bluuebunny/crossref_metadata_2025 huggingface dataset:
The Spread of African Cassava Mosaic Virus into and within Cassava Fields
Authors: Fargette D. , Fauquet C. , Grenier E. , Thresh J. M.
Published: May 2008

Only a small proportion of Bemisia tabaci collected in totally infected cassava fields at a site in Côte d'lvoire transmitted African cassava mosaic virus (ACMV) to test plants. Nevertheless, the monthly increase in disease incidence in an experimental planting was directly related to numbers of adult whiteflies counted on plants 6 weeks earlier.

In plots at different spacings, the greatest incidence of ACMV expressed as a percentage of the total stand occurred at the lowest plant density. Much speread into the spacing trial and into two other experimental plantings occurred from outside sources and followed downwind gradients. By contrast, spread from ACMV‐infected sources within plantings was limited. It occurred in all directions but over distances of only a few metres. These contrasting patterns of spread are attributed to the differentbehavior of B. tabaci above and within the crop canopy.

It is concluded that contamination of cassava fields in the coastal forest area of Côte d'Ivoire is due mainly to rapid spread from outside sources which leads to internal foci that contribute to some further, although limited, spread. These findings are discussed in relation to possible control strategies based on the release of healthy cuttings, dense planting and subsequent roguing. Such measures are unlikely to be effectve in the coastal forest region of Côte d'Ivoire and adjacent countriesunless varieties are grown with greater resistance to infection than those currently used.
Purification and Partial Characterization of Isometric Virus‐like Particles in Kalanchoe Species
Authors: Izaguirre‐Mayoral Maria Luisa , Carballo O. , Gil F.
Published: May 2008

Isometric virus‐like particles (IVLP) were detected in crude sap from Kalanchoe pinnata, K. daigremontiana and K. tubiflora plants showing a mild mosaic on the leaves. These particles of 35 nm in diameter were transmitted mechanically to several test plants but not to healthy Kalanchoe. Air temperatures above 30 °C hindered the infection process. The IVLP were purified from systematically infected Nicotiana benthamiana using Triton X‐100 as clarifying agent followed byP, EG precipitation. IVLP were degraded by organic solvents and formed aggregates in the presence of 2 mmol/1 CaCl2. The particles occurred in relatively low concentration in plant sap and lost infectivity in leaves frozen at ‐70 °C for one week and in purified preparations kept at 4 °C. In buffer crude sap of N. benthamiana IVLP had a thermal inactivation point between 45 and 50 °C on a longevity in vitro of 20 h at 25 °C. Particles contained one nucleoprotein component witha molecular weight of 46,000 daltons and a ssRNA species which, when denatured, had a molecular weight of 1.2 × 106. IVLP purified preparations exhibited a typical nucleoprotein absorption spectrum with a maximum at 254–260 nm and a minimum at 240,–243 nm and a A 260/280 ratio of 1.56. The buoyant density of the IVLP was 1.32 g/ml calculated by isopycnic centrifugation on CsCl.

Ultrastructural studies in infected leaves of K. pinnata indicated that IVLP caused an increase in chloroplast volume, distortion of the grana and reduced the number of thylakiods per grana. IVLP infection also impared the diurnal pattern of synthesis and hydrolysis of starch, characteristic of CAM plants. The non‐serological reaction of the IVLP with antisera specific to members of 7 different groups of spherical viruses as well as the combination of physicochemical properties and host range, exhibited by these particles impeded their taxonomic location. In nature, young Kalanchoe plantlets acquire the IVLP through their physical connections with the infected mature leaves.
Tillage Effects on the Incidence and Severity of Root and Stalk Rot of Maize Caused by Fusarium moniliforme and Macrophomina phaseolina in South‐Western Nigeria
Authors: Osunlaja S. O.
Published: May 2008

Conventional tillage methods were compared with no tillage systems for the control of root and stalk rot disease of maize caused by Macrophomina phaseolina and Fusarium moniliforme in a field with a recent history of high stalk rot incidence in south‐western Nigeria. The incidence of stalk rot was significantly less under no‐tillage practices than in conventionally tilled plots during the twoseason trial. Application of paraquat or burning of crop residue had no apparent influence ond isease incidence. None of the treatments affected the severity of the diseases.
Characterization of Closterovirus‐like Particles Associated with Grapevine Leafroll Disease
Authors: Hu J. S. , Gonsalves D. , Teliz D.
Published: May 2008

Abstract A purification procedure (Zeeet al. 1987) for closterovirus‐like particles associated with grapevine leafroll disease was improved after various sources of plant tissues, extraction buffers, pH values, and centrifugation techniques had been examined. An antiserum against the CA‐4 isolate was produced and used in ELISA. The virus‐like particles of the NY‐1 isolate measured in crude plant preparations were about 1,800 to 1,900 nm long. The molecular weight of coat protein of the NY‐1and NY‐2 isolates were ca. 43 × 103 daltons in SDS‐PAGE analysis; and bands having this molecular weight reacted in Western blotting tests with specific polyclonal and monoclonal antibodies. A large dsRNA molecule (ca. 10 × 106 Mr) along, with lower molecular weight species were isolated from leafroll diseased grapevines, but not from healthy grapevines. Seven leafroll isolates were tested for their serological relatedness in a protein A‐gold labelling immunosorbent electron microscopy, assay. Results indicated that serologically distinct serotypes existed, and mixed infection of grapevines with different scrotypes was common. A grouping of isolates into serotype I, II, III, IV is proposed.
The Loss of Structural Integrity in Damaged Spruce Needles from Locations Exposed to Air Pollution
Authors: Hasemann Gudrun , Jung Georg , Wild Aloysius
Published: May 2008

Abstract Within the framework of appraising the new type of forest damage, the epidermis of two‐year‐old spruce (Picea abies) needles was investigated as a possible site for primary attack by air pollutants using light and scanning electron microscopy.

