bluuebunny/crossref_metadata_2025 huggingface dataset:
Compartment Analysis of Disease Progression in Time. II. Restricted Disease Increase
Authors: Analytis S.
Published: May 2008

Three‐compartmenl analysis was performed to describe the disease motion through presporulating (latent), sporulating (infectious) and postsporulating (removal) stages in the general case, where total disease increase is density dependent. A second‐order Runge‐Kutta method for numerical integration of the system of difterential equations was used to solve the equations. Total and postsporulating disease progress curves are S‐shaped while latent and infectious disease progress in the form of optimum curves. The curve of a composite variable defined as total (latent and infectious) inoculum reservoir of the host progresses also in the form of an optimum curve showing a maxi at the total disease level yt/K = 1 − 1/iR, where K is the total population of infection sites, i is the infectious period, R the intrinsic infection rate and iR ≥ 1/(1 − Vo/K). The size of this maxi is a monotone increasing function of the product iR by given initial disease level Vo. Condition iR =1/(1−yo/K) is a threshold condition for total inoculum to increase over yo, or alternatively a threshold condition for a rapid disease increase at the start resulting, possibly, in a large epidemic. Condition iR = O is a threshold condition for total disease to increase over initial disease level. Total disease reaches an asymptotic value less than unity if and only if infectious period is linite (existence of removals). In the compartment system there is a consistency regarding the threshold conditions for total disease to increase over initial disease level in the cases with and without a density‐dependent factor. Conversely, in the Vanderplankian system of differential‐difference equation the threshold conditions are iR = 0 and iR = 1 respectively due to the assumption of an exponential increase of total disease early in the epidemic. The particular cases without latent period and without removals are treated separately. The implications derived from the compartment analysis are compared with those derived from the Vanderplankian system of epidemiological analysis.
Production of the Phytoalexin Resveratrol by Grapes as a Response to Botrytis Attack Under Natural Conditions
Authors: Jeandet P. , Bessis R. , Sbaghi M. , Meunier P.
Published: May 2008

Resveratrol (3,5,4′‐trihydroxystilbene) is one of the stress metabolites produced by grapevines in response to fungal infection or injury. The distribution of this compound in limited lesions caused by Botrytiscinerea on ripe grape clusters in the vineyard has been examined. Resveratrol was present predominantly in the non‐infected fruits close to the necrotic area. This localized response can help to arrest the spread of established B. cinerea lesions as long as climatic conditions are unfavourable to the pathogen. When conditions become favorable, i.e. after a mild and humid period rapidly spreading lesions are observed on fruits despite the continued increasing production of resveratrol in the grapes which can reach three‐ to five‐fold the value found before rot intensification. Significant amounts of resveratrol can be found prior to any detectable lesions in fruits collected from apparently healthy clusters thus suggesting that phytoalexin response in initiated soon after the recognition of the pathogen by the plant. The involvement of one or more endogenous signals coming from either the fungus or the plant in the induction of host defence responses has also been discussed.
Infection Biology of Bacterial Wilt of Forage Grasses
Authors: Wang Hui Min , Sletten A.
Published: May 2008

Infection of perennial ryegrass (Lolium perenne L.), Italian ryegrass (Loliummultiflorum L.), and timothy (Phleum pratense L.) by Xanthomonas campestris pv. graminis and Xanthomonas campestris pv. phlei occurred mainly via wounds rather than natural openings. Nevertheless, bacteria were detected by isolation and immunofluorescence in plants sprayed with the pathogen without prior wounding and in plants in which intact ears had been dipped in inocula. High concentrations of bacteria were observed around the stomata of perennial ryegrass and timothy by scanning electron microscopy 48 h after inoculation. Perennial ryegrass and Italian ryegrass and individual plants of ryegrass and timothy differedin susceptibility to the pathogens.
Development of Eyespot and Brown Foot Rot in Wheat Plants Inoculated with Mixtures of Pseudocercosporella herpotrichoides Types and Fusarium Species
Authors: Bateman G. L. , Munnery I. C.
Published: May 2008

The effects of Fusarium avenaceum, F. culmorum and Microdochium nivale on eyespot development and of types of the eyespot fungus Pseudocercosporella herpotrichoides on brown foot rot caused by the Fusarium or Microdochium spp. were investigated by sequential inoculation of wheat plants grown in pots in a controlled environment. The W‐type of the eyespot fungus induced more severe disease than the R‐type, but its symptons were suppressed to a greater extent by Fusarium spp., especially F. avenaceum. Brown foot rot symptoms were sometimes suppressed by P. herpotrichoides but were occasionally more severe when the Fusarium inoculum was applied after the P. herpotrichoides. There, sults are discussed in relation to observations of natural infections.
Study of Nutritional and Environmental Factors Affecting the Fruiting Competence of Rhizoctonia solani AG‐1
Authors: Noel T. , Axiotis S. , Labarère J.
Published: May 2008

The study of nutritional, physiological and physical factors affecting basidiospore development in Rhizoctonia solani evidenced the critical influence of the physiological state of the mycelium subjected to a nutritional stress for fruiting induction. Comparison of four preculture media allowed identification of the optimal nutrient status provided by glucose, yeast extract and bacto‐peptone, for subsequent basidial differentiation on a starved water agar medium. While variations of glucose and yeast extract concentrations are not determinant for basidial differentiation, the breakdown observed with a low bactopeptone concentration underscores a major role for the nitrogen content which however should be considered in a balance with the carbon source. The basidial differentiation was shown: (i) to increase as the age of the preculture used to inoculate water agar increases; (ii) to be stimulated by a dark/light regime, and (iii) to be induced and increased by a cold temperature shock (8oC) when the mycelium was derived from young precultures. The effect of the cold temperature shock indicates that the preculture conditions can induce long‐term physiological modifications in the myccelia. While the fruiting response to nutritional factors is similar whatever the strain used the response to environmental factors depends mainly on the genotype of the strains.
Micro Morphological and Chemical Investigation into the Effects of Fungal Diseases on Melissa officinals L., Mentha×Piperita L. and Salvia officinalis L.
Authors: D'Aulerio A. Zechini , Zambonelli A. , Bianchi A. , Albasini A.
Published: May 2008

