Showing papers in "Journal of Phytopathology in 1989"

Ampelomyces quisqualis for biological and integrated control of powdery mildews in Israel

Abstract: An isolate of Ampelomyces quisqualis obtained from a Oidium sp. infecting Catha edulis in Israel, proved to be infective to several powdery mildew fungi belonging to the genera Oidium, Erysiphe, Sphaerotheca, Podosphaera, Uncinula, and Leveillula. In field trials, A. quisqualis parasitized the powdery mildews of cucumber, carrot and mango and reduced the disease. Hyperparasitism on Oidium mangiferae is reported for the first time. A. quisqualis was tolerant to many fungicides currently used to control powdery mildews and/or other plant diseases. In one experiment, treating powdery mildew of cucumber (cv. Hazera 205) with spores of A. quisqualis alone, significantly decreased disease severity and increased cucumber yields by approximately 50%. However, a greater increase in yield was obtained by using the fungicide pyrazophos alone or in combination with the hyperparasite. In a second experiment, using cv. Dalila, all treatments increased the yield over the untreated control which did not produce fruits. Zusammenfassung Ampelomyces quisqualis in der biologischen und integrierten Bekampfung des Echten Mehltaus in Israel Festgestellt wurde, das ein Ampelomyces quisqualis-Stimm, der aus einer Oidium sp. an Catha edulis in Israel isoliert wurde, einige der Pilze des Echten Mehltaus der Gattungen Oidium, Erysiphe, Sphaerotheca, Podosphaera, Uncinula und Leveillula parasitisieren konnte. In Feldversuchen konnte A. quisqualis Gurken-, Mohren- und Mangomehltau parasitisieren und dadurch den Krankheitsbefall reduzieren. Der Hyperparasitismus an Oidium mangifera wird zum ersten Mal dokumentiert. Es wurde auch festgestellt, das A. quisqualis gegen einige Fungizide, die ihren Einsatz als Mehltaufungizide oder auch gegen andere Krankheiten finden, unempfindlich ist. In einem Versuch wurde ermittelt, das nach der Anwendung von A. quisqualis-Sporen gegen Gurkenmehkau (Sorte Hazera 205) eine deutliche Reduzierung der Befallsintensitat und eine Erhohung des Gurkenertrages um 50% erzielt wurde. Jedoch wurden noch hohere Ertrage erzielt, wenn entweder das Fungizid Pyrazophos alleine oder in Kombination mit dem Hyperparasit angewandt wurde. In einem zweiten Versuch mit der Sorte Dalila wurden bessere Ertrage mit allen Behandlungen erzielt als in der unbehandelten Kontrolle, wo keine Gurken wuchsen.

Differences Between Aggressive and Non‐Aggressive Single Spore Lines of Leptosphaeria maculans in Cultural Characteristics and Phytotoxin Production

Abstract: Stems of oilseed rape (Brassica napus) bearing pseudothecia of Leptosphaeria maculans were collected in different parts of West Germany. From single ascospores of this material a total of 352 fungal lines were derived, tested on rape cotyledons and devided into 124 aggressive and 228 non-aggressive pathotypes. The two groups could be distinguished by certain characteristics. On nutrient agar, aggressive strains grew more slowly. In liquid cultures, non-aggressive types produced a yellow-brown pigment whereas the culture filtrates of aggressive strains remained unpigmented. The culture filtrates of aggressive lines contained phytotoxic compounds which were identified as sirodesmins. These compounds were absent in culture filtrates of non-aggressive pathotypes. The very close correlation between aggressiviness as a pathogen and the phytotoxin production indicates that phytotoxins of Leptosphaeria maculans could be involved in the disease development. Zusammenfassung Unterschiede zwischen aggressiven und nichtaggressiven Einzelsporlinien von Leptosphaeria maculaos in den Kulturcharakteristiken und der Phytotoxinproduktion Rapsstengel (Brassica napus) mit Pseudothecien von Leptosphaeria maculans wurden in verschiedenen Teilen der Bundesrepublik gesammelt. Aus einzelnen Ascosporen dieses Materials wurden insgesamt 352 Pilzisolate hergestellt, an Rapskotyledonen getestet und in 124 aggressive und 228 nichaggressive Pathotypen unterteilt. Die beiden Gruppen unterschieden sich in bestimmten charakteristischen Eigenschaften voneinander. Auf Nahrboden wuchsen die aggressiven Stamme langsamer. In Flussigkulturen bildeten die nichtaggressiven Pathotypen gelb-braune Pigmente, wahrend die Kultur-filtrate der aggressiven Stamme ungefarbt blieben. Die Kulturfiltrate der aggressiven Linien enthielten dagegen phytotoxische Verbindungen, die als Sirodesmine identifiziert wurden. Diese Verbindungen fehlten in den Kulturfiltraten der nichtaggressiven Pathotypen. Die sehr enge Korrelation zwischen der Aggressivitat als Pathogen und der Toxinproduktion deutet darauf hin, das die Phytotoxine von Leptosphaeria maculans an der Krankheitsentwicklung beteiligt sein konnten.

