More years of field trials against Plasmopara viticola in organic viticolture

The organic viticulture assumes a decisive role in the national agricultural sector. More impelling problems in the management of organic vineyards are represented from the plants pathology defence and particularly of Plasmopara viticola containment. Copper represents one of the few usable fungicides in the organic farming and the only effective against downy mildew. With Regulation EC n. 473/2002, fixed maximum quantity usable of copper compounds, owing to the environment problems due to the copper accumulation in the soil. To reduce quantity of metal copper or replace it with natural products, are conducted field trials with copper compounds at a low rate or alternative to copper products. Besides, we are estimating possibility to reduce the operations against P. viticola optimizing fungicidal treatments. Field trials in the organic farms located near Rome, have been carried out. Guidelines EPPO/OEPP PP 1/31 (3) have been carried out. The results of the trials have showed that, using cupric products with low metallic content, to reduce copper quantities used, always allowed to respect the limits established by Regulation EC. The alternative products that were investigated have not guaranteed, instead, an adequate protection in high pressure of grapevine downy mildew. It was possible to reduce treatments against P. viticola through control of different environmental parameters. The trials confirm that the copper is indispensable for plant protection in organic farming as it is not possible to replace it with natural extracts substances. We can reduce, instead, the copper quantities used trough the use of new products with low quantity metal copper or through the evaluation of climatic and pedologic data that allow to rationalize the fungicidal treatments.     

Natural products alone or with copper vs. grape downy mildew: efficacy, costs, Cu impact

In organic farming copper is one of the few fungicides that can be used and the only effective against downy mildew. Due to the problems of environmental impact associated with the use of this heavy metal, the European Union decided to restrict its use (Annex II Regulation EC n. 889/2008). In order to assess the possibility of replacing the copper or reduce the quantities used, we tested natural products and low rate copper formulations in field trials. The anti-downy mildew activity of these formulations has been studied in an organic vineyard. During the two years of activity we also estimated the economic cost of use of the products to assess their possible use in agricultural practice.     

寡雄腐霉施用时期对设施黄瓜霜霉病的防治试验

寡雄腐霉是一种对多种植物病害有很好防治效果的新型生物农药。本文通过田间试验明确了寡雄腐霉在黄瓜霜霉病不同发病时期使用时的防治效果。结果表明,寡雄腐霉对黄瓜霜霉病预防效果达到68.9%,发病初期防治效果达到61.9%,发病后期防治效果只有23.5%。因此,在使用寡雄腐霉防治黄瓜霜霉病时一定要在未发病或发病早期使用才能达到理想的防病效果。     

Pearl millet downy mildew as affected by integrating seed dressing,sowing date and cultivar

The effects of seed dressing, sowing date and cultivar on incidence and severity of downy mildew of pearl millet induced by Sclerospora graminicola and yield were studied in a two-year field trial conducted at the Research farm of University of Maiduguri. The millet cultivars, Ex-Borno, SOSAT-C88, GB 8735 and Gwagwa were each dressed with metalaxyl at 0.75 and 1.50 g a.i./kg seed; and a batch of undressed seeds of each cultivar served as control. Both dressed and undressed seeds were used for dry-planting and wet-planting in early and late seasons. The results showed that seed dressing with the fungicides significantly (p ≤ 0.05) reduced the incidence and severity of downy mildew and increased grain yield. Dry-planting also significantly (p ≤ 0.01) increased grain yield irrespective of disease incidence. Delay in sowing led to a significant reduction in incidence and severity of downy mildew. Differences between the cultivars in relation to incidence and severity of downy mildew and grain yield were significant. SOSAT-C88 developed low or no downy mildew in both seasons. Sowing of dressed SOSAT-C88 as soon as rainfall established appeared most beneficial in the control of downy mildew. Dry- or wet-planting Ex-Borno dressed with any of the metalaxyl formulations proved to be effective for downy mildew management and for high yield.     