A micro‐morphological study of infected tissues and a chemical investigation into the volatile fraction of secretory tissues of healthy and infected plants were carried out. The botanic species were: Melissa officinalis L. (infected by Erysiphe galeopsidis and Septoria melissae); Salvia officinalis L. (infected by Erysiphe salviae); Mentha piperita L. (infected by Puccinia menthae).

The results show that pathogenic fungal infection seriously damages the secretory tissues and stomata, causing a decrease in the amount of essential oil contained in infected plants, and modifying the composition of the plant's volatile fraction.
Studies on the Concentration of Ramularia beticola Conidia in the Air Above Sugar Beet fields in Denmark
Authors: Hestbjerg H. , Dissing H.
Published: May 2008

Concentrations of Ramularia beticola Faut. & Lamb. conidia in the air above 3 sugar beet (Beta vulgaris L.) field were registered for a period of 41 days altogether. A significant diurnal periodicity was revealed. Two periods of 3 and 5 days, respectively, included peaks of several thousands of conidia per m3 of air. The conidial concentrations were related to temperature, relative humidity (RH) and vapour pressure of the air, and to wind speed, dew point, rainfall and hours of sunshine. A significant effect of vapour pressure was observed for 2 fields. In one field with very low conidial concentrations, vapour pressure was nearly significant. In this field only wind speed significantly influenced dispersal of conidia. In an analysis of covariance including all data, 50% of the variation was explained by field, time of day, vapour pressure and number of hours of RH above 95% in the preceding 24h.
Comparative Antagonistic Properties of Gliocladium virens and Trichoderma harzianum on Sclerotium rolfsii and Rhizoctonia solani—its Relevance to Understanding the Mechanisms of Biocontrol
Authors: Mukherjee P. K. , Mukhopadhyay A. N. , Sarmah D. K. , Shrestha S. M.
Published: May 2008

An isolate of Trichoderma harzianum which is less effective than G. virens in suppressing S. rolfsii and R. solani was compared with G. virens for various mechanisms of antagonism in vitro, viz., antagonism in dual culture/hyphal parasitism, parasitism of sclerotia and antibiosis. G. virens and T. harzianum were equally effective in parasitizing the hyphae of R. solani. Only T. harzianum parasitized the hyphae of S. rolfsii, and the two antagonists were comparable with respect to antibiosis on the test pathogens. However, G. virens readily parasitized the sclerotia of the test pathogens and was found to be more effective than T. harzianum in destroying the sclerotia. Under SEM, G. virens was found to colonize, penetrate, and sporulate inside the sclerotia of the test pathogens.Parasitism of sclerotia is suggested as the principal mechanism of biological control of S. rolfsii and R. solani by G. virens.
Virulence Gene Frequency Change in Erysiphe graminis f. sp. hordei Due to Selection by Non‐Corresponding Barley Mildew Resistance Genes and Hitchhiking
Authors: Huang R. , Kranz J. , Welz H. G.
Published: May 2008

Individual isolates (in total 4040) of Erysiphe graminis f. sp. hordei were collected between 1989 and 1991 in fields of spring barley varieties with resistance genes Mla9, Mla12 and Ml(La) in the local air spora, i.e. remote from barley fields, in Hesse, Germany. Their virulence pattern was determined on a 13‐partite differential set. In the air spora. virulence complexity (the number of virulence genes per isolate) increased by 30% (4.2 vs. 5.5) between 1989 and 1991. This was mainly due to an increase of pathotypes with virulence genes Va7, Val3, Vk and V(La). In each mildew field population, frequencies of several non‐corresponding virulence genes, e.g. V(La) on Mla9 variety, greatly increased during the period. Such change can be caused by hitchhiking selection, i.e. indirect selection resulting from asexual reproduction, and direct selection by non‐corresponding resistance genes. To separate the two effects, the aerial barley mildew population of 1991 was sampled on cv. Pallas and near‐isogenic lines of Pallas. Frequencies of non‐corresponding virulence genes as observed in samples from the near‐isogenic lines were compared to expected non‐corresponding virulence frequencies which were obtained by subdividing the sample on Pallas into 12 subsamples, comprising all isolates virulent to line 1 through 12, respectively. Among 90 resistance/virulence gene combinations selection for non‐cor‐responding virulence was significant in five cases (e.g. Va9 on Mla7 host) and against non‐corresponding virulence in nine cases (e.g. Vk on Ml(La) host). Hitchhiking selection was significant in eight cases. In 11 cases the two types of selection were significant in combination but not individually. It is suggested to monitor the stability of selection against non‐corresponding virulence genes in race surveys and utilize it in diversified barley crops such as variety mixtures in order to retard the evolution of complex races.
Faba Bean Necrotic Yellows Virus Naturally Infects Phaseolus Bean and Cowpea in the Coastal Area of Syria
Authors: Franz A. , Makkouk K. M. , Vetten H. J.
Published: May 2008

