Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) as a potential mycoparasite on Sphaerotheca fuliginea (Ascomycotina: Erysiphales)

Hyphomycete Paecilomyces fumosoroseus that is well known as saprophytic and entomopatogenic fungus was investigated for its mycoparasitism on the cucumber powdery mildew pathogen. Mycoparasitism was documented by using standard bioassay and SEM. Effects of mycoparasitism were evaluated in three types of experiments. Paecilomyces fumosoroseus was applied in the form of graded suspensions into a colony of powdery mildew on a leaf segment. Interaction between both fungi was observed as the percentage of colonized area vs. experimental time. In the second experiment, young cucumber plants were sprayed with a suspension of Paecilomyces fumosoroseus 24 h before inoculation of Sphaerotheca fuliginea. Pre-treatment with P. fumosoroseus reduced development and spreading of powdery mildew infection significantly 15 days post-inoculation in contrast to pre-treatments with sulfur fungicide and distilled water. The development of pure culture powdery mildew under determined experimental conditions was observed and compared with treated variants. In the third experiment, mildewed plants were treated with a suspension of P. fumosoroseus. The control treatments with sulfur fungicide and distilled water were tested. Effects of P. fumosoroseus on the dispersion of powdery mildew during a 21-day period were observed.P. fumosoroseus suppressed the development and spread of cucumber powdery mildew significantly during the time of the experiment. The mechanical and physical damages and disruptions of vegetative and fruiting structures of powdery mildew were recorded under light microscopy and S.E.M.Results were concluded in pursuance to differences between the natural behaviour and development of S. fuliginea on cucumber plants treated with P. fumosoroseus and non-treated plants.     

Oleozon: A novel control strategy against powdery mildew in cucumber

Ozonized sunflower oil (oleozon) is an effective agent for controlling powdery mildew in cucumber. In this study, the mechanisms of oleozon in the control of powdery mildew were determined. The development of Podosphaera xanthii on cucumber leaves treated with oleozon (2%) and water was investigated at different times after inoculation. The germinating conidia, hyphae and conidiophores of the pathogen were severely damaged by oleozon. No visible phytotoxic effect was observed on cucumber after the application of oleozon. This compound had highly preventive effects as well as curative effects against powdery mildew based on in vivo potted seedling assays. The control effects of oleozon were further confirmed in a greenhouse trial. These results may provide a basis for further development of a natural fungicide against cucumber powdery mildew.     

Fungicide programmes for the control of spur blight, powdery mildew and grey mould on raspberry

Five sprays of dichlofluanid (0–1% a. i.) reduced spur blight (Didymella applanata) on canes and powdery mildew (Sphaerotheca macularis) on fruit more than five sprays of captan (0–1% a. i.). Omission of the first three applications resulted in little increase in disease but when the fourth (full bloom) application also was omitted the incidence of disease was comparable with that on untreated plants. The final (fruitlet stage) application did not further reduce disease incidence. Five sprays of dichlofluanid reduced grey mould (Botrytis cinerea) on stored fruit more than five sprays of captan. There was an increase in grey mould with progressive reductions in the number of sprays. Incidence on canes was slight and was unaffected by treatments. A programme of five dichlofluanid sprays applied at 14-day intervals until c. 2 wk before harvest and supplemented by a single early full bloom spray of either dinocap (0–025% a. i.), binapacryl (0–05% a. i.), triforine (0–025% a. i.), benomyl (0–025% a. i.) or replaced by benomyl (0–025% a. i.) all halved both the number of fruits infected by powdery mildew and the number of spur blight lesions on canes, compared with unsprayed controls. Six applications of any of the following fungicides at 7-day intervals from 23 May until 29 June 1977 reduced powdery mildew incidence on fruit, the last fungicide being particularly effective: dinocap (0–0125%), dichlofluanid (0–075%), binapacryl (0–025%), triforine (0–0125%), bupirimate (0–0075%), ditalimfos (0–01875%) and fenarimol (0–0036%). Only triforine and bupirimate reduced the incidence of mildew on shoots. Dichlofluanid, binapacryl, triforine and fenarimol all reduced the amount of spur blight on canes. The largest fruit occurred on plants sprayed with bupirimate, ditalimfos and fenarimol, and late ripening was associated with triforine treatments.     

