Podosphaera Fusca Research Articles

First Report of Powdery Mildew Caused by Golovinomyces cichoracearum on Gerbera (Gerbera jamesonii) in Italy.

Gerbera (Gerbera jamesonii) is one of the top 10 economically important flower crops in Europe as well as the United States. The acreage devoted to this crop continues to increase especially for use in landscape typologies. Abundant flowering from spring until autumn allows the use of this plant to decorate gardens, terraces, and borders. During the summer of 2009, an outbreak of a previously unknown powdery mildew was observed on potted gerbera 'Mini Yellow' growing in a private garden in Turin (northern Italy). Adaxial leaf surfaces were covered with white mycelium and conidia, and as the disease progressed, infected leaves turned yellow and died. Conidia were hyaline, ellipsoid, borne in chains (three conidia per chain), and measured 16 to 45 × 10 to 30 μm. Conidiophores measured 109 to 117 × 11 to 13 μm and had a foot cell measuring 72 to 80 × 11 to 12 μm followed by two shorter cells measuring 19 to 29 × 11 to 14 and 20 to 32 × 12 to 14 μm. Fibrosin bodies were absent and chasmothecia were not observed in the collected samples. On the basis of its morphology, the pathogen was identified as Golovinomyces cichoracearum. The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and sequenced. BLASTn analysis of the 548-bp fragment showed an E-value of 0.0 and a percentage homology of 99% with G. cichoracearum isolated from Coreopsis leavenworthii (Accession No. DQ871605) confirming diagnosis inferred by morphological analysis. The nucleotide sequence has been assigned GenBank Accession No. GQ870342. Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of three healthy potted plants of Gerbera 'Mini Yellow'. Three noninoculated plants served as the control. Plants were maintained in a greenhouse at temperatures ranging between 20 and 30°C. Inoculated plants developed signs and symptoms after 8 days, whereas control plants remained healthy. The fungus present on inoculated plants was morphologically identical to that originally observed on diseased plants. To our knowledge, this is the first report of the presence of powdery mildew caused by G. cichoracearum on gerbera in Italy. Specimens are available at the Agroinnova Collection at the University of Torino. Gerbera is also susceptible to different powdery mildews. Powdery mildew of Gerbera jamesonii caused by Sphaerotheca fusca was reported in Italy (4). G. cichoracearum on Gerbera jamesonii was reported in North America (2), Argentina (3), and Switzerland (1).

First Report of Powdery Mildew Caused by Podosphaera xanthii on Sechium edule in the United States.

Sechium edule (Jacq.) Sw., also known as mirliton or chayote, is a perennial, monoecious, cucurbitaceous plant native to Mexico and Central America. It is cultivated worldwide for a variety of uses (4). Mirliton fruit is rich in carbohydrates, has 16 amino acids, and is a traditional staple in New Orleans, LA. During the spring of 2009, the LSU AgCenter's Plant Disease Diagnostic Clinic received diseased mirliton plants from a small commercial grower in New Orleans. Symptoms included yellow, irregular spots on both surfaces of the leaves. Microscopic examination revealed the presence of powdery mildew conidia and conidiophores. Initially, white, cottony mycelial colonies were present on the abaxial surface, but as the disease progressed, white, cottony colonies developed on the adaxial surface, the spots coalesced, and the entire leaf turned yellow and necrotic. Conidia were hyaline, ovoid, borne in long chains with crenate edges, and measured 25.6 to 36.6 μm long (mean = 31.2) × 14.6 to 18.3 μm wide (mean = 17.1). Conidia contained fibrosin bodies and produced a lateral germ tube with a simple appressorium. Conidiophores were erect, simple, unbranched, and measured 54.9 to 76.9 μm long (mean = 66.4) × 11.0 to 14.6 μm wide (mean = 12.9). The cylindrical foot cell had a simple base with basal septum adjacent to the mycelium. No teleomorph was observed. Morphologically, this powdery mildew fits either Podosphaera fusca or P. xanthii so DNA analysis was conducted. We designed Podosphaera-specific primers PFITS-F (5'-CCAACTCGTGCTGTGAGTGT-3') and PF5.8-R (5'-TGTTGGTTTCTTTTCCTCCG-3') to amplify and sequence the internal transcribed spacer region (ITS) of the nuclear rDNA. The 331-bp sequence (GenBank Accession No. GQ902939) was identical with haplotype 27 of P. fusca (GenBank Accession No. AB040324) (3), which is now called P. xanthii (1). Pathogenicity tests were conducted by pressing infected leaves against healthy leaves of two vines. A noninoculated vine served as a control. Plants were maintained in a greenhouse at 30°C. Five days after inoculation, yellow, irregular spots appeared on the inoculated vines and white, powdery mildew colonies appeared on the abaxial surface. Spots coalesced and the entire leaf turned yellow 8 days after inoculation and necrotic 12 days after inoculation. No symptoms developed on the controls. On the basis of DNA sequence data, this powdery mildew is identified as P. xanthii sensu (1). Erysiphe cichoracearum has been previously reported to cause powdery mildew on mirlitons in Florida and Hawaii (2). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on mirliton in the United States. A voucher specimen has been deposited in the Bernard Lowy Mycological Herbarium (LSUM 185359).

