bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Affecting Germination of Oospores of Phytophthora infestans
Authors: Chang T. T. , Ko W. H.
Published: May 2008

When oospores from the pairing between A1 and A2 mating types of Phytophthora infestans were treated with 0.25 % KMnO4 solution for 15 min and incubated at 19 °C under light on a modified S+L medium, germination commenced within 4 days and reached about 70 % after 20 days. Under these conditions, more than 25 % of oospores obtained from a 4‐day‐old culture germinated. To obtain a high germination rate of P. infestans oospores, light was essential during germination but not during growth and oospore formation. The optimum time for activation of oospores with 0.25 % KMnO4 was 15 to 30 min and a suitable concentration of KMnO4 for 15 min activation was 0.25 to 0.45 %.
Fluorescent Pseudomonads Associated with Diseases of Wheat in South Africa1
Authors: Smith J. , Hattingh M. J.
Published: May 2008

A survey of fluorescent pseudomonads associated with diseased wheat was conducted in South Africa during 1987 and 1988. Phenotypic features of 87 local strains were compared with those of 10 reference strains. Five groups were distinguished. Group 1 (nine reference and 16 local strains) was classified as Pseudomonas syringae pv. syringae. Group 2 (four local strains) was similar to group 1 but did not produce levan on nutrient sucrose agar. Group 3 (one reference and 33 local strains) also resembled P. s. pv. syringae, but did not elicit a hypersensitive reaction on tobacco. Group 4 (20 local strains) was mostly isolated from plants with atypical symptoms (total melanism) found in a single geographical region (Villiers) within South Africa. These strains had uniform characteristics, but failed to induce melanism on inoculated test plants. Group 5 (14 local strains) was not uniform. Twenty‐eight representative local strains, selected from each of the five groups, and the 10 reference strains were used in pathogenicity and virulence tests. The four most virulent local strains were used to screen 14 wheat cultivars grown commercially in South Africa. Five of the cultivars were susceptible to these strains. Symptoms on leaves of naturally‐infected plants corresponded with those already described, but the typical ear symptom (basal glume rot) was absent.
Further Investigation of the Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola
Authors: Lebeda A. , Boukema I. W.
Published: May 2008

Specificity of interactions between eight Lactuca species (L. saligna, L. virosa, L. altaica, L. dregeana, L. perennis, L. tenerrima, L. tatarica, L. viminea) and two related genera (Mycelis muralis, Chondrilla juncea) and seven Bremia lactucae isolates from Lactuca serriola was studied in 96 accessions. The 35 L. saligna accessions gave no evidence for race‐specificity and a non‐host resistance is expected. L. virosa (36 accessions) showed a highly various response. A substantial part of the studied sets expressed a race‐specific resistance. L. altaica (one accession), which is closely related to L. serriola, was susceptible to all isolates used. L. dregeana (2 accessions) showed also a race‐specific response. The accessions of L. perennis (7), L. tatarica (2) and L. viminea (1) were resistant. The susceptibility of L. tenerrima (3 accessions), which is related to L. perennis, is unexpected. In Mycelis muralis (8 accessions) very often a incomplete resistance was observed. Chondrilla juncea (1 accession) was resistant to all isolates used. It can be concluded that the genetic distances between species cannot be used as a prediction for resistance or susceptibility.
Aphid Vectors of Barley Yellow Dwarf Virus in West‐Central Morocco
Authors: El Yamani M. , Hill J. H.
Published: May 2008

The ability of seven aphid species, collected in west‐central Morocco, to transmit barley yellow dwarf virus (BYDV) was determined. Aphids were either collected from grasses showing symptoms of BYDV infection or were allowed acquisition access to plants infected with a PAV‐like isolate of BYDV before transfer to oat test plants. BYDV transmission by six of the seven aphid species was confirmed by ELISA test; only Melanaphis donacis failed to transmit. The six newly defined BYDV vector species brings the total known to occur in Morocco to ten.
Effect of Time of Inoculation with Xanthomonas campestris pv. mangiferaeindicae on Mango Fruits Susceptibility Epiphytic Survival of X. c. pv. mangiferaeindicae on Mango Fruits in Relation to Disease Development
Authors: Pruvost O. , Luisetti J.
Published: May 2008

Susceptibility of mango fruits to bacterial black spot disease was related to the stage of fruit development and to climatic factors (rainfall and temperature). The highest percentages of infected fruits occurred when inoculations were performed during the month just before harvest.

Wounds and lenticels are effective entry sites for the bacterium. The ability of lenticels to take up bacterial inoculum was estimated using safranin. The susceptibility of lenticels to entry of the pathogen was directly related to the fruit age.

X. c. pv. mangiferaeindicae can survive epiphytically on immature mango fruits. Bacterial populations around 105 c.f.u./fruit are commonly detected. Epiphytic X. c. pv. mangiferaeindicae were not detected on symptomless mature fruits. Those resident populations are an important source of inoculum for fruit infection. The number of bacterial spots occurring on the fruits is directly related to epiphytic populations.
Wind Dispersal of Alternaria alternata, a Cause of Leaf Blight of Cotton
Authors: Bashan Yoav , Levanony Hanna , Or Reuven
Published: May 2008