A Tobamovirus Causing Heavy Losses in Protected Pepper Crops in Spain

Abstract: During a four-year (1982–1985) survey of plant viruses infecting pepper cultivars grown under plastic in the Southeastern region of Spain, a tobamovirus was found to be the major disease agent of this crop. The virus produces slight or no symptoms on the leaves, but causes chlorotic mottling, malformation and reduction in size with occasional necrosis on the fruits and was able to infect all commercial pepper cultivars tested, including those resistant to other tobamoviruses, causing a catastrophic disease. The biological and serological characterization of the virus showed that it is very similar to pepper mild mottle virus (PMMV) (Wetteret al. 1984) and therefore we have termed it as Spanish strain of PMMV (PMMV-S). The need of grouping all the so-called “pepper strains” of tobacco mosaic virus (TMV) as a new distinct member of the tobamovirus group with the name of PMMV is emphasized.

Suppression of Root Rot on Peas, Beans and Beetroots Caused by Pythium ultimum and Rhizoctonia solani through the Amendment of Growing Media with Composted Organic Household Waste

Abstract: In pot experiments under controlled environmental conditions, composted organic household waste showed a suppression of soilborne plant pathogens. The addition of 8 %, 10 % and 30 % compost to the potting material which was artificially infested with Pythium ultimum or Rhizoctonia solani considerably reduced the incidence of disease in different varieties of host plants. It became evident that the degree of protection provided by compost depends upon the amount of compost added and upon the vulnerability of the host plant to infection. In an experiment using increasing levels of inoculum, the compost proved suppressive to the pathogen even under extreme disease conditions. This suppressive effect was still evident in compost which had been stored for prolonged periods.

Epidemics of diseases and pests of winter wheat at different levels of agrochemical input : a study on the possibilities for designing an integrated cropping system

Abstract: A study to what extent the level of fertilization effects epidemics of pests and diseases, compared to the well-known effects of pesticides and cultivars

Base Composition of the DNA of Mycoplasma‐Like Organisms Associated with Various Plant Diseases

Abstract: DNA was isolated from periwinkle plants infected by various mycoplasma-like organisms (MLOs), and from apple trees affected by apple proliferation. The DNA of the causal agents was separated from the host plant DNA by repeated bisbenzimide-CsCl buoyant density gradient centrifugation which resulted in highly enriched MLO DNA bands characterized by a lower buoyant density than that of the host DNA. The MLO DNAs were hydrolyzed to free bases which were determined by HPLC. The analyses revealed a similar low G + C content as found in the DNAs of several culturable mycoplasmas and spiroplasmas. The values of the DNA of the agents of the diseases investigated were as follows: European aster yellows 23.0, periwinkle virescence 23.5, apple proliferation 23.7, rape virescence 24.2, and phyllody of Diplotaxis erucoidcs 26.2 mol % G + C, respectively. Methylated bases were detected in low amounts only.

Erwinia amylovora infection of hawthorn blossom. I: The anther

Abstract: Stamens of freshly opened flowers of hawthorn were inoculated with E;. amylovora and the development of blossom infection was monitored by viable bacterial counts and light and electron microscopy. Some bacterial multiplication occurred on the anther surface, over the dehiscence zone and over the junctions ot the anther-wall cells. bacteria invaded the anther loculc, via the ruptured dehiscence zone, and possibly also vid the stomata surrounding the filament insertion. bacteria within the locule multiplied rapidk with estimated doubling-times which were longer than those derived from in vitro data. Pollen grains Irom infected anthers were found to be heavily eontaminated with bacteria. The invasion of anther tissue, with the production of contaminated pollen, may be important epidemiologieally both as a phase of rapid bacterial multiplication and in the insect-mediated spread of this disease. Zusammenfassung Erwinia amylovora-Infektion von Weisdornbluten. I. Die Anthere Staubgefase frisch geoffneter Bluten von Weisdorn wurden mit E. amylovora inokuliert und die Entwicklung der Bluteninfektion durch bakteriellc Zahlungen sowie Licht- und Elektronenmikroskopie verfolgt. Einige Bakterienvermehrung fand auf den Antheren-Oberflachen statt sowie uber den Dehiszcnzbereich und die Verbindungen der Antheren-Zellwande. Bakterien siedelten sich uber die Bruchstelle des Dehiszenzbereichs, und moglicherweise auch durch die Stomata der Staubfadenansatze, in den Antherenkammern an. Innerhalb der Staubgefaskammern vermehrten sich die Bakterien rapide, wobei die geschatzten Verdoppelungszeiten langer waren als die bei in vitro-Versuchen ermittelten. Pollenkorner von infizierten Antheren wiesen eine schwere Bakterienverseuchung auf. Die Invasion von Antheiengewebe mit nachiolgender Pioduktion von infiziertem Pollen hat wahrscheinlich epidemiologische Bedeutung sowohl als Phase einer rapiden Bakterienvermehrung als auch in der durch Insekten verursachten Ausbreitung dieser Krankheit.