First Occurrence of Cucurbit Powdery Mildew Caused by Race 3-5 of Podosphaera fusca in Spain.

A new race of cucurbit powdery mildew was observed for the first time on melon (Cucumis melo) in three research greenhouses in the Axarquia area of southern Spain during the spring of 2008. Fungal growth appeared as white powdery colonies initially restricted to the upper leaf surfaces. Morphological characteristics of colonies, conidiophores, conidia, germ tubes, and appressoria indicated that the powdery mildew fungus was Podosphaera fusca (also known as P. xanthii) (3), a fungal pathogen extensively reported in the area (1). However, the fungus developed on plants of melon cv. PMR 6, which is resistant to races 1 and 2 of P. fusca, suggesting that the fungus could belong to race 3, a race of P. fusca not yet reported in Spain. Race determination was carried out by inoculating the third true leaf of a set of differential melon genotypes that were maintained in a greenhouse. Symptoms and colonization observed on cvs. Rochet, PMR 45, PMR 6, and Edisto 47 indicated that the isolates belonged to race 3-5 of P. fusca. Fungal strains of races 1, 2, and 5 of P. fusca (all present in Spain) were used as controls. Pathotype designation was determined by inoculating different cucurbit genera and species (2). In addition to melon, the isolates were pathogenic on zucchini (Cucurbita pepo) cv. Diamant F1, but failed to infect cucumber (C. sativus) cv. Marketer and watermelon (Citrullus lanatus) cv. Sugar Baby; therefore, the isolates were pathotype BC (2). Races 1, 2, 4, and 5 of P. fusca have been previously reported in the area (1). The occurrence of race 3-5 represents another challenge in the management of cucurbit powdery mildew in Spain.

Control of Powdery and Downy Mildews of Cucumber by Using Cooking Oils and Yolk Mixture

Powdery and downy mildews caused by Sphaerotheca fusca and Pseudoperonospora cubensis are the most common and serious diseases of cucumber worldwide. In spite of the introduction of highly effective systemic fungicides, control of these diseases remains elusive. Hence, this study aimed to develop an alternative method to chemicals in controlling the diseases by using different types of cooking oil. Egg yolk, which contains a natural emulsifier, lecithin, was selected as a surfactant to emulsify the oils. Among the different cooking oils used, soybean, canola (rape seed), safflower, sunflower, olive, and corn oils showed over 95% control values against powdery mildew of cucumber in a greenhouse test. In particular, 0.3% canola oil emulsified with 0.08% yolk (1 yolk and 60 ml canola in 20 l spray) was found to be the most effective. The treatment resulted in 98.9% and 96.3% control efficacies on powdery and downy mildews, respectively, of cucumber in the field. Canola oil exhibited direct and systemic effect, wherein powdery mildew of cucumber was suppressed only on treated leaves but not on non-treated leaves in a plant, while mycelia and conidia of the pathogen were severely distorted or destroyed by the treatment. The prospect of using the canola oil and yolk mixture as a natural fungicide is highly promising because of its effectiveness, availability, low cost, simple preparation, and safety to humans and the environment. The use of the canola oil and yolk mixture is expected to be an effective fungicide for use in organic farming and home gardening.