Introducing Alternaria alternata, the cause of blight disease of cotton plants, into a field of young healthy plants growing in rows cross‐wind, yielded disease foci which were spread downwind up to 7 m from the infection sources. Only light disease incidence was found in the remainder of the field. When the disease was introduced into a field of mature cotton plants grown in rows cross‐wind, randomly scattered disease foci occurred. In mature plantations where rows were parallel to the average wind direction, only limited size disease foci developed downwind, up to 16 m from the source. These foci did not developed further during the season. The number of air‐borne spores of A. alternata was significantly increased by the presence of diseased cotton plants, being highest close to the diseased plants. The spores were transferred to a distance of at least 20 m. However, the number of air‐borne spores significantly decreased 6 m from the infection source. Periodical trapping of air‐borne spores of A. alternata in a cotton growing region for 2 years, revealed that their air dispersal is local, probably at the field level. A. alternata in a cotton growing region for 2 years, revealed that their air dispersal is local, probably at the field level. A. alternata air‐borne spores were also trapped in rather low numbers regardless of the presence of infected cotton plants. However, the number of the air‐borne spores trapped was dependent mainly on the average wind direction and on the Alternaria blight epidemics occurring in the fields twice a year. It is suggested that A. alternata spores are transferred by wind for short distances but are constantly present in small numbers in the atmosphere throughout the whole year. The two peaks recorded for the number of spores present in the air above cotton crops correlate with the annual two outbreaks of Alternaria blight epidemics. In addition, both wind and plant row direction affect disease development in the fields.
DNA Sequence of Genes for Detoxification of Fusaric Acid, a Wilt‐inducing Agent Produced by Fusarium Species
Authors: Toyoda H. , Katsuragi K. , Tamai T. , Ouchi S.
Published: May 2008

Isolation and nucleotide sequence determination of fusaric acid‐detoxification genes are described in this paper. For screening the genes, bacteria collected from soil were positively selected in a selective medium containing fusaric acid. The capability of fusaric acid‐resistant isolates to detoxify the toxin was assayed by examining the survival of tomato callus cells in culture filtrates prepared from the bacterial culture, in the presence of fusaric acid. The isolate (HY‐1) showing the highest detoxification was selected and identified as Klebsiella oxytoca. Chromosomal DNA of this isolate was digested with Bam HI and shotgun‐cloned to fusaric acid‐sensitive E. coli. The DNA fragment carrying fusaric acid‐detoxification genes was further shortened by enzyme digestion and the open reading frames in the fragment were analyzed by determining total nucleotide sequences of the fragment. Finally, three open reading frames were shown to be essential for expressing the detoxification of fusaric acid. These frames possessed a single promoter sequence at the upstream region of the first open reading frame. Northern blot analysis showed that these genes were polycistronically transcribed to express the fusaric acid detoxification, strongly supporting th results of DNA sequence analysis.
Inorganic Pyrophosphatase from E. coli as a Label for the Detection of Plant Viruses by ELISA
Authors: Mizenina O. A. , Borisova O. V. , Novikov V. K. , Evtushenko O. A. , Baykov A. A. , Atabekov J. G.
Published: May 2008

Inorganic pyrophosphatase (PPase) from E. coli was used as label in enzyme immunoassay for the detection of different plant viruses. The use of PPase‐conjugated antibodies and tetrasodium pyrophosphate as a substrate in ELISA provides some advantages in detection of plant viruses in purified preparations and extracts from plant specimens: high sensitivity, negligible level of background reactions in control samples, bright blue‐greenish colour which allows to detect the reaction visually and high stability of PPase‐conjugated antibodies.
The Status of Cassava Bacterial Blight Caused by Xanthomonas campestris pv. manihotis in Trinidad
Authors: Joseph Jann , Elango Fritz
Published: May 2008

Disease surveys conducted in Trinidad between 1985—1987 showed that Cassava Bacterial Blight (CBB) is present in all but one county of the country with disease severity ratings varying from 1—5 depending on day/night temperatures. Field and greenhouse screening identified varieties such as Point Fortin fine leaf and CMC 40 as being resistant whereas M col 22 was moderately resistant to susceptible. Using a combination of antiserum produced to whole cells of Xanthomonas campestris pv. manibotis and a broth enrichment technique, dissemination of the pathogen by flood water was confirmed. The pathogen was detected at distances of up to 300 meters from infected fields. The significance of this mode of pathogen dissemination in initiating primary infection in Trinidad is discussed.
Further Observations on the Effects of Cymbidium Mosaic Virus and Odontoglossum Ringspot Virus on the Growth of Cymbidium Orchids
Authors: Pearson M. N. , Cole J. S.
Published: May 2008

Two cultivars of Cymbidium orchid were mechanically inoculated with Odontoglossum ringspot virus (ORSV) and Cymbidium mosaic virus (CyMV), individually and in combination, one year after transfer from in vitro culture to the glasshouse. Plant growth and disease symptoms were monitored over the following 4 years. Plants infected with CyMV showed severe mosaic symptoms with necrotic streaks and the virus was easily detectable by ELISA throughout the experiment. Plants infected with ORSV alone showed no obvious symptoms, and by the end of the experiment the virus could not be detected in the new growth using ELISA. Both viruses reduced plant growth, the effect of CyMV being more severe than that of ORSV.
Light‐ and Electron Microscopic Studies of Cherry Leaf Roll Virus (CLRV) on European Ash (Fraxinus excelsior L.)
Authors: Hamacher J. , Quadt A.
Published: May 2008

Deformed leaves of CLRV‐infected ash trees exhibited hyperplasia of mesophyll cells, multilayered palisade parenchyma, undulated lower epidermis, and meandering vascular bundles. The development of phloem and xylem cells was greatly inhibited. In tissues from chlorotic ringspots and line patterns, chloroplasts were highly inflated by starch grains and phloem necrosis could be observed. Plasmodesms in these tissues were dilated and revealed enhanced contrast. Fingerlike protrusions of polysaccharidic material enclosed the elongations of plasmodesms. Vesiculated paramural bodies were connected with altered plasmodesms. Virus‐like particles could neither be observed in altered plasmodesms nor elsewere in the cytoplasm. Chloroplasts in infected tissues frequently were deformed as a result of cytoplasmic invaginations. The outer chloroplast membrane protruded into the cytoplasm at several locations. Thylakoid membranes were partly dilated.
Differentiation of Potyviruses through Peptide Mapping of Cytoplasmic Inclusion Proteins
Authors: Albrechtsen M. , Paludan N. , Heide M.
Published: May 2008