The disease cycle of Mango malformation induced by Fusarium moniliforme var. subglutinans and the curative effects of mangiferin-metal chelates

Abstract: Evidence is presented to suggest that the bunchy top, die-back, abnormal inflorescence and blossom blight disease of Mangifera indica are interlinked and can be expressed as a disease cycle in mango malformation. The morphological and biochemical connections among these symptoms, induced by Fusarium moniliforme var. subglutinans Wollenw. and Reink., are appraised. Partial control of the mango malformation has been accomplished by spraying the diseased parts with mangiferin-Zn2+ and mangiferin-Cu2+ chelates. The salutory effect of niangiferin-metal chelates is evidenced by the revival of normal balance of mangiferin and the micronutrients in the diseased parts, dechne in the fungal population and emergence of healthy shoots.

Correlations between Accumulation of Dianthramides, Dianthalexin and Unknown Compounds, and Partial Resistance to Fusarium oxysporum f. sp. dianthi in Eleven Carnation Cultivars

Abstract: The accumulation of dianthramides, dianthalexin and other phenolic compounds in carnation cells at different times before and after inoculation of plants with Fusarium oxysporum f. sp. dianthi, and the development of wilt symptoms were compared for eleven carnation cultivars. Untreated and water-treated controls contained only a little acetone-extractable phenolics. Upon inoculation with F. oxysporum f. sp dianthi, all cultivars accumulated the same range of phenolic compounds, including several dianthramides and dianthalexin, but in different proportions. The total amount of accumulated phenolic compounds per fresh material weight of the extracted stem segments could not be related to the disease resistance level of the different cultivars. However, the accumulation of dianthramides and dianthalexin in the cultivars was positively correlated to resistance, while the accumulation of two other, as yet unidentified, compounds was inversely related to resistance. Zusammenfassung Korrelationen zwischen der Ansammlung von Dianthramide, Dianthalexin sowie unbekannten chemischen Verbindungen und einer partieilen Resistenz gegen Fusarium oxysporum f. sp. dianthi in elf Nelken-Sorten Die Ansammlung von Dianthramide, Dianthaiexin sowie anderer Phenoiverbindungen in Nelkenzellen zu verschiedenen Zeiten vor und nach Inokulation der Pflanzen mit Fusarium oxysporum f. sp. dianthi wurde ebenso wie die Entwicklung von Welke-Symptomen an elf Nelkensorten untersucht. Unbehandeite und mit Wasser behandelte Kontrollen enthieln nur wenig acetonlosliche Phenole. Nach Inokulation mit F. oxysporum f. sp. dianthi sammelten alle Sorten die gleichen Pbenolverbindungen, einschlieslich mehrerer Dianthramide und Dianthaiexin an, jedoch in verscbiedenen Proportionen. Zwischen der Cesamtmenge der angesammelten Phenolverbindungen pro Frischgewicht der extrahierten Pflanzenstengelsegmente und dem Resistenzniveau der verschiedenen Sorten gegen die Krankheit konnte kein Zusammenhang hergestelli werden. Die Ansammlung von Dianthramide und Dianthaiexin in den Sorten hatte jedoch einen positiven Einflusi auf die Resistenz, wahrend die Ansammlung zweier atiderer Verbindungen, die noch nichi identifizien werden konnten, eine gegenteilige Wirkung auf die Resistenz hatte.

Erwinia amylovora infection of hawthorn blossom. II: The stigma

Abstract: (...) The population developed in a biphasic manner, with an epiphytic phase up to 48 h after inoculation, (in which bacteria were restricted to the intercellular spaces between the papillae) followed by an invasive phase (where bacteria invaded the secretory tissue below the papillae). In the epiphytic phase the bacteria multiplied rapidly, with doubling-times approaching those observed for in vitro multiplication, reaching a population of ca. 10 6 cfu/flower. After the second phase of multiplication the population attained a final level of ca. 10 8 cfu/flower. At no stage was the style invaded by bacteria. Stigma infection does not appear to lead directly to blossom-blight in hawthorn, but bacteria were carried down the style in stigmatic secretions, where they may cause infection of the nectarial surface and subsequent disease

Monoclonal Antibodies for Detection and Serotyping of Cucumber Mosaic Virus

Abstract: Two monoclonal antibodies (MAbs) to cucumber mosaic virus (CMV) were selected from a panel of MAbs for use in the direct DAS (double antibody sandwich)-ELISA. Two different test procedures were developed: an ELISA with polyclonal and monoclonal antibodies (mixed ELISA) for the routine detection of CMV and a MAb-ELISA with two MAbs directed against different epitopes for the specific detection of the N serotype which is prevalent in GDR. The conventional two-step incubation of plates precoated with IgG was compared with simultaneous incubation of test sample and labelled antibody (one-step incubation). The mixed ELISA proved to be more sensitive than the direct DAS-ELISA with polyclonal antisera in detecting CMV in crude sap of infected plants. On the other hand, the MAb-ELISA could be used for serotyping of CMV isolates which is important in epidemiological investigations and in resistance breeding. Both the two-step and the one-step procedures gave similar results with some advantages of the latter procedure. One-step incubation is not only time-saving but seems to be also more sensitive with regard to the detection limit. However, care must be taken to circumvent the hook-effect occurring at high virus concentrations.