Dual role of nitric oxide in Solanum spp.–Oidium neolycopersici interactions

The role of nitric oxide in the pathogenesis of Oidium neolycopersici was studied on leaf discs of three Solanum spp. genotypes differing in their susceptibility to powdery mildew infection. The germination of pathogen conidia, development of infection structures and reaction of host tissues were compared for S. lycopersicum (susceptible), S. chmielewskii (moderately resistant) and S. habrochaites f. glabratum (highly resistant genotype) in presence of compounds modulating NO levels. The effect of NO donor sodium nitroprusside varied among genotypes and studied time intervals whereas NO scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide accelerated fungal development in all three Solanum spp. genotypes. The exposure of leaf discs to NOS inhibitor N^G-nitro-l-arginine methyl ester decreased powdery mildew growth namely in S. chmielewskii. Confocal laser scanning microscopy using the fluorescent probe 4-amino-5-(N-methylamino)-2′,7′-difluorofluorescein diacetate localised NO accumulation both in pathogen germ tubes and appressoria and in penetrated cells of resistant genotypes of S. chmielewskii and S. habrochaites f. glabratum. Our results confirm an essential role for NO in powdery mildew pathogenesis including the penetration of biotrophic pathogen and the initiation of hypersensitive reaction, and suggest the contribution of NO to molecular mechanisms of diversity in interactions of Solanum spp. with O. neolycopersici.     

The hop downy mildew pathogen Pseudoperonospora humuli

Pseudoperonospora humuli is an obligate biotrophic oomycete that causes downy mildew, one of the most devastating diseases of cultivated hop, Humulus lupulus. Downy mildew occurs in all production areas of the crop in the Northern Hemisphere and Argentina. The pathogen overwinters in hop crowns and roots, and causes considerable crop loss. Downy mildew is managed by sanitation practices, planting of resistant cultivars, and fungicide applications. However, the scarcity of sources of host resistance and fungicide resistance in pathogen populations complicates disease management. This review summarizes the current knowledge on the symptoms of the disease, life cycle, virulence factors, and management of hop downy mildew, including various forecasting systems available in the world. Additionally, recent developments in genomics and effector discovery, and the future prospects of using such resources in successful disease management are also discussed.TaxonomyClass: Oomycota; Order: Peronosporales; Family: Peronosporaceae; Genus: Pseudoperonospora; Species: Pseudoperonospora humuli.Disease symptomsThe disease is characterized by systemically infected chlorotic shoots called “spikes". Leaf symptoms and signs include angular chlorotic lesions and profuse sporulation on the abaxial side of the leaf. Under severe disease pressure, dark brown discolouration or lesions are observed on cones. Infected crowns have brown to black streaks when cut open. Cultivars highly susceptible to crown rot may die at this phase of the disease cycle without producing shoots. However, foliar symptoms may not be present on plants with systemically infected root systems.Infection processPathogen mycelium overwinters in buds and crowns, and emerges on infected shoots in spring. Profuse sporulation occurs on infected tissues and sporangia are released and dispersed by air currents. Under favourable conditions, sporangia germinate and produce biflagellate zoospores that infect healthy tissue, thus perpetuating the infection cycle. Though oospores are produced in infected tissues, their role in the infection cycle is not defined.ControlDowny mildew on hop is managed by a combination of sanitation practices and timely fungicide applications. Forecasting systems are used to time fungicide applications for successful management of the disease.Useful Websites https://content.ces.ncsu.edu/hop‐downy‐mildew (North Carolina State University disease factsheet), https://www.canr.msu.edu/resources/michigan‐hop‐management‐guide (Michigan Hop Management Guide), http://uspest.org/risk/models (Oregon State University Integrated Plant Protection Center degree‐day model for hop downy mildew), https://www.usahops.org/cabinet/data/Field‐Guide.pdf (Field Guide for Integrated Pest Management in Hops).     

