bluuebunny/crossref_metadata_2025 huggingface dataset:
Virulence of Gaeumannomyces graminis var. tritici from fields under short‐term and long‐term wheat cultivation in the Pacific Northwest, U.S.A.
Authors: COOK R. J. , NAIKI T.
Published: April 2007

Gaeumannomyces graminis var. tritici was recovered from 63% of 731 winter wheat plants collected randomly from six sites where wheat had been grown in monoculture for the previous 7–22 years. Typical take‐all was not evident at the time the plants were collected. The fungus was isolated by a baiting method without regard to the presence of take‐all on the plants. Isolates from fields under short‐term wheat cultivation (3 years or less after a break crop) were obtained by plating directly from infected roots of plants with typical take‐all. Virulent isolates comprised 89 and 99% of those collected from long‐ and short‐term wheat cultivation respectively. There was also only a slight difference in the proportions of virulent isolates among monoascosporic subcultures from the two groups of isolates. There was thus little evidence that, during prolonged wheat cultivation, declining virulence in the population of G. graminis var. tritici could account for the absence of take‐all.
Control of cucumber powdery mildew by the hyperparasite Ampelomyces quisqualis and fungicides
Authors: SUNDHEIM L.
Published: April 2007

Application of conidial suspensions of the hyperparasite Ampelomyces quisqualis to greenhouse cucumbers inoculated with Sphaerotheca fuliginea increased cucumber yield compared with an untreated control. Similar yield increases were obtained with triforine and also when a reduced rate of triforine and the hyperparasite were combined. A. quisqualis extensively parasitized S. fuliginea and also, in experiments with commercial cucumber crops, Erysiphe cichoracearum.
Further studies on root symptoms in coconut palms affected by lethal yellowing disease in Jamaica
Authors: EDEN‐GREEN S. J.
Published: April 2007

Roots were induced by banking moist coir dust around the boles of apparently healthy coconut palms growing in an area where lethal yellowing was spreading rapidly. Samples of roots were removed for inspection at 1–2 wk intervals after the detection of the first symptoms in palms. Frond symptoms were recorded weekly. Comparison of symptoms in roots and fronds of 28 of the 36 palms that developed lethal yellowing confirmed the earlier observations that the roots usually remained symptomless for a variable period of up to 4 months following detection of the first symptoms of the disease. When root symptoms appeared, most of the actively‐growing root tips became necrotic within a period of 2–4 wk and the collapse of the root system was closely correlated with the onset of progressive yellowing of fronds.
The relative susceptibility of some cucurbits to an Iranian isolate of Phytophthora drechsleri
Authors: ALAVI A. , STRANGE R. N. , WRIGHT G.
Published: April 2007

When zoospores of Phytophthora drechsleri were added to a hydroponic medium in which roots of cucurbit plants were immersed, marrow and pumpkin (Cucurbita spp.) remained symptomless but cantaloup, melon and cucumber (Cucumis spp.) wilted. Symptom development was proportional to the logarithm of day number after inoculation and approximately proportional to the logarithm of zoospore number in cantaloup and melon but not cucumber which was also less susceptible. The fungus became established preferentially in the hypocotyls of cantaloups. Ten times as many chlamydospores differentiated on infected cantaloup hypocotyls as on lupin roots when both tissues were buried in moist soil.
Detection of corn stunt spiroplasma in vivo by ELISA using antisera to extracts from infected corn plants (Zea mays)
Authors: EDEN‐GREEN S.J.
Published: April 2007

Antisera were raised in rabbits to extracts from healthy corn plants and from plants infected with corn stunt spiroplasma (CSS); they were prepared by partially purifying sap or tissue homogenates from whole stems by differential centrifugation and filtration. The titres of CSS‐specific antibody in the antisera to diseased plant extracts (DPE) were monitored by spiroplasma deformation tests. After cross‐absorption against healthy plant extracts, the DPE antisera detected cultured CSS at concentrations exceeding 106 cells/ml, compared with less than 105 cells/ml for homologous antiserum, and reacted more strongly against extracts from diseased than from healthy plants. A comparison of techniques for extracting diseased plant tissues showed that the reaction of stems and midribs against cultured CSS antiserum was two to three times stronger if the samples were lyophilized before extraction. When extracts from lyophilized tissues were used as test antigens the DPE antisera discriminated between diseased and healthy corn stems, midribs and roots as effectively as antiserum to cultured CSS. Preliminary attempts to detect CSS in its vector, Dalbulus maidis, were complicated by non‐specific reactions of insect tissue extracts but concentrations equivalent to at least one CSS‐infected insect/ml of sample were detected by antiserum to cultured CSS.
Colonization and sporulation of Peronospora viciae on cultivars of Pisum sativum
Authors: DICKINSON C. H. , SINGH H.
Published: April 2007