The efficacy of spraying programmes and treatment methods against downy mildew in two grapevine cultivars in Kosovo

The present study aimed to assess the efficacy of applied programmes and treatment methods against downy mildew (Plasmopara viticola). Two vine cultivars (Frankovka and Game) were tested in an experimental field (in Rahovec, Kosovo) for a two-year period (2010–2011). The fungicides used were Quadris (azoxystrobin), Antracol EP-70 (propineb), Dithan M-45 (mancozeb), Ridomil (metalaxyl), Curzate (cymoxanil), Bordeaux mixture (calcium hydroxide and copper sulphate) and Mikal (fosetyl-aluminium) applied three treatment methods. The evaluation of the disease severity was performed using the McKinney index. In both tested cultivars and in both treatment years (2010 and 2011), all of the programmes tested significantly reduced the severity of grape downy mildew compared to the control. The highest efficacy against grape downy mildew was achieved with the combined use of Ridomil and Dithan (programme 3); this treatment was more than 80% effective in both cultivars and in both years.     

Preliminary experiments on the use of oil-soluble copper compounds as fungicides

Tests were made of the solubility of a number of copper compounds in mineral and vegetable oils. Phytocidal tests on onion foliage showed that turpentine, pine oil and white spirit were damaging whereas cottonseed oil and white oil were innocuous. Copper salts in white oil, white spirit, turpentine or pine oil showed a higher fungicidal value than in cottonseed oil. In laboratory tests, a solution of copper 3:5-di- iso propyl salicylate was more fungicidal than Bordeaux mixture of the same copper concentration. In a small field trial, copper 3:5-di- ios propyl salicylate dissolved in white oil to give a concentration of 0.01% Cu was atomized three times at monthly intervals on to onion foliage without damage. The same material at 0.1% Cu in white oil was phytocidal. No control of onion downy mildew ( Peronospora schleideniana ) was obtained in this trial. The method of atomization was convenient and practicable for small-scale operation. It gave perfect wetting of the foliage and was very economical of material.     

Grape downy mildew spread and mite seasonal abundance in vineyards: effects on Tydeus caudatus and its predators

Tydeus caudatus (Acari: Tydeidae) can prey upon grape eriophyoid mites but little is known about its alternative foods. Observations carried out during 1999–2003 in a commercial vineyard located in northeastern Italy showed that densities of T. caudatus were often correlated to downy mildew spread on the vegetation. Densities of T. caudatus increased in late summer when downy mildew symptoms occurred on a high number of leaves. The predatory mite Paraseiulus talbii (Acari: Phytoseiidae) increased in late season following the increase of tydeids. On several sampling dates, T. caudatus populations were significantly higher on leaves with downy mildew symptoms than on leaves without symptoms. Tydeid densities were often positively correlated to the extent of leaf surface showing symptoms. These relationships were sometimes found regarding P. talbii. In two experimental vineyards colonised by T. caudatus, untreated plots or plots treated with different fungicides to control downy mildew were monitored during 2002. Downy mildew infections rapidly spread in the control plots while they were effectively controlled on fungicide-treated plots. In both vineyards, T. caudatus densities reached significantly higher densities in the control than on fungicide-treated plots. A field study showed that most of these fungicides did not reduce tydeid populations when downy mildew was virtually absent. Isoelectric-focusing electrophoresis (IEF) was used to detect downy mildew in mites. Glucose phosphate isomerase (GPI) was selected from among different enzymes. A high proportion of T. caudatus females, collected from infected leaves, and analysed under IEF showed a GPI isozyme allele corresponding to the downy mildew isozyme in addition to the tydeid intrinsic alleles. This phenomenon was also observed for P. talbii but with a lower incidence. All T. caudatus females confined on symptomatic leaves became positive by IEF after few hours but the same did not occur with P. talbii. A high proportion of P. talbii females became positive after preying on tydeids collected from symptomatic leaves or reared on pollen and then confined on symptomatic leaves.     

