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.     

Comparison of resistance-inducing abilities of virulent and avirulent races of Erysiphe graminis f.sp. hordei and a race of Erysiphe graminis f.sp. tritici in barley

Resistance to powdery mildew was induced in barley by preinoculation with virulent and avirulent races of barley powdery mildew ( Erysiphe graminis f.sp. hordei ), and with a race of wheat powdery mildew ( E. graminis f.sp. tritici ). Four inducer densities were tested in 13 different induction periods between 1 and 24 h. Generally, the resistance induced by barley powdery mildew increased up to 10-12 h of induction and was maintained in longer induction periods. The inducing abilities of virulent and avirulent races could not be distinguished up to 10-12 h of induction, after which the inducing ability of avirulent races increased significantly in relation to virulent races. Wheat powdery mildew was able to induce more resistance than barley powdery mildew in induction periods up to 8 h. In a single inoculation procedure the number of haustoria developing from virulent barley powdery mildew decreased as inoculum density increased. The effect was ascribed to induction of resistance. This reduction of infection efficiency in the compatible interaction was compared to induced resistance. However, the inoculum density needed for 50% resistance induction in the double inoculation procedure was approximately 40 times higher than the inoculum density needed for 50% reduction in infection efficiency in the single inoculation procedure.     

Genetic variation in Danish populations of Erysiphe graminis f.sp. hordei: estimation of gene diversity and effective population size using RFLP data

Genetic variation of the barley powdery mildew fungus ( Erysiphe graminis f.sp. hordei ) was estimated in three Danish local populations. Genetic variation was estimated from the variation amongst clones of Egh , and was therefore an estimate of the maximum genetic variation in the local populations. The average gene diversity, Ĥ , was estimated as 0.84. The effective population size was estimated as: log₁₀ ( N^ _e ) = 0.64 − log₁₀(μ), or 4.4 × 10⁹, assuming a nucleotide mutation rate ( μ) of 10⁻⁹ per base per generation. There was no significant genetic differentiation between locations.     

Relating disease progress to cumulative numbers of trapped spores: apple powdery mildew and scab epidemics in sprayed and unsprayed orchard plots

A technique for relating the progress of plant diseases caused by airborne fungal pathogens to cumulative numbers of trapped spores is proposed. The relationship involves two epidemiological parameters—a disease asymptote and the infection efficiency (disease units/spore) of inoculum. The technique was evaluated using data on apple powdery mildew and scab epidemics in sprayed and unsprayed apple orchard plots. For powdery mildew, the observed relationships were close to those proposed in the unsprayed plot, but changed after or during the period of fungicide application in sprayed plots. Parameter estimates gave useful comparative information on the epidemics. The technique was not useful for scab because of the discontinuous patterns of infection.     

Reduced sensitivity of Cercospora beticola isolates to sterol-demethylation-inhibiting fungicides

In a survey conducted during October 1995, single-lesion isolates of the sugar beet leaf-spot fungus, Cercospora beticola , were tested for sensitivity to the sterol demethylation inhibiting fungicides (DMIs) flutriafol and bitertanol. The isolates were collected from fields in three different areas of northern Greece. Fields at Serres and Imathia had been sprayed with DMIs for about 15 years to control sugar beet leaf-spot. At the third site, Amyndeon, DMI fungicides had not been used. From each area 150 isolates were tested. ED₅₀ values were calculated for individual isolates by regressing the relative inhibition of colony growth against the natural logarithm of the fungicide concentration. The mean ED₅₀ values for flutriafol for the Serres, Imathia and Amyndeon populations were 1·07, 0·73 and 0·5 µg mL⁻¹, respectively (significantly different at P  = 0·05). For bitertanol the mean ED₅₀ values for the Serres and Imathia populations were 0·72 and 0·81 µg mL⁻¹, respectively, which were not significantly different at P  = 0·05. The mean ED₅₀ value of the Amyndeon population was 0·48 µg mL⁻¹, which was significantly lower than those of the other two populations ( P  < 0·05). A cross-resistance relationship was found to exist between the two triazole fungicides tested when log transformed ED₅₀ values of 60 isolates were subjected to a linear regression analysis ( r  = 0·81).     

