bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability of Xanthomonas Campestris pv. vasculorum From Sugarcane and Other Gramineae in Reunion Island. Characterization of a Different Xanthomonad
Authors: Péros J. P. , Girard J. C. , Lombard H. , Janse J. D. , Berthier Y.
Published: May 2008

Stains presumed to be of Xanthomonas campestris pv. vasculorum (Cobb.) Dye, obtained from sugarcane and other gramineae in Réunion Island, were compared in terms of cultural aspects, pathogenic and physiological reactions, fatty acid profiles and restriction fragment length polymorphism (RFLP) of genomic DNA. The strains could be divided into two separate groups (G1 and G2). The G1 strains were identical to strains described as X. campestris pv. vasculorum; they showedan important variability in their cultural characteristics and in their aggressiveness. The G2 strains did not induce the usual symptoms of gumming disease on sugarcane cultivars infected under natural conditions or inoculated in the greenhouse. The G2 strains grew faster on agar medium, their colonies were more pigmented and less fluidal and had a different morphology on agar slant. Unlike the G1 strains, G2 strains hydrolyzed starch weakly and casein strongly; they utilized L‐fucose and, to a lesser extent, melibioze. The fatty acid and genomic DNA profiles differed between the groups. Differences seemed large enough to support separation of G1 and G2 strains into distinct taxonomic entities, namely G1 as Xanthomonas campestris pv. vasculorum and G2 as a different pathovar of X. campestris. The taxonomic position of G2 strains is discussed.
Angular Leaf Spot of Iron Wood Incited by a Pathovar of Pseudomonas syringae
Authors: Rahimian H.
Published: May 2008

A fluorescent pseudomonad inciting brown angular leaf spots on iron wood (Parotia persica) in Mazandaran forest was isolated and identified as a pathovar of Pseudomonas syringae. Strains assimilated adonitol and L‐tartrate but not lactate or D‐tartrate as carbon sources for growth. The electrophoretic profiles of cell proteins of strains isolated from iron wood were very similar but differred markedly from protein profile of P. syringae pv. syringae.
New Races of Sunflower Downy Mildew (Plasmopara Halstedii) in Germany
Authors: Spring O. , Miltner F. , Gulya T. J.
Published: May 2008

Plasmopara halstedii, the causal agent of downy mildew of cultivated sunflower (Helianthus annuus), was documented in Germany for the first time in commercial fields. The pathogen was first observed in the Württemberg area, where races 1 and 4 were identified using a set of differential lines. Later, commericial fields near Baden were found to be infected by race 5, which is the first occurrence of that race outside of North America. Withthe discovery of race 5, there are now eight races of the sunflower downy mildew fungus that have been found in Europe. The sunflower cultivars most frequently grown in Germany were investigated for resistance to race 1, 4 and 5; while all were resistant to race 1, none were resistant to either race, 4 or 5.
Occurence of grapevine chrome mosaic nepovirus in Austria
Authors: Dimou D. , D'Onghia A.M. , Laimer da amara Machado M. , Savino V.
Published: May 2008

A virus recovered by inoculation of sap from Austrian vines with yellow mosaic symptoms was compared with, and found virtually indistinguishable from, an authentic Hungarian isolate of grapevine chrome mosaic nepovirus. This seems to be the first record of the virus in Austria.
Induction of Resistance or Susceptibility in Pea to Races of Pseudomonas syringae pv. pisi
Authors: Akpa A. D. , Archer S. A.
Published: May 2008

The phenomena of induced resistance and induced susceptibility were investigated in the pea‐Pseudomonas syringae pv. pisi system, using two pea cultivgars, Early Onward and Hurst Green Shaft, and races 1 and 2 of the pathogen. Preliminary treatment with heat‐killed bacteria induced resistance in peas to infection by P. s. pv. pisi; the resistance induced was dependent on the time interval between the preliminary and challenge inoculations. The mechanism of induced resistance appears to vary between the cultivars. Similarly, both races of the pathogen appear to have different resistance‐inducing efficiencies. Resistance in cvs Early Onward and Hurst Green Shaft to the compatible bacterium could not be induced by preliminary inoculation with live cells of an incompatible race. Heat‐killed cells of the races failed to induce the hypersensitive reaction in cultivars that normally show this response when challenged with live avirulent bacteria. Preliminary inoculation with live race 1 cells failed to induce susceptibility in cv. Early Onward to live race 2 cells, irrespective of the challenge inoculation interval. On cv. Hurst Green Shaft, however, preliminary inoculation with live race 2 cells induced limited susceptibility to live race 1 cells. Preliminary treatment with sterile distilled water followed by challenge of the same leaves 24 h later with a compatible race induced a moderate resistance response in both cultivars.
Patterns of protein synthesis in infected and stressed sugar beet (Beta vulgaris L.)
Authors: Coutts R. H. A. , Linton D. J. , Bolwell G. P.
Published: May 2008

Patterns of protein synthesis have been investigated in infected and stressed sugar beet roots and suspension cultured cells by two‐dimensional, iso‐electric focussing/sodium dodecyl sulphate polyacrylamide gel electrophoresis. Comparisons have been made between the protein complement of dormant field‐grown sugar beet roots and rhizomania‐infected roots originating from a UK outbreak, hydroponically grown, uninfected control and Polymyxa betae‐infected sugar beet seedlings and control, biotic and abiotic elicitor‐treated sugar beet suspension cultured cells. Rhizomania‐infected roots and elicitor‐treated cells, but not roots, infected with P. betae alone showed large differences in the total protein complement. This result is consistent with the ability of P. betae to infect roots without inducing increased transcription of infection stress‐related genes and is clearly different from a large number of other biotrophic plant/fungus interaction in which a sub‐set of defence proteins are induced even in susceptible interactions in an atempted limitation of damage. Suppression of defence responses might be the mechanism by which P. betae is able to succesfully colonise sugar beet. Beet plants with symptoms of rhizomania did not express polypeptides with mobilities characteristic of stress‐related products. However, polypeptides of mobilities characteristic of sub‐sets found within young roots were observed which is compatible with the typical symptoms of the disease.
Two Circular Single‐stranded DNAs Associated with Banana Bunchy Top Virus
Authors: Wu R. Y.
Published: May 2008