The effect of fungicides, irrigation and plant density on the development of Peronospora sparsa, the cause of downy mildew in rose and blackberry

Downy mildew of rose (Rosa spp.) and blackberry (Rubus fructicosus), caused by Peronospora sparsa, can cause significant losses in production. In a series of experiments, fungicides with different modes of action to the commonly used phenylamide‐based products were examined for efficacy on both crops. Cymoxanil + mancozeb + oxadixyl and fluazinam gave good downy mildew control on both rose and blackberry. On outdoor, container‐grown rose, high volume sprays of fosetyl‐aluminium were also effective, but on young micropropagated blackberry plants, application as a drench treatment was better than as a spray. Good control was also achieved on blackberry with chlorothalonil and with metalaxyl in formulation with either thiram or mancozeb. There was no evidence of loss of control with phenylamide fungicides due to resistance. Irrigation regimes were also examined on blackberry and sub‐irrigation of plants in propagation on a sand bed led to significantly lower disease levels than those found where plants had been irrigated by overhead sprinklers. Reducing the density of container‐grown rose plants had a measurable effect on the progress of downy mildew, though this was small and temporary when compared with the effect of fungicide treatment. Fungicide programmes which gave season‐long control of rose downy mildew resulted in significantly improved extension growth.     

Identification of QTLs conferring resistance to downy mildews of maize in Asia

Downy mildew is one of the most destructive diseases of maize in subtropical and tropical regions in Asia. As a prerequisite for improving downy mildew resistance in maize, we analyzed quantitative trait loci (QTLs) involved in resistance to the important downy mildew pathogens--Peronosclerospora sorghi (sorghum downy mildew) and P. heteropogoni (Rajasthan downy mildew) in India, P. maydis (Java downy mildew) in Indonesia, P. zeae in Thailand and P. philippinensis in the Philippines--using a recombinant inbred line population derived from a cross between Ki3 (downy mildew resistant) and CML139 (susceptible). Resistance was evaluated as percentage disease incidence in replicated field trials at five downy mildew 'hotspots' in the four countries. Heritability estimates of individual environments ranged from 0.58 to 0.75 with an across environment heritability of 0.50. Composite interval mapping was applied for QTL detection using a previously constructed restriction fragment length polymorphism linkage map. The investigation resulted in the identification of six genomic regions on chromosomes 1, 2, 6, 7 and 10 involved in the resistance to the downy mildews under study, explaining, in total, 26-57% of the phenotypic variance for disease response. Most QTL alleles conferring resistance to the downy mildews were from Ki3. All QTLs showed significant QTL x environment interactions, suggesting that the expression of the QTL may be environment-dependent. A strong QTL on chromosome 6 was stable across environments, significantly affecting disease resistance at the five locations in four Asian countries. Simple-sequence repeat markers tightly linked to this QTL were identified for potential use in marker-assisted selection.     

Seed treatment with aqueous extract of Viscum album induces resistance to pearl millet downy mildew pathogen

Abstract

Downy mildew (Sclerospora graminicola [Sacc.] Schroet.) is a serious agricultural problem for pearl millet (Pennisetum glaucum [L.] R. Br.) grain production under field conditions. Six medicinally important plant species Azadirachta indica, Argemone mexicana, Commiphora caudata, Mentha piperita, Emblica officinalis and Viscum album were evaluated for their efficacy against pearl millet downy mildew. Seeds of pearl millet were treated with different concentrations of aqueous extract of the plants to examine their efficacy in controlling downy mildew. Among the plant extracts tested, V. album treatment was found to be more effective in enhancing seed quality parameters and also in inducing resistance against downy mildew disease. Germination and seedling vigor was improved in seeds treated with V. album extracts over control. Seeds treated with 10% concentration of V. album showed maximum protection against downy mildew disease under greenhouse and field conditions. The downy mildew disease protection varied from 44–70% with different concentrations. Leaf extract of V. album did not inhibit sporulation and zoospore release from sporangia of Sclerospora graminicola, indicating that the disease-controlling effect was attributed to induced resistance. Seed treatment with V. album extract increased pearl millet grain yield considerably. In V. album, treated pearl millet seedlings increased activities of peroxidase, and phenylalanine ammonia-lyase enzyme was detected. FTIR analysis of V. album extracts showed the presence of amides and other aromatic compounds which are antimicrobial compounds involved in plant defense.     