Effect of early infection on pathotype frequencies in barley powdery mildew (Blumeria graminis f.sp. hordei) populations in field plots

A field experiment with barley powdery mildew ( Blumeria graminis f.sp. hordei ) was designed in order to study how the time of arrival of inoculum in the field influenced pathotype frequencies in the resulting populations. Three isolates belonging to pathotypes that were absent or rare in the local aerial inoculum were used to inoculate field plots of winter barley cv. Plaisant. Two successive inoculations with different combinations of the three isolates were performed with an approximately two-generation delay, and frequencies of inoculated pathotypes were assessed four and nine generations after the first inoculation. Pathotypes of the first inoculated isolates generally persisted throughout the period of sampling; this is described as an 'early arrival' effect. During the epidemics the inoculated isolates were not replaced by isolates from the natural airborne inoculum. Pathotype frequencies depended mainly on the time of arrival of inoculum in the plot, but frequencies also depended on the isolate that had been inoculated. The most frequent isolate, GL1, belonged to the clonal lineage dominant in powdery mildew populations on winter barley in the north of France. These results confirmed that the composition of a powdery mildew population in a field is largely determined by the composition of the initial inoculum.     

Resistance to Sphaerotheca pannosa in roses induced by 2,6-dichloroisonicotinic acid

The susceptible rose cv. Madelon and the partially resistant cv. Sonia both responded with reduced development of rose powdery mildew when they were treated with the synthetic inducer 2,6-dichloroisonicotinic acid (INA). The EC₅₀ for number of colonies cm⁻² was approximately 0.4 mg L⁻¹ in both cultivars when treated 4 days prior to inoculation. However, conspicuous differences were observed with respect to number of spores per cm². For sporulation, the EC₅₀ was 0.37 mg L⁻¹ in cv. Madelon and only 0.08 mg L⁻¹ in cv. Sonia. A comparison with the pathosystems cucumber/ Sphaerotheca fuliginea and red cabbage/ Peronospora parasitica is made and the importance of the observed phenomenon for the selection of parents in a breeding programme for (partial) resistance is discussed.     

INFLUENCE OF SOIL PROPERTIES ON PHYTOTOXICITY OF 4–AMlNO-3,5,6–TRICHLOROPICOLINIC ACID (PICLORAM)

Summary. Effective dosages of picloram (4–amino-3,5,6–trichloropicolinic acid) required to reduce fresh weight of sunflowers ( Helianthus annuus L. var. Menonite) were determined for seven Saskatchewan soils under controlled environmental conditions. The relationships between ED₅₀ value and clay content, organic matter content and cation exchange capacity were evaluated by correlation and regression analysis for possible usefulness in predicting dose requirements. ED₅₀ values were also determined for Weyburn loam and in culture solutions adjusted to various pH levels.
There Was no significant correlation between ED₅₀ values of picloram and soil clay content or cation exchange capacity. ED₅₀ values were highly correlated with soil organic matter content, and they increased as the soil pH was lowered or raised from pH 6.5. The increase in ED₅₀ values in the acidic range was attributed to adsorption of the unionized molecules of picloram on the organic matter in the soil. The increase in ED₅₀ values in the alkaline range may be mainly due to reduced uptake of the ionized acid by plant roots.     

Nitrogen-induced changes in colony density and spore production of Erysiphe graminis f.sp. hordei on seedlings of six spring barley cultivars

The influence of increasing nitrogen supply (30, 60, 120 and 240 mg N per pot) on susceptibility was studied on seedlings of six cultivars of spring barley inoculated with virulent isolates of powdery mildew. The colony density (CD) measured as colonies per cm² was significantly increased with increasing application of nitrogen on all cultivars, and a significant interaction was found between N and cultivar. The different reactions of the cultivars could not be ascribed to lack of N uptake. In general, increasing N application enhanced the sporulation capacity of colonies (CSC) irrespective of increased CD and the cumulative production of spores per cm² leaf (CSCM) increased strongly with N application in all cultivars. No interaction between N and cultivar was found for the latter component. The increase in CSCM closely corresponded with the increase in N content and fresh weight of uninoculated leaves. No interaction between N treatment and powdery mildew isolates was found for infection efficiency and spore production per colony, when tested on one cultivar. The N-induced changes in infection and sporulation can explain the main part of the increasing effect of N fertilization on powdery mildew development in the field. The results indicate that it may be possible to breed for or select barley cultivars with low N impact on powdery mildew development.     

