Understanding pathogen population structure and virulence variation for efficient resistance breeding to control cucurbit powdery mildews

Cucurbit powdery mildew (CPM) is caused most frequently by well-differentiated obligate erysiphaceous ectoparasites Golovinomyces orontii and Podosphaera xanthii, which vary in their ecology and virulence. All economically important cucurbit crops host both of these CPM species. Breeding of cucurbits for CPM resistance is highly important worldwide, but adequate knowledge of CPM species determination, as well as virulence structure, population dynamics, and spatiotemporal variation of these pathogens, has not yet been achieved. New tools have been developed to enhance research on CPM virulence variation for more efficient breeding and seed and crop production. A set of differential genotypes of Cucumis melo, with high differentiation capacity, may contribute substantially to understanding of variation in CPM virulence at both individual and population levels. Long-term observations (2001–2012) of CPM pathogens in the Czech Republic were used to analyse virulence variation within and among annual CPM populations and demonstrate the utility of recently developed tools for studying species variability and virulence variation of CPM pathogens worldwide. Detailed analyses of diversity and spatiotemporal fluctuations in the composition of CPM populations provide crucial information for shaping breeding programmes and predicting the most effective sources of race-specific resistance. The primary aim of this work was to create a uniform framework for determination of CPM species structure and diversity, virulence phenotypes, virulence and phenotype frequencies, phenotype complexity, dynamics, and variation within and among CPM populations. In addition, practical advice is presented on how to select the most relevant data and interpret them for use in cucurbit resistance breeding.     

Effect of potassium silicate on epidemic components of powdery mildew on melon

The effects of silicon (Si) supplied in the form of potassium silicate (PS) were evaluated on epidemic components of powdery mildew of melon under greenhouse conditions. The PS was applied to the roots or to leaves. In the first experiment, epidemic components were evaluated after inoculation with Podosphaera xanthii. In the second experiment, the disease progress rate was evaluated on plants subjected to natural infection. The area under the disease progress curve was reduced by 65% and 73% in the foliar and root treatments, respectively, compared to control plants, as a consequence of reductions in infection efficiency, colony expansion rate, colony area, conidial production and disease progress rate. However, root application of PS was more effective than foliar application in reducing most of the epidemic components, except for infection efficiency. This can be explained by the high Si concentration in leaf tissues with root application, in contrast to the foliar treatment where Si was only deposited on the external leaf surfaces. The effects of PS reported in this study demonstrated that powdery mildew of melon can be controlled, and that the best results can be achieved when PS is supplied to the roots.     

Effects of temperature and atmospheric moisture on the early growth of apple powdery mildew (Podosphaera leucotricha) colonies

Effects of four temperatures and nine water vapour pressure deficits on the early growth of apple powdery mildew colonies on young leaves inoculated with conidia were studied on potted apple rootstocks in controlled environment cabinets. The number of hyphae (germ tubes + primary and secondary hyphae) per colony, total hyphal length per colony and the length of time from inoculation to the first observation of secondary hyphae were recorded on the upper surfaces of stained preparations of leaves sampled at three intervals up to 60 h after inoculation. Analyses of variance of these variables describing colony growth revealed significant differences between treatments (temperature × vpd), with most (c. 61–79%) of the treatment effects due to temperature, as shown by regression analysis. The response to temperature (13–28 °C) was non-linear, with the optimum c. 22 °C. In contrast, there was no detectable trend in the response of colony growth to vapour pressure deficit (1.6–10.4 mmHg). The results suggest that the rate of development of young colonies depends more on temperature than on moisture stress.     