Microwave-assisted synthesis and antimicrobial activities of 2-aryl-3-(naphthalene-1 or 2-yl)-1,3-thiazolidin-4-ones

2-aryl-3-(naphthalene-1 or 2-yl)-1, 3-thiazolidin-4-ones 4 and 5 were synthesized in 41%–67% yield by using microwave-assisted one-pot protocol. The structures of the new compounds 4l, 4m, 5c, 5e, 5g, 5h, and 5j–5m were confirmed by IR, NMR, MS, and elemental analysis. The antimicrobial activities of the compounds against Pseudomonas syringae pv. lachrymans (Smith et Bryan) Young, Dye & Wilkie, Botrytis cinerea Pers., and Sphaerotheca fusca Blum. were examined. Some of the compounds showed good antifungical activity against Sphaerotheca fusca Blum.

The powdery mildew fungus Podosphaera fusca (synonym Podosphaera xanthii), a constant threat to cucurbits

Numerous vegetable crops are susceptible to powdery mildew, but cucurbits are arguably the group most severely affected. Podosphaera fusca (synonym Podosphaera xanthii) is the main causal agent of cucurbit powdery mildew and one of the most important limiting factors for cucurbit production worldwide. Although great efforts have been invested in disease control, by contrast, many basic aspects of the biology of P. fusca remain unknown. Podosphaera fusca (Fr.) Braun & Shishkoff. Kingdom Fungi; Phylum Ascomycota; Subdivision Pezizomycotina; Class Leotiomycetes; Order Erysiphales; Family Erysiphaceae; genus Podosphaera; species fusca. Superficial persistent mycelium. Conidia in chains, hyaline, ellipsoid to ovoid or doliform, about 24-40 x 15-22 microm, with cylindrical or cone-shaped fibrosin bodies, which often germinate from a lateral face and produce a broad, clavate germ tube and cylindrical foot-cells. Unbranched erect conidiophores. Cleistothecia globose, mostly 70-100 microm in diameter, dark brown/black. One ascus per cleistothecium with eight ascospores. Angiosperm species that include several families, such as Asteracea, Cucurbitaceae, Lamiaceae, Scrophulariaceae, Solanaceae and Verbenaceae. White colonies develop on leaf surfaces, petioles and stems. Under favourable environmental conditions, the colonies coalesce and the host tissue becomes chlorotic and usually senesces early. Chemical control and the use of resistant cultivars. Resistance has been documented in populations of P. fusca to some of the chemicals registered for control.

Evaluation of Silicon for Managing Powdery Mildew on Gerbera Daisy

ABSTRACT Powdery mildew, caused by Erysiphe cichoracearum or Podosphaera fusca, is a common disease of gerbera daisy (Gerbera jamesonii) grown in Florida. Previous studies demonstrated that silicon reduces powdery mildew in Arabidopsis, cucumber, grape, strawberry, and wheat. In this study, two silicon (Si) sources, calcium silicate and potassium silicate, were evaluated for their ability to reduce powdery mildew in gerbera ‘Snow White’. The effect of calcium silicate in flower quality and the silicon uptake was also determined. Calcium silicate was not effective in reducing powdery mildew or in improving flower quality. The silicon content of gerberas treated with potassium silicate was slightly greater than that in plants treated with calcium silicate. However, the severity of powdery mildew was not reduced by potassium silicate. The results suggest that silicon may not be useful for managing this disease of gerbera daisy, possibly due to the low accumulation of silicon by gerbera leaves.

경기 지역 오이 흰가루병균(Sphaerotheca fusca)의 살균제 저항성 검정

Fungicide resistance of cucumber powdery mildew was screened among the pathogens isolated from diseased plants in main cucumber productuion areas in Gyeonggi Province. Each fungicide from different activity group for the control of powdery mildew were sprayed on cucumber leaves according to application concentration. Each conidia mixed with sterilized water isolated of pathogens were transferred on the cucumber leaf disks treated with each fungicide. At 7 to 9 days after inoculation of pathogen, disease severity was recorded under the microscope. Most of pathogen isolates showed moderate resistance to difenoconazole belonged to DMI group fungicide while some isolates from Osan were resistant even . Isolates from Pyeongtaek, Osan and Yongin area also showed moderate resistance to fenarimol while one isolate showed resistant to fenarimol even . Most of isolates from Pyeongtaek, Osan and Yongin showed highly resistant to azoxystrobin belonged to strobilurin group fungicide. Standard sensitive isolates the minimum inhibition concentration(MIC) value for azoxystrobin showed while resistance isolates showed above . Resistant isloates also showed cross resistance among strobilurin group fungicides and low control efficacy in the field test. These results suggest that treatment of strobilurin fungicides should be reduced for the control of powdery mildew.