Cytoplasmic inclusion proteins (CIP) from 15 isolates representing 12 different potyviruses were purified and compared by peptide mapping in sodium dodecylsulphate polyacrylamide gels. Enzymatic cleavage by endoproteinase Glu‐C from Staphylococcus aureus V8 was performed in the gel during electrophoresis. Distinct patterns were obtained for all different potyviruses, while different isolates of the same virus produced identical patterns. When performed under standardized conditions this method produced very reproducible peptide maps.

Chemical cleavage at tryptophan residues by N‐chlorosuccinimide produced very similar peptide patterns for CIP from all potyviruses studied with the exception of leek yellow stripe virus.

The results suggest that peptide mapping of CIP using endoproteinase Glu‐C can be used in the identification and differentiation of potyviruses.
“Ermioni” a new Lemon Cultivar Resistant to Mal secco Disease (Phoma tracheiphila)
Authors: Thanassoulopoulos C. C.
Published: May 2008

A lemon tree resistant to citrus tracheomycotic disease Mal secco (Phoma tracheiphila) found in a Greek orchard and its progenies were evaluated.

Scions budded on sour orange and Volkameriana rootstocks or cuttings rooted in mist were placed under natural infections or inoculated artificially with Mal secco inoculum. No disease symptoms appeared on the original tree, while in bud‐progenies only 16 out of approximately 2500 field grown trees were diseased by Mal secco. In 45 artificially inoculated trees only two were infected by the fungus.

Analysis of leaf proteins using electrophoresis and further genetic control of gene/enzyme 6‐Phosphogluconate dehydrogenase (6‐PGD) system were carried out for the resistant selection: the Greek varieties Maglini, Adamopoulou, Karystini and the Italian Monachello and Interdonato. Protein analysis showed a close relationship of the resistant selection with var. Maglini, of which a scion is the resistant selection, while the isozyme genetic marker showed three different electrophoretic patterns, the resistant selection being in a separate pattern.

Some phenotypical differences between the resistant selection and Maglini were also observed.

The phenotypical differences, the resistance to Mal secco, the differences in proteins from all other varieties except Maglini and the different electrophoretic pattern of 6‐PGD of this selections vs other varieties, suggest a new cultivar, for which the name “Ermioni” is proposed.
Ascochitine Production by Fungi Responsible for Ascochyta Diseases of Pea
Authors: Marcinkowska Joanna , Klos B. , Shcherbakova Anna
Published: May 2008

Ascochitine production by 24 isolates of three fungal species causing the Ascochyta disease complex in pea plants, was examined. All eight isolates of Ascochyta pisi Lib. secreted ascochitine to liquid nutrient medium in amounts of 0.1 to 1.2 mg/l. However, no ascochitine was found in culture filtrates of Mycosphaerella pinodes (Berk. and Blox.) Vestergr. or of Phoma medicaginis var. pinodella (Jon.) Boerema although the aggressiveness of these two species as pathogens was shown to be higher than that of A. pisi. Individual isolates of each of the three fungal species examined did not differ in their pathogenicity.
Histological, Physiological and Biochemical Interactions between Vesicular‐Arbuscular Mycorrhizae and Thielaviopsis basicola in Tobacco Plants
Authors: Giovannetti M. , Tosi L. , Torre G. Della , Zazzerini A.
Published: May 2008

Interactions between the mycorrhizal fungus Glomus monosporum and the root rot pathogen Thielaviopsis basicola and their effects on tobacco plants were investigated over a 4 week period.

Mycorrhizal tobacco plants, obtained by preinoculation with G. monosporum, showed a better tolerance to T. basicola than non‐mycorrhizal seedlings. Root and leaf dry weights of mycorrhizal plants were greater than those of controls. Mycorrhizal plants inoculated with T. basicola showed higher root and leaf dry weights than non‐mycorrhizal infected plants, but lower values than mycorrhizal plants which were not infected.

No appreciable differences in free aminoacid composition were observed among the different treatments with two exceptions: proline content was higher in infected and mycorrhizal infected plants compared to control and mycorrhizal plants; arginine content was higher in infected and mycorrhizal infected plants compared to control and mycorrhizal plants; arginine content was higher in mycorrhizal plants than in all the other treatments.

The mechanisms by which (VAM) fungi can reduce disease incidence and pathogen development are discussed.
Evaluation of Oospore Hyperparasites for the Control of Phytophthora Crown Rot of Pepper
Authors: Sutherland E. D. , Papavizas G. C.
Published: May 2008

Nine isolates of known oospore mycoparasites comprised of six actinomycetes (Actinoplanes missouriensis, A. philippinensis, A. utahensis, Amorphosporangium auranticolor, Ampullariella regularis, Spirillospora albida) and three fungi (Acremonium sp., Humicola fuscoatra, Verticillium chlamydosporium) were tested in the greenhouse for their ability to suppress or delay the onset of crown rot of pepper caused by Phytophthora capsici. Verticillium chlamydosporium applied as a root dip increased the number of healthy plants by more than 100% when peppers were transplanted into soil artificially infested with oospores of Phytophthora capsici, but not when peppers were transplanted into soil naturally infested with P. capsici. The other mycoparasites were ineffective in the greenhouse. All the mycoparasites tested parasitized oospores of P. capsici in vitro.
Carbohydrate, Amino acid, Phenolic and Mineral Nutrient Contents of Pepper Plants in Relation to Age‐Related Resistance to Phytophthora capsici
Authors: Jeun Yong Chull , Hwang Byung Kook
Published: May 2008