Effects of foliar- and root-applied silicon on the enhancement of induced resistance to powdery mildew in Cucumis sativus

Two cucumber ( Cucumis sativus ) cultivars differing in their resistance to powdery mildew, Ningfeng No. 3 (susceptible) and Jinchun No. 4 (resistant), were used to study the effects of foliar- and root-applied silicon on resistance to infection by Podosphaera xanthii (syn. Sphaerotheca fuliginea ) and the production of pathogenesis-related proteins (PRs). The results indicated that inoculation with P. xanthii significantly suppressed subsequent infection by powdery mildew compared with noninoculation, regardless of Si application. Root-applied Si significantly suppressed powdery mildew, the disease index being lower in Si-supplied than in Si-deprived plants, regardless of inoculation treatment. The resistant cultivar had a more constant lower disease index than the susceptible cultivar, irrespective of inoculation or Si treatment. Moreover, with root-applied Si, activities of PRs (for example peroxidase, polyphenoloxidase and chitinase) were significantly enhanced in inoculated lower leaves or noninoculated upper leaves in inoculated plants of both cultivars. Root-applied Si significantly decreased the activity of phenylalanine ammonia-lyase in inoculated leaves, but increased it in noninoculated upper leaves. However, Si treatment failed to change significantly the activity of PRs in plants without fungal attack. Compared to the control (no Si), foliar-applied Si had no effects either on the suppression of subsequent infection by P. xanthii or on the activity of PRs, irrespective of inoculation. Based on the findings in this study and previous reports, it was concluded that foliar-applied Si can effectively control infections by P. xanthii only via the physical barrier of Si deposited on leaf surfaces, and/or osmotic effect of the silicate applied, but cannot enhance systemic acquired resistance induced by inoculation, while continuously root-applied Si can enhance defence resistance in response to infection by P. xanthii in cucumber.     

Changes in carbohydrate composition of cucumber leaves during the development of powdery mildew infection

Within 3 days after inoculation, greater rates of decrease of hexoses, and of increases in inositol and α-glucans, were detected in leaves of cucumber leaves infected with Sphaerotheca fuliginea (now reclassified as Podosphaera xanthii ) than in healthy leaves, together with synthesis of fungal mannitol, arabitol and trehalose. With the onset of sporulation (5 days after inoculation, dai), glucose, polyols, trehalose and glycogen content, as well as fresh and dry weight of leaf tissue, increased more rapidly than in healthy plants, while sucrose, raffinose and starch declined. Starch, glycogen and other α-glucans, extracted from ethanol-insoluble tissue fractions of different water-solubility from healthy and infected leaves, were quantified after amyloglucosidase treatment. Infection-induced alterations in partitioning of photosynthate during a 14 h photoperiod at 7 dai, including a close correspondence in patterns of synthesis of glucose, polyols and glycogen, further clarified the process of diversion of host assimilate to the pathogen. The presence of glucose, but only traces of sucrose in spores, supported evidence from other powdery mildew infections for photosynthate being transferred to S. fuliginea as glucose.     

电解水对黄瓜白粉病的防效以及对黄瓜生长和品质的影响

利用电解水喷施大棚黄瓜,研究其对黄瓜白粉病的防治效果,以及对植株生长指标、果实品质及产量的影响。结果表明,施用农药、先喷酸性电解水后喷碱性电解水、酸性电解水、及先喷碱性电解水后喷酸性电解水4个处理后黄瓜叶面病情指数显著降低,最终防治效果分别为88.5%、75.1%、72.8%、57.6%,碱性电解水处理防效为15.5%。电解水除对黄瓜植株具有一定的促徒长作用外,对黄瓜果实品质和产量未见不利影响,且酸性电解水和先喷酸性电解水后喷碱性电解水可增加植株根部、地上部分干重,促进黄瓜叶面生长。     

