Pre-inoculation with Hyaloperonospora parasitica reduces incubation period and increases severity of disease caused by Albugo candida in a Brassica juncea variety resistant to downy mildew

Studies were undertaken to determine any interaction of an asymptomatic isolate of Hyaloperonospora parasitica (downy mildew) with a virulent isolate of Albugo candida (white rust) and Brassica juncea. White rust symptoms appeared 4 days earlier and were significantly more severe when a variety of B. juncea resistant to downy mildew but highly susceptible to white rust was first inoculated with A. candida followed 10 days later with H. parasitica. DNA extractions of tissues indicated H. parasitica had colonized the asymptomatic plants systemically. These are the first reports of (a) the systemic colonization by H. parasitica in a host resistant to downy mildew, and (b) the increase in susceptibility of a Brassica to white rust disease from asymptomatic colonization by H. parasitica.     

Some factors affecting the activities of dinitrophenol fungicides

The vapour phase and protectant activities of members of seven homologous series of alkyldinitrophenols against cucumber powdery mildew (Oidium sp.) are discussed. No correlation existed between vapour activities in vitro or in vivo and vapour pressure, but a positive correlation between Vapour' protection in vivo and conventional protectant activity was evident. Although vapour activity occurs with some homologues, results obtained for zone assays in vivo are probably better explained in terms of easy movement of the compound in the leaf surface than in terms of vapour transmission. Alkyldinitrophenyl-crotonates showed no zone activity in vivo but often good protectant activity. The possible existence of two optimum π-values for protectant activity is suggested. No appreciable systemic activity was found with these compounds.     

Fungicidal activity of substituted quinoxalines

Twenty substituted quinoxalines based on the structure of 6 (or 7)-methyl-3-phenyl-1, 2-dihydroquinoxalin-2-one, a fungicidally active photodegradation product of quinomethionate, were synthesised. Eleven of these compounds had ED₅₀ values, as protectant sprays against Podosphaera leucotricha, of 0.1 mmol or less; these compounds had an aromatic substituent at the 3-position of the quinoxaline ring. They were less active as protectant leaf dips against Erysiphe graminis f. sp. hordei than against Podosphaera leucotricha; none showed any systemic activity as a soil-applied treatment against Podosphaera leucotricha. One compound was more active than quinomethionate as an eradicant spray. In spore germination tests on fungi from different taxonomic groups, the quinoxaline derivatives were active against only one basidiomycete (Uromyces fabae), whereas quinomethionate showed a broad spectrum of activity. The possible significance of this difference in spectrum of activity with respect to the mode of action is discussed.     

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.     

Synergistic interaction between BABA and mancozeb in controlling<Emphasis Type="Italic">Phytophthora infestans</Emphasis> in potato and tomato and<Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis> in cucumber

Spray mixtures consisting of the plant activator BABA (DL-3-aminobutyric acid) and the protectant fungicide mancozeb were significantly more effective than BABA or mancozeb alone in controlling late blight (Phytophthora infestans) in potato and tomato and downy mildew (Pseudoperonospora cubensis) in cucumber. A mixture composed of 5 parts BABA and 1 part mancozeb (w/w, a.i.) exhibited a higher synergy factor than the 1+1 or the 1+5 (BABA + mancozeb) mixtures. No synergistic interaction was detected between BABA plus mancozeb in controlling sporangial or cystospore germination, nor mycelial growth ofP. infestans in vitro. The results showed enhanced effect of mancozeb in BABA-induced plants, suggesting, therefore, that lower dosages of this fungicide may be sufficient to control late blight or downy mildew under field conditions. http://www.phytoparasitica.org posting July 15, 2003.     

Fungitoxicity of bromo- and iodo-3,5-dinitrobenzoates

Esters of 2-bromo-, 4-bromo-, 2-iodo- and 4-iodo- 3,5-dinitrobenzoic acids show considerable antifungal activity in spore germination tests against Alternaria brassicicola, Botrytis cinerea, Septoria nodorum and Uromyces fabae. They act as protectant fungicides against Erysiphe graminis, Puccinia recondita and Septoria nodorum on wheat and Botrytis fabae on broad bean. The most active compounds are methyl and ethyl 4-bromo-3,5-dinitrobenzoates which give better control of wheat rust than oxycarboxin and methyl 4-iodo-3,5-dinitrobenzoate which is at least as effective as captan against Septoria leaf spot on wheat. Several of the esters are superior to captan in controlling chocolate spot on broad bean.     