新型杀菌剂苯噻菌酯的抑菌活性及生物学特性

报道了新型Qo I类杀菌剂苯噻菌酯(试验代号Y5247)的生物学特性。在含50μg/m L水杨肟酸(SHAM)旁路氧化专化性抑制剂的AEA培养基上,该杀菌剂抑制水稻纹枯病菌、稻瘟病菌、油菜菌核病菌及草莓灰霉病菌菌丝生长的有效中浓度(EC50)分别为0.004、0.009、0.016和0.023μg/m L;其抑制辣椒炭疽病菌和草莓灰霉病菌孢子萌发的EC50值分别为0.448和0.019μg/m L。苯噻菌酯对防治小麦白粉病具有保护和治疗作用,EC50值分别为0.991和1.823μg/m L。其在小麦叶片上内吸输导性差,但具有一定的渗透性、良好的粘着性、耐雨水冲刷和较长的持效期。用有效成分为25μg/m L的苯噻菌酯药液喷雾处理的麦苗,14 d后接种小麦白粉病菌,其防效仍达72.48%。     

黄瓜白粉病菌接种及对杀菌剂敏感性测定方法

建立了孢子悬浮液接种黄瓜子叶测定黄瓜白粉病菌杀菌剂敏感性的简便方法。比较了白粉病菌分生孢子悬浮液涂抹法和喷雾法接种黄瓜幼苗子叶的效果,结果表明,涂抹法发病率高,均匀度更好;测定了接菌后不同时间施药,白粉病菌对己唑醇、腈菌唑、三唑酮、甲基硫菌灵和百菌清等5种杀菌剂的敏感性,结果表明,接菌后96h施药较为敏感,测得的EC50较小。最后确定接种及毒力测定方法为:接种时白粉病菌分生孢子悬浮液使用十二烷基硫酸钠水溶液分散悬浮,孢子浓度为15×10倍显微镜下每视野30~40个,接种后96h施药,发病后直接利用病斑数来计算毒力测定结果。该方法可用于黄瓜白粉病菌抗药性监测和对杀菌剂敏感性测定。     

Sensitivity of fungi from cereal roots to fluquinconazole and their suppressiveness towards take-all on plants with or without fluquinconazole seed treatment in a controlled environment

The take-all fungus, Gaeumannomyces graminis var. tritici , was highly sensitive to fluquinconazole ( in-vitro EC₅₀ 0·016–0·018 mg L⁻¹), a fungicide developed for use as a seed treatment to control take-all, and to prochloraz (EC₅₀ 0·006 mg L⁻¹). Fungi of other genera that were commonly isolated from cereal roots were sensitive in varying degrees to prochloraz but were relatively insensitive (e.g. Fusarium culmorum , EC₅₀ > 20 mg L⁻¹) or slightly sensitive (e.g. Epicoccum purpurascens , EC₅₀ 0·514 mg L⁻¹) to fluquinconazole. Gaeumannomyces graminis var. graminis and G. cylindrosporus , weak parasites that can protect roots against take-all, and an unnamed Phialophora sp., all closely related to the take-all fungus, were highly or moderately sensitive to fluquinconazole. Alternaria infectoria and E. purpurascens were most consistently effective in suppressing development of take-all on pot-grown wheat plants dual-inoculated with G. graminis var. tritici and the nonpathogen. Take-all was decreased more on dual-inoculated wheat plants grown from seed treated with fluquinconazole or fluquinconazole plus prochloraz than when only an antagonistic fungus ( A. infectoria , E. purpurascens , Fusarium culmorum or Idriella bolleyi ) or a seed treatment was applied. These fungi were less effective in combination with seed treatments on barley. Gaeumannomyces graminis var. graminis and G. cylindrosporus , tested on wheat, suppressed take-all only in the absence of fungicides. It is suggested that the performance of seed treatment containing fluquinconazole against take-all may in some circumstances be enhanced by its partial specificity for the take-all fungus.     