Comparative histochemical analyses of oxidative burst and cell wall reinforcement in compatible and incompatible melon–powdery mildew ( Podosphaera fusca) interactions

The spatial-temporal expression patterns of oxidative burst and cell wall reinforcement were analyzed in leaves of resistant and susceptible melon (Cucumis melo L.) cultivars in response to Podosphaera fusca (Fr.) Braun & Shishkoff, the main causal agent of powdery mildew in cucurbits. Extensive development of powdery mildew mycelia and a progressive increase in haustorial count were recorded in the susceptible cultivar after 4d, while in the resistant cultivar powdery mildew failed to grow and small brownish and necrotic leaf areas were frequently observed. Rapid generation of the reactive oxygen intermediates hydrogen peroxide and superoxide radicals 4h after pathogen challenge, but before the fungal haustoria formation, stood upstream in the cascade of events induced during these interactions. This oxidative burst was followed by the accumulation of strengthening polymers of callose and lignin at the cell wall of attacked resistant plant cells. Interestingly, the transcriptional levels of phenylalanine ammonia-lyase (PAL), an important enzyme for phenylpropanoid metabolism, did not significantly change throughout the experiments. Although these physiological changes were observed in both cultivars, their faster kinetics and amplitude in the resistant line compared to the susceptible cultivar governed the differential visual response of these cultivars against P. fusca. These findings, along with data obtained in previous studies, have provided the bases for an integrated model in which the spatial-temporal response patterns of these resistance mechanisms have been arranged, which may ultimately lead to successful protection of melon plants against P. fusca.

First Report of Powdery Mildew Elicited by Podosphaera fusca (Synonym Podosphaera xanthii) on Euryops pectinatus in Spain.

Euryops pectinatus Cass. is an evergreen shrub that is planted extensively in Spain for landscape use. In 2007, powdery mildew outbreaks were observed on E. pectinatus in several nurseries located in the Axarquia area (Malaga, southern Spain). Fungal growth appeared as typical, white, powdery mildew colonies that were restricted to upper leaf surfaces. Initially, individual colonies were small and nearly circular, but later enlarged and coalesced to cover the whole leaf surface. With progress of the disease, all green parts (leaves, stems, and petioles) were covered with a white mycelium. Newly developed leaves especially became rapidly infected. Diseased leaves ultimately dried up and senesced, making nursery plants aesthetically unattractive and unsaleable. Conidiophores were erect, had crenate edge lines, cylindrical foot cells that measured 37.5 to 45.0 × 10.0 to 12.5 μm, and were followed by one to three shorter cells. Conidia were hyaline, ellipsoid to ovoid, borne in chains, and measured 27.5 to 35.0 × 12.5 to 17.5 μm. Conidial length-to-width ratios ranged from 1.6 to 2.4. Conidia possessed conspicuous fibrosin bodies and from their sides produced short germ tubes. No chasmothecia were found. The nuclear rDNA internal transcribed spacer (ITS) regions were amplified by PCR and sequenced (GenBank Accession No. EU424056). On the basis of morphological characteristics of the imperfect state and ITS sequence data, this powdery mildew was identified as Podosphaera fusca (Fr.) U. Braun & N. Shishkoff (1), this isolate belonging to ITS haplotype 15 (group III) (3); this group is considered a separate species, P. xanthii (Castagne) U. Braun & N. Shishkoff by some authors (2). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of healthy E. pectinatus plants. Plants were incubated in a growth chamber at 25°C, and after 14 days, powdery mildew colonies developed. A similar disease of E. pectinatus was observed in 1999 in California (4). P. fusca parasitizes a large number of asteraceous species including field marigold (Calendula arvensis) and fleabane (Erigeron sp.) weeds, as previously reported in the same area, and ornamentals such as Calendula officinalis, Chrysanthemum spp., and Gerbera spp., which are also grown in the same nurseries and frequently attacked by powdery mildew.