The relationship between age‐related resistance of peper plants to Phytophthora capsici and contents of carbohydrates, amino acids, phenolics and mineral nutrients in pepper stems was studied using two pepper cultivars, Hanbyul (susceptible) and Kingkun (resistant). With increasing age of pepper plants, the two cultivars, which differ in their susceptibility to Phytophthora blight, became gradually resistant to the disease. The cultivar Kingkun distinctly showed the age‐related resistance to Phytophthora blight at the second branch stage. The weight of dry matter in healthy stems of pepper plants at the second branch stage was twice that at the six leaf stage. The resistant cultivar Kingkun contained lower levels of fructose, glucose and sucrose in stems than the susceptible cultivar Hanbyul at the different developmental stages. No consistent differences between the developmental stages of the plants were recognized with regard to their glucose content. However, the contents of fructose and sucrose in the cultivar Hanbyul greatly increased at the second branch stage. The levels of inositol reduced in both pepper cultivars during plant development. In view of the fact that there were only slight changes in the amount of total amino acids, it seems unlikely that there is a relationship between the amino acid metabolism and the retardation of Phytophthora infection during plant development. The amounts of total phenolic compounds in pepper stems were relatively low at the later growth stages of the plants and also in the resistant cultivar Kingkun. The contents of macroelemental nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium were drastically reduced in pepper stems at the later plant growth stage. No significant differences between the cultivars or the plant growth stages were found in the silicon and microelemental nutrients such as sodium, iron, zinc and manganese. These results suggest that the expression of age‐related resistance of pepper plants may be due to the morphological and nutritional changes in tissues of pepper stems during ageing, i.e. the pronounced increase in weight of dry matter, the significant decrease in amounts of mineral nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium, and the tow contents of fructose, glucose and sucrose in the stem tissues.
Reduction of Bacterial Blight Infestation of Cotton Seeds by Treatment with Sodium Hypochlorite
Authors: Zachowski M. A. , Rudolph K.
Published: May 2008

The efficacy of sodium hypochlorite (NaOCl) for restraining cotton seed infestation by Xanthomonas campestris pv. malvacearum was studied. Seeds of three cotton cultivars were artificially inoculated by soaking in suspensions (ca. 5.10 8 CFU/ml) of different strains of Xcm. Twelve h after soaking (at 30°C) various dilutions of NaOCl were added to the soaking suspensions and incubated for another 12 h. The infestation rate of cotyledons and effect on germination were determined 14 and 21 days after treatment under the standardized conditions of a growth chamber (12 h 20,000 Lux at plant height, 30/20 °C day/night, ca. 100 % relative humidity). Cbncentrations below 0.15 % of active chlorine in the soaking‐water had no marked effect on reduction of the disease. Goncentrations between 0.45 % to 0.60 % appeared to be most effective without reducing germination rate. Seed germination was affected, however, by concentration of active chlorine above 0.6 %. Seed quality during sodium hypochlorite treatment obviously influenced the effectivity of this measure.
Simultaneous Detection of Several Nepoviruses Infecting Grapevine in a Single DAS‐ELISA Test Using Mixed Antisera
Authors: Etienne L. , Clauzel J. M. , Fuchs M.
Published: May 2008

Single and mixed antisera have been compared in DAS‐ELISA for the routine diagnosis of nepoviruses infecting grapevine. The use of mixed polyclonal antibodies allowed in a single test the simultaneous detection of several nepoviruses (ArMV + GFLV) or serotypes of nepoviruses (TBRV serotypes G + S and RRV serotypes E + G) whatever the nature of the antigens, e.g. purified virions, diseased grapevine leaves or grapevine wood shavings. The detection was as reliable and efficient as with simple antibodies. The plant samples which were positively diagnosed by mixed antisera often showed an increase of their absorbance values, in comparison with the detection using simple antisera, while the background level was unchanged. The origin of this enhancement remains unclear, but it seems to be closely related to the mixing of the conjugated antibodies.
Increased Levels of Cytokinins in Barley Leaves Having the Systemic Acquired Resistance to Bipolaris sorokiniana (Sacc.) Shoemaker
Authors: Sarhan A. R. T. , Király Z. , Sziráki I. , Smedegaard‐Petersen V.
Published: May 2008

The role of endogenously induced higher level of cytokinins and exogenously applied kinetin in relation to the development of barley leaf spot caused by Bipolaris sorokiniana (Sacc.) Shoemaker (syn. Helminthosporium sativum Pammel, King and Bakke) was studied. Spraying barley leaves with kinetin suppressed the number and the size of necrotic spots caused by the fungus. Inoculation of the lower leaves of barley by a spore suspension of the fungus B. sorokiniana induced resistance on the upper leaves against a subsequent challenge inoculation by the same pathogen 10 days later. An increase in the level of cytokinins was observed in these resistant leaves. Elevated levels of cytokinins may cause a type of juvenility in leaf tissues. The juvenile state could be in a causal relationship with the suppression of necrotic spots caused by the fungus.
Biochemical and Molecular Tools for the Differentiation of Aggressive and Non‐Aggressive Isolates of the Oilseed Rape Pathogen, Phoma lingam
Authors: Hassan A. K. , Schulz C. , Sacristan M. D. , Wöstemeyer J.
Published: May 2008