Depending upon the extent of the macroscopically visible needle leaf disease, a degeneration process of the cuticular, stomatal and epidermal structures leading to the lethal destruction of the needle surface was observed.

Stomatal and epidermal cells become increasingly deformed or collapsed showing increasing discolouration due to phenolic deposits. Additionally, the erosion of stomatal waxes is accelerated, leading initially to a temporary occlusion of the stomata, and then to a wide opening of the antechamber following a complete decomposition of the plug.

Surface lesions indicating early damage to the epidermal tissue already occur on slightly yellowed needles. The barrier effect of the spruce needle epidermis on exogenous stressors could thereby already be reduced at an early stage, triggering incipient losses of structural resistance.
Primary Infection of Barley by Erysiphe graminis f. sp. hordei in Relation to Leaf‐Age Dependent Resistance and the Roles of the Epidermis and Mesophyll in this Resistance
Authors: Nelson Henry , Shiraishi Tomonori , Oku Hachiro
Published: May 2008

Abstract The infection frequency of both compatible and incompatible races of Erysiphe graminis f. sp. hordei decreased gradually with increasing leaf age on undetached primary barley leaves. The length of secondary hyphae of the compatible race was approximately the same regardless of age, but secondary hyphae were slightly longer on younger seedlings than on older seedlings in the case of the incompatible race. Both the infection frequency and length of secondary hyphae of the two races weredistinctly different. On composite sections produced by exchanging the epidermal layers of young and relatively mature primary leaves, the infection frequency of the compatible race was higher on the epidermis of young leaves than on the epidermis of older, leaves, regardless of which mesophyll was under the epidermis. The epidermis appears to play a major role in age‐dependent resistance, while the mesophyll may act disparately by providing a factor promotive to mildew infection in addition to supporting the resistance function of the epidermis.
Analysis of Pectic Enzyme Zymograms of Fusarium Species I. Fusarium lateritium and Related Species
Authors: Szecsi A.
Published: May 2008

Abstract Zymograms of the extracellular pectic enzymes (pectinesterase, polygalacturonase) of Fusarium lateritium and related species were prepared by electrophoresis from untreated culture filtrates. The zymogram technique gave evidence to conclude that F. lateritium, F. stilboides and F. xylarioides are distinct species. “pini” isolates are rather “subglutinans”‐like fusaria than “lateritium”‐like, while F. udum represents a genetical variant of F. oxysprorum.
Chemical Composition of Phloem Exudate of Mycoplasma–infected Apple Trees
Authors: Kollar A. , Seemüller E.
Published: May 2008

Abstract Phloem exudate was obtained by incision from different apple cultivars affected by apple proliferation disease. The exudate was analyzed by high–performance liquide chromatography (HPLC), some compounds also by thin–layer chromatography, gel filtration chromatography and polyacrylamide gel electrophoresis. Sorbitol and sucrose were the most prevalent sugar, alcohol and sugar, respectively, while stachyose, raffinose, fructose, and myo–inositol were present to a much lower extent. Glucose was absent or occurred at very low concentrations only. All common amino acids with the exception of arginine and cysteine were detected, aspartic acid and glutamic acid together with the corresponding amides being predominant. Citric acid and malic acid werether major organic acids while shikimic, succinic and fumaric acid were present at considerably lower amounts. The inorganic constituents were (in decreasing order) potassium, magnesium, sodium, sulphate, chloride, phosphate, calcium, and nitrate. Approximately 100 ppm protein were found consisting mainly of two major fractions with a molecular weight of 110,000 and 28,000 Dalton, respectively. Only two lipid classes were detected which were represented by 0.4 ppm β–sitosterol and by 50 ppm of a sterylester with a long chain fatty acid moiety. DNA and RNA could not be found, but all RNA nucleotides were present and also UPD–glucose, which was predominant. The significance of the results obtained for culturing mycoplasma–like organisms (MLOs), is discussed.
Production and Characterization of Monoclonal Antibodies to Potato Virus A
Authors: Boonekamp P. M. , Pomp H. , Gussenhoven G. C.
Published: May 2008

Abstract Purified potato virus A (PVA) was used for immunization to produce monoclonal antibodies (MAb). The type of ELISA with purified PVA or non–purified PVA, played an essential role in selecting MAb with different specificity.

Two MAb's (MAb–1 and MAb–2) were selected, using indirect ELISA (I–ELISA) with purified PVA. Competition experiments suggested that MAb–1 and MAb–2 reacted with the same epitope on purified PVA (epitope 1). ELISA, IEM and SDS–PAGE–immunoblotting experiments showed that epitope–1 was only present on purified PVA but not on non–purified PVA, suggesting that this epitope was introduced during the purification. Assays at different steps during purification indicated that epitope–1 was only exposed after plant components and reducing agents were removed from the PVA extract.