난황유와 공기순환팬의 상추 흰가루병 방제효과 및 생산에 미치는 영향

Podosphaera fusca에 의한 상추 흰가루병은 최근에 보고된 새로운 병해이나 심하게 발생될 경우에는 수량을 50% 이상 감소시켜 유기농 상추재배에 큰 위협요인 되고 있다. 본 연구에서는 비닐하우스 내부에 소형의 공기순환팬을 6 m 간격으로 설치하여 상추 주변의 기상환경을 개선한 결과 수량 57% 증가와 정식묘 고사율 71.4% 감소 효과를 얻었다. 공기순환팬을 설치한 하우스에서 식용유를 계란노른자로 유화시킨 난황유 0.3% 용액을 처리한 경우에는 농가 관행재배 하우스에 비해 묘 고사율은 <TEX>$89.3{\sim}92.9%$</TEX> 감소되었고 상추 흰가루병 방제효과는 89.6-96.3%로 매우 높게 나타나 살균제(azoxystrobin)와 대등하였다. 난황유 처리구별로 상추 수량은 <TEX>$23.3{\sim}26.5\;kg$</TEX>으로 대조 하우스의 11.86 kg과 비교할 때 약 2배 정도 높았고 상추 잎의 경도는 다소 낮고 엽록소 함량은 높아지는 등 상추 품질을 개선하는 효과도 나타났다. 본 연구 결과를 볼 때 채종유를 계란노른자로 유화시켜 만든 난황유는 상추 흰가루병 방제효과가 매우 높고 유기농 상추 생산에 유용하게 활용할 수 있을 것으로 기대되는데 공기순환팬을 설치하여 재배환경을 개선하면 상승효과를 얻을 수 있는 것으로 나타났다. Powdery mildew of lettuce that is a newly reported disease became a threat to organic cultivation of lettuce in Korea since the disease caused by Podosphaera fusca resulted in a half of yield loss in heavily infected fields. To improve micro-environmental conditions around lettuce, ACF (air-circulation fan) was installed on inside roof of plastic house at 6 m intervals. The ACF increased 57% of lettuce yield and reduced 71.4% of lettuce seedling death. COY (cooking oil and yolk mixture) consisted of cooking oil 0.3% and egg yolk 0.08% reduced lettuce seedling death from 89.3% to 92.9% under the greenhouse. Seven-day interval spray of COY resulted in high control values of powdery mildew of lettuce ranging from 89.6% to 96.3%, which was comparable to a fungicide, Azoxystrobin. Lettuce yield was increased about two times compared to a non-treated conventional cultivation. Qualities of lettuce such as hardness and chlorophyll content were also improved by COY and ACF combination. Effect of COY on control of the disease was improved when <TEX>$CaCO_3$</TEX> or <TEX>$SiO_2$</TEX> 1,000 ppm was supplemented. Results indicated that the COY made of cooking oil such as canola emulsified with yolk was highly effective on control of powdery mildew of lettuce and suitable for organic agriculture, especially when combined with ACF.

Field resistance to QoI fungicides in Podosphaera fusca is not supported by typical mutations in the mitochondrial cytochrome b gene

