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     

创制农药氯啶菌酯对小麦白粉病防治效果

对我国新创制的甲氧基丙烯酸酯类杀菌剂氯啶菌酯防治小麦白粉病进行了试验。小麦白粉病菌孢子萌发抑制试验表明,20、10、1 μg/mL氯啶菌酯对孢子萌发的抑制率为83.54%、67.78%、19.24%。室内盆栽试验确定氯啶菌酯对小麦白粉病的EC50为4.172 3 μg/mL。田间试验结果表明,15%氯啶菌酯乳油有效用量60、40 g/hm2防治效果极显著高于20 g/hm2,与对照15%三唑酮可湿性粉剂防效相当。     

Effects of adjuvants on the performance of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine

The effects of adjuvants on the performance of a dispersible concentrate formulation (DCI) of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine (I) were investigated. The method involved assessment, under glasshouse conditions, of the therapeutic (curative) control of infections of powdery mildew (Erysiphe graminis DC f.sp. hordei Marchal) on barley (Hordeum vulgare, L.) eight to nine days after spray application to plants that had been inoculated one day prior to spraying. The results from the first trial showed that marked improvements (∽five-fold) in the performance of DCI could be obtained by the spray tank addition of some types of surfactant adjuvants and a series of further trials investigating a wide range of adjuvants was conducted. Nonylphenol, alkylamine and alcohol ethoxylates varying in mean ethylene oxide content between 5 and 20 moles were highly effective. There were indications that optimum performance enhancements were obtained with these surfactants containing between 5 and 10 moles ethylene oxide. Lower enhancements, sometimes only marginal, were obtained from trisiloxane, phosphate ester, propylene oxide, alkylamine-propylene oxide and castor oil ethoxylates and also alkyl polyglucoside biosurfactants. Negligible adjuvant enhancements were observed with emulsifiable paraffinic/naphthenic and rape seed oils, though slightly better enhancements were seen with an emulsifiable transmethylated rape seed oil and, interestingly, larger enhancements with an emulsifiable lipophilic alcohol. A final trial identified the alcohol ethoxylate, ‘Dobanol’ 91-6, as the most effective adjuvant and that its optimum application rate under glasshouse conditions was 250 g ha^-1. This information will be used to guide the design of field trials. © 1997 SCI     

Residual effects of triadimefon in soil on powdery mildew and yield of spring barley

Residual triadimefon (or a breakdown product), from a spray application (2 kg/ha) to field soil in 1978, significantly decreased powdery mildew on spring barley throughout two subsequent growing seasons, with consequent yield increases of 42% in 1980 and 18% in 1981.
In other field experiments triadimefon applied to soil at rates >0.06 kg/ha decreased mildew in barley growing in the soil 11 months later. In these experiments triadimefon, but not benomyl, imazalil or prochloraz (all at 0.5 kg/ha) significantly decreased mildew up to harvest and increased yield by 22%.
Triadimefon incorporated into a loam soil and a peat-based compost at rates >0.1 ng/g significantly decreased mildew on barley grown in pots under glasshouse conditions. Plants grown in the treated compost at the same time but in isolated pots supplied with filtered moistened air and capillary watering required more triadimefon (>100 ng/g) in soil for significant mildew control.
Despite strong adsorption of triadimefon to soil (Kd 19.4), an active substance appears to remain available for uptake and translocation by barley plants over long periods. The sensitivity of barley mildew to extremely small residues of triadimefon is discussed in relation to the siting of field experiments on mildew control. The implications for widespread commercial use of formulations containing triadimefon are discussed in relation to disease control practice in cereal growing systems.     

不同机制杀菌剂对小麦白粉病的敏感性及与三唑酮的交互抗性

为明确三唑酮和氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚5种不同作用机制的杀菌剂对小麦白粉病的敏感性及交互抗性,采用田间小区试验和室内喷雾离体叶段法测定了不同杀菌剂对小麦白粉病的防治效果。结果表明,5种不同作用机制杀菌剂对小麦白粉病的防治效果可达90%以上,而三唑酮最高的防治效果仅为72.17%;小麦白粉病菌群体对氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚的敏感性EC50分别在0.087~1.901、0.058~1.402、0.186~3.014、0.222~6.005、0.006~1.742μg/mL之间,5种不同作用机制杀菌剂的敏感性均呈连续单峰曲线,可作为小麦白粉病菌对5种不同作用机制杀菌剂的敏感基线。研究表明,三唑酮与氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚之间不存在交互抗性。     

Metrafenone: studies on the mode of action of a novel cereal powdery mildew fungicide

