Spinach: better management of downy mildew and white rust through genomics

Spinach (Spinacia oleracea) has become an increasingly important vegetable crop in many parts of the world. Significant changes in production practices, particularly in the U.S. and E.U., have occurred in the past 10–15 years as a result of increased product demand. These changes likely increased the incidence and severity of downy mildew, caused by Peronospora farinosa f. sp. spinaciae. Recently, progress has been made to define the genetics of resistance to this pathogen and the closely related white rust pathogen, Albugo occidentalis. In this paper, we outline the genetic and genomic resources currently available for spinach, draw parallels between spinach diseases and more thoroughly characterized pathosystems, and describe efforts currently underway to develop new genetic and genomic tools to better understand downy mildew and white rust of spinach. Presently, many crucial tools and resources required to define the molecular underpinnings of disease are unavailable for either spinach or its pathogens. New resources and information for spinach genomics would provide a jumpstart for ongoing efforts to define (and deploy) genetic resistance against downy mildew and white rust.     

Occurrence of powdery mildews on new hosts in Turkey

Erysiphe convolvuli onConvolvulus lanatus, C. pentapetaloides, C. siculus subsp.siculus andIpomoea sagittata; Erysiphe ranunculi onRanunculus marginatus var.trachycarpus; Erysiphe clandestina onUlmus minor subsp.canescens; Podosphaera fusca onConyza canadensis; andPodosphaera ferruginea onSanguisorba minor subsp.magnolii were identified and the associated host plants were found to be new for the Turkish mycoflora. http://www.phytoparasitica.org posting Sept. 17, 2006.     

peronospora radii de by., a causal agent of downy mildew of anthemideae: complementary description and new hosts recorded in Israel

Peronospora radii de Bary 1863, a new record in Israel, was found in January 1985 to be the cause of a downy mildew of cultivated marguerite daisies, cv. ‘Scheine von Nizza’ (a cultivar ofArgyranthemum frutescens: Anthemideae: Compositae), grown in an unheated greenhouse in the Coastal Plain. The same fungal species was found in February 1986 on the very common, wildChrysanthemum coronarium (Anthemideae), 13 km distant from the previous year’s location. Conidia of the fungus on ‘Nizza’ leaves had average dimensions similar to those on ‘Nizza’ flowers, but differed in variance (minimal and maximal length and width) and 40% of them had papillate apicesvs 4% in conidia from flowers. The average length and width of conidia from both leaves and flowers of ‘Nizza’ were slightly above those already described forP. radii in the literature. The conidia fromCh. coronarium had average lengths, widths and quotients significantly higher than those from ‘Nizza’ and from the previously published data, extending the range to 43.8 x 24.3 μm, quotient: 1.83vs the highest published averages of 34.2 x 23.74 μm, quotient: 1.70. OnCh. coronarium, the dimensions of conidia had great variance within samples from the same plant and differed significantly even between plants at the same time and location, showing this fungus to have more variability than was previously known. Oospores, known elsewhere for this species, were not found in Israel. The disease was successfully transmitted from diseasedCh. coronarium to healthyCh. coronarium and ‘Nizza’(A. frutescens) but not to another, white-flowered cultivar ofA. frutescens, when all these different plants were transplanted and grown together in physical contact. Isozyme analysis, performed on conidial samples ofP. radii from leaves of both species of hosts and flowers ofCh. coronarium, corroborated that the pathogen was the same on each host and on both petals and leaves. The disease was eradicated by chemical treatment in the commercial greenhouse and also disappeared without treatment in infected plants kept over summer in a dry, airconditioned glasshouse.     

Advances in sunflower downy mildew research

This review summarises the progress in research on sunflower downy mildew as reported in publications of the past 10 to 15 years, the period since the last comprehensive review on Plasmopara halstedii. Particular attention is paid to subjects that showed much progress and may be of particular interest to sunflower pathologists, mycologists or molecular biologists. Accordingly, single sections are devoted to the problems of taxonomic and phylogenetic aspects, host specificity, the host—pathogen interaction including resistance phenomena, as well as epidemiology and disease management. Reflecting the progress achieved in some fields and illuminating the deficits in others should stimulate the reader's interest in this very significant pathosystem.     

黄瓜霜霉病生态防治技术研究

对大棚黄瓜设计了地膜覆盖双垄,膜下垄间浇水防治黄瓜霜霉病的生态防治措施.试验结果表明,这种防治措施可使大棚内的相对湿度在晴天时控制在85%以下,比膜外浇水显著降低了棚内的湿度,使感病和抗病品种的病情指数均控制在6.0以内,相对防效可达90%以上.与通常的明沟浇水相比,可提早上市1周,推迟拉秧30天,折合每亩增产3107.8kg,增收9323.4元.     

