bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyrenophora japonica occurring on barley in South Africa
Authors: LOUW J. P. J. , CROUS P. W. , HOLZ G.
Published: April 2007

A Pyrenophora teleomorph was recently found on barley stubble in South Africa. Single‐ascospore isolates, mated on water agar containing sterile pieces of barley stubble, produced the teleomorph within 12 months of incubation at 15°C in the dark. Based on morphological characteristics and symptom expression on barley plants, the teleomorph is ascribed to P. japonica (anamorph Drechslera tuberosa). This is the first report describing the occurrence of the teleomorph of D. tuberosa in South Africa.
Use of soil solarization for controlling bacterial canker of tomato in plastic houses in Greece
Authors: ANTONIOU P. P. , TJAMOS E. C. , PANAGOPOULOS C. G.
Published: April 2007

Soil solarization provided effective control of bacterial canker of tomato in plastic houses. Trials in plastic houses in Preveza County, Greece, during the period 1990–1992 showed that soil solarization (approximately 6 weeks of soil mulching with transparent polyethylene sheets) drastically reduced disease incidence throughout the cropping season. In contrast, soil fumigation with a recommended rate of methyl bromide (70 g/m2) was ineffective. Both wild‐type and antibiotic‐resistant strains of Clavibacter michiganensis subsp. michiganensis, growing on Nutrient Agar Glycerol (NAG) medium within covered and screwed vials and embedded at various soil depths (5, 15 or 25 cm) before soil solarization, were studied. Weekly sampling of bacteria during treatment showed a sharp decline of populations in the solarized soil compared to the non‐treated control plots 4–6 weeks after soil tarping. Populations of marked strains infiltrated into tomato stem segments and buried in the soil decreased significantly after 5–6 weeks of solarization compared to non‐treated control plots. The data presented here suggest that soil solarization is useful for the control of bacterial canker of tomato in plastic houses in Greece.
Effectiveness of systemic resistance in bean against foliar and soilborne pathogens as induced by biological and chemical means
Authors: DANN E.K. , DEVERALL B.J.
Published: April 2007

Unifoliate leaves of 9‐day‐old green bean, Phaseolus vulgaris cv. Redlands Pioneer, were inoculated with 104 conidia/ml Colletotrichum lindemuthianum, causing local lesions, or sprayed with 20 μg 2, 6‐dichloro‐isonicotinic acid/ml formulated by Ciba‐Geigy Ltd as CGA 41396. At various times afterwards (7–16 days), first, second or third trifoliate leaves of these plants were challenge‐inoculated with 105 conidia/ml C. lindemuthianum or with the rust pathogen, Uromyces appendiculatus. The numbers of anthracnose lesions or rust uredinia resulting from challenge‐inoculation were reduced to similar extents by both pre‐treatments compared with control plants. Halo blight, caused by Pseudomonas syringae pv. phaseolicola, was reduced in first trifoliates following treatment of unifoliate leaves 6 days earlier with CGA 41396. Induced resistance to root‐infecting pathogens was not observed when stems of either 14‐ or 16‐day‐old plants were inoculated with mycelial plugs of Fusarium solani f. sp. phaseoli, or when 11‐ and 15‐day‐old plants were inoculated with Rhizoctonia sp., Treatment with CGA 41396 did not protect seedlings when they were transplanted into a mix containing the Fusarium sp. 1 day later.
Biocontrol of seedling diseases of barley and wheat caused by Fusarium culmorum and Bipolaris sorokiniana: effects of selected fungal antagonists on growth and yield components
Authors: KNUDSEN I. M. B. , HOCKENHULL J. , JENSEN D. F.
Published: April 2007

The purpose of this study was to verify, under natural conditions, biological control effects obtained in a former screening programme against Fusarium culmorum. The most successful antagonists against seedborne Fusarium culmorum and Bipolaris sorokiniana were isolates of Chaetomium sp., Idriella bolleyi and Gliocladium roseum. These results were also obtained when the antagonists were applied to B. sorokiniana‐infected barley sown in field soil in pots. In field experiments, G. roseum gave the best control of F. culmorum in winter wheat. One month after sowing, germination increased by 170%, the disease index decreased by 73% and plant dry weight increased by 25%, compared to untreated plots. At harvest, the number of tillers per row was found to have increased by 53%, yield had increased by 160% and the 1000‐grain weight had increased by 4%. For all evaluated parameters the effect was significantly different from the untreated plots and not significantly different from the plots treated with the fungicide, Sibutol LS 280. I. bolleyi gave a lower but still significantly effective control, when evaluated for disease index and numbers of tillers per row, while Chaetomium sp. did not show any reduction in the disease. Furthermore, in field experiments using barley infected with B. sorokiniana, a significant effect of G. roseum was demonstrated as increased plant dry weight after 1 month and increased 1000‐grain weight at harvest. The disease‐controlling effect of G. roseum on F. culmorum was shown in a field experiment with spring barley.
Studies on the epidemiology of the tar spot disease complex of maize in Mexico
Authors: HOCK J. , KRANZ J. , RENFRO B. L.
Published: April 2007