Transition of secondary to systemic infection of sunflower with Plasmopara halstedii – An underestimated factor in the epidemiology of the pathogen

Plasmopara halstedii, the downy mildew pathogen of sunflower causes significant economic loss world-wide, mostly through soilborne systemic infection of seedlings. Natural infection of sunflower with P. halstedii was monitored in a sunflower field cultivated for ornamental purpose in soil where no sunflower had been grown before. Local and systemic infections were observed in plants of different developmental stages which were sown in five consecutive field plots between Apr. and Jul. The airborne origin of the infection by zoosporangia was concluded from field history, pathogenic symptoms, time course of infection and microscopic investigation of mycelium distribution in stems. A high potential for transition from local to systemic infection was found, at least in ornamental sunflower cultivation under the typical weather conditions in Central Europe. This questions the paradigm that economically and epidemiologically relevant sunflower downy mildew incidences are only derived from subterranean infections. Airborne secondary infections, as they may occur in all developmental stages and on all organs of the host plant, are responsible for late systemic infection and can play a key role in the production of contaminated seeds carrying the pathogen into the next season.     

Intracellular Localization of the Systemic Fungicide Triadimenol in Phytopathogenic Fungi

The intracellular localization of the radioactively labelled fungicide (³H)triadimenol A in the in vitro grown sporidia of Ustilago avenae and in the in vivo cultured powdery mildew (Erysiphe graminis f. sp. hordet) on barley (Hordeum vulgare) is described. The specimens were prepared by low temperature techniques: shock freezing, freeze substitution and embedding in Spurr's low viscosity resin. The localization of the fungicide was achieved by means of conventional electron microscopic autoradiography. The available experimental data allow a first qualitative analysis of the distribution of silver grains on freeze substituted sporidia of U. avenae and the infection structures of Erysiphe graminis f. sp. hordei. Concerning U. avenae the fungicide is detected preferentially over the vacuoles, the cytoplasm, and the cell walls after a six month exposure. The host pathogen system powdery mildew on barley exhibits an accumulation of silver grains in the host cell wall adjacent to the infection site and the papillae whereas decisively fewer grains occur inside the haustoria. Apart from this general localization pattern the haustoria show ultrastructural changes caused by the fungicide treatment: vesiculation and collapse of the sheath membrane as well as a diffuse appearance of the haustorial cytoplasm. Around the haustoria an aggregation of host cytoplasm material is observed.     

Synthesis and antifungal activity of six benzylic diamines

Six benzylic diamines were synthesised and examined for antifungal activity. Four of the compounds, KB 2, KB 4, KB 5 and KB 6, reduced radial growth of the oat leaf stripe pathogen Pyrenophora avenae, the largest reduction obtained with 25 μM KB 4, which reduced radial growth by 47%. Surprisingly, these four amines had no effect against infection of barley seedlings with the powdery mildew fungus Erysiphe graminis f.sp. hordei. Instead, two different amines, KB 1 and KB 3, reduced powdery mildew infection on barley. The greatest reduction was obtained with 25 μM KB 3, which reduced mildew infection by 69%. All of the amines which exhibited antifungal or fungicidal properties perturbed polyamine formation as measured by the incorporation of labelled ornithine into polyamines.     