Induction of Resistance in Barley against Erysiphe graminis f. sp. hordei after Preinoculation with the Saprophytic Fungus, Cladosporium macrocarpum

Abstract: The experiments presented here revealed a significant induction of resistance in barley leaves against Erysiphe graminis f. sp. hordei following 72 h of incubation with the saprophytic fungus, Cladosporium macrocarpum. The level of induced resistance ranged from 16.7% to 37.4% in three different experiments. The induction of resistance was paralleled by interactions between the fungus and the plant tissue at the cellular level resulting in the formation of papilla-like structures. The results indicate that, not only fungi with pathogenic traits, but also fungi, normally considered as purely saprophytic, can induce resistance in plants. The implications from the results are discussed in relation to the nature of defence reactions in plants and in relation to disease development under field conditions. Zusammenfassung Die Induktion einer Resistenz der Gerste gegen Erysiphe graminis f. sp. hordei durch eine Prainokulation mit dem saprophytischen Pilz Cladosporium macrocarpum In Versuchen wurde festgestellt, das ein beachtlicher Resistenzgrad in Gerstenblattern gegen Erysiphe graminis f. sp. hordei induziert werden konnte, wenn die Blatter zuvor 72 h mit dem saprophytischen Pilz Cladosporium macrocarpum inokuliert wurden. Der induzierte Resistenzgrad, der in drei verschiedenen Versuchen ermittelt wurde, lag zwischen 16,7% und 37,4%. Gleichzeitig mit der Resistenzinduktion wurden Interaktionen zwischen dem Pilz und den Pflanzenzellen beobachtet, die mit der Bildung von Papilla-ahnlichen Strukturen zu erkennen war. Die Ergebnisse deuten darauf hin, das eine Resistenz in den Pflanzen nicht nur von pathogenen Pilzen, sondern auch von Pilzen, die normalerweise als saprophytische Arten bezeichnet werden, induziert werden kann. Diskutiert wird die Bedeutung dieser Ergebnisse in Zusammenhang mit der Art der Abwehrmechanismen in Pflanzen und der Krankheitsentwicklung im Feld.

Biological Activity of Four Antifungal Compounds in Immature Avocado

Abstract: Anthracnose caused by Colletotrichum gloeosporioides in ripe avocados originates as latent infections in the immature fruits. Concentrated ether extract of the peel of apparently healthy, immature avocados when bioassayed on thin layer chromatographic plates with conidia of either Cladosporium cladosporioides or C. gloeosporioides produced four inhibition areas at Rf 0.30, 0.32, 0.70 and 0.75 (these were denoted as AvIV, AvIII, AvII and AvI respectively). A hot chloroform extract was partitioned on a silica gel column and the four antifungal compounds were separated. Spectroscopic data revealed that one of these compounds, AvII, was similar to cis-l-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene and another (AvIV) was a long chain saturated compound comprising hydroxyl group(s) having molecular weight of 268. Toxicity of AvII to C. gloeosporioides was 2 times that of AvIV and 6.5 and 7.5 times that of AvIII and AvI respectively. The amounts of these four antifungal compounds increased gradually during fruit development and reached their maxima at harvest. The concentration of AvI, AvII, AvIII and AvIV was 1300, 920, 1050 and 780 μg/g fresh peel respectively in the fruit at harvesting maturity. The amount of AvII and AvIV decreased to 53 and 64 μg/g fresh peel respectively in the fruit at the ripe stage at which neither AvI nor AvIII was detected. This took place in coincidence with the onset of progressive lesion development by the fungus. Zusammenfassung Eine Anthraknose, die durch Colletotrichum glocosporioides verursacht ist, geht in reifen Avocadofruchten von latenten Infektionen der unreifen Fruchte aus. Konzentrierter Atherextrakt der Schale aus scheinbar gesunden, unreifen Avocadofruchten, der nacli dunnschichtchromatographischer Trennung mit Konidien von entweder Cladosporium cladosporioides oder C. gloeosporioides entwikkelt wurde, zeigte vier Hemmzonen mit Rf-Werten 0,30, 0,32, 0,70 und 0,75 (die als AvIV, AvIII, AvII bzw. AvI bezeichnet wurden). Nach einer heisen Chloroformextraktion wurde der Extrakt an einer Silicagelsaule fraktioniert, und die vier fungiziden Verbindungen getrennt. Spektroskopische Analyse ergab, das die Verbindung AvII eine Ahnlicbkeit mit eis-l-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-dien besas und AvIV eine langkettige, saturierte Verbindung, die aus Hydroxylgruppe (n) mit einem Molekulargewicht von 268, ist. Die Toxitat von AvII gegenuber C. gloeosporioides wurde als 2-, 6,5- bzw. 7,5mal hoher als AvIV, AvIII bzw. AvI ermittelt. Der Gehalt der fungitoxischen Verbindung stieg mit der Fruchtentwicklung langsam an, um zur Zeit der Ernte lhr Maximum erreicht zu haben. Bei der Ernte betrug die Konzentradon von AvI, AvII, AvIII bzw. AvIV in frischen Schalen 1300, 920, 1050 bzw. 780 mg/g. In der Zeit bis zur Reife verringerte sich der Gehalt an AvII und AvIV in frischen SchaJen auf 53 bzw. 64 mg/g; zu djcsem Zeitpunkt konntc ein AvI- bzw. AvIII-Gehalt nicht festgestellt werden. Mit der Abnahme der fungitoxischen Verbindungen wurde eine Lasionenentwicklung durch den pilzlichen Befall beobachtet.

