Powdery Mildew Severity Research Articles

First Report of Powdery Mildew Caused by Erysiphe berberidicola on Berberis thunbergii var. atropurpurea in China

Berberis thunbergii var. atropurpurea Chenault, family Berberidaceae, is an important deciduous shrub native to China. It is widely used in hedgerows in common gardens and along roadsides. In the summer of 2017, symptoms of severe powdery mildew were observed on about 80% of B. thunbergii var. atropurpurea plants grown in several gardens in Qingdao (northern China). The white mycelium was mainly observed on the adaxial surface of the leaves and caused leaf discoloration and early dying. Conidia formed singly and were cylindrical without distinct fibrosin bodies, 28 to 35 μm long and 10 to 16 μm wide as observed in a 40× microscope. Chasmothecia were brown or light brown, spherical or oblate with age, ranging from 72 to 106 μm in diameter, with 5 to 16 appendages and 3 to 7 ovoid asci per fruiting body. The appendages were 152 to 245 μm long, aseptate, transparent, and dichotomously branched 3 to 5 times at the apices. The asci were ellipsoid to ovoid and contained 4 to 6 ellipsoid ascospores, 13 to 23 μm long and 9 to 13 μm wide. Based on its morphological characteristics and measurements, this fungus was identified as Erysiphe berberidicola (Braun and Cook 2012; Lee et al. 2016). A 611-bp internal transcribed spacer region was generated by PCR amplification with primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) and deposited in GenBank (accession no. MF494606). The isolate showed 99% identity to E. berberidicola (LC009951) (Takamatsu et al. 2015). Therefore, these data confirmed the identity of the Chinese pathogen as E. berberidicola. To confirm fungal pathogenicity, conidia isolated from 12 infected leaves were inoculated by gently pressing diseased leaves onto four fresh and healthy B. thunbergii var. atropurpurea leaves. Three plants were randomly chosen for inoculation and three noninoculated plants served as controls. Inoculated leaves showed powdery mildew symptoms on their surfaces whereas leaves on the control plants showed no disease symptoms after 3 weeks. The fungus on the inoculated plants was identical in morphology to that found on the original sample collected in the field, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of E. berberidicola infecting B. thunbergii var. atropurpurea in China. The presence of powdery mildew on B. thunbergii var. atropurpurea detracts from the aesthetic value of these plants, in some instances even resulting in premature death.

Reaction of commercial clones of cashew to powdery mildew in northeastern Brazil

Cashew powdery mildew, caused by Erysiphe quercicola, is one of the main disease problems of cashew trees in Brazil. Thus, research to study the reaction of commercial cashew clones under different epidemiological stages of the disease is very important for identifying resistant clones. The objective of this research was to evaluate the reaction of commercial clones of cashew to powdery mildew by monitoring the disease during three disease cycles. The study was carried out at Embrapa Agroindústria Tropical, Pacajus Experimental Field, Ceará, Brazil, during 2012, 2013 and 2014 using eleven commercial clones of cashew (CCP 09, CCP 76, CCP 100, CCP 06, EMBRAPA 51, EMBRAPA 50, BRS 265, BRS 189, BRS 274, BRS 275 and BRS 226). Powdery mildew severity on inflorescences was estimated using a descriptive scale of severity consisting of scores ranging from 0 to 4. The transformed data were used to estimate the area under the disease progression curve (AUDPC) and the rate of infection. Based on similarities in disease severity estimates with time, clones were clustered using multivariate clustering analysis. Epidemics of cashew powdery mildew differed between the three cycles in terms of duration and severity. The clones were classified into four clusters of similar clones, defined by the graphical analysis on the basis of the powdery mildew severity. Clones BRS 274, BRS 275, CCP 1001 and BRS 226 attained lower AUDPC and clones BRS 189 and CCP 06 showed higher AUDPC. The results show evidence of partial resistance to powdery mildew among commercially grown cashew clones. Clones BRS 274, BRS 275, BRS 226 and CCP 1001 were the most resistant, while CCP 06 and BRS 189 clones were the most susceptible to powdery mildew. The AUDPC seems to be suitable for discriminating between genotypes, whereas the rate of disease progression may be used for establishing a threshold in the evaluation of other control methods, as it does not clearly differentiate between disease reactions.