During the period 1986–1988 field studies were conducted on the epidemiology of the tar spot disease complex (TDC) of maize (Zea mays) caused by Phyllachora maydis, Monographella maydis and Coniothyrium phyllachorae. Under field conditions we found that P. maydis symptoms always appeared first, followed by symptoms of either M. maydis or C. phyllachorae. M. maydis causes leaf necrosis and has the most devastating effect. The primary symptoms covered about 12% of the leaf area below the ear leaf, whereas the total necrotic leaf area amounted to 30–60%, here considered as a secondary effect. Maximum TDC severity occurred during the winter season of 1988, which was characterized by a temperature range of 17–22°C, a mean RH >75%, and > 7h of leaf wetness per night. The highest numbers of windborne ascospores of P. maydis were trapped at an RH > 85% and at temperatures of 17 to 23°C in the winter of 1987 and 1988, although large numbers were also caught at temperatures of >23°C and RH <70%. Spore release was strongly influenced by light conditions and followed a similar diurnal curve throughout three seasons, reaching a maximum at 17.00–21.00 hours. The spread off. maydis within the field was very homogeneous. The incubation period of P. maydis was 12 to 15 days, and most of the ascospores were released within 3 weeks after formation of the ascostromata. M. maydis inoculum in plant debris was reduced by 90% within 3 to 4 months.
Focus expansion of bean rust in cultivar mixtures
Authors: ASSEFA HABTU , VAN DEN BOSCH F , ZADOKS J. C.
Published: April 2007

Radial expansion of foci in mixtures of susceptible and resistant bean cultivars was studied at two sites in Ethiopia. The foci expanded in a wave‐like fashion. At Ambo (1990), radial expansion velocity ranged from 6 cm per day in mixtures with 20% susceptible plants to 15 cm per day in plots with the susceptible plants only. At Debre Zeit, the velocity ranged from 3 cm per day in a mixture with 20% susceptible plants to 16 cm per day in plots with 100% susceptible plants. At both sites the radial expansion velocity of foci correlated linearly with the logarithm of the fraction of susceptible plants in the mixture. Velocities of focus expansion at Ambo and Debre Zeit were approximately equal in plots consisting of susceptible plants only. At lower proportions of susceptible plants the velocities at Debre Zeit were lower than at Ambo. Indications were given as to the environmental factors responsible for the observed difference between sites. At each site, the variation between plots showed a clear spatial pattern, probably due to environmental factors.
Biological diversity of cauliflower mosaic virus isolates expressed in two Brassica species
Authors: AL‐KAFF N. S. , COVEY S. N.
Published: April 2007

Infection characteristics and symptom pathology of 39 isolates of cauliflower mosaic virus (CaMV), obtained worldwide, were compared following infection of a susceptible host (Brassica‐rapa‐rapifera‐turnip) and a tolerant host (Brassica oleracea‐gongylodes‐kohlrabi). Considerable variation in symptom expression between isolates was observed in turnip plants. Local lesions appeared between 4 and >10 days post inoculation (dpi) and systemic symptoms appeared from 10 to 20 dpi depending upon the CaMV isolate. Leaf coloration effects due to systemic infection ranged from generation of dark green tissue through various patterns of vein clearing and vein banding to severe chlorosis. Plant distortions in turnip varied from mild to severe stunting, and various types of leaf wrinkling and rugosity. In contrast, symptoms caused by the same CaMV isolates in kohlrabi were restricted to older leaves and were much milder, showing vein clearing, some chlorosis, but no plant distortions. Kohlrabi plants infected by all isolates tested eventually showed recovery and became asymptomatic. One symptom character in turnip, veinlet necrosis, was dependent upon time of inoculation rather than infection by a particular isolate. Virus titre was estimated by dot‐blot analysis of CaMV DNA. The greatest difference in viral DNA amounts was observed between turnip and kohlrabi plants for all isolates. A significant decline in viral DNA occurred in kohlrabi, concomitant with plant recovery from infection. Variations in virus titre observed early in infection (10 dpi) tended to become more uniform with time. We observed no clear correlation between virus titre and symptom type and severity in turnip, although plants infected with viral isolates producing mild symptoms generally, but not always, contained less viral DNA than isolates causing more severe symptoms. The great variety of CaMV biotypes we have characterized offer considerable scope for investigating mechanisms of plant viral pathogenesis.
Variation for pathogenicity among isolates of bean common mosaic virus in Africa and a reinterpretation of the genetic relationship between cultivars of Phaseolus vulgaris and pathotypes of BCMV
Authors: SPENCE N. J. , WALKEY D. G. A.
Published: April 2007

Bean common mosaic virus (BCMV) isolates were collected from crops of Phaseolus vulgaris (bean) and from wild legume species in 13 African countries. Isolates of pathotype VIa from both beans and wild legume species were predominant in central, eastern and southern Africa. Isolates of pathotypes I, III, IVa, IVb and Va were also found. Some isolates did not conform to previously published pathotypes, and therefore represent records of novel pathotypes. The susceptibility of various wild legume species to BCMV was investigated and isolates of the virus obtained from Crotalaria incana, Rhynchosia sp., Macroptilium atropurpureum and Cassia occidentalis (synonym Senna occidentalis) were aphid‐transmitted both from P. vulgaris to their original host species and to P. vulgaris. Isolates of BCMV from wild legume species were seed‐transmitted in bean and in several other legume species. The natural occurrence of BCMV in wild legume species in Africa is probably a significant factor in the ecology and epidemiology of the virus and possibly the evolution of isolates of the ‘A’ serotype which induce necrotic reactions in cultivars carrying the I gene for resistance. The occurrence of viruses other than BCMV from P. vulgaris and other legume hosts is also reported. The gene‐for‐gene model described by Drijfhout (1978) is reinterpreted to explain the variation for pathogenicity, and it is proposed that there may be genes which control the temperature sensitivity of necrosis in combination with the I gene.
Variation in the Fusarium section Liseola: pathogenicity and genetic studies of isolates of Fusarium moniliforme Sheldon from different hosts in Ghana
Authors: AMOAH B. K. , REZANOOR H. N. , NICHOLSON P. , MACDONALD M. V.
Published: April 2007

