Powdery mildew (Oidium sp.) on tomatoes in Bulgaria

In 1989, powdery mildew (Oidium sp.) was found on tomatoes (Lycopersicon esculen-tum L. Mill.) under glass in Bulgaria. Microscopic examinations indicated that the mildew was typical ofOidium sp. Forty species, forms, breeding lines and cultivars of tomato were evaluated for their susceptibility to powdery mildew. Seven of them were immune to the disease.     

Powdery mildew resistance in selections from moroccan barley landraces

Thirty barley landraces collected from Morocco in 1985 and 1989, and held in the Polish Gene Bank, IHAR, Radzików, Poland, were screened for resistance to powdery mildew. Fifteen tested landraces (50%) showed powdery mildew resistance reactions and 24 single plant lines were selected. Eighteen lines originating from 13 landraces were tested with 17 isolates of powdery mildew and another six lines originating from six landraces were tested with 23; the isolates were chosen according to their virulence spectra observed on the ‘Pallas’ isolines differential set. Three lines (E 1090-2-2, E 1110-3-2 and E 1077-1-1) showed resistance to all powdery mildew virulence genes prevalent in Europe. In 21 lines, unknown genes alone or in combination with specific ones were detected. Five different resistance alleles(Mlat, Mlal, Mla3, Mlg andMl(CP)) were postulated to be present in the tested lines, alone or in combination:Mlat was postulated to be present in nine (~38%) lines;Mlg andMl(CP) in two lines, andMla1 andMla3 in one tested line each. The use of newly identified sources of resistance in barley breeding as a means of controlling powdery mildew is discussed.     

纤用型亚麻白粉病及其综防技术

亚麻白粉病病原为亚麻粉孢(Oidium lint Sko-ric),属半知菌亚门真菌,其有性态为二孢白粉菌(Erysiphe cichoracearum Dc.)是制约亚麻原茎和麻籽优质、高产的主要病害。在大理宾川县和祥云县、丽江永胜县等地区发生危害严重,宾川县发生面积2002年为1100 hm~2,2003年1400 hm~2,给亚麻生产造成了较大损失。针对这种情况,本县及时进行了亚麻白粉病综合防治技术研究,并应用于生产实践,取得了显著效果。     

台湾青枣白粉病的发生为害初报

台湾青枣又名印度枣 ,学名毛叶枣 ( Zizyphusmauritians L an) ,属鼠李科 ( Rhamnaceae)枣属( Zizyphus)的一种 ,与中国枣同属而不同种 ,是我国台湾果农利用从印度引进的毛叶枣经多年选育得出的一些极具开发价值的鲜食优良品种。台湾青枣具有生长旺盛 ,适应性强 ,耐瘠耐旱 ,丰产稳产 ,当年种植当年可结果的特点 ,且果实大 ,口感好 ,营养价值丰富 ,耐贮运 ,上市季节好 ,经济价值较高。近年来我国华南地区广泛推广种植 ,北方一些省市也开始在大棚内试种 ,发展前景良好。白粉病是台湾青枣常见的一种病害 ,国内尚未见有正式报道。1　发病情况…     

Powdery mildew on winter wheat in Bulgaria, 1980: Relations between disease incidence,disease severity,and yield

Mildew epidemics in 1980 on winter wheat cv. Sadovo 1 near Sofia, Bulgaria, were studied in detail. Half of the experimental plots were artificially inoculated, whereas the others were naturally infected. Fungicide treatments on all plots consisted of from nil to three applications of triadimefon. On four days, mildew severity, plant height and the yield components ear length, number of kernels, and grain weight per ear were determined. Mildew incidence showed to be a simple and reliable predictor of yield loss. It is suggested that mildew incidence can be used for decision making in the supervised control of wheat mildew in Bulgaria.Samenvatting Sofia, Bulgarije, in detail bestudeerd. Van 32 veldjes van 1 m² groot, in vier blokken van acht veldjes verdeeld over een groot tarweperceel, werd de helft kunstmatig geïnfecteerd met meeldauw, terwijl de andere helft aan natuurlijke infectie werd blootgesteld. De bespuitingen variëerden van een tot drie bespuitingen met triadimenfon, alsmede een onbespoten controle. Op drie dagen werden aantastingsgraad en incidentie van meeldauw bepaald aan de drie bovenste bladlagen. Een aantal relaties werd berekend tussen incidentie, aantastingsgraad en opbrengstvariabelen (planthoogte, aarlengte, aantal korrels per aar, korrelgewicht per aar). In ontwikkelingsstadium F 10.1 bleek meeldauw-incidentie een eenvoudige en betrouwbare maat te zijn voor toekomstige opbrengstderving. Meeldauw-incidentie kan als maat gebruikt worden bij de geleide bestrijding van meeldauw in Bulgarije, maar er zullen nog veel proeven nodig zijn om dit doel te bereiken.     

