Identification and distribution of mating‐type idiomorphs in populations of Podosphaera macularis and development of chasmothecia of the fungus

Podosphaera macularis, the causal agent of hop powdery mildew, is known to produce chasmothecia (formerly cleistothecia) in eastern North America and Europe. Ascocarps have not yet been reported from the Pacific Northwestern region of North America. Reasons for the apparent absence of chasmothecia in the Pacific Northwest were unknown. This study established that P. macularis is heterothallic and ascocarp ontogeny, maturation, dehiscence and ascospore infection proceed similarly to other powdery mildew fungi. Genome sequencing of a MAT1‐1 isolate revealed the structure of the MAT1 locus and presence of MAT1‐1‐3, demonstrating further similarities to other powdery mildew fungi. PCR assays with primers designed from conserved domains of the MAT1 idiomorphs were developed to characterize the frequency of idiomorphs in populations of P. macularis. Amongst 317 samples of P. macularis collected during 2012 and 2013 from the Pacific Northwest only the MAT1‐1 idiomorph was found. In contrast, among 56 samples from the eastern United States and Europe, MAT1‐1 and MAT1‐2 idiomorphs were detected at equivalent frequencies. At temperatures representative of late season conditions in the Pacific Northwest, chasmothecia formed readily when a Pacific Northwest MAT1‐1 isolate was paired with a MAT1‐2 isolate collected from outside the region. Although these findings do not encompass all climatic, geographic or temporal barriers that could inhibit the formation of chasmothecia, the current absence of the ascigerious stage of P. macularis in the Pacific Northwest could be explained by the absence of the MAT1‐2 mating type idiomorph.     

Species spectra,distribution and host range of cucurbit powdery mildews in the Czech Republic,and in some other European and Middle Eastern countries

The occurrence and geographic distribution of powdery mildew on cucurbits was studied in the Czech Republic, Austria, France, Germany, Great Britain, Italy, Slovakia, Slovenia, Spain, Switzerland, the Netherlands, as well as in Turkey and Israel, during the period 1995–2000. In total, 599 leaf samples with powdery mildew symptoms were collected from cucurbits from 166 locations within the Czech Republic; an additional 69 samples were collected from 42 locations elsewhere. Two powdery mildews (Golovinomyces cichoracearum and Podosphaera xanthii) were identified. The host range included the cultivated cucurbits (Cucumis melo, C. sativus, Cucurbita pepo, C. maxima, and Citrullus lanatus) and several other species. P. xanthii was the only powdery mildew pathogen found in Spain, Israel, and Turkey. P. xanthii and G. cichoracearum were detected in the other surveyed countries, occurring in both mixed infections and separately. In the more northerly latitudes and higher elevations, G. cichoracearum is more often the single species. G. cichoracearum was the dominant powdery mildew species in the Czech Republic (detected in 98.8% of the locations there); P. xanthii was found as the lone species in 1.2% of locations. At 28.4% of locations, G. cichoracearum was found with P. xanthii as mixed infections. The hyperparasitic fungus Ampelomyces quisqualis was found in 30% of the samples from the Czech Republic and was also recorded in Austria, Italy, Slovenia, Switzerland, and Great Britain.     

Differentiation of two powdery mildews of sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis>) by a PCR-mediated method based on ITS sequences

Powdery mildew can be found in most sunflower fields during the winter season in Taiwan and causes severe yellowing on the blade, petiole, stem, and calyx, as well as serious defoliation. Two types of powdery mildew fungi isolated from sunflower leaves showed variable status for fibrosin bodies. But only the cleistothecium of Podosphaera xanthii, one of the pathogens causing this disease, was observed on samples from Chungpu County at the beginning of 2005. With a species-specific primer pair, PN23/PN34, no specific PCR product was amplified from the pathogen’s genomic DNA. Based upon the ITS sequence of rDNA, three PCR primer sets (S1/S2, G1/G2, and L1/L2) specific to P. xanthii, Golovinomyces cichoracearum and Leveillula taurica, respectively, were designed to detect and differentiate pathogens causing powdery mildews on sunflower. Only the primer pairs S1/S2 and G1/G2 could amplify PCR products, with product sizes of 454 and 391 bp, respectively. Four samples of fungal DNA were subjected to a multiplex PCR amplification with primer pairs S1/S2 and G1/G2; P. xanthii and G. cichoracearum were successfully detected. These results suggest that the multiplex PCR method is a rapid, simple, and effective technique to detect and differentiate powdery mildews, for example P. xanthii and G. cichoracearum, found on sunflower. With morphologic characteristics, ITS sequence analysis and pathogenicity testing, P. xanthii and G. cichoracearum, the first case, are two powdery mildews on sunflower in Taiwan.     