In an attempt to identify possible summer hosts of the faba bean necrotic yellows virus (FBNYV), a field survey was conducted in the coastal area of Syria. Using a monoclonal antibody to FBNYV in indirect ELISA, FBNYV was detected in a large number of samples from Phaseolus vulgaris L. and in a few samples from Vigna unguiculata (L.) Walp. in which it caused severe symptoms. This is the first report of natural infection of P. vulgaris and V. unguiculata with FBNYV.
Effect of Four Fungicides on Barley Net Blotch Caused by Drechslera teres
Authors: Toubia‐Rahme H. , Ali‐Haimoud D‐E. , Barrault G. , Albertini L.
Published: May 2008

The effect of four fungicides (benomyl, carbendazim, triadimefon and sulp hur), used in intensive barley cropping on the epidemiology of Drechslera teres f. maculata and f. teres, was investigated under a controlled environment. Two fungicides (benomyl and carbendazim) increased disease development, especially at the recommended field rate, sulphur had the same effect at lower concentrations and triadimefon promoted net blotch caused by D. teres f. teres. At the recommended field rate, carbendazim enhanced sporulation in the two pathogen forms, whereas benomyl and sulphur enhanced 14 sporulation only on the maculata form. The results showed that, under controlled conditions, most of the fungicides promotednet blotch development and that sporulation increased either as a result of the pathogen form or of the concentration of the active ingredient.
Electron Microscope Studies on Pseudomonas syringae pv. phaseolicola Isolated From Inoculated Tobacco Leaves: Changes in Flagellation, Biomass and Elemental Composition During the Hypersensitive Reaction
Authors: Hodson N. , El Masry M. H. , Sigee D. C.
Published: May 2008

Cells of Pseudomonas syringae pv. phyaseolicola were infiltrated into tobacco leaves, recovered from tissue macerates at various time intervals during the course of the hypersensitive reaction, then investigated by analytical electron microscopy to determine changes in flagellation, cell size/biomass and elemental composition.

In this interaction, the rapid fall in viable count was paralleled by an immediate and progressive decrease in mean cell biomass and a delayed decrease in mean cell size. The percentage occurrence of flagella also showed a sharp fall, suggesting a marked inhibition of bacterial motility.

X‐ray microanalysis of individual cells in air‐dried preparations revealed the routine presence of detectable levels of P, K and Ca throughout the time course. Although signifificant changes in mean mass fractions did occur, the elemental composition of bacterial cells remained relatively stable throughout. The maintenance of substantial levels of K during the hypersensitive reaction suggests that direct damage to bacterial cells, with resulting ion leakage, does not occur.
The Presence of the N' Gene in Nicotiana tabacum L. cv. Samsun NN
Authors: Piccirillo P. , Porrone F.
Published: May 2008

The N′ gene was shown to be present in the ‘Samsun NN’ line of Nicotiana tabacum by its differential response to tobacco mosaic (TMV) and tomato mosaic (ToMV) viruses in the segregating and test‐cross generations of the cross ‘Samsun NN’×‘Samsun nn’. The appearance of phenotypes reacting with local necrosis to ToMV and with systemic mosaic to TMV confirmed that the genes N and N′ are on distinct loci. An isogenic N′;N′ Samsun line was selected.
The Nucleotide Sequence of the 3′‐Terminal Region of Clover Yellow Vein Potyvirus Isolated from Calanthe sp.
Authors: Ikegami M. , Isomura Y. , Maeda T. , Inouye N.
Published: May 2008

The sequence of 1399 nucleotides from the 3'region of the RNA of clover yellow vein potyvirus (CIYVV‐C) isolated from Calanthe sp. was determined. The capsid protein cistron was composed of 915 nucleotides, and corresponded to a region encoding 305 amino acids with a calculated Mr of 34900: the adjacent 3'non‐coding region was 74 nucleotides long. The length of the capsid protein gene of CIYVV‐C is longer, but the 3'non‐coding region is shorter than those of other CIYVV strains (CIYVV‐30.CIYVV‐NZ and CIYVV‐B). The nucleotide sequence of the capsid protein gene and the 3'non‐coding region of CIYVV‐C RNA showed significantly higher homology with those of other CIYVV strains. These data suggest that the CIYVV‐C capsid gene arose from a frame‐shift mutation of the capsid gene of another CIYVV strain. or vice versa. CIYVV‐C has a closer affinity to other CIYVV strains and to bean yellow mosaic virus than to the other potyviruses.
Crop Growth, Disease and Yield Components of Rusted Phaseolus Beans in Ethiopia
Authors: Habtu A. , Zadoks J. C.
Published: May 2008

Crop growth and disease epidemics in sprayed and non‐sprayed bean plots, artificially infected with rust (Uromyces appendiculatus) 3 weeks after emergence. were assessed weekly in two cultivars, at two locations for two seasons. Disease intensity was regulated by the application of a fungicide at 5 spray frequencies. Fungicide application influenced leaf area index (LAI) and reduced rust intensity. The fungicide had no significant effect on other diseases and dead leaf area. Fungicide application increased seed yield (SY) by increased numbers of pods per plant (PP). Rust severity was strongly correlated with pustule density but the overall relationships among rust assessment parameters depended on cultivar and location. Seed yield and pods per plant were highly correlated with LAI. The relationships between LAI and seeds per pod or seed weight depended on cultivar and location. Overall rust assessment parameters (rust severity and pustule density) showed close, negative relationships with seed yield. seed weight and pods per plant but not with seeds per pod. The relationships obtained in the partially resistant line 6‐R‐395 were less definite than those in the susceptible line Mexican 142. The yield parameters seed yield and pods per plant, showed strong positive relationships.
Comparative Resistance Patterns of Fludioxonil and Vinclozolin in Botryotinia fuckeliana
Authors: Hilber U. W. , Schwinn F. J. , Schüepp H.
Published: May 2008