Taxonomie bekannter und neuer Ceratocystis-Arten an Eiche (Quercus robur L.) Institut für Pflanzenschutz im Forst der Biologischen Bundesanstalt für Land- und Forstwirtschaft Braunschweig

Abstract: Taxonomy of known and new species of Ceratocystis from oak (Quercus robur L.) A description is given of six species of the ascomycetous genus Ceratocystis isolated from Quercus robur L. in Poland. Two of these — Ceratocystis grandicarpa sp. nov. and C. prolifera sp. nov. — are described as new species based on the characteristics of their ascospores, ascocarps and conidial states in culture; Ceratocystis introcitrina Olchow. & Reid, C. moniliformis (Hedge.) C. Moreau, C. piceae (Munch) Bakshi and C. stenoceras (Robak) C. Moreau were isolated more or less frequently from oak xylem. Zusammenfassung Es wird die Beschreibung von sechs Ceratocystis-hrten gegeben, die in Polen aus dem Holz stehender Stieleichen isoliert worden sind. Neben den bekannten Formen von Ceratocystis introcitrina Olchow. & Reid, C. moniliformis (Hedge.) C. Moreau, C. piceae (Munch) Bakshi und C. stenoceras (Robak) C. Moreau werden Ceratocystis grandicarpa sp. nov. und C. prolifera sp. nov. als neue Arten vorgestellt.

Mechanical inoculation of sugarbeet roots with isolates of beet necrotic yellow vein virus having different RNA compositions

Abstract: Attempts were made to introduce three different isolates of beet necrotic yellow vein virus (BNYW) into the roots of sugarbeets by means of mechanical inoculation. In Chenopodium quinoa these isolates had produced different patterns of viral RNA. The RNA pattern of isolate P was similar to that found in sugarbeets infected naturally by means of the vector Polymyxa betae. RNA 3 and 4 were partially deleted in isolate Y and apparently absent in isolate R. About 20% of the sugarbeet roots inoculated either with isolate P or Y became infected systemically, but with isolate R no systemic infections were recorded. In tap and side roots of plants infected with isolate P the virus concentration remained high for at least ten months and the tap roots of these plants showed a very poor growth. In tap and side roots of plants infected with isolate Y the virus concentration gradually dropped until it reached the limit of detectability. The tap roots of these plants became about five times as big as those infected with isolate P. Our results indicate that BNYW with full length RNA 3 and 4 can cause heavy damage to sugarbeets also in the absence of Polymyxa betae and that RNA 3 and/or 4 — in addition to a recently suggested involvement in virus transmission by P. betae — apparently also facilitate the persistent spread of the virus in sugarbeet roots. Zusammenfassung Mechanische Inokulation von Zuckerrubenwurzeln mit Rizomaniavirus-Isolaten unterschiedlicher RNA-Zusammensetzung Es wurde versucht, durch mechanische Inokulation Isolate des Rhizomaniavirus (BNYVV) unterschiedlicher RNA-Zusammensetzung in Zuckerruben-Keimlingswurzeln einzubringen. Das Isolat P hatte in Chenopodium quinoa ein RNA-Muster gezeigt, das von dem in naturlich infizierten Ruben nicht zu unterscheiden war, beim Isolat Y waren RNA 3 und 4 in verkurzter Form aufgetreten, beim Isolat R fehlten sie vollstandig. Systemische Wurzelinfektionen wurden 7 Wochen p.i. bei ca. 20% der entweder mit Isolat P oder Y inokulierten Pflanzen festgestellt, aber nicht bei den mit Isolat R inokulierten. Die BNYW-ELISA-Werte blieben in den Wurzeln der mit Isolat P beimpften Pflanzen wahrend der gesamten einjahrigen Versuchsdauer hoch, in den Wurzeln der mit Isolat Y beimpften Pflanzen wurden sie dagegen immer niedriger, etwa 5 Monaten p.i. war das Virus in der Mehrzahl dieser Pflanzen nicht mehr nachweisbar. Die Rubenkorper dieser Pflanzen wurden etwa funf Mal groser als die mit Isolat P infizierten. Daraus ergibt sich, das BNYW mit intakter RNA 3 und 4 auch in Abwesenheit von Polymyxa betae zu einer schweren Schadigung der Ruben fuhren kann. Unsere Ergebnisse deuten auserdem darauf hin, das intakte RNA 3 und/oder 4 die Ausbreitung des Virus in der Rube erleichtern und nicht nur, wie kurzlich vermutet wurde, seine Ubertragung durch P. betae.