叶绿素荧光成像技术监测苗期小麦白粉病初探

为探究叶绿素荧光成像技术在小麦白粉病监测应用中的可行性, 本研究对接种6个不同浓度小麦白粉菌分生孢子的小麦幼苗离体叶段?一叶一心期幼苗和二叶一心期幼苗以及接种后不同时期进行叶绿素荧光成像测定, 并对导出的叶绿素荧光参数与病情严重度的关系进行分析?结果发现, 接种不同浓度白粉菌分生孢子的小麦离体叶段或幼苗的Fv/Fm图像可以在一定程度上反映出小麦白粉病菌的侵染程度?接种小麦白粉菌后第3天, Fv/Fm值随接种浓度的变化规律不明显, 但从接种后第5天开始, Fv/Fm值随接种浓度的增加而下降, 且未接种的小麦幼苗或离体叶段的Fv/Fm值显著高于接种处理, 接种浓度最高(5 mg/mL)的处理其Fv/Fm值显著低于同时期其他接菌处理?小麦白粉病严重度与叶绿素荧光参数之间的相关性分析表明, Fv/Fm和Chlidx与病害严重度均极显著负相关, 在此基础上, 分别建立了小麦离体叶段?一叶一心幼苗及二叶一心幼苗的基于参数Fv/Fm或Chlidx的病害严重度估计模型?对模型的拟合效果进行比较发现, 基于Fv/Fm或Chlidx的病害估计模型其RMSE或R2比较接近, 因此叶绿素荧光参数Fv/Fm或Chlidx用来估计苗期小麦白粉病发生程度是可行的?本研究为叶绿素荧光成像技术在小麦白粉病监测预警中的应用奠定了理论基础, 具有一定的应用前景?     

小麦白粉病菌分生孢子田间传播的初步研究

2015年度采用定容式孢子捕捉器对田间空气中小麦白粉病菌分生孢子传播的初步研究表明,在病害发生初期病菌分生孢子捕捉量比较低,但随着菌源中心病害的逐渐加重,病菌分生孢子在距菌源中心20 m和40 m远处捕捉量随之增大。线性弧度相关分析结果发现,距菌源中心北向20 m和40 m处的孢子捕捉量与风向存在显著正相关性;距菌源中心不同距离处的孢子捕捉量之间均存在极显著正相关性,且在相同方向上,距菌源中心20 m处孢子捕捉量显著高于40 m处孢子捕捉量。     

A rapid method of counting spores of fungal pathogens by infra-red reflectance analysis

A method of counting freshly harvested spores of powdery mildew ( Erysiphe graminis f.sp. hordei ), yellow rust ( Puccinia striiformis ) and brown rust ( P. hordei ) of barley as well as brown rust ( P. recondita ) of wheat, using infra-red reflectance spectrophotometry was investigated. A Neotec 6350 Research Composition Analyser was used to scan spore samples on glass-fibre filter disks in the near infra-red region of the spectrum (1100–2500 nm) and the amount of energy reflected at 1400 different wavelengths recorded. Three wavelengths (1900, 2252 and 2308 nm) that together gave the best multiple correlation with spore populations counted on a haemocytometer slide were selected. Partial regression coefficients for each fungal species were derived by relating reflectance energy values to direct spore counts. Utilizing these and the energy reflected at the three selected wavelengths, it was possible to count spore samples with high precision. Correlations >0.9 between numbers estimated by the instrument and those obtained using a haemocytometer slide (within the range 0–30000 spores) were achieved with all the fungi examined. Application of the technique to smaller, fixed-filter instruments as a routine method of counting spores is discussed.     

An apparatus for collecting total conidia of Blumeria graminis f.sp. hordei from leaf colonies using electrostatic attraction

Conidia from living conidiophores of barley powdery mildew ( Blumeria graminis f.sp. hordei ) on host leaves were collected consecutively using an electrostatic spore collector. The collector consisted of an electrical conductor plate linked to an electrostatic voltage generator and insulator plates placed abreast on a timed conveyer. The conductor plate was negatively charged by the potential supplied from the voltage generator. The negatively charged conductor plate caused dielectric polarization of the insulator plate, and the surface charge on the insulator plate attracted mature conidia abstricted from conidiophores on colonies growing on leaves placed 2 cm from the insulator plate. The surface charge on the insulator plate was proportional to the voltage applied to the conductor plate. Under optimized conditions, abstricted conidia were attracted to the electrostatically activated insulator plates without any detriment to their survival. During a colony's life span of c . 460 h, conidia were released throughout the day and c . 12 × 10⁴ conidia were collected during the lifetime of the colony. This is the first report on the direct quantification of progeny conidia produced by powdery mildew infecting host leaves.     

