南瓜白粉病病原菌鉴定及寄主范围测定

通过对南瓜白粉病病原菌的闭囊壳、分生孢子及萌发方式的观察和鉴别寄主感病反应鉴定,结果表明引起甘肃省武威地区南瓜白粉病的病原菌为苍耳单囊白粉菌Podosphaera xanthii。该白粉病菌闭囊壳形成的最适条件为温度20℃、相对湿度70%和光照强度4,400lx。寄主范围测定结果表明,该病菌不侵染丝瓜、小麦、辣椒、番茄、苜蓿、红三叶草、架豆和菜豆,可侵染除丝瓜之外的其余9种瓜类植物和绿豆、红小豆、向日葵,其中对南瓜、绿豆、西葫芦、红小豆、向日葵、甜瓜和黄瓜的致病性最强,发病率均达到100%,病情指数分别为15.56、14.51、13.33、13.33、13.07、12.22和12.22。侵染过程观察发现,感病南瓜人工接种白粉菌12h后,分生孢子芽管从侧面萌发,于24h芽管伸长,于36h形成菌丝,于72h形成稠密的网状菌丝,于96h形成分生孢子梗及串生分生孢子。     

青岛地区茄白粉病的病原菌鉴定

在青岛地区的保护地和露地发现茄白粉病,通过形态学和分子生物学进行鉴定以及致病性测定。结果将青岛地区茄白粉病的病原鉴定为Podosphaera xanthii,本文为该菌在我国茄子上的首次报道。     

中国长春瓜类白粉菌Podosphaera xanthii形态学和分子系统学研究

2009年长春农博园瓜类白粉病大发生,而且大量闭囊产生在葫芦科的四个属（葫芦属、黄瓜属、栝楼属、南瓜属）植物上。对病害发生的严重度和病情指数进行了调查,结果表明园中栽培的所有品种均为感病品种。形态学观察显示分子孢子串生,具纤维体,闭囊壳只含有一个子囊,内含8个子囊孢子,子囊顶端孔较宽（15.6－28.8μm）。有性和无性形态学特征表明该菌应属于Podosphaera xanthii。基于rDNA ITS序列的分子系统学分析表明该菌与GenBank中已报道的该种在其他地区瓜类上的序列以及在其他寄主上的序列聚     

吉林省香菜一新病害——白粉病

通过病害症状和病原形态学特征对吉林省香菜种植区白粉病病原菌进行鉴定,结果为该病由独活白粉菌（Erysiphe heraclei DC．）引起。香菜白粉病为吉林省香菜一新病害,且芫荽属为东北地区白粉菌属级新记录寄主。     

江苏白粉菌研究Ⅱ:云台山白粉菌简志

报道了江苏省云台山地区的白粉菌目5属19种和变种,其中,散生单囊白粉菌Podosphaera sparsa(U. Braun) U. BraunS.Takam.为国内新记录种,千里光单囊白粉菌Podosphaera senecionis U. Braun为江苏省新记录种。所有引证标本分别保存在中国科学院微生物研究所菌物标本馆(HMAS)和连云港市植保植检站标本室(Y)。     

黑龙江省葫芦科白粉病菌RAPD分析

2010年采集黑龙江省不同生态区不同设施内的甜瓜、黄瓜、南瓜、西瓜等瓜类白粉病菌菌株17份,采用国际通用的瓜类白粉病菌生理小种鉴别寄主对17份白粉病菌进行了生理小种鉴定。根据13个鉴别寄主的抗感反应,初步确定黑龙江省葫芦科作物白粉病菌存在3个生理小种,即单囊壳白粉菌Podosphaera xanthii的生理小种1和生理小种N1号及一个新生理小种,其中生理小种1为优势小种。通过对13份白粉病菌的RAPD分析,从119个随机引物中筛选出10个条带清晰而且重复性好的引物,扩增得到157个位点,其中多态性位点为138个,多态性位点频率为97.89%,表明黑龙江省葫芦科作物白粉菌具有丰富的遗传多样性。利用NTSYS-PC软件进行数据分析,结果表明13个菌株之间遗传相似系数的变化幅度为0.52－0.75。根据遗传相似系数用类平均法（UPGMA）对其聚类,以遗传相似系数0.60为阈值,供试菌株可区分为4个类群。同是生理小种1的菌株部分聚到了同一类,新生理小种与部分生理小种1菌株聚到同一类,同是生理小种N1的两个菌株未聚到同一类;相同地理来源或相同寄主来源的白粉菌也未聚到一类。初步确定葫芦科白粉病菌致病性与DNA多态性不形成对应关系,菌株的遗传多样性与菌株地理来源、寄主来源及设施类型亦无明显的直接关系。     

