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     

Impact of proquinazid on appressorial development of the barley powdery mildew fungus Blumeria graminis f.sp hordei

The effect of a novel mildew-specific quinazolinone fungicide, proquinazid, on the barley powdery mildew fungus, Blumeria graminis f.sp. hordei, has been studied using scanning electron microscopy and quantitative RT-PCR. Proquinazid has previously been shown to perturb conidial morphogenesis, similar to quinoxyfen, a currently widely used mildewicide. In this study, we confirm an effect of proquinazid on appressorial differentiation. By comparison to quinoxyfen, however, proquinazid affects this highly coordinated process differently, with more deformed appressorial germ tubes observed, often growing away from the leaf surface. Comparison of the expression of genes involved in the transduction of signals directing conidial development has also suggested differences in the affects of proquinazid and quinoxyfen. In particular, the expression of the Ras-type GTPase activating gene, previously implicated in quinoxyfen resistance, is distinctly affected by proquinazid treatment at time points critical to normal conidial morphogenesis. Together, these data indicate differences in the mechanisms by which proquinazid perturbs appressorial differentiation in comparison with quinoxyfen.     

Fungicide sensitivity of populations of wheat powdery mildew (Erysiphe graminis f.sp. Tritici) in Central Europe in 1993

In 1993 we observed the sensitivity of wheat powdery mildew populations (Erysiphe graminis DC f.sp. tritici Marchal) from the Czech Republic, Austria, Hungary and Slovakia to the fungicides triadimenol, tebuconazole, propiconazole, flutriafol and fenpropimorph. The highest resistance value was shown to triadimenol, which attained a mean resistance factor (MRF) of 29 (expressing how many times the population is more resistant than are standard sensitive isolates) in the mildew population from the Czech Republic. The mildew populations from eastern Slovakia and eastern Hungary, populations geographically isolated from the other populations, showed very high sensitivity to all fungicides tested. There was most sensitivity to fenpropimorph (smallest MRF values) compared with the other fungicides. Cross-resistance was established among all triazoles used, but not between triazoles and fenpropimorph. Sensitivity of wheat powdery mildew populations from Central Europe to these fungicides is considered adequate, and the development of resistance has shown a decreasing tendency in recent years.     

甘肃小麦白粉病抗源材料的筛选及抗病基因库的组建

2002-2005年,对收集到的30份已知抗白粉病基因载体品种在甘肃省的不同生态区进行了抗病性监测,结果表明:Pm1、Pm3 a、Pm3 b、Pm3 c、Pm3 f、Pm4 a、Pm5、Pm6、Pm7、Pm8、Pm17在田间抗病性丧失,失去利用价值;Pm2、Pm19、Pm4+8、Pm4、Pm5+6、Pm13在田间抗病性较低,不宜单独作为亲本利用;Pm1+2+9、Pm2+6、Pm2+mld、Pm2+talent、Pm4+2 x、Pm4 b、Pm4 b+5、Pm20、Pm21、Pmxbd在田间抗性表现良好,在今后的育种工作中应充分加以利用。同时经过4年抗病性监测,从省内外2 638份小麦品种(系)材料中筛选出了抗病性强、综合农艺性状优良的92R137、贵农21等优异材料10余份,初步组建了抗白粉病基因库。文中还对抗病基因现状和利用及今后如何避免由于抗源单一化带来的白粉病流行进行了初步探讨。     

我国小麦地方品种蚂蚱麦、小白冬麦、游白兰、红卷芒抗白粉病性遗传分析

我国地方品种是小麦白粉病抗性的重要来源之一,为了对地方品种抗源的利用奠定基础,采用常规杂交方法,以感病品种Chancellor分别与我国小麦抗病地方品种蚂蚱麦、小白冬麦、游白兰、红卷芒进行正交和反交,获得F₁、F₂代。根据白粉菌菌株的毒谱选用E09菌株对Chancellor与小白冬麦、游白兰、红卷芒的杂交后代进行苗期抗性鉴定和统计分析,选用E30菌株对Chancellor与蚂蚱麦的杂交后代进行苗期抗性鉴定和统计分析。结果表明4个品种在正、反交情况下均表现出由一对隐性基因控制的抗性,说明这4个地方品种属于核遗传,其抗性是由一对隐性基因控制的。     