Occurrence of powdery mildew on aubergine in West Sussex

A powdery mildew ( Erysiphe sp.) was found on the upper surfaces of leaves of a glasshouse-grown aubergine ( Solanum melongena ) crop in West Sussex during Autumn 1992. It could be readily transferred to tomato ( Lycopersicon esculentum ) and tobacco ( Nicotiana tabacum ), but produced restricted growth and sporulation on cucumber ( Cucumis sativus ). Sweet pepper ( Capsicum annuum ), Chinese cabbage ( Brassica campestris var. chinensis ), lettuce ( Lactuca sativa ), chrysanthemum ( Dendranthema x grandiflorum ) and Nicotiana benthamiana did not show symptoms. When transferred to tomato and cucumber, the morphology of aubergine powdery mildew resembled the natural glasshouse powdery mildew on the two crops, respectively, rather than powdery mildew on aubergine. Powdery mildew from naturally infected tomato could infect aubergine directly, and also after one, but not two, generations on cucumber.     

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。     

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.     

Effects of powdery mildew and weather on winter wheat yield. 2. Effects of mildew epidemics

Wheat yield losses caused by powdery mildew were computed based on effects of the disease on leaf photosynthesis. Powdery mildew was introduced in a crop model of wheat by quantification of five parameters, taking the vertical and horizontal distribution of mildew in the crop into account. The most important parameters were those of the mildew intensity, the distribution of mildew in the crop, and the effect of mildew on assimilation at light saturation. Measured mildew epidemics in field experiments in three different years, were used to compute yield losses. Computed losses were compared to measured losses. On average, computed yield loss approached measured, but measured yield loss was underestimated, especially in early mildew epidemics due to the computation of partitioning and reallocation of assimilates. Other processes which may cause an underestimation are described. The use of crop models as a method to upgrade disease management systems is discussed.Samenvatting Opbrengstderving van wintertarwe werd berekend aan de hand van het effect dat meeldauw heeft op de blad-fotosynthese. Een rekenmodel voor de gewasgroei van tarwe werd uitgebreid met meeldauw. Met inachtneming van de vertikale en horizontale verdeling van meeldauw in het gewas, werd meeldauw in het model gekwantificeerd door vijf parameters. De belangrijkste parameters waren die van de meeldauwintensiteit, de verdeling van meeldauw in het gewas en het effect van meeldauw op de assimilatie bij een overvloed aan licht. Epidemieën van meeldauw, gemeten in veldproeven in drie verschillende jaren, werden gebruikt om opbrengstdervingen te berekenen. Gemiddeld kwam deze redelijk overeen met de in de veldproeven gemeten opbrengstderving. De gemeten opbrengstderving werd echter onderschat, vooral bij vroege epidemieën van meeldauw door de wijze waarop de (her)verdeling van assimilaten wordt berekend. Andere mechanismen, die een onderschatting van opbrengstderving kunnen veroorzaken worden besproken. Of deze modellen als methode gebruikt kunnen worden om systemen voor de geleide bestrijding van ziekten te verbeteren wordt bediscussieerd.     

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.     

Germination of powdery mildew conidia in vitro on cellulose membranes

Conidia of several powdery mildews were found to germinate to a high and reproducible percentage on 25 m thick cellulose membranes, laid on modified Czapek Dox agar in Petri dishes. Germination on 45 m thick, uncoated cellulose, coated cellulose, cellulose acetate and collodion membranes always was lower and more irregular than on 25 m thick cellulose. Probably, the water permeability of the membranes is of importance in causing a humidity gradient favourable for germination of powdery mildew conidia.Samenvatting Bij incubatie van conidiën van echte meeldauwschimmels op 25 m dikke cellulosemembranen, gelegd op agar in Petri-schalen werden hoge kiemingspercentages verkregen. Kieming op 45 m dikke, ongecoate cellulose, gecoate cellulose, cellulose-acetaat- en collodionmembranen was altijd slechter en onregelmatiger dan op 25 m dikke cellulosemembranen. Waarschijnlijk is de waterdoorlaatbaarheid van de membranen van belang voor de kieming door de vorming van een vochtigheidsgradient.