Fludioxonil is a new non‐systemic phenylpyrrole fungicide. It is a derivative of the antibiotic pyrrolnitrin and is highly active against Ascomycetes. Basidiomycetes and Deuteromycetes. In the present study we determined the baseline sensitivity of B. fuckeliana for fludioxonil in comparison to the dicarboximide vinclozolin. Subsequently these baselines were compared with the sensitivity of dicarboximide‐resistant field isolates and with resistant laboratory strains selected on media amendedwith vinclozotin or fludioxonil, respectively. Additionally, sensitivities of genetically homogeneous ascospore progenies of sexual crosses of sensitive isolates with dicarboximide‐resistant field isolates or resistant laboratory strains were compared to, the baselines. Baseline ECst, values for the inhibition of germination ranged from 0.07 to 0.20 μg ml‐1 of vinclozolin and for mycelial growth from 0.003 to 0.016 μg ml’ of fludioxonil and from 1.7 to 2.0 μg ml‐1 of vinclozolin and for mycelial growth from 0.003 to 0.016 μg ml‐1 of fludioxonil and from 0.13 to 0.27 μg ml‐1 of vinclozolin. Sensitivity to fludioxonil of all dicarboximide‐resistant field isolates did not differ from their baseline. However, resistant laboratory strains that were selected either on media amended with fludioxonil or vinclozolin showed decreased sensitivities to both active ingredients. All sexual progenies of the crosses described above were of the parental phenotypes. We found no independent segregation of the resistance markers.
Fingerprinting of Xanthomonas campestris pv. pelargonii and Related Pathovars Using Random‐Primed PCR
Authors: Sulzinski M. A. , Moorman G. W. , Schlagnhaufer B. , Romaine C. P.
Published: May 2008

Polymerase chain reaction (PCR) amplification of total DNA was evaluated as a method to distinguish Xanthomonas campestris pv. pelargonii from other pathovars within this species. Two sets of highly conserved enterobacterial consensus sequences were used as targets for PCR amplification: (a) enterobacterial repetitive intergenic consensus [ERIC] and (b) repetitive extragenic palindromic [REP] sequences. Nucleic acid was extracted from a total of 37 isolates of bacteria: 19 isolates ofX campestris pv. pelargonii and 18 isolates representing 10 other pathovars of X. campestris. After PCR amplification using the ERIC primer pair the DNA fingerprints of X. campestris pv, pelargonii contained two major DNA products (estimated size 500 and 740 pp) that were conserved among all 19 isolates. With the REP primer pair, the fingerprints were more complex and major DNA products ranging from ‐690 to 1650 bp were detected. Using information from both ERIC‐ and REP‐primed Imgerprints, the X. campestris pv. pelargonii fingerprints were distinguishable from the fingerprints of the other pathovars examined: pvs. citrumelo. citri, beganiae, vittans B and C. phaseoli. campestris, manihotis, juglandis, carotae and pruni.
An Electron Microscopic Study of the Infection of Spikelets of Rice by Pyricularia oryzae
Authors: Koga H.
Published: May 2008

Penetration and colonization of spikelet tissue of a susceptible line of rice. ZTS, by Pyricularia aryzae was investigated by scanning and transmission electron microscopy. Application of a modified embodding procedure in which the period of resin infiltration was extended, gave excellent fixation of the hard spikelet tissue. Conidia germinated to produce appressoria and the epidermal cell walls were penetrated within 24 h. Hyphae had colonized sclerenchyma, parenchyma, vascular bundles, andlarge trichomes within 48 h after inoculation. Invasion of the sclerenchyma appeared to occur through pit‐pairs, where the host cell wall is thin. Conidiophores erupted directly from the epidermis, from minute protuberances and from large trichomes on the spikelet 4 days after inoculation.
Relative Wilt‐Inducing Capacity of the Culture Filtrates of Isolates of Fusarium oxysporum f.sp. radicis‐lycopersici, the Tomato Crown and Root Rot Pathogen
Authors: Madhosingh C.
Published: May 2008

Cell‐free 30‐day‐old culture filtrates of 24 isolates of Fusarium oxysporum f.sp. radicis‐lycopersici (FORL) differed considerably in their capacity to induce wilting in 28‐day‐old tomato seedings and to inhibiting the germination of tomato seeds. The wilt effects ranged from mild on leaves and lateral stems, to total collapse of the seedlings in 24 h. Wilt, leaf curl and leaf chlorosis, appearing in this sequence, were the three symptoms clicited by the culture filtrates. Boiled and non‐boiled filtrates elicited similar sympotoms. The high wilt capacity filtrates were pH 7.2; the others were generally below pH 6. The high wilt capacity filtrates showed polyphenoloxidase activity but the overall pattern of this activity did not correlate consistently with wilt capacity. The majority of the lower wilt capacity filtrates showed a net inhibition of dihydroxy‐phenylalanine (DOPA) oxidation. The study suggests that the symptoms in the tomato seedlings were elicited by toxins in the culture filtrates. Further, it appears that the differences obtained in the wilt capacity of filtrates from the isolates were due, at least in part, to inherent differences in the concentration of the toxic factors. The rapidity of the onset of wilt, the total, collaps of filtrate‐treated seedlings and the absence of fungi in wilted seedlings suggest further that the operative mechanisms are physiological and biochemical and not impairment of the seedlings’ translocation system by physical blockage with mycelia.
Agarose Medium for Germination of Oospores of Phytophthora cactorum
Authors: Shim J. O. , Yu M. Q. , Ko W. H.
Published: May 2008