樟树枝叶提取物防治葡萄霜霉病的效果

为明确樟树枝叶提取物对葡萄霜霉病的防治效果,采用混合液滴显微镜观察法研究了樟树枝叶提取物及其活性成分对病原菌孢子囊萌发的抑制作用,利用高效液相色谱法鉴定了枝叶乙酸乙酯萃取物的化学成分,测定了其活性成分对葡萄霜霉病的室内和田间防治效果。结果表明,浓度为0.1 g/mL以上的樟树枝叶提取物对孢子囊萌发均有很好的抑制效果,抑制率达100.0%;樟树枝叶提取物经不同极性有机溶剂萃取后,分别获得正己烷、乙酸乙酯、正丁醇和水相分离物,浓度为1.0%时各分离物对孢子囊萌发的抑制率分别为58.4%、92.4%、32.5%和58.7%,乙酸乙酯相富集了主要抑菌活性成分,经液相色谱分析并与色谱库数据比对,确定其活性成分中含有芦丁和槲皮素;浓度为1.0%的芦丁和槲皮素对孢子囊具有抑制作用;田间试验显示,浓度为0.3 g/mL以上的枝叶提取物对葡萄霜霉病预防效果显著,治疗效果在60.0%以上。研究表明,樟树枝叶提取物可以有效控制葡萄霜霉病,提取物的活性成分芦丁和槲皮素可以作为植物源药剂。     

Synthesis of some 3-phenyl-1-substituted(or 1,1- disubstituted)prop-2-yn-1-ols and their in-vivo activity against some phytopathogenic fungi

Thirty-two 3-phenyl-1-monosubstituted(or 1, 1-disubstituted)prop-2-yn-1-ols, mostly with heterocyclic substituents, and four derivatives, were synthesised and tested in vivo against eight fungal plant pathogens of different taxonomic classes. No compound showed a wide spectrum of activity, however, nine of them were effective against Sphaerotheca fuliginea on Cucumis sativus, both in direct protectant tests and in systemic protectant tests by root application.     

Leaf position,leaf age and plant age affect the expression of downy mildew resistance in <Emphasis Type="Italic">Brassica oleracea</Emphasis>

Downy mildew caused by the oomycete Hyaloperonospora parasitica (formerly Peronospora parasitica) is a worldwide foliar disease of Brassica vegetables, which may cause seedling loss in the nurseries and damage to adult plants in the field. Disease symptoms start from the lower leaves and progress upwards. Three experiments were conducted under controlled environment conditions, using inoculated leaf discs, to determine the influence of leaf position, plant age, and leaf age on the expression of resistance to downy mildew in various Brassica oleracea genotypes. The upper leaves were more resistant than the lower leaves when 7–19 week-old plants of broccoli and Tronchuda cabbage were tested. Broccoli lines ‘PCB21.32’ and ‘OL87123-2’ were fully susceptible at the cotyledon stage, showed a clear resistance increase from lower to upper leaves at 6 weeks and ‘PCB21.32’ was fully resistant 16 weeks after sowing. Immature leaves were more resistant than adjacent fully expanded mature leaves. Susceptibility increased with leaf age when the same leaf was tested at two to 4-week intervals. Leaf age and upper-leaf position on the stem had opposite effects on disease score, since younger leaves collected from lower positions and older leaves collected from upper positions tended to score similarly in compatible interactions. The progression of downy mildew from the base of the plant upwards on B. oleracea in the field could be due to differences in leaf resistance in addition to environmental variation. To maximise the expression of a compatible reaction in adult plants lower leaves of Brassica plants that are at least 12 weeks-old should be used.     