Fusarium moniliforme, the imperfect stage of the ascomycete Gibberella fujikuroi, is an economically important pathogen with a very wide host range. The genetic characteristics of isolates of the fungus collected from different regions of Ghana from maize, rice and sorghum were determined using the random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) techniques. The pathogenicity of the isolates was also compared on maize and rice. DNA fingerprints detected as RFLPs of ribosomal DNA and RAPDs separated the isolates into discrete groups which were generally host‐related. The possibility of a sub‐structuring of the maize population of the fungus into tissue‐related subgroups was suggested by the results. A dendrogram of the relatedness of the isolates is presented. However, the pathogenicity of the isolates on rice, measured by their ability to cause ‘bakanae’ symptoms, did not resolve the isolates into the clearly defined groups suggested by the genetic studies, and maize isolates of the fungus could cause ‘bakanae’ symptoms to the same extent as rice isolates. Similarly, some isolates identified as rice‐type isolates caused as much shoot stunting in maize as maize isolates. However, the effects of the isolates on root growth of maize seedlings showed a broad correlation with the defined genetic groups, with maize isolates of the fungus showing the greatest tendency to cause root stunting
Accumulation of isoflavonoid phytoalexins in leaves of Arachis hypogaea differing in reaction to rust (Puccinia arachidis) and early leafspot (Cercospora arachidicola)
Authors: EDWARDS C. , STRANGE R. N. , COLE D. L.
Published: April 2007

Groundnut leaves, naturally infected in the field with Cercospora arachidicola or artificially infected in the greenhouse with C. arachidicola or Puccinia arachidis, accumulated isoflavonoid phytoalexins. Major compounds included medicarpin, formononetin, demethylmedicarpin, three isoflavanones and the isoflavone, daidzein. In both greenhouse and field experiments cv. Egret was less susceptible than cv. P84/5/244 to both pathogens, and accumulated phytoalexin (medicarpin) concentrations which were up to three times greater. Higher concentrations and greater variation of phytoalexins were detected when both cultivars were infected with C. arachidicola than when they were infected with P. arachidis.
Physiological alterations in pepper during wilt induced by Phytophthora capsici and soil water deficit
Authors: AGUIRREOLEA J. , IRIGOYEN J. , SÁNCHEZ‐DÍAZ M. , SALAVERRI J.
Published: April 2007

Capsicum annuum cv. Morrón inoculated at the collar with Phytophthora capsici developed cortical stem necrosis and severe wilting soon after infection. Water potential, specific conductivity, ethylene evolution, CO2 and water vapour exchange rates and chlorophyll content were monitored during symptom development. Well watered and non‐inoculated water‐stressed plants were used as controls. Necrosis developed upwards from the collar 4 days after inoculation coupled with a 80% reduction in hydraulic conductivity. Leaf water potential progressively decreased from ‐0.17 to ‐2.41 MPa in 2 weeks. The rate of ethylene evolution was significantly higher in infected than in non‐inoculated stressed plants for similar water potentials and originated in the necrotic segment of disease stem tissue. Net photosynthesis and leaf conductance markedly decreased (74%) 4 days after infection, coupled to a burst in dark respiration (1.5 times) but were not associated with water stress alone. This suggests that the pathogen reduced photosynthesis initially through stomatal closure which was not directly mediated by water stress. The possible implication of ethylene in impaired stem conductivity and altered gas exchange of infected plants is discussed.
Effects of SSF‐126, a novel alkoxyiminoacetamide blasticide, on mycelial growth and oxygen consumption of Pyricularia oryzae
Authors: SHIRANE N. , MASUKO M. , TAKEDA R.
Published: April 2007

SSF‐126, (E)‐2‐methoxyimino‐N‐methyl‐2‐ (2‐phenoxyphenyl)acetamide, inhibited mycelial growth (IC50 7·7 μM) of Pyricularia oryzae. The inhibited mycelium, which was incubated for 30 h in the presence of SSF‐126, grew vigorously after transfer to a fungicide‐free medium, indicating that SSF‐126 is a fungistatic compound. SSF‐126 strongly inhibited oxygen consumption by P. oryzae at low concentrations (IC50 0·8 μM). However, the initial inhibition of oxygen consumption was followed by normal mycelial respiration that was insensitive to SSF‐126. These results suggest that SSF‐126 has a new type of antifungal action.
Early development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to temperature and leaf wetness.
Authors: FIGUEROA L. , FITT B. D. L. , WELHAM S. J. , SHAW M.W. , McCARTNEY H. A.
Published: April 2007