Effect of exogenous cytokinins on dynamics of development and differentiation of infectious structures of the pathogen of wheat powdery mildew

The infectious structures for the development and differentiation of Erysiphe graminis DC. f. sp. tritici March., the pathogen of wheat powdery mildew, under the effects of exogenous zeatin was studied by methods of light and electron scanning microscopy. It was shown for the first time that physiologically active substances, specifically phytohormones of the cytokinin type, can affect dimensions of the halo revealed in the pathogen penetration site at cytochemical staining. Treatment with zeatin affected conidia germination and pathogen growth in the ectophytic stage. The concentration curve of the action of zeatin for the number of mature pathogen colonies (6 days after infection) was represented by a multiphase curve with two maxima (1 and 3 μM) and one minimum (1.5 μM). Similar curves have been obtained for the number of normal appressoria and for large halo diameters, which possibly indicates the existence of the factors affecting these both parameters, as well as the final number of pathogen colonies. The obtained data indicate that the origin of the multiphase dose response curve for effect of cytokinins on the development of powdery mildew pathogen is connected with factors that are active at the early stages of pathogenesis.     

Genetic characterization of five powdery mildew disease resistance loci in Arabidopsis thaliana

This paper reports on six Arabidopsis accessions that show resistance to a wild isolate of the powdery mildew pathogen, Erysiphe cichoracearum . Resistance at 7 days post-inoculation in these accessions was characterized by limited fungal growth and sporadic development of chlorotic or necrotic lesions at inoculation sites. Three accessions, Wa-1, Kas-1 and SI-0, were highly resistant, while the other accessions permitted some fungal growth and conidiation. Papilla formation was a frequent host response; however, cell death appeared to be neither a rapid nor a common response to infection. To determine the genetic basis of resistance, segregation analyses of progeny from crosses between each of the resistant accessions and Columbia ( gl1 ), which is susceptible to the powdery mildew pathogen, were performed. For all accessions except SI-0, resistance was conferred by a single locus. SI-0 was unique in that two unlinked loci controlled the disease reaction phenotype. In accessions Wa-1, Kas-1, Stw-0 and Su-0, powdery mildew resistance was encoded by a semi-dominant allele. However, susceptibility was dominant to resistance in accessions Te-0 and SI-0. Mapping studies revealed that powdery mildew resistances in Kas-1, Wa-1, Te-0, Su-0 and Stw-0 were controlled by five independent loci. This study suggests that the Arabidopsis powdery mildew disease will be a suitable model system in which to investigate powdery mildew diseases.     

The effects of innovative silicon applications on growth and powdery mildew control in soilless-grown cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) and zucchini (<Emphasis Type="Italic">Cucurbita pepo</Emphasis> 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.     

Evaluation of microcapsule trunk injections for the control of apple scab and powdery mildew

A 3‐year field trial was conducted using established apple cv. Crown Gold and English oak (Quercus robur L.) to assess the efficacy of eight fungicides applied via microcapsule trunk injection against the foliar pathogens apple scab (Venturia inaequalis) and powdery mildew (Phyllactinia sp). In both apple cv. Crown Gold and English oak, the fungicide myclobutanil was not taken up when microcapsules were inserted into the tree vascular system at the root flare. Disease severity in injected trees, excluding myclobutanil, was lower over the following two growing seasons compared to water‐injected controls indicating seven of the eight fungicides used in this study provided a significant degree of protection against scab and powdery mildew infection. A difference in the magnitude of pathogen control achieved was recorded between fungicides. Of the fungicides tested, penconazole, pyrifenox and carbendazim significantly reduced disease severity and significantly increased leaf chlorophyll (Fv/Fm) and SPAD values as a measure of tree vitality and chlorophyll content, respectively, in both apple cv. Crown Gold and English oak over two growing seasons after microcapsule injection. Based on the results of this investigation, it is suggested that these three fungicides be used in preference to thiabendazole, fosetyl‐aluminium, triadimefon and propiconazole for the control of apple scab and powdery mildew where outbreaks of these foliar pathogens are problematic.     