荒漠固沙植物河西菊的白粉病菌

2009–2011年间,在对新疆塔里木盆地进行白粉菌物种多样性调查时,发现荒漠固沙植物河西菊Hexinia polydichotoma白粉病大发生,导致植株大面积死亡。通过对病原菌形态学特征观察和rDNA-ITS序列分析,证明引发新疆塔里木盆地河西菊白粉病大发生的病原菌为野莴苣内丝白粉菌Leveillula lactucae-serriolae,为中国新记录种,河西菊为新寄主。     

内蒙古白粉菌区系多样性

为阐明内蒙古白粉菌区系组成特点、探讨其起源和演化,对其区系多样性进行了分析.区系中含有10种以上的属为自粉菌属(Erysiphe)、单囊白粉菌属(Podosphaera)和高氏白粉菌属(Golovinomyces),3属共104种,占总种数的84.55%.根据地理分布资料,内蒙古白粉菌可划分为世界广布种(13.82%)...     

孜然种子提取物枯茗醛和枯茗酸抑菌作用研究

以番茄早疫病菌、棉花黄萎病菌、小麦纹枯病菌、烟草赤星病菌、小麦全蚀病菌、油菜菌核病菌、辣椒疫霉病菌、水稻纹枯病菌、小麦白粉病菌和番茄灰霉病菌等为供试菌种,采用离体与活体相结合的方法系统地测定了枯茗醛和枯茗酸的抑菌活性。离体抑菌活性测定结果表明,枯茗醛和枯茗酸对多种病原菌具有一定的抑制效果,其中对油菜菌核病菌菌丝生长的抑制效果高于其它供试病原菌,有效中浓(EC50)分别为2.1和7.3 mg/L;枯茗醛和枯茗酸对小麦白粉病的防治实验结果表明,供试浓度为1000 mg/L时,两种药剂的保护防效均高于50%;相同处理浓度下,枯茗酸对油菜菌核病的保护防效与速克灵处理相当,达到57.52%。     

吉林省枸杞白粉病病原菌鉴定

对枸杞白粉病病原菌形态进行详细观察,发现了引起枸杞白粉病的病原菌—穆氏节丝壳Arthrocladiella mougeotii。节丝壳属为吉林省新记录属,枸杞白粉病为吉林省新病害。另外还发现了枸杞上同时寄生有反卷白粉菌Erysiphe kenjiana,通过对采集环境、病菌分生孢子形态观察和萌发试验的研究分析,确定这种寄生现象为"假寄生"。     

Inoculum production and long-term conservation methods for cucurbits and tomato powdery mildews

The behaviour of cucurbit powdery mildews (Podosphaera xanthii and Golovinomyces cichoracearum) and tomato powdery mildew (Oidium neolycopersici) infesting detached cotyledons of Lagenaria leucantha cv. ‘Minibottle’ was studied in order to develop an easy culture method for pure inoculum production. High spore production was found with a combination of mannitol (0.1 m), sucrose (0.02 m) and agar (8 g l⁻¹) in the cotyledon survival medium. Sporulation on cotyledons and viability of conidia were affected by the age of culture for the three species of powdery mildew tested. The age of cotyledons had also an impact of the spore production. This method was used to produce large amounts of inoculum for P. xanthii, G. cichoracearum and O. neolycopersici and enable the development of other species of powdery mildew like Leveillula taurica. Freezing conidia in liquid nitrogen enabled the long-term conservation of P. xanthii without any loss of virulence. The same method was unsuccessful with G. cichoracearum, and L. taurica and partly successful with O. neolycopersici.     

Gaps and perspectives of pathotype and race determination in <Emphasis Type="Italic">Golovinomyces cichoracearum</Emphasis> and <Emphasis Type="Italic">Podosphaera xanthii</Emphasis>

Golovinomyces cichoracearum and Podosphaera xanthii (family Erysiphaceae) are the most important species causing cucurbit powdery mildew (CPM), a serious disease of field and greenhouse cucurbits. Both species are highly variable in their pathogenicity and virulence, as indicated by the existence of large number of different pathotypes and races. Various independent systems of CPM pathotype and race determinations and denominations are used worldwide. CPM pathotype identification is based on intergeneric and interspecific differences in host-CPM interactions. The most commonly used set of CPM pathotype differentials includes one genotype from four species representing three agriculturally important cucurbit genera plus two genotypes from a fifth species, melon Cucumis melo L. CPM races are characterized by specialization on different cultivars or lines of one host species and have, to date, been differentiated only on melon (C. melo L.). The most frequently used set of melon differentials includes 11 genotypes that can differentiate CPM races originating from melon and other cucurbits, e.g., cucumber, Cucurbita spp., and watermelon. In this paper, we critically review the current state, gaps, and perspectives in our understanding of pathogenicity variation in these two CPM pathogens at the pathotype and race levels.     