Understanding pathogen population structure and virulence variation for efficient resistance breeding to control cucurbit powdery mildews

Cucurbit powdery mildew (CPM) is caused most frequently by well-differentiated obligate erysiphaceous ectoparasites Golovinomyces orontii and Podosphaera xanthii, which vary in their ecology and virulence. All economically important cucurbit crops host both of these CPM species. Breeding of cucurbits for CPM resistance is highly important worldwide, but adequate knowledge of CPM species determination, as well as virulence structure, population dynamics, and spatiotemporal variation of these pathogens, has not yet been achieved. New tools have been developed to enhance research on CPM virulence variation for more efficient breeding and seed and crop production. A set of differential genotypes of Cucumis melo, with high differentiation capacity, may contribute substantially to understanding of variation in CPM virulence at both individual and population levels. Long-term observations (2001–2012) of CPM pathogens in the Czech Republic were used to analyse virulence variation within and among annual CPM populations and demonstrate the utility of recently developed tools for studying species variability and virulence variation of CPM pathogens worldwide. Detailed analyses of diversity and spatiotemporal fluctuations in the composition of CPM populations provide crucial information for shaping breeding programmes and predicting the most effective sources of race-specific resistance. The primary aim of this work was to create a uniform framework for determination of CPM species structure and diversity, virulence phenotypes, virulence and phenotype frequencies, phenotype complexity, dynamics, and variation within and among CPM populations. In addition, practical advice is presented on how to select the most relevant data and interpret them for use in cucurbit resistance breeding.     

Both Mating types of Phaeosphaeria (anamorph Stagonospora) nodorum are Present in Western Australia

Phaeosphaeria (anamorph Stagonospora) nodorum is the most serious fungal pathogen of wheat in the West Australian (WA) wheat belt and is a diallelic heterothallic loculoascomycete. Its population genetics has received considerable attention. A recent study, which sampled isolates from diverse locations worldwide, has indicated that the mating-type idiomorph MAT1-1 is considerably more frequent than MAT1-2 in many populations. To investigate this, we developed PCR primers that amplify each idiomorph. In a sample of 23 isolates cultured from ascospores collected in the field, nine amplified DNA with the MAT1-1 primers and 14 amplified DNA with the MAT1-2 primers. The virulence of a MAT1-2 isolate was comparable with MAT1-1 isolates. Although these sample sizes are small, we suggest that this result is consistent with the presence of equal numbers of both mating types in populations of ascospores in WA.     

Biological control mechanisms of D-pinitol against powdery mildew in cucumber

D-pinitol is an effective agent for controlling powdery mildew (Podosphaera xanthii) in cucumber. In this study, we determined the mechanisms of D-pinitol in controlling powdery mildew in cucumber plants. We compared P. xanthii development on cucumber leaf surface treated with D-pinitol or water (2 mg ml⁻¹) at different time points after inoculation. The germinating conidia, hyphae, and conidiophores of the pathogen were severely damaged by D-pinitol at any time of application tested. The highest level of suppression of fungal development was obtained at 3 days after inoculation. The contents of chlorophyll, total phenolics, flavonoid, and gallic acid and its derivatives (GAD); the activities of phenylalanine ammonialyase (PAL), polyphenoloxidase (PPO), peroxidase (POX), and superoxide dismutase (SOD); and the expression of the genes encoding for PR-1, peroxidase (POX), lipoxygenase (LOX1), chitinase (Chit1) were higher in the cucumber leaves treated with D-pinitol and inoculated than in the leaves either treated with D-pinitol or inoculated with the pathogen. These results suggest that D-pinitol triggers several plant defense responses in cucumber leading to pathogen suppression and resistance to powdery mildew.     