Gas Chromatography-Mass Spectrometry (GC-MS) Analysis of Sugar Beet Leaf Extracts in Response to Exogenous Application of Resistance Inducers to Manage Sugar Beet Powdery Mildew

The effect of foliar application of some chemical resistance inducers i.e., chitosan, ascorbic acid, salicylic acid and tap water as a control were tested to evaluate their efficacy to induce systemic resistance against Erysiphe betae, the causal agent of sugar beet powdery mildew (Herkl cv.) versus the traditional fungicide Opera under greenhouse and field conditions at Gemmeiza Agric. Res. Sta., Agric. Res. Cent. (ARC), Egypt during two successive winter seasons (2014/2015 and 2015/2016). Under greenhouse conditions, results revealed that spraying plants with all the tested IRCs reduced the disease severity of powdery mildew. The fungicide Opera was the most effective treatment in reducing disease severity and increasing the efficacy followed by chitosan and salicylic acid. Also, all treatments significantly increased total phenols and orthodihydric (OD) phenol content of the leaves compared to the control at 15, 30 and 45 days after inoculation. The GC-MS analysis of methanol extracts of 60 days old leaves of sugar beet plants under the greenhouse conditions, which have been treated with chitosan, ascorbic acid, salicylic acid as inducers to the systemic resistance of sugar beet against Erysiphe betae recorded the highest concentration (peak area %) for all bioactive phytochemical compounds such as flavonoids, alcohols, aldehydes, aromatic compounds, fatty acid methyl esters, terpenoids, phenolics and steroids that can be postulated for antimicrobial activity compared to control (tap water). Under field conditions, results indicated that the fungicide Opera was the most effective treatment for controlling powdery mildew followed by ascorbic acid. Meanwhile, all treatments showed lower effect than the fungicide Opera in this regard but higher than control. All treatments increased root yield per feddan compared to the control. The fungicide Opera and salicylic acid gave the highest root yield per feddan followed by ascorbic acid then chitosan. Moreover, salicylic acid and the fungicide Opera gave the highest percentages of total soluble solids (T.S.S.) and sucrose percentages, whereas salicylic acid, ascorbic acid and fungicide Opera gave the highest percentages of purity in sugar beet roots.

Powdery mildew on hazelnut (Corylus avellana) caused by Erysiphe corylacearum in Iran

AbstractCommon hazel (Corylus avellana) is an economically valuable nut crop worldwide. Phyllactinia guttata is a widespread powdery mildew species on this host in many hazelnut‐producing countries including Iran. Here, we report a new powdery mildew species on C. avellana in Iran. Hazelnut trees showing severe powdery mildew infection symptoms on leaves and fruit clusters were collected from forest areas in the Ahar (East Azerbaijan province) and the Khodaafarin (Ardabil province) regions of Iran. Based on a polyphasic taxonomic approach including morphological features of asexual and sexual states and phylogenetic inference based on ITS‐rDNA sequences, the identity of the species was determined as Erysiphe corylacearum. This study provides the first report on the occurrence of E. corylacearum on common hazel in Iran.

Zucchini Yellow Mosaic Virus Infection Limits Establishment and Severity of Powdery Mildew in Wild Populations of Cucurbita pepo.