Powdery mildew fungi are among the major pathogens causing diseases of cereals in the world. The mode of action of a novel systemic benzophenone fungicide, metrafenone, which is based on a precursor that is discussed in the preceding paper, has been analysed on the powdery mildew fungi of barley (Blumeria graminis Speer f. sp. hordei Marchal) and wheat (Blumeria graminis Speer f. sp. tritici Marchal). Preventive treatments reduced germination and blocked development beyond formation of appressoria, which penetrated less often. Moreover, metrafenone turned out to be an efficient curative fungicide, which rapidly affected fungal survival at low concentrations. The fungicide induced swelling, bursting and collapse of hyphal tips, resulting in the release of globules of cytoplasm. Bifurcation of hyphal tips, secondary appressoria and hyperbranching were also frequently observed. A histochemical analysis showed that metrafenone caused disruption of the apical actin cap and apical vesicle transport as well as weakening of the cell wall at hyphal tips. Finally, metrafenone strongly reduced sporulation. Reduced sporulation was associated with malformation of conidiophores that showed irregular septation, multinucleate cells and delocalisation of actin. Microtubules appeared to be only secondarily affected in metrafenone-treated B. graminis. The results suggest that the mode of action of metrafenone interferes with hyphal morphogenesis, polarised hyphal growth and the establishment and maintenance of cell polarity. Metrafenone likely disturbs a pathway regulating organisation of the actin cytoskeleton.     

Factors affecting build-up of fungicide resistance in powdery mildew in spring barley

In replicate-plot field experiments done in the UK, at one site in Avon for 3 years and another in Warwickshire for 2 years, application of ethirimol or triadimenol sprays or seed treatments was followed by decreases in sensitivity of mildew samples to the particular fungicide applied. Application of ethirimol-triadimenol or tridemorph-triadimenol mixtures caused smaller or no decreases in sensitivity. Differences between isolates in responses to ethirimol and to triadimenol treatment were usually negatively correlated. Early-season inoculum differed in fungicide sensitivity between sites. At one site sensitivity shifted markedly from one season to another. No clear interactions between cultivar, mildew pathotype and shifts in fungicide response could be discerned. There were no major differences in resistance build-up between seed or spray treatments.In veldexperimenten met herhalingen uitgevoerd in Engeland, gedurende een periode van 3 jaar in Avon en gedurende een periode van 2 jaar in Warwickshire, werd na behandeling van zomergerst met ethirimol of triadimenol een verminderde gevoeligheid van meeldauw voor deze fungiciden waargenomen.Behandelingen met mengsels van ethirimol-triadimenol of tridemorf-triadimenol gaven weinig tot geen verminderde gevoeligheid. Verminderde gevoeligheid van isolaten voor ethirimol was meestal gecorreleerd met een verhoogde gevoeligheid voor triadimenol en omgekeerd. Vroeg in het seizoen werd in de meeldauwpopulatie op de twee proefvelden een verschil in gevoeligheid voor de fungiciden waargenomen. Op één proefveld trad van het ene op het andere seizoen een aanzienlijke verandering in de gevoeligheid voor de fungiciden op. Er was geen duidelijke correlatie tussen de waargenomen verminderde gevoeligheid voor de fungiciden en de gebruikte cultivars of voorkomende fysio's. Verminderde gevoeligheid voor de fungiciden werd zowel bij zaadbehandeling als bij het bespuiten van planten waargenomen.     

Factors affecting build-up of fungicide resistance in powdery mildew in spring barley

In replicate-plot field experiments done in the UK, at one site in Avon for 3 years and another in Warwickshire for 2 years, application of ethirimol or triadimenol sprays or seed treatments was followed by decreases in sensitivity of mildew samples to the particular fungicide applied. Application of ethirimol-triadimenol or tridemorph-triadimenol mixtures caused smaller or no decreases in sensitivity. Differences between isolates in responses to ethirimol and to triadimenol treatment were usually negatively correlated. Early-season inoculum differed in fungicide sensitivity between sites. At one site sensitivity shifted markedly from one season to another. No clear interactions between cultivar, mildew pathotype and shifts in fungicide response could be discerned. There were no major differences in resistance build-up between seed or spray treatments.     