Nucleic acids extracted from partially purified banana bunchy top virus (BBTV) consisted of 20 Kb DNA, 0.9‐1.1 Kb DNA and 0.3 Kb RNA. Partially purified BBTV preparations predigested with DNase and RNase before particle disruption and nucleic acid isolation yielded only the 0.9‐1.1 Kb DNA, but no corresponding nucleic acid band was obtained in total nucleic acid isolated from healthy banana tissue. Analysis of two BBTV cDNA clones showed that clone 1 consisted of 287 nucleotides and clone 2 contained a 1.0 Kb DNA insert. Clone 1 is not part of clone 2. When two pairs of primers, each pair in opposite orientation were used to amplify BBTV DNA by PCR using the total DNA from diseased banana tissues or DNA encapsidated in BBTV particle as the template, a DNA product of 1.1 Kb was generated by both, results indicating that the BBTV DNAs are circular. Additional results suggested that BBTV contained at least two circular ssDNAs designated BBTV essDNA I (containing clone 1 nucleotide sequence) and BBTV, cssDNA II (containing clone 2 nucleotide sequence).
Production of Intraspecific Hybrids of Fusarium oxysporum f. sp. radicis‐lycoperisici and Fusarium oxysporum f. sp. lycopersici by Protoplast Fusions
Authors: Madhosingh C.
Published: May 2008

The fusion of protoplasts from the cycloheximide‐resistant mutant FOL(C) of Fusarium oxysporum f. sp. lycopersici (FOL) and the mycostatin‐resistant mutant FORL(M) of F. oxysporum f. sp. radicis‐lycopersici (FORL), produced hybrids which expressed significant differences from the parents in their pathogenicity and growth and in the electrophoretic separation patterns of their proteins, enzymes and isoenzymes. The results suggest a transformed genetic basis for these altered expressions and the feasibility of using protoplast fusion technology for examining the biology of pathogenicity genes and for elucidating the disease and virulence potential for new races from within hybridisable taxa of Fusarium spp. Such information would be useful for the design and development of long‐term control systems for Fusarium diseases, particularly in breeding programs for disease resistance in crops.
Occurrence of Anomalous Mycoplasma‐like Organisms in Grapevine Yellows‐diseased Phloem
Authors: Credi R.
Published: May 2008

Pathological changes in Vitis vinifera cv. Caveccia phloem from leaves showing symptoms of a flavescence doreé‐like disease consisted of obliteration, necrosis and collapse of the sieve elements and associated companion cells, and excessive callose accumulation in lateral sieve areas and sieve plates of apparently normal mature sieve elements. Unusual structures, also found in degenerate sieve elements of diseased leaf vein specimens, were strongly electron‐dense and bounded by a unit membrane or an electron‐transparent border, and considered to be senescent forms of mycoplasma‐like organisms. The significance of these findings in relation to possible host responses to the yellows pathogen is discussed.
Detection of the 3a Protein of Cucumber Mosaic Virus in a Cell Wall Fraction from Infected Nicotiana clevelandii Plants
Authors: Burman A. J. , Osman T. A. M. , Buck K. W.
Published: May 2008

The 3a protein of cucumber mosaic virus was expressed in Escherichia coli and, after purification, used to produce an antiserum. The 3a protein was detected in a cell wall fraction obtained from infected Nicotiana clevelandii leaf tissue by immunoblotting using the 3a antiserum. The 3a protein reached a maximum level 4 days after inoculation and remained at this level for a further 8 days before slowly declining. In contrast, the virus capsid protein, detected in an 80 000 g pellet byimmunoblotting using a virus particle antiserum, reached a maximum 5 days after inoculation and remained at this level for at least a further 16 days.
Effects of Leaf Wetness Duration and Inoculum Level on Resistance of Wheat Genotypes to Pyrenophora tritici‐repentis
Authors: Sah D. N.
Published: May 2008

Percent leaf necrosis and lesion length on wheat genotypes increased markedly with increasing duration of leaf wetness (up to 24h or 48 h) following inoculation with Pyrenophora tritici‐repentis. A long wetting duration favoured less disease development on resistant (Fink's'), and moderately resistant (Bon/YR/3/F3570/KAL/BB) genotypes than on susceptible Glenlea. No significant difference in percent necrosis was detected among the upper three leaf positions within a genotype. A long wetnessduration had a varying effect on the resistance of wheat genotypes, depending upon the inoculum level. Increasing the inoculum level along with the leaf wetness period increased the per cent leaf necrosis on all three wheat genotypes tested. However, the, ranking of the genotype for resistance did not alter even after prolonged duration of leaf wetness (up to 96 h) and/or high inoculum level (12000 conidia/ml water). Various post‐inoculation wet‐periods in combination with high conidia concentrations in inoculum should be used in identifying highly resistant germplasm in breeding populations at the seedling stage of the wheats.
Use of Polyclonal Antibodies to Identify Mycoplasma‐like organisms (MLOs) From the Sudan and from Thailand
Authors: Saeed E. , Sarindu N. , Davies D. L. , Clark M. F. , Roux J. , Cousin M. T.
Published: May 2008

Rabbit polyclonal antibodies prepared against faba bean phyllody MLO from the Sudan reacted with its homologous antigen and with extracts of Catharanthus roseus experimentally infected with the same or a related MLO from Crotalaria saltiana showing symptoms of phyllody disease, as well as with extracts of naturally MLO‐infected C. saltiana growing in the field in the Sudan. The antibodies also reacted positively with extracts of C. roseus experimentally infected with Crotalaria juncea phyllody MLO and soybean phyllody MLO from Thailand.