The behaviour of Peronospora viciae was examined on four pea (Pisum sativum) cultivars (Maro, Superb, Victory Freezer and Surprise) which appeared to exhibit varying degrees of resistance to this pathogen. Penetration into all cultivars was similar and mainly by direct entry through the cuticle. The pathogen grew in a similar manner and at a similar rate in all the cultivars during the early stages (<96 h) of tissue colonization. As it approached the onset of sporulation its growth slowed down in the more resistant cultivars but in no instance were any hypersensitive or other host cell reactions observed. Greater differences between the cultivars were seen in the extent of sporulation, with the least resistant cultivar (Superb) bearing the largest number of sporangiospores. There was much less sporulation on the most resistant cultivar (Maro) and the process was more dependent on temperature than it was on Superb. The development of mature plant resistance occurred in a similar way and on a similar time‐scale in all cultivars. The youngest leaflets on plants which were less than 8 weeks old at inoculation showed the least resistance to infection and colonization.
Development and physiology of infection by the downy mildew fungus Peronospora parasitica (Pers. ex Fr.) Fr. in susceptible and resistant Brassica species
Authors: KLUCZEWSKI S. M. , LUCAS J. A.
Published: April 2007

The growth of two isolates of the downy mildew fungus Peronospora parasitica, one obtained from cauliflower (Brassica oleracea) and the other from oilseed rape (B. napus) was assessed in their respective hosts of origin, and also in the alternative combination. Both isolates were capable of infecting either host, but there were marked contrasts in the time course and extent of mycelial development, the amounts of associated host‐cell necrosis, and eventual intensity of sporulation. Oilseed rape, which was partially resistant to the isolate from cauliflower, exhibited extensive necrosis of mesophyll cells, in conjunction with reduced mycelial development, and delayed and reduced sporulation by the pathogen. The isolate from oilseed rape was virulent on both host species. Pathogenesis in the susceptible combinations was accompanied by large increases in electrolyte leakage, and increased activity of the enzymes β‐glucosidase, ribonuclease, and peroxidase. Effects on chlorophyll content were variable and activities of acid phosphatase and acid phosphodiesterase were unaffected. Electrophoretic analyses of extracts from fungal sporangia and infected seedlings indicated that the large increases in β‐glucosidase were of pathogen origin, while evidence from inhibitor studies suggested that enhanced ribonuclease activity was due to a new post‐infectional form of the enzyme. The significance of these findings is discussed in relation to pathogenesis and host resistance mechanisms.
Measurement of spore‐carrying splash droplets using photographic film and an image‐analysing computer
Authors: FITT B. D. L. , LYSANDROU M. , TURNER R. H.
Published: April 2007

An improved method for the sampling of splash droplets carrying fungal spores uses fixed photographic film. Droplets left clear, permanent traces within which spores were easily visible. The droplet spread factor was constant because the gelatine layer was uniform. A comparison of estimates of the numbers of splash droplets, spore‐carrying droplets and spores dispersed by a 5 mm drop falling onto a spore suspension (depth 0.5 mm) with those obtained by other workers demonstrated the reliability of this method. The accuracy was improved by semi‐automatic analysis of the spore‐carrying splash droplet traces with an image‐analysing computer.
Temperature‐sensitive resistance of the wheat cultivar Maris Fundin to Puccinia recondita
Authors: HYDE P. M.
Published: April 2007

The infection of seedlings of the wheat cultivar Maris Fundin by Puccinia recondita f.sp. tritici was investigated at three temperatures and compared with that on Armada, which always gave a compatible reaction, Maris Fundin gave an incompatible reaction at 20° C, a compatible reaction at 9° C and an intermediate reaction at 15° C. At 15° C Maris Fundin developed fewer uredosori and had a longer latent period than Armada.
Effect of fungicide treatment on yield of winter wheat and spring barley cultivars
Authors: PRIESTLEY R. H. , BAYLES ROSEMARY A.
Published: April 2007

Analyses of the results of 21 winter wheat and 32 spring barley trials showed that cultivars differed significantly in their yield response to a standard fungicide treatment. Responses were also strongly influenced by differences between sites and between years. Regression analyses showed that responses were significantly related to reductions in foliar disease, particularly that of mildew, although the proportion of variance accounted for was small. Measurements made on seven winter wheat trials indicated that the percentage of leaf area remaining green after anthesis was increased by the fungicide treatment to a greater extent than could be attributed to reduction in foliar disease alone. In one of these trials, yield response was more closely correlated with the increase in leaf area remaining green than with reduction in foliar disease.
The effect of bacterial fermentation of couch grass rhizomes and Fusarium culmorum on the growth of barley seedlings
Authors: PENN D. J. , LYNCH J. M.
Published: April 2007

Phytotoxic concentrations of acetic acid were found in extracts of decaying rhizomes of couch grass (Agropyron repens) kept in sand at different moisture levels. Leaf extension of barley seedlings was inhibited by inoculating the radicles before planting with Fusarium culmorum and this inhibition was increased by 5 mM acetic acid. Seed dressings of benomyl and thiram alleviated the inhibition of leaf growth of seedlings grown in sand containing rhizomes inoculated with F. culmorum.
A genetic study of the relationship between height, time of ear emergence and resistance to Septoria nodorum in wheat
Authors: SCOTT P. R. , BENEDIKZ P. W. , COX CHERYL J.
Published: April 2007

Winter wheat cultivars of varying height were intercrossed and the progeny were studied in field trials to determine whether the greater resistance to S. nodorum of the taller cultivars was fortuitous or the result of genetic association.