Effect of temperature on infection and development of powdery mildew on cucumber

Podosphaera xanthii and Golovinomyces orontii are the causal agents of cucurbit powdery mildew. The effect of temperature on conidial germination, infection and sporulation was studied under controlled conditions. Conidia were inoculated on cucumber leaf discs, and incubated at six constant temperatures (from 10 to 35 °C in 5 °C steps) for 3 to 72 h to evaluate conidial germination and infection, and for 6–15 days to evaluate sporulation intensity. Germination took place at all tested temperatures, but was close to zero at 35 °C. The longest germ tubes measured in this experiment were 141.74 μm for the secondary germ tube of P. xanthii at 20 °C after 48 h of incubation, and 67.92 μm for G. orontii for the primary germ tube at 20 °C after 48 h of incubation. The optimal temperatures for conidial germination, infection and sporulation were 24.4, 25.7 and 22.3 °C, respectively, for P. xanthii, and 17.9, 17.3 and 14.9 °C, respectively, for G. orontii. Equations were developed to describe conidial germination with a coefficient of determination (R²) of 0.85 and 0.90 for P. xanthii and G. orontii, respectively. Infection equations resulted in R² of 0.94 and 0.93 for P. xanthii and G. orontii, respectively; and for sporulation, R² of 0.75 and 0.76 for P. xanthii and G. orontii respectively, as a function of temperature. These results can be used to develop models for the risk of cucurbit powdery mildew under field conditions.     

Asexual fungus <Emphasis Type="Italic">Verticillium dahliae</Emphasis> is potentially heterothallic

Verticillium dahliae, a soilborne plant pathogen, causes wilt disease in many important crops. We reported previously that the mating type gene MAT1-2-1 is spread to isolates of this asexual fungus. However, we did not determine whether V. dahliae is homothallic or heterothallic because the opposite mating type gene, MAT1-1-1, had not been identified. In the present study, we identified the MAT1-1-1 gene from an isolate lacking MAT1-2-1 and the mating type idiomorphs of V. dahliae. Each isolate we tested contained either the MAT1-1 or MAT1-2 idiomorph, indicating that the asexual fungus V. dahliae is potentially heterothallic.     

Occurrence of metalaxyl-resistant isolates of Pseudoperonospora cubensis in Israel: a 5-year survey1

The occurrence of metalaxyl-resistant isolates of Pseudoperonospora cubensis, the causal agent of downy mildew in cucurbits, was surveyed during 1980–1984 subsequent to their first appearance in December 1979. Metalaxyl use was abandoned in mid-1981 and resistant isolates diminished in late 1981. Metalaxyl use was renewed in 1982 and a gradual increase in frequency of resistant (R) strains was detected. In 1983, 31 out of 40, and in 1984, 43 out of 47 isolates tested were highly resistant to the fungicide with 65 and 91% of them, respectively, collected from plastic houses or fields not treated with metalaxyl. The survey indicates a rapid build-up of R strains of the fungus and the need for alternative chemicals for combating downy mildew in cucurbits.     

Monitoring physiological races of<Emphasis Type="Italic">Podosphaera xanthii</Emphasis> (syn.<Emphasis Type="Italic">Sphaerotheca fuliginea</Emphasis>), the causal agent of powdery mildew in cucurbits: Factors affecting race identification and the importance for research and commerce

Identification of the physiological races ofPodosphaera xanthii (syn.Sphaerotheca fuliginea), the causal agent of powdery mildew in cucurbits, is based upon the differing responses of various melon cultigens to the pathogen. Eight races of the pathogen have been identified to date in the USA, Africa, Europe and around the Mediterranean Sea, and four new races were reported from greenhouse melons in the major growing area of Japan. Plant responses to powdery mildew may be affected by environmental factors such as light intensity, temperature and humidity, as well as by age and nutritional status of the plants. The same factors affect the accuracy and reliability of race identification. In an attempt to overcome those obstacles, the genetic diversity ofP. xanthii was studied using molecular markers. Unfortunately, no correlation was found between DNA polymorphism and the race of the pathogen as identified by biological tests. The usefulness of race identification as a guide for the grower in selecting appropriate cultivars is limited because changes or shifts in the pathogen population are common. Such changes may be found among growing seasons, geographic regions and hosts, and also within a single greenhouse during a single season. On the other hand, race identification is important for basic research and is especially important for the commercial seed industry, which requires accuracy in declaring the type and level of resistance to powdery mildew in its products. http://www.phytoparasitica.org posting March 2, 2004. Contribution from the Agricultural Research Organization. No. 501/04.     