小麦品种对白粉病慢发性抗病性的因素分析

近年来,小麦发生白粉病日趋严重。由于存在着比较复杂的生理小种,品种抗性不能稳定。从我们多年积累品种资源资料中,选择高抗秆、叶锈病的小麦品种27个,经过温室和田间苗期和成株鉴定,分成四类作为试材。沈阳地区小麦白粉病菌株属于 Pm/Pmx,4/1,2,3a,3b,3c,5型。试验结果表明,小麦白粉病慢发抗性的品种,具有:(1)普遍率和严重率低和上升速度缓慢;(2)菌落小而少;(3)分生孢子发生少,菌落再生力弱;(4)菌落扩展缓慢;(5)产量上影响不显著。利用严重率指数可以作为选择慢发抗病性的指标。     

Effect of application rate on the sensitivity of Erysiphe graminis f.sp. tritici to fenpropimorph

Two sprays of fenpropimorph per season were applied to a winter wheat field trial, at a range of rates, which included the full commercial rate, in order to test the effect of fenpropimorph sprays on the sensitivity of Erysiphe graminis f.sp. tritici. While a reduction in the sensitivity of the mildew isolates was detected after fungicide application, this was not dependent on the rate of fungicide applied. Reduced rates were not found to induce a larger shift towards insensitivity than the full commercial rate. Powdery mildew isolates were collected from 1993 to 1996 and their sensitivity to fenpropimorph determined in order to monitor sensitivity changes in the population. While a decline in sensitivity was noted from season to season, there was no correlation between a lower sensitivity and the rate of fenpropimorph previously used. Isolates collected in Scotland were found to be significantly less sensitive than those sampled in the south of England. ©1997 SCI     

Mechanisms of powdery mildew resistance of wheat – a review of molecular breeding

Powdery mildew (Blumeria graminis f. sp. tritici) results in serious economic loss in wheat production. Exploration of plant resistance to wheat powdery mildew over several decades has led to the discovery of a wealth of resistance genes and quantitative trait loci (QTLs). We have provided a comprehensive summary of over 200 powdery mildew genes (permanently and temporarily designated genes) and QTLs reported in common bread wheat. This highlights the diverse and rich resistance sources that exist across all 21 chromosomes. To manage different data for breeders, here we also present a bridged mapping result from previously reported powdery mildew resistance genes and QTLs with the application of a published integrated wheat map. This will provide important insights to empower further breeding of powdery mildew resistant wheat via marker-assisted selection (MAS).     

Calcium ion promotes successful penetration of powdery mildew fungi into barley cells

To determine whether Ca²⁺ promotes powdery mildew penetration, Ca²⁺-treated barley coleoptiles were inoculated with conidia of pathogenic and nonpathogenic fungi. Penetration efficiency of the pathogenic powdery mildew Blumeria graminis was enhanced by Ca²⁺ treatment, but that of the necrotrophic pathogen Helminthosporium sp. remained unaffected. Similarly, when actin-dependent penetration resistance is suppressed with cytochalasin A, Ca²⁺ treatment specifically enhanced penetration of the nonpathogenic powdery mildew Erysiphe pisi but not that of other nonpathogens. Calmodulin inhibitors suppressed the promotive effect of Ca²⁺ on B. graminis penetration. These results suggest that barley powdery mildew specifically requires Ca²⁺ and calmodulin for penetration.     