In controlled environment experiments to study early development of light leaf spot, lesions developed with leaf wetness durations of 16 to 48 h after inoculation of oilseed rape with conidial suspensions of Pyrenopeziza brassicae at 12 or 18°C, but not with leaf wetness durations of 0 to 13h. The incubation period was 21 to 22 days at 12°C and 14 to 18 days at 18°C for leaf wetness durations of 16 to 48 h. The latent period was 21 to 23 days at 12°C and 18 to 19 days at 18°C, and the total number of lesions increased with increasing leaf wetness duration at both temperatures. In field experiments, light leaf spot always developed on oilseed rape with a leaf wetness duration of 48 h after inoculation in both 1990/1991 and 1991/1992, but the percentage leaf area affected was less on plants placed in an oilseed rape crop than on those placed in a glasshouse. Plants moved to an oilseed rape crop immediately after inoculation nearly always developed light leaf spot symptoms when they were inoculated between 19 October 1990 and 1 March 1991 or between 27 September 1991 and 14 February 1992, but plants inoculated between 31 August and 16 October 1990 or on 20 September 1991, when estimated leaf wetness duration was less than 16 h for several days after they were placed in crops, did not develop symptoms. The latent period of light leaf spot on plants transferred to the oilseed rape crop was 15 to 40 days, and there was an approximately linear relationship between 1 (latent period) and mean temperature during this period. The accumulated temperature during the latent period ranged from c. 150 to 250 day‐degrees. The severity of lesions on these plants increased with increasing temperature from 5 to 15°C.
Incidence and control of barley leaf stripe (Pyrenophora graminea) in Scottish barley during the period 1987–1992
Authors: COCKERELL V. , RENNIE W. J. , JACKS M.
Published: April 2007

The incidence of Pyrenophora graminea was determined in winter and spring barley seed harvested in each of the 6 years 1987 to 1992. The occurrence of P. graminea was highest in spring barley seed harvested in 1989 and 1990, with 69% of samples in 1989 and 82% in 1990 infected. The mean infection levels were 6·1% in 1989 and 7·5% in 1990. The introduction of a voluntary Code of Practice in January 1991 significantly reduced infection: in 1992 only 10% of spring barley samples were infected, and the mean infection level was less than 0·2%. In spring barley, there was a significant relationship between the level of seed infection and the percentage of diseased tillers in commercial crops (r= 0·890, P < 0·001). However, tiller infection was consistently lower than seed infection. During the period of the study the mean annual leaf stripe infection on winter barley seed did not exceed 1%.
Root exudates associated with the resistance of four chickpea cultivars (Cicer arietinum) to two races of Fusarium oxysporum f.sp. ciceri
Authors: STEVENSON P. C. , PADGHAM D. E. , HAWARE M. P.
Published: April 2007

The germination of race 1 spores of Fusarium oxysporum f. sp. ciceri was significantly inhibited by the root exudate of the wilt‐resistant chickpea cvs CPS1 and WR315 compared to untreated spores and spores treated with root exudates from susceptible cultivars. The effect was concentration dependent, such that the exudate from 1 g of root in 2 ml of water almost completely inhibited spore germination, whereas the exudate from 1 g of root in 20 ml water did not do so. The inhibitory effects of the active exudates were negated when the apolar components of the exudates were removed by extraction with ethyl acetate. The root exudates of the susceptible cv. JG62 and the late wilting cv. H208 did not inhibit germination. The hyphal growth of germinated spores was also strongly inhibited by the concentrated exudates of CPS1 and WR315, and diluted exudates were less potent. The highest concentration of the exudate of the susceptible cv. JG62 showed some inhibition of hyphal growth, whereas none of the exudates of H208 were found to contain any antifungal activity. The effect of the exudates on the spores of race 2 was similar to that reported for race 1, except that the water‐soluble components of the crude root exudate of WR315 after ethyl acetate extraction were also found to inhibit germination significantly. Overall, the spores of race 2 appeared to be more susceptible to the effects of the exudates. The ethyl acetate fractions of the root exudates of CPS1 and WR315 strongly inhibited germination and hyphal growth of both race 1 and race 2, the effect being concentration dependent. The results suggest that the resistance of chickpeas to vascular wilt depends, at least in part, upon the antifungal activity of the root exudates. Differences in the expression of resistance in the field could depend upon the concentration or rate of production of constitutive antifungal components by the root.
Effects of cucumber genotype on the induction of resistance to powdery mildew, Sphaerotheca fuliginea, by 2, 6‐dichloroisonicotinic acid
Authors: HIJWEGEN T. , VERHAAR M.A.
Published: April 2007

Conspicuous differences in inducibility of resistance to powdery mildew between susceptible and partially resistant cucumber cultivars were found when 2, 6‐dichloroisonicotinic acid (INA) was used as a model substance. In the partially resistant cv. Flamingo, EC50 was approximately 0·25 mg/1. In the susceptible cvs Corona and Lange Groene Gigant it was approximately 6mg/1. In greenhouse experiments with cv. Flamingo, powdery mildew could be well controlled with fortnightly applications in doses as low as 0·5 mg/1. The effect was highly cumulative.
Temporal patterns of airborne conidia ofPodosphaera leucotricha, causal agent of apple powdery mildew
Authors: Xu X.‐M. , Butt D. J. , Ridout U. S.
Published: April 2007