ENHANCED DISEASE RESISTANCE4 Associates with CLATHRIN HEAVY CHAIN2 and Modulates Plant Immunity by Regulating Relocation of EDR1 in Arabidopsis

Obligate biotrophs, such as the powdery mildew pathogens, deliver effectors to the host cell and obtain nutrients from the infection site. The interface between the plant host and the biotrophic pathogen thus represents a major battleground for plant-pathogen interactions. Increasing evidence shows that cellular trafficking plays an important role in plant immunity. Here, we report that Arabidopsis thaliana ENHANCED DISEASE RESISTANCE4 (EDR4) plays a negative role in resistance to powdery mildew and that the enhanced disease resistance in edr4 mutants requires salicylic acid signaling. EDR4 mainly localizes to the plasma membrane and endosomal compartments. Genetic analyses show that EDR4 and EDR1 function in the same genetic pathway. EDR1 and EDR4 accumulate at the penetration site of powdery mildew infection, and EDR4 physically interacts with EDR1, recruiting EDR1 to the fungal penetration site. In addition, EDR4 interacts with CLATHRIN HEAVY CHAIN2 (CHC2), and edr4 mutants show reduced endocytosis rates. Taken together, our data indicate that EDR4 associates with CHC2 and modulates plant immunity by regulating the relocation of EDR1 in Arabidopsis.     

The integration of host resistance with fungicides in the control of oat powdery mildew

Treatment of seed with the systemic fungicides triadimenol plus fuberidazole as Baytan significantly decreased powdery mildew in field experiments involving eight oat cultivars differing widely in their resistance to the disease. This was so up to growth stage G.S. 61 (Zadoks) even in a year of high mildew incidence, although the effect diminished after flowering. Significant (P≥ 0.001) interactions between fungicide treatments and cultivars occurred in each of three years at nearly all assessment times. In years of high mildew incidence (1983 and 1984), susceptible cultivars developed similar levels of mildew in seed-treated and untreated plots by about flowering time, although cultivars with adult plant resistance (APR) had significantly less mildew when seed-treated than when left untreated. Later, as the APR was fully expressed and the fungicide effectiveness was declining, similar mildew levels were recorded on treated and untreated plots. Untreated APR cultivars generally had less mildew than treated susceptible cultivars and in a year of late and light mildew, APR alone provided good protection. Seed treatments combined with foliar sprays of tridemorph as Calixin almost completely controlled mildew except on very susceptible cultivars late in the season in high mildew years. Over all cultivars, seed treatment gave yield advantages of 5.3% (1983) and 6.6% (1984) but in 1982, a year of low mildew, the response was small. The possible influence of integrated host resistance and fungicides in stabilising the pathogen population at economically unimportant levels and the environmental benefit of using host resistance to minimise fungicide usage is discussed.     

Use of blue-green and chlorophyll fluorescence measurements for differentiation between nitrogen deficiency and pathogen infection in winter wheat

In recent years, several sensor-based approaches have been established to early detect single plant stresses, but the challenge of discriminating between simultaneously occurring stressors still remains. Earlier studies on wheat plants strongly affected by pathogens and nitrogen deficiency indicated that chlorophyll fluorescence might be suited to distinguish between the two stressors. Nevertheless, there is lack of information on the pre-symptomatic detection of synchronized occurrence of slight N-deficiency and the early stages of pathogen infection. The usefulness of the blue, green, and yellow fluorescence signals in this context has not yet been explored. We hypothesized that differentiation between wheat plants’ physiological reaction due to N-deficiency and leaf rust (Puccinia triticina) as well as N-deficiency and powdery mildew (Blumeria graminis f. sp. tritici) might be accomplished by means of UV laser-induced fluorescence spectral measurements between 370 and 620 nm in addition to chlorophyll fluorescence (640-800 nm). Plants were provided with either a normal or a modified Hoagland nutrient solution in order to induce a slight N deficit. Pathogen inoculation was carried out on the second fully developed leaf. Four experimental groups were evaluated: (a) N-full-supply [N+]; (b) N-deficiency [N−]; (c) N-full-supply + pathogen [N+/LR] or [N+/PM]; (d) N-deficiency + pathogen [N−/LR] or [N−/PM]. The results revealed that, in addition to the amplitude ratio of R/FR fluorescence, B/G fluorescence also facilitated reliable and robust discrimination among the four experimental groups. The discrimination among the experimental groups was accomplished as early as one and two days after inoculation for powdery mildew and leaf rust infection, respectively. During the 3 days evaluation period, the differences among the treatment groups became more evident. Moreover, several other amplitude ratios and half-bandwidth ratios proved to be suited to early detect fungal infection, irrespective of the nitrogen status of the plant.     

