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.     

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.     

Quantitative evolution of aggressiveness of powdery mildew under two-cultivar barley mixtures

The effects of cultivar mixtures on the evolution of aggressiveness of barley powdery mildew ( Blumeria graminis f.sp . hordei ) were modelled. It was found that the rate and direction of evolution of pathogen aggressiveness in a race-non-specific system and value at equilibrium, depends on initial resistance levels, proportions of component cultivars, autodeposition rates, the relative magnitude of the benefit of autoinfection, and the cost of alloinfection of spores. In the model, mixing cultivars in any proportions tended to reduce the aggressiveness of pathogens at equilibrium compared with pure stands, but this effect decreased when two mixture components were extremely unbalanced in proportion. Under low and medium autodeposition rates, the best control of the evolution of the pathogen was achieved by mixing two components in roughly equal proportions. The magnitude of aggressiveness at equilibrium increased as autodeposition rates increased. Though the level of initial resistance of mixture components did not have an impact on the aggressiveness of pathogens at equilibrium, it strongly influenced the transient values of aggressiveness and therefore the total amount of disease caused over an evolutionary period. The cost to the pathogen of alloinfection and benefit of autoinfection per se did not affect the final level of aggressiveness, but did affect the time to reach equilibrium. However, the ratio of the cost to the benefit did influence the final aggressiveness of the pathogen.     

Local and systemic effects of oxylipins on powdery mildew infection in barley

Treatment of the first leaves of barley seedlings with the oxylipin colneleic acid, or the two trihydroxy oxylipins 9,12,13-trihydroxy-11(E)-octadecenoic acid and 9,12,13-trihydroxy-10(E)-octadecenoic acid, reduced infection of that leaf by the powdery mildew fungus Blumeria graminis Speer f sp hordei Marchal. When applied to first leaves, etheroleic acid and colneleic acid, as well as the trihydroxy oxylipin 9,12,13-trihydroxy-10(E),15(Z)-octadecadienoic acid, also reduced mildew infection in second leaves. In all cases where local and systemic effects against mildew were observed, activity of the defence-related enzyme phenylalanine ammonia lyase (PAL) was increased, but only following challenge inoculation with powdery mildew. Peroxidase activity was not affected by oxylipin treatment or mildew inoculation. Whether the effects observed were due to the oxylipins or to breakdown products is not known, since no information is available on the stability of these particular oxylipins on leaf surfaces. Nevertheless, these data represent the first report of systemic effects against pathogen infection following pre-treatment with oxylipins.     

白粉病菌侵染诱导的大麦叶肉细胞变化的超微结构与细胞化学

 从超微结构和细胞化学角度对大麦白粉病菌侵染诱导的寄主叶肉细胞变化进行了研究。结果发现,病原菌接种后12 h,叶肉细胞光合作用的标志性酶RCA和Rubisco含量发生迅速的变化,感病大麦(Ingrid)中RCA和Rubisco含量急剧减少,而抗病大麦(mlo-3)中则趋势相反。随后,不论在感病或抗病大麦中这2种蛋白的含量一直下降,但感病品种中一直维持相对较高水平。超微结构观察表明,病原菌侵染能够诱导侵染点附近叶肉细胞中叶绿体的增殖,新叶绿体的不断产生,从而延缓了叶肉细胞的衰老和死亡,增加了光合产物的形成。以上结果说明,叶肉细胞可能从养分供给上影响到了表皮细胞中病原菌吸器的发育。     

Spectral signatures in the UV range can be combined with secondary plant metabolites by deep learning to characterize barley–powdery mildew interaction