Few studies have examined the combined effect of multiple parasites on host fitness. Previous work in the Cucurbita pepo pathosystem indicates that infection with Zucchini yellow mosaic virus (ZYMV) reduces exposure to a second insect-vectored parasite (Erwinia tracheiphila). In this study, we performed two large-scale field experiments employing wild gourds (Cucurbita pepo ssp. texana), including plants with a highly introgressed transgene conferring resistance to ZYMV, to examine the interaction of ZYMV and powdery mildew, a common fungal disease. We found that ZYMV-infected plants are more resistant to powdery mildew (i.e., less likely to experience powdery mildew infection and when infected with powdery mildew, have reduced severity of powdery mildew symptoms). As a consequence, during widespread viral epidemics, proportionally more transgenic plants get powdery mildew than non-transgenic plants, potentially mitigating the benefits of the transgene. A greenhouse study using ZYMV-inoculated and non-inoculated controls (non-transgenic plants) revealed that ZYMV-infected plants were more resistant to powdery mildew than controls, suggesting that the transgene itself had no direct effect on the powdery mildew resistance in our field study. Additionally, we found evidence of elevated levels of salicylic acid, a phytohormone that mediates anti-pathogen defenses, in ZYMV-infected plants, suggesting that viral infection induces a plant immune response (systemic acquired resistance), thereby reducing plant susceptibility to powdery mildew infection.

Phosphites and acibenzolar-S-methyl alone and combined with fungicides for the control of biotrophic pathogens of wheat

ABSTRACT Damage to wheat crop is associated with leaf rust (Puccinia triticina) and powdery mildew (Blumeria graminis f. sp. tritici). The present study aimed to evaluate the effect of potassium phosphite and acibenzolar-S-methyl alone or associated with the fungicide epoxiconazole + pyraclostrobin on powdery mildew and leaf rust control, as well as on grain yield. The experiments were designed as randomized blocks with four replicates consisting of plots with 17 planting rows spaced at 0.17 m, with dimensions of 2.89 x 5.0 m each. Severity of powdery mildew and leaf rust was assessed in ten flag leaves and ten whole plants all over the crop season; yield was also evaluated. Severity data were used to calculate the area under the disease progress curve. There was no effect of phosphite applied alone or associated with the fungicide epoxiconazole + pyraclostrobin at different times on mildew. Acibenzolar-S-methyl controlled, on average, 70% powdery mildew. Phosphites applied alone and/or associated with the fungicide had an effect on leaf rust, reducing the severity by 59 and 62%, compared to control. Applications of phosphites alone did not affect the yield components.

Elaboration and validation of diagrammatic scale for lettuce powdery mildew

ABSTRACT Powdery mildew, caused by Oidium sp., is a disease of great importance in hydroponic crops of lettuce. However, in Brazil, there is scarce research focused on the epidemiological study of this disease, as standardized methods are necessary to quantify the disease severity in hydroponic systems. Thus, a logarithmic scale was developed at levels of 0.37, 1, 2, 4, 8, 16, 32 and 74% injured leaf area, testing the parameters accuracy and precision. The proposed scale was validated by eight evaluators, of whom four were experienced and four were inexperienced, and they used 50 leaves showing symptoms of the disease at different severity levels, previously measured with the aid of QUANT® software. Two evaluations were performed with a 48-h interval, in which the evaluators visually estimated distinct sequences of leaves. Linear regression was used to determine the accuracy and the precision of each evaluator. The proposed scale showed satisfactory results of accuracy and precision, and despite the inexperience of four evaluators, absolute errors were in the range of 8% after training. The proposed scale was adequate to estimate the severity of powdery mildew on lettuce.

Variation in Sensitivity of Different Grapevine Genotypes to Erysiphe necator Growing under Unfavourable Climatic Conditions

This paper reports the susceptibility to powdery mildew of 41 grapevine genotypes growing in the north and northwest of Spain over a three-year period. Although the humid climate of these vine-growing areas is not particularly favourable to the development of this disease, serious damages appears in some years when dry weather alternates with times of some rain. All the examined genotypes belonged to the collection of the Mision Biologica de Galicia (CSIC) (Pontevedra, Galicia, Spain). The incidence and severity of powdery mildew were determined on leaves three weeks after the onset of flowering and on clusters at harvest. The values for both variables were smaller than those recorded for other fungal diseases, although great differences in susceptibility between the different genotypes were observed. The most susceptible was Castanal (recently included in the Spanish Registry of Commercial Varieties), a genotype native to the O Rosal subzone of the Rias Baixas denomination of origin area. The present results could help viticulturalists grow different grapevine genotypes more successfully in regions with climatic conditions similar to those where the study was undertaken.