Phytophthora and Pythium in Pot Plant Cultures Grown on Ebb and Flow Bench with Recirculating Nutrient Solution

Abstract: The occurrence of pythiaceous fungi in pot plant cultures grown in ebb and flow bench systems was investigated monthly from May to December, Phytophthora, Pythium and Saprolegnia (in all 351) were isolated from water samples and identified. Nearly all the isolates of Pythium produced zoospores in water. A pathogenicity test involving 15 isolates of Pythium“group P”, and 7 of Pythium“group F” showed that 73 % were pathogenic on cucumber, 66 % on Gerbera, 59 % on lettuce, 50 % on tomato, and 32 % on cress. Control of Pythium and Phytophthora is important in order to improve the health of plants grown in ebb and flow systems.

Tomato Yellow Leaf Curl Virus DNA Forms in the Viral Capside, in Infected Plants and in the Insect Vector

Abstract: Tomato yellow leaf curl virus (TYLCV) DNA was used as a probe to identify and analyze virus-related DNAs in the viral capside, in infected tomato plants and in the virus vector, the whitefly. In addition to the single-stranded viral genomic DNA, double-stranded virus-related DNA molecules were detected in infected plants. Not all of the virus-related DNA forms are present simultaneously in the infected plant. The double-stranded molecules, which are probably the replicative form of the viral genome, have been purified from an infected tomato plant. In the viruliferous whitefly, only the single-stranded unit-size viral genome was detected.

Genetic Adaptation of Erysiphc graminis f. sp. Hordei to Barley with Partial Resistance

Abstract: Ten Isolates of powdery mildew were tested on three spring barley cultivars known to express partial resistance and on Golden Promise. Measurements of colony lengths were made under several different environments and compared with similar data produced from several cultivars containing one of two major resistance genes. Significant isolate, cultivar and environment interactions were recorded and one isolate in particular showed adaptation to a partially resistant cultivar. Measurements of infection frequency were also made under two temperature regimes. Again significant isolate, cuitivar and temperature interactions were recorded and the same isolate showed adaptation to the same partially resistant cultivar. This indicates that adaptation to a source of partial resistance can be found amongst unselected isolates and that pleiotropically adapted genotypes may rapidly overcome such resistance in the field following its widespread deployment. Other genes for resistance were detected in the major gene cultivars, including partial resistance in the ml-v genotypes.

Effect of different strains of soybean mosaic virus on growth, maturity, yield, seed mottling and seed transmission in several soybean cultivars.

Abstract: Eighty soybeans (Glyane max Merr) cultivars, includingx a resistant line Oxley 615 were each inoculated with seven streams of soybean mosaic virus SMV. Susceptible cultivers produced smaller plants with delaved maturity, and reduced seed yield relative to the non inoculared plants Someptible cultivars had.a higher level of morrled seeds and seat transmission ot SMV from the morrled seeds than the resistance line Oxley 615. The SMV strain cultivar interaction was significant for all traits, suggsesting that soybean cultivars should be tested against specific SMV strains to determine their response to this virus.

The role of non-vectored soil transmission as a primary source of infection by pepper mild mottle and cucumber mosaic viruses in glasshouse-grown Capsicum in Australia.

Abstract: Virus disease limit glasshouse production of capsicums in the Supraysia District of New South Wales. Symptoms develop on plants about 4 weeks after planting; and up to 83° of plants are infected. The major virus is cucumber mosaic (CMV) with some pepper mild niottle (PMMV) also present. Evidence is presented to show that the primary source of intection of both viruses is most likely to be debris from previous crops remaining in the soil. It demonstrates a previously unconsi-dered mechanism tor survival and spread of labile viruses such as CMV and the ecological ecological consequence of these results are considerable. Zusammenfassung Die Rolle nicht-vektorbedingter Bodenubertragung als Hauptursache von Infektionen durch Pepper Mild Mottle und Gurken-Mosaik-Virus bei im Gewachshaus gezogenem Capsicum in Australien Virtiskrankheiten beentrachutigen die Gewachshaus. sproduktion von Capsieum-Arten im Sunraysia- Bezirk von Neusudwales. Vier Wochen nach dem Auspflanzen treten die ersien Symptome auf etwa 80 % der Pflanzen sind befallen. Hauptsaehlieh tritt der Gurken-Mosaik Virus auf CMV), aber auch etwds Pepper Mild Mottle (PMMV). Die Studie liefert Beweise dafur. das die Hauptiniektionsquelle durch beide Virusarten in Uberresten fruherer Bepflanzung liegt, die in der Erde verblieben sind. Die Arbeit beschreibt einen bislang nicht beobachtenen Uberlebensmechanismus sowie die Ausbreitungsweise von labilen Virusarten wie CMV, deren okologischie Auswirkungen beitratlich sind.

Decay of Sclerotia of Botrytis cinerea by Trichoderma spp. at Low Temperatures

Abstract: In vitro, tests were conducted at 10°C and 5°C against sclerotia of Botrytis cinerea with 58 isolates of Trichoderma spp., highly antagonistic at 24°C but differing in their cold tolerance. Some isolates macerated and colonized sclerotia even at 5 °C. With 19 isolates of Trichoderma spp. less than 10 % of the sclerotia remained viable after 42 d at 5 °C. Conidia ol some Trichoderma spp. germinated at 5 °C within a few days and reached germination rates higher than 80 %. It seems to be feasible to use selected isolates of Trichoderma spp. for biological control of sclerotia of s. cinerea also during the colder season.