Polyclonal antibodies prepared against an MLO associated with witches' broom disease in C. juncea reacted positively in ELISA tests with homologous antigen extracts from naturally infected C. juncea as well as with extracts from experimentally infected C. roseus and with extracts prepared from Sesamum indicum plants with phyllody symptoms growing in Thailand. There was no reaction between these antibodies and extracts from C. roseus plants infected with the MLOs associated with C. juncea phyllody or with soybean phyllody.

No cross reactions were observed among the antigens and antibodies of the two MLO groups by immunoflorescence, ELISA or western blotting. However, the molecular weight of the principal protein antigen, determined by SDS‐polyacrylamide gel electrophoresis (SDS‐PAGE) and western blotting was the same for both types of MLO.

Serologically‐similar MLOs thus occur in the Sudan and in Thailand, where they are associated with phyllody symptoms in C. saltiana and faba bean and with C. juncea and soybean, respectively. A second, serologically distinct MLO group was also found infecting C. juncea and S. indicum in Thailand but MLOs from this group have not yet been identified in crops from the Sudan.
Origin of Early Attacks of Sclerotinia Stem Rot on Winter Oilseed Rape (Brassica napus sub. sub. sp. oleifera var. biensis) in the UK
Authors: McQuilken M.P. , Mitchell S. J. , Archer S. A.
Published: May 2008

Studies in artificially infested field plots of winter oilseed rape showed that mycelia originating from both sclerotia and ascospores of Sclerotinia sclerotiorum can initiate early attacks of sclerotinia stem rot. Disease symptoms appeared in early November in plots previously infested with sclerotia in September. There was a 6–7 week period from artificially inoculating plants with ascospores in October to observing disease symtoms in December. The primary sites of infection for both typesof inocula were the laminae and petioles of senescent and frost‐damaged leaves. Following primary infection, mycelia of the pathogen spread by plant to plant contact, causing secondary infections of neighbouring plants. Sclerotia developed on diseased plants and high numbers were returned to the soil. The importance of these findings to the epidemiology of the disease are discussed.
The Efficacy of Mixtures of Susceptible and Resistant Hosts to Two Wheat Rusts of Different Lesion Size: Controlled Condition Experiments and Computerized Simulations
Authors: Lannou C. , de Vallavieille‐Pope C. , Biass C. , Goyeau H.
Published: May 2008

Controlled‐environment experiments and computerized simulations on wheat yellow rust and wheat brown rust epidemics indicated that mixtures of resistant and susceptible hosts controlled parasites with small lesions more effectively than parasites with large lesions. Experiments were conducted on seedlings, during two parasitic cycles. Yellow rust lesions were about 200 times larger than those of brown rust. The measured efficacy of seedling mixtures in reducing disease spread was 22 % for yellow rust and 46 % for brown rust. Computerized simulations suggested that, for a given quantity of inoculum, mixture efficacy was limited for a large‐lesion parasite because of fast host‐plant saturation.
Brown Discolouration of Mushrooms Caused by Pseudomonas agarici
Authors: Geels F. P. , Hesen L. P. W. , Van Griensven L. J. L. D.
Published: May 2008

Incidence of brown‐discoloured mushrooms, differing from brown blotch disease caused by Pseudomonas tolaasii, has increased in the Netherlands and been responsible for considerable economic losses. A comparative SEM‐study of diseased tissue revealed that hyphae were collapsed and covered with a plaque in which numerous bacteria were embedded. The predominant bacterium identified was Pseudomonas agarici. Both our isolated P. agarici strain and the type strain P. agarici LMG 2112 caused brown discolouration of mushrooms after spraying with bacterial suspensions. Drippy‐gill symptoms were not observed.
Interference Between Two Strains of Bean Common Mosaic Virus is Accompanied by Suppression of Symptoms Without Affecting Replication of the Challenging Virus
Authors: Khan J. A. , Lohuis D. , Bakardjieva N. , Peters D. , Goldbach R. , Dijkstra J.
Published: May 2008

An unusual type of interference between two strains of bean common mosaic virus, viz. NY15 and NL3, infecting bean plants, was investigatred. Wdhen a primary leaf was inoculated with NY15 as inducer and 1–8 days later, the opposite leaf with NL3 as challenger, the plant did not develop symptoms characteristic of NL3, i.e. systemic necrosis in the top, stem and wilting and withering of the youngest trifoloclate leaves. A7‐h interval between the inoculations with inducer and challenger already sufficed to reduce the number of plants showing NL3 symptoms. Surprisingly, the amount of NL3 in the challenge‐inoculated leaf was always than that in the singly infected control, Furthermore, NY15 could not be detected in the opposite leaf until 8 days post‐inoculation and appered enen later in that leaf when challenge‐inoculated. Histological studies showed that NL3 appered later in the xylem of bothe the petiole and stem between primary leaves and first trifoliolate leaf, as compared with the singly inoculated control.

