bluuebunny/crossref_metadata_2025 huggingface dataset:
Some properties of a virus‐like agent found in Brachypodium sylvaticum in the United Kingdom
Authors: EDWARDS M.–L. , COOPER J. I. , MASSALSKI P. R. , GREEN B.
Published: April 2007

A spherical virus–like agent ($$32 nm in diameter) was isolated from a plant of Brachypodium sylvaticum (Huds.) Beauv. growing in a botanic garden in England and showing yellow streaks in the leaves. The agent was readily purified and sedimented as a single component in sucrose density rate gradients. The particles had a sedimentation coefficient at infinite dilution of $$122S and a buoyant density of 1.35 g/cm3 in CsCl and 1·33 in CS2SO4. The particles were stable at acid pH but above pH 7·0 in the presence of EDTA dissociated. A protein having a major polypeptide with a molecular weight of $$3·76 × 104 and a species of single stranded RN A with a MW of 1·67 × 106 were detected in the particles. The agent was not transmitted by manual inoculation, by the insects Myzus persicae Sulzer, Rhopalosiphum padi L. or Nephotettix virescens Distant, through soil by leakage from roots or by seed. The particles had physicochemical properties in common with tombus– and sobemoviruses but were not serologically related to 10 members of these groups or to 57 other small spherical RNA plant viruses.
Heterokaryon compatibility and genetic recombination within a host plant between hop wilt isolates of Verticillium albo–atrum
Authors: CLARKSON JOHN M. , HEALE J. B.
Published: April 2007

Heterokaryon compatibility was tested by pairing complementary auxotrophic mutants of three fluctuating (M18, M33 and M50) and three progressive (PV1, PV2 and PV3) hop wilt isolates of Verticillitim albo–atrum. The criteria of compatibility adopted were prototrophic growth on a glucose minimal medium at 26°C and the presence of diploid conidia. Most pairings produced at least some heterozygous diploids, showing there was no complete incompatibility barrier to hyphal and nuclear fusion on an agar medium. The incidence of prototrophic diploidy was greater within paired mutants of progressive isolates, and between PV1 and the three fluctuating isolates. A recombinant haploid prototroph was re–isolated following inoculation of Antirrhinum plants with a pair of complementary auxotrophs (M18 nic‐4 cob‐26 and PV3 arg‐8 pyr‐2). In hop, this recombinant was of intermediate pathogenicity compared with the two parental wild–type isolates. Four large–spored, diploid isolates were obtained from Antirrhinum following inoculation with heterozygous diploid conidia (M18 nic‐4 cob‐26/PV3 arg‐8 pyr‐2) from diploids synthesized on agar. All four diploids remained stable on agar and one showed moderately high pathogenicity in hop, from which it was re–isolated as a stable diploid 10 weeks later.
Contamination of potatoes by Erwinia carotovora during grading
Authors: ELPHINSTONE J. G. , PEROMBELON M. C. M.
Published: April 2007

Considerable tuber contamination by soft rot erwinias in rotting tubers can occur when grading potato stocks. Erwinia carotovora pv. carotovora, from a single rotting tuber, contaminated c. 100 kg of potatoes during mechanical grading, c. 50% being contaminated with 104–105 bacteria per tuber. Survival of the bacteria during storage was related to the degree of damage sustained by the tubers during grading which in turn depended on the model of oscillating riddle grader used and the cultivar of potato. Chemical disinfection of the grader immediately before use and of tubers immediately after grading reduced contamination.
Five new hosts of Pseudomonas andropogonis occurring in eastern Australia: host range and characterization of isolates
Authors: MOFFETT MELDA L. , HAYWARD A. C. , FAHY P. C.
Published: April 2007

Pseudomonas andropogonis was recorded for the first time as the cause of lesions on blueberry (Vaccinium sp.). carob (Ceratonia siliqua L.), Gypsophila paniculata L. G. elegans Bieb. and statice (Limonium sinuatum (L.) Mill). Cross‐inoculation studies with 13 isolates from 10 host plants showed that sorghum, sweet corn, vetch, carnation and Gypsophila elegans were hosts in common, whereas clovers (Trifolium repens and T. pratense) were infected only by isolates from clover, Gypsophila paniculata and vetch. Seventeen isolates subjected to bacteriological characterization tests formed a uniform phenotype. A single isolate from sorghum produced an antimetabolite inhibitor of Escherichia coli B which was reversed by L‐glutamine. but not by other amino acids.
The effect of powdery mildew (Erysiphe graminis f. sp. hordei) and leaf rust (Puccinia hordei) on spring barley in New Zealand. I. Epidemic development, green leaf area and yield
Authors: LIM L. G. , GAUNT R. E.
Published: April 2007

Powdery mildew and leaf rust caused large yield losses in spring barley grown near Christchurch, New‐Zealand, in two seasons. Disease present during early growth stages was as damaging to yield as disease late in the season. Moderate leaf rust severities after anthesis were most damaging when combined with earlier mildew epidemics. Later growth did not compensate for reduced yield potential induced by early infection. This was attributed, at least in part, to an effect on leaf size, and therefore on green leaf area, at later growth stages. There was a closer relationship, by regression analysis, of yield to green leaf area than to disease severity in three cultivars.