When oospores of Phytophthora caetorum from 30‐day‐old culture were treated with 0.25% KMnO4 for 20 min and incubated at 24°C under light for 10 days, 65–75% germinated on water agar and water agarose but only 1–21% germinated on V‐8 agar and S+L agar. Water agarose was selected because germinated oospores formed restrieted colonies on this medium that could be isolated easily. KMnO4 treatment killed sporangia, chlamydospores and mycelial fragments present in oospore suspensions. Under the above conditions, approximately 44% of oospores from 10‐day‐old culture germinated and the optimum germination rate of about 75% was obtained when oospores reached about 20 days old.
Studies on Variability of Peanut Clump Virus: Symptomatology and Serology
Authors: Manohar S. K. , Dollet M. , Dubern J. , Gargani D.
Published: May 2008

Intensive survcys of groundnut virus diseases were carried out in Senegal from 1986 to 1990. Peanut clump virus (PCV; furovirus group) was detected in several regions in groundnuts (Arachis hypogaea), showing typical symptoms namely, small dark green leaves, short petioles and internodes, and reduced shoot size resulting in a dwarfed and bushy appearance (clumping) of the infected plants. PCV was also detected in groundnuts exhibiting variable symptoms like chlorotic leaf spots, specking, chlorotic rings or ringspots, line patterns, vein yellowing, mottle or light mosaic etc. with or without clumping. Symptoms induced by these different isolates on the test plant Chenopodium amaranticolor also showed considerable variability. Serological studies of 41 isolates of PCV (collected from Senegal, Burkina Faso, Niger and India), using seven monoclonal antibodies in Triple Antibody Sandwich ELISA (TAS‐ELISA), permitted us to distinguish five different serogroups based on their reaction profiles. However, these did not correspond to the five groups formed in an arbitrary classification based on the symptomatology of C. amaranticolor. Serogroups do not correlate with the geographic origin.
Phenylalanine Ammonia‐lyase Activity in Barley After Infection with Bipolaris sorokiniana or Treatment with its Purified Xylanase
Authors: Peltonen S. , Karjalainen R.
Published: May 2008

Phenylalanine ammonia‐lyase (PAL) activity was determined from leaves and roots of two barley (Hordeum vulgare L.) cultivars after infection with a necrotrophic pathogen, Bipolaris sorokiniana (Sacc.) Shoem., and treatment with its purified xylanase. PAL activity increased in leaves of both cultivars 16 h after fungal inoculation but two phases, with activity peaks at 24–32 h and 40 h, were recorded only for the more resistant cultivar, Agneta. Attempts to use a PAL inhibitor, χ‐amin, ooxyacetic acid, to increase susceptibility to B. sorokiniana in barley leaves were unsuccessful. Treatments of leaves with purified xylanase resulted in more rapid (4–12 h after injection), although reduced, induction of PAL compared with fungal injection. The higher the concentration of xylanase applied the earlier the activity peaks were detected. Fungal inoculation only slightly increased PAL activity in barley roots while xylanase treatment had no effect. The basal level of PAL was however much higher in roots than in leaves. In wheat, Triticum aestivum L. resistant to B. sorokiniana, the time‐course of PAL induction after fungal infection and xylanase treatment resembled that for cv. Agneta, while in oats, Avena sativa L. (non‐host) PAL activity did not change after the treatments. The results suggest that the second phase of PAL induction, associated only with responses of barley cv. Agneta and wheat, is linked with their resistance to B. sorokiniana infection. The possible role of xylanase as an elicitor of PAL is discussed.
Evidence for Complementation of Plant Potyvirus Pathogenic Strains in Mixed Infection
Authors: Mansky L. M. , Durand D. P. , Hill J. H.
Published: May 2008

Several strains of soybean mosaic virus (SMV) can be differentiated on the basis of the phenotypic response of various soybean cultivars (e.g., the soybean line Williams ‘82 is susceptible to all SMV strains, whereas the lines P. I. 96983, L78‐379, and Davis are functionally immune to SMV strain G2 but susceptible to strains G7 and G7a). Inoculation of the immune lines with G2, followed 2 days later by inoculation with G7 or G7a, resulted in systemic spread of the avirulent SMV G2. Further evidence, suggests that complementation groups of SMV strains may exist.
Analysis of Variance‐Mean Relationships of Plant Diseases
Authors: Yang X. B.
Published: May 2008

Disease variance‐mean relationships and the underlying mechanisms were examined using three approaches. First, data on four foliar diseases were collected, the variance of a disease increased geometrically, reached the maximum, and decreased geometrically when disease means were low, mediate, and high, respectively. There were great variations of variance values in the mediate ranges. Second, it was mathematically proven that the variance of a disease has an upper limit of variance (Vmax)that follows a quadratic function. When a disease is rated in a range from 0 to C, the upper limit of variance (Vmax) follows a quadratic function as Vmax=CM‐M2 where M is disease mean. For the scale 0–10 or percentage [0–100]. the functions are Vmax= 10M‐M2 or Vmax=100M‐M2, respectively. A variance‐mean relationship is dis‐tributed within the region defined by the V,max function. Third, a spatio‐temporal simulation model was used to examine the effect of three spatial components, dispersal capacity, aggregation of initial inoculum, and geographic distribution of initial inoculum, on disease variance‐mean relationship. The variance values inreased as the dispersal capacity decreased. The variance values inreased when pattern of mitial inoculum changed from regular pattern to aggregation or as the degree of aggregation increased. There was an interactive, effect between the two components on the variance values. Furthermore, when epi‐demics started from situations having the same degree of aggregation but different geographic distributions for initial inoculum, the variance‐mean relationships weredifferent. Variance values varied greatly even the degree of aggregation was constant. The inportance of these results in relation to interpretation of field experiments was discussed.
Further evidence for the recognition of Ullucus Mild Mottle Virus as a Distinct Tobamovirus
Authors: Offei S. K. , Ibidapo O. , Brunt A. A. , Coutts R. H. A.
Published: May 2008