Suppression of Damping off on Pepper Caused by Pythium ultimum Trow and Rhizoctonia solani Kühn by Some New Antagonists in Comparison with Trichoderma harzianum Rifai

Abstract: Pot experiments were designed to evaluate the efficacy of Streptomyces nobilis, S. ochraceiscleroticus, Neocosmospora vasmfecta var. Africana and Acrophialophora levis isolates in reducing the damping-off on pepper in comparison with a strong mycoparasitic isolate of Trichoderma harzianum. Two pathogenic and five potential antagonistic isolates were grown seperately m flasks containing a mixture of sand-perlite-corn meal and potato-sucrose broth for 4 weeks. Soil infestation was achieved by mixing these stock cultures separately into the pot soils. Disease incidence was expressed as the percentages of dead seedlings in each pot and the protective values of the antagonists were calculated according to Abbott formula. Results indicated that all of the five test isolates have provided the seedhngs with protection of statistical value against Pythium uhimum and Rhizocionia solani reducing disease incidence between 28.14 to 79.14 % and 22.76 to 66.83 %, respectively. However, T. harzianum isolate proved to be the least effective antagonist against both pathogens.

Studies of Didytmella bryoniae (Auersw.) Rehm: Development in the Host

Abstract: Growing hyphae of Didymella bryoniae (Auersw.) Rehm are found in the stem tissue of cucumber, and the fungus can colonize nearly all types of tissue. The presence of the pathogen in the lignified elements suggests a spread of the disease up and down from the site of primary infection, even when the stem is strongly decomposed. The fungus dtsplays hyphal dimorphism in the infected tissue and a remarkable feature is stromatic-like structures in the host tissue close to fruiting bodies. Staining reveals no histological host reaction to fungal penetration of cell walls. The pathogen is characterized by the early development of its sexual stage.

Occurrence in soil and primary infections of Pseudomonas corrugata Roberts and Scarlett.

Abstract: The occurrence of Pseudomonas corrugata in soil has been checked Semiselective medium TNR (a modified SNR) permitted to isolate the causal agent of “tomato pith necrosis” from that source The average soil population of the bacteria was 31 × 104 CFU × g of soil P corrugata was also isolated from plants sowed in the naturally infected soil It was supposed that primary infections came from here

Production of Phytotoxic Sirodesmins by Aggressive Strains of Leptosphaeria maculans Differing in Interactions with Oil Seed Rape Genotypes

Abstract: Sirodesmins were extracted from culture filtrates of 3 aggressive strains of Leptosphaeria maculans which showed different specific interactions with the oilseed rape cultivars Quinta and Jet Neuf. Up to 8 compounds were detectable showing reactions on thin layer plates which are characteristic for sirodesmins. Sirodesmin PL, sirodesmin C, deacetylsirodesmin PL and deacetyl-sirodesmin C were identified on the basis of their UV-spectra, by various conversion reactions and by cochromatography with known standards. Two further compounds were tentatively identified as sirodesmin B and deacetylsirodesmin B on the basis of conversion reactions only. In the cultures of all strains sirodesmin PL was the main component, followed by deacetylsirodesmin PL, sirodesmin C, and deacetylsirodesmin C. These 4 metabolities were mainly responsible for the phytotoxic activity of all culture filtrates. They were systemically transported to leaves of root treated rape seedlings. No correlation was found between the production of the 4 main sirodesmins and the differential host parasite interactions of the 3 aggressive strains of Leptosphaeria maculans.

An Investigation of Pathogenicity of four Isolates of Fusarium oxysporum from South America, Africa and Malaysia to Clonal Oil Palm

Abstract: The pathogenicity of four isolates of Fusarium oxysporum from Brazil, Zaire and Malaysia, to clonal oil palm (Elaeis guineensis) was examined. The isolates from Brazil and Zaire were virulent pathogens which extensively colonized inoculated plantlets, producing severe stunting and chlorosis and significantly reducing plant growth. In contrast, two isolates from Malaysia were avirulent or only weakly virulent; nevertheless, both systemically colonized plantlets and one was present in amounts comparable to the virulent isolates. The implications of these findings with regard to the planting of clonal oil palm in each of these three main growing areas is discussed. Zusammenfassung Untersuchung der Pathogenitat von vier Fusarium oxysporum-lsolaten, die von geklonten Olpalmen aus Sud-Amerika, Afrika und Malaysia isoliert wurden Untersucht wurde die Pathogenitat von vier Fusarium oxysporum-Isohten aus Brasilien, Zaire und Malaysia auf geklonten Olpalmen (Elaeis guineensis). Die Isolate aus Brasilien und Zaire zeigten sich als virulente Pathogene, die inokulierte, junge Pflanzen sehr stark kolonisierten und starke Wachstumshemmung und Chlorose verursachten. Dagegen waren die zwei aus Malaysia stammenden Isolate avirulent bzw. nur schwach virulent. Trotzdem waren diese Isolate in der Lage, junge Pflanzen systemisch zu kolonisieren, ein Isolat war sogar genau so stark vertreten wie virulente Isolate. Die Bedeutung dieser Ergebnisse bezuglich der Pflanzung von geklonten Olpalmen in diesen drei Anbaugebieten wird diskutiert.