The cucurbit downy mildew pathogen Pseudoperonospora cubensis

Pseudoperonospora cubensis[(Berkeley & M. A. Curtis) Rostovzev], the causal agent of cucurbit downy mildew, is responsible for devastating losses worldwide of cucumber, cantaloupe, pumpkin, watermelon and squash. Although downy mildew has been a major issue in Europe since the mid-1980s, in the USA, downy mildew on cucumber has been successfully controlled for many years through host resistance. However, since the 2004 growing season, host resistance has been effective no longer and, as a result, the control of downy mildew on cucurbits now requires an intensive fungicide programme. Chemical control is not always feasible because of the high costs associated with fungicides and their application. Moreover, the presence of pathogen populations resistant to commonly used fungicides limits the long-term viability of chemical control. This review summarizes the current knowledge of taxonomy, disease development, virulence, pathogenicity and control of Ps. cubensis. In addition, topics for future research that aim to develop both short- and long-term control measures of cucurbit downy mildew are discussed. TAXONOMY: Kingdom Straminipila; Phylum Oomycota; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; Genus Pseudoperonospora; Species Pseudoperonospora cubensis. DISEASE SYMPTOMS: Angular chlorotic lesions bound by leaf veins on the foliage of cucumber. Symptoms vary on different cucurbit species and varieties, specifically in terms of lesion development, shape and size. Infection of cucurbits by Ps. cubensis impacts fruit yield and overall plant health. INFECTION PROCESS: Sporulation on the underside of leaves results in the production of sporangia that are dispersed by wind. On arrival on a susceptible host, sporangia germinate in free water on the leaf surface, producing biflagellate zoospores that swim to and encyst on stomata, where they form germ tubes. An appressorium is produced and forms a penetration hypha, which enters the leaf tissue through the stomata. Hyphae grow through the mesophyll and establish haustoria, specialized structures for the transfer of nutrients and signals between host and pathogen. CONTROL: Management of downy mildew in Europe requires the use of tolerant cucurbit cultivars in conjunction with fungicide applications. In the USA, an aggressive fungicide programme, with sprays every 5-7 days for cucumber and every 7-10 days for other cucurbits, has been necessary to control outbreaks and to prevent crop loss. USEFUL WEBSITES: http://www.daylab.plp.msu.edu/pseudoperonospora-cubensis/ (Day Laboratory website with research advances in downy mildew); http://veggies.msu.edu/ (Hausbeck Laboratory website with downy mildew news for growers); http://cdm.ipmpipe.org/ (Cucurbit downy mildew forecasting homepage); http://ipm.msu.edu/downymildew.htm (Downy mildew information for Michigan's vegetable growers).     

THE FUNGICIDAL CONTROL OF LETTUCE DOWNY MILDEW, CAUSED BY BREMIA LACTUCAE

Protection experiments carried out in the greenhouse showed that preparations of thiram, zineb, ferbam and ziram were superior to cuprous oxide and copper oxy-chloride preparations, in controlling downy mildew of lettuce and in lack of phytotoxic effect.
Tests made in winter on lettuce seedlings grown in Dutch lights, showed that Bremia lactucae attack reduced the stand of seedlings, diminished their size and weight, and, when the crop was planted out into the open ground, reduced survival in the field and slightly delayed the date of reaching maturity. The best overall results in protecting foliage against downy mildew were given by thiram and zineb preparations.     

Occurrence of downy mildews on ornamental plants and their control by chemical compounds

The downy mildew on Coreopsis grandiflora caused by Plasmopara halstedii was observed during summer, mainly in July and August. Symptoms of the disease were first seen on external leaves and progressively spread to inner parts of plant rosette. On Alyssum saxatile downy mildew symptoms induced by Peronospora parasitica were observed during whole vegetation period with the strongest expression in early spring and late summer. Amistar 250 SC (25% azoxystrobine), Mildex 711,9 WG (66.7% phosethyl aluminium + 4.4% fenamidone), Previcur Energy 840 SL (530 g/l propamocarb + 310 g/l phosetyl aluminium) and Tanos 50 WG (25% cymoxanil + 25% famoxate) were used for pathogens control. In the protection of Coreopsis grandiflora against P. halstedii all tested compounds, applied curatively, decreased sporulation of the pathogen. On treaded plants at least 4-time less leaves were diseased. In the control of P. parasitica on Alyssum saxatile, the smallest number of swallowed structures on leaves was noticed on plants treated with azoxystrobine at conc. 250 microg/cm3.     