A single nucleotide polymorphism in the mitochondrial cytochrome b gene confers resistance to strobilurin (QoI) fungicides in phytopathogenic fungi. Recent studies have revealed worrying levels of resistance to strobilurins in Podosphaera fusca (Fr.) U Braun & N Shishkoff comb. nov. [ = Sphaerothecafusca (Fr.) S Blumer], the main causal agent of cucurbit powdery mildew in Spain. In the present study the underlying resistance mechanism to QoI fungicides in the Spanish populations of P. fusca was investigated. Analysis of the Q(o) domains of cytochrome b in a collection of isolates revealed that none of the typical mutations conferring resistance to QoI, including the G143A and F129L substitutions, was present in the QoI-resistant isolates. Moreover, although different amino acid polymorphisms were observed in the two regions spanning the Q(o) site, none of them consistently distinguished QoI-resistant from QoI-sensitive strains. Exposure to salicylhydroxamic acid (SHAM), a specific inhibitor of alternative oxidase, in the presence of trifloxystrobin did not have any effect on QoI resistance, ruling out alternative respiration as the mechanism of resistance. Sensitivity tests to a battery of respiration inhibitors revealed high levels of cross-resistance to all Qo-inhibitors tested but not to Qi-inhibitors, these features resembling those of a target-site-based resistance. The results indicate that the mechanism responsible for QoI resistance in P. fusca is not linked to typical mutations in cytochrome b gene and that the absence of the G143A substitution cannot be explained by an intron following codon 143. These are important observations, especially in relation to the possible molecular diagnosis of resistance.

Characterization of powdery mildews strains from soybean, bean, sunflower, and weeds in Brazil using rDNA-ITS sequences

Soybean powdery mildew (Erysiphe diffusa) was considered a minor disease in Brazil in the decades immediately after its identification. However, since the outbreak in 1996/97 in all cultivated areas the disease has become a constant threat to farmers and losses of up to 25% have been reported. The report of a new species, E. glycines, infecting soybean in Japan, and the occurrence of the disease in other plant species (Phaseolus vulgaris, Helianthus annuus,Sonchus oleraceus,Hypochaeris brasiliensis, and Bidens pilosa) commonly found growing nearby soybean fields, raised questions in relation to the taxonomy of the powdery mildew strains found in or around soybean fields in Brazil. Analysis of the internal transcribed sequence (ITS) of the rDNA was undertaken to ascertain the pathogen species associated to each of the hosts. Powdery mildew strains isolated from Glycine max were identified as E. diffusa. Strains from P. vulgaris were very similar to E. diffusa, with 4 nt differences, and differed from Erysiphe poligony by 11 nt. Strains from H. annuus and S. oleraceus grouped with the species Golovinomyces cichoracearum, while strains from H. brasiliensis and B. pilosa were similar to Podosphaera fusca and Neoerysiphe cumminsiana, respectively. To our knowledge this is the first molecular identification of powdery mildew in Brazil based on rDNA sequence comparison. In addition, this study presented evidence for the occurrence of N. cumminsiana in America.

Podosphaera fusca에 의한 상추 흰가루병의 발생원인과 방제

Podosphaera fusca에 의한 상추 흰가루병은 상추 발생 병해중에서 가장 중요한 병해중 하나이다. 흰가루병 발생으로 상추재배가 피해로 인하여 재배자와 소비자를 위하여 좋은 품질의 상추를 생산하기 위한 방제법 개발이 필요하다. 상추 흰가루병 발생이 증가되는 원인은 계속적인 연중재배, 병든 식물체의 미제거, 흰가루병을 노균병으로 오인에 의한 부적절한 약제 처리 등이다. 경기도 수원시 근교에 상추 시설 재배 포장에서 미생물농약을 포함한 5가지 살균제에 대한 상추 흰가루병 방제 실험을 실시하였다. 상추 흰가루병이 발생 초기에 10일 간격 3회 분무 처리하여 최종 약제 처리 8일 후에 흰가루병 발생을 조사하였다. kresoxim-mothy SC, azoxystrobin SC, Ampelomyces quisqualis AQ94013 WP, Paenibacillus polymyxa AC-1 SC와 Bacillus Y 1336 WP를 처리한 흰가루병의 발생은 0.7%, 0.7%, 26.0%, 36.7% 각각 발생하였으며, 무처리는 55.3% 발병하였다. 상추유묘에 대하여 이들 약제의 기준량과 배량에서 약해는 없었다. Powdery mildew caused by Podosphaera fusca is one of the most important diseases in leafy lettuce (Lactuca sativa L.). Since the disease has been a threat to safe cultivation of leafy lettuce, its control methods have to develop to produce good quality of lettuce for farmer and consumer. Occurrence of lettuce powdery mildew is increasing more and more due to continuous cultivation of lettuce all through the year, non-removal of diseased plant parts of lettuce, spray of inadequate fungicides by mistaken acknowledge of lettuce powdery mildew for lettuce downy mildew, etc. The control effect of five fungicides against lettuce powdery mildew was examined in a plastic greenhouse located in Suwon. When fungicides were sprayed three times at 10 days-intervals in the early stage of occurrence of powdery mildew, the incidence of powdery mildew in the plants treated with kresoxim-methy SC, azoxystrobin SC, Ampelomyces quisqualis AQ94013 WP, Paenibacillus polymyxa AC-1 SC and Bacillus subtilis Y 1336 WP was 0.7%, 0.7%, 26.0%, 36.7% and 42.0%, respectively, whereas the incidence of non-treated control was 55.3% on eight days after final application. Phytotoxicity of five fungicides tested was not observed in lettuce seedling plants.