Variation in height, in resistance and in time of ear emergence was continuous, providing no evidence of the existence of individual genes of major effect. In F2 and backcross generations, the inheritance of all three characters was principally additive. Among random F3 and F4 families there was a clear tendency for tall straw and resistance to segregate together, proving that the association between these characters was not fortuitous and providing evidence of linkage or pleiotropy in their genetic control. There was a similar though less consistent tendency for late ear emergence and resistance to segregate together. There was substantial residual variation in resistance, not associated with variation in height or time of ear emergence, but its heritability was difficult to prove by comparisons between F3 and F4 generations, perhaps partly because of genotype x environment interaction.

It is proposed that resistance is under polygenic control and pleiotropy rather than linkage is suggested as the explanation of its genetic association with height and with time of ear emergence. The existence of genes affecting resistance independently of height and time of ear emergence is also inferred. It is suggested that they permit the breeding of resistant cultivars of any height, though with increasing difficulty as height is reduced.
The effect of humidity on potato gangrene development in naturally contaminated tubers
Authors: CROKE F. , LOGAN C.
Published: April 2007

During the winters of 1977/78 and 1978/79 tubers of cv. Arran Banner naturally contaminated with Phoma exigua var, foveata were kept at either high or low humidity and at 5, 10, 15 or 20 C. During the 1978/79 winter cv. Majestic tubers were stored under similar conditions at 5 and 10°C only. At monthly intervals tubers from each lot were damaged to encourage gangrene development and returned to their storage condition except the Majestic tubers which were switched from high to low humidity or vice versa and returned to the appropriate temperature. No gangrene rots developed in tubers kept at 1 5 or 20°C at either humidity. At 5 and 10°C fewer rots developed at high humidity compared with low humidity including Majestic tubers kept Initially at high humidity. Inoculum levels in soil on tubers were not markedly affected by storage conditions.
The cause of smoulder and the infection of narcissus by species ofBotrytis
Authors: O'NEILL T. M. , MANSFIELD J. W.
Published: April 2007

Cultures ofBotrytisisolated from narcissus were readily identified from their sclerotial characteristics on potato dextrose agar.B. narcissicolawas isolated most frequently from typical smoulder symptoms. Infection of narcissus by isolates ofB. narcissicolaandB. cinereawas investigated using conidial and mycelial inocula on detached leaves and bulb scales. Only mycelial inocula ofB. narcissicolaisolates consistently caused spreading lesions. Conidial inocula of both species typically failed to colonise healthy narcissus tissue when inoculated in sterile distilled water butB. narcissicolacaused some spreading lesions after tissue damage, in senescent tissue, or following the addition of certain nutrients (including pollen) to inoculum droplets. Cultivars differed in the resistance of their bulb scales. The specificity ofBotrytis‐narcissusinteractions is discussed.
Surveys of beet cyst nematode in England 1977–80
Authors: SOUTHEY J.F. , ALPHEY T.J.W. , COOKE D. A. , WHITEWAY JENNIE A. , MATIIIAS P. L.
Published: April 2007

Surveys of sugar beet crops for beet cyst nematode (Heterodera schachtii Schmidt) in seven selected areas of England have provided data on distribution of the pest and on some factors affecting its occurrence. These data were mapped by CAMGRID computer program.

Infestations occurred mostly on the East Anglian fenland (14% of fields infested) and in this area were more frequent nearer the sugar beet processing factory. In the remaining areas the few infested fields (5% or less) were generally scattered but a small concentration of infestation occurred in the West Midlands in an area of intensive horticulture with frequent brassica crops. The survey data did not support the view that beet cyst nematode infestations occur more frequently near access points to the crop. In the surveyed areas frequency of host crops appears to be more important than soil type in determining the likelihood of infestation.
Analysing epidemics in time and space
Authors: JEGER M.J.
Published: April 2007

Simple models of disease increase in time and space are developed by considering the rate of isopath movement (change in distance of a given level of disease in unit time) from a focal centre. Linear equations for simultaneously estimating parameters of temporal progress and spatial spread are derived for different types of epidemics. The uses of the models in estimation and interpretation are demonstrated by reference to published epidemic data.
Flavor and odour characteristics of species of Allium in relation to their capacity to stimulate germination of sclerotia of Sclerotium cepivorum
Authors: ESLER G. , COLEY‐SMITH J. R.
Published: April 2007

Of many species or cultivars of Allium tested only six ornamental species showed little or no capacity to stimulate germination of sclerotia of Sclerotium cepivorum. All six species had S‐methyl‐L‐cysteine sulphoxide as their principal flavour and odour precursor and their overall flavour and odour levels were low. All other species and cultivars were highly stimulatory, contained considerahle amounts of S‐1 or S‐2‐propenyl‐L‐cysteine sulphoxide as flavour and odour precursors and, with a few exceptions, they possessed high overall flavour and odour levels. These included several species which are thought to be related to cultivated edible forms. With the possible exception of A. caeruleum and A. cyaneum no evidence of resistance to infection by S. cepivorum was detected.
The occurrence ofAltemaria brassicicola, Altemaria brassicaeandLeptosphaeria maculansin brassica seed crops in south‐east England between 1976 and 1980
Authors: HUMPHERSON‐JONES F. M.
Published: April 2007