Two new records of downy mildews (Peronosporaceae) in Turkey and a new host

Peronospora crucianellae Maire onCrucianella latifolia L. andPeronospora trifolii-arvensis Syd. onTrifolium sp. were collected for the first time in Turkey. The plant speciesSinapis arvensis L. is reported as a new host forPeronospora brassicae Gäum. from Turkey. The peronosporaceous fungi recorded since the beginning of microfungal studies from Turkey are given along with their collection sites.     

Occurrence and molecular characterization of strobilurin resistance in cucumber powdery mildew and downy mildew

ABSTRACT Between 1998 and 1999, control failure of powdery mildew (Podosphaera fusca) and downy mildew (Pseudoperonospora cubensis) by the strobilurin fungicides azoxystrobin and kresoxim-methyl was observed in cucumber-growing areas of Japan. Results from inoculation tests carried out on intact cucumber plants and leaf disks clearly showed the distribution of pathogen isolates highly resistant to azoxystrobin and kresoximmethyl. Fragments of the fungicide-targeted mitochondrial cytochrome b gene were polymerase chain reaction amplified from total pathogen DNA and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochrome b gene, resulting in substitution of glycine by alanine at position 143, was found in resistant isolates of downy mildew. This substitution in cytochrome b seemed to result in high resistance to strobilurins in this pathogen. The same mutation was found in some but not all resistant isolates of powdery mildew. This study suggests that a mutation at position 143 in the target-encoding gene, resulting in an amino acid substitution, was probably a major cause of the rapid development of high strobilurin resistance in these two pathogens.     

葡萄霜霉病对葡萄叶片代谢的影响

葡萄霜霉病是一种世界性病害,对葡萄生产影响极大,是葡萄栽培中主要病害之一。基于非靶向代谢组学研究技术,分析鉴定对照组与霜霉病组代谢物含量的变化,采用正交偏最小二乘判别分析并结合t检验的结果,筛选出造成健康和发病的葡萄叶片显著差异的20种主要代谢物质。其中,霜霉病处理组差异代谢物含量显著上升(P<0.05)的物质主要分为4类：氨基酸类、核酸代谢类、植物激素类和其他化合物;显著下降(P<0.05)的物质分6类：糖类、羧酸类、甾类、二萜醇类、三萜类和其他化合物。KEGG通路富集分析发现差异代谢物主要富集在氨酰tRNA生物合成,ABC转运蛋白,戊糖磷酸途径,二苯乙烯类、二芳基庚烷类和姜辣素生物合成,缬氨酸、亮氨酸和异亮氨酸生物合成和植物激素信号转导6条代谢通路中。由此可知,葡萄霜霉病侵染导致了葡萄叶片糖、核酸、氨基酸等相关代谢物的显著变化,相关代谢途径可能是霜霉菌侵染葡萄的主要机制。     

大棚黄瓜霜霉病的发生原因和防治

温度、湿度是影响黄瓜霜霉病发生的主要因素。黄瓜的品种、叶片生理年龄不同1栽培和肥水管理不一,黄瓜霜霉病发生程度也不一样,防治药剂有25％瑞毒霉可湿性粉剂、75％百菌清、25％甲霜灵等 。     

芽孢杆菌对黄瓜霜霉病的防治效果研究

经黄瓜霜霉病孢子囊萌发抑制试验明确,芽孢杆菌菌株Z-X-3、Z-X-10对黄瓜霜霉病菌有较强拮抗作用。离体叶片法和温室防病试验表明,两菌株对黄瓜霜霉病有较好的防治效果,相对保护效果分别达46.42％、41.55％;治疗效果分别达46.30％、44.44％,高于农药克霜氰的31.81％、37.03％。     

基于流式细胞术的黄瓜霜霉病菌孢子囊计数研究

 为病原菌时空流行动态监测及病害预测模型构建提供病原菌快速计数方法,以卵菌中代表——葫芦科霜霉病病原菌古巴假霜霉菌(Pseudoperonospora cubensis)为例,研究了孢子囊悬浮液的荧光染色方法和基于流式细胞术计数方法。研究表明EDTA和SYBR Green Ⅰ 的联合作用能够对孢子囊进行荧光标记。对SYBR Green Ⅰ 染色剂的最佳染色条件进行研究,结果表明在染色时间相同时,荧光染色剂浓度越高,染色效果越好;同一浓度荧光染色剂,随着染色时间的增加,孢子囊染色率增加。使用流式细胞术对荧光染色的孢子囊进行计数,并与显微镜血球计数板计数结果进行比较,结果显示:流式细胞仪计数结果与显微镜血球计数板计数结果得到的孢子囊浓度没有显著差异(P<0.01),对两种方法获得的孢子囊浓度取对数后进行相关性分析,显示流式细胞仪测定的孢子囊浓度与显微镜血球计数板计数得到的孢子囊浓度高度相关,相关系数为 0.993 4,表明流式细胞术可以应用于古巴假霜霉菌孢子囊的计数。     

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。     

Effect of downy mildew disease on photosynthesis and chlorophyll fluorescence in Plantago ovata Forsk

Journal of Plant Diseases and Protection - Plantago ovata is commercially grown in India for its dietary fibre. The crop is affected by downy mildew caused by Peronospora plantaginis Underwood...     