Three MAb's (MAb–3, MAb–4 and MAb–5) were selected by indirect double antibody sandwich ELISA (IDAS–ELISA) with non–purified PVA. These MAb's reacted in I–ELISA or IDASELISA with purified PVA as well as with non–purified PVA and might be useful for routine diagnosis. MAb–3, 4 and 5 cross–reacted with some other potyviruses in I–ELISA and in IDAS–ELISA. MAb–1 cross–reacted with 5 out of 7 other potyviruses in I–ELISA, but not in IDAS–ELISA.
Virulence of Septoria nodorum as Affected by Passage Through Detached Leaves of Wheat and Barley Cultivars1
Authors: Berecket T. , Hebert T. T. , Leonard K. J.
Published: May 2008

Abstract Three genetically marked, single–spore isolates of Septoria nodorum from wheat were passed through detached leaves of wheat cvs Blueboy and Coker 747 and the barley cv. Boone to produce three sub–isolates per original isolate. Each sub–isolate was cultured for three pycnidiospore generations on its respective host. Virulence of each sub–isolate on detached leaves of Blueboy, Caldwell, Coker 747, and NK81W701 wheat, and Boone and Surry barley was compared with that of the original single–spore isolate from which it was derived. In most cases, sub–isolates passed through wheat were significantly more virulent than the originals on wheat cultivars. They also were more virulent to barley than the original isolates but they were less virulent to barley than to wheat cultivars. Isolate × cultivar interactions were statistically significant (P < .0001) for isolates passed through wheat or barley and were greater than isolate × cultivar interactions among the original isolates. In seven of eight isolates passed through wheat or barley, only the original genetic marker was recovered after three generations, indicating that cross–contamination could not account for the observed change of virulence. In the single case of apparent contamination, of a sub–isolate, virulence declined.
The Use of a Green–Grafting Technique for the Detection of Virus–like Diseases of the Grapevine
Authors: Walter B. , Bass P. , Legin R. , Martin C. , Vernoy R. , Collas A. , Vesselle G.
Published: May 2008

Abstract A new green–grafting technique developed for vegetative propagation (MARTIN et al. 1987) is currently being used for the rapid indexing of grapevine virus diseases. By this method, leafroll, fleck, corky bark, vein mosaic, vein necrosis and graft incompatibility were detected under greenhouse conditions. The symptoms appear sooner than by the usual indexing method involving field planted woody indicators. Another advantage of green–graft indexing is the high saving of space and labour. This, method provides a valuable tool for routine control of the sanitary selection of disease–free grapevines.
Purification and Characterization of Banana Bunchy Top Virus
Authors: Wu R. Y. , Su H. J.
Published: May 2008

Abstract Banana bunchy top virus (BBTV) was successfully purified by a procedure which included pulverizing diseased tissues frozen in liquid nitrogen, clarification of the extract with chloroformbutanol, concentration of the virus by cycles of differential centrifugation, stirring and incubating at 4°C followed by a second cycle of differential centrifugation and sucrose density gradient centrifugation. The concentrations of BBTV obtained from leaf blades and midribs plus petioles were up to 0.34 and 0.56mg/kg tissue, respectively. The virus concentration was highest in diseased leaves collected from October to December, and lowest in those collected from June to September. BBTV is a luteovirus (particles 20– 22 nm in diameter), preparations of which have maximum absorbance at 257 nm, minimum absorbance at 240 nm and a A260/280 ratio of 1.46. The relative molecular mass (Mr) of BBTV coat protein subunit is 21,000, and that of its ssRNA is 2.0 × 106.
Yield Loss in Sweet Corn in Response to Defoliation or Infection by Exserohilum turcicum
Authors: Levy Yehouda , Leonard KurtJ.
Published: May 2008

Abstract Net CO2 assimilation was reduced in sites of infection by Exserohilum turcicum in leaves of Seneca 60 sweet corn before lesions appeared. In leaf tissue adjacent to infected areas, there was an early small increase in CO2 assimilation followed by a gradual decline to nearly 0 net CO2 exchange by 7 days after inoculation. Translocation of photosynthates in to disease lesions from healthy tissue distal to the lesions was observed within 1 h after exposure of 1.2–cm2 areas of the leaf blade to 14CO2. No translocation from lesions to healthy leaf tissue was observed. The effects of defoliation at specific leaf positions on yield of sweet corn plants were accurately simulated by a model in which yield is expressed as a function of healthy leaf area absorption of incident insolation. Removal of leaves from the bottom third of the plants caused no yield loss, whereas removal of leaves above the ear caused significant losses. The model underes, timated the yield loss caused by infection by E. turcicum by approximately 22 %. The observed effects of infection by E. turcicum on photosynthetic efficiency in leaf tissue adjacent to lesions and on translocation of photosynthates into lesion from distal parts of the leaf show that the effect of northern leaf blight on yield is greater than can be accounted for by the direct loss of healthy leaf area through necrosis within disease lesions.
Inheritance of Pathogenicity of Progeny from an F1 Culture of Melampsora lini
Authors: Statler GlenD.
Published: May 2008

Abstract Races 1 and 400 of Melampsosau bni the causal agent of flax [Lmum usitatissimum]), were crossed and the resulting F2 progeny evaluated on near‐isogcnic fiax lines. The infection type of the parental cultures, the F12 and the segregating f2 progeny were used to evaluate the inheritance of pathogenicity. Races 1 and 400 as well as the F2 and all the F2 progeny were avirulent on lines N and P4 genes. This indicated both races to be homozygous avirulent. The F2 and all the F2 progeny were virulent on lines containing L9, M1, M4, and P. This indicated the F to be homuzygous for virulence at these loci. Segregation ratios of the F2 cultures fit monogenic ratios on lines with host genes K. L2, L5, L6, L7, L11, M, M2, M3, N1, P1, P2, and P3. Race 1 was avirulent, race 400 virulent and tht F, avirulent on these lines. Several linkage groups were indicated including close linkage at Ap1, Ap2 and Ap3. Segregation on lines L, L3, M5, M6 and cultivars Flor, Dufferin, Linott, and Wishek fit a digenic model. The infection tvpes of the parents, the F1 and the F2, segregations could usually be explained by classical gene‐for‐gene interactions. Possible exceptions were segregations on L4, L8 and N2 which did not fit a 3: 1 ratio but did fit a 9: 7 ratio. Segregation on L 10 fit a 7: 9 ratio but line L10 may be temperature sensitive. Segregation on L1 indicated a single dominant gene for pathogenicity.
Microscopic Studies of the Interaction Between Barley and the Saprophytic Fungus, Cladosporium macrocarpum
Authors: Christiansen Solveig K. , Smedegaard V.
Published: May 2008