Surveys of brassica seed crops in Essex and Suffolk showed thatAlternariaspp. occurred in many crops ofBrassica oleraceain the years 1977–1980 affecting up to 100% of pods in each year.A. brassicicolawas the only species present in 1976 and was the domioant pathogen in succeeding years butA. brassicaeincreased in frequency from 1977, causing 24% of the pod infections onB. oleraceain 1980. The latter fungus was the dominant species in crops of oilseed rape (B. napus), the mean incidence of infected pods increasing from 0.5% in 1977 to 2.9% in 1980.Leptosphaeria maculanswas not found in horticultural brassica seed crops in 1976 but occurred abundantly in these crops and in oilseed rape crops in each of the following years.
The effect of variety mixtures on the development of swede powdery mildew
Authors: SITCH LESLEY , WHITTINGTON W. J.
Published: April 2007

Infection by Erysiphe polygoni was followed on the components of five mixed populations containing different proportions of a partially resistant swede variety, Ruta Øtofte (RØ), and a highly susceptible variety, Ne Plus Ultra (NPU) (100:0; 75:25; 50:50; 25:75; 0:100). Disease levels remained much lower on RØ than on NPU in all populations. For several weeks, disease on NPU was greatest in pure plots and was progressively reduced in mixtures with increasing proportions of RØ. Later, disease levels on NPU were similar in all populations. Disease on RØ was not increased in mixtures with NPU. Root yield of NPU, but not of RØ, was greater in mixtures than in pure stands. The possible use of variety mixtures to control powdery mildew in swede crops is discussed.
The effect of Phragmidium mucronatum on rose understocks and maiden bush roses
Authors: SHATTOCK R. C. , BHATTI M. H. RAHBAR
Published: April 2007

Persistent infection of field‐grown Rosa laxa hort, by the rust fungus Phragmidium mucronatum was observed throughout summer and autumn in 1979 and 1980. Rust significantly reduced shoot number, length and fresh weight (to 85 and 54% of the control after one and two seasons respectively) along with flower number and fruit yield. Root weight was also reduced to 55% of the control over two seasons.

The growth of four bush rose cultivars budded on to rusted Laxa stocks was reduced, affecting bush quality. Overall, rust‐free stocks produced twice as many saleable maidens as rusted stocks but bud take was not affected by P. mucronatum.
The effects of various crops on the survival and carry‐over of the wheat take‐all fungus Gaeumannomyces graminis var. tritici
Authors: KOLLMORGEN J. F. , GRIFFITHS J. B. , WALSGOTT D. N.
Published: April 2007

The effects of various crops on the saprophytic survival and carry‐over of Gaeumannomyces graminis var. tritici were studied in the glasshouse and field.

In the glasshouse, survival of G. g. tritici was greater in unplanted pots than in pots planted with either cereals or non‐cereals. In the field, fallow and various non‐cereal crops reduced carryover of take‐all but the disease was severe after wheat, barley and triticale. Grain yields were higher after fallow and non‐cereals than after cereal crops.
The expression of partial resistance to Erysiphe graminis in spring barley
Authors: ASHER M. J. C. , THOMAS C. E.
Published: April 2007

The development of powdery mildew on five barley varieties selected for partial resistance in the field and lacking identifiable, effective race‐specific resistance factors was examined. Inoculation tests demonstrated that a reduction in the number of colonies was a major component of this resistance. Microscopic examination of segments from the fourth and fifth leaf revealed several stages at which colony development was arrested. The failure of individual penetrations to establish compatible colony growth was classified as being due either to hypersensitive or to non‐hypersensitive resistance in host epidermal cells. Varying proportions of these two types of resistance mechanism were evident in all varieties examined, including the susceptible controls. In four resistant varieties, one or other mechanism predominated. The possibility of enhancing partial resistance by combining sources in which different mechanisms operate is discussed.
The control of bubble diseases and cobweb disease of mushrooms with prochloraz
Authors: FLETCHER J. T. , HIMS M. J. , HALL R. J.
Published: April 2007

Fungicides were compared for the control of the mushroom pathogens Verticillium fungicola (dry bubble disease), Mycogone perniciosa (wet bubble disease) and Hypomyces rosellus (cobweb disease). Prochloraz, applied as a manganese complex, consistently gave significantly greater control of a benomyl‐resistant strain of V. fungicola. Captafol gave some reduction in disease. Benomyl, thiabendazole and prochloraz all gave significant control of M. perniciosa and H. rosellus. Prochloraz residues in mushrooms were measured by gas chromatography after extraction in acetone and purification by means of solvent partition, When pure prochloraz was added to homogenized mushroom tissue, 77–98% was recovered by this procedure. The residue levels in sporophores from crops treated with prochloraz were low, Prochloraz appears to be an effective fungicide for the control of the major fungal pathogens of the mushroom crop, particularly where benzimidazole‐resistant strains of V. fungicola occur.
Effects of pre‐ and post‐inoculation photoperiod on the severity of Melampsora medusae leaf rust of Populus species
Authors: SINGH S. J. , HEATHER W. A.
Published: April 2007