Bioassay‐Guided Isolation of Antifungal Compounds from Disporopsis aspersa (Hua) Engl. ex Diels against Pseudoperonospora cubensis and Phytophthora infestans

Oomycetes are one type of the most highly destructive of the diseases that cause damage to some important crop plants, such as potato late blight, cucumber downy mildew, and grape downy mildew. As main approach of the ongoing search for new botanical fungicide from plant, the secondary metabolites of D. aspersa were investigated. Through efficient bioassay‐guided isolation, two new ( 1 and 2 ) and 12 known compounds ( 3  –  14 ) were isolated, and their structures were determined via extensive NMR, HR‐ESI‐MS, and IR. They were isolated from this genus for the first time except for compounds 11 and 12 . The biological properties of 1  –  14 were evaluated against Pseudoperonospora cubensis and Phytophthora infestans. Compounds 1  –  8 showed potent antifungal activity in vitro. Additionally, compound 3 has preferable control effect on cucumber downy mildew, showing dual effect of protection and treatment in vivo.     

Surfactin and fengycin contribute to the protection of a Bacillus subtilis strain against grape downy mildew by both direct effect and defence stimulation

Bacillus subtilis GLB191 (hereafter GLB191) is an efficient biological control agent against the biotrophic oomycete Plasmopara viticola, the causal agent of grapevine downy mildew. In this study, we show that GLB191 supernatant is also highly active against downy mildew and that the activity results from both direct effect against the pathogen and stimulation of the plant defences (induction of defence gene expression and callose production). High-performance thin-layer chromatography analysis revealed the presence of the cyclic lipopeptides fengycin and surfactin in the supernatant. Mutants affected in the production of fengycin and/or surfactin were thus obtained and allowed us to show that both surfactin and fengycin contribute to the double activity of GLB191 supernatant against downy mildew. Altogether, this study suggests that GLB191 supernatant could be used as a new biocontrol product against grapevine downy mildew.     

Control of pearl millet downy mildew caused by Sclerospora graminicola with systemic fungicides in an artificially-contaminated plot

Among four fungicides, viz. metalaxyl (two formulations), fosetyl-Al, pro-pamocarb and cyomaxanil tested in vitro against sporangial germination inhibition of Sclerospora graminicola, cyomaxanil was found to be most inhibitory. In an artificially contaminated plot, when used as seed treatment or foliar spray for the control of downy mildew of pearl millet, only metalaxyl was effective. Metalaxyl 25 (Ridomil) and metalaxyl 35 (Apron) seed treatments protected the pearl millet plants from downy mildew up to 30 days. As a foliar spray, metalaxyl 25 used once at 20 days or twice after 20 and 38 days of plant growth gave less disease at harvest time. Seed treatment (metalaxyl 25 or 35) followed by one metalaxyl 25 spray was found to be effective in controlling the downy mildew. These treatments improved the growth of plants and yield significantly.     

Screening and evaluation of resistance to downy mildew (Peronospora parasitica) and clubroot (Plasmodiophora brassicae) in genetic resources of Brassica oleracea

52 entries including landraces, old cultivars and wild accessions of B. oleracea and closely related Brassica species were screened for resistance against downy mildew and clubroot. Several accessions resistant to downy mildew and a few to clubroot were found. Genetic inheritance of the resistance in downy mildew was investigated by screening F1 and BC1F1 offspring from three resistant landrace accessions crossed with both a resistant and a susceptible father. The seedling resistance against downy mildew was found to be inherited recessively. This is a bit surprising as earlier papers mostly report of inheritance controlled by a single dominant gene. Previous screenings of B. oleracea resistance against downy mildew at the cotyledon stage have been done with P. parasitica isolated from B. oleracea as the original host plant. The recessive nature of the cotyledon resistance found in this screening might be due to the fact that the P. parasitica isolate was collected from B. napus fields. The clubroot seedling resistance was found to be controlled by recessive inheritance after screening the F1 offspring, this in agreement with earlier results/reports.     