The effect of fungicide dose on the composition of laboratory populations of barley powdery mildew

The effect of the use of different doses of the fungicide fenpropimorph on populations of barley powdery mildew Blumeria ( Erysiphe ) graminis f. sp. hordei was investigated in a laboratory selection experiment. A sample from the Danish aerial population of powdery mildew was split into populations, and these were kept separately for 31 generations on susceptible barley seedlings treated with fungicide at two concentrations, as well as on a control. Samples from these populations were tested for their resistance to fenpropimorph and their virulence spectra. There was a large amount of environmental variation in the ED₅₀ values used to measure fungicide resistance. In both treated populations, the average level of fungicide resistance increased, this increase being faster and greater in the population treated with the high dose. The diversity of pathotypes of the treated populations decreased, with the decline being more rapid in the population treated with the high dose, where one pathotype dominated the population after 31 generations. This pathotype was apparently not the fittest in the population treated with the low dose. This implies that knowledge of ED₅₀ is not sufficient to predict pathotype evolution under different fungicide treatments. The dominant pathotype in the high-dose treatment may not have been clonal, as there was evidence of two levels of fungicide resistance. The large environmental variation observed in estimated ED₅₀ values for resistance towards fenpropimorph may help to explain why this resistance has evolved at a slower rate than resistance towards other fungicides.     

新型植物源农药0.5%大黄素甲醚水剂对黄瓜白粉病菌的毒力测定及田间药效

0.5%大黄素甲醚水剂是湖北省农科院植保土肥所和内蒙古清源保生物科技有限公司联合创制的一种新颖的植物源杀菌剂,其化学结构式为1,8-二羟基-3-甲氧基-6-甲基蒽醌。室内孢子萌发抑制试验结果表明,大黄素甲醚对黄瓜白粉病菌孢子萌发的抑制中浓度EC50为0.37μg/mL;田间药效试验结果表明,0.5%大黄素甲醚水剂对黄瓜白粉病菌具有良好的保护和防治效果,有效成分用量18~45 g/hm2的防治效果明显高于15%三唑酮可湿性粉剂135 g/hm2的防效。     

防治西葫芦和黄瓜白粉病的生物制剂的筛选

瓜类白粉病是蔬菜上的重要病害之一,为加大对该病害的生物防治力度,本研究采用课题组研发的1×109cfu/g玫瑰黄链霉菌水剂和10亿芽胞/g枯草芽胞杆菌悬浮剂以及市场上常用的枯草芽胞杆菌、哈茨木霉菌、寡雄腐霉、武夷菌素、多抗霉素等多种生物制剂进行田间药效试验,比较几种生物制剂的防治效果。结果表明,供试生物制剂对西葫芦白粉病的防效为57.65%~84.98%,其中3%多抗霉素水剂600倍液的防效最好,为84.98%,且具有明显的促生长作用,增产率达12.65%。其次为1 000亿芽胞/g枯草芽胞杆菌可湿性粉剂(武汉天惠)400倍液、2%武夷菌素水剂600倍液和3×108 cfu/g哈茨木霉菌可湿性粉剂300倍液,可作为西葫芦白粉病防治的选用药剂。1×109 cfu/g玫瑰黄链霉菌水剂对西葫芦和黄瓜白粉病均具有较好的防效,分别为78.68%和73.59%,具有开发和应用的市场价值。     

Saccharin-induced protection against powdery mildew in barley: effects on growth and phenylpropanoid metabolism

Treatment of barley ( Hordeum vulgare ) with 3 m m saccharin, applied as a foliar treatment to the first leaf or as a soil drench, provided significant control of powdery mildew ( Blumeria graminis f.sp. hordei ) on first and second leaves. This was unlikely to be the result of a direct effect of saccharin on the fungus, as application of the chemical to first leaves 2 h before inoculation did not affect conidial germination or formation of appressoria. Saccharin treatment had no significant effect on plant growth, except for a reduction in total leaf area in plants treated with a saccharin drench 14 days before inoculation with mildew. Phenylalanine ammonia-lyase activity was reduced significantly in second leaves 18 and 48 h after inoculation in plants treated with saccharin 14 days earlier. Peroxidase activity increased significantly in plants challenged with mildew within 6 days of saccharin application, although changes were not apparent until 48 h after pathogen challenge. On these occasions, treatment with saccharin resulted in a 33% increase in peroxidase activity compared with controls. In plants inoculated 10 or 14 days after saccharin application, cinnamyl alcohol dehydrogenase (CAD) activity increased prior to, and 18, 24 and 48 h after, inoculation of the barley plants with mildew. CAD activity increased approximately twofold compared with controls. However, in contrast to peroxidase, CAD activity was significantly higher in saccharin-treated plants prior to and after inoculation with powdery mildew, suggesting that saccharin primes CAD activity prior to pathogen challenge.     