Disease severity, based on six parameters (time from inoculation to flecking, and eruption of uredinia, uredinial density and the amounts of urediniospoies produced), was assessed on leaf discs cut from four cultivars of Populus spp. raised with either a long (15 h) or a short (10 h) photoperiod. The discs were inoculated with race 4 of Melampsora medusae and subsequently incubated with either a long (15 h) or a short (10 h) photoperiod. While disease severity, based on most parameters, was lower in discs from the continuing long photoperiod (15 h pre‐ and 15 h post‐inoculation) than from the continuing short photoperiod (10 h pre‐ and 10 h post‐inoculation), maximum severity was developed by discs given a combination of a short pre‐ and a long post‐inoculation photoperiod. The relative contribution of the cultivar, the pre‐ and the post‐inoculation photoperiod and their second‐ and third‐order interactions to variation in disease severity depended on the parameter employed to assess severity. The parameters used are elements of disease monocycles and their possible significance in modelling epidemics is discussed.
The use of methyl bromide and carbendazim for the control of lettuce big‐vein disease
Authors: WHITE J.G.
Published: April 2007

Lettuce seedlings raised in peat blocks placed on contaminated soil subsequently developed lettuce big‐vein disease symptoms when grown in pots of sterilized compost. Incorporation of 0.01 g carbendazim per 4.3 cm3 peat block reduced the number of plants with disease symptoms but did not prevent root infection by Olpidium brassicae, the vector of the big‐vein agent. Similar results were obtained when seedlings propagated in the absence of big‐vein disease were grown in pots of contaminated soil but carbendazim was less effective when the treated blocks were planted in contaminated field plots. Methyl bromide applied at 500, 750 or 1000 kg/ha temporarily controlled the disease but re‐contamination occurred and was complete after three consecutive crops.

Bromide residues in lettuce heads reached 9240 μg/g dry tissue in the first crop but fell to a maximum 772 μg/g by the third crop. Bromide residues in soil fell to natural levels over this period.
Variability of Cryptostroma corticale, the causal fungus of sooty bark disease of sycamore
Authors: ALCOCK SUSAN , WHEELER B. E. J.
Published: April 2007

The rate at which 19 isolates of Cryptostroma corticale grew on 3% malt agar varied considerably but the growth of each isolate was optimal at 25°C. The isolates also varied considerably in their ability to grow in young sycamores (Acer pseudoplatanus) in the glasshouse and in 15‐year‐old trees in the field. Growth rates on agar and in the host were not related but isolates which grew most rapidly in young sycamores in the glasshouse had the greatest tendency to become black on Sabouraud dextrose agar and on malt agar. The results did not support the hypothesis that the 1976–77 outbreak of sooty bark disease in England was associated with a more virulent strain of the fungus.
Dispersal of Synchytrium psophocarpi in Papua New Guinea
Authors: DRINKALL M. J. , PRICE T. V.
Published: April 2007

Airborne sporangia of Synchytrium psophocarpi showed a diurnal periodicity, maximum numbers occurring between 1600 and 1800 h and minimum numbers between 0600 and 0700 h. There wers significant correlations between the amounts of airborne sporangia and temperature (positive), relative humidity (negative) and dew (negative). The numbers of airborne sporangia increased following the onset of the wet season (November—April) but declined after the onset, of the dry season (May—October). Most airborne sporangia appeared to deposit within 15 m of their source. The potential for dispersal of sporangia by rain splash was demonstrated.
Studies on infection of bean (Phaseolus vulgaris) and soybean (Glycine max) by ascospores of Sclerotinia sclerotiarum
Authors: SUTTON D. C. , DEVERALL B. J.
Published: April 2007

Factors influencing the infection of bean and soybean by ascospores of Sderotinia sclerotiorum were studied. In the absence of an exogenous nutrient source, ascospores on intact host tissues produced a short and usually sub‐polar germ‐tube but only young host tissues were penetrated by the infection hypha arising from the germinated spore. There was a hypersensitive response by cells to penetration and generally the fungus remained restricted to these cells, though it continued to grow within them. Water‐soaked lesions characteristic of successful infections only developed when many individual infection sites coalesced following inoculation with high concentrations of ascospores. Flowers or parts of flowers provided a suitable nutrient base for initial colonization from ascospore inoculum. Mycelium extending from this base initiated infection of intact host surfaces. Pollen stimulated growth from germinating ascospores in vitro and in vivo but did not stimulate infection of bean.
The effectiveness of 1,3‐dichloropropene for controlling vims vector nematodes with reference to the MAFF Certification Scheme for strawberry nursery stock
Authors: CHAPMAN P. J.
Published: April 2007

Field trials for the control of Xiphinema diversicaudatum and Longidorus elongatus in a peat soil, L. macrosoma in a fine sandy loam soil, and L. attenuatus and L. leptocephalus in a sandy soil were done using 1,3‐dichloropropene applied at various rates injected to either 15 cm or split injected at cither 15 and 30 cm or 15 and 45 cm. Good control of all the nematode species was obtained at two of the three sites to at least 60 cm though very intensive sampling revealed small residual populations following most treatments. The degree of control achieved at these two sites would probably reduce the risk to high‐grade strawberry nursery stock grown on the sites from reservoirs of virus outside the site.
Interaction of root‐lesion nematodes, Pratylenchus thornei and P. crenatus, with the fungus Thielaviopsis basicola and a grey sterile fungus on roots of pea (Pisum sativum)
Authors: GREEN C. D. , GHUMRA M. F. , SALT G. A.
Published: April 2007