Evaluation of biological control agents for managing cucurbit powdery mildew on greenhouse‐grown melon

An evaluation was made of the ability of two mycoparasite‐based products AQ10® (Ampelomyces quisqualis) and Mycotal® (Lecanicillium lecanii), as well as three strains of Bacillus subtilis, to manage powdery mildew disease, caused by Podosphaera fusca on melon seedlings maintained under different regimes of relative humidity and on plants grown under greenhouse conditions in Spain. In every case fungal and bacterial biocontrol agents (BCAs) performed better under conditions of high relative humidity (90–95% RH). In greenhouse experiments, the effectiveness of the mycoparasites to manage powdery mildew was absolutely dependent on mineral oil. The strains of B. subtilis provided disease control similar to that achieved with the mycoparasites or the fungicide azoxystrobin. Microscopic analysis showed the ability of these bacterial strains to efficiently colonize leaf surfaces and revealed the occurrence of antagonistic interactions between biological agents and P. fusca structures. These results confirmed the usefulness of these BCAs for managing powdery mildew on greenhouse‐grown cucurbits either as single products or as a component of integrated control programmes.

First Report of Powdery Mildew Caused by Podosphaera fusca on Coreopsis lanceolata in Italy.

Coreopsis lanceolata L. (Asteraceae) is an ornamental species grown in parks and gardens and very much appreciated for its long-lasting flowering period. During the summer and fall of 2006, severe outbreaks of a previously unknown powdery mildew were observed on plants in several gardens near Biella (northern Italy). Both surfaces of leaves of the affected plants were covered with dense white mycelia and conidia. As the disease progressed, infected leaves turned yellow and died. Mycelia and conidia also were observed on stems and flower calyxes. Conidia were hyaline, ellipsoid, borne in short chains (5 to 6 conidia per chain) and measured 33 × 20 (27 to 35 × 17 to 22) μm. Conidiophores, 68 × 11 (62 to 76 × 10 to 12) μm, showed the foot cell measuring 50 × 11 (38 to 58 × 10 to 12) μm, followed by one shorter cell measuring 18 × 12 (13 to 19 × 12 to 13) μm. Fibrosin bodies were present. Chasmothecia were spherical and amber with a diameter of 99 (93 to 105) μm. Each chasmothecium contained one ascus with eight ascospores. On the basis of its morphology, the causal agent was determined to be a Podosphaera sp. (1). The ITS region (internal transcribed spacer) of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 531 bp obtained showed an E-value of 0.0 with Podosphaera fusca (3). The nucleotide sequence has been assigned GenBank Accession No. EF 442023. Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy C. lanceolata plants. Three plants were inoculated. Three noninoculated plants served as the control. Plants were maintained in a greenhouse at temperatures ranging from 20 to 28°C. Twelve days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on C. lanceolata in Italy. Species of Coreopsis were previously described as host to Erysiphe cichoracearum, Sphaerotheca macularis and Leveillula taurica and S. fusca (2,4). Voucher specimens are available at the AGROINNOVA Collection, University of Torino.