The three cultivars. which differed in yield potential and disease resistance, were not equally sensitive to disease. It is proposed that high yielding cultivars may be the most sensitive to yield constraint by disease.
A comparative study of the pathogenicity and epidemiology of strains of Pseudomonas syringae pv. tabaci that cause wildfire and angular leaf spot diseases of tobacco in Zimbabwe
Authors: DEALL M. W. , COLE J. S.
Published: April 2007

The population dynamics of two strains of Pseudomonas syringae pv. tabaci that cause the foliar spot diseases of tobacco known as wildfire (WF) and angular leaf spot (ALS) were significantly different in leaves of a susceptible tobacco cultivar. After 48 h the population of WF strains changed abruptly from exponential growth to stationary phase, whereas there was a more gradual transition by the ALS strains. This resulted in smaller stationary‐phase populations for WF than for ALS. The decline of the WF population started soon after the stationary phase was reached, whereas the ALS stationary phase was relatively stable.

The strains reacted differently to climatic factors. On plants inoculated and exposed to the weather at weekly intervals, WF lesions grew faster when vapour pressure deficits, maximum temperatures and radiation were low. Multiple regression analysis showed that over 70% of the variation in WF infection was accounted for by variation in VPD, radiation and mean temperature. Variation in ALS infection was less easily explained in relation to the weather variables measured.

Plant age and stalk position had a differential effect on the pathogenicity of the two strains. Lower leaves of young plants (42 days) were most susceptible to WF and top leaves of older plants (84 days) were most susceptible to angular leaf spot. Differences in pathogenicity and occurrence in the field suggest that pathovar status should be considered for the ALS pathogen of tobacco.
Virus‐induced changes in the response of faba bean to infection by Botrytis
Authors: OMAR S. A. M. , BAILISS K. W. , CHAPMAN G. P.
Published: April 2007

Prior infection of faba bean with the viruses bean yellow mosaic and bean leaf roll increased host susceptibility to subsequent infection by Botrytis fabae and B. cinerea. Cell necrosis beneath inoculum droplets, rate and extent of lesion spread and sporulation of B. fabae were all increased on detached leaves from virus‐infected compared with healthy plants. Changes were most marked in young leaves showing conspicuous symptoms of systemic virus infection and in plants virus‐infected for at least 2‐4 weeks. Localized lesions produced by B. cinerea or a low concentration of B. fabae conidia (103 spores/ ml) showed increased cell necrosis but were not transformed into aggressive, spreading lesions on virus‐infected leaves.
Effect of alfalfa mosaic virus isolates on forage yield of lucerne (Medicago sativa) in Britain
Authors: BAILISS K. W. , OLLENNU L. A. A.
Published: April 2007

The effect of alfalfa mosaic virus (A1MV) on lucerne forage yield was investigated in experimental plots in which all plants were indexed for freedom from seed‐borne A1MV. Plants which were artificially inoculated with A1MV were tested for successful infection prior to transfer to the plots. Inoculated plots yielded 14‐8‐22‐8% (fresh weight) and 15.0 18.1% (dry weight) less than uninoculated plots. Isolate A1MV‐I reduced the yield of five lucerne cultivars and yield was decreased by several A1MV isolates in cv. Vertus. Yield decreases tended to be greatest at the first harvest and progressively smaller at the second and third. Despite aphicide treatments and a cereal barrier crop, ELISA indexing showed natural infection developed in control plots. Most known infected plants failed to produce symptoms and yield decreases were associated with predominantly symptomless infection.
The use of biplots as an aid to interpreting interactions between potato clones and populations of potato cyst nematodes
Authors: PHILLIPS M. S. , McNICOL J. W.
Published: April 2007

Biplots were used to re‐examine potato clone by nematode population interactions in six sets of data. The interactions are represented by principal components. The resulting biplots are shown to provide a simple but comprehensive picture of the interactions. The comparison between populations of Globodera rostochiensis and of G. pallida is highlighted, and it is evident from all the data sets which include both species that there are bigger interactions with clones within the former. In a data set involving only G. pallida some of the normally accepted pathotypes are found to show differences in their pattern of interaction with clones. Clones considered as non‐resistant interacted with nematode populations no less than resistant clones. A description of the biplot technique is included.
Relationship between physiological response of French beans of different age to Meloidogyne incognita and subsequent yield loss
Authors: MELAKEBERHAN H. , BROOKE R. C. , WEBSTER J. M.
Published: April 2007

A study was made of the effect of a single generation of the root‐knot nematode Meloidogyne incognita on the growth of potted French bean plants (Phaseolus vulgaris) inoculated at different stages of plant maturity. In separate experiments. 3‐, 11‐ and 13‐day‐old plants were inoculated before primary leaf expansion (BPLE). at the appearance of trifoliate leaves (TRIF) and at the flower bud (BDS) stages respectively, with 0, 2000, 4000 or 8000 second‐stage juvenile nematodes and maintained in a growth chamber under controlled conditions. The photosynthetic rate of the plants inoculated at the TRIF and BDS stages decreased significantly with increasing inoculum level 7 days after inoculation. Although the respiration rate did not significantly change throughout the experimental period, the ratio of photosynthetic to respiration rate decreased significantly with increasing nematode inoculum level and duration of infection. Chlorophyll content, plant dry weight and the numbers of buds, flowers, pods and seeds were significantly lower in infected plants than in the controls; this effect increased with increasing levels of nematode inoculum for all three plant stages. The leaf area was significantly smaller only when nematode infection occurred at the BPLE stage. The plants which were youngest at the time of nematode infection produced the lowest yield; this appeared to result from the effect of nematodes on photosynthesis and related physiological processes.
Diversity of virulence within Ascochyta pisi and resistance in the genus Pisum
Authors: DARBY P. , LEWIS B. G. , MATTHEWS P.
Published: April 2007