Seasonal variations in the occurrence of Golovinomyces orontii and Podosphaera xanthii,causal agents of cucurbit powdery mildew in Northern Italy

Powdery mildew, caused by Golovinomyces orontii and Podosphaera xanthii, is a widespread disease that causes important losses in cucurbit production. To determine the aetiology and the epidemiology of cucurbit powdery mildew disease in the North of Italy, observations on the occurrence of the main disease‐causing fungal species were conducted during the 2010, 2011 and 2012 growing seasons. Samples of infected leaves of zucchini, melon and pumpkin plants, either from field or greenhouse crops, were collected every 15–18 days from May to September/October. To identify the fungal species, both morphological observations based on the asexual stage and molecular identifications by a Multiplex‐PCR reaction with species‐specific primers were performed. Climatic parameters of temperature and relative humidity were also monitored. Pearson's correlation coefficient and Principal Component Analysis showed a negative significant correlation between the two species, and a peculiar epidemiological behaviour was also observed: the earlier infections were caused by G. orontii, which was the predominant species till the end of June–middle of July. At this time, this species progressively decreased in frequency and was replaced by P. xanthii that became the main species infecting cucurbits till the end of the growing season. As the two species have different ecological requirements, these seasonal variations in the cucurbit powdery mildew species composition could possibly be explained by the influence of temperature and relative humidity on the pathogen epidemiology during the growing season but also by the different overwintering strategies adopted by the two species.     

First report of powdery mildew caused by Podosphaera xanthii on Luffa acutangula in Odisha State,India

Abstract

Ridge gourd (Luffa acutangula) is an herbaceous perennial twining vine cultivated globally as vegetable and medicinal plant. During October to January in 2014 and 2015, 40% powdery mildew disease incidence was observed in different areas of Odisha state, India. The pathogenicity experiments confirmed the powdery mildew disease symptoms on artificially inoculated L. acutangula seedlings. Causal organism was identified as Podosphaera xanthii on the basis of morphological and molecular studies. This is the first report of powdery mildew disease on L. acutangula caused by P. xanthii.     

Distribution,Host Range and Disease Severity of Pseudoperonospora cubensis on Cucurbits in the Czech Republic

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is a major cucumber disease in the Czech Republic. Disease prevalence, host range and disease severity were evaluated from 2001 to 2009. The geographical distribution of P. cubensis was assessed on ca 80–100 locations per year in two main regions of the Czech Republic (central and southern Moravia, and eastern, northern and central Bohemia). Infection by P. cubensis was observed primarily on cucumber (Cucumis sativus) but only on the leaves. During the study, disease prevalence ranged from 66 to 100%. The majority of C. sativus crops were heavily infected at the end of the growing season (second half of August). Generally, P. cubensis was present at high or very high disease severity. The loss of foliage results in the reduction in the quality and quantity of marketable yield of fruit. Pseudoperonospora cubensis was widespread across the whole area of the Czech Republic studied. Very rarely, infection was recorded in muskmelon (Cucumis melo) and Cucurbita moschata. Of other pathogens, the most frequently recorded was the cucurbit powdery mildew (Golovinomyces cichoracearum and Podosphaera xanthii).     

Transient transformation of Podosphaera xanthii by electroporation of conidia

Background

Powdery mildew diseases are a major phytosanitary issue causing important yield and economic losses in agronomic, horticultural and ornamental crops. Powdery mildew fungi are obligate biotrophic parasites unable to grow on culture media, a fact that has significantly limited their genetic manipulation. In this work, we report a protocol based on the electroporation of fungal conidia, for the transient transformation of Podosphaera fusca (synonym Podosphaera xanthii), the main causal agent of cucurbit powdery mildew.

Results

To introduce DNA into P. xanthii conidia, we applied two square-wave pulses of 1.7 kV for 1 ms with an interval of 5 s. We tested these conditions with several plasmids bearing as selective markers hygromycin B resistance (hph), carbendazim resistance (TUB2) or GFP (gfp) under control of endogenous regulatory elements from Aspergillus nidulans, Neurospora crassa or P. xanthii to drive their expression. An in planta selection procedure using the MBC fungicide carbendazim permitted the propagation of transformants onto zucchini cotyledons and avoided the phytotoxicity associated with hygromycin B.