In each of the five years 1969 and 1971‐1974 inclusive a volumetric spore trap was used in an apple orchard to monitor changes in the number of airborne conidia ofPodosphaera leucotricha, the causal agent of apple powdery mildew. The number of trapped conidia varied greatly between years. Time‐series analyses, using autoregressive integrated moving average (ARIMA) models, revealed that the temporal pattern of the number of airborne conidia was similar in all years, generally following a diurnal pattern with an afternoon peak. A strong correlation between consecutive hourly counts indicated that the number of trapped conidia depended on the strength of sporulating sources. Using the time‐series transfer function (TF) method, it was shown that in each year the most important weather variables influencing the number of airborne conidia were vapour pressure deficit (VPD) and rainfall. Variation between years in the dynamic effects of these variables on conidium numbers was detected, and may reflect weather differences between years. Stepwise regression analysis was applied to the combined daily data for 1973 and 1974 using a subset of weather variables as independent variables, chosen on the basis of TF analysis. A resulting regression model accurately predicted the temporal pattern of conidium numbers (expressed as a percentage of the maximum daily number trapped in the same year) in both years. When this model was applied to the other three years there was good agreement between predicted and observed temporal patterns. Application of this regression model for practical disease control is discussed.
Population dynamics of epiphytic mycoflora and occurrence of bunch rots of wine grapes as influenced by leaf removal
Authors: Duncan R. A. , Stapleton J. J. , LEAVITT G. M.
Published: April 2007

Population dynamics of epiphytic fungi associated with the summer bunch rot complex of five wine grape (Vitis vinifera) varieties in commercial vineyards in the San Joaquin Valley of California were monitored every two weeks by berry washings during 1989‐1992. Vines in the five replicated experiments were subjected to basal leaf removal or left unaltered. Although numerous genera of fungi were isolated, species of Cladosporium, Aspergillus, Penicillium and Alternaria predominated. Population densities of most fungal taxa increased at or after véraison. Leaf removal in the fruiting zones of bilateral cordon‐trained vines generally reduced (P >0·05) mid to late season numbers of epiphytic mycoflora: species of Penicillium, Botrytis and Aspergillus were most commonly reduced. Populations of Alternaria spp. and yeasts were not consistently affected by leaf removal. Numbers of fungi were no lower on berries when leaves were removed from both sides of vines than when leaves were removed only from the shaded side. Incidence and severity of bunch rots (sour rot, rots caused by Botrytis cinerea, Aspergillus niger, and total rot) at harvest were consistently reduced where leaves had been removed in comparison to vines where no leaves were removed. In one experiment, berries from vines sprayed with the grower's choice of pesticides at 50% or 100% of label rates had similar numbers of epiphytic mycoflora in both cases frequently lower than those from unsprayed controls. There was a significant interaction between chemical rate and leaf removal on the incidence of sour rot at harvest. Timing and extent of leaf removal did not affect population dynamics of epiphytic fungi, or incidence or severity of bunch rots (P≤0·05) at harvest in other trials.
Evidence for the physical integrity of flavescence dorée phytoplasmas purified by immunoaffinity from infected plants or leafhoppers and the plant pathogenicity of phytoplasmas from leafhoppers
Authors: SEDDAS A. , MEIGNOZ R. , KUSZALA C. , BOUDON‐PADIEU E.
Published: April 2007

Phytoplasmas were extracted from flavescence dorée‐infected broadbean (Vicia faba) using a vacuole isolation medium, and were immunoaffinity purified from infected leafhoppers. Purified phytoplasmas from both host sources were immunolabelled and observed under the electron microscope. The infectivity of the purified phytoplasmas from leafhoppers was checked by injecting healthy leafhoppers which were then allowed to feed on healthy V. faba seedlings. The appearance of typical symptoms in these plants, and the positive results obtained in ELISA with extracts of some of the injected leafhoppers and with symptomatic V. faba, indicated that the purified phytoplasmas had retained their infectivity and had multiplied in the injected leafhoppers which had become infective. These results support a previous report that phytoplasmas purified by immunoaffinity chromatography are well preserved.
An unusual Phytophthora associated with widespread alder mortality in Britain
Authors: BRASIER C. M. , ROSE J. , GIBBS J. N.
Published: April 2007

During 1993 and 1994 an unusual Phytophthora was consistently isolated from bark lesions at the stem bases of dying alder in Southern Britain. The Phytophthora resembles P. cambivora in both its gametangial and sporangial morphology. However, it is distinct from this species in being homothallic rather than outcrossing; in producing a significant proportion of small and sometimes partially developed oogonia; in having a high frequency of oosphere abortion; in having an appressed felty colony type with little or no aerial mycelium; and in exhibiting a lower optimum temperature for growth (c.22‐5°C) and lower growth temperature maximum (c.29°C) on carrot agar than P. cambivora (c.27‐5° and 33‐5°C respectively). An inoculation test confirmed its pathogenicity to Alnus. The status of the alder Phytophthora is discussed. On the basis of its unusual characteristics and unusual host it is suggested that it might be a new or recently introduced organism rather than a previously unrecorded indigenous variant of P. cambivora.
Effects of Ca2+ and Mg2+ on Botrytis cinerea and Penicillium expansum in vitro and on the biocontrol activity of Candida oleophila
Authors: WISNIEWSKI M. , DROBY S. , CHALUTZ E. , EILAM Y.
Published: April 2007