Effect of lipopeptides of antagonistic strains ofBacillus subtilison the morphology and ultrastructure of the cucurbit fungal pathogenPodosphaera fusca

To analyse the morphological and ultrastructural effects of lipopeptides of cell-free liquid cultures from the antagonistic Bacillus subtilis strains, UMAF6614 and UMAF6639, on the cucurbit powdery mildew fungus, Podosphaera fusca, conidial germination. Butanolic extracts from cell-free supernatants of B. subtilis cultures were tested for their ability to arrest P. fusca conidial germination using the zucchini cotyledon disc method. Previously, the occurrence of lipopeptide antibiotics fengycin, iturin/bacillomycin and surfactin in the extracts was verified by diverse chromatographic approaches. Conidial germination was strongly reduced by antifungal extracts obtained from liquid cultures of both B. subtilis strains. Scanning electron microscopy analysis showed morphological damage in conidia characterized by the presence of large depressions and loss of turgidness. Transmission electron microscopy analysis revealed severe modifications in the plasma membrane and disorganization of the P. fusca cell cytoplasm. The lipopeptides produced by the two strains of B. subtilis are able to reduce cucurbit powdery mildew disease by arresting conidial germination, which seems to result from the induction of important cytological alterations. We elucidated the mechanisms employed by these antagonistic strains of B. subtilis to suppress cucurbit powdery mildew disease and delineate the ultrastructural damages responsible for their suppressive effect.

The Iturin and Fengycin Families of Lipopeptides Are Key Factors in Antagonism of Bacillus subtilis Toward Podosphaera fusca

Podosphaera fusca is the main causal agent of cucurbit powdery mildew in Spain. Four Bacillus subtilis strains, UMAF6614, UMAF6619, UMAF6639, and UMAF8561, with proven ability to suppress the disease on melon in detached leaf and seedling assays, were subjected to further analyses to elucidate the mode of action involved in their biocontrol performance. Cell-free supernatants showed antifungal activities very close to those previously reported for vegetative cells. Identification of three lipopeptide antibiotics, surfactin, fengycin, and iturin A or bacillomycin, in butanolic extracts from cell-free culture filtrates of these B. subtilis strains pointed out that antibiosis could be a major factor involved in their biocontrol ability. The strong inhibitory effect of purified lipopeptide fractions corresponding to bacillomycin, fengycin, and iturin A on P. fusca conidia germination, as well as the in situ detection of these lipopeptides in bacterial-treated melon leaves, provided interesting evidence of their putative involvement in the antagonistic activity. Those results were definitively supported by site-directed mutagenesis analysis, targeted to suppress the biosynthesis of the different lipopeptides. Taken together, our data have allowed us to conclude that the iturin and fengycin families of lipopeptides have a major role in the antagonism of B. subtilis toward P. fusca.

Multiple displacement amplification, a powerful tool for molecular genetic analysis of powdery mildew fungi

Powdery mildew fungi (Erysiphales) are probably the largest group of plant pathogens that remain uncharacterized from genetic and molecular points of view, with the only exception of the powdery mildew of cereals, Blumeria graminis. Their nature as obligate biotrophic parasites and consequent inability to grow on culture media has significantly hampered research. A common bottleneck to the molecular genetic analysis of powdery mildew fungi is the availability of genomic DNA of suitable quality and in sufficient quantity. The so-called whole genome amplification technology has the potential to overcome this limitation. Here we present the application of phi29 DNA polymerase-mediated multiple displacement amplification (MDA) to amplify the whole genome of Podosphaera fusca, the main causal agent of powdery mildew in cucurbits, to address this problem. The genome coverage and fidelity of the MDA process was evaluated by PCR amplification and sequencing of two genetics markers: the nuclear rDNA internal transcribed spacer (ITS) regions and the mitochondrial cytochrome b gene (CYTB). Our results show that MDA is a valuable tool for molecular genetic analysis of powdery mildew fungi that can be used for a number of downstream applications in different fields, such as epidemiology and population genetics or systematics.

Powdery mildews on weeds in the Pacific Northwest: a miscellany of new records

Erysiphe polygoni on Rumex crispus , documented previously in California, is reported for the first time in the Pacific Northwest. Podosphaera ( Sphaerotheca) fusca is reported in the Pacific Northwest for the first time on Taraxacum laevigatum , a host record documented previously in Europe. New host records for Idaho are Golovinomyces sordidus on Plantago major , Erysiphe convolvuli on Convolulus arvensus , and Podosphaera ( Sphaerotheca) aphanis on Geum macrophyllum . Golovinomyces (Erysiphe) cichoracearum on Cirsium arvense is reported for the first time in Washington.