Abstract Scanning electron microscopy of the saprophytic fungus Cladosporium macrocarpum on barley leaves revealed characteristic bar‐shaped appressoria. They were almost always located either above a stomatal opening or above the anticlinal cell walls. It was shown with light microscopy that the fungus was able to penetrate via stomatal openings. No successful direct penetrations were observed. The barley tissue responded to direct penetration attempts by formation of papillae and accumulation of fluorescent compounds. Fluorescence microscopy revealed fluorescent compounds in papillae, haloes, hypersensitively reacting epidermal cells, mesophyll cells, and in stomatal areas. The induced resistance reactions are similar to those described earlier for, pathogenic fungi, indicating that they are part of general resistance phenomena.
Transformation by Agrobacterium tumefaciens Changes Graft Compatibility of Tissues of Nicotiana tabacum L.
Authors: Schlitzberger A. , Beidlrbeck R.
Published: May 2008

Abstract Shoots, callus or tumor tissues of N. tabacum have been grafted to stock plants of different species of Solanaceae. The graft compatibility ranges of the three grafted tissue types were different. For example; shoots of N. tabacum united easily with root‐stocks of Lycopersicum esculencum. Tumors of the same variety of N. tabacum transformed by different strains of Agrobacterium tumefaciens did not produce transplantation tumors on L. esculentum. These results are discussed with respect to recognition events at the graft contact zone.
Structural Transitions in Southern Bean Mosaic Virus and their Correlation with Infectivity and Ribonuclease Sensitivity
Authors: Sehgal O. P.
Published: May 2008

Abstract Southern bean mosaic virus (SBMV) virions swell when the capsid‐associated divalent cations are removed with EDTA at pH 7.5, resulting in an approximate 99% decline in the specific infectivity. Recompacting swollen virions either with divalent cations at pH 7.5, or by lowering the pH to 5.0 (in the absence or in presence of divalent cations) fails to restore complete infectivity. In contrast to swollen SBMV, RNA within the recompacted virions is fully protected from ribonuclease attack. Removing divalent cations with EDTA at pH 5.0 causes no infectivity loss or conformational change. These results indicate that if SBMV conformation is altered once then an irreversible loss in the infectivity occurs and the divalent cations play no role per se, in the infection process. Furthermore, observations based upon the sedimentation behaviour of ribonuclease‐treated SBMV indicate that RNA must be physically intact for capsid recompaction to occur. Obviously, structural rearrangements at the capsidsurface (e.g., regeneration of intersubunit interactions) and at the virion interior (i.e., RNA‐protein linkages) are involved collectively in conferring conformational stability to the recompacted SBMV.
Isozyme Variation and Genetic Distances of Erysiphe graminis DC. Formae Speciales
Authors: Koch G. , Köhler W.
Published: May 2008

Abstract Isozymes of ten different enzymes and unspecific stained proteins were used as biochemical genetic markers to study genetic variation within and between E. graminis ff. sp. hordei, avenae, secalis and tritici. In addition, grainproteins of the corresponding host species were examined. In each forma specialis, one genotype proved to be predominant. 131 distinct isozyme and 93 protein bands were distinguishable in these genotypes. However, divergent banding patterns differed only in 8 bands from the predominant banding patterns found within the formae speciales avena, secalis and tritici. The genetic relationships between powdery mildew formae speciales and host species were computed by cluster analysis from similarity (F) and dissimilarity (D) coefficients and illustrated by phylogenetic trees. Marked correspondence was found between E. graminis ff. sp. secalis and tritici (F: 82–90%). Lower homologies were obtained from the comparison ofthese formae speciales respectively with E. graminis ff. sp. hordei (F: 28–34%) and avenae (F: 24–32%). All phylogenetic trees constructed revealed the same arrangement classification of the formae speciales with similar graduation. The comparison of the host species revealed the highest similarity between S. cereale and T. aestivum (F: 74%). Regression analysis confirmed significant correlation between the genetic relationships within host species and powdery mildew formae speciales (r2= 0.81).
Einfluß der Behandlung von Rübensaatgut mit Rhizosphärebakterien auf den Befall durch Pilze der Gattung Pythium I. Antagonistische Wirkung verschiedener Bakterienisolate gegenüber Pythium spp.
Authors: Sikora R. A. , Bodenstein F. , Nicolay R.
Published: May 2008

Abstract The influence of a seed‐dressing with rhizosphere bacteria on the infection of sugarbeet by fungi of the genus Pythium I. Antagonistic effect of different bacterial isolates towards Pythium spp.

Seed treatment with selectively isolated rhizosphere bacteria from the fluorescent pseudomonad group can protect sugar beet seedlings from damping‐off caused by species of Pythium. The antagonistic rhizobacteria were equally effective in different soil substrates, both unsterilized and steam‐sterilized. Antagonistic activity of an isolate was similar within seeds of a sugarbeet cultivar but different when different cultivars were compared. The number of bacteria adhering to the seed of eachcultivar which influenced the level of antagonism to Pythium infection, varied with seed morphology. A mixture of the three different isolates did not increase antagonistic activity when compared to the activity of the isolates individually.
Einfluß der Behandlung von Rübensaatgut mit Rhizosphärebakterien auf den Befall durch Pilze der Gattung Pythium II. Untersuchungen zum Wirkungsmechanismus
Authors: Sikora R. A. , Bodenstein F. , Nicolay R.
Published: May 2008

Abstract The influence of a seed‐dressing with rhizosphere bacteria on the infection of sugarbeet by fungi of the genus Pythium II. Studies on the mode of action

Studies were conducted to determine the mode of action responsible for the reduction of Pythium infection of sugarbeet seedlings caused by an inoculation with rhizosphere bacteria. It was shown that the bacteria reduced Pythium ultimum, sporangia germination. More detailed studies with the bacterial isolate T58 demonstrated that activity was related to both presence of the living bacteria as well as to inoculum density.