In recent studies, the potential of hyperspectral sensors for the analysis of plant–pathogen interactions was expanded to the ultraviolet range (UV; 200–380 nm) to monitor stress processes in plants. A hyperspectral imaging set-up was established to highlight the influence of early plant–pathogen interactions on secondary plant metabolites. In this study, the plant–pathogen interactions of three different barley lines inoculated with Blumeria graminis f. sp. hordei (Bgh, powdery mildew) were investigated. One susceptible genotype (cv. Ingrid, wild type) and two resistant genotypes (Pallas 01, Mla1- and Mla12-based resistance and Pallas 22, mlo5-based resistance) were used. During the first 5 days after inoculation (dai) the plant reflectance patterns were recorded and plant metabolites relevant in host–pathogen interactions were studied in parallel. Hyperspectral measurements in the UV range revealed that a differentiation between barley genotypes inoculated with Bgh is possible, and distinct reflectance patterns were recorded for each genotype. The extracted and analysed pigments and flavonoids correlated with the spectral data recorded. A classification of noninoculated and inoculated samples with deep learning revealed that a high performance can be achieved with self-attention networks. The subsequent feature importance identified wavelengths as the most important for the classification, and these were linked to pigments and flavonoids. Hyperspectral imaging in the UV range allows the characterization of different resistance reactions, can be linked to changes in secondary plant metabolites, and has the advantage of being a non-invasive method. It therefore enables a greater understanding of plant reactions to biotic stress, as well as resistance reactions.     

Levels of resistance of Erysiphe graminis f.sp. hordei to the systemic fungicide triadimenol

A random sample of conidiospores ofErysiphe graminis f.sp.hordei was obtained from the atmosphere above Cambridge, England, by incubating them on barley seedlings exposed on three dates in 1985. The asexual progeny of each spore was tested for its response to a range of doses of a systemic triazole fungicide, triademenol. Principal components analysis of the data revealed that the majority of isolates had a distinct level of response to triadimenol, being resistant to triadimenol at the rate apoplied to seed commercially. The remaining isolates appeared either to be sensitive to the lowest dose of triadimenol used, or to have one of two intermediate levels of resistance. There was a significant increase in the frequency of isolates with higher levels of resistance to triadimenol during 1985. This is likely to have been a response to the continuing widespread use of demethylation inhibitor (DMI) fungicides by British farmers.     

燕麦种质资源抗白粉病鉴定及利用评价

采用田间自然感病的方法,于2009-2011年在甘肃省天水市甘谷县对128份燕麦品种进行了由白粉菌(Blumeria graminis f.sp.avenae)引起的燕麦白粉病田间抗性鉴定和评价,该地区属于白粉菌病害常发区。结果表明,所有供试材料均程度不同地感染燕麦白粉病,无免疫材料,2份材料‘MF9715’、‘4607’表现高抗;8份材料‘QO245-7’、‘白燕2号’、‘VAO-1’、‘709’、‘4663’、‘4641’、‘4628’和‘青永久307’表现中抗;其余118份材料表现中感、高感和极度感病。说明抗燕麦白粉病的材料严重匮乏,可利用的抗性种质资源相对更少。筛选出的高抗和中抗材料对燕麦白粉病有较好抗性,是今后可利用的抗性种质资源。     

小麦新品系抗白粉病基因分析

 本文对6个小麦新品系所含的抗白粉病基因进行了遗传分析。将感病品种Liaochun10分别与SM 20121、SM 203390、SM 20125、SM 200332、SM 20126、SM 20005杂交和自交,并将这6个品系互配成半双列杂交组合。用小麦白粉菌15号小种的单孢堆菌系对各杂交组合的亲本、F₁、F₂代群体及F₃代家系进行了苗期抗病性鉴定。遗传分析表明,供试的6个品系对小麦白粉菌15号小种的抗性均由1对显性基因控制。等位性分析推断:SM 20121、SM 203390、SM 20125和SM 200332含有抗白粉病基因Pm12;SM 20126含有抗白粉病基因Pm21;SM 20005含有抗白粉病基因Pm16。建议将这6个品系作为优良抗病亲本利用。     