The affinities of Ullucus mild mottle virus (UMMV). purified by a modified procedure. were examined by immunoblotting and probing with antisera to five distinct tobamoviruses. RNA. isolated from purified virus, was used for in vitro protein translation in a wheat germ system and the products examined by denaturing polyacrylamide gel electrophoresis. The results of these investigations, together with a study of the double‐stranded RNAs associated with infection. confirm that UMMV is a distinct, tobamovirus which has close affinities with tobacco mosaic, tomato mosaic and cucumber green mottle tobamoviruses and more distant relationships with ribgrass mosaic and odontoglossum ringspot tobamoviruses.
Identification of Xanthomonas campestris pv. Juglandis from (Persian) English Walnut Nursery Trees in South Africa
Authors: Du Plessis H. J. , van der Westhuizen T. J.
Published: May 2008

Bacterial isolates producing yellowish colonies on Nutrient Agar were recovered from symptoms of suspect walnut blight disease on leaves of nursery trees in the southwestern Cape Province of South Africa. The isolates were identified by pathogenicity tests on leaves of walnut and plum trees in the greenhouse. Fifteen isolates from four cultivars at two nurseries produced typical lesions of blight on walnut and one isolate. typical lesions of bacterial spot disease on plum leaves. Cluster analysis was done on 28 characteristics recorded from colony growth. colour. form. and elevation on four different culture media, and starch hydrolysis on a semi‐selective medium for the isolation of Xanthomonas campestris pv. juglandis. Total DNA of the isolates was digested with restriction endonuclease Spel and resolved by contour‐clamped homogeneous electric field (CHEF) electrophoresis. Two phenotypic clusters were distinguished among the 15 South African and one reference strain of X.c.pv. juglandis at the 54%Ssm level. The isolate which induced disease symptoms on plum grouped with reference strains of Xanthomonas campestris pv. pruni in a third cluster. Two‐thirds of the isolates were not characterized on the semi‐selective medium for X.c. pv. juglandis. DNA restriction fragment banding patterns were similar for most isolates of X.c.juglandis in the same phenotypic cluster. However, DNA banding patterns were non‐distinct for some isolates with similar phenotypic characters. Phenotypic characteristics and DNA restriction fragment banding patterns of the isolates were not correlated with geographical origin or cultivar specificity.
Detection of Tobacco Rattle Virus in Potato Tubers and Roots by Polymerase Chain Reaction (PCR)
Authors: Weidemann H.‐L.
Published: May 2008

Tobacco rattle virus (TRV) was detected by PCR in potato tubers and in root samples. Oligonucleotide primers were synthesized to nucleotides of the 16 k protein gene of RNA‐1 of the TRV strain ‘SYM’. After phenol extraction of the total nucleic acids of the samples and reverse transcription. the PCR reaction mixture was subjected to 25 cycles and the amplification product was detected by electrophoresis. TRV RNA was found in roots and in freshly harvested tubers in September, as well as in tubers which were stored until March. This indicates that there was no elimination of TRV during the storage period. The field samples of potato cv. Désirée tested in September were symptomlessly infected. whereas the stored tubers of various cultivars showed, internal symptoms. Nucleic acids extracts of latently‐infected and spraing‐affected tubers inoculated on tobacco plants led to local necrotic rings. Nucleic acids from infected tobacco cv. Samsun plants led to systemic symptoms as well. TRV was identified by ISEM and ELISA only in the systemically‐infected tobacco plants, but not in the locally infected tobacco plants. This suggests the presence of the ‘NM’ type of TRV in tubers, which produces only RNA‐1 but no complete virus particles.
Routing of the G Protein During Maturation of Festuca Leaf Streak Rhabdovirus in its Plant Host
Authors: Lundsgaard T.
Published: May 2008

By immunogold labelling the location of Festuca leaf streak virus glycoprotein (FLSV‐G) was investigated in developing phloem and mature leaf parenchyma of Festuca gigantea infected with Festuca leaf streak virus (FLSV: Rhabdotiridae). In developing phloem cells, FLSV‐G was detected in endoplasmic reticulum (ER). at perinuclear membranes, and in assembled virions, but neither in Golgi stacks and Golgi vesicles nor at the plasma membrane of infected cells. These results indicate that FLSV‐G stays in the ER after transmembrane synthesis, and is not routed through the secretory pathway in F. gigantea. The membranous inclusions, present in infected mature leaf parenchyma cells were found to contain FLSV‐G. It is suggested that the, virus‐induced membranous inclusions have developed from FLSV‐G‐containing ER.