Water soluble extracts from the seed of different sugarbeet cultivars stimulated P. ultimum sporangia germination to different degrees, Germination, however, decreased as the density of the fluorescent pscudomonad T58 was increased. Reductions in mycelial growth, caused by a number of isolates, indicated the presence of antibiotic activity.

The addition of high levels of iron to the substrate caused a reduction in the level of antagonism of two pseudomonad isolates on the seed of the cultivar Kawevera. The rate of reproduction of two bacterial isolates was slower on extracts from the seeds of the cultivar Primahill than on the cultivar Kawevera. Rhizobacteria colonization of the root as well as the hypocotyl was observed with one isolate.
Some Properties of a Phloem‐Limited Non Mechanically‐Transmissible Grapevine Virus
Authors: Boulila M. , Boscia D. , Di Terlizzi B. , Castellano M. A. , Minafra A. , Savino V. , Martelli G. P.
Published: May 2008

Abstract Grapevine phloem‐limited isometric virus (GPLIV) is the name proposed for a non mechanically‐transmissible virus found in Italian and Tunisian grapevines. In density gradient centrifugation purified virus preparations sedimented as two components: T, made up of empty protein shells, and B, composed of intact nucleoprotein particles. B particles had a buoyant density of 1.45 g/cm3 at equilibrium in CsCl and contained 35% RNA consisting of a single molecule with an apparent size of 7.4 kb. The coat protein consisted of a single species with a mol.wt of 28,000 daltons. Purified virus preparations did not infect herbaceous hosts by manual inoculation. A specific antiserum with a titre of 1: 64 raised in rabbits, was used for identification of, GPLIV in field‐grown Tunisian grapevines and in leafroll‐affected Italian vines before and after heat treatment. Although heat treatment eliminated the virus from the majority of the plants, leafroll symptoms persisted in several GPLIV‐free vines, indicating that there is no clear‐cut relationship between GPLIV and this disease.
In vitro‐Selektion bei Gerste (Hordeum vulgare L.) auf Resistenz gegen Drechslera teres
Authors: Hunold R. , Krämer R. , Kunert R. , Peterka H.
Published: May 2008

Abstract Von haploiden und diploiden unreifen Embryonen der Gerste (Hordeum vulgare L.) wurden Kalluskulturen auf einem modifizierten MS‐Medium (3,0 mg/1 2.4‐D) induziert und teilweise einer Mutagenbehandlung mit Natriumazid unterzogen. Die in vitro‐Selektion auf Resistenz gegen Drechslera teres (Sacc.) Shoem. erfolgte auf einem MS‐/B5‐Medium, das mit dem Kulturfiltrat‐Methanol‐überstand des Erregers angereichert war. In Abhängigkeit von Basalmedium und Ploidieniveau der Genotypen kam es zu einer differenzierten Hemmwirkung des Toxins. Nach einer zweimaligen Selektion von 28 Tagen je Passage auf 200% und 300%igen Toxinmedien (Kulturfiltrat = 100%) wurde eine reproduzierbare Sproßregeneration von ca. 0,6% erzielt. Erste Prüfungen, von Nachkommenschaften regenerierter Pflanzen auf Toxin‐ und Erregerresistenz ergaben Verbesserungen im Resistenzniveau gegenüber dem jeweiligen Ausgangsmaterial auch aus der Kontrollvariante, so daß somaklonale Variation in diesem Merkmal vermutetwerden kann.
Anfälligkeit von entomopathogenen Nematoden gegenüber nematodenfangenden und endoparasitären Pilzen
Authors: Van Sloun P. , Nicolay R. , Lohmann U. , Sikora R. A.
Published: May 2008

Abstract Susceptibility of entomopathogenic nematodes to nematode‐trapping and endoparasitic fungi

Laboratory tests in petri dishes demonstrated that the nematode‐trapping fungi Arthrobotrys superba and A. robusta preyed upon the entomopathogenic nematodes Steinernema bibionis, S. feltiae and a species of Heterohabditis. Up to 100% of the nematodes were trapped 48 h after application. Large differences existed in the time required for trapping as well as for mortality after trapping and was dependent on the fungal or nematode species studied. Arthrobotrys robusta, reduced S. bibionis densities in sand‐block bioassay chambers. The prior introduction of a microphagous nematode, Panagrellus redivivus, to induce trap formation caused a 52% reduction in S. bibionis levels.

The endoparasitic fungi Harposporium anguillulae and Drechmeria coniospora did not parasitize the entomopathogenic nematodes in petri dish tests. However, Verticillium balanoides, was shown to be a parasite of S. bibionis. Predivivus and a mycophagous species of Ditylenchus were more quickly parasitized than S. bibionis, with parasitism reaching 100, 90 and 30% after 42 days, respectively. In the sand‐block chambers V. balanoides did not reduce the, number of recovered S. bibionis juveniles after 14 or 28 days.
Reaction of Muskmelon Collections to Cucumber Green Mottle Mosaic Virus
Authors: Rajamony L. , More T. A. , Seshadri V. S. , Varma A.
Published: May 2008