When a range of genotypes of the genus Pisum was inoculated with Ascochyta pisi some remained uninfected or symptomless whereas the reactions of others ranged from a hypersensitive resistance through various levels of susceptibility to almost lethal infection. This variation, categorized on a six‐class scale, was used to describe the reactions of 57 isolates of A. pisi collected from pea crops widely distributed in Britain when inoculated on to 14 differential lines of Pisum. Five major pathotype groups were distinguished and a set of lines nominated as standard differential hosts.
The occurrence of virulent pathotypes of Leptosphaeria maculans in brassica seed crops in England
Authors: HUMPHERSON‐JONES F. M.
Published: April 2007

Virulent and non‐virulent pathotypes of Leptosphaeria maculans were differentiated on the basis of cultural characteristics and virulence to cabbage plants. Surveys of isolates obtained from oilseed rape crops grown in England in 1982 and 1983 showed that virulent pathotypes predominated in some areas whereas in others they were infrequent or absent. Overall 41% of isolates from this crop were of the virulent type. Virulent types usually occurred most frequently in areas with a long history or a high density of oilseed rape. In vegetable and forage brassica seed crops in Essex virulent isolates formed a small proportion of the population, except in one swede crop from which 95% of isolates were virulent. Host specificity was not detected in cross‐infection experiments using isolates from different hosts and localities.
Effects of fungicides on powdery mildew, tree growth and cropping of apple
Authors: LOCKE T. , ANDREWS LINDA
Published: April 2007

In a 6‐year orchard experiment, seven fungicide programmes were assessed for control of powdery mildew (Podosphaera leucotricha) and for long‐term effects on growth and cropping of the apple cultivar Cox's Orange Pippin. Programmes based on binapacryl, bupirimate, fenarimol, nitrothal‐isopropyl and triadimefon gave better control than dinocap or triforine. The heaviest cumulative yields of marketable fruit were obtained with the non‐systemic fungicides binapacryl and nitrothal‐isopropyl, the former significantly outyielding triadimefon and triforine over 6 years. Tree vigour, as assessed by extension shoot length and internode length, was found to be better after 4‐5 years of programmes based on binapacryl than on triadimefon or fenarimol. A relation was demonstrated between cumulative marketable yield and mean annual mid‐season incidence of secondary mildew on extension shoot leaves.
Effects of temperature and leaf wetness on Pyrenophora teres growing on barley cv. Sonja
Authors: SHAW M. W.
Published: April 2007

Conidia ofPyrenophora teresgerminated only in the presence of liquid water and at temperatures above 2°C. The speed with which germination occurred was inversely proportional to temperature measured from a base of 2°C, up to the maximum temperature tested of 21°C. Once conidia on leaves had been wetted, about 40% of all infections that would eventually occur were established within 100°C‐hours. Subsequent lesion extension was rapid, with area doubling times of about 1 day between 10 and 20°C.

If conidia germinated, up to 80% formed successful infections on young, susceptible leaves. On older leaves fewer spores germinated and the proportion that then infected was smaller.

The latent period, defined as the time before which sporulation did not occur under any wetness conditions, ranged from about 25 days at 5°C to 11 days at 20°C under dry conditions. Under continuously wet conditions it was about 20% shorter at all temperatures. Its inverse had a curvilinear relation to temperature.

Spores were produced after one to several days of humidity above 95%. The precise period decreased with increasing temperature, but at 25°C spores never appeared. The drier a dead leaf was, the longer the pathogen in it look to produce spores.
The effects of infection by barley yellow mosaic virus on the yield and components of yield of barley
Authors: PLUMB R. T. , LENNON E. A. , GUTTERIDGE R. A.
Published: April 2007

Infection by barley yellow mosaic virus (BaYMV) was greater in a crop sown in October than in November and in cv. Maris Otter than in cv. Sonja. However, a greater proportion of plants of Sonja than of Maris Otter were infected, and more severely, with the soil‐borne fungus vector of BaYMV. Polymyxagraminis. Indifferent years the yield of individual plants of Maris Otter was decreased by 15% and of Sonja by 40%. The spring barley cultivars Athos. Porthos. Georgie and Ark Royal were all infected with BaYMV when sown in autumn in infected soil. Infected winter barley cv. Igri lost up to 50% of yield when this was measured across a naturally infected patch of crop.
Asymptotic behaviour and threshold criteria in model plant disease epidemics
Authors: JEGER M. J.
Published: April 2007

Two qualitative results concerning threshold criteria and asymptotic behaviour in plant disease epidemics are derived from Vanderplank's differential‐difference equation. Analysis shows the dependence of these results on initial disease and clarifies some confusion in the literature. Results from the deterministic theory of medical epidemics, based on linked differential equations describing the dynamics of different categories of diseased individuals, are compared with the results derived from the differential‐difference equation. Generally, the results correspond although the effects of initial disease need clarification. The need for a strict operational definition of the progeny‐parent ratio limits its present use in plant disease epidemiology. In particular the numerical value of the ratio is not a sufficient basis for distinguishing between endemic and epidemic disease. There is a need to link theory in plant disease epidemiology with similar theory in other areas of population biology. The use of linked differential equations, rather than the differential‐difference equation, provides a more flexible analytical tool.
A new procedure to detect a low incidence of Ustilago nuda in seed barley
Authors: HEWETT P. D. , DAMGACI E.
Published: April 2007

Partial enzymic digestion of extracted barley embryos enabled the mycelium of Ustilago nuda to be separated and collected on a nylon mesh filter. Mycelium from samples with less than 0.1% seeds infected was readily detectable. The procedure promises to be a new and sensitive routine method.
Dicarboximide resistance in Botrytis cinerea in protected lettuce
Authors: WANG ZU‐NAN , COLEY‐SMITH J. R. , WAREING P. W.
Published: April 2007

In surveys of protected lettuce crops in the Humberside area of the UK during 1984‐5, 47.3% ofBotrytis cinerea isolates were resistant to dicarboximides and 25% to benomyl. Dicarboximide‐resistant isolates obtained direct from the field had a moderate degree of resistance with ED50 values for mycelial growth on agar of 1.0‐2.4 μg/ml vinclozolin for all except two of 30 isolates.