暗黑链霉菌PY-1活性产物分析及其对葡萄霜霉病田间防效评价

为探究暗黑链霉菌Streptomyces atratus PY-1对葡萄霜霉病菌Plasomopara viticola的抑制作用,通过扫描电镜观察PY-1发酵滤液对葡萄霜霉病菌孢子囊的影响,检测PY-1的活性物质种类,并测定其对葡萄霜霉病的田间防效。结果表明,PY-1发酵滤液能够导致葡萄霜霉病菌孢子囊和孢子囊梗出现褶皱、破裂和畸形,进而使其丧失侵染功能。PY-1菌株代谢产物中包含几丁质酶、蛋白酶、嗜铁素、1-氨基环丙烷-1-羧酸脱氨酶、氰化氢、吲哚乙酸,不含纤维素酶。PY-1菌株对葡萄霜霉病具有较好的田间防效,发酵原液对葡萄霜霉病的田间中期防效可达到89.17%以上,末期防效达86.28%以上,比52.5%噁唑菌酮·霜脲氰2 000倍液的防效略低,但显著高于58%甲霜·锰锌1 000倍液的防效;PY-1菌株发酵液稀释700倍后对葡萄霜霉病的末期防效与甲霜锰锌1 000倍液防效相当。表明PY-1菌株具有研制防治葡萄霜霉病生防制剂的潜力。     

Design, synthesis and structure-activity relationship of novel coumarin derivatives

BACKGROUND: The lead coumarin derivative (E)‐methyl 3‐methoxy‐2‐[2‐(4‐methylcoumarin‐7‐yloxymethyl)phenyl]acrylate was discovered by using an intermediate derivatisation method. To discover new coumarin derivatives with improved activity, a series of substituted coumarins were synthesised and bioassayed. RESULTS: The compounds were identified by ¹H NMR, IR, MS and elemental analysis. Bioassays demonstrated that some of the title compounds exhibited excellent fungicidal activity against cucumber downy mildew at 25 mg L^?1. The relationship between structure and fungicidal activity is reported. CONCLUSION: The present work demonstrates that coumarin derivatives containing methoxyacrylate moieties can be used as possible lead compounds for developing novel fungicides. Copyright © 2011 Society of Chemical Industry     

Unsaturated fatty acids from zoospores of <Emphasis Type="Italic">Sclerospora graminicola</Emphasis> induce resistance in pearl millet

Downy mildew of pearl millet, caused by Sclerospora graminicola, is a devastating disease, resulting in high economic losses in the semi-arid regions of the world. Recently, induction of host plant resistance using biotic and abiotic inducers are included among disease management practices as an eco-friendly approach. Unsaturated fatty acids are considered as a new generation of plant disease resistance inducers. In the present study, six unsaturated fatty acids, viz. docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), arachidonic acid (AA), linolenic acid, linoleic acid and oleic acid, all originally detected in the zoospores of S. graminicola,were applied to seeds of susceptible cultivars of pearl millet to examine their ability to protect against downy mildew under greenhouse and field conditions. In greenhouse experiments, EPA and AA induced a maximum of 78.6% and 76.5% protection, whereas linoleic acid, DHA and linolenic acid provided up to 66.3%, 61.2% and 24.5% protection, respectively. Oleic acid was not effective in protecting pearl millet (only 5.1% protection). A time interval of four days between treatment of seeds and challenge inoculation was required to obtain optimum protection. Plants raised from treated seeds and challenge inoculated at the tillering and inflorescence stages showed enhanced resistance, resulting in higher grain yield compared to untreated plants of the same cultivar. Chitinase activity was found to be higher in susceptible seedlings of pearl millet after treatment with the fatty acids and pathogen inoculation than in seedlings only inoculated with the pathogen. This indicates that host defence responses are activated and thus that induced resistance is involved in the protection observed. The role of unsaturated fatty acids as activators of resistance against downy mildew in pearl millet is discussed.     