Calcium salts have been reported to play an important role in the inhibition of postharvest decay of apples and in enhancing the efficacy of postharvest biocontrol agents. Therefore, the present study was conducted in order to examine and compare the effects of calcium and magnesium salts on the germination and metabolism of the postharvest pathogens Botrytis cinerea and Penicillium expansum, and to determine the effects of these salts on the biocontrol activity of two isolates (182 and 247) of the yeast Candida oleophila. Increasing concentrations of CaCl2 (25–175 mM) resulted in decreased spore germination and germ‐tube growth of both pathogens. The greatest effect was observed in the case of B. cinerea. The inhibitory effect could be overcome by the addition of glucose to the germination medium. MgCl2 (25–175 mM) had no effect on germination or germ‐tube growth of either pathogen, indicating that the calcium cation rather than the chloride anion was responsible for the inhibition. The pectinolytic activity of crude enzyme obtained from the culture medium of both pathogens was also inhibited by 25–175 mM CaCl2, with the greatest effect on the crude enzyme from P. expansum. Biocontrol activity of isolate 182 was enhanced by the addition of 90 or 180 MM CaCl2, whereas there was no effect on the biocontrol activity of isolate 247. This was apparently due to the inability of isolate 247 to proliferate in apple wounds. It is postulated that enhanced biocontrol activity of isolate 182 of the yeast C. oleophila in the presence of Ca2+ ions is directly due to the inhibitory effects of calcium ions on pathogen spore germination and metabolism, and indirectly due to the ability of isolate 182 to maintain normal metabolism in the presence of“toxic” levels of calcium.
Race and mating type identification of powdery mildew on cucurbits in Greece
Authors: VAKALOUNAKIS D. J. , KLIRONOMOU E.
Published: April 2007

Sphaerotheca fusca was confirmed, by the formation of cleistothecia on artificially inoculated detached cotyledons of melon in Petri dishes, as the main powdery mildew pathogen on Cucurbitaceae in Crete during 1993–94. Among 41 single‐spore isolates of S. fusca from Cucumis sativus, C. meto, Cucurbita pepo and Cucurbita sp., two races (1 and 2) were identified, in an approximately equal ratio, by using four melon differential lines. All 41 single‐spore isolates of S. fusca were grouped into two mating types, indicating that the fungus is bipolarly heterothallic and that both mating types are present in Greece. By examining mycelial and conidial features, one single‐spore isolate of powdery mildew from C. pepo was identified as belonging to Erysiphe cucurbitacearum.
Genetics of avirulences in Erysiphe graminis f.sp. hordei
Authors: BROWN J. K. M. , JESSOP A. C.
Published: April 2007

The genetics of avirulences towards barley mildew resistances were analysed in crosses of the Ervsiphe graminis f.sp. hordei isolate DH14 with CC107 and with CC138. Nine avirulences, Avra9, Avra10, Avra11, Avra12, AvrAb, AvrCP, Avrh, Avrk and AvrLa, segregated as single genes in one or other cross. However. F1 segregation data were consistent with avirulence matching the Mla7 resistance gene being controlled by two genes, designated Avra71 and Avra72. Infection types of avirulent isolates differed on varieties in which Mla7 had been derived from each of the four known sources of that resistance. Linkage was detected between Avra71 and Avrh in the cross CC107 × DH14, and between Avra10 and Avrk, Avra11 and AvrLa, and Avrh and the triadimenol response gene Tdl2 in CC138 × DH14.
Single‐plant chambers to control humidity for pathological studies
Authors: BUTLER D. R. , REDDY R. K. , WADIA K. D. R.
Published: April 2007

The construction of a set of controlled‐humidity chambers for single plants is described. Accurate control of relative humidity (r.h.) between 40% and 99% was achieved by mixing dry air with a saturated air stream using solenoid valves controlled by a programmable data logger. At values of r.h. >90%, mean values over periods greater than 1 min were constant to within ±0·1% and spot measurements at 3 s intervals were within 0‐3% of the mean value. The system responded to a step change of r.h. in about 6‐10 min and diurnal changes of r.h. were reproduced, similar to those observed in nature. The stability of control made it possible to differentiate between the requirement of liquid water and very high humidity (98% r.h.) for conidial germination and subsequent infection of groundnut by Phaeoisariopsis personata, the cause of late leaf spot disease.
Effects of temperature on the development of light leaf spot (Pyrenopeziza brassicae) on oilseed rape (Brassica napus)
Authors: FIGUEROA L. , FITT B. D. L. , SHAW M. W. , McCARTNEY H. A. , WELHAM S. J.
Published: April 2007

The effects of temperature on the development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape were investigated in controlled‐environment experiments. The proportion of conidia which germinated on leaves, the growth rate of germ tubes, the severity of light leaf spot and the production of conidia increased with increasing temperature from 5 to 15 C. The time to 50% germination of conidia and the incubation and latent periods of light leaf spot lesions decreased when temperature increased from 5 to 15°C. At 20°C, however, light leaf spot severity and production of conidia were less and the incubation and latent periods were longer than at 15 C. There were differences between P brassicae isolates and oilseed rape cultivars in the severity of light leaf spot, the production of conidia and the length of the incubation period but not in the length of the latent period. The responses to temperature for lesion severity and incubation and latent periods appeared to be approximately linear over the temperature range 5‐15°C and could be quantified using linear regression analysis.
Susceptibility of conifer and broadleaf seedlings to Swedish S and P strains of Heterobasidion annosum
Authors: SWEDJEMARK G. , STENLID J.
Published: April 2007