Isolates which were resistant to vinclozolin were also resistant to iprodione, myclozolin and procymidone. Thirty dicarboximide‐resistant isolates obtained direct from the field were capable of infecting cucumber cotyledons sprayed with field‐strength Ronilan (250 μg/ml vinclozolin) whereas sensitive strains were not. Strains showing different degrees of resistance to dicarboximides developed after incubation of sensitive and resistant strains on agar supplemented with vinclozolin. Some of these strains had ED50 values for mycelial growth on agar of more than 100 μg/ml vinclozolin. No highly resistant isolates were obtained direct from the field. Resistance to dicarboximides in field isolates was stable.
Linkage of the genes determining mating type and fungicide tolerance in Ophiostoma ulmi
Authors: WEBBER JOAN , MITCHELL A. G. , SMITH FRANCES
Published: April 2007

Two allelic mutations conferring high and low levels of in vitro tolerance to the fungicide methyl benzimidazole‐2‐ylcarbamate (MBC) were identified in the elm pathogen Ophiostoma ulmi. Variants expressing a third and intermediate level of tolerance were also identified. The locus for fungicide tolerance was linked to the mating type locus in both the aggressive and non‐aggressive strains of the fungus.
Effect of temperature on potato virus X infection in potato cultivars carrying different combinations of hypersensitivity genes
Authors: ADAMS SALLY E. , JONES R. A. C. , COUTTS R. H. A.
Published: April 2007

In potato cultivars reacting non‐hypersensitively, systemic mosaic symptoms were obvious at 10‐20°C for potato virus X (PVX) isolate DX, and at 10 and 15°C for PVX isolate B: systemic movement was slowest at 10°C especially with DX. Viral antigen accumulation in non‐inoculated leaves was greatest at 15 and 20°C with B. but with DX accumulation was as great at 25°C, The highest viral antigen concentrations reached were less with B than with DX. No PVX was detected in plants grown at 30°C.

In potato cultivars carrying gene Nx, necrotic local lesions appeared at 10‐25°C in DX‐inoculated lea ves within 8 days; systemic necrosis developed soon after at 15 and 20°C, but was very slow to appear or failed to develop at 10 and 25°C, Necrosis was more conspicuous when gene Nb was also present. Except at 10°C in the Nx:nb cultivar used, presence of Nx decreased accumulation of DX antigen.

Although numerous necrotic lesions developed in B‐inoculated leaves at 10°C in the presence of gene Nb, very few formed at 15 and 20°C, and none at 25°C. In B‐inoculated leaves from plants at 15‐25°C, no new lesions were induced by temperature shock treatments and no starch lesion formation was detected. Gene Nb completely prevented movement of isolate B out of inoculated leaves at all temperatures regardless of whether infection was symptomless or necrotic local lesions developed, The concentration of B‐antigen was considerably decreased by Nb.

It was possible to quantify the general effects of genes Nx and Nb on accumulation of DX‐ and B‐antigens: in the combination Nx:Nb the ineffective gene interacted with the effective gene to cause a greater depression of viral antigen accumulation than expected. Unlike hypersensitivity genes for tobacco mosaic virus in tomato and tobacco, Nx and Nb in potato did not lose their effectiveness with increasing temperature. Differences in virus accumulation and in temperature optima for multiplication between PVX strain groups may account for the lack of competitiveness shown by those belonging to group two.
Studies on some characteristics of dicarboximide‐resistant isolates of Botrytis cinerea from protected lettuce
Authors: WANG ZU‐NAN , COLEY‐SMITH J. R.
Published: April 2007

Isolales of B. cinerea obtained directly from protected lettuce crops were either sensitive or moderately resistant to dicarboximides. Types with a high level of resistance to dicarboximides developed under laboratory conditions. Isolates with a high level of resistance grew poorly and sporulated feebly on cucumber cotyledons or lettuce leaves whereas growth and sporulation of moderately resistant isolates were only slightly poorer than of sensitive isolates. Moderately resistant isolates were stable in culture and there was no evidence that they produced mixtures of sensitive and resistant conidia. In polythene tunnel studies with mixed B. cineaea populations, in the absence of dicarboximides. no highly resistant isolates and only a small percentage of moderately resistant isolates were recovered.
Detection of prunus necrotic ringspot virus in several rosaceous hosts by enzyme‐linked immunosorbent assay
Authors: STEIN ADINA , LEVY S. , LOEBENSTEIN G.
Published: April 2007