The activation of triadimefon and its role in the selectivity of fungicide action

The uptake and metabolism of triadimefon by mycelia of fungi, sensitive or resistant to triadimefon, were studied. In the mycelia the triadimefon content accumulated to 20-40-fold of the external concentration, irrespective of the sensitivity of the fungus. In the course of the metabolism a highly fungitoxic product, triadimenol, was formed. In mycelia of sensitive fungi this transformation was at a high rate whereas it could not be demonstrated or only to a low extent in resistant types. The material produced by the sensitive fungi was effective also against fungi basically resistant to triadimefon. Based on these observations, triadimefon has to be regarded as the precursor of triadimenol. In the species investigated, selectivity may be related mainly to the rate of activation. In higher plants the metabolism of triadimefon showed a similar pattern, but was slower than with fungi. As the transformation into triadimenol (activation) begins thus early in the host tissues, the systemic fungitoxic effect is also influenced by the host plant itself. Regarding the speed of activation differences were found between the four plant species investigated.     

Light quality affects incidence of powdery mildew,expression of defence-related genes and associated metabolism in cucumber plants

To determine whether light quality affects the incidence of disease, we exposed cucumber (Cucumis sativus L. cv. Jinyan No. 4) plants at the 4-leaf stage to white and other monochromatic lights and tested the effects on plant response to Sphaerotheca fuliginea, defence-related gene expression and metabolic changes. Exposure to red light resulted in higher levels of H₂O₂ and salicylic acid (SA), and stronger expression of defence genes such as PR-1 than exposure to white or other monochromatic lights. In comparison, plants grown under purple and blue light had higher activities of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO) and higher level of flavonoids than plants grown under other lights. Furthermore, plants grown under red light were more resistant whilst plants grown under other monochromatic lights were less resistant to Sphaerotheca fuliginea than plants grown under white light. These results suggest a role of red light in light-enhanced resistance, which correlates with enhanced SA-dependent signaling pathway.     

Variation in the response of cashew genotypes to the targeted application of fungicide to flower panicles for control of powdery mildew disease

Application of the fungicide triadimenol (Bayfidan) directly to inflorescences of cashew was investigated as a means of controlling powdery mildew disease caused by Oidium anacardii. Disease development and nut production were studied in 12 cashew genotypes that differed in their susceptibility to mildew. Panicle colonization by O. anacardii reached 100% coverage in all genotypes without fungicide treatment, but rates of infection differed significantly. Triadimenol sprays reduced mildew to less than 9%, even in panicles of highly susceptible genotypes. In the absence of disease, particularly good yield responses with more than nine times more nuts set than untreated controls were achieved by AM6 and AC1, which were categorized as highly susceptible and intermediate, respectively, in reaction to powdery mildew. By contrast, the partially resistant genotypes AZA2 and AC6 both produced yield response ratios of less than 3·0. The targeted treatment of flower panicles to control mildew is recommended, rather than the current practice of wastefully treating whole trees on which all mature leaves are naturally immune to infection.     

Characteristics and host range of tomato powdery mildew

The anamorphic state of a powdery mildew, which first appeared on tomato in the UK in 1987, currently listed as Erysiphe orontii (anamorph Oidium violae ), was examined microscopically on both tomato and alternative hosts. Host range studies were also carried out. In 1993–95, species and cultivars of plants from 26 of the 30 families listed as hosts of E. orontii were inoculated with tomato powdery mildew in the glasshouse and assessed for susceptibility on a 0–3 scale based on degree of sporulation and growth. Thirteen families contained species or varieties that were susceptible and a total of 80 varieties, including many economically important Cucurbitaceae and Solanaceae, supported sporulation to some extent (susceptibility score 1–3). Necrosis was not a constant feature of plants exhibiting resistance, as it could accompany sporulation on some susceptible varieties. Microscopic measurements showed that conidial size, conidiophore length, conidiophore foot-cell length and width, and the number of cells distal to the foot-cell were remarkably constant between samples of powdery mildew taken from tomato each year and from the various alternative hosts. Based on the production of conidia singly, the presence of nipple-shaped to moderately lobed appressoria, and occurrence of straight conidiophores, it is concluded that this fungus on tomato should more correctly be named Oidium lycopersicum until the sexual stage is discovered. The highly polyphagous nature of this powdery mildew would suggest that it represents a potential risk to UK agriculture and horticulture, but the failure to recover any powdery mildew from 120 samples of potato, including varieties Cara and Maris Piper, on which the tomato powdery mildew could sporulate in the glasshouse, suggests that environmental factors may play a key role in preventing establishment of this powdery mildew on alternative hosts on a commercial scale in the field.