Variation in sensitivity to fungicides which inhibit ergosterol biosynthesis in wheat powdery mildew

Fungicides which inhibit ergosterol biosynthesis have been in use for control of wheat powdery mildew (Erysiphe graminis f. sp.tritici) in the Netherlands since 1978. Mildew populations were tested for their variation in sensitivity to triadimefon from 1982 to 1984.In 1982 isolates from the province Limburg, with a triazole spray-regime history, were less sensitive to triadimefon than isolates from the provinces Gelderland and Noord-Brabant, where triazoles had not been used. In the following years isolates with reduced sensitivity were also detected in the latter provinces and other parts of the country. This spread correlates with the increased use of triazoles, both in frequency and space, from 1983 onwards. The reduced sensitivity can as a whole or in part be responsible for the decline in field performance of triazoles, observed during these years.Cross-sensitivity to the triazoles triadimefon and propiconazole was established, but not to triazoles and the morpholine fungicide fenpropimorph. Effectiveness of the latter compound was similar to all isolates from Limburg tested in 1984. Field performance of fenpropimorph, introduced in 1983, appeared to be normal. It is recommended to counteract further development of resistance by sequential use of fenpropimorph early in the season (May) and triazoles at the end (June–July).Samenvatting Fungiciden die de ergosterolbiosynthese remmen worden in Nederland sinds 1978 gebruikt bij de bestrijding van tarwemeeldauw (Erysiphe graminis f. sp.tritici) Meeldauwpopulaties werden getoetst op hun variatie in gevoeligheid voor triadimefon van 1982 tot 1984.In 1982 bleken isolaten afkomstig uit de provincie Limburg, waar voordien triazolen werden toegepast, minder gevoelig te zijn voor triadimefon dan isolaten uit de provincies Gelderland en Noord-Brabant, waar nog geen triazolen werden gebruikt. In de daaropvolgende jaren werden isolaten met een verminderde gevoeligheid ook in laatstgenoemde provincies en in andere delen van het land gevonden. Deze uitbreiding is gecorreleerd met een toename in het gebruik van triazolen vanaf 1983 in areaal en frequentie. De afname in gevoeligheid kan geheel of gedeeltelijk verantwoordelijk zijn voor de verminderde meeldauwwerking van triazolen die gedurende deze jaren werd waargenomen.Kruisgevoeligheid werd vastgesteld voor de triazolen triadimefon en propiconazool, maar niet voor triazolen en het morfoline-derivaat fenpropimorf. De werking van dit middel was tegen alle isolaten uit Limburg die in 1984 werden getoetst, gelijk. De meeldauwwerking van fenpropimorf, dat in 1983 werd geïntroduceerd, was normaal. Aanbevolen wordt om verdere resistentie-ontwikkeling tegen te gaan door afwisselend gebruik van fenpropimorf vroeg in het groeiseizoen (mei) en een triazool aan het eind (juni-juli).     

Evidence of host‐range expansion from new powdery mildew (Blumeria graminis) infections of triticale (×Triticosecale) in France

This study aimed to determine whether powdery mildew caused by Blumeria graminis is an endemic pathogen of triticale (×Triticosecale: Triticum × Secale), emerging as a result of recent changes in its pathogenicity, or whether it is a new pathogen, possibly resulting from hybridization between ff. spp. tritici and secalis. A secondary aim was to consider breeding practices that may have favoured this emergence. Phylogenetic analyses based upon six genes revealed the close relatedness of the novel entity and the ff. spp. tritici and secalis, but the IGS marker finally grouped together the isolates collected on triticale and on wheat, supporting the scenario of a recent host‐range expansion from wheat to triticale. Pathotype analyses concluded that virulence spectra of B. graminis infecting triticale were new in comparison to those observed for other reference formae speciales, and lack of fungicide resistance in triticale isolates strengthens the hypothesis of no or little genetic exchange between wheat and triticale populations of powdery mildew. This adaptation may follow the breakdown of plant resistance genes, which are probably not very diverse in current triticale cultivars since this criterion was not considered as a major one until recent years. Moreover, the complex selection and genetics of this hybrid cereal makes it difficult to predict the transmission of powdery mildew resistance genes.     