The results suggest that suppression of Nl3 symptoms by Ny15 is not caused by impeding its multiplication, but by delaying the transport of NL3 to the xylem of petiole and stem.
Determination of Races of Pseudomonas syringae pv. glycinea Occurring in Europe
Authors: Abo‐Moch F. , Mavridis A. , Rudolph K.
Published: May 2008

Fifty‐eight strains of Pseudomonas syringae pv. glycinea were collected from France, Germany, Hungary, Italy, Poland, The Ukraine and the former Yugoslavia. The bacterial cultures were fluorescent on King's medium B, oxidase negative, produced levan, and induced a hypersensitive reaction (HR) on tobacco leaves within 24h. The race of each strain was determined by inoculating a set of seven differential soybean cultivars: Acme, Chippewa, Flambeau, Harosoy, Lindarin, Merit and Norchief.Conditions of plant cultivation, bacterial inoculation and plant incubation had to be standardized scrupulously to obtain reproducible results.

Authentic strains belonging to races 1, 4, 5, and 6 produced the expected reactions on the differentials. However, strains of race 2 and race 4 induced identical responses on the differential cultivars. The differentiating critierion between these two races was the ability of race 2 to produce a brown diffusable pigment on King's medium B.

The most prevalent race, occurring in every European country studied, was race 4. This is the most aggressive race of P. glycinea, since it infects all the cultivars of the set of differentials. From 58 strains tested, 42 belonged to race 4, 4 to race 6, and 6 to race 9. For two strains race identification was impossible. The remaining 4 isolates did not fit into the pattern of known races. It is proposed that these strains belong to a new race (no. 10) which is similar to race 5, but can inf, ect the soybean cultivar ‘Lindarin’. On the other hand, race 10 can not infect cv. ‘Chippewa’, in contrast to race 9.
The Role of Cellulase (Endo‐1,4‐β‐Glucanase) in Gummosis Diseases in Apricot
Authors: Rotem Y. , Shoseyov O. , Sztejnberg A.
Published: May 2008

Apricot gummosis pathogens — the fungi Hendersonula toruloidea, a Cytosporina sp. and a Cytospora sp., produce cellulase (endo‐1,4‐β‐glucanase, carboxymethylcellulase, CMCase) in culture. Cytospora sp. produced significantly lower amounts of cellulase than H. toruloidea and Cytosporina sp. The tendency of cellulase accumulation inside apricot stems infected with either H. toruloidea or Cytosporina sp. is similar: most of the cellulase was found in the necrotic area, whereas comparatively small amounts accumulated at the advancing edge of the disease symptom. H. toruloidea produces cellulase with a molecular mass of 76 kDa.
Efficacy of Foliar Application of Phosphates in Controlling Powdery Mildew Fungus on Field‐Grown Winegrapes: Effects on Cluster Yield and Peroxidase Activity in Berries
Authors: Reuveni M. , Reuveni R.
Published: May 2008

Seven foliar applications of 0.025M K2HPO4 and KH2PO4 (both plus Tween 20) and the commercial systemic fungicides, Dorado (Pyrifenox) 480 EC, Penconazole EC and Benomyl, were applied at 14‐day intervals starting at 10‐cm shoot length on field‐grown Chardonnay winegrapes. Both phosphates and systemic fungicides inhibited development of powdery mildew fungus (Uncinula necator, Schw., Burr.) on fruit clusters, as compared with untreated control vines. Diseases, everity on clusters of plants treated with K2HPO4 and fungicides was 0.3 and 0.2, respectively, as compared with 1.3 on control clusters (on a 0–4 scale), for the first rating, conducted 10 days after the fifth application of fungicides and phosphates, Five days after the last application, disease severity was 3.5 on non‐treated control clusters and 0.3 and 0.8 on clusters treated with Dorado and K2HPO4, respectively. Powdery mildew infection remarkably reduced the weight of non‐treated control clusters as compared with Dorado and phosphate treated clusters. Phosphate treatment caused an increase (3‐fold) of peroxidase activity in the soluble fraction of non‐infected control berries. A remarkable peroxidase enhancement was detected in the soluble (8‐fold) and ionically bound (2‐fold) fractions from the phosphate‐treated and infected berries. Results indicate that phosphates can be used as foliar fertilizers for disease control in the field and that peroxidase might, be involved in the defense process.
Systemically Induced Resistance in Potato Cultivars with Different Degree of Resistance to Late Blight caused by Phytophthora infestans (Mont.) de Bary
Authors: Strömberg Anita
Published: May 2008

Systemically induced resistance in potato plants (Solanum tuberosum L.) against late blight Phytophthora infestans was studied macroscopically on three potato cultivars with different degrees of resistance to late blight. The cultivars, were Bintje(2), Elin(3) and Matilda(4). Figures within brackets represent resistance to leaf late blight on a scale from 1 to 5, where 5 denotes the highest level of resistance. In vitro propagated cuttings were used in the experiments, which were, performed under controlled environmental conditions. Disease resistance was induced by a local pre‐infection with P. infestans or with the nonpathogen P. cryptogea. Induced resistance was observed on all cultivars. The protection causedby, induced resistance tended to be most intense on cv. Matilda, with 50–60% reduction in lesion formation 4 days after challenge inoculation.
Isolation and Partial Purification of a Phytotoxin Related to Pathogenic Verticillium species
Authors: Mansoori B. , Milton J. M. , Smith C. J.
Published: May 2008

The low molecular weight metabolites are considered as phytotoxins of pathogenic Verticillum species. The resin, Amberlite XAD‐4 was used for isolation of toxin from log‐phase culture fluids of the fungus. The toxin was purified further using, gel permeation. The isolated toxin induced chlorosis and necrosis in detached‐leaflets of susceptible tomato and potato cultivars similar to natural symptoms. The metabolite is polar, multifunctional, heat stable, cold labile with molecular weight less than 1000. The activity was retained in dried samples of the crude filtrate and kept at room temperature for up to 8 months.
Phytophthora and Pythium Associated with Feeder Root Rot of Citrus in the Transvaal Province of South Africa
Authors: Thompson A. H. , Phillips A. J. L. , Nel E.
Published: May 2008