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。     

三类杀菌剂对牡丹腔孢叶斑病菌生长和发育的影响

腔孢叶斑病是牡丹生产上出现的一种新病害,近几年在洛阳及菏泽牡丹种植园危害越来越重。为了筛选防治该病的化学药剂,本文采用菌丝生长速率法测定了3类8种杀菌剂对病菌菌丝生长的抑制活性,采用涂布平板法测定了多菌灵、戊唑醇及嘧菌酯对病菌孢子萌发和芽管伸长的影响,并在含药平板上测定了3种药剂对病菌产孢量的作用。结果表明:三唑类药剂对病菌菌丝生长的毒力最强,EC50为0.020~0.096μg/mL,且戊唑醇对孢子萌发和产孢也有很强的抑制活性,在0.1μg/mL时孢子即不能萌发;甲氧基丙烯酸酯类药剂对菌丝生长的毒力较强,EC50为0.408~0.939μg/mL,嘧菌酯对芽管伸长和产孢量均表现出很强的抑制活性,10μg/mL时,芽管几乎不再伸长,对产孢的抑制率可达到99%以上;而苯并咪唑类药剂对菌丝生长的毒力较弱,EC50为12.167~30.104μg/mL,多菌灵对孢子萌发的抑制作用弱,100μg/mL时孢子萌发率仍达到90%以上,对产孢的抑制作用也较弱,为63.02%。根据药剂对病菌生长和发育各阶段的影响,生产中应采用适宜的施用方法:戊唑醇和嘧菌酯可作为保护剂在病害发生前期喷施,也可作为治疗剂在病害发生流行期应用,但为防止抗药性菌株的出现,两者应当轮换或复配使用。     

Effects of temperature and leaf age on conidial germination and disease development of powdery mildew on rubber tree

Powdery mildew is an important disease of rubber trees worldwide. To assess the effects of temperature and leaf age on conidial germination and disease development, conidia were inoculated onto rubber tree seedlings with leaves at three phenological stages (copper bronze, colour-changing, and light green) and then incubated at six constant temperatures (10, 15, 20, 25, 30, and 35°C). Leaf age did not affect conidial germination (p = .296) whilst temperature did (p < .0001), although conidia were able to germinate at all tested temperatures. The estimated optimal temperature for conidial germination was 23.2°C. Leaf age, temperature, and their interactions had significant effects on conidial infection and hypha number (p < .0001). At 10 and 35°C, more than 2 and 4 days were needed for infection to complete, respectively, compared to <2, 1, 0.5, and 0.5 days for 15, 20, 25, and 35°C, respectively. Sporulation and mildew symptoms were only observed on those inoculated leaves of all stages at 20 and 25°C, and at the copper bronze stage only at 15°C. The latent period on the copper bronze leaves at 15°C was longer (9 days) than at 20 and 25°C (4 days). The latent period at 20 and 25°C increased from 4 to 7 days as the leaf development stage increased from copper bronze to light green. Therefore, temperature affected germination and postgermination growth of rubber tree powdery mildew, whereas leaf age primarily affected postgermination growth of the pathogen.     

Effect of seventeen fungicolous fungi on sporulation of cucumber powdery mildew

Nineteen isolates of 17 different fungal species thriving upon other fungi were tested for their ability to control sporulation of cucumber powdery mildew,Sphaerotheca fuliginea. More than half of the fungi reduced the number of healthy conidiophores to less than 10%.Tilletiopsis albescens was superior toAmpelomyces quisqualis. Three species, viz.A. quisqualis, Aphanocladium album andT. albescens, were selected for further greenhouse experiments.Samenvatting Negentien isolaten behorend tot 17 verschillende schimmelsoorten werden getoetst op hun bruikbaarheid voor de biologische bestrijding van komkommermeeldauw aan de hand van effecten op sporulatie. Meer dan de helft van de getoetete isolaten reduceerde het aantal gezonde conidioforen tot minder dan 10%. De werking vanTilletiopsis albescens was enigszins beter dan die van de meestal gebruikte hyperparasietAmpelomyces quisqualis. Van de getoetste schimmels werden er drie, n.l.A. quisqualis, Aphanocladium album enT. albescens, geselecteerd voor kasproeven.     