A number of aggressive and non‐aggressive isolates of the rape seed (Brassica napus) pathogen Phoma lingam (teleomorph: Leptosphaeria maculans) were analyzed by three different biochemical approaches: the quantitative measurement of extracellular enzymes, which are believed to be involved in plant attack, the electrophoretic analysis of fungal surface proteins, and the analysis of restriction fragment length polymorphisms (RFLPs) in Southern blot experiments. Aggressive strains show elevated activity levels for cellulase, α‐ and β‐glucanase as well as for polygalacturonase. Furthermore, aggressive and non‐aggressive isolates can clearly be characterized by their pattern of surface associated proteins and by RFLP analysis in Southern type experiments, using molecular probes for actin, ubiquitin, ribosomal RNA and the gene for elongation factor EFl (TEF). Seven out of nine aggressive isolates but only one out of eleven non‐aggressive strains contained plasmid‐like DNA.
Reduction in Grain Yield Attributable to Neckblast (Pyricuhria oryzae) Infection in Liberia
Authors: Awoderu V. A. , Bangura N. S.
Published: May 2008

The loss in grain yield due to neckblast (Pyricularia oryzae) in rice cultivars IR5 and C22 was determined by using fungicides to control the disease in two different experiments made in two consecutive seasons. Yield increases, obtained as a result of fungicide treatments compared with the control plots ranged from 9.5 % with cv. IR5 on Benlate treated plots to 117.4 % with cv. C22 in PP389 treated plots. The percentage neckblast‐reducing efficiency obtained for PP389 varied from 58.3 % with IR5 to 66.7 % with C22. The increases in yield over the control achieved by fungicide treatment depended largely on the neckblast‐reducing efficiency of the fungicide.

Eine Reduzierung des Kornertrages in Liberia, der einem Pyricularia oryzae‐Befall zuzuschreiben war

Auf einen Befall mit Pyricularia oryzae zurückzuführende Kornertragsverluste wurden bei zwei Reissorten IR5 und C22 mit Hilfe von Fungiziden, die die Krankheit in zwei verschiedenen Versuchen und in zwei aufeinanderfolgenden Saisons bekämpften, untersucht. Ertragssteigeningen gegenüber der Kontrolle, die durch den Fungizideinsatz entstanden, streuten zwischen 9,5 % bei der Sorte IR5 nach einer Benomylbehandlung bis zu 117,4 % bei der mit PP389 behandelten Sorte C22. Der P. oryzae‐Befall wurde durch die Anwendung von PP389 um 58,3 % bzw. 66,7 % bei der Sorte IR5 bzw. C22 reduziert. Verglichen mit der Kontrolle hingen die Ertragssteigerungen, die auf eine Fungizidanwendung zurückzufiihren waren, hauptsächlich von der Wirksamkeit der Fungizide gegen P. oryzae ab.
An Extended Progeny/Parent Ratio Model I. Application to Experimental Data
Authors: Blaise Ph. , Gessler C.
Published: May 2008

A new version of Vanderplank's epidemic model corrected for removals is presented. Incorporation of host growth and variable latent period allow a more realistic modelling of epidemic development while preserving the simplicity and biological meaningfulness of the original model. Host growth is driven through degree‐day accumulation. The length of the latent period varies with temperature according to a beta function. Calculations are made through numerical integration combined with boxcar trains. The model has been implemented in a program called “Epiphyt” which runs on personal computers. Typical output produced by the program is shown.

Ein erweitertes Nachkommen‐/Eltern‐Modell: Theoretischer Teil

Eine neue Version von Vanderplanks verbessertem Modell der Entwicklung einer Epidemie wird vorgestellt. Der Einbezug von Wirtswachstum und einer variablen Latenzperiode erlauben eine realistischere Modellierung des Verlaufs einer Epidemie, wobei die Einfachheit und die biologische Relevanz des ursprünglichen Modells erhalten wird. Das Wirtswachstum wird durch Akkumulation von Tagesgraden gesteuert. Die Relation zwischen Länge der Latenzperiode und Temperatur wird mit einer Beta‐Funktion simuliert. Das Modell wird durch Kombination von numerischer Integration und boxcar train gerechnet. Dieses Modell wurde in dem Programm “Epiphyt’ auf Personal Computer implementiert. Typische durch das Programm produzierte Resultate werden präsentiert.
Induction of Inaccessibility to Pyricuhria oryzae by Pre‐inoculation of P. grisea, in Rice Leaf‐Sheath Cells
Authors: Arase S. , Fujita K.
Published: May 2008

When spores of Pyricularia oryzae were inoculated onto the inner surface of detached rice leafsheaths after a pre‐inoculation of the non‐pathogenic P. grisea, penetration and intracellular hyphal growth of P. oryzae were significantly inhibited. Most epidermal cells under the appressoria degenerated. Spores of P. grisea germinated and formed appressoria 12–24 h after inoculation on the inner surface of rice leaf‐sheaths. However, few infection hyphae were formed from the appressoria. The results suggest that P. grisea induces inaccessibility against a subsequent infection by P. oryzae in rice leaf‐sheath cells.