Pratylenchus thornei invaded excised pea roots in agar in greater numbers and penetrated the cortex more deeply than P. crenatus. Both species fed on the roots ectoparasitically and displaced root cells into the surrounding medium. The cytoplasm of cortical cells near cither nematode became granulated, with enlarged vacuoles and nuclei. P. thornei also caused these responses in the endodermis. Infection of the root surface with a grey sterile fungus inhibited invasion by P. crenatus and P. thornei. Infection by Thielaviopsis basicola inhibited P. thornei invasion but encouraged penetration by P. crenatus and the hyphae were found deeper in the cortex when P. crenatus was present.
Comparison of methods of assessing field populations of Heterodera schachtii
Authors: COOKE D. A. , MATHIAS P. L. , CHAWARSZCZYNSKA DAPHENE M. , COPPOCK L. J.
Published: April 2007

Population assessment methods for Heterodera schachtü were compared in two tests. In the first there were no consistent differences between numbers of H. schachrü extracted by Fenwick cans (at two laboratories), a flotation column and an automatic cyst extraction apparatus, from dried soils from three sites containing no other cyst nematodes. The second, made on 54 commercial sugar beet fields, compared numbers of H. schachtü extracted from dried soil samples by Fenwick cans (at two laboratories) with results of a bioassay of soil samples and a subsequent examination of roots in the field. Most samples were placed into the same broad groups by the cyst extraction and bioassay methods and the two techniques were equally good at predicting field infestations.
Effect of viruses on pollen morphology
Authors: HAIGHT FMELINE , GIBBS ADRIAN
Published: April 2007

Many pollen grains from Chenopodium quinoa plants infected with sowhane mosaic sobemovirus (SMV) were collapsed, grooved and had sunken opercula, whereas those from the first flowers of virus‐free plants were smooth, rounded and with protuberant opercula. However, pollen grains from later flowers of virus‐free plants were similar in appearance to those from the virus‐infected plants. Similar but less obvious symptoms were found in pollen of Plantago lanccoiata infected with either ribgrass mosaic tobamovirus or broad bean wilt virus. No symptoms were found in pollen of Hordeum vulgare cv. clipper, H. sponiaitcum or Triticum acstivum infected with barley suripe mosaic hordeivirus, nor in pollen of a Cardaminc sp. naturally infected with a strain of turnip yellow mosaic tymovirus. The symptoms, even those shown by pollen from SMV‐infected C quinoa, seemed not to be sufficiently characteristic for diagnosis of virus infection.
Effect of invasion by cereal cyst nematode (Heterodera avenue) on the growth and development of the seminal roots of oats and barley
Authors: PRICE N. S. , CLARKSON D. T. , HAGUE N. M. G.
Published: April 2007

The effect of juvenile cereal cyst nematodes (Heterodera avenae) on the root growth of oat and barley seedlings was tested in three pot experiments. Invasion by juveniles hindered the extension of the seminal root axes of both cereals; after invasion, axes took 2–3 days to attain normal rates of extension. This response was found in susceptible and resistant cultivars. When oats and barley were exposed to continued invasion over 9 days, barley produced a larger root system than oats and was less stunted by nematode invasion. The density of nematodes per unit of root was less in barley than in oats. The effects on root growth were similar to reported responses of roots to mechanical damage.
Resistance to benzimidazole fungicides in the gummy stem blight pathogen Didymelta bryoniae on cucurbits
Authors: MALATHRAKIS N. E. , VAKALOUNAKIS D. J.
Published: April 2007

Benzimidazoles were used successfully against gummy stem blight of cucurbits for only one growing season (1980). It was soon noticed in experiments in vivo that they were not effective against some isolates of the pathogen. In a survey during the 1981 crop season, 76 out of 102 isolates collected from 20 plastic greenhouses all over the main cucurbit‐growing areas of Crete were resistant to benomyl. The average benomyl concentrations that reduced mycelial growth rates of seven resistant and seven sensitive isolates by 50% were 716 ± 49 and 1.2 ± 0.34μg/ml respectively. The average growth rate of resistant isolates was lower than that of sensitive isolates but there were no differences in spore production and spore germination. The pathogenicity of resistant isolates on young cucumber plants was lower than that of sensitive isolates. The application of benomyl, carbendazim, cypendazole and thiophanate methyl to young cucumber plants at the rate of 300μg a.i./ml 1 day before inoculation with 500 000 spores/ml of the resistant isolates did not affect the infection rate of the disease after 4 days. Sensitive isolates caused no onslight symptoms on similarly treated plants.
Dispersal of Pseudocercosporella herpotrichoides and Pyrenopeziza brassicae spores in splash droplets
Authors: FATEMI F. , FITT B. D. L.
Published: April 2007

Splash dispersal of conidia which differ in shape and size, those of Pseudocercosporella herpo ichoides (needle‐shaped, 52×2 μm) and Pyrenopeziza hrassicae (cylindrical, 12×3 μm), was studisd by allowing 5 mm drops to fall 13 m on to suspensions (depth 0.5 mm, concentration 120, 000 spores/ml) of each. The resulting splash droplets were collected on photographic film. The pattern of spore dispersal with distance and the distribution of spore‐carrying droplets and spores within droplet‐size categories were similar for both fungi. Regressions of square root spore number) on droplet diameter gave lines with slopes of 0.0138 for P. herpotrichoides and 0.0167 for P. brassicae.
The relationship between genotypes of three Brassica species and collections oi Plasmodiophora brassicae
Authors: CRUTE I. R. , PHELPS KATHLEEN , BARNES A. , BUCZACKI S. T. , CRISP P.
Published: April 2007