Genetics of resistance to downy mildew in Brassica oleracea and breeding towards durable disease control for UK vegetable production

Downy mildew resistance was previously identified from screening a Brassica oleracea collection against two standard UK isolates of Hyaloperonospora parasitica. Sources of resistance were chosen from this material and developed further in this study by generating doubled haploid (DH) and inbred lines. Seedlings from the new lines were tested for resistance to a larger collection of H. parasitica isolates collected in 2001–2002 and 2007–2008 from the main broccoli and cauliflower production regions of the UK. Three lines (derived from borecole or summer cabbage) were broadly resistant to the pathogen isolates. Three of the remaining lines exhibited strong isolate‐specific resistance; several examples of weak or basal level of resistance to some isolates were observed. A new H. parasitica variant collected in 2008 was virulent in the broadly resistant lines, but was avirulent in a line with narrow specificity of resistance. The F₂ and BC₁ seedlings derived from outcrossing each of the three broadly resistant lines to susceptible broccoli and cauliflower lines segregated in a manner indicating that the resistance was controlled by a single dominant gene. No susceptibility was observed amongst F₂ seedlings derived from intercrossing the three resistant lines, indicating that they all share the same or closely linked broad‐spectrum resistance gene(s). DH lines were produced from F₁ plants, and resistant plants were further backcrossed to produce broccoli and cauliflower‐like lines that could be useful pre‐breeding material. A combination of resistance from lines with broad and narrow specificity is recommended for controlling downy mildew in UK brassica production.     

Protection of Brassica seedlings against downy mildew and damping-off by seed treatment with CGA 245704, an activator of systemic acquired resistance

Control of seedling diseases is a major priority in many crop systems. Seed treatments that induce systemic resistance after seedling emergence may be an ideal way to provide protection against disease during the establishment of the crop. CGA 245704, a chemical activator of systemic acquired resistance, was tested as a seed treatment against two Brassica diseases with contrasting infection biologies, the airborne downy mildew pathogen, Peronospora parasitica, and the soilborne fungus, Rhizoctonia solani. Seeds of two Brassica spp. were either imbibed with various concentrations of the compound or imbibed and then dried. Both the imbibition treatment alone and the imbibition treatment followed by seed drying had a significant effect on the sporulation intensity of P. parasitica for all concentrations of the compound used, whereas the imbibition treatment provided some control of damping-off caused by R. solani, with the degree of control being highly dependent on the concentration applied to the seed. Seed treatment with the plant activator CGA 245704 might therefore simultaneously control several seedling diseases, thereby providing a novel option for management of these diseases. © 1998 SCI.     

Chitosan enhances disease resistance in pearl millet against downy mildew caused by Sclerospora graminicola and defence-related enzyme activation

BACKGROUND: The present study investigated the effect of chitosan seed priming on the induction of disease resistance in pearl millet against downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroet. RESULTS: Pearl millet seeds were primed with chitosan at different concentrations: 0.5, 1.5, 2.5 and 3 g kg^?1 seed. Of the different concentrations, 2.5 g kg^?1 was found to be optimum, with enhanced seed germination of 99% and seedling vigour of 1782, whereas the untreated control recorded values of 87% and 1465 respectively. At optimum concentration, chitosan did not inhibit sporulation and release of zoospores from sporangia. Furthermore, pearl millet seedlings raised after seed treatment with chitosan showed an increased level of the defence‐related enzymes chitosanase and peroxidase as compared with the untreated pearl millet seedlings on downy mildew pathogen inoculation. The effect of chitosan in reducing downy mildew incidence was evaluated in both greenhouse and field conditions, in which respectively 79.08 and 75.8% disease protection was obtained. CONCLUSION: Chitosan was effective in protecting pearl millet plants against downy mildew under both greenhouse and field conditions by inducing resistance against the pathogen. Thus, chitosan formulation can be recommended for seed treatment in the management of downy mildew disease. Copyright © 2008 Society of Chemical Industry     

The use of rainfall and accumulated mean temperature to indicate fungicide activity in the control of leaf diseases of winter wheat in the UK1