First Report of Powdery Mildew Caused by Erysiphe macleayae on Corydalis edulis in China

Corydalis edulis Maxim. is a common ornamental plant in China. It is also an important Chinese medicinal herb for its antipyretic action and the ability to flush out toxic materials. In October 2016, severe powdery mildew infections were observed on C. edulis in Mengdatianchi (35.82°N, 102.69°E), China. Voucher specimens were deposited in the Herbarium of Plant Pathology at Qinghai University under accession no. QH2016001. This powdery mildew is morphologically characterized as follows. Mycelium amphigenous, thin, effuse or in irregular patches, often around leaf veins, sometimes covering the entire surface, white, evanescent to persistent; hyphae sparingly branched, thin-walled. Hyphal appressoria well-developed, lobed, 3 to 8 µm diam. Conidiophores erect, arising from the top and mostly toward one end of the mother cell, 40 to 150 µm long, foot-cells straight to often curved-sinuous, 25 to 120 μm long and 6 to 10 µm wide, followed by 1 to 3 cells shorter than or about as long as the foot cell. Conidia ellipsoid-ovoid, 25 to 60 × 10 to 29 μm, length/width ratio 1.8 to 3.4. Chasmothecia 70 to 100 μm diam., solitary or in groups, with dark brown mycelioid, unbranched appendages, 0.5 to 7 times as long as the chasmothecial diameter, 5 to 9 µm wide, septate, thin-walled, brown at the base and paler toward the apex. Asci 2 to 5 per chasmothecium, saccate-clavate, subsessile to short-stalked, 40 to 75 × 25 to 60 μm, and 2- to 5-spored. Ascospores ellipsoid-ovoid, rarely slightly curved, 18 to 38 × 12 to 18 μm, often with oil drops, colorless to yellowish. This fungus was identified as Erysiphe macleayae based on the morphology of its asexual and sexual morphs (Braun and Cook 2012). To confirm identification, the 28S rDNA and ITS region were amplified. The ITS5/p3 and PM5/ITS4 primers were used to amplify the ITS region by nested PCR. Primers LSU1/LSU2 were used to amplify the 28S rDNA, and the cloned fragments were sequenced. The 28S rDNA and ITS region sequences were deposited in GenBank (accession nos. KX817183 and KX817184). A BLAST search analysis of the two sequences revealed 100% identity with E. macleayae infecting Macleaya cordata (Willd.) R.Br. in Japan. Based on the ITS rDNA phylogenetic tree, the sequences retrieved from the Chinese specimen clustered within a strongly supported clade (bootstrap value 100%) with E. macleayae (AB016048). Cladistic trees were constructed using the neighbor-joining method with the Kimura 2-parameter substitution model in MEGA 5.0. Branch robustness was assessed via bootstrap analysis with 1,000 replicates. Phylogenetic analysis data agree with morphological characters (Takamatsu et al. 1999, 2009). For Koch’s postulate, inoculated and noninoculated plants were maintained separately in different rooms of a greenhouse at 20 to 24°C. Inoculated plants developed signs and symptoms after 12 days, whereas control plants remained symptomless. The morphology of the fungus on inoculated leaves was identical to that originally observed on diseased plants. To our knowledge, this is the first report of powdery mildew caused by E. macleayae on C. edulis worldwide. Infection of Corydalis by E. macleayae is very unusual since this powdery mildew species naturally occurs on Chelidonium majus, Meconopsis cambrica, and Macleaya spp. In inoculation experiments, it could be demonstrated that E. macleayae from Chelidonium majus was able to infect Argemone, Glaucium, and Papaver spp. (Pastircakova et al. 2016). The present record of this species on C. edulis supports a wider host range of E. macleayae among papaveraceous genera.

Virulence of Egyptian Blumeria graminis f. sp. tritici Population and Response of Egyptian Wheat Cultivars.