Relationship between the Spray Droplet Density of Two Protectant Fungicides and the Germination of Mycosphaerella fijiensis Ascospores on Banana Leaf Surfaces

The effect of fungicide spray droplet density (droplet cm^-2), droplet size, and proximity of the spray droplet deposit to fungal spores was investigated with Mycosphaerella fijiensis ascospores on the banana (Musa AAA) leaf surface for two contact fungicides: chlorothalonil and mancozeb. When droplet size was maintained at a volume median diameter (VMD) of 250 μm while total spray volume per hectare changed, M. fijiensis ascospore germination on the leaf surface fell below 1% for both fungicides at a droplet deposit density of 30 droplet cm^-2. At a droplet deposit density of 50 droplet cm^-2, no ascospores germinated in either fungicide treatment. When both droplet size and droplet cm^-2 varied while spray volume was fixed at 20 litre ha^-1, ascospore germination reached 0% at 10 droplet cm^-2 (VMD=602 μm) for both fungicides. At lower droplet densities (2–5 droplet cm^-2 VMD=989 μm and 804 μm respectively), ascospore germination on the mancozeb-treated leaves was significantly lower than on the chlorothalonil-treated leaves. The zone of inhibition surrounding a fungicide droplet deposit (VMD=250 μm) on the leaf surface was estimated to extend 1·02 mm beyond the visible edge of the spray droplet deposit for chlorothalonil and 1·29 mm for mancozeb. The efficacy of fungicide spray droplet deposit densities which are lower than currently recommended for low-volume, aerial applications of protectant fungicides was confirmed in an analysis of leaf samples recovered after commercial applications in a banana plantation. Calibrating agricultural spray aircraft to deliver fungicide spray droplets with a mean droplet deposit density of 30 droplet cm^-2 and a VMD between 300 and 400 μm will probably reduce spray drift, increase deposition efficiency on crop foliage, and enhance disease control compared to aircraft calibrated to spray finer droplets. © 1997 SCI.     

Atmospheric moisture influences on conidia development in Podosphaera xanthii through host-plant morphological responses

This study investigated the effects of atmospheric moisture on conidia development in cucurbit powdery mildew fungus (Podosphaera xanthii) through host-plant responses. Cucumber (Cucumis sativus L.) seedlings were grown under a high vapour pressure deficit (VPD) (3.8 kPa) or a low VPD (0.4 kPa). When the cotyledons had expanded, spores of P. xanthii were inoculated onto the adaxial surface. Inoculated seedlings for both treatments were then placed in a growth chamber maintained at a VPD of 2.1 kPa. The density of visible P. xanthii colonies on the high-VPD-acclimated cotyledons was 0.46 to 0.85 times that of the low-VPD-acclimated cotyledons 7 days after inoculation. It is likely the post-germination behaviour of P. xanthii such as the infection and consequent hyphal development was affected because spore germination did not differ between the treatments. The percentage of adaxial epidermal leaf cells with haustoria was also lower in the seedlings which had acclimated to a higher VPD. The high-VPD-acclimated cotyledons were thicker and had greater dry mass per area. The water potential of cotyledons did not differ between the treatments, although the stomatal conductance of high-VPD-acclimated cotyledons was lower than that of low-VPD-acclimated cotyledons. From these results, we conclude that the inhibition of P. xanthii conidia development on high-VPD-acclimated cotyledons was mainly caused by changes in leaf morphological properties.     