Seeldings of conifer and broadleaf species, 2‐4 years old, were inoculated with 10 Swedish S and P intersterility group strains of Heterobasidion annosum under greenhouse conditions. There were significant differences in infection incidence, growth in sapwood and mortality rates. Conifers were generally more susceptible to infection than broadleaf trees. Both intersterility groups developed poorly on Alnus glutinosa, Abies grandis, Poputus tremuta×tremutoides and Quercus robur, but the S‐interstedlity group also grew poorly on Pinus sp. and Betula pendula. Results were compared with field observations reported in the literature.
Variations in isolates of Mycogone perniciosa and in disease symptoms in Agaricus bisporus
Authors: FLETCHER J. T. , JAFFE B. , MUTHUMEENAKSHI S. , BROWN A. E. , WRIGHT D. M.
Published: April 2007

Eight isolates of Mycogone perniciosa, five from Agaricus bisporus and three from Agaricus arvensis, were studied. One isolate of Mycogone rosae was also included. Aleuriospore and phialospore morphology varied among the isolates as did other characteristics, but M. rosae was the only isolate to produce a red colouration of the medium. Growth was also variable, with three isolates of M. pemiciosa growing at about half the rate of the fastest. The slow‐growing isolates contained virus‐like particles, 36 nm diameter, and produced sclerodermoid mushrooms. The fast‐growing isolates did not contain virus‐like particles and caused cap spotting, a symptom not previously described for M. perniciosa. M. rosae produced characteristic cap spots and no scierodermoid mushrooms. A comparison of two isolates of St. perniciosa. one from A. bisporus and one from A arvensis, showed a much greater yield reduction as a result of symptoms caused by the isolate from A. bisporus. The isolate of M. rosae had no significant effect on yield.

Restriction fragment banding patterns of ribosomal DNA showed no differences among the seven isolates of M. perniciosa from England, but the isolate from China was slightly different. The single isolate of M. rosae was distinct from M. perniciosa.
Sequences of the internal transcribed spacers of the ribosomal RNA genes and relationships between isolates of Verticillium alboatrum and V. dahliae
Authors: MORTON A. , CARDER J. H. , BARBARA D. J.
Published: April 2007

The sequences of the internal transcribed spacers (ITS) 1 and 2 of the rRNA genes of 38 Verticillium alboatrum and V. dahliae isolates have been determined. The isolates represented RFLP groups of both species, V. dahliae vegetative compatibility groups and pathotypes, and V. alboatrum‘group 2’(the majority of the V. alboatrum isolates studied were in‘group 1′). The ITS sequences of a single V. tricorpus isolate were also determined. RFLP groups L and NL of V. atboatrum were distinct, with a maximum of three nucleotide differences between any isolate. Most haploid V. dahliae isolates were identical and separated from most L/NL V. alboatrum isolates by differences at five or six positions. A few haploid V. dahtiae isolates, not forming any obvious grouping, differed from the majority, each at a single position. Diploid isolates of V. dahtiae were identical but only one nucleotide difference separated them from some RFLP group L V. alboatrum isolates. At least six differences separated the diploid isolates of V. dahliae from the haploid ones. The‘group 2’V. atboatrum isolates were more distantly related to‘group 1’isolates (at least 17 positions different) than was V. tricorpus. The possibility of defining specific primers for use in PCR to discriminate species and subspecific groups is discussed.
High and low pre‐inoculation temperatures decrease the effectiveness of the Lr 20 and Sr 15 rust resistance genes in wheat
Authors: RAMAGE R. A. , SUTHERLAND M. W.
Published: April 2007

Spring wheat seedlings containing Lr 20 and Sr 15 resistance alleles were raised at 30° C, prior to inoculation with leaf rust (Puccinia recondita race 76–2,3) and stem rust (Puccinia graminis f.sp, tritici race 343–1,2,3,5,6) pathogens, respectively. Infected plants were then grown at one of seven temperatures in the range 18–30 C and infection types were scored at 10 days post‐inoculation. These results were compared with those obtained for plants raised at a pre‐inoculation temperature of 18° C. In both 18° C and 30° C pre‐grown plants, a progressive increase in infection type was observed on resistant lines as post‐inoculation temperature increased. However, resistant lines raised at 30°C had significantly higher infection types than plants raised at 18° C at all post‐inoculation temperatures for which some degree of resistance was still evident in the plants raised at 18°C, The maximum temperature for expression of resistance was significantly higher for Lr 20 than for Sr 15. irrespective of pre‐inoculation temperature. A lowering of the resistance expression was also evident in Sr 15‐bearing lines raised at a very low pre‐inoculation temperature (4°C). The effects of low pre‐inoculation temperature on resistance were assessed in both winter and spring wheat lines. These results are discussed in the light of current ideas concerning the host membrane location of pathogen recognition events.
Characteristics and pathogenicity of Pythium spp. associated with root rot of tomatoes in soilless culture in Brittany, France
Authors: RAFIN C. , TIRILLY Y.
Published: April 2007

Pythium species cause necrotic lesions and root rots on tomato in soilless culture. Epidemiological studies conducted in Brittany, France, revealed the precocity and the frequency of the contamination of tomato roots by these fungi, even in symptomless roots. The colonization, estimated by culture‐plate methods, could reach levels as high as 105 propagules/gram of root. The frequent occurrence of Pythium with filamentous non‐inflated sporangia, representing 75% of the total isolates, was observed during both latent infections and necrotic phases. Those Pythium spp., grouped as Pythium F, induced variable necrotic lesions in tomato roots in soilless culture. This group, which had been overlooked previously in favour of known pathogenic species such as P. ultitnum var. ultimum, can be pathogenic to tomato plants and therefore form a component of a potential disease complex.
A Japanese powdery mildew isolate with exceptionally large infection efficiency on Mlo‐resistant barley
Authors: LYNGKJÆR M. F , JENSEN H. P , ØSTERGÅRD H.
Published: April 2007