Powdery mildew, caused by Blumeria graminis (DC.) Speer f. sp. tritici (Em. Marchal), is a serious disease of wheat that can cause a large reduction in yield. In Egypt, high powdery mildew severity has been observed in the past few years on many commercial cultivars of both bread and durum wheat. Little information is available about virulence characteristics of the Egyptian B. graminis f. sp. tritici population in Egypt or the resistance of Egyptian wheat cultivars to powdery mildew. Virulence frequencies of a representative sample of the Egyptian B. graminis f. sp. tritici population were studied. Seven provinces were chosen to represent the country: two in Upper Egypt (Qena and Sohag), one in Middle Egypt (El Minia), and four in the north (Alexandria, Kafr Elsheikh, Dakahlia, and Sharqia). Ten isolates from each province (70 isolates total) were derived from single ascospores and used for this study. They were inoculated individually on 21 powdery mildew differential lines, each bearing a single resistance (Pm) gene. Also, the responses of 14 Egyptian bread wheat cultivars and 6 durum cultivars to each of the 70 isolates were evaluated individually. Among all tested Pm genes, only seven (Pm1b, Pm2, Pm21, Pm34, Pm36, Pm37, and Pm53) were effective against B. graminis f. sp. tritici isolates from all provinces. Several other genes were effective against most or all isolates from a majority of provinces. All tested bread wheat cultivars showed full susceptibility to all isolates, whereas two durum wheat cultivars, Beni-Suef-5 and Beni-Suef-6, had intermediate responses to a large percentage of the isolates, likely indicating partial resistance. To enhance mildew resistance in Egyptian wheat cultivars, it is recommended to use combinations of genes that are nationally effective or effective against multiple provincial B. graminis f. sp. tritici populations.

Phenotypic characterization of papaya genotypes to determine powdery mildew resistance

Abstract In support of breeding of papaya (Carica papaya), the disease incidence and severity of powdery mildew (Ovulariopsis caricicola) were evaluated in papaya genotypes. Two experiments in complete randomized blocks were carried out, one in the field and the other in a greenhouse. In field experiments, the lowest mean disease incidence was observed on the genotypes ‘Costa Rica’ and ‘Baixinho Super’, and the lowest mean disease severity on ‘Caliman M5’, ‘GTF’, ‘SH 11-08’, and ‘JS 11’. In the greenhouse experiment, the genotypes ‘Caliman M5’, ‘Golden’, ‘Kapoho Solo’, ‘Waimanalo’, ‘Mamao Bene’, ‘SH 12-07’, ‘JS 12’, and ‘GTF’ had the lowest mean incidence in at least one evaluation. On the other hand, for severity, the genotypes ‘Diva’, ‘Sunrise Solo 72/12’, ‘Kapoho Solo PA’, ‘Waimanalo’, ‘Maradol’, ‘Maradol GL’, ‘SH 15-04’, ‘FMV, ‘JS 12-4’, ‘SH 12-07’ and ‘Sekati FLM’ had the lowest means. These results indicate these genotypes for a possible use in breeding for reduction of powdery mildew intensity.

Plant age and ambient temperature: significant drivers for powdery mildew (Erysiphe cruciferarum) epidemics on oilseed rape (Brassica napus)

Powdery mildew (Erysiphe cruciferarum) is an important disease in oilseed rape crops worldwide, but of sporadic importance in most southern Australian crops. Six Brassica napus cultivars were exposed to E. cruciferarum simultaneously in four plant age cohorts. First symptoms of powdery mildew appeared 9 days after inoculation (dai) on the oldest plants [42 days after seeding (das)], but 44 dai in the youngest plants that were exposed to inoculum from sowing, although final disease severity did not differ with the plant age at exposure. The maximum level of pod peduncle infestation was unaffected by plant age (P = 0.37) or cultivar (P = 0.28). The effect of temperature was also investigated. The development of disease on plants was slower and final severity reduced at a day/night temperature 14/10 °C compared with 22/17 °C. In vitro, maximum growth of germ tubes from conidia of E. cruciferarum was at 15–20 °C and survival of conidia reduced by temperatures >30 °C. The results explain the sporadic nature of powdery mildew outbreaks in winter‐grown oilseed rape in Australia, where slow rates of infection occur when seasonal colder prevailing winter conditions coincide with the presence of younger plants, together curtailing rapid disease development until temperatures increase in late winter/early spring. These results explain why epidemics are most severe in the two warmer cropping regions, viz. the northern agricultural region of Western Australia and New South Wales. This study suggests that with increases in winter temperatures under future climate scenarios, earlier and more severe powdery mildew outbreaks in Australia will be favoured.