小麦慢白粉品种的抗性组分研究

 2003~2004年度和2004~2005年度在田间测定了16个小麦品种(系)对小麦白粉菌E20菌株的抗性组分,包括潜育期、侵染几率、产孢量、病斑扩展和传染期。结果表明,小麦慢白粉品种(系)与高感对照品种相比,表现为潜育期长、侵染几率低、产孢量低、病斑扩展慢的特点,且这4个抗性组分与对照的差异都达到了显著和极显著水平,但慢白粉品种的传染期变化无一定规律。参试慢白粉品种的抗性组分参数与病情曲线下面积(AUDPC)的相关分析表明,潜育期与AUDPC呈负相关,但相关性不显著;产孢量和病斑扩展与AUDPC呈正相关,两年数据相关性均达到显著水平;侵染几率与AUDPC呈正相关,但2003-2004年度相关性不显著,而2004~2005年度相关性显著;传染期与AUDPC相关关系不明显。由此可见,在慢白粉品种的病害流行中起主要作用的是产孢量、病斑扩展,而侵染几率、潜育期和传染期作用相对较小。     

Systemic activity of simeconazole and its derivatives in plants

The systemic activity of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) and a number of its derivatives in plants has been investigated to establish which portion of the structure of the molecule contributes to this outstanding activity. The results revealed that the hydroxyl group of the simeconazole moiety is essential for vapour-phase activity and translocation from roots of the compound. They showed that the presence of a fluorine atom in the structure was not indispensable for vapour-phase activity or translocation from roots, although the fluorine atom contributed to these systemic movements. In addition, it was found that the fungicidal activity of simeconazole against Rhizoctonia solani Kühn and Blumeria graminis DC fsp hordei Marchal is potentiated by the fluorine atom, since the activity of a compound which lacked fluorine in the 4-position of the phenyl ring was inferior to that of simeconazole. A compound in which the silicon atom of simeconazole was replaced by a carbon atom showed lower antifungal activity than simeconazole, while phytotoxicity was caused in rice plants by soil drench of the compound. Therefore, the silicon atom of simeconazole may contribute to its selectivity between fungi and plants.     

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.     

几丁质寡糖诱导小麦抗白粉病作用的研究

试验表明 ,应用工业化生产的几丁质寡糖液 (COS)可以减轻小麦白粉病的发生。随着COS浓度的增加 ,其诱导小麦产生抗白粉病的效果越好。通过不同施用方式的比较 ,表明小麦的抗性是由于植株吸收COS后 ,引发体内系统诱导抗性而表达的。     

2007年我国部分麦区小麦白粉菌对三唑酮的抗药性监测

采用拌种离体叶段法测定了我国9个省（市）的112个小麦白粉菌株对三唑酮的抗性。结果表明,供试菌株的平均EC50为57.25mg/L,平均抗性水平为27.39倍,其中86.61%供试菌株已经产生抗性,抗药性比敏感菌株高出10~40倍的菌株占47.32%,四川、山东、甘肃和贵州等地菌株的抗性高于其他地区。此结果可为三唑类杀菌剂在我国的推广应用和制定合理的抗药性治理措施提供依据。     

Exploration and Exploitation Strategies of Powdery Mildew on Barley Cultivars with Different Levels of Nutrients

The mass fractal dimension (MFD) of colonies of mildew (Erysiphe graminis f.sp. hordei) growing on barley was calculated as a measure of their spatial structure. Despite the elongated shape of the colonies imposed by the leaf cellular structure, the MFD remained constant with scale. The mildew MFD differed on different cultivars of barley, and was greater on leaves produced under higher nutrient level indicating a physiological component. Lower MFD values correspond with the thin spreading growth associated with exploration strategies and higher values correspond to the denser, more branched structure associated with exploitation of the substrate. Cultivars showing exploration strategies induced by resistance expression responded to increased nutrient levels more than those expressing little resistance such as Golden Promise.     