The residence of FLSV‐G in ER (present study) is in contrast to results with vesicular stomatitis virus (VSV; vertebrate rhabdovirus). Here the G protein is known to be routed to the plasma membrane through the secretory pathway.
A Stochastic Model Incorporating the Effect of Weather Conditions on Anthracnose Development in Stylosanthes scabra
Authors: Chakraborty S. , Smyth G. K.
Published: May 2008

Spatial and temporal progress of anthracnose caused by Colletotrichum gloeosporioides in quantitatively resistant accessions of the tropical pasture legume Stylosanthes scabra were studied in a field experiment at the Southedge Research Station, Queensland, Australia. In a previously published work a conditional ordinal logistic regression model was developed to explain the probability of a plant developing a given disease severity level, depending on its previous disease state and that of its neighbours. In the present study this model is augmented to incorporate the effects of three weather variables which were measured daily during a growing season. Two approaches were used: (a) threshold values for relative humidity (RH), rainfall and net evaporation were used to classify days as suitable or unsuitable for anthracnose growth; (b) days were assumed to vary continuously in their rate of anthracnose growth depending on the numerical values of the weather variables. High 9am RH, low net evaporation and low 9am temperatures are significantly associated with anthracnose growth. Net evaporation proved to be a better index than rainfall and heavy rainfall was not conducive to high levels of anthracnose; however, rainfall was useful once evaporation was taken into account. The effect of 9am RH can be described either by a threshold value around 70% or by a quadratic function. A two‐variable model with net evaporation and log(rain+1) explains 97.6% of the available deviance.
Rhizoctonia spp. Associated with Container‐Grown Ericaceous Plants in Scotland
Authors: Litterick A. M. , McQuilken M. P. , Holmes S. J.
Published: May 2008

Fungi with Rhizoctonia‐like mycelia were isolated from the foliage, stem‐base and roots of ericaceous plants collected from nurseries in Scotland. Isolated fungi were identified as either binucleate Rhizoctonia spp. or Rhizoctonia solani on the basis of hyphal characteristics and nuclear number. The optimum temperature range for growth of binucleate Rhizoctonia spp. and R. solani was 20 and 25 C, resepctively. All isolates tested for pathogenicity caused foliar browning, and webs of mycelial growth were observed on dead and dying foliage. Binucleate Rhizoctonia spp. and R. solani are recorded for the first time on container‐grown ericaceous plants in Scotland.
Development of Hemileia vastatrix in Coffee Plants With Genetic or Induced Resistance
Authors: Martins E. M. F. , Moraes W. B. C.
Published: May 2008

Systemic resistance to coffee rust (Hemileia vastatrix) was induced in susceptible cv, ‘Mundo Novo’ by spraying foliage with a yeast filtrate. The stages of fungal development were compared in leaves of untreated (MN), induced ‘Mundo Novo’ (MN‐I) and coffee rust resistant segregants of the hybrid ‘Sarchimor’ (Sch). Development of H. vastatrix was observed at intervals of 228 h after inoculation. The expression of resistance was detected 48–72 h after inoculation. In Sch, it occurred at the one haustorial mother cell (HMC) stage, whereas in MN‐I, it occurred at the 2nd HMC stage. In Sch the majority of aborted colonies were associated with necrotic host cells, and the collapsed fungal hyphae exhibited a yellow autofluorescence which was observed in necrotic cells of the host. In MN‐I, 80% of the colonies could not be visualized 72 h after inoculation and host cells at the infection sites were not necrotic.
Septoria Leaf Speck, a New Disease of Sunflower, Caused by Septoria helianthina sp. nov.
Authors: Petrov Marija , Arsenijevic M.
Published: May 2008

Many strains of a pathogenic fungus were isolated from diseased sunflower leaf tissue. According to their characteristics they belonged to the genus Septoria. Leaf speck symptoms, characteristic for spontaneous infection, were also reproduced by artificial inoculation of sunflower plants in the greenhouse.

Comparing the morphological, cultural and pathogenic properties of the isolated fungus with other sunflower pathogens, it was indicated that the strains, originating from diseased sunflower leaves represented a new, so far not described species. Therefore, for the causal agent of this disease, the name Septoria helianthina Petrov & Arsenijevic was suggested.
Molecular Characterization of the Plant Pathogen Verticillium dahliae Kleb. Using RAPD‐PCR and Sequencing of the 18SrRNA‐Gene
Authors: Messner R. , Schweigrofler W. , Ibl M. , Berg G. , Prillinger H.
Published: May 2008

Thirty‐four isolates of Verticillium dahliae Kleb. from nine different genera of dicotyledonous host plants and a broad range of geographic regions were analysed genotypically, Random amplified polymorphic DNA (RAPD) markers were used for the estimation of the genetic variability within the species. Using four primers for the analysis, 79 distinct fragments were obtained. The derived phenogram clustered the isolates in two main groups; one consisted almost entirely of V. dahliae isolates from oilseed rape (Brassica napus napus), the other group comprised isolates from a wide range of host plants. No correlation between geographic location of the isolates and the RAPD‐pattern was observed.

Sequencing of the gene for the 18SrRNA and calculation of the phylogenetic tree integrated the deuteromycetous fungus V. dahliae into the sexual system of the filamentous ascomycetes.
Relationships Among Group IV Phytophthora Species Inferred by Restriction Analysis of the ITS2 Region
Authors: Tooley P. W. , Carras M. M. , Falkenstein K. F.
Published: May 2008