Disease–weather relationships for wheat powdery mildew under climate change in China

SUMMARYLittle is known about the quantitative relationships between wheat powdery mildew (Blumeria graminisf.sp.tritici) epidemics and climatic variables at the provincial scale in China, particularly under climate change. The present study assesses the actual disease process and corresponding impact on wheat yield and addresses climatic-driven variables that affect a powdery mildew epidemic. Powdery mildew increased in frequency from 1981 to 2010, and wheat yield decreased in most regions. It was clear that differences in disease and yield loss occurred temporally and spatially. Although particular weather variables were positively or negatively related to the disease, multiple stepwise regression analysis indicated that mostly fewer than three variables affected prevalence and severity of powdery mildew in each province. In most cases, some combination of higher temperature, humidity, rainfall and wind led to higher disease severity. These weather factors had different effects on disease development. The influence of climatic variables on powdery mildew tended to decrease from 1981 to 2010, whereas the effect of non-climatic factors increased and was attributed mainly to the use of fungicides and resistant cultivars. Therefore, the results of the current study suggest that wheat powdery mildew in China will not increase consistently in the future. In addition, the quantitative assessment method used in the current study can generally provide a good way to identify disease epidemics under climate change.

Role of some Non-traditional Compounds in Managing Sugar Beet Powdery Mildew

Certain non-traditional compounds such as compost tea, humic acid and sulphated canola oil were tested as foliar application to evaluate their efficacy to induce systemic resistance against Erysiphe betae, the causal agent of powdery mildew in sugar beet (Herkl cv.) versus the traditional fungicide Opera under greenhouse and field conditions at Gemmeiza Agricultural Research Station, Agricultural Research Center (A.R.C.), Egypt during two successive winter seasons (2014/2015 and 2015/2016). Under greenhouse conditions, results revealed that spraying plants with all the tested compounds reduced disease severity of powdery mildew. The fungicide Opera was the most effective treatment in reducing disease severity and increasing the efficacy followed by Sulplex, compost tea and humic acid. Also, all treatments significantly increased total phenols and orthodihydric (OD) phenol content of the leaves compared to the control 15, 30 and 45 days after inoculation. Also, spraying plants with the tested compounds increased the activity of peroxidase (PO), polyphenoloxidase (PPO) and chitinase enzymes compared to the control, 15, 30 and 45 days after artificial inoculation. Inthe detection of chitinase activity by using SDS-glycol chitin polyacrylamide gel electrophoresis the molecular weight for all samples ranged from 28 to 30 kDa. high intensity band expressing the highest chitinase activity was found in compost-tea treatment followed by Sulplex. Moreover, control, fungicide Opera and humic acid treatments showed low chitinase activity. Under field experiments, results indicated that the fungicide Opera was the most effective treatment for controlling powdery mildew followed by Sulplex and compost tea. Meanwhile, humic acid was the lowest effective one in this regard. All treatments increased root yield per feddan compared to the control. The fungicide Opera and Sulplex gave the highest root yield per feddan followed by compost tea then humic acid. Moreover, compost tea and Sulplex gave the highest percentages of total soluble solids (T.S.S.), sucrose percentages in beet roots and purity.