Die Auslösung einer Unzugänglichkeit für Pyricularia oryzae in Reisblattscheidezellen durch eine Präinokulation mit P. grisea

Nach einer Präinokulation der inneren Seite getrennter Reisblattscheiden mit dem nicht pathogenen Pilz Pyricularia grisea und anschließender Inokulation mit P. oryzae‐Konidien, wurde das Eindringen und intrazellulare Hyphenwachstum von P. oryzae deutlich unterdrückt. Die epidermalen Zellen, die sich unter den Appressorien befanden, waren zum größten Teil degeneriert. Auf der inneren Seite von Reisblattscheiden keimten die Konidien von P. grisea aus und bildeten Appressorien 12–24 h nach der Inokulation. Jedoch wurden nur wenige Infektionshyphen aus den Appressorien gebildet. Die Ergebnisse deuten daraufhin, daßP. grisea eine Unzugänglichkeit für P. oryzae in Reisblattscheidezellen auslöst.
Isometric Plant Viruses in Ditches and Streams in Agricultural Areas: Recovery of Previously Found Viruses and Identification of hitherto Unrecorded Carmoand Tombusviruses Including Grapevine Algerian Latent Virus
Authors: Yi Li , Lesemann D.‐E. , Koenig R. , Rüdel M. , Pfeilstetter E.
Published: May 2008

During a survey of plant viruses in ditches and streams in agricultural areas we obtained sixteen isolates of isometric viruses. Seven of them were identified as carnation ringspot dianthovirus and four as tobacco necrosis necrovirus which both had already been detected in water samples in previous occasions. Three of the remaining isolates proved to be tombusviruses and two to be carmoviruses. One of the tombusviruses was found to be closely related to grapevine Algerian latent virus. For the other tombusvirus (two isolates) and the two carmoviruses the natural hosts are unknown and serological relationships with other viruses of the same group were not found. The assignment to the respective groups was based on particle morphology, coat protein molecular weight, cDNA hybridization tests and cytopathological effects.

Isometrische Pflanzenviren in Gräben und Bächen in landwirtschaftlich genutzten Gebieten: Erneuter Nachweis bereits früher gefundener Viren und Identifizierung bisher nicht nachgewiesener Carmo‐ und Tombusviren einschließlich grapevine Algerian latent virus

Bei Untersuchungen über das Vorkommen von pflanzenpathogenen Viren in Gräben und Bächen in landwirtschaftlich genutzten Gebieten erhielten wird sechzehn Isolate von isometrischen Viren. Sieben davon erwiesen sich als carnation ringspot virus, vier als tobacco necrosis virus; beide Viren waren auch früher schon in Oberflächengewässern nachgewiesen worden. Drei der übrigen Isolate konnten als Tombus‐ und zwei weitere als Carmoviren identifiziert werden. Das eine Tombusvirus zeigte eine enge serologische Verwandtschaft mit dem grapevine Algerian latent virus. Für das andere Tombusvirus (zwei Isolate) und die beiden Carmoviren sind natürliche Wirte nicht bekannt. Serologisch zeigten sie keine Verwandtschaft zu den bekannten Vertretern der entsprechenden Gruppen. Die Gruppenzuordnung erfolgte auf Grund der Partikelmorphologie, des Molekulargewichtes des Hüllproteins, der Ergebnisse von cDNA‐Hybridisicrungstesten und der zytopathologischen Effekte.
Influence of Heterodera schachtii on Verticllium Wilt Symptoms in Oilseed Rape
Authors: Gröntoft M. , Jonasson T.
Published: May 2008

The effects of a Verticillmm dahliae, a Heterodera schachtii, and a combined V. dahliae+H. schachtii infestation in summer rape (cv. Topas) were studied in a glasshouse experiment. The seed yield reduction caused by V. dahliae and H. schachtii was 29 and 23 per cent respectively. A combined, simultaneous infestation (V. dahliae+H. schachtii) resulted in a 53 per cent reduction, indicating a purely additive effect of yield losses due to the two parasites. Wilt symptoms, i.e. premature leaf fall and stem necrosis, were equally expressed in the V. dahliae and V. dahliae+H. schachtii treatments. Plant height was significantly reduced in treatments which included nematodes. Stem diameter of the plants was significantly reduced in all treatments which included pathogens. The number of newly formed females on the plant roots was reduced by 30 per cent when V. dahliae was present. No synergistic effects between the fungus and the nematode in the expression of wilt symptoms could be detected, and we conclude from the experiment that the addition of nematodes will not improve the screening for Verticillium resistant plant types.

Einfluß von Heterodera schacbtii auf die Verticillium‐Wdkesymptomc beim Raps

Untersucht wurden die Einflüsse eines Verticillium dahliae‐, eines Heterodera schachtii‐ und eines kombinierten V. dahliae+H Schachtii‐Befalls an Sommerraps (Sorte Topas) in einem Gewächshausversuch. Die Körnerertragsreduktion, verursacht durch V. dahliae und H. schachtii, betrug 29 bzw. 23 %. Ein kombinierter und gleichzeitiger Befall (V. dahliae+H. schachtii) verursachte eine 53 %ige Reduktion, die auf einen reinen additiven Effekt der Ertragsverluste, verursacht durch die zwei Parasiten, hindeutet. Welkesymptome, d. h. frühzeitiges Abfallen der Blätter und Stengelnekrosis, waren in den Behandlungen V. dahliae und V. dahliae+H. schachtii gleich stark ausgedrückt. Die Pflanzenhöhe war in den Nematoden enthaltenden Behandlungen signifikant reduziert. Der Stengeidurchmesser wurde in alien Behandlungen mit Pathogenen signifikant reduziert. Die Anzahl an neu gebildeten, weiblichen H. schachtii wurde bei Vorhandensein von V. dahliae um 30 % reduziert. Signifikante Einflüsse zwischen dem Pilz und den Nematoden bei der Äußerung der Welkesymptome konnten nicht festgestellt werden. Zusammenfassend kann gesagt werden, daß die Ergebnisse dieser Versuche darauf hindeuten, daß eine Beimischung von Nematoden das Screening für Verticillium‐resistente Pflanzen nicht verbessert.
Inhibition of Hypersensitive Response by Allopurinol Applied to the Host in the Incompatible Relationship between Phaseolus vulgaris and Uromyces phaseoli
Authors: Montalbini P.
Published: May 2008