Mild to extensive feeder root rot was present in all 23 orchards, with trees showing symptoms of citrus decline from nine areas in the Transvaal Province of South Africa. Phytophthora nicotianae and Pythium spp. were isolated from diseased roots and rhizosphere soils in all areas sampled. Isolations from diseased feeder roots showed P. nicotianae present in 26% of orchards during Spring and 61% of orchards during Autumn, while Pythium spp. were present in 56% of orchards during Spring and 65% of orchards during Autumn. In isolations from baited rhizosphere soils, P. nicotianae was present in 56% of orchards during Spring and 52% of orchards during Autumn, while Pythium spp. were present in 69% of orchards during Spring and 82% of orchards during Autumn. In rhizosphere soils, the mean population density of Pythium spp. was higher than that of P. nicotianae throughout the season. Only P. nicotianae was consistently isolated during thesurvey. Different Pythium spp. were isolated of which two were tentatively identified as P. paroecandrum and Pythium‘Gp.G’.
The Relationship between Systemic Resistance Induced by Pruning and Accumulation of Antifungal Substances in Barley Seedlings
Authors: Hiramoto T. , Abe N. , Tobimatsu R. , Shiraishi T. , Oku H. , Yamada T. , Ichinose Y.
Published: May 2008

Infection by a compatible race of Erysiphe graminis f. sp. hordei on barley secondary leaves was significantly suppressed upon pruning of the primary leaves when E. graminis hordei was inoculated 3–12 h after the pruning, but it, was rather enhanced during 15–21 h. The accumulation of antifungal substances was detected in hot ethanol extracts of barley seedlings from 15–27 h after pruning the primary leaves. Taking the time of the infection process of a challenger (E. graminis, hordei) into consideration, timing of systemic resistance induced upon pruning coincided with the accumulation of antifungal substances.
The Infection of Festuca arundinacea by Puccinia graminis subsp. graminicola
Authors: Kulik M. M. , Dery P. D.
Published: May 2008

Puccinia graminis subsp. graminicola has caused economically important losses of tall fescue (Festuca arundinacea Schreb.) in North America. This rust infects leaves, culms, and spikelets of the host. Initital symptoms consist of very small, chlorotic flecks, followed by long, narrow lesions. Invasive hyphae were diffuse and filamentous, changing to dense and blocky with the formation of hymenia. Tissues were extensively colonized, including development caryopses. Seedborne infection consisted of mycelium within the embryo and urediniospores carried on both surfaces of the glumes. It is not known whether caryopses that are internally infected can germinate to produce infected individuals, but this could be an important quarantine consideration. Although, at the ultrastructural level, urediniospore development in this fungus is similar to that of other rusts, we detected an additional layer at the interface of the urediniospore and its pedicel. This layer may play a role in the, release of urediniospores from their pedicels.
Damping‐off of Some Cucurbitaceous Crops in Saudi Arabia with Reference to Control Methods
Authors: Shahda W. T. , Al‐Rahma A. N. A. N. , Rageh S. A.
Published: May 2008

Isolation of seed borne fungi from sweet melon (najed and red Queen varieties) and vegetable marrow (squash) using PDA, Plain agar media and blotters revealed the presence of Alternaria alternata (Fr.) Keissler, Fusarium semitectum var,majus from Najed melon, A. alternata (Fr.) Keissler, F. sambucinum Fuckel from Red Queen melon and A. chlamydospora Mouchacca, Cephalosporium sp., and F. oxysporum schlecht from squash. Pathogenicity tests showed, that all these fungi were highly pathogenic on their respective hosts. The optimum temperature for its growth ranged from 25–30°C and the optimum pH was 6.0.

In pot trials, seed dressing with Banrot, Bavistin and Topsin‐M at the rate of 4 g/kg seed was superior in controlling the damping‐off of melon and squash. These fungicides were effective in inhibiting mycelial growth, spore germination and development of the isolated fungi. Hot water treatment at 55 C/20 min or solar heating (av. 37°C) for 90 min were next to fungicides.
Do Pathogenic Fungi Have the Potential to Inhibit Biocontrol Fungi?
Authors: Lewis J. A. , Lumsden R. D.
Published: May 2008

Metabolites produced by the soilborne plant pathogen Rhizoctonia solani (R‐23) and Pythium ultimum (PuZ3) grown on cellophane disks placed on potato‐dextrose agar (PDA), molasses brewer's yeast agar (MYA) and wheat bran extract agar (BEA) did not significantly affect the rate of growth of isolates of the antagonists Trichoderma viride (TS‐I‐R3. Tv‐101), T. harzianum (Th‐57, Th‐87), T. hamatum (Tm‐23, TRI‐4), or Gliocladiun virens (GI‐3, GI‐21) when these antagonists were grown on the three agars containing pathogen metabolites. However. in some instances. density of antagonist mycelium growing on the agar media as well as the observable production of antagonist conidia on the agar media were reduced. Using four antagonists in liquid cultures of potato‐dextrose broth (PDB) containing metabolites of the pathogens grown on bran extract broth, metabolites from R‐23 significantly reduced mycelial dry weight of Th‐87 and GI‐21 but not that of TRI‐4 and GI‐3. On the contrary. metabolites of PuZ3 increased the mycelial dry weight of all four antagonists, Metabolites of R‐23 reduced production of conidia of only TRI‐4; metabolites of PuZ3 significantly reduced production of conidia of all four antagonists. Pathogen metabolites did not affect germination of conidia in the system used.
Apical Chlorosis Disease of Chickpea (Cicer arietinum) Caused by Tomato Spotted Wilt Virus in Brazil
Authors: Botteux L. S. , De ÁVila A. C. , Giordano L. B. , Lima M. I. , Kitajima E. W.
Published: May 2008