采用孢子萌发法测定化合物对黄瓜白粉病菌的生物活性

接种黄瓜白粉菌后16 h的黄瓜叶片用透明胶带在子叶表面粘孢子取样的平均发芽率与用台盼蓝染色后在光学显微镜下调查的发芽率分别为83.7%和85.0%,t测验无显著差异,表明透明胶带取样的发芽率可以代表黄瓜叶片上白粉病菌孢子的发芽率。采用孢子萌发法和叶碟法分别测定了醚菌酯、植物源活性组分大黄素甲醚(P3D)对8个黄瓜白粉菌菌株的EC₅₀。统计结果表明:采用两种方法测定醚菌酯P、3D对黄瓜白粉菌的EC₅₀的相关系数的平方值分别为0.880、.99,表明两种方法的测定结果有很强的相关性;采用该孢子萌发法可评价化合物对植物专性寄生病菌如白粉菌孢子萌发的生物活性。     

Modelling and forecasting epidemics of apple powdery mildew (Podosphaera leucotricha)

A model developed to simulate epidemics of powdery mildew on vegetative shoots of apple generates two types of output. Firstly, it forecasts disease severity (percentage of host tissue infected) by incorporating effects on disease development of the amount of healthy susceptible tissue and current infectious (sporulating) disease, the level of initial inoculum (overwintered 'primary' mildew) and weather conditions. The effects of weather variables are considered on only two aspects of the fungal life cycle: initial spore germination and the subsequent development during the incubation period. Secondly, the model generates indices of the relative favourability of weather conditions on disease development by incorporating effects of weather on conidial production/dispersal and germination. On each day, forecasts of the (relative) severity of new infection and total current infectious disease are given for both types of output. The model was evaluated by comparing its predictions with the mildew epidemics observed in two unsprayed orchards over four years. In all the years, the temporal patterns of the predicted and the observed disease were generally similar. The pattern of the disease severity forecasts was marginally closer to the observed than that derived from two weather indices. Potential roles of the model in practical management of apple powdery mildew are discussed.     

小麦白粉病与温度的定量关系研究

温度对小麦白粉病影响试验的结果表明,此病害适宜发生的温度为15～20℃,低于10℃或高于25℃对该病有明显抑制作用。当温度高于26℃时,试验显示随着温度的升高,终止小麦白粉病病程的时间缩短,据此建立了不同温度(x)与相应终止病程的时间(y)的关系模型为y=21 900e^{-0.303 5x}(χ²=1.65<χ²_0.05,7=14.07)。同时,根据高温区病害的严重度(y)与温度(x)的试验数据,建立了其关系模型为:y=-3.00x+76.60(r²=0.922 1^**),由此计算获得了连续10 d(一个病程时间)温度为25.53℃即可终止此病害的病程。该试验结果将为小麦白粉病的越夏区划提供基础数据。     

一体化智能孢子捕捉系统在黄瓜霜霉病和黄瓜白粉病预测上的应用

为探索国内研制的新型一体化智能孢子捕捉系统在黄瓜霜霉病和黄瓜白粉病预测预报上的应用,在田间自然发病情况下,通过对捕捉孢子的形态进行识别,优化一体化智能孢子捕捉系统主要工作参数如有/无空气切割头、空气采集口高度和空气采集时间;通过病害及孢子的动态监测分析大棚黄瓜霜霉病和黄瓜白粉病病情指数与孢子捕捉量的关系。结果表明,当不加装空气切割头、空气采集口高度为70 cm、孢子捕捉时间在10:00—10:30时段有利于孢子的捕捉。黄瓜霜霉病和黄瓜白粉病病情指数与连续7 d孢子捕捉总量具有强正相关性。连续多日监测到黄瓜霜霉病菌孢子囊且数量快速增加是黄瓜霜霉病发生或快速上升的一个预测指标。黄瓜白粉病发病之前没有监测到黄瓜白粉病菌分生孢子,且在病害盛发期分生孢子捕捉量仍较少。研究表明,一体化智能孢子捕捉系统适用于黄瓜霜霉病的预测,但在黄瓜白粉病的预测上尚存在一定问题。     