Assessment of the Effect of Oil on the Potyvirus Aphid Transmission Process

Abstract: Mineral oil sprays applied to plants or to artificial membranes were assessed for their effect on virus and helper component (HC), both of which are required for aphid transmission Probing oil-treated surfaces prior to or after probing a virus-HC mixture, HC, or virus, reduced or abolished transmission Oil also inhibited transmission when contacted after aphids had penetrated membranes which contained a virus + HC mixture Oil had no apparent effect on aphid probing behaviour The data support the hypothesis that oil affects the interaction of virus and HC with aphid mouthparts or alimentary tract

Rapid Immunofluorescent Detection of the Grapevine Flavescence Doree Mycoplasmalike Organism in the Salivary Glands of the Leafhopper Euscelidius variegates Kbm

Abstract: Polyclonal rabbit antibodies, prepared against partially purified mycoplasmalike-organisms (MLO) from Grapevine Flavescence Doree-infected plant extracts, were used to detect MLO in situ in excised salivary glands of the experimental vector Euscelidius variegates Kbm by an indirect immunofluorescent staining technique. Glands were examined from the fourth to the tenth week after the start of MLO acquisition. MLO detection was compared using this method, the transmission test and the ELISA technique applied to insects corpses after removal of salivary glands.

Induced Accessibility and Inaccessibility of Barley Cells in Seedling Leaves Inoculated with Two Leaf Rust Species

Abstract: Primary seedling leaves of two barley lines inoculated first with the pathogenic Puccinia hordei and 24 h later with the nonpathogenic P. recondita f. sp. recondita were screened for cells attacked by both rust fungus species. Cells in which P. hordei had formed a haustorium were hardly or not at all able to prevent formation of a haustorium by P. recondita. There was little evidence for diffusion of this induced accessibility to surrounding tissue. Comparison of the maturity degrees of the haustoria of the two species in the same cell suggests an induction of accessibility about or at the moment of cell wall penetration by P. hordei. Observations on leaves first inoculated with P. recondita and 24 h later with P. hordei led to the conclusion that cells in which P. recondita had failed to form a haustorium could still be infected by P. hordei. There was no evidence for induction of inaccessibility in such a cell as the result of an earlier attack by the non-pathogenic fungus. Zusammenfassung Induzierte Zuganglichkeit und Nichtzuganglichkeit von Zellen in Gerstesamlingsblatter, die mit zwei Blattrostspezies inokuliert wurden Untersucht wurden die Primarsamlingsblatter von zwei Gestenlinien, die zuerst mit dem Pathogen Puccinia hordei und 24 Stunden spater mit dem Nichtpathogen P. recondita f. sp recondita inokuliert worden waren, um festzustellen, ob Zellen durch beide Rostpilzspezies befallen worden waren. Festgestellt wurde, das Zellen, in denen sich ein P. hordei-Haustorium gebildet hat, kaum in der Lage waren, die Haustoriumbildung von P. recondita zu unterdrucken. Es gab wenig Hinweise dafur, das diese induzierte Zuganglichkeit sich im umgebenden Gewebe ausbreitete. Ein Vergleich des Reifegrades der Haustorien der zwei Spezies in einer Zelle deutete darauf hin, das eine Auslosung der Zuganglichkeit zur Zeit der Zellwandpenetration durch P. hordei stattfand. Beobachtungen an Blattern, die zuerst mit P. recondita und 24 Std. spater mit P. hordei inokuliert worden waren, zeigten, das in Zellen, wo eine P. recondita-Haustoriumbildung gescheitert war, eine P. hordei-Infektion noch moglich war. Keine Hinweise deuteten auf einer Auslosung einer Unzuganglichkeit dieser Zellen hin, die durch den Infektionsversuch des nichtpathogenen Pilzes zuruckzufuhren ware.

ACC Synthesis as the Activated Step Responsible for the Rise of Ethylene Production Accompanying Citrus Exocortis Viroid Infection in Tomato Plants

Abstract: Ethylene production was stimulated during the period when systemic symptoms appeared in tomato plants infected with citrus exocortis viroid (CEV). Neither methionine nor S-adenosylmethionine increased ethylene production in leaf discs. In contrast, 1-aminocyclopropane-l-carboxylic acid (ACC) stimulated ethylene production notably. Whether viroid infection acted upon ACC production, its conversion to ethylene, or both, was studied by determining the time course of the concentration of ACC and its in vivo production and conversion rates. During early symptoms, ACC synthesis increased and then remained steady during the development of symptoms, but no difference in the capacity of conversion of ACC to ethylene between healthy and CEV-infected tissues was observed. This indicates that ethylene production in tomato leaves showing systemic symptoms to CEV is activated at the level of ACC production.