During 1988/1990, a series of 21 experiments was established in commercial crops of winter wheat. Chlorothalonil, fenpropimorph and propiconazole were chosen as protectant, eradicant or curative fungicides active against leaf diseases of winter wheat in the UK. To test their properties each one was applied once only to separate plots during a period of 7–8 consecutive weeks in May and June (GS 32–39). Disease progress was assessed weekly on adjacent unsprayed control and sprayed plots up to GS 85. Septoria tritici leaf blotch (Mycosphaerella graminicola) was the disease that occurred most frequently and severely across the 21 sites. Powdery mildew (Erysiphe graminis), brown rust (Puccinia recondita) and yellow rust (P. striiformis) occurred at fewer sites and were sufficiently severe to distinguish differences between the active ingredients at only two or three sites. Analysis of the disease progress curves for 75% control of each disease at one site only indicated that chlorothalonil possessed very good protectant but shorter-term eradicant activity against M. graminicola and P. striiformis. Fenpropimorph exhibited only short-term eradicant control of M. graminicola, but gave excellent protectant and eradicant control of E. graminis and P. striiformis; against P. recondita only eradicant activity was apparent. Propiconazole showed activity similar to that of fenpropimorph against P. recondita and excellent protectant and eradicant activity against M. graminicola and P. striiformis; against E. graminis, it gave good protectant and eradicant control. From disease progress curves, it was possible to calculate the period of protectant and eradicant activity in thermal time (accumulated degree days above zero) for each of the three active ingredients and to identify the most effective timing(s) for fungicide application in relation to rainfall or imputed infection.     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.     

Fungicidal activity and chemical constitution. Part XXI: The activity of substituted 1, 4-naphthoquinones and quinoline-5, 8-diones against apple powdery mildew

Several series of alkyl-substituted amino-, bromo-, chloro-, fluoro- and hydroxy-1, 4-naphthoquinones, as well as some 6-alkylaminoquinoline-5, 8-diones and 7-alkyl-6-hydroxyquinoline-5, 8-diones were prepared and tested as protectant fungicides against apple powdery mildew (caused by Podosphaera leucotricha). While most of the compounds did not reduce infection when applied at 10^?3M, several 3-alkyl-2-bromo-and 3-alkyl-2-chloro-1, naphthoquinones were found to have ED₅₀ values below 50 × 10^?5M.     

Isolation, screening and identification of antagonistic downy mildew endophytic bacteria from cucumber

Cucumber is a common vegetable all over the world; however, its production is seriously affected by cucumber downy mildew caused by Pseudoperonospora cubensis. Endophytes have great potential to control such fungal diseases. The aim of the study was to isolate, screen and identify endophytic bacteria, which show antagonistic activity to downy mildew, in cucumbers. Here, surface sterilized leaves were used for endophytic bacteria isolation. All the isolates were further screened for the antagonistic activities against P. cubensis by leaf discs assay, separate leaves assay and sporangia releasing inhibition assay. The control efficacies of the endophytic bacteria (screened above) were finally evaluated through field tests. In this study, a total of 81 endophytic bacteria were isolated from cucumber leaves sampled at blossoming and fruiting stages, respectively, among which, six (strains CE1, CE8, CE9, Y1, Y2 and Y22) were tested for their strong antagonistic activity in vitro. In the field test, strain CE8, identified as belonging to Bacillus sp. based on 16S rDNA phylogenetic analysis, showed a strong control efficacy of 42.1 %, a value almost two times as high as that using 69 % metalaxyl-mancozeb WG, a widely used antifungal chemical in China. Based on the results above, CE8 was finally screened out for its great potential in cucumber downy mildew control, implicating a powerful value of the strain in the production practice.     

Synthesis,fungicidal activity and structure-activity relationships of a series of 1-(3-pyridyl)-1-substituted-but-3-yn-1-ols

A series of 1-(3-pyridyl)-1-substituted-but-3-yn-1-ols and some related compounds were synthesised and tested for antifungal activity against eight phytopathogenic fungi of different taxonomic classes. High activity was shown in particular against Sphaerotheca fuliginea on Cucumis sativus. The compounds containing aromatic substituents gave the best results, not only in protectant but also in systemic and eradicant tests. The quantitative structure-activity relationship suggests that steric effects play an important role in determining fungicidal activity.