Abstract In a preliminary trial 187 collections of muskmelon comprising dessert and non‐dessert types and wild Cucumis species were screened against cucumber green mottle mosaic virus (CGMMV) under field conditions. Based on the reaction to CGMMV, 64 were studied further in detail. Thirteen collections were found to be resistant in two field screenings (summer and rainy seasons). Results on screening under artificial conditions against pure isolate of CGMMV indicated that Cucumis figarei, C. myriocarpus 1, C. myriocarpus 3, C. africanus 1, C. africanus 2, C. meeusii, C. ficifolius and C. zeyheri 2 were resistant to virus. Immune nature of resistance was later confirmed by back inoculation technique and, transmission electron microscopic study of C. figarei, C. ficifolius, C. meeusii, C. africanus 1 and C. zeyheri 2. Phoot (C. melo var. momordica) and Kachri (non‐dessert types), FM 1 and FM 2 (Cornell breeding lines) and C,. myriocarpus 2 were also resistant to CGMMV with very mild symptoms.
Flame Chlorosis: a New, Soil‐transmitted, Virus‐like Disease of Barley in Manitoba, Canada
Authors: Haber S. , Kim W. , Gillespie R. , Tekauz A.
Published: May 2008

Abstract “Flame Chlorosis” of barley was first observed in two fields of spring barley near Newdale, Manitoba, Canada in late June, 1985. Disease symptoms included leaf chlorosis in a “flame” ‐like pattern, severe stunting, and failure to produce fertile heads. Afflicted plants were found in circular patches in two adjoining fields, and scattered diseased plants were identified in several nearby fields. Surveys in 1986 and 1987 identified scattered diseased plants in a small number of barley fields, most within 50 km of the original Newdale site. In 1988, the disease was identified at many more locations near Newdale, and at two neighbouring sites the disease occurred at levels sufficient to cause economic loss. In addition, flame chlorosis was identified at several locations outside the Newdale region.

To date the flame clorosis agent has been transmitted only by planting seed or seedlings in soil where plants with symptoms of flame chlorosis had grown earlier. After transfer to sterile potting medium, afflicted plants continued to produce leaves with symptoms. The cytopathology of flame chlorosis differed from that of the known soil‐borne viruses of cereals. No inclusions of particles were observed, and instead of the characteristic pinwheel‐inclusions, there was massive vesiculation and peripheral distortion of chloroplasts and mitochondria. A set of double‐stranded (ds) RNAs, ranging in size from about 900 to 2800 base‐pairs (bp) and distinct from any described for a known cereal virus, was isolated from plants afflicted with flame chlorosis, while no dsRNA was isolated from healthy tissue of the same cultivar.
Degradation of Uredospores of the Soybean Rust Fungus (Phakopsora pachyrhizi Syd.) by Cell‐Free Culture Filtrates of the Mycoparasite Verticillium Psalliotae Treschow
Authors: Saksirirat W. , Hoppe H.‐H.
Published: May 2008

Verticillium psalliotae isolates Taiw and Thai C are effective parasites of the soybean rust fungus. Cell‐free culture filtrates of these fungi, prepared after growth on autoclaved uredospores, contained β‐1,3‐glucanase, chitinase and protease activities and caused degradations, when rust spores were treated with them for 24 or 72 h. During these lytic processes carbohydrates, amino compounds and N‐acetylhexosamine were released. The carbohydrate fraction was composed of mannitol, arabitol, trehalose, glucose and unidentified substances showing low Rf‐values during thin layer chromatography. The amino compounds consisted of 10 amino acids (leucine and/or isoleucine, phenylalanine, glutamic acid, valine, arginine, asparagine, glutamine, serine, aspartic acid, histidine) and 5—7 substances which could not be identified. Verticillium lecanii isolate Konz is a weak parasite of soybean rust. During growth on uredospores the fungus produced culture filtrates without chitinase activity and with low total activities of β‐1,3‐glucanase and protease. Compared with V. psalliotae, culture filtrates of V. lecanii exerted lower lytic activities on soybean rust uredospores. The results are consistent with the aspect that the rapid growth of V. psalliotae on soybean rust fungus is primarily based on the secretion of lytic enzymes which make nutrients available to the mycoparasite.
Interactions between Fusarium oxysporum f. sp. lycopersici and Callus of Susceptible and Resistant Tomato Lines: Fungal Growth and Phytoalexin Accumulation
Authors: Kroon B. A. M. , Scheffer R. J. , Elgersma D. M.
Published: May 2008

Callus cultures derived from isogenic lines of the tomato cultivars Moneymaker and Craigella, resistant or susceptible to F. oxysporum f. sp. lycopersici, were inoculated with Fusarium oxysporum f. sp. lycopersici race 1. Fungal growth was restricted on callus derived from resistant plants, after inoculation with a conidial suspension, whereas callus derived from susceptible plants was totally overgrown by the fungus within 7 days. The concentration of the phytoalexin rishitin was significantly higher in the callus culture derived from a resistant tomato line compared with the callus culture from a susceptible line, 2 and 3 days after inoculation with mycelium. The results of the experiments were compared with experiments with whole plants. Rishitin production as well as growth of the fungus was comparable with responses in plant‐fungus interaction. Therefore callus culture may be useful in studying the interaction between tomato plants and race 1 of F. oxysporum f. sp. lycopersici.
Elimination of Strawberry Mottle Virus and Strawberry Crinkle Virus from Isolated Apices of Three Strawberry Varieties by the Addition of 2,4‐Dioxohexahydro‐1,3,5‐triazine (5‐Azadihydrouracil) to the Nutrient Medium
Authors: Kondakova V. , Schuster G.
Published: May 2008

Following the addition of 0.2 mg 2,4‐dioxohexahydro‐1,3,5‐triazine (DHT, formulation CKB 1130) to 1 l Gamborg's medium for organogenesis, the two viruses strawberry mottle virus and strawberry crinkle virus could not be detected in 74.4, 63.6 or 65.1%, respectively, of the plants regenerated from 0.8mm apices of the varieties Redgauntlet, Vesper and Pokahontas after their inoculation onto the indicator strain of Fragaria vesca EMK. In contrast, control explants which were not exposed to DHT proved to be 100% virus infected.
Prediction of Eyespot Severity on Winter Wheat or Winter Barley Inoculated with W‐type or R‐type Isolates of Pseudocercosporella herpotrichoides
Authors: Goulds A. , Fitt B. D. L.
Published: May 2008