四氟醚唑对黄瓜的安全性及其对黄瓜白粉病的防治效果

为明确四氟醚唑对黄瓜植株的安全性,采用浸种及茎叶喷雾处理的方法测定其对不同生长时期黄瓜植株的影响,采用子叶保湿培养法测定白粉病菌对其敏感性,并在田间进行防治白粉病的药效试验,综合评价了四氟醚唑对黄瓜白粉病的效果。浸种处理后,黄瓜子叶上白粉病发病率明显降低,对黄瓜株高和根长的抑制率、茎周增长率及叶绿素含量增加率与己唑醇相比均较低;发芽期及幼苗期的黄瓜植株使用四氟醚唑处理,新生节间均出现轻微的抑制伸长现象;4％四氟醚唑水乳剂对黄瓜白粉病菌的EC50为0．8146mg／L,敏感毒力高于50％醚菌酯水分散粒剂;田间间隔期10天喷雾,在末次药后7天对黄瓜白粉病的防治效果为76．02％～85．77％,与5％己唑醇水乳剂防效相当,明显高于50％醚菌酯水分散粒剂的防效。表明四氟醚唑对黄瓜生长安全且用药间隔期长,是防治白粉病的高效轮换药剂。     

多功能生物制剂对黄瓜白粉病的防治效应

通过盆栽和田间药效试验,研究了多功能生物制剂多霸2对黄瓜白粉病的防治效应。盆栽试验结果表明,先施用多霸2的100、200倍液后接种病原菌,可显著提高黄瓜的抗病能力,降低发病率,防效达到72.0%和69.2%,差异极显著(P<0.01);先接种后喷药多霸2的100、200倍液,在一定程度上能抑制病原菌的扩展,也具有防治作用,相对防效达到26.5%和23.1%,差异显著(P<0.05)。田间调查表明,在黄瓜苗期开始施用或未发病前施用多功能制剂,能有效预防白粉病的发生,具有很好的防治效应。多霸2的100、200倍液对黄瓜白粉病的防效与清水对照和常用药剂粉锈宁相比,差异都达到显著或极显著水平。其中,多霸2的100倍液使用效果最好,优于200倍液。     

Effect of culture filtrates of seventeen fungicolous fungi on sporulation of cucumber powdery mildew

Culture filtrates of 17 different fungal species thriving upon other fungi were tested for their ability to reduce sporulation of cucumber powdery mildew,Sphaerotheca fuliginea.All culture filtrates reduced the number of healthy conidiophores. However, the differences in activity between the various treatments were not as conspicuous as after application of spore suspensions. The best results were obtained with culture filtrates ofCalcarisporium arbuscula. These reduced the number of healthy conidiophores to ca. 2% of the unsprayed control plants.     

Effect of culture filtrates of seventeen fungicolous fungi on sporulation of cucumber powdery mildew

Culture filtrates of 17 different fungal species thriving upon other fungi were tested for their ability to reduce sporulation of cucumber powdery mildew,Sphaerotheca fuliginea.All culture filtrates reduced the number of healthy conidiophores. However, the differences in activity between the various treatments were not as conspicuous as after application of spore suspensions. The best results were obtained with culture filtrates ofCalcarisporium arbuscula. These reduced the number of healthy conidiophores to ca. 2% of the unsprayed control plants.     

不同硅源制剂对小麦白粉病的作用效果及对白粉病菌孢子萌发的影响

 研究了不同形态硅源制剂二氧化硅纳米粒子溶胶(60nm和100nm)、正硅酸乙酯、硅酸钠对小麦白粉病的作用效果以及对白粉病菌孢子萌发的影响。结果表明,在相同浓度下几种硅源制剂处理盆栽小麦幼苗对白粉病防效分别为48.78%、43.73%、40.31%和33.29%,室内处理小麦离体叶段对白粉病抑制率分别为59.67%、53.51%、51.10%和42.22%。离体叶段接种白粉菌后1.5~2h、6~7h取样,在相差显微镜下观察白粉菌孢子萌发过程,发现这几种硅制剂对白粉菌孢子初生芽管(PGT)的形成几乎没有影响,但对附着胞(AM)的形成有较大影响,其中以二氧化硅纳米粒子溶胶对AM的影响最大。