Microclimate in agrosilvopastoral system enhances powdery mildew severity compared to agropastoral and non-integrated crop

While integrated crop-livestock systems including trees have received more attention during the last two decades, the epidemiology of plant diseases in these production systems is still poorly understood. Microclimatic modifications due to the type of cropping system adopted may affect the epidemic patterns. This work aimed to evaluate whether powdery mildew severity on oats (Avena strigosa and A. sativa) and on soybean (Glycine max) are affected by the cropping system and which microclimatic factors are associated with disease development. A long-term experiment was conducted to compare three systems: agropastoral (AP), agrosilvopastoral (ASP) and non-integrated crop (CO). Two rates of nitrogen (N) were applied for AP and ASP. Powdery mildew severity on oats in ASP was approximately 20× greater than in the others systems. On soybean, powdery mildew varied across systems but it was more severe in ASP, with at least 4× greater disease severity than in the other systems. Likewise, conidia of Microsphaera diffusa collected in spore traps in ASP were consistently higher than in the others systems. ASP showed shorter leaf wetness duration, higher daylight relative humidity (RH), and lower temperature amplitude compared with the other systems. Multiple regression analysis showed that leaf wetness duration and daylight RH explained best the disease variation on soybean. Our data suggest that microclimatic conditions in the ASP system are likely the main drivers of more severe powdery mildew epidemics.

Silicon Transporters and Effects of Silicon Amendments in Strawberry under High Tunnel and Field Conditions.

Together with longer production periods, the commercial transition to day-neutral strawberry (Fragaria × ananassa) varieties has favored the development of diseases such as powdery mildew (Podosphaera aphanis) that thrives in late summer-early fall. In an attempt to find alternative solutions to fungicides currently employed to curb the disease, we wanted to investigate the potential of silicon (Si) amendments that have been associated with prophylactic properties against powdery mildews. To this end, our first objective was to determine if strawberry was a Si-competent species following the recent characterization of the properties of Si transporters that plants must carry to uptake silicic acid. Based on genomic data, we were able to conclude that strawberry contained both functional influx (Lsi1) and efflux (Lsi2) transporters for Si uptake. Subsequently commercial experiments under high tunnel and field conditions were conducted with different Si fertilization regimes: constant soluble Si feeding in high tunnel, and bi-weekly soluble Si feeding or three concentrations of calcium silicate fertilization in the field. Results from high tunnel experiments showed that strawberry could accumulate as much as 3% Si on a dry-weight basis, the highest concentration ever reported for this species. All six tested cultivars contained roughly the same concentration, thereby confirming the limited genetic variability, also observed in other species, associated with the trait. Silicon fertilization under high tunnel led to a significant reduction of powdery mildew severity in both years and on all cultivars, and a significant increase in yield of marketable fruits reaching as much as 300% with cv. Monterey. By contrast, Si fertilization under field conditions in soils deficient in plant available Si, either in soluble or solid form, did not result in significant accumulation of Si in plants, regardless of the cultivars, year or concentrations. Our results have thus provided both genotypic and phenotypic proof that strawberry can greatly benefit from Si fertilization, but have also highlighted the importance of validating the fertilization regime to ensure that Si is properly absorbed and/or available to the plant.

Susceptibility of Cold-Climate Wine Grape Cultivars to Downy Mildew, Powdery Mildew, and Black Rot.

Lack of knowledge regarding the susceptibility of cold-climate hybrid wine grape cultivars may be leading to the overuse of fungicides and underutilization of plant host resistance to combat disease in the northern United States. To provide new insights on diseases of cold-climate cultivars and to update management recommendations, disease was evaluated in three vineyards containing eight cultivars that were not sprayed with fungicides in 2015 and 2016. Disease severity or incidence of downy mildew (Plasmopara viticola), powdery mildew (Erysiphe necator), and black rot (Guignardia bidwellii) were measured from bud break until 2 weeks after harvest. Cold-climate cultivars ranged widely in susceptibility to different diseases and, although several cultivars were relatively resistant to two diseases, no cultivar was highly resistant to all three diseases. Additionally, a difference between foliar and fruit susceptibility for all three diseases was noted in several cultivars. These data provide a foundation for developing low-spray and certified organic disease management strategies for cold-climate wine grape cultivars based on susceptibility to disease.

