarded seedlings.     

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.     

Effects of impacting rain drops on the growth and development of powdery mildew fungi

The effects of rain on different stages of powdery mildew development were investigated quantitatively for Erysiphe graminis on barley, Erysiphe pisi on pea and Sphaerotheca pannosa on rose. Water drops 4 mm in diameter released from a height of 2·5 m onto target leaves reduced the numbers of conidia on the impacted surfaces and inhibited subsequent mildew development, the effects declining as the interval between inoculation and impaction increased. Simulated rainfall applied after inoculation reduced the numbers of conidia on leaves and inhibited mildew development, the effect declining as the interval between inoculation and treatment lengthened. Simulated rainfall applied to infected plants reduced their capacity to inoculate other plants, the effect declining as the interval between treatment and use as inoculum lengthened. Controlled exposure of infected peas and roses to natural rain reduced the numbers of conidia on leaves and inhibited subsequent mildew development, especially on upper leaf surfaces.     

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     

Suppression of conidial germination and appressorial formation by silicate treatment in powdery mildew of strawberry

The mode of action of soluble silicon against strawberry powdery mildew (Sphaerotheca aphanis var. aphanis) was investigated in four experiments. First, silicon-treated leaves from plants grown with silicate (Si+) and control leaves were excised, inoculated with conidia, and subsequent germination and formation of appressoria in a petri dish was assessed after 24 h. The germination rate was 49.7% on Si+ leaves, and was 67.2% on control leaves (t-test, P < 0.01). Second, we soaked cellulose membranes in various solvents and then placed the membranes on 4% water agar, dusted the membranes with conidia, and examined after 12 h. No difference was apparent between any treatment and the control (distilled water). Third, strawberries growing hydroponically with additional silicon in the medium were inoculated with conidia, and leaves were observed with a scanning electron microscope 1–2 days after inoculation. Germ tubes and secondary hyphae were shorter and had fewer branches on Si+ leaves than on the control. Moreover, penetration appeared to be inhibited. Fourth, the cuticle was separated from leaves from plants grown as in the third experiment, placed on water agar, and dusted with conidia. Germination of conidia, observed with a light microscope, on Si+ leaves was suppressed markedly to 40%–60% of that of the control. These results suggested that soluble silicon induced physiological changes in the cuticle layer after absorption by the plant. In addition, soluble silicate reduced germination of conidia, formation of appressoria, and possibly the penetration of powdery mildew.     

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.     

Detection of Erysiphe necator in Air Samples Using the Polymerase Chain Reaction and Species-Specific Primers

ABSTRACT A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or chasmothecia that were collected from grape leaves with a Burkard cyclonic surface sampler. To differentiate E. necator from other erysiphaeceous fungi, primer pairs Uncin144 and Uncin511 were developed to select unique sequences of the internal transcribed spacer regions of E. necator. Using these primers in PCR amplifications, a 367-bp amplicon specific to E. necator was generated, but no amplicons were generated from other erysiphaceous species collected from 48 disparate hosts representing 26 vascular plant families. The PCR limit of detection was one to five conidia of E. necator placed directly into reaction mixtures or 100 to 250 conidia placed on glass rods coated with silicon grease. During field studies, this PCR assay facilitated the detection of E. necator inoculum in air samples within hours of sample rod collection and prior to disease onset. Amplification of E. necator DNA did not occur when the PCR assay was conducted on vineyard air samples collected while grapes were dormant or during periods when vine growth occurred but E. necator remained dormant. The initial PCR detection of E. necator of the season occurred during seasonal ascospore releases caused by precipitation events between bud burst and the prebloom period during the 3 years of the study. Detection ceased for 7 to 11 days following ascospore release and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew in the field. Results of this study represent the initial step toward the goal of incorporating an inoculum availability component into current and future grapevine powdery mildew risk assessment models.     

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.     

白粉寄生孢寄生黄瓜白粉菌的特性研究

采用白粉寄生孢（Ampelomyces quisqualis Ces.AQ）接种离体条件下赛璐酚上黄瓜白粉菌［Sphaerotheca fuliginea (Schlecht)Poll.］和活体条件下黄瓜白粉菌后,通过棉兰染色和显微观察分析,初步明确了白粉寄生孢的侵染寄生过程。白粉寄生孢分生孢子产生芽管可入侵黄瓜白粉菌的分生孢子、菌丝、分生孢子梗;有时黄瓜白粉菌串生的分生孢子、分生孢子梗可被2~3条白粉寄生孢的菌丝寄生,随着寄生过程的进一步发展,黄瓜白粉菌的分生孢子梗基部膨大成无色的椭圆形或球形,其上逐渐产生由黄色至褐色的白粉寄生孢的分生孢子器,器内含有大量的分生孢子。     