Phyllosphere and rhizosphere microflora of pearl millet with reference to downy mildew incited bySclerospora graminicola (Sacc.) Schroet

Summary Analysis of phyllosphere microflora showed that in the resistant cultivar (PHB-14) there was a significantly higher population of fungi, gram positive and gram negative bacteria, compared to susceptible cultivar (NHB-3) under healthy and diseased situations. The cultivars during earhead stage supported maximum phyllosphere fungal and gram negative bacterial populations.The rhizosphere of the susceptible cultivar under downy mildew influence supported maximum fungal and gram negative bacterial populations and the rhizosphere effect was the highest in downy mildew colonized susceptible NHB-3 at the earhead stage (95 days after planting).Among the fungi isolated Cladosporium dominated the phyllosphere of resistant, susceptible and susceptible cultivar under the influence of downy mildew.Among the rhizosphere microflora the population ofAspergillus sp. was found to be greatest in resistant, susceptible and the susceptible cultivar under the influence of downy mildew.     

Basic compatibility of Albugo candida in Arabidopsis thaliana and Brassica juncea causes broad-spectrum suppression of innate immunity

A biotrophic parasite often depends on an intrinsic ability to suppress host defenses in a manner that will enable it to infect and successfully colonize a susceptible host. If the suppressed defenses otherwise would have been effective against alternative pathogens, it follows that primary infection by the "suppressive" biotroph potentially could enhance susceptibility of the host to secondary infection by avirulent pathogens. This phenomenon previously has been attributed to true fungi such as rust (basidiomycete) and powdery mildew (ascomycete) pathogens. In our study, we observed broad-spectrum suppression of host defense by the oomycete Albugo candida (white blister rust) in the wild crucifer Arabidopsis thaliana and a domesticated relative, Brassica juncea. A. candida subsp. arabidopsis suppressed the "runaway cell death" phenotype of the lesion mimic mutant lsd1 in Arabidopsis thaliana in a sustained manner even after subsequent inoculation with avirulent Hyaloperonospora arabidopsis (Arabidopsis thaliana downy mildew). In sequential inoculation experiments, we show that preinfection by virulent Albugo candida can suppress disease resistance in cotyledons to several downy mildew pathogens, including contrasting examples of genotype resistance to H. arabidopsis in Arabidopsis thaliana that differ in the R protein and modes of defense signaling used to confer the resistance; genotype specific resistance in B. juncea to H. parasitica (Brassica downy mildew; isolates derived from B. juncea); species level (nonhost) resistance in both crucifers to Bremia lactucae (lettuce downy mildew) and an isolate of the H. parasitica race derived from Brassica oleracea; and nonhost resistance in B. juncea to H. arabidopsis. Broad-spectrum powdery mildew resistance conferred by RPW8 also was suppressed in Arabidopsis thaliana to two morphotypes of Erysiphe spp. following pre-infection with A. candida subsp. arabidopsis.     

Enhancement of downy mildew of sorghum by some organic soil amendments: a caution to organic farmers

Matured botanical compost of Croton sparsiflorus and Azadirachta indica were evaluated for promotion of sorghum downy mildew at the rate of 0.5% (w/w). Exceptionally high promotional rates of 26.9% (C. sparsiflorus) and 30.1% (A. indica) were observed as compared to negative control (8.8%). The enhancement of disease was higher than that obtained by the supply of recommended dose of urea (13.3%). As the pathogen (Peronosclerospora sorghi) is a biotroph and cannot multiply by using organics as nutrient source in the absence of a host, the mechanism of disease enhancement is inferred to be through stimulation of oospore germination by organic compounds.