In crops of winter wheat (1986—88) or winter barley (1987—88) inoculated with W‐type or R‐type isolates of Pseudocercosporella herpotrichoides and sown on different dates (1986) or at different seed rates (1987,1988) eyespot epidemics developed in different ways. Methods of measuring eyespot incidence/severity during crop growth were compared for their ability to predict eyespot severity at grain filling. Regressions were calculated for eyespot severity score at GS 71 on earlier measurements, either at GS 30/31 (11 methods) or from GS 22 to GS 65 (3 methods). Based on measurements at GS 30/31, all the methods predicted eyespot severity at GS 71 well in plots of winter barley inoculated with W‐type isolates (r, 0.83—0.97) but the accuracy of predictions in plots inoculated with R‐type isolates was very variable (r, 0.09—0.71). Predictions for 1987 and 1988 were less accurate in wheat than in W‐type plots of barley, but did not differ between W‐type and R‐type plots (r, 0.70—0.89). When the wheat data for 1986 were also included predictions were less accurate, especially in R‐type plots (r, 0—0.59). Generally, it was easier to predict eyespot severity at GS 71 in W‐type than in R‐type plots, especially in barley and in wheat before GS 37/39. Predictions of eyespot severity at GS 71 based on measurements before GS 25 were inaccurate for both wheat and barley. After GS 25 the accuracy of the prediction was generally good in W‐type plots and did not improve greatly except in wheat after GS 59. However, there was a steady improvement in the accuracy of the prediction in R‐type plots of barley from GS 24 to GS 53. Assessments of eyespot incidence on stems predicted eyespot severity at GS 71 more accurately than assessments on leaf sheaths on wheat after GS 37/39, but were not as good on barley until GS 53.
Abscisic Acid Suppresses the Hypersensitive Necrosis of Potato Tubers and Reverses the Arachidonic Acid‐Induced Inhibition of Plasma Membrane‐Bound ATPase
Authors: ÉRsek T. , Ladyzhenskaya E. P. , Korableva N. P. , ÁDám A.
Published: May 2008

Abscisic acid (ABA) fully suppressed the development of the hypersensitive necrosis of potato tuber slices to crude elicitor from Phytophthora infestans and arachidonic acid (AA) if supplied before or up to 6 to 8 h after elicitor treatments. Later application of ABA only reduced the necrotic response. Added to highly purified plasma membrane preparation from tuber tissue, ABA eliminated the AA‐induced inhibition of the plasma membrane‐bound (K++ Na++ Mg2+) ATPase. It is suggested that ABA counteracts AA in the membrane.
Effect of DHT (2,4‐Dioxohexahydro‐1,3,5‐triazine) as Well as a Combination of DHT, Alkane Monosulfonate and N‐Phenyl‐N'‐p‐carboxyphenyl Thiourea on Tomato Mosaic Virus in Infected Glasshouse Tomato Plants
Authors: Christova D. , Schuster G.
Published: May 2008

In two consecutive trials, three treatments of tomato plants of the variety Rivermoon with the antiphytoviral substance DHT (2,4‐dioxohexahydro‐1,3,5‐triazine, 0.15%) 2 d a.i. and 2 and 7 d p.i. reduced the concentration of ToMV (tomato mosaic virus) by 62.3 and 60.5%. The average tomato yields increased by 40 and 26 % compared with the virus diseased, untreated controls, but the yields of the healthy controls were not achieved. A combined treatment of DHT, alkane monosulphonate and N‐phenyl‐N'‐p‐carboxyphenyl thiourea only resulted in a minor reduction in the ToMV titre and only a slight increase in yield, compared with the DHT‐solo treatment.
Evaluation of Tip Culture, Thermotherapy and Chemotherapy for Elimination of Peanut Mottle Virus from Arachis hypogaea
Authors: Chen W. Q. , Sherwood J. L.
Published: May 2008

Peanut (Arachis hypogaea L.) plants (cvs Florunner and Pronto) were inoculated at the two‐leaf stage with peanut mottle virus (PMV) to obtain PMV‐infected plants. Shoot‐tips from plants grown in the glasshouse (27°C) or from plants maintained at 35°C were used for tip culture. In some experiments ribavirin was added to the culture medium at 5 mg/1, 10 mg/1, 15 mg/1 or 20 mg/1. Plants regenerated from meristems or shoot‐tips taken from virus‐infected plants were not virus‐free. After 45 days at 35°C, foliar tissue of 93 % of Florunner and 95 % of Pronto plants tested negative for PMV by enzyme‐linked immunosorbent assay (ELISA). When shoot‐tips from the plant that tested negative by ELISA were used for tip culture, no virus‐free plants were obtained. No virus‐free plants were obtained from tips cultured on medium supplemnted with ribavirin. However, when tip culture, thermotherapy and chemotherapy were combined; 80 % of Florunner and 100 % of Pronto plants were found negative for PMV.
Detection of Artichoke Latent Virus by an Indirect Dot‐ELISA
Authors: Cugusi M. , Foddai A. , Idini G.
Published: May 2008

An indirect Dot‐ELISA was compared with DAS‐ELISA for detecting Artichoke Latent Virus (ALV) both in purified preparations and in crude sap from “Spinoso sardo” artichoke leaves.

Antigen diluted samples (1 μl) were first spotted on nitrocellulose (NC) and polyvinylidene difluoride (PVDF) membranes. After blocking, the membranes were incubated in rabbit anti‐ALV IgG, then in goat anti‐rabbit IgG—alkaline phosphatase conjugate, and finally exposed to substrate and examined for a coloured precipitate.