The effect of allopurinol [4‐hydroxypyrazolo (3,4‐d) pyrimidine], an analogue of purine and a tightly binding inhibitor of xanthine oxidizing enzyme, when applied to bean plants by root absorption from a 400 μM solution, was evaluated as a potential compound to interfere with the expression of the hypersensitive reaction in the incompatible host‐pathogen relationship between Phaseolus vulgaris and Uromyces phaseoli. Allopurinol proved to be efficient in preventing the formation of hypersensitivity‐induced macroscopic necrotic local lesions and the associated electrolyte leakage, which is a measure of permeability changes. In contrast, allopurinol treatment did not affect peroxidase activity enhancement. These results support the hypothesis that early activation of the superoxide‐producing xanthine oxidase in bean leaves, induced by the incompatible interaction between Phaseolus vulgaris and Uromyces phaseoli, may lead to superoxide anion generation. This in turn is primarily responsible for those alterations which lead to the increase in permeability of the host membrane and is associated to hypersensitive cell death.

Hemmung der hypersensitiven Reaktion durch Allopurinol nach einer Behandlung des Wirtes in der inkompatiblen Wechselwirkung zwischen Phaseolus vulgaris und Uromyces phaseoli

Beurteilt wurde der Einfluß von Allopurinol [4‐Hydroxypyrazolo (3,4‐d) pyrimidin], einem Purinanalogon und fest bindendem Hemmstoff des Xanthinoxidase‐Enzyms, als eine potentielle Verbindung, die den Ausdruck einer hypersensitiven Reaktion in der inkompatiblen Wechselwirkung zwischen Phaseolus vulgaris und Uromyces phaseoli stört. Die Behandlung der Bohnenpflanzen erfolgte durch Tauchen in eine 400 μM Lösung der Verbindung. Allopurinol hemmte die Bildung von hypersensitiv‐induzierten, makroskopisch nekrotischen Lokalläsionen und den assoziierten Elektro‐lytenverlust, ein Maßstab für Änderungen der Durchlässigkeít sehr gut. Im Gegensatz dazu beein‐flußte eine Allopurinol‐Behandlung eine Steigerung der Peroxidase‐Aktivität nicht. Diese Ergebnisse unterstiitzen die Hypothese, daß eine frühe Aktiviemng der Superoxid produzierenden Xanthinoxi‐dase in Bohnenblättem, die durch die inkompatible Wechselwirkung zwischen Phaseolus vulgaris und Uromyces phaseoli induziert wird, zu einer Superoxid‐Anion‐Bildung führen könnte. Dies wiederum ist hauptsächlich für die Veränderungen verantwortlich, die zu einer Erhöhung der Durchlässigkeit der Wirtsmembran führt und mit dem hypersensitiven Absterben der Zellen assoziiert ist.
Susceptibility to Bacterial Canker in Sour Cherry Varieties. Orchard Observations and Inoculation Trials
Authors: Bech Karen
Published: May 2008

Field susceptibility to bacterial canker was monitored in sour cherry varieties. The varieties ‘Fanal’ (synonyms ‘Heimanns Konservenweichsel’, Heimanns 23)‘Nefris’ and ‘Rexelle’ were evaluated as highly susceptible following natural infection. ‘Stevnsbär’, which is the main variety in Denmark, ‘Schattenmorelle’ and ‘Kelleriis 16’ (synonym:‘Morellenfeuer’) were not attacked.

Monthly inoculations in the field revealed that cankers arose on branches from inoculations in September to March, the largest cankers resulted from inoculations in November and December, when the trees were dormant. Leaf scar infection declined with increasing time between removal of the leaf petiole and inoculation.

As an alternative to field evaluation susceptibility in detached branches and seedlings to an inoculation was assessed. However, field performance over many years appears to be the only true assessment of disease resistance.

Anfälligkeit von Sauerkirschensorten für Bakterienbrand (Pseudomonas syringae pv morsprunorum) Beobachtungen in Obstgärten und in Infektionsversuchen

Die Anfälligkeit von 32 Sauerkirschensorten für Bakterienbrand wurde unter Obstgärtenver‐hältnissen untersucht. Eine hohe Anfälhgkeit wurde bei den Sorten ‘Fanal’ (Syn.‘Heimanns Konser‐venweichsel’),‘Nefris’ und ‘Rexelle’ nach einer natürlichen Infektion beobachtet. Die wichtigste Sorte in Dänemark ‘Stevnsbar’ sowie die Sorten ‘Schattenmorelle’ und ‘Kelleriis 16’ (Syn.‘Morellenfeuer’) wurden nicht befallen.

Monatliche künstliche Feldinokulationen von Zweigen zeigten, daß Rindenbefall nach Inokulationen in der Periode von September bis März entstehen kann. Der starkste Rindenbefall wurde nach Inokulationen im November und Dezember beobachtet, einer Zeit, wenn die Bäume ruhen. Die Blattnarbeninfektionen nahmen mit steigendem zeitlichem Abstand zwischen dem Entfemen des Blattstiels und dem Ausbringen des Inokulums ab.