Sensitivity of Wheat Powdery Mildew (Blumeria graminis f.sp. tritici) towards Metrafenone

A monitoring study on the current sensitivity situation of wheat powdery mildew (Blumeria graminis f.sp. tritici) towards metrafenone was performed in 2009 with 2509 isolates. Airborne isolates were randomly collected in different regions of the most important European cereal growing regions. The sensitivities of the majority of isolates were comparable to the baseline sensitivity, which was determined in 2000 before market launch of the compound. Ninety-two isolates showed sensitivities outside the baseline. Eighty-four of them were classified as moderately adapted and could still be inhibited with registered rates of metrafenone in glasshouse tests under various preventive or curative conditions. Eight isolates were identified to be resistant, which were not fully inhibited at registered rates. Resistance management strategies and further extensive monitoring studies are indicated for a sustainable use of metrafenone against wheat powdery mildew.     

Resistance of Erysiphe graminis on barley and wheat to sterol C-14-demethylation inhibitors1

Isolates of Erysiphe graminis f. sp. hordei and tritici with decreased sensitivity to triadimefon showed cross-resistance to other inhibitors of sterol C-14-demethylation, such as triadimenol, propiconazol, diclobutrazol, prochloraz and nuarimol. The isolates exhibited a moderate degree of resistance to these compounds. No cross-resistance was detected to tridemorph, fenpropimorph and pyrazophos. The resistant hordei isolates were more sensitive to ethirimol than the sensitive isolate. The competitive abilities of resistant hordei and tritici isolates were inferior to that of the sensitive isolates. In the presence of the fungicides no differences in germination, appressorium formation and penetration between the sensitive and resistant isolates were observed; 48 h after inoculation the sensitive isolate showed several morphological alterations and further fungal development was arrested. At four to five times higher doses of triadimefon, similar morphological alterations were detected in the resistant isolate. Low concentrations of triazole fungicides which slightly affected mycelium growth of both the sensitive and the resistant isolate of f.sp. hordei severely inhibited development of conidiophores of the sensitive isolate whereas that of the resistant isolate was hardly affected.     

Sterol composition of isolates of Erysiphe graminis f.sp. tritici differing in sensitivity to fenpropimorph

Isolates of Erysiphe graminis f.sp. tritici with wild-type or reduced sensitivity to fenpropimorph were similar in sterol composition, viz. ergosta-5,24(28)-dienol (±90%) and episterol (±10%). Following treatment with fenpropimorph, the relative content of episterol increased in conidia of all isolates tested, while that of ergosta-5,24(28)-dienol decreased. These results suggest that fenpropimorph, under the test conditions used, does not inhibit activity of sterol Δ¹⁴-reductase or Δ⁸→Δ⁷-isomerase but probably interferes with the final part of the demethyl sterol synthesis. However, modifications in this part of the pathway are probably not responsible for the decreased sensitivity of the pathogen to the fungicide. © 1998 SCI.     

2009年我国部分麦区小麦白粉菌群体对三唑酮和嘧菌酯的敏感性测定

自1976年以来,三唑酮一直就是我国防治小麦白粉病的主要药剂.1991年首次在山东省发现抗性菌株,之后其他地区也相继有抗药性菌株的报道.本实验室从1995年就开始监测小麦白粉菌对三唑酮的抗药性,研究结果表明,平均抗性水平和抗性菌株的频率均总体呈上升趋势[1-3].     

Assessment of fungicide resistance and pathogen diversity in Erysiphe necator using quantitative real-time PCR assays

BACKGROUND: Management of grapevine powdery mildew Erysiphe necator Schw. requires fungicide treatments such as sterol demethylation inhibitors (DMIs) or mitochondrial inhibitors (QoIs). Recently, reduction in the efficacy of DMIs or QoIs was reported in Europe and the United States. The aim of the present study was to develop real‐time qPCR tools to detect and quantify several CYP51 gene variants of E. necator: (i) A versus B groups (G37A) and (ii) sensitive versus resistant to sterol demethylase inhibitor fungicides (Y136F). RESULTS: The efficacy of the qPCR tools developed was better than the CAPS method, with a limit of 2 pg for E necator DNA, 0.06 ng for genetic group A and 1.4 ng for the DMI‐resistant allele. The detection limits of qPCR protocols (LOD) ranged from 0.72 to 0.85%, and the quantification limits (LOQ) ranged from 2.4 to 2.85% for the two alleles G47A and Y136F respectively. The application of qPCR to field isolates from French vineyards showed the presence of DMI‐resistant and/or QoI‐resistant alleles in French pathogen populations, linked to genetic group B. CONCLUSION: The real‐time PCR assay developed in this study provides a potentially useful tool for efficient quantification of different alleles of interest for fungicide monitoring and for population structure of E. necator. Copyright © 2010 Society of Chemical Industry     