Resistance to acylalanines in Pseudoperonospora cubensis1

Resistance to acylalanine fungicides in Pseudoperonospora cubensis, the downy mildew of cucurbits, is reviewed. Insensitive strains of the fungus predominated during the second year of metalaxyl application in cucumber glasshouses in Greece and Israel. Resistance was detected either on detached cucumber leaves floated on metalaxyl solutions or on potted plants treated (sprayed or drenched) with this fungicide. Metalaxyl-resistant strains of P. cubensis showed good pathogenicity and fitness, and competed favorably with the sensitive strains in the absence of the fungicide. A synergism between these two biotypes resulted in an increased virulence of the resistant forms on metalaxyl-treated plants. Metalaxyl-resistant strains of the pathogen exhibited cross resistance to other acylalanine fungicides. Strains resistant to acylalanines and to the chemically unrelated oomycete-fungicides fosetyl-Al and propamocarb were isolated in Israel, as well. In Greece, however, protective sprays with fosetyl-Al, cymoxanil and mancozeb gave good control of cucumber downy mildew when the pathogen was resistant to metalaxyl. P. cubensis is the first case of fungus which developed resistance to acylalanines in the field.     

Defining the resistance risk of the new powdery mildew fungicide quinoxyfen

The new powdery mildew fungicide quinoxyfen belongs to the novel quinoline class of chemistry. Although its biochemical mode of action is unknown, quinoxyfen does not act in the same way as other cereal fungicides. It is a systemic protectant which inhibits the early stages of mildew infection on a wide range of crops, and provides season-long protection from a single early-season spray applied around GS 31. The base-line sensitivity profile of quinoxyfen was defined for barley powdery mildew (Erysiphe graminis f.sp. hordei) from over 340 field isolates collected from different parts of the UK from 1991 onwards. Sensitivities ranged from <0·0001→0·16 mg litre^-1 with a mean of 0·003 mg litre^-1. Current work is extending the base-line sensitivity studies to wheat powdery mildew (E. graminis f.sp. tritici), and includes isolates from European trials, but so far this new data set has shown no differences from barley powdery mildew. Quinoxyfen-resistant mutants were generated in the laboratory, and some similar resistant strains were obtained from treated field crops. These laboratory and field strains were always defective, in some way, for sporulation and, curiously, all required the presence of quinoxyfen for survival in culture. Attempts to generate resistant mutants that sporulated normally were unsuccessful. These studies suggested that the resistance risk for quinoxyfen is low. The recommended anti-resistance strategy accompanying introduction of quinoxyfen avoids seed treatments and late-season applications. Instead, a single early (GS 31) treatment using either pre-formulated mixtures or alternating with a fungicide with different mode of action is recommended. This strategy will be supported by continued monitoring of wheat and barley powdery mildew. ©1997 SCI     

Activity of the New Fungicide Benthiavalicarb Against Plasmopara viticola and its Efficacy in Controlling Downy Mildew in Grapevines

Benthiavalicarb is a new fungicide active against Oomycetes fungal plant pathogens. The present study shows that benthiavalicarb is effective for controlling the Oomycete fungal pathogen Plasmopara viticola, which causes downy mildew in grapevines. The fungicide did not affect zoospore discharge from sporangia of P. viticola, but strongly inhibited zoospore encystment, cystospore germination in vitro and mycelial growth, together with sporangial production in vivo. Benthiavalicarb showed strong prophylactic and local activity in intact plants or detached leaves and low translaminar activity. The compound was not translocated from leaf to leaf in either a acropetal or basipetal direction. Benthiavalicarb applied at 1, 3 and 6 days post-inoculation protected grapevine plants against downy mildew and inhibited sporulation of the pathogen. Similar results were obtained on leaf disks if benthiavalicarb was applied up to 96 h post-inoculation. Benthiavalicarb diminished the sporulation of P. viticola when applied to established disease in the tissue. Benthiavalicarb remained active on leaves for a period up to 28 days. Two foliar applications of benthiavalicarb, 2 weeks apart, to field-grown grapevines inhibited downy mildew development and were as effective as the standard metalaxyl-Cu treatment in controlling the disease. A formulated mixture of benthiavalicarb + Folpet was similar or superior in performance to metalaxyl-Cu and the new strobilurin trifloxystrobin in controlling downy mildew. The effectiveness of benthiavalicarb makes it well suited for integration into a control programme against downy mildew disease in vineyards, and as a component to delay resistance buildup.     