In vitro gas production kinetics and short-chain fatty acid production from rumen incubation of diets supplemented with hop cones (Humulus lupulus L.)

The aim of this study was to assess the effects of hop cones (Humulus lupulus L.) from two varieties Aurora and Dana, differing in their α- and β-acid contents, on rumen microbial activity measured with in vitro gas production kinetics and short-chain fatty acids (SCFA) production. Hop cones were added to the total mixed dairy cow ration (CONT) in concentrations simulating a cow’s daily intake of 50, 100 and 200 g of hop cones – the concentrations of hop cones expressed on a substrate basis were 43, 82 and 153 mg/g of substrate. Substrates were anaerobically incubated in glass syringes, and gas production kinetic parameters were determined by fitting data with the Gompertz model. Gas produced after 24 h (Gas24), maximum fermentation rate (MFR) and time of maximum fermentation rate (TMFR) were calculated from the estimated gas production kinetic parameters. After 24 h of incubation, the fermentation liquids of each substrate were taken for the determination of SCFA. Increasing the hop cone concentration decreased the total potential gas production, Gas24, MFR and shortened TMFR. The highest hop cone concentration significantly decreased acetic and butyric acid productions and total SCFA production after 24 h of incubation, but not propionic acid production, resulting in a decreased ratio between acetic acid and propionic acid.     

Synthesis and antifungal activity of two novel spermidine analogues

Two spermidine analogues were synthesised and examined for antifungal activity. Both compounds used as 1 mM post-inoculation sprays reduced infection of barley seedlings by the powdery mildew fungus, Erysiphe graminis f.sp. hordei, infection of broad bean seedlings by the rust fungus, Uromyces viciae-fabae, and infection of apple seedlings by the powdery mildew fungus, Podosphaera leucotricha. Since these fungal pathogens cannot be cultured axenically, the effects of the two spermidine analogues on mycelial growth in vitro, as well as preliminary investigations on polyamine biosynthesis, were undertaken using the oat stripe pathogen, Pyrenophora avenae. Although neither compound affected radial growth of the fungus on plates, both analogues reduced fungal biomass in liquid culture substantially. The two spermidine analogues, used at a concentration of 1 mM, had no significant effect on the conversion of labelled ornithine into polyamines in P. avenae.     

Control of powdery mildew in okra using cultural filtrates of certain bio-agents alone and mixed with penconazole

This study was carried out to evaluate the culture filtrates of certain bio-agents (Epicoccum nigrum, Epicoccum minitans, Epicoccum sp., Trichoderma harzianum, Trichoderma viride and Bacillus pumilus) alone and mixed with penconazole against powdery mildew in okra. The results showed that the culture filtrate of E. nigrum induced the highest efficacy against powdery mildew relative to other treatments in both tested seasons. Moreover, culture filtrate of E.nigrum mixed with the tested fungicide gave higher efficiency against powdery mildew than use of the fungicide alone. The efficacy of the tested culture filtrates against powdery mildew due to the presence of different antifungal compounds identified by (GC–MS) analysis. This study suggests the ability of using the culture filtrates of the tested bio-agents as alternative of fungicides to control powdery mildew in okra. Furthermore, the results implied the possibility to minimise the use of fungicides by mixing with the microbial culture filtrates.