Detection of prunus necrotic ringspot virus (PNRSV) by enzyme‐linked immunosorbent assay (ELISA) in rose, peach and almond was improved by absorbing the enzyme‐conjugated γ‐globulin with healthy leaf extracts. Non‐specific reactions were reduced markedly, thereby increasing the infected/healthy A405 ratio several‐fold. Absorbing the conjugate with peach leaf extract was most effective in lowering the non‐specific reaction in peach and rose, especially during the summer. Consequently, absorption of the enzyme conjugate with peach extract is now used in routine indexing for PNRSV in rose and peach.
Isolation, culture and ultrastructure of a xylem‐limited bacterium associated with Sumatra disease of cloves
Authors: BENNETT CHRIS P. A. , JONES PHILIP , HUNT PETER
Published: April 2007

A xylem‐limited bacterium (XLB) previously shown to be associated with Sumatra disease of clove trees was consistently isolated from diseased but not from healthy trees. Isolation of the XLB was most successful using freshly expressed bacterial ooze obtained from root and branch tissues with low to moderate levels of xylem vessel invasion in trees at early stages of disease. XLB were commonly isolated from trees with the rapid form of disease but infrequently from those with slow decline. Bacterial colonies grew slowly on nutrient agar, reaching a maximum diameter of 1 mm in 5‐7 days at 28oC. Cells of the bacterium were 0.5‐0.6 μm in width and 1.0‐1.5 μm in length and did not possess flagella. The bacterial envelope was strongly rippled and Gram negative.
Variation in stem infections caused by aggressive and non‐aggressive isolates of Leptosphaeria maculans on Brassica napus var. oleifera
Authors: HAMMOND KIM E. , LEWIS B. G.
Published: April 2007

Development of stem cankers in seedlings of Brassica napus var. oleifera inoculated with Leptosphaeria maculans was studied in growth cabinets. As the pathogen progressed from the petiole into the stem, hyphae invaded parenchyma cells for the first time, initiating a necrotrophic phase which resulted in the formation of a lesion. Ultimate containment of the pathogen was associated with a sequence of host reactions including lignification, cambium formation and callose deposition at the perimeter of the lesion. Two isolates of L. maculans differed in the pattern of stem infection. One was confined to the cortex and the other passed through the leaf gap into the pith. Variation in response between cultivars Rapora, Primor and Jet Neuf modified these two colonization patterns but did not eliminate the main differences. There were qualitative and quantitative differences in host cell reactions. The significance of these findings is discussed in relation to differences in resistance of the cultivars in the field.
Effects of barley yellow dwarf and ryegrass mosaic viruses alone and in combination on the productivity of perennial and Italian ryegrasses
Authors: CATHERALL P. L.
Published: April 2007

Moderately severe strains of barley yellow dwarf virus (BYDV) and ryegrass mosaic virus (RMV) significantly reduced the heights and yields of perennial (Lolium perenne) and Italian (L. multifiorum) ryegrasses. BYDV caused greater reductions in perennial ryegrass than in Italian, whereas the converse was true of RMV. Both viruses together rarely caused greater damage than the most damaging virus on its own. BYDV reduced the aggressiveness of perennial ryegrass more than of Italian, whereas with RMV the converse was true. In mixtures of perennial and Italian ryegrasses, the perennial was suppressed by the Italian when only BYDV was present, the Italian was suppressed by the perennial when only RMV was present, and the status quo was maintained when both viruses were present, even though they reduced the yield of the mixture by over 16%.
Spatial distributions of Septoria nodorum and S. tritici within crops of winter wheat
Authors: SHAW M. W. , ROYLE D. J.
Published: April 2007

In some crops of winter wheat selected from a range monitored in Western Europe during 1981‐83,Septoria nodovumand S. triticiwere spatially very uniformly distributed from the beginning of the growing season onwards. A cube root transformation produced a constant variance in lesion numbers per leaf, similar for both pathogens at about 0.5. This permits the sample size needed for a given accuracy to be estimated. Counts of conidia washed from leaves by a standard procedure had a constant coefficient of variation, independent of disease level. Large samples would be necessary for accurate counts, particularly if leaves from different layers were examined separately. The pattern of lesion numbers on leaves was best described by a negative binomial distribution: this predicts an incidence‐severity curve to which the data conformed closely. Hence incidence estimates can be used to estimate severity, which may be more economical of sampling effort. Correlations between lesion counts on different leaves of the same tiller were negative and highly significant forS. nodorumin 1982, but positive and significant forS. triticiin 1983. The causes of this difference are unknown.
Biology of the Acacia gall rust, Uromycladium tepperianum
Authors: MORRIS M. J.
Published: April 2007

Germinating teliospores of Uromycladium tepperianum formed penetration pegs, which directly penetrated host epidermal cells, on the tip cell of three‐celled germ tubes. Diploid nuclei within teliospores appeared to divide soon after germination commenced. Only one of the daughter nuclei moved out of the teliospores with the developing germ tubes. Reactions of seedlings inoculated with teliospores from different host species and differences in teliospore dimensions indicated that distinct genotypes of U. tepperianum adapted to particular host species occur in Australia. Limited hyphal growth occurred in two of 20 African Acacia spp. inoculated with teliospores from Acacia saligna. Fungal development was, however, restricted by necrosis of surrounding host cells. U. tepperianum appears to be suitably host‐specific for use as a biological control agent against Ac. saligna, a weed in South Africa.
Effects of recombination on races of a barley powdery mildew population
Authors: WELZ G. , KRANZ J.
Published: April 2007