Mining wild barley for powdery mildew resistance

Powdery mildew, caused by Blumeria graminis f. sp. hordei (Bgh), is a worldwide disease problem on barley (Hordeum vulgare) with potentially severe impact on yield. Historically, resistance genes have been identified chiefly from cultivated lines and landraces; however, wild barley (H. vulgare subsp. spontaneum) accessions have proven to be extraordinarily rich sources of powdery mildew resistance. This study describes the characterization of a collection of 316 wild barley accessions, known as the Wild Barley Diversity Collection (WBDC), for resistance to powdery mildew and the genetic location of powdery mildew resistance loci. The WBDC was phenotyped for reaction to 40 different Bgh isolates at the seedling stage and genotyped with 10 508 molecular markers. Accessions resistant to all 40 isolates of Bgh were not found; however, three accessions (WBDC 053, 085 and 089) exhibited resistance to 38 of the isolates. Gene postulation analyses revealed that many accessions, while resistant, contained none of the 12 genes present in the Pallas near‐isogenic lines Mla1, Mla3, Mla6, Mla7, Mla9, Mla12, Mla13, Mlk1, MlLa, Mlg, Mlat and Ml(Ru2), suggesting that the accessions carry novel genes or gene combinations. A genome‐wide association study of powdery mildew resistance in the WBDC identified 21 significant marker‐trait associations that resolved into 15 quantitative trait loci. Seven of these loci have not been previously associated with powdery mildew resistance. Taken together, these results demonstrate that the WBDC is a rich source of powdery mildew resistance, and provide genetic tools for incorporating the resistance into barley breeding programmes.     

Morphological,molecular phylogenetic and pathogenic analyses of Erysiphe spp. causing powdery mildew on cashew plants in Brazil

Cashew powdery mildew is presently the most important disease of cashew trees in all Brazilian growing regions. Although it was described over a century ago, it had never threatened the Brazilian cashew industry until the first decade of the 21st century. Morphological and pathogenic evidence indicated the possibility of different pathogen species being involved in early and late types of cashew powdery mildew. This study was designed to elucidate this issue by comparing two different powdery mildew fungi occurring on cashew plants in Brazil according to the morphological characteristics, phylogenetic relationships with closely related powdery mildew fungi and pathogenic relationships. Based on morphology, molecular phylogenetics and pathogenicity on cashew, it was shown that two species of powdery mildew specimens are without question associated with cashew trees. One species, which infects young immature tissues such as shiny leaves, flowers and young fruits, is Erysiphe quercicola, while Erysiphe necator is associated exclusively with mature leaves. This is the first report of both E. quercicola and E. necator causing cashew powdery mildew, and the first detection of E. necator on cashew.     

New tools for studying epidemiology and resistance of grape powdery mildew to DMI fungicides

Using a Random Amplified Polymorphic DNA (RAPD) assay, we investigated the genetic polymorphism existing among 62 European isolates of the grape powdery mildew fungus (Uncinula necator [Schw.] Burr.). Isolates overwintering as mycelium in buds were genetically distinct from isolates overwintering as ascospores, suggesting the existence of two genetically isolated powdery mildew populations, and consequently of two independent sources of inoculum in the vineyard. Isolates resistant to fungicides inhibiting sterol 14α-demethylation (DMIs) were found in both populations, suggesting that resistance to DMIs may arise independently in the two powdery mildew populations. A PCR assay targeting the gene encoding U. necator 14α-demethylase has been developed which will permit an early, specific detection of U. necator infections, and may be useful for spraying programmes. ©1997 SCI