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

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

Resistance levels of cucumber to <Emphasis Type="Italic">Podosphaera xanthii</Emphasis> in a growth chamber are related to haustorial formation and hyphal branching frequency

To clarify relationships between powdery mildew resistance of cucumber and hyphal developmental state of the pathogen, haustorial formation and the hyphal branching frequency were compared among cucumber varieties that differ in resistance levels to powdery mildew pathogen Podosphaera xanthii. Cotyledons of four cultivars were inoculated with P. xanthii. By 2 days after inoculation, secondary haustoria had developed from the first hyphal cell that formed beside the conidium in susceptible cultivars. The fungus on susceptible cultivars also tended to have hyphal branches just after the hyphal cell producing haustoria.     

Behaviour of famoxadone deposits on grape leaves

Famoxadone is a new fungicide developed for the control of crop diseases, including grape downy mildew (Plasmopara viticola). The majority (>90%) of the spray deposit from a famoxadone 500 g kg⁻¹ water‐dispersible granule formation on a grape leaf were found on the leaf surface or associated with epicuticular waxes. A significant fraction of this deposit could not be removed by a water wash, suggesting strong binding to the waxes. Nearly 100% of the spray deposit was still recovered after 12 days of exposure to a dry environment, confirming the good residual properties of the substance. Thirty per cent of the applied active ingredient was lost after exposure to a wet environment, probably via hydrolysis or wash‐off. Studies with radiolabelled famoxadone formulated as a suspension concentrate indicated that redistribution occurred both in dry conditions, via diffusion in the cuticular waxes, and in wet conditions via dissolution in water followed by re‐deposition. No systemic movement of famoxadone was observed within the treated plant. Grape plants treated with famoxadone alone or in mixture with cymoxanil and subjected to up to 50 mm of artificial rain remained well protected against downy mildew infections. Good rain‐fastness was observed even 2 h after fungicide application. Despite low water solubility, famoxadone spray residues on grape leaves were reactivated in surface water sufficiently quickly to prevent infection by P viticola. © 2000 Society of Chemical Industry     

Within‐ and between‐orchard variability in the sensitivity of Venturia inaequalis to myclobutanil,a DMI fungicide,in the UK

BACKGROUND: Myclobutanil, a demethylation inhibitor (DMI) fungicide, is an important fungicide for controlling apple scab and powdery mildew. Overuse of this fungicide has led to establishment of scab isolates with reduced sensitivity to this fungicide in several countries. Experiments were conducted to determine the sensitivity of the causal agent of apple scab, Venturia inaequalis (Cooke) Winter, to myclobutanil in the UK, in order to assess whether there is a relationship between fungal insensitivity and the number of DMI applications, and establishing whether fungal sensitivity varied greatly within an orchard. RESULTS: Reduced sensitivity of V. inaequalis to myclobutanil was positively related linearly to the number of DMI applications. ED₅₀ values ranged from 0.028 to 1.017 mg L^?1 (average = 0.292) for the baseline population, whereas isolates from two other orchards had much greater ED₅₀ values, ranging from 0.085 to 5.213 mg L^?1 (average = 1.852). There was significant variation in fungal sensitivity to myclobutanil among fungal isolates from different locations within a single orchard. CONCLUSIONS: Spatial spread of insensitive isolates of V. inaequalis to myclobutanil is likely to be limited in distance. Conidia may be an important source of primary inoculum. Myclobutanil should still be effective for most field isolates, but its use should be strategically integrated with other groups of fungicides. Copyright © 2009 Society of Chemical Industry     

Efficacy of biocontrol agents and natural compounds against powdery mildew of zucchini

The activity of different types of natural compounds and of two biofungicides based on Bacillus subtilis and Ampelomyces quisqualis alone and in combination with fungicides was tested against powdery mildew of zucchini. The efficacy was compared to the activity of fungicides used alone in four experimental trials carried out in the open field and under greenhouse conditions. The Podosphaera xanthii population used throughout the work was partially resistant to azoxystrobin, whereas it was susceptible to mychlobutanil. Sulphur plus terpenes and mustard oil consistently controlled powdery mildew, followed by mychlobutanil alone or in combination with A. quisqualis. B. subtilis and A. quisqualis when tested alone were partially effective. The combination of azoxystrobin and B. subtilis only delayed the spread of the pathogen.