A severe new disease was observed in field‐grown chickpea (Cicer arietinum L.) plants in Brasilia‐DF, central Brazil. Symptoms were mainly general chlorosis accompanied by necrosis of the new growth and plant stunting, but pods were symptomless. Host range studies, serology, particle morphology, and cytopathology showed that tomato‐spotted wilt tospovirus (TSWV) was the cause of the disease. This is apparently the first report of a chickpea disease caused by natural infection of a tospovirus.
Tissue Culture Technique to Determine the Viability of Peronospora parasitica in Brassica oleracea
Authors: Achar P. N.
Published: May 2008

The seed‐borne nature of Peronospora parasitica in cabbage cultivar is well established. Pure axenic growth of downy mildew of cabbage is established in vitro using modified Murashige and Skoog medium. The tissue culture technique is used to test the viability of seed borne mycelium of P. parasitica in cabbage. The percentage of seeds showing viable mycelium varied from cultivar to cultivar and a direct correlation was noticed between embryo infection and seed transmission in callus. A similar correlation was established with the seedling symptom test. The tissue culture technique to test the viability of downy mildew mycelium in cabbage was a quicker and more reliable method than the seedling symptom test. The possibility of adopting the technique by quarantine stations for seed health testing and for the in vitro studies of P. parasitica and other host systems in crucifers is discussed.
Analysis of the Long‐term Dynamics of Stem and Leaf Rusts of Wheat in North America Using a Time‐series Approach
Authors: Yang X. B.
Published: May 2008

Historical data on wheat stem rust in the US and wheat leaf rust in Canada were analysed using a time‐series approach to detect patterns in their long‐term dynamics. Three sets of historical data were analysed, the first of which described the annual appearance of wheat‐stem rust in six regions of the western Mississippi Basin from 1921 to 1961. Models developed from these data had significant autocorrelation components of AR(1) or AR(2), indicating that the date of disease appearance in 1 year wasstatistically related to the dates of appearance in the previous 1–2 years. The series of six regions were spatially significantly correlated with each other. Values of the cross‐correlation coefficient increased from 0.20 to 0.83 as the distance between, two regions decreased. The second data set represented relative diversity of physiological races of wheat stem rust from 1918 to 1982. Analysis suggested that a change in race diversity may occur in the US every 5–6 years, based on AR(5) and AR(6) patterns. The third data set had two series on the phenotypes of leaf rust in the eastern and prairie regions of Canada. Analysis indicated that there was a 2‐year autoregressive component AR(2) in each of these two time series. Analysis further suggestedthat the prairie population differed from the eastern population in having a 4‐year moving average component, MA(4), in the majority of individual races.
New Sources of Resistance in Cauliflower (Brassica oleracea var. botrytis) to Crucifer Downy Mildew Caused by Peronospora parasitica
Authors: Silué D. , Laviec C. , Tirilly Y.
Published: May 2008

A total of 81 accessions of cauliflower (Brassica oleracea var. botrytis) were inoculated at the seedling stage with three isolates of Peronospora parasitica. All isolates used were derived from cauliflower crops in France and could be described as three distinct pathotypes, based on their virulence patterns on the accessions tested.

The three isolates were virulent on F1 hybrids Vega and Billabong. In the UK, two isolates were found to be avirulent on Vega. This result indicates that pathotypes indentified in the UK are different from those in this study and that hybrid Vega has isolate‐specific resistance genes.

Eleven differential responses to the pathogen were identified among cauliflower accessions. Thirty‐five accessions tested were susceptible to all three isolates. This susceptibility may be due to the presence of genes shared by these accessions and the resistance it confers is overcome by the three isolates.

Twenty‐four accessions tested were derived from single plants selected from populations. Segregation for resistance was found in lines belonging to family F45. This result indicates that the parental plant of these lines was heterozygous. On the other hand, lines of families A 39 and 48 showed no segregation for resistance indicating that the parental plants of both families were homozygous for resistance to the isolates of the study.

Four accessions were resistant to the three isolates tested. The differential accessions identified in this study are possible candidates for inclusion in a set of genotypes carrying known resistance genes of differentiating pathotypes.
Effects of Nitrogen Fertilization on Disease Severity and Infection Type of Yellow Rust on Wheat Genotypes Varying in Quantitative Resistance
Authors: Danial D.L. , Parlevliet J. E.
Published: May 2008

Two experiments were carried out to study the effect of nitrogen level on disease severity of genotypes of wheat (Triticum aestivum) varying in quantitative resistance to yellow rust, caused by Puccinia striiformis. In 1990, nine wheat genotypes were exposed to 0.20, 40 and 80 kg N per ha. In 1991, six genotypes, selected from experiment I, were examined at 0. 30 and 90 kg N per ha. The N was applied in the form of calcium ammonium nitrate (NH4NO3+CaCO3). In both years the disease severity increased strongly with increased N‐levels. The infection types also increased with increased N‐levels. Compared with the main effects, the Genotype X N‐level, the Genotype X Year and the Genotype X N‐level, X Year interactions were small, but highly significant (at P = 0.01). Selection for quantitative resistance therefore has to be carried out at the N‐levels used in the regions the breeding is aiming at.
Factors Affecting Potato Soft‐rot Resistance to Pectolytic Erwinia Species in a Tuber‐slice Assay
Authors: Allefs J. J. H. M. , van Dooueweert W. , de Jong E. R. , Prummel W. , Hoogendoorn J.
Published: May 2008