The minimum detection levels for ALV by Dot‐ELISA were 125 pg of purified virus and 1/2,000 dilution of virus‐infected sap on NC, and 83.3 pg of purified virus and 1/4,000 dilution of virus‐infected sap on PVDF, as compared with 50 ng of purified virus and 1/1,000 dilution of virus‐infected sap detectable by DAS‐ELISA.

This indirect Dot‐ELISA proved to be more sensitive and more economical than DAS‐ELISA, and can be completed in as little as 5—6 hours.
Effect of Placement and Sequence of Inoculation with Fusarium oxysporum on its Interaction with Meloidogyne arenaria on Subterranean Clover
Authors: Pung S. H. , Sivasithamparam K. , Barbetti M. J.
Published: May 2008

The effect of the placement of inoculum of Fusarium oxysporum at two soil depths, and the sequences of inoculations with Meloidogyne arenaria and Fusarium oxysporum on root growth and development of root disease in Trifolium subterraneum L. (subterranean clover) were investigated. The timing of infection and the proximity of root tips of the host root system to infection by M. arenaria and F. oxysporum appeared to be the major determining factors of root growth and of disease development in plants exposed to the pathogens. Immediate contact of roots with F. oxysporum (where the fungus was placed at seed level of 10 mm depth) appeared to result in more severe effects on roots in the presence of the nematode than later infection by the fungus placed at 30 mm depth. The production of galls by the nematode and early infection by F. oxysporum at 10 mm depth resulted in a severe inhibition of root growth, particularly of the lateral roots. But no such growth inhibition was evident when F. oxysporum and M. arenaria were introduced together at the lower depth of 30 mm. The lowest density of M. arenaria inoculum was sufficient to cause severe root rot if F. oxysporum was present at the host seed level. With the fungus at 30 mm depth, however, the expression of root rot appeared to be influenced by the inoculum level of the nematode. In sequential inoculation with F. oxysporum or M. arenaria, the organism added 2 weeks later had little or no effect on root development. The first organism (M. arenaria or F. oxysporum) to infect the germinated seedlings was the main cause of root growth inhibition. The organism that came into contact with the roots 2 weeks later had little or no effect on the roots. Concurrent infection by F. oxysporum and M. arenaria resulted in less M. arenaria gall production on the tap root system than those added with the nematode alone or in advance of the fungus.
Comparison of Fusarium oxysporum and Fusarium oxysporum var. redolens by Analyzing the Isozyme and Serological Patterns
Authors: Rataj‐Guranowska M. , Wolko B.
Published: May 2008

Extracts from Fusarium oxysporum (F.o.) and F. oxysporum var. redolens (F.o.r.) isolates were compared by means of electrophoresis and crossed immunoelectrophoresis. The polymorphism of five isozyme systems allowed a distinction between F.o. and F.o.r. isolates. The isozyme patterns of three other isozyme systems did not allow this distinction between F.o. and F.o.r. to be made. Both fungi appeared almost identical serologically. Relative amounts of their corresponding proteins differed but the qualitative patterns of the proteins were nearly the same with the anti‐F.o.r. serum, only one specific antigen was detected in the extracts from F.o.r., isolates. Although the results obtained indicate a strong similarity between F.o. and F.o.r., they are not sufficient for an unequivocal statement that the fungi belong to the same species.
An Association Between High Peroxidase Activity in Lettuce (Lactuca sativa) and Field Resistance to Downy Mildew (Bremia lactucae)
Authors: Reuveni R. , Shimoni M. , Crute I. R.
Published: May 2008

The association between variation for pre‐infection peroxidase activity and levels of field resistance‐susceptibility to downy mildew (Bremia lactucae) was investigated in lettuce (Lactuca sativa) cultivars, accessions of L. serriola (prickly lettuce), segregating F2 populations and selected F3 families from a cross between field resistant and susceptible lettuce cultivars. A trend was apparent in this series of experiments indicating that one component of field resistance could be related to a high level of peroxidase activity prior to infection. The data suggest that in breeding programmes there could be merit in imposing primary selection for high peroxidase activity prior to field selection for resistance.
Identification of an Antifungal Compound in Unripe Avocado Fruits and its Possible Involvement in the Quiescent Infections of Colletotrichum gloeosporioides1
Authors: Prusky D. , Kobiler I. , Fishman Y. , Sims J. J. , Midland S. L. , Keen N. T.
Published: May 2008

A new antifungal compound was isolated from peel and flesh of unripe avocado fruits and identified as 1‐acetoxy‐2,4‐dihydroxy‐n‐heptadeca‐16‐ene. The maximal concentration of the anti‐fungal monoene in unripe fruits was about 800 μg. g−1 fr.wt. During ripening the monoene decreased to 40 μg. g−1 fr.wt. concomitantly with the appearance of disease symptoms. The concentration of the previously described antifungal diene, 1‐acetoxy‐2‐hydroxy‐4‐oxo‐heneicosa‐12,15‐diene (Pruskyet al. 1982), in avocado peel was 1,600 μg. g−1 fr.wt. in unripe fruits, decreasing during ripening to 120 μg. g−1 fr.wt. At 750 μg. ml−1 the inhibition of germ tube elongation of germinated conidia by the antifungal monoene and the antifungal diene was 15 % and 44 %, respectively. A 1: 1 mixture of both antifungal compounds in concentrations ranging from 50 to 750 μg. ml−1, showed synergistic activity and increased the percent of inhibited germ tubes of germinated conidia up to 15 % over the sum of activities of the separate compounds.

The results are discussed in relation to the hypothesis that the antifungal diene and the antifungal monoene are involved in the quiescence of the germinated appressoria of Colletotrichum gloeosporioides in unripe avocado fruits.