Analyses of virulence were performed with isolates from ascospore populations and their possible parental populations in order to measure the potential effect of recombination on the pathogenic variation in populations of Erysiphe graminis f. sp. hordei. The conidial isolates and cleistothecia were sampled from a field of spring barley cv. Golden Promise. Compared to the summer conidial populations, higher frequencies of rare races and rare virulence factors together with greater diversity were observed among progeny from ascospores, and the most frequent race was less abundant. The contribution of ascospores to primary infection of barley in autumn could not be measured directly, but analyses of the conidial populations on volunteer seedlings of Golden Promise suggested that sexual recombination was one of the mechanisms that had caused the change in population structure.
The occurrence, characteristics and distribution in the United Kingdom of resistance to phenylamide fungicides in Bremia lactucae (lettuce downy mildew)
Authors: CRUTE I. R. , NORWOOD JUDITH M. , GORDON PAMELA L.
Published: April 2007

Failure to control Bremia lactucae (lettuce downy mildew) with metalaxyl in an intensive lettuce‐producing region of Lancashire at the end of 1983 was shown to be due to the occurrence of a high level of resistance to this fungicide (isolates capable of growth at < 100 μg/ml metalaxyl). During most of 1984, metalaxyl‐resistant isolates were obtained from numerous sites but all within a 20‐km radius of the initial outbreak. Thereafter, at the end of 1984 and during 1985, metalaxyl‐resistant isolates were recovered from most major lettuce‐producing regions in the UK with protected crops more affected than field crops. AH metalaxyl‐resistant isolates tested were identical in their response to fungicide, sexual compatibility type (B2) and virulence phenotype, probably representing a clone from a single origin. The resistant pathotype was virulent on resistance factors R 1‐10 and 12‐15 but lacked virulence for R 11 and 16‐18. This was also the most common virulence phenotype among sensitive isolates collected at the same time. Cross‐resistance to other phenylamide fungicides was demonstrated but isolates resistant and sensitive to phenylamide showed a similar response to the unrelated systemic fungicides propamocarb and fosetyl‐Al. An F1 sexual progeny isolate from a cross between a phenylamide‐sensitive and a phenylamide‐resistant isolate (presumed heterozygous at the locus or loci regulating response to phenylamide fungicides) exhibited an intermediate response to phenylamide fungicides. No isolates of this type were obtained from the field. At the high concentrations affecting spore germination, phenylamide fungicides exhibited lower activity against a resistant isolate compared with a sensitive isolate. The findings are discussed in relation to future control strategies, the population biology of the fungus and possible directions for lettuce breeding programmes.
The effect of crown gall on growth of cherry trees
Authors: GARRETT CONSTANCE M.E.
Published: April 2007

Over 1000 cherry trees, as rootstocks, nursery sweet cherry or ornamental cultivars or orchard trees up to 7 years old, with or without galls, were examined to determine the effect, if any, of crown gall disease on tree growth. No clear, consistent differences between healthy and galled trees were found. Healthy 1‐year‐old F12/ 1 rootstocks were smaller than their galled counterparts but the reverse was true for 2‐year‐old sweet cherries and ornamental cultivars. The mean girth of non‐galled 6‐year‐old trees of cv Schrecken was greater than that of galled trees from the same orchard. Detailed records on two sweet cherry cultivars, Napoleon and Roundel, revealed some differences in growth rate in the early years between healthy trees and those with various levels of galling at planting, but these differences were not sustained. Irrespective of gall status at planting no correlation was detected between final gall status and ultimate tree size. The data support the view that there is no consistent effect of crown gall on cherry tree growth and that the adverse appearance of affected nursery material is the main problem with this disease.
A note on the use of Merckoquant test strips for detection of nitrate reduction in plant pathogenic bacteria
Authors: COTHER E. J.
Published: April 2007

Merckoquant nitrate test strips gave reactions identical to standard sulphanilamide N‐I‐naphthylethyl‐enediamine reagents for determining nitrate reduction in several bacterial genera. The strips obviate the need for fresh reagents and are useful as an off‐the‐shelf test.
Transmission of tobacco streak virus by Thrips tabach a new method of plant virus transmission
Authors: SDOODEE RATANA , TEAKLE D. S.
Published: April 2007

When adults or nymphs of Thrips tabaci were mixed with virus‐carrying pollen from Lycopersicon esculentum infected with tobacco streak virus and then placed on Chenopodium amaranticolor test seedlings, the virus was regularly transmitted. The virus was also regularly transmitted when virus‐carrying pollen was placed on the leaves of C amaranticolor test seedlings and the thrips then introduced. No transmission occurred when test seedlings were exposed to virus‐carrying pollen in the absence of the thrips or to the thrips without pollen. Further, no transmission occurred when the thrips were fed on virus‐infected leaves and then transferred to test seedlings in the absence of virus‐carrying pollen. The evidence indicates that the transmission of tobacco streak virus by Thrips tabaci depends on the presence of pollen‐borne virus, which presumably infects via wounds made by the thrips. This method of virus transmission has not previously been reported.
Occurrence of the Andean strain of potato virus S in imported potato material and its effects on potato cultivars
Authors: DOLBY CHRISTINE A. , JONES R. A. C.
Published: April 2007