Internationally collected data concerned with variation for pathogenicity in Plasmodiophora brassicae and for clubroot resistance in three Brassica species, together with additional experimental evidence, were used to elucidate the major genetic features of this host‐parasite relationship. The major components of resistance in B. campestris and B. napus were differential and xobahly oligogenic. Good agreement was found between the data and simple gene‐for‐gene schemes. In contrast, the major component of resistance in most B. oleracea genotypes appeared to be non‐differential and there was evidence of pathogen variability for non‐differential pathogenicity. A strong association between pathogenicity on any resistant B. campestris genotype and on all resistant B. napus genotypes was apparent, suggesting the possibility of genes in common. There was evidence that P. brassicae collections carrying certain characters for differential pathogenicity on these two species were less pathogenic on B. oleracea. However, there was no ether evidence of pathogenic specialization to a particular host species. Several analytical procedures were employed which may prove useful in clarifying the important features of other host‐parasite combinations.
Effect of barley yellow dwarf virus on susceptibility of barley cultivars to net blotch (Pyrenophora teres) and leaf blotch (Rhynchosporium secalis)
Authors: VARUGHESE J , GRIFFITHS ELLIS
Published: April 2007

The effect of barley yellow dwarf virus (BYDV) on the development of net blotch (Pyrenophora eves) and leaf blotch (Rhynchosporium secalis) was examined on seven barley cuitivars. Seedlings were infected with BYDV at the two‐leaf stage (G.S. 12). Their susceptibility to three isolates of p teres and isolates of two races (U.K. 1, U.K. 2) of R. secalis was examined at the four‐leaf stsge (G.S. 14) and when plants were more mature (G.S. 33/38). At G.S. 14 numbers of lesions produced by P. teres and R. secalis were reduced, on average, by 37 and 72% respectively, and at G.S. 33/38 by 61 and 74%.
The use of a tomato cotyledon test to identify Corynebacterium michiganense pv. michiganense
Authors: CHALDECOTT M. A. , PREECE T. F.
Published: April 2007

When cotyledons of 4‐day‐old tomato seedlings (Lycopersicon esculentum cv. Sonato) were inoculated with Corynebacterium michiganense pv. michiganense and kept at 25°C with a 16 h light period per day, white raised blisters were produced which coalesced to give white, scurfy, cracked areas after 3 days. This symptom did not develop when Gram‐positive coryneform bacteria isolated from, and near, tomato crops were used as inoculum. Pre‐inoculation abrasion of cotyledons, an inoculum concentration of at least 105 bacteria/ml, and high humidity after inoculation were important factors in the expression of this host reaction. The cotyledon test may be of value in laboratories where more detailed tests for C. michiganense pv. michiganense are not possible.
Methods for assessing the susceptibility of potato tubers of different cultivars to rotting by Erwinia carotovora subspecies atroseptica and carotovora
Authors: LAPWOOD D. H. , READ P. J. , SPOKES JANIS
Published: April 2007

The susceptibility of tubers of different potato cultivars to soft rot by Erwinia carotovora subspp. uroseptica and carotovora was assessed in 3 years by two methods. In one method, whole tubers inoculated at wounds with either bacterium were incubated under anaerobic conditions for 5 or o days at 15°C. In the other method, wounds made in tuber slices were allowed to heal or not, before inoculation with different concentrations of each bacterium and were then incubated under aerobic conditions for 3 days at 15°C. Most cultivars gave consistent reactions in repeated experiments using the same method, but there was some seasonal variation. A few cultivars were consistently susceptible (Klondyke and Manna) or resistant (Drayton) in both methods but others gave completely contrasting results (Record). In both methods and with all cultivars more rotting was caused by subsp. atroseptica than by subsp. carotovora because of the temperature of Incubation.
An investigation of the reliability of ELISA as a practical test for detecting potato leaf roll virus and potato virus Y in tubers
Authors: HILL S. A. , JACKSON ELIZABETH A.
Published: April 2007

Enzyme‐linked immunosorbent assay (ELISA), involving mechanical sampling of tubers, was compared with a growing‐on test in which virus was assessed visually, and with ELISA on leaves. The percentage infection of potato leaf roll virus and potato virus Y on samples of potential seed tubers sent for advisory test during the winter, was determined by each method. The tuber ELISA underestimated the incidence of both viruses, and was less accurate than the growing‐on or leaf ELISA. The effect on the reliability of tuber ELISA of the amount and distribution of virus in the tuber, the compromises made to make the test fast and simple, and the quality of anti‐serum and composition of the extraction buffer are discussed.
The nature and distribution of Verticillium albo‐atrum strains highly pathogenic to the hop
Authors: SEWELL G. W. F. , WILSON J. F.
Published: April 2007

During routine, annual, field wilt‐resistance trials of hop progeny, ‘breakdowns’ of resistance occurred in control varieties. Pot‐plant pathogenicity tests of isolates from these trials, and other isolates obtained during farm surveys, confirmed the existence of apparently new strains potentially highly pathogenic to resistant cultivars. Results of the tests provided little evidence that enhanced pathogenicity was associated with specificity. The assumption of essentially host nonspecific pathogenicity was consistent with other observations on the inheritance of resistance.