Potato‐tuber slices and small tubers of 12 cultivars were inoculated with isolates of Erwinia carotovora subsp. atroseptica (Eca), E. c. subsp. carotovora (Ecc) and E. chrysanthemi (Ech). Cultivar resistance was expressed as the mean diameter of the rotted‐tissue area. Grouping of the cultivars into classes of relatively high, intermediate or low resistance, was different after incubation in air in comparison to incubation under anaerobic conditions, and depended on the (sub‐)species of bacteria used. When compared to the effect of inoculation with different (sub‐)species, grouping of the cultivars was less affected by isolates within (sub‐)species. Cultivar grouping was hardly affected by site of inoculation, being either in the medullary tissue or in the cortex. In general, the results of experiments with either field‐grown seed tubers or glasshouse‐grown small tubers from 2 years were reproducible, except when tuber tissue was inoculated with Ech and incubated, aerobically, in which case cultivars only showed relatively small differences for resistance. Correlation coefficients between the results from slice and small‐tuber screenings were 0.71 and 0.64 for Eca and Ecc, respectively. This implies, some potential for applying the method in the early stages of potato‐breeding programmes.

The results of this study show that soft‐rot resistance of clones to different pectolytic Erwinia spp. can be determined efficiently and reproducibly if the oxygen concentration during incubation is standardized.
Production of Inter‐ and Intra‐strain Hybrids of Trichoderma spp. by Protoplast Fusion and Evaluation of Their Biocontrol Activity Against Soil‐borne and Foliar Pathogens
Authors: Migheli Q. , Whipps J. M. , Budge S. P. , Lynch J. M.
Published: May 2008

Protoplast fusion techniques were used for the production of new antagonistic strains of Trichoderma spp. Two British and two Italian strains of Trichoderma with different biocontrol potential against Botrytis cinerea, Sclerotinia sclerotiorum and Pythium ultimum, were treated with u.v. radiation and mutants resistant to hygromycin B or propiconzole were selected. Protoplasts were obtained from these mutants after digestion of young hyphae with Novozym 234 and used in inter‐ and intra‐strain protoplast fusion experiments. Hybrids were obtained in 13 crosses isolated on fungicide‐amended media by the inheritance of resistance markers from both parental strains. Selected, fast‐growing, stable mutants were tested in biocontrol trials against P. ultimum on lettuce seedlings and B. cinera on grape bunches in comparison with their parental strains. Intra‐strain hybrids derived from cross XIII were tested in vitro for their mycoparasitic ability on sclerotia of S. sclerotiorum. A high degree of variability in the biocontrol and the mycoparasitic ability of the fusants was observed but no significant increase in the activity was accomplished after fusion, the hybrids being generally less activewas accomplished after fusion, the hybrids being generally less active than their parental strains.
Genetic Diversity in W‐ and R‐type Populations of Pseudocercosporella herpotrichoides Based on DNA Restriction Fragment Length Polymorphisms
Authors: Poupard P. , Frei U. , Cavelier* N. , Lind V.
Published: May 2008

Thirty‐seven isolates of Pseudocercosporella herpotrichoides belonging to W‐type and 31 isolates belonging to R‐type were analysed for DNA restriction fragment length polymorphisms (RFLPs). They represent diverse geographic origins and different phenotypes related to sensitivity to fungicides. Total DNA digested with EcoRI was hybridized with 22 random DNA probes from a P. herpotrichoides EcoRI‐restricted DNA library. Four probes showing polymorphisms among isolates within W‐type and R‐type and generating a total of 44 RFLPs were retained for cluster analysis. Two main groups were distinguished corresponding to W‐ and R‐types. The genetic diversity among isolates was greater for the W‐type than for the R‐type isolate, four and three distinct EcoRI‐restricted mitochondrial DNA patterns were identified in W‐ and R‐type isolates, respectively. The variability of profiles within each pathotype confirmed a higher degree of polymorphism in the W‐type.
Effect of Brown Stem Rot on Water Relations of Soybean
Authors: Higley P. M. , Martinson C. A. , Tachibana H.
Published: May 2008

To investigate the effects of brown stem rot, a vascular disease of soybean (Glycine max) induced by Phialophora gregata, on the water relations of diseased plants, stems of greenhouse‐grown plants of susceptible (Pride B216) and resistant (BSR 201) cultivars were injected with the pathogen at vegetative growth stage VI. Plants of both cultivars developed internal stem browning, but those of Pride B216 developed more severe symptoms of water stress (reduced leaf water potential and stem conductance). Inoculated plants of both cultivars also had reduced stem conductance and increased stomatal conductance and transpiration. Disease‐related water stress can be attributed to the combined effects of reduced stem conductance and increased water loss resulting from increased stomatal conductance.
Evidence for Differential Resistance to Peronospora parasitica (downy mildew) in Accessions of Brassica juncea (mustard) at the Cotyledon Stage
Authors: Nashaat N. I. , Awasthi* R. P.
Published: May 2008