Evaluation of the systemic activity of simeconazole in comparison with that of other DMI fungicides

The systemic activity of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) in plants was compared with those of eight other sterol demethylation inhibitor (DMI) fungicides. Simeconazole prevented the infection of Blumeria graminis (DC) Speer f sp hordei Marchal on barley leaves within a radius of several centimeters from the edge of local treatment on the leaves when the compound was separated from the leaves by glass coverslips. This reveals that simeconazole has prominent vapour-phase activity. Simeconazole showed excellent curative activity against barley powdery mildew when treated 1-3 days after inoculation. Furthermore, this indicates that simeconazole has notable translaminar activity because, when the compound was applied onto either the adaxial or abaxial leaf surface, it showed excellent efficacy against powdery mildew on the opposite side of the leaf surface of barley and cucumber. Simeconazole also showed excellent efficacy against barley powdery mildew by soil drench 24h after inoculation. This suggests that simeconazole was absorbed very quickly into the barley plant after treatment. The permeability of the compound through cuticular membranes prepared from tomato fruits was about 20% at 22 h after the treatment and was much superior to that of the other DMI fungicides tested.     

36个小麦审定和区试品种(系)的抗白粉病基因推导

明确我国当前小麦审定和区试品种含有的抗白粉病基因, 可为这些品种在小麦抗病育种中的应用及品种合理布局和轮换提供依据。本研究采用24个不同毒性的小麦白粉菌菌株对36个小麦审定和区试品种(系)进行抗白粉病基因推导, 参试品种(系)与46个已知抗病基因小麦品种(系)抗谱比较的结果表明, 11个小麦审定品种中有5个品种对所有供试白粉菌菌株表现抗性, 结合亲本溯源, 推测其中有3个品种可能携有Pm21基因; 另外6个审定品种中有5个品种可能含有抗病基因Pm2, 且其对应的亲本或亲本组合中含有抗病基因Pm2。25个区试品种(系)中有3个可能含有Pm21, 10个含有Pm2, 1个含有Pm2+6,2个含有Pm4b,1个含有Pm8。另外, 参试的36个品种(系)中还有9个品种(系)和已知基因品种抗谱存在一定差异。总体上, 推导出已知基因的品种以含有Pm2基因的品种最多, Pm21基因的品种次之, 建议在生产上加强对Pm21基因品种(系)特别是已审定的携有Pm21基因品种的推广和应用, 应该注意一些省份在育种和生产上应慎用或少用含Pm2基因的品种(系)。     

Baseline sensitivity to proquinazid in Blumeria graminis f. sp. tritici and Erysiphe necator and cross‐resistance with other fungicides

BACKGROUND: Proquinazid is a new quinazolinone fungicide from DuPont registered in most European countries for powdery mildew control in cereals and vines. The aim of this paper is to present baseline sensitivity data in populations of Blumeria graminis f. sp. tritici EM Marchal and Erysiphe necator (Schw) Burr as well as results from cross‐resistance studies with other fungicides. RESULTS: Proquinazid exhibited a high intrinsic activity on B. graminis f. sp. tritici isolates at rates ranging from 0.000078 to 0.02 mg L^?1. Erysiphe necator isolates were comparatively less sensitive to proquinazid, with EC₅₀ values ranging from 0.001 to 0.3 mg L^?1. Proquinazid controlled equally well B. graminis f. sp. tritici isolates sensitive and resistant or less sensitive to tebuconazole, fenpropimorph, fenpropidin, cyprodinil and kresoxim‐methyl. A positive correlation (r = 0.617) between quinoxyfen and proquinazid sensitivities was found among 51 B. graminis f. sp. tritici isolates. Quinoxyfen‐resistant B. graminis f. sp. tritici isolates were slightly less sensitive to proquinazid than the quinoxyfen‐sensitive isolates; however, proquinazid remained much more active than quinoxyfen on these isolates. A stronger sensitivity relationship (r = 0.874) between proquinazid and quinoxyfen was found among 65 E. necator isolates tested in a leaf disc assay. The sensitivity values for proquinazid were significantly lower than those for quinoxyfen, confirming the higher intrinsic activity of proquinazid on both pathogens. CONCLUSION: Given the history of resistance development in powdery mildew and the observed sensitivity relationship with quinoxyfen, specifically in E. necator, we conclude that the risk of resistance developing to proquinazid might be influenced by the use of quinoxyfen. Based on these results, the authors recommend that proquinazid and quinoxyfen be managed together for resistance management. Copyright © 2009 Society of Chemical Industry