The polymerase chain reaction (PCR) was used to amplify the ITS2 region of nuclear ribosomal DNA from six Phytophthora species which comprise taxonomic Group IV. Digestion of the ca. 600 bp PCR product with restriction enzymes Alu I, Dra I, Hha I, Hinf I, Msp I, and Taq I revealed variation which allowed relationships among the species to be assessed. P. infestans, P. mirabilis and P. phaseoli were indistinguishable from one another with all enzymes tested. With Alu I and Taq I. P. ilicis, P. colocasiae. and P. hibernalis each showed unique banding patterns different from the common banding pattern shared by P. infestans. P. mirabilis. and P. hibernalis. Dra I allowed differentiation of P. ilicis and P. colocasiae from P. infestans, P. mirabilis, P. phaseoli, and P. hibernalis. all of which shared a common banding pattern. Hha I allowed differentiation of P. colocasiae and P. hibernalis from P. infestans, P. mirabilis, P. phaseoli, and P. ilicis. Hinf I allowed differentiation of P. ilicis and P. hibernalis, (each of which showed a unique banding pattern) from P. infestans, P. mirabilis, P. phaseoli, and P. colocasiae. Msp I allowed differentiation of P. hibernalis from the other five species. Species groupings determined by restriction analysis of ITS2 were consistent with those based on morphological criteria. These results show that restriction analysis of PCR‐amplified TS2 regions can be useful as an adjunct to morphological criteria in Phytophthora species identification.
Extraction of DNA from Phytophthora infestans Using QIAGEN Columns
Authors: Tooley P. W. , Carras M. M.
Published: May 2008

High molecular weight DNA of Phytophthora infestans was extracted using a modification of the commercial QIAGEN column procedure. Both a ‘maxi’ and ‘mini’ procedure are described. The maxi procedure utilizes a QIAGEN‐tip 500 column while the mini procedure utilizes a QIAGEN‐tip 20 column. When fungal protoplasts were used as starting material from 9 g (fresh weight) of mycelium, nearly 500 μg of DNA in the size range of 20–200 kb was obtained and the product was successfully used in construction of a lambda genomic library. The modified QIAGBN method can replace the more timeconsuming, and expensive cesium chloride density gradient centrifugation for extraction of ultra‐pure DNA from P. infestans.
Incorporating an Asymptotic Parameter into the Weibull Model to Describe Plant Disease Progress
Authors: Xiao C. L. , Subbarao K. V. , Zeng S. M.
Published: May 2008

The Weibull model is a flexible growth model that describes both general population growth and plant disease progress. However, lack of an asymptotic parameter has limited its wider application. In the present study, an asymptotic parameter K was introduced into the original Weibull model, written as; y=K{1 − exp [− (t−a)c]}, in which a, b, c and K are location, scale, shape, and asymptotic parameters, respectively, y is the proportion of disease and t is time. A wide range of simulated disease progress data sets were generated using logistic, Gompertz and monomolecular models by specifying different parameter values, and fitted to both original and modified Weibull models. The modified model provided statistically better fits for all data than the original model. The modified model can thus improve the curve‐fitting ability of the original model which often failed to converge, especially when the asymptote is less than 1.0. Actual disease progress data on wheat leaf rust and tomato root rot with different asymptotic values were also used to compare the original and modified Weibull models. The modified model provided a statistically better fit than the original model, and model estimates of asymptotic parameter K were nearly identical to the actual disease maxima reflecting the characteristics of the host‐pathosystem. Comparison of logistic, Gompertz, and Weibull models including parameter K by fitting to the observed data on wheat leaf rust and tomato root rot revealed the applicability of the modified Weibull model, which in a majority of cases provided a statistically superior fit.
Characteristics of a PCR‐Based Assay for In Planta Detection of Xanthomonas campestris pv. pelargonii
Authors: Sulzinski M. A. , Moorman G. W. , Schlagnhaufer B. , Romaine C. P.
Published: May 2008

Polymerase chain reaction (PCR) amplification was carried out with a primer pair targeting a sequence in the genome of Xanthomonas campestris pv. pelargonii, the causative agent of bacterial blight in geraniums. PCR amplification with the primer pair XcpMl/XcpM2 using total nucleic acid preparations from 22 geographicallydiverse isolates of X. campestris pv. pelargonii generated a major 197 bp DNA product. In contrast, no major amplification products were consistently generated from 12 other pathovars of X. campestris or from 19 isolates representing 10 different plant pathogenic bacteria, including two other bacterial pathogens of geraniums, Corynebacterium fascians and Pseudomonas cichorii. After PCR using this primer pair, between 1380 and 13800 copies of the X, campestris pv. pelargonii bacterial DNA target as template were detected by ethidium bromide staining of agarose gels, and between 13.8 and 138 copies by blot hybridization to a pathovar‐specific biotinylated probe. Similarly, between 630 and 6300 colonyforming units (CFU) of X. campestris pv. pelargonii could be detected after ethidium bromide staining of agarose gels, and between 63 and 630 CFU after blot hybridization. The PCR‐based assay was used to identify X. campestris pv. pelargonii in diseased geraniums; whereas discrete amplification products were not obtained with healthy plants.
Genetic Relatedness Among Strains of Heterobasidion annosum as Detected by Random Amplified Polymorphic DNA Markers
Authors: Karjalainen R.
Published: May 2008

Heterobasidion annosum, the casual agent of root and butt rots of trees is one of the most important plant pathogens in temperate coniferous regions of the world. It is comprised of several intersterility groups with different host preferences. Of the H. annosum isolates from various geographical regions belonging to various intersterility groups, 36 showed group‐specific banding patterns in RAPD assay. More polymorphisms were found within the S‐ and F‐group isolates than in the P group. Genetic similarities among the isolates were determined by UPGMA clustering revealing the presence of four major clusters: P, S, F, and the North American S. The P group was the most distinctive of all the other groups, while the European S and F and the North American S were more closely related. The P group showed only 20% similarity to the other groups and may be referred to as a subspecies. The North American S group was separate from the European S group. The potential influence of the historical spread of coniferous trees in the isolate genetic differentiation in Europe is discussed.