Conclusion

This is the first report on the transformation of P. xanthii and the transformation of powdery mildew fungi using electroporation. Although the transformants are transient, this represents a feasible method for the genetic manipulation of this important group of plant pathogens.     

Oleozon: A novel control strategy against powdery mildew in cucumber

Ozonized sunflower oil (oleozon) is an effective agent for controlling powdery mildew in cucumber. In this study, the mechanisms of oleozon in the control of powdery mildew were determined. The development of Podosphaera xanthii on cucumber leaves treated with oleozon (2%) and water was investigated at different times after inoculation. The germinating conidia, hyphae and conidiophores of the pathogen were severely damaged by oleozon. No visible phytotoxic effect was observed on cucumber after the application of oleozon. This compound had highly preventive effects as well as curative effects against powdery mildew based on in vivo potted seedling assays. The control effects of oleozon were further confirmed in a greenhouse trial. These results may provide a basis for further development of a natural fungicide against cucumber powdery mildew.     

The Podosphaera fusca TUB2 gene,a molecular “Swiss Army knife” with multiple applications in powdery mildew research

The powdery mildew fungus Podosphaera fusca (synonym Podosphaera xanthii) is the main causal agent of cucurbit powdery mildew and one of the most important limiting factors for cucurbit production worldwide. Despite the fungus' economic importance, very little is known about the physiological and molecular processes involved in P. fusca biology and pathogenesis. In this study, we isolated and characterised the β-tubulin-encoding gene of P. fusca (PfTUB2) to develop molecular tools with different applications in powdery mildew research. PfTUB2 is predicted to encode a protein of 447 amino acid residues. The coding region is interrupted by six introns that occur at approximately the same positions as the introns present in other fungal TUB2-like genes. Once cloned, the PfTUB2 sequence information was used in different applications. Our results showed that the TUB2 gene is a good marker for molecular phylogenetics in powdery mildew fungi but it is unsuitable for the analysis of intraspecific diversity in P. fusca. The expression of PfTUB2 was proven to be stable in different temperature conditions, supporting its use as a reference gene in quantitative gene expression studies. Furthermore, an allele-specific PCR assay for the detection of resistance to methyl-2-benzimidazole carbamate (MBC) fungicides in P. fusca was developed based on the correlation between the single amino acid change E198A in β-tubulin and the MBC resistance phenotype. Lastly, PfTUB2 was used as a target gene in the development of a high-throughput method to quantify fungal growth in plant tissues.     

Isolation and evaluation of antagonistic bacteria towards the cucurbit powdery mildew fungus<Emphasis Type="Italic"> Podosphaera fusca</Emphasis>

Powdery mildew is one of the most important limiting factors for cucurbits production in Spain, its management being strongly dependent on chemicals. The aim of this work was to evaluate the possibility of exploiting antagonistic bacteria in the biological control of the cucurbit powdery mildew fungus Podosphaera fusca (syn. Sphaerotheca fusca). Among a collection of bacterial strains isolated from distinct cucurbit powdery mildew diseased plants and rhizospheric soils, four isolates were selected, by means of a screening method based on antibiotic production, and identified as Bacillus spp. These isolates proved to be efficacious in the control of cucurbit powdery mildew in in vitro detached leaves and seedling biocontrol assays, where reductions of disease severity of up to 80% were obtained. Furthermore, bacterial populations on melon leaves remained at similar levels (10⁵ cfu cm^–2) over the 16-day period studied and, as observed by scanning electron microscopy analysis, they were able to establish microcolonies associated with an extracellular matrix, which reveals that these isolates efficiently colonize melon phylloplane. These results indicate that the bacterial isolates selected are promising candidates for biological control agents of cucurbit powdery mildew in southern Spain.     

Interactions between mycorrhiza and powdery mildew of cucumber

Interactions between the arbuscular mycorrhizal fungus Glomus intraradices and the powdery mildew fungus Podosphaera xanthii were examined with cucumber as the host plant in pot experiments under greenhouse conditions. Plants were inoculated with mildew two weeks after seedling emergence. Plants were mycorrhizal or not, prior to mildew infection and were harvested two weeks after mildew inoculation. We found no influence of the cucumber — G. intraradices symbiosis on development of cucumber mildew in terms of numbers of colonies per unit area. Similarly, biomass and amount of energy reserves of G. intraradices as examined with signature fatty acids were unaffected by mildew. Both biotrophs caused growth depressions of the host plant. Plant carbon allocation is discussed in relation to biotrophs as sinks.