Fungicide sensitivity in Swedish isolates of Phaeosphaeria nodorum

This is the first report of variability in sensitivity of Phaeosphaeria nodorum to the fungicide azoxystrobin, and also reports on sensitivity to propiconazole, prothioconazole and cyprodinil. An in vitro sensitivity test of 42 isolates from five Swedish winter wheat fields, collected in 2003–2005, was performed on malt extract agar amended with six concentrations of each fungicide. Four isolates collected during the early 1990s, before azoxystrobin had been commercially used in agriculture, were used as references. Fragments of DNA from 231 isolates, including the reference isolates, were sequenced for the genes of cytochrome b and CYP51 in search for amino acid substitutions known to cause loss of sensitivity to strobilurins and triazoles, respectively. The majority of the P. nodorum isolates possessed the amino acid substitution G143A, associated with loss of sensitivity in fungi to strobilurins, except in one field where only half of the isolates had the substitution. The EC₅₀ values varied between 0·66 mg L⁻¹ to estimations far above 1000 mg L⁻¹, with an estimated median value of 366 mg L⁻¹. The EC₅₀ values of the reference isolates ranged from 0·02 to 80·72 mg L⁻¹. The P. nodorum population is still sensitive to propiconazole, prothioconazole and cyprodinil, even though some isolates varied in sensitivity to triazoles. Part of the CYP51 gene, a possible target for triazole sensitivity, was sequenced but no nonsynonymous substitutions were found.     

Sensitivity of Sclerotinia homoeocarpa to demethylation-inhibiting fungicides in Ontario, Canada, after a decade of use

In late 2003, nine populations of Sclerotinia homoeocarpa in Ontario Canada (seven of which had been previously sampled in early 1994, prior to the registration of sterol demethylation-inhibiting (DMI) fungicides for turf disease control in Canada) were sampled and tested for sensitivity to propiconazole. Four of the nine populations had not been treated with DMI fungicides during the intervening years, and isolates from these locations were sensitive to propiconazole (geometric mean EC₅₀ values of 0·005–0·012 µ g mL⁻¹, compared with 0·005–0·008 µ g mL⁻¹ for the original 1994 populations). Among the five populations from 2003 that had been exposed to DMI fungicides, mean EC₅₀ values were significantly greater, ranging from 0·020 to 0·048 µ g mL⁻¹. A significant correlation of determination was found between estimated number of fungicide applications and log EC₅₀ ( R ² = 0·832, P  = 0·0001), and the equation predicted that 42·3 applications of propiconazole would be needed to bring a sensitive population (EC₅₀ < 0·01  µ g mL⁻¹) to a resistant level (EC₅₀ > 0·10  µ g mL⁻¹). Fungicide sensitivity vs. duration of fungicide efficacy was also tested, and it was found that isolates with decreased sensitivity were able to more quickly overcome the inhibitory effects of fungicide application, reducing the duration of control from 3 weeks to 2 weeks.     

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。     

Effects of Uncinula necator on the yield and quality of grapes (Vitis vinifera) and wine

The effects of powdery mildew ( Uncinula necator ) on grape yield, juice and wine quality were quantified for cultivar Cabernet Sauvignon (CSa) in 1997 and 1999, and for Sauvignon blanc (Sa) in 1999. Analyses were carried out on batches of healthy berries to which known percentages (0–50%) of diseased berries were added, and on natural clusters that were classified into four visual classes from low (C₁) to high (C₄) disease severity. CSa diseased berries showed an average weight reduction of 12% (1997) and 20% (1999). The direct consequence of a higher percentage of smaller, diseased berries was a reduction in yield. The accompanying loss of weight in must from C₁ to C₄ clusters increased from 10 to 45%. Sugar content in diseased berries was not significantly different from disease-free berries in 1997, but was 20–21% (CSa) and 14% (Sa) higher in 1999. Severely infected batches also showed a higher total acidity than healthy ones. The total anthocyanin content of CSa was decreased by 0·91% (1997) and 0·66% (1999) per percentage mildewed berries added by weight. In Sa wines the concentration of 3-mercaptohexanol, a component of varietal aroma, was decreased by powdery mildew. Multidimensional analyses, based on all the variables studied, successfully grouped batches of CSa according to disease severity. Using directional triangular tests wine experts were able to recognize CSa wines produced from berries with ≈25% of powdery mildew; the threshold for nonexperts was 50%. CSa wines obtained from samples with more than 30% of diseased berries by weight were significantly classified as the worst according to preference order criteria, but below this value the preference was not significant. Sa wines with <50% mildewed berries could not be differentiated significantly by organoleptic tests performed by nonprofessionals.