Als Alternative zu einer Feldbeurteilung wurde die Anfälligkeit an abgeschnittenen Zweigen und Sämlingen geprüft. Es hat sich jedoch gezeigt, daß Feldbeobachtungen über mehrere Jahre die beste Auskunft über die Anfälligkeit der verschiedenen Sorten geben.
Temperature and Ageing of Host Tissue Affect the Interactions between Different Oilseed Rape Cultivars and Pathotype Groups of Leptosphaeria maculans
Authors: Badawy H. M. A. , Kakau J. , Hoppe H.‐H.
Published: May 2008

The population of Leptosphaeria maculans is composed of different pathotype groups (PG). Among these are non‐aggressive (PG NA) and aggressive ones (PG A). The latter can be divided into at least 5 subgroups (PG AO to PG A4). On cotyledons of all rape cultivars tested (Quinta, Lirasol, Jet Neuf) NA isolates caused small necrotic lesions, when the plants were grown at 18°C. At 27°C these lesions were enlarged but remained necrotic and incompatible. On the contrary, the necrotic defense reaction of Quinta cotyledons to A2 isolates was only detectable at 18°C. This interaction reacted completely compatible at 27°C. Generally, canker symptoms were promoted by higher temperatures. However, the low aggressiveness of NA isolates, the resistance of Jet Neuf and the differential resistance of Quinta to A2 isolates remained visible on hypocotyls at 27°C. When the interactions of Quinta and Jet Neuf with NA, A1 and A2 isolates were studied on detached leaves or excised leaf petiole and hypocotyl segments all resistance reactions were broken or at least strongly weakened. On ageing host tissue even non‐aggressive isolates caused severe symptoms with heavy sporulation.

Temperatur und Alterung des Wirtsgewebes beeinflussen die Interaktionen zwischen verschiedenen Rapssorten und Pathotypgnippen von Leptosphaeria maculans

Die Population von Leptosphaeria maculans besteht aus verschiedenen Pathotypgruppen (PG). Unter ihnen befinden sich nichtaggressive (PG NA) und aggressive Gruppen (PG A). Die letzteren konnen in wenigstens 5 Untergruppen unterteilt werden (PG AO bis PG A4). An Kotyledonen aller getesteten Rapssorten (Quinta, Lirasol, Jet Neuf) verursachten NA‐Isolate kleine, nekrotische Läsionen, wenn die Pflanzen bei 18°C angezogen wurden. Bei 27°C waren diese Läsionen vergrö‐ßert, sie blieben aber nekrotisch und inkompatibel. Im Gegensatz dazu war die nekrotische Abwehr‐reaktion von Quintakotyledonen gegenüber A2‐Isolaten nur bei 18°C erkennbar. Diese Interaktion reagierte bei 27°C völlig kompatibel. Wurzelhalssymptome wurden generell durch höhere Temperaturen gefördert. Dabei blieben aber die geringe Aggressivität der NA‐Isolate, die Resistenz der Jet Neuf und die differenzierende Resistenz der Sorte Quinta gegen A2‐Isolate auch bei 27°C an Hypokotylen sichtbar. Wurden die Interaktionen der Sorten Quinta und Jet Neuf mit NA‐, A1‐ und A2‐Isolaten an abgetrennten Blättern oder Blattstiel‐ und Hypokotylsegmenten getestet, so wurden alle Resistenzreaktionen durchbrochen oder zumindest stark abgeschwächt. Auf alterndem Wirtsgewebe verursachten selbst nichtaggressive Isolate schwere Symptome mit starker Sporulation.
Plant Virus Diseases of Importance to African Agriculture*
Authors: Thottappilly G.
Published: May 2008

In subsistence agriculture of the tropics, yields of crops are often low due to pests and diseases. Among other pathogens, several viruses have been associated with the poor yields. This paper reviews present knowledge on viruses of importance to African agriculture. A number of viruses identified in crops in Africa are listed, and few important ones are discussed in detail.

Virus diseases constitute a major threat to the large‐scale production of crops in several African countries. The geographical distribution of several viruses is not yet accurately determined, and many virus diseases are yet to be accurately identified. Control of virus diseases has been largely concentrated on the identification and development of resistant materials to suit the subsistence farming systems that prevail in the continent.

Wichtige Viruskrankheiten bei Pflanzen in der afrikanischen Landwirtschaft

In der Subsistenzlandwirtschaft der Tropen werden die Erträge der Kulturpflanzen häufig durch Krankheiten und Schädlinge niedrig gehalten. Zusammen mit anderen Pathogenen wurden einige Virusarten mit den niedrigen Erträgen assozüert. In dieser Arbeit wird ein Überblick über das heutige Wissen der in der afrikanischen Landwirtschaft wichtigen Viren gegeben. Einige aus Kulturen in Afrika isolierte Viren werden aufgelistet, ein paar davon werden ausführlich behandelt.

In mehreren afrikanischen Ländern stellen die Viruskrankheiten eine große Bedrohung für die Massenproduktion von Kulturpflanzen dar. Die geographische Verteilung von verschiedenen Viren ist bis Jetzt nicht genau bestimmt, und viele Viruskrankheiten müssen noch identifiziert werden. Die Kontrolle von Viruserkrankungen hat sich hauptsachlich auf die Identifiziening und Entwickiung von resistenten Materialien konzentriert, die zu den Systemen der Subsistenzlandwirtschaft, vorherrschend in diesem Kontinent, passen.
An In Vivo Screening Method for Antifungal Activity Against the Plant Pathogen Pythium ultimum Trow
Authors: Rosendahl C. N. , Olson L. W.
Published: May 2008

A new assay which can be used for in vivo screening of fungicides and microbiologically produced metabolites against Pythium ultimum is described. The assay uses cress (Lepidium sativum L.) as a test plant, and can be performed quickly and does not require more space than many in vitro tests.

Eine in vivo‐Screeningmethode für fungizide Aktivität gegenüber dem Pflanzenpathogen Pythium ultimum Trow

Beschrieben wird ein neuer Assay, der Anwendung beim in vivo‐Screening von Fungiziden und Metaboliten aus Mikroorganismen findet, um Aktivität gegen Pythium ultimum festzustellen. Die Kresse (Lepidium sativum L.) wird als Testpflanze im Assay verwendet. Der Assay ist schnell in der Durchführung und nimmt nicht mehr Platz in Anspruch als viele in vitro‐Tests.