Infection with potato virus S Andean (PVSA) and ordinary (PVSo) strains was found in potato breeder's selection No. 8163‐511 imported from West Germany; the two PVS strains were differentiated by their reactions on Chenopodium quinoaTests on potato leaf samples using enzyme‐linked immunosorbent assay followed by inoculation to Cquinoa were subsequently used to detect PVSA and PVSo in a large‐scale survey of imported and domestic potato material. PVSA was detected in breeders' selections and cultivars imported from the Netherlands and West Germany, but not in domestic certified seed potato stocks or farmers' once‐grown stocks. PVSo was found in both imported and domestic certified stocks, but infection was commoner in the imported ones. When plants of C. quinoa, C. amaranticolor, C. murale and Nicotiana debneyi were inoculated with four isolates of PVSA, one induced mild symptoms while the reactions of the others ranged from moderate to severe. When plants of different potato cultivars were inoculated with three isolates, the plants were mostly infected without symptoms. However, when tubers from some were grown on, the progeny plants of most of the different combinations of cultivar and isolate of PVSA developed one or more of the following symptoms: vein deepening, rugosity, interveinal chlorosis, premature senescence and early loss of lower leaves.
Dieback and death of larch caused by Ceratocystis laricicola sp. nov. following attack by Ips cembrae
Authors: REDFERN D. B. , STOAKLEY J. T. , STEELE H. , MINTER D. W.
Published: April 2007

Circumstantial and experimental evidence suggests that the bark beetle Ips cembrae acts as a vector for Ceratocystis laricicola sp. nov. which it introduces into larches during breeding attacks. The fungus kills bark and cambium, and invades the sapwood causing the formation of areas of ‘blue stain’ surrounded by dry wood. Multiple inoculations resulting from numerous beetle attacks may totally disrupt conduction causing dieback and death of whole trees. Attacks seem frequently to be associated with drought and other forms of stress. Trees damaged by I. cembrae and C. laricicola may be attacked subsequently by the woodwasp Urocerus gigas which introduces a sapwood decay fungus, Amylostereum chailletii.

This is the first record of an association between I. cembrae and a species of Ceratocystis and the first record of dieback in larch caused by I. cembrae and C. laricicola. I. cembrae was introduced into Britain from mainland Europe and a similar association may occur there.
Influence of the d2 factor on survival and infection by the Dutch elm disease pathogen Ophiostoma ulmi
Authors: WEBBER J. F.
Published: April 2007

A particular form of mycovirus, the d2 factor, which attacks the elm pathogen Ophiostoma ulmi, was found to be extremely deleterious to this fungus both in vitro and in vivo. Most significantly, d2‐infected conidia were poor at persisting in feeding grooves, the usual infection court of the pathogen, and also showed a 50‐fold reduction in successful xylem infection compared with their healthy counterparts. In addition, transmission of the d2 factor from diseased to healthy isolates of O. ulmi was found to take place in feeding grooves, indicating that the fungus exists in a mycelial phase prior to invading xylem vessels.
Sources of Verticillium fungicola on a commercial mushroom farm in England
Authors: WONG W.C. , PREECE T. F.
Published: April 2007

From 1979 to 1981 Verticillium fungicola, a pathogen to Agaricus bisporus, was detected in 47 out of 485 samples of baled peat and in one out of 126 samples of bagged limestone arriving at an isolated mushroom farm in the UK. The pathogen was not detected in 875 samples of water, soil, mushroom spawn or spawned compost. Casing (a mixture of peat and limestone) prepared and used on the farm contained detectable V. fungicola in 25 out of 108 samples. The primary sources of V fungicola were thus the two constituents of casing, especially peat.

Secondary sources of V. fungicola were numerous and included symptomless and diseased mushrooms, pickers and other staff, floors and doors and the principal pests (sciarid flies and mites).

Viable airborne spores of V. fungicola were detected with an Andersen sampler in farm buildings at all stages in crop production. The spore load increased with the age of the crop. Few airborne spores were detected immediately outside affected buildings, and very few at the farm entrance 30 m away. There was no evidence that V. fungicola reached the farm from the surrounding air. despite substantial soil disturbance nearby.

Selective media for V. fungicola are described.
Disinfection of pepper seed infected with different strains of capsicum mosaic virus by trisodium phosphate and dry heat treatment
Authors: RAST A. Th. B. , STIJGER C. C. M. M.
Published: April 2007

Disinfection of pepper seed infected with capsicum mosaic virus (CaMV) by immersion in 100 g/1 Na3 P04 solution was compared with dry heat treatment at 76°C. The virus content of the seed varied with the CaMV strains used to infect the pepper cultivars and the time of harvest of seeds from infected plants. Immersion times in Na3PO4 had to be increased from 15 min to 2 h to obtain near‐complete virus inactivation; these treatments had no effects on germination.

Heating seed in an oven at 76°C for 3 days following a waiting period of 3 months after harvest always eliminated all the virus present, but adversely affected germination. This resulted in delayed emergence and a reduction in the number of seedlings suitable for further raising. The viability of heat‐treated seeds also decreased with continued storage after treatment.

There were inconsistent differences in germination of seed from healthy plants and plants infected with the CaMV strains P8 or P11. The possibility of internal seed infection and practical consequences are discussed.
Survey of benomyl resistance in Fusavium species on winter wheat in England and Wales in 1986
Authors: LOCKE T. , MOON LYNN M. , EVANS JANET
Published: April 2007

In 1986, samples from 109 winter wheat crops in England and Wales were examined for benomyl resistance in Fusarium species. Of the 704 isolates obtained, 581 were identified as Fusarium nivale, of which 92.1 % were resistant to benomyl. Of the remaining isolates, 82 were identified as F. avenaceum, 40 as F. culmorum and one as F. poae; none of these isolates were resistant to benomyl. The vast majority of isolates of Fusarium spp. were obtained from superficial nodal or internodal lesions on the stems.
Control of seed‐borne Sclerotinia sclerotiorum by fungicidal treatment of sunflower seed
Authors: HERD G. W. , PHILLIPS A. J. L.
Published: April 2007