苦瓜白粉病病原菌和生理小种的鉴定及苦瓜对白粉病的抗性遗传分析

为明确海南省苦瓜白粉病的病原菌、生理小种及苦瓜对白粉病的抗性遗传规律,结合形态学鉴定和分子鉴定解析白粉病菌及生理小种种类,通过显微镜观察白粉病菌侵染过程,并应用主基因+多基因混合遗传模型分析法探讨苦瓜对白粉病的主要抗性遗传规律。结果表明:采集自海南省6个市(县)的苦瓜白粉病病原菌均为单囊壳白粉菌Sphaerotheca fuliginea,属生理小种2F,该菌在侵染苦瓜叶片时有4个关键时期:接种后4 h为分生孢子萌发高峰期,8 h为附着孢形成高峰期,16～24 h为次生菌丝形成高峰期,5 d为分生孢子梗形成高峰期。将其接种于苦瓜抗、感品系,对白粉病的抗性符合2对加性-显性-上位性主基因+加性-显性多基因模型,主基因和多基因共同控制苦瓜对白粉病的抗性,其中以主基因遗传为主,且会受到环境变异的影响。根据苦瓜抗性遗传规律,F2代主基因遗传率最高,受环境影响最小,在苦瓜的白粉病抗性育种中,以早期世代F2代作为有效选择世代。研究表明白粉病菌侵染叶片的前2 d是白粉病防治的最佳时期,所以在白粉病易发的物候期,可将防治时间提前1～2 d。     

Survival of Oidium anacardii on cashew (Anacardium occidentale) in southern Tanzania

During March and April of 1993 and 1994, surveys on the incidence and severity of cashew powdery mildew ( Oidium anacardii ) were conducted in the Newala, Mtwara, Nachingwea and Tunduru areas of southern Tanzania to determine the variation in perennation between localities. Only immature cashew shoots, panicles and fruit can be infected by O. anacardii conidia. Cashew trees at sites in each district were assessed for shoot and panicle production and cashew powdery mildew. Survival of O. anacardii between seasons, in any area, was determined by the degree of production of shoots that were within the canopy and by the incidence of infection. Immature shoots produced from the main branches within the tree canopy were the main source of active powdery mildew in all districts; trees in the Newala district had the highest numbers of infected immature shoots in comparison with survey sites in the other areas. During the 1994 cashew-growing season (June–August), powdery mildew developed more rapidly and affected more shoots on the inside of the tree canopy than on the outside. Germination of conidia was reduced after aqueous suspension for 3 h. Germination on cashew leaves submerged under 2 mm of water was not affected. Appressorial and hyphal formation by germinating conidia on leaves decreased with increasing duration under water. Germination of conidia on glass slides at 100% r.h. was higher at 25 and 30°C than at 15°C and there was no germination at 35°C.     

Evaluation of the systemic activity of simeconazole in comparison with that of other DMI fungicides

The systemic activity of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) in plants was compared with those of eight other sterol demethylation inhibitor (DMI) fungicides. Simeconazole prevented the infection of Blumeria graminis (DC) Speer f sp hordei Marchal on barley leaves within a radius of several centimeters from the edge of local treatment on the leaves when the compound was separated from the leaves by glass coverslips. This reveals that simeconazole has prominent vapour-phase activity. Simeconazole showed excellent curative activity against barley powdery mildew when treated 1-3 days after inoculation. Furthermore, this indicates that simeconazole has notable translaminar activity because, when the compound was applied onto either the adaxial or abaxial leaf surface, it showed excellent efficacy against powdery mildew on the opposite side of the leaf surface of barley and cucumber. Simeconazole also showed excellent efficacy against barley powdery mildew by soil drench 24h after inoculation. This suggests that simeconazole was absorbed very quickly into the barley plant after treatment. The permeability of the compound through cuticular membranes prepared from tomato fruits was about 20% at 22 h after the treatment and was much superior to that of the other DMI fungicides tested.     

Occurrence of powdery mildew on aubergine in West Sussex

A powdery mildew ( Erysiphe sp.) was found on the upper surfaces of leaves of a glasshouse-grown aubergine ( Solanum melongena ) crop in West Sussex during Autumn 1992. It could be readily transferred to tomato ( Lycopersicon esculentum ) and tobacco ( Nicotiana tabacum ), but produced restricted growth and sporulation on cucumber ( Cucumis sativus ). Sweet pepper ( Capsicum annuum ), Chinese cabbage ( Brassica campestris var. chinensis ), lettuce ( Lactuca sativa ), chrysanthemum ( Dendranthema x grandiflorum ) and Nicotiana benthamiana did not show symptoms. When transferred to tomato and cucumber, the morphology of aubergine powdery mildew resembled the natural glasshouse powdery mildew on the two crops, respectively, rather than powdery mildew on aubergine. Powdery mildew from naturally infected tomato could infect aubergine directly, and also after one, but not two, generations on cucumber.     

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.