A Japanese field isolate (Race I) of Erysiphe graminis f.sp, hordei was tested on 17 barley lines carrying the mlo powdery mildew resistance gene. Race I produced many successful infections with infection type larger than or equal to 2 on six lines (M66, MC20, SRI, SR7, A tem and Totem), On the remaining 11 lines it reacted with infection type 0. Colony numbers on the Mlo‐lines were between 26% and 12 9% of the numbers on a susceptible cultivar Manchuria, These numbers were larger than, or similar to those produced by isolate HL3/5, which has the highest recorded infection efficiency on Mlo‐resistant cultivars. The interaction between isolates and lines was highly significant. The isolate GE3, from which HL3/5 was derived by selection, gave rise to occasional colonies corresponding to less than 03° o of the number produced on cv. Manchuria.
Analysis of fatty acids in lipids of Verticillium dahliae and induction of lubimin accumulation in eggplant
Authors: CASTORIA R. , FANELLI C. , ZOINA A. , SCALA F
Published: April 2007

The unsaturated fatty acid pattern and content of the main lipid fractions of three isolates of Verticillium dahliae were investigated, Oleic (C18:1), linoleic (C18:2) and linolenic (C18:3) acids were the unsaturated fatty acids detected in the polar lipids and in the free fatty acids extracted from myceha of three isolates of the fungus. The concentration of the three fatty acids in polar lipids was about double that in free fatty acids, Linoleic acid was the predominant fatty acid in both lipid fractions. The capacity of linoleic and linolenic acids to induce lubimin accumulation in eggplant fruit discs was evaluated in comparison with that of the polyunsaturated fatty acid arachidonic acid, which is a known elicitor of phytoalexin synthesis in potato tuber. The accumulation of moderate levels of the phytoalexin was induced by arachidonic and linolenic acids, A higher induction was observed when browning of the tissue was inhibited by phenylthiourea. Under these conditions, linoleic acid induced only a slight accumulation of lubimin. The possible role of linolenic acid in triggering defence reactions in eggplant is discussed.
Isolation and characterization of Clavibacter tritici associated with Anguina tritici in wheat from Western Australia
Authors: RILEY I. T. , REARDON T. B.
Published: April 2007

Two infestations of Anguina tritici in Western Australia were investigated for the presence of Clavibacter tritici. Five strains of C tritici were isolated from each site and compared with strains from Egypt, India, Iran and Iraq by allozyme electrophoresis. The Australian strains were genetically homogeneous but distinct from the non‐Australian strains. A. tritici galls were found to be colonized by C. tritici, a feature of C. tritici infection not previously reported. C. tritici strains from Australia adhered to A, tritici but not to Anguina funesta. No corynetoxins were detected in C. tritici‐infected galls. The potential of non‐toxigenic Clavibacter species, such as C. tritici, for biocontrol of Clavibacter toxicus, the species responsible for poisoning livestock, is discussed.
Characterization of cereal bare patch isolates of Rhizoctonia solani by random amplified polymorphic DNA analysis
Authors: YANG H. A. , SIVASITHAMPARAM K. , BARTON J. E. , O'BRIEN P A.
Published: April 2007

RAPD‐PCR was used to characterize isolates of Rhizoctonia solani from bare patches in cereal and pasture crops at two locations in Western Australia, Newdegate and Esperance. All of the isolates belonged to anastomosis group 8, pectic zymogram group 1‐1 or 2. The pectic zymogram assignment could be confirmed by RAPD‐PCR. There was no difference in RAPD‐PCR pattern between highly virulent and weakly virulent isolates at Newdegate, or between isolates from different patches at Newdegate. The Newdegate isolates were identical to isolates from Esperance, and to isolates from various locations in South Australia.
Comparison of mobile and stationary spore‐sampling techniques for estimating virulence frequencies in aerial barley powdery mildew populations
Authors: HOVMØLLER M. S. , MUNK L. , ØSTERGÅRD H.
Published: April 2007

Gene frequencies in samples of aerial populations of barley powdery mildew (Erysiphe graminis f.sp. hordei), which were collected in adjacent barley areas and in successive periods of time, were compared using mobile and stationary sampling techniques. Stationary samples were collected from trap plants in three periods within 1 week at a distance of more than 1000 m from the nearest barley field. At four dates within the same 8‐day period, other samples were collected by a mobile spore trap along four sampling routes of a total distance of 130 km around the stationary stand of exposure. The samples were characterized by virulence genotypes defined according to infection types on 12 near‐isogenic barley lines, and frequencies of single virulence genes were subsequently calculated. The three samples collected at the stationary site differed significantly with respect to allele frequencies at three loci. The main wind direction was different in the three sampling periods, implying different powdery mildew sources. For the mobile exposure, the differences between routes were not significant for any locus. However, the routes differed most for the loci under direct selection by host resistances genes, indicating a different distribution of source varieties along routes. There was no difference between allele frequencies at different dates, indicating that the proportions of spores from different source varieties were similar at these dates. In conclusion, samples collected by the stationary technique will mainly reflect the source varieties present in the local area, whereas samples collected by the mobile spore trap will mainly reflect sources close to the sampling route. Therefore, sampling sites as well as sampling routes should be defined such that source varieties are representative for the overall varietal distribution in the survey region considered.