Treatment of sunflower seeds with benomyl, vinclozolin, iprodione or procymidone virtually eliminated seed‐borne Sclerotinia sclerotiorum. Applications of fungicides increased the number of surviving seedlings when seeds were sown in vermiculite or in steam‐sterilized soil. With the exception of benomyl, fungicides were significantly more effective when applied in acetone solutions than when 100 g a.i./100 kg of seed was applied as conventional dry dressings. There was no difference in effectiveness between the two application methods when the dry dressings were applied at 200 g a.i/100 kg of seed. The acetone infusion method had no deleterious effects on germination of disease‐free seed nor on seedling vigour. For a comparable level of control, less fungicide was needed in the infusion treatment than in the dust treatment. If fungicidal treatment of sunflower seeds is used routinely then the introduction of S. sclerotiorum into uninfested land could be controlled.
Effect of MBC fungicide tolerance on the fitness of Ophiostoma ulmi
Authors: WEBBER JOAN F.
Published: April 2007

Isolates of Ophiostoma ulmi with mutations conferring high or low levels of tolerance to MBC‐generating fungicides were selected in the laboratory. Comparisons between these tolerant forms and their wild type equivalents indicated that the acquisition of a mutation in the tol locus was associated with decreased growth on agar medium. Pathogenicity and bark‐colonizing ability were also found to be significantly reduced, indicating that the fitness of tolerant individuals was impaired.
Downy mildew of boysenberry and tummelberry in the UK
Authors: McKEOWN B.
Published: April 2007

Peronospora rubi was observed in the UK on boysenberry, a blackberry x red raspberry hybrid, and on tummelberry, a cross between tayberry (blackberry cv. Aurora x tetraploid red raspberry) and another tayberry seedling from the same cross. These findings were new UK and world records respectively. The principal disease symptoms were leaf spots and blotches. The source of infection could not be identified.
Pseudocercosporella anguioides, a weakly pathogenic fungus associated with eyespot in winter wheat at a site in England
Authors: BATEMAN G. L.
Published: April 2007

Pseudocercosporella anguioides is reported for the first time from Britain. Isolates were made from the leaf sheaths of four plants of a sample of 2716 with suspected eyespot lesions taken in April 1986 from a winter wheat crop. The eyespot pathogen, P. herpotrichoides, was isolated from 724 plants in the same sample. P. anguioides was not found in a sample of eyespot‐infected straws taken from the same crop in July 1986. In infection tests, the P. anguioides isolates produced no obvious lesions on the leaf sheaths of wheat seedlings grown in pots, but were sometimes reisolated from symptomless leaf sheaths. Although P. anguioides occurred infrequently, care is needed to distinguish it from P. herpotrichoides when monitoring the eyespot pathogen.
Relationships between the spatial pattern and number of apothecia of Sclerotinia sclerotiorum and stem rot of soybean
Authors: BOLAND G. J. , HALL R.
Published: April 2007

Relationships between the spatial patterns and numbers of apothecia of Sclerotinia sclerotiorum and incidence of sclerotinia stem rot of soybean (Glycine max) were investigated in a field plot in 1981 and 1982. Apothecia and disease were both spatially aggregated and were most consistently described by the negative binomial distribution, although the Poisson‐binomial and logarithmic with zeros distributions sometimes gave significant fits to data. Numbers of apothecia and disease incidence were correlated within quadrats of 1.4 m2 (r = 0.04‐0.57), 36 m2 (r = 0.44‐0.87) and 108 m2 (r = 0.44‐0.99). The results suggest that disease incidence was determined primarily by inoculum produced within the field. This information may be important in developing models for disease production.
Incidence of benomyl and iprodione resistance in isolates of Botrytis cinerea in tomato crops in England and Wales in 1986
Authors: LOCKE T. , FLETCHER J. T.
Published: April 2007

In 1986, mass‐mycelial isolates of Botrytis cinerea from 67 tomato crops in England and Wales were examined for benomyl and iprodione resistance. Of the 706 isolates obtained, 62.7% were resistant to benomyl at 2μg/ml and 43.2% were resistant to iprodione at 2 μg/ml. Iprodione resistance persisted in the absence of a dicarboximide spray programme. The incidence of benomyl resistance has not decreased since the last survey in 1984 in spite of a considerable reduction in the use of benzimidazole fungicides. There were no clear indications that the use of dichlofluanid influenced the incidence of benomyl or iprodione resistance. Disease control was poorer in crops with a higher incidence of iprodione resistance.
Cane spot (Elsinoë veneta) in red raspberry: infection periods and fungicidal control
Authors: MUNRO J. M. , DOLAN A. , WILLIAMSON B.
Published: April 2007

Dichlofluanid controlled cane spot (Elsinoë veneta) of raspberry cv. Mailing Jewel when applied before harvest in a four‐spray programme, but carbendazim, vinclozolin and iprodione were ineffective. Lesions predominated in the fruit‐bearing region of canes in a zone 46‐120 cm above soil level. Bait plants exposed for periods of 2 weeks in two infected plantations in north‐east Scotland developed lesions, after incubation for 4‐6 weeks, only on internodes which were the youngest at the time of exposure. Infection occurred in all periods from mid‐April to late July. The infection of bait plants was related to the distribution of lesions on canes in the spray trial.

An isolate of E. veneta obtained from a plantation sprayed with carbendazim and vinclozolin was resistant when tested in vitro to carbendazim, benomyl and thiophanate‐methyl. This isolate and another MBC‐sensitive strain were both relatively insensitive to the dicarboximide fungicides iprodione and vinclozolin.