The effects of innovative silicon applications on growth and powdery mildew control in soilless-grown cucumber (Cucumis sativus L.) and zucchini (Cucurbita pepo L.)

Silicon (Si) is one of the most beneficial microelements for several plants, in mediating the growth regulation in horticultural species. This research evaluated the effects of innovative Si-applications on. soilless-grown Cucumis sativus L. and Cucurbita pepo L. Crop growth, powdery mildew incidence and abiotic stress resistance were evaluated. Two experiments were carried out in a nonheated glasshouse on benches. Two new Si treatments (Si–Nanosponge complex, and one experimental fertilizer) were compared with the traditional K2SiO3. Topas® EC 10 was used as control fungicide treatment. Biometric parameters, and incidence and severity of powdery mildew were measured. Cucumis sativus plants showed a severe powdery mildew infection, and no significant effect of the Si treatments was found. Cucurbita pepo plants were initially grown under lower disease pressure conditions, and the positive effect of Si treatments was found. The innovative use of Si–Nanosponge complex and the new experimental fertilizer can be considered a good alternative to traditional compounds for plant growth stimulation.

Effects of Powdery Mildew ( Leveillula Taurica and Erysiphe Polygoni ) on Yield and Yield Components of Fenugreek in the Mid-Altitudes of Bale, South Eastern Ethiopia

Fenugreek (Trigonella foenum-graecum L.) is one of the most important seed spice crops in Ethiopia in general and in the mid-altitudes of Bale in particular. Powdery mildew caused by Leveillula taurica and Erysiphe polygoni is a common disease of fenugreek in the mid-altitudes of Bale. To determine the effects of this disease on yield and yield components of the crop, a field experiment was conducted using an improved variety, Hunda’ol, at Goro research site of Sinana Agricultural Research Center, south eastern Ethiopia. Four different spray intervals of a systemic fungicide, Lunar sensation (Fluopyram 250 g/L+ Trifloxystrobin 250 g/L), were used to create different levels of powdery mildew severity. The plots were arranged in Randomized Complete Block Design (RCBD) with three replications. There was severe powdery mildew development on plants in the unsprayed plots. The disease had significant effect on two of the yield parameters, number of seeds per pod and thousand seed weight. It inflicted the total yield loss up to 40%. Hence, application of control measure to minimize this loss is necessary. Resistant varieties are cultural tools that could be used for the management diseases of several crops. However, so far there is no powdery mildew resistant fenugreek variety released in this country. Fungicides can be used to effective control of this disease. The present study revealed that powdery mildew of fenugreek can be controlled by applying lunar sensation twice between 21-days starting from the onset of the disease.

Can Oak Powdery Mildew Severity be Explained by Indirect Effects of Climate on the Composition of the Erysiphe Pathogenic Complex?

Coinfection by several pathogens is increasingly recognized as an important feature in the epidemiology and evolution of plant fungal pathogens. Oak mildew is induced by two closely related Erysiphe invasive species (Erysiphe alphitoides and E. quercicola) which differ in their mode of overwintering. We investigated how climate influences the co-occurrence of the two species in oak young stands and whether this is important for the disease epidemiology. We studied the frequency of flag-shoots (i.e., shoots developing from infected buds, usually associated with E. quercicola) in 95 oak regenerations over a 6-year period. Additionally, in 2012 and 2013, the oak mildew severity and the two Erysiphe spp. relative frequencies were determined in both spring and autumn in 51 regenerations and 43 1-year-old plantations of oaks. Both the frequency of flag-shoots and the proportion of Erysiphe lesions with E. quercicola presence were related to climate. We showed that survival of E. quercicola was improved after mild winters, with increase of both the flag-shoot frequency and the proportion of Erysiphe lesions with E. quercicola presence in spring. However, disease severity was not related to any complementarity effect between the two Erysiphe spp. causing oak powdery mildew. By contrast, increased E. alphitoides prevalence in spring was associated with higher oak mildew severity in autumn. Our results point out the critical role of between-season transmission and primary inoculum to explain disease dynamics which could be significant in a climate-warming context.