水杨酸诱发黄瓜幼苗对霜霉病抗性的研究

 由霜霉病菌(Pseudoperonospora cubensis)引发的霜霉病是威胁黄瓜生产尤其是保护地黄瓜生产的主要因素之一。目前,生产上多采用嫁接育苗和农药防治来缓解该病的危害,但由于农药用量大及次数频繁,往往导致黄瓜中农药残留量增加,严重影响了黄瓜的品质,因此,黄瓜的抗病性育种及寻求提高黄瓜对霜霉病抗性的方法是科研工作者的重要课题。     

Three-dimensional representation of downy mildew development in a spinach crop

The development of downy mildew on spinach (Peronospora farinosa f. sp.spinaciae) was stratified according to leaf layers and represented in three-dimensional computer graphics, in which percentage diseased leaf area was plotted against time for each leaf layer. Distinction was made between a point source and an area source. Inoculations were made at three growth stages of the crop.More information could be gathered on the course of disease development on the upper leaf layers, for the first true leaf pair sporulates longer and more intensively, masking the disease development on the other leaf layers in this way.Samenvatting De ontwikkeling van valse meeldauw op spinazie (Peronospora farinosa f. sp.spinaciae) werd geanalyseerd aan de hand van drie-dimensionale grafische voorstellingen, waarbij percentage ziek bladoppervlak per bladetage werd uitgezet tegen tijd. Onderscheid werd gemaakt tussen de ontwikkeling vanuit een puntbron en vanuit een oppervlaktebron, bij inoculatie in drie groeistadia van het gewas.Het bleek dat hierbij meer informatie kon worden verkregen over het verloop van de ziekte-ontwikkeling op de bovenste bladetages, omdat het eerste echte bladpaar langduriger en heviger sporuleert, en zo de ziekte-ontwikkeling op de overige bladetages maskeert.     

Exploring host-pathogen combinations for compatible and incompatible reactions in grapevine downy mildew

Rhizoctonia leguminicola, the traditional name for the causal agent of blackpatch of red clover (Trifolium pratense) and other legumes, produces alkaloids, one of which causes livestock to salivate excessively. Fungal presence is generally confirmed by microscopy, disappearance of symptoms in livestock after removal of suspect forage, and chromatography of the alkaloid slaframine, in legume tissue. Use of the polymerase chain reaction (PCR) to amplify a pathogen-specific DNA fragment would complement the other methods of pathogen identification. Primers were designed to the R. leguminicola ITS region, sequence provided by another laboratory. Two separate primer pairs each amplified a different fragment–one ~250 bp long (expected length 249 bp), and the other 300 to 400 bp long (expected length 368 bp)–in DNA extracted from cultures of R. leguminicola. Under the experimental conditions, the primers to the larger fragment amplified a stronger band, and a minimum of 0.1 ng DNA per reaction was needed to produce a detectable band. With the primers to the 368-bp fragment, a band 300 to 400 bp long was also amplified in DNA extracted from red clover (cultivar Kenland) inoculated with R. leguminicola and harvested 70 h post inoculation. No amplification with this primer set occurred in DNA extracted from mock-inoculated red clover plants, supporting the likelihood that the primers amplified R. leguminicola DNA extracted from inoculated red clover. This primer set did not amplify DNA extracted from a red clover isolate of the legume pathogen Stemphylium sarcinaeforme, or DNA extracted from two isolates of the legume pathogen Colletotrichum trifolii, indicating specificity for R. leguminicola DNA. Lack of amplification of alfalfa DNA indicated that the R. leguminicola primers will be useful for testing for the presence of blackpatch in alfalfa.     

Disease-weather relationships for powdery mildew and yellow rust on winter wheat

Key weather factors determining the occurrence and severity of powdery mildew and yellow rust epidemics on winter wheat were identified. Empirical models were formulated to qualitatively predict a damaging epidemic (>5% severity) and quantitatively predict the disease severity given a damaging epidemic occurred. The disease data used was from field experiments at 12 locations in the UK covering the period from 1994 to 2002 with matching data from weather stations within a 5 km range. Wind in December to February was the most influential factor for a damaging epidemic of powdery mildew. Disease severity was best identified by a model with temperature, humidity, and rain in April to June. For yellow rust, the temperature in February to June was the most influential factor for a damaging epidemic as well as for disease severity. The qualitative models identified favorable circumstances for damaging epidemics, but damaging epidemics did not always occur in such circumstances, probably due to other factors such as the availability of initial inoculum and cultivar resistance.