Thirty‐one Brassica juncea accessions were screened at the cotyledon stage for resistance to four isolates of Peronospora parasitica. Isolates R1 and P003 were derived from crops of oilseed rape (B. napus ssp. oleifera) in the UK and isolates IP01 and IP02 were derived from crops of mustard (B. juncea) in India. B. napus cv. Ariana, which was used as a susceptible control for isolates from B. napus, was resistant to isolates from B. juncea. All, B. juncea accessions were resistant to isolates from B. napus except one accession which expressed moderate resistance to isolate P003. Five groups of B. juncea accessions with differential resistance were identified. Lines homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to isolates from B. juncea. The differential resistance identified in the B. juncea‐P. parasitica combination can be used as a foundation for future studies of the genetics of the host‐pathogen interaction and for breeding for disease resistance.
Active Oxygen‐producing and ‐scavenging Enzymes in Pepper Leaves Infected with Xanthomonas campestris pv. vesicatoria
Authors: Buonaurio R. , Umesh Kumar N. N.
Published: May 2008

Lipoxygenase (LOX), peroxidase (POX), superoxide dismutase (SOD) and catalase (CAT) activities were determined in pepper (Capsicum annuum) leaves infected with Xanthomonas campestris pv. uesicatoria, from 3 to 15 days after inoculation, before symptom appearance and during the development of the disease. Strong Stimulation of LOX and POX activities was observed in infected leaves at an advanced stage of the disease (12–15 days after inoculation), when bacterial water‐soaked spots and a slight chlorosis of the inoculated leaf areas were evident and a decrease in chlorophyll content of infected tissue was detected. The infection also induced a significant increase in CAT activity at the day 9 and a decrease in SOD and CAT activities at the day 12. On the basis of the changes observed, uncontrolled production of active oxygen species at advanced stages of infection is hypothesized.
Restriction Fragment Length Polymorphism Analyses of the Plasmid DNAs in Strains of Xanthomonas campestris pv. vesicatoria from Different Geographic Areas
Authors: Hwang Byung Kook , Lee Jong Tag , Hwang Byung Gap , Koh Young Jin
Published: May 2008

Restriction fragment length polymorphisms (RFLPs) of plasmid DNAs in Xanthomonas campestris pv. vesicatoria were analysed using 77 strains from the United states, Argentina, Australia, Taiwan, and Korea. One or more plasmids were detected in all tested strains, irrespective of geographic origin, host plant from which isolated, or chemical resistance. All Korean strains contained a few plasmids of similar high molecular weight, whereas some small plasmids occured only in strains from the United States, Argentina, and Taiwan. After digesting total plasmid DNAs with each of four restriction endonucleases, 18 fragments with sizes from about 1 to 23 kb were visualized. Seventy‐seven strains of diverse geographic origins, with different levels of resistance to streptomycin and copper, were classified into the 14 RFLP groups based on the restriction endonuclease digestion patterns of their plasmid DNAs. Strains belonging to each group shared DNA fragments of identical size, suggesting the possible presence of similar plasmids in these strains. A 5.8‐kb EcoRI plasmid DNA probe prepared from the United States strain 81‐23 hybridized to EcoRI plasmid digests from all tested strains. Other plasmid DNA fragments of the strain81‐2,3 used as probes had no homology to plasmid DNA fragments from several strains around the world. The variation in hybridization profiles of plasmid DNA was very similar to the results obtained by RFLP analysis of plasmid DNA digested by four restriction enzymes. Most of the Korean strains tested were highly sensitive to streptomycin and copper, whereas most strains from other geographic areas showed a high level of resistance to one or two of the chemicals. Cluster analysis of genetic distance between the strains based on the data obtained generated the dendrograms that separated all Korean strains from the other strains, suggesting that plasmid DNA of the Korean strains may be genetically very different from those of the others.
MLO‐Infected Weeds in the Vineyards of North‐western Italy
Authors: Arzone A. , Alma A. , Bosco D. , Patetta A.
Published: May 2008

Ten species of herbaceous plants and shrubs with MLO symptoms such as stunting, bushing, yellowing, reddening, virescence or phyllody were collected in both grapevine yellows (GY)‐infected and uninfected vineyards. By electron microscopy, MLOs were found in the sieve tubes of eight species. The presence of MLOs in Picris echioides is demonstrated for the first time. The possible role of MLO‐infected weeds in the spread of GY disease is discussed.
Histology of the Infection and Development of Puccinia recondita f. sp. tritici in a Wheat Line with Lr37
Authors: Kloppers F. J. , Pretorius Z. A.
Published: May 2008

The degree of adult‐plant resistance conferred by the gene Lr37 in RL6081 (Thatcher*8/Lr37) to four avirulent leaf rust pathotypes was quantified by assessing histological components as well as latent period, uredinium density and uredinium size. Histological observations on the adaxial flag leaf surfaces revealed significant arrest of fungal structures in RL6081 at early infection stages. Furthermore, host cell necrosis typical of a posthaustorial host‐resistance mechanism was conspicuous in sizeably reduced colonies on this genotype. Lr37 significantly decreased the rate of uredinial appearance of all four pathotypes. Compared with Thatcher, fewer uredinia of smaller dimensions developed on flag leaves of RL6081. Characterization of resistance indicated that disease development in genotypes with the gene Lr37 should be extremely limited.
Isolation of Race‐and Cultivar‐Specific Elicitors from Intercellular Fluids of Compatible Interactions of Pseudomonas syringae pv. pisi and Pea
Authors: Mwang'ombe A. W. , Archer S. A.
Published: May 2008

Intercellular fluids obtained by an in vacuo infiltration technique from compatible race‐cultivar interactions of five races of Pseudomonas syringae pv. pisi and pea induced extensive light brown necrotic (hypersensitive type of) lesions in resistant but not susceptible cultivars. In susceptible cultivars the intercellular fluids induced extetensive water soaking symptoms. The intercellular fluids elicited intermediate reactions in pea cultivars of moderate resistance. The intensity of the light brown necrotic reactions in pea appears to be positively correlated with the degree of resistance.