Highly pathogenic strains were identified among isolates from nine farms in Kent. The locations and ownership of these farms, and their wilt histories, provided strong circumstantial evidence that these strains had spread from a single focus, as did progressive wilt originally. Legislation, introduced to restrict further spread, may have been too late.
Inoculating plant material by jet injection
Authors: WASTIE R. L.
Published: April 2007

Both tubers and plants of potato were successfully inoculated with Erwinia carotovora subsp. itroseptica by means of a needle‐less medical jet injector. The instrument has also been used to infect potato tubers with Phorna exigua var. foveata, Fusarium solani var. coeruleum and F. sulphureum. It is suggested that high‐pressure injection is a potentially useful tool for introducing pathogens into plant materials.
Comparison of cuprous oxide and metalaxyl with mixtures of these fungicides for thecontrol of Phytophthora pod rot of cocoa
Authors: McGREGOR A. J.
Published: April 2007

Experiments were conducted using small‐scale, detached pod evaluation methods to compare the likely effectiveness in controlling black pod of cuprous oxide‐metalaxyl mixtures with these fungicides alone at approximately equivalent cost doses. All fungicide treatments were about equally effective and persistent except when rain fell soon afterspraying. Treatments containing cuprous oxide then gave very poor control of artificialinoculations with Phytophthora palmivora zoospores. Further laboratory' scale tests confirmed that cuprous oxide was readily leached by washing before the deposit completely dried whereas metalaxyl was very rapidly adsorbed on to ihe pods. A black pod control strategy is proposed using metalaxyi during critical wet periods and cuprous oxide for the rest of the year to reduce the possibility of metalaxyl resistance becoming apractical problem.
Carbendazim resistance in the eyespot pathogen Pseudocercosporella herpotrichoides
Authors: BROWN M. C. , TAYLOR G. S. , EPTON H. A. S.
Published: April 2007

Mycelial isolates (115) of Pseudocercosporella herpotrichoides were obtained from five field sites in England. Carbendazim‐resistant isolates were detected by their mycelial growth on agar containing 1 μg/ml carbendazim. Resistant isolates were found at two of the five sites examined and one of these had never been treated with benzimidazole fungicides. Amongst the carbendazim‐ resistant isolates there was a predominance of isolates with pale mycelium, an irregular colony margin and a relatively slow growth rate; however, this association was not absolute. Large differences in the effects of carbendazim on mycelial growth of sensitive and resistant isolates were demonstrated; growth of sensitive isolates was completely inhibited at 0.5 μg /ml carbendazim whilst five of the six resistant isolates examined grew on agar containing 1000 μg/ml fungicide. The carbendazim‐resistant isolates were cross‐resistant to benomyl, thiophanate‐methyl and to a Icsser degree thiabendazole, but not to prochloraz. Conidia of carbendazim‐resistant isolates were as resistant. Carbendazim‐resistant isolates were just as pathogenic to wheat as sensitive isolates. The implications of these results and other reports of benzimidazole resistance in P. herpotrichoides are discussed in relation to disease control.
Components of partial resistance to Erysiphe graminis in spring barley
Authors: ASHER M. J. C. , THOMAS C. E.
Published: April 2007

The development of powdery mildew on seven spring barley varieties lacking effective major resistance factors was compared in a small‐plot field trial. Differences were observed at later growth stages indicating partial resistance in some varieties. Latent period and sporulation capacity were examined on the fifth or sixth leaf of these varieties plus several known to be susceptible, using plants raised under spore‐free conditions. Latent period was extended in most partially resistant varieties compared with susceptible controls, more so at 5°C than at 10°C. Cumulative total spore production per colony over the 16‐day sporulation period differed markedly between varieties, the most resistant yielding one‐third as many spores as the susceptible controls. There was evidence that these resistance components were correlated with each other and with previous estimates of infection frequency. The significance of this finding, in relation to selection for improved levels of partial resistance, is discussed.
A taxonomic study of the host ranges of tymoviruses
Authors: GUY P. L. , DALE J. L. , ADENA M. A. , GIBBS A. J.
Published: April 2007

Published data on the susceptibility of plant species to 18 tymoviruses were collated. These data showed that tymoviruses infected more species from the family of their natural field host than species from other families. The data also indicated that tymoviruses infected a greater proportion of species from the same primary division of the dicotyledons (crassinucellate or tenuinucelate) as their natural host than other species, but the correlation was not statistically significant.

The susceptibility of 18 crassinucellate and 18 tenuinucellate test plant species to 10 tymoviruses was determined. The viruses infected about three times more plant species from the primary taxonomic division that contained the family of their field host than species from the other division; this difference was statistically significant.

The separation of tymoviruses into two groups based on the taxonomic division containing their natural hosts and most of their experimental hosts correlates broadly with a classification of the tymoviruses based on the serological relationships of their particle coat proteins.
The sensitivity and specificity of a rapid nucleic acid hybridization method for the detection of potato virus X in crude sap samples
Authors: BAULCOMBE D. , FLAVELL R. B. , BOULTON R. E. , JELLIS G. J.
Published: April 2007

A DNA copy (cDNA) of the common European strain (strain‐group 3) potato virus X RNA (PVX3‐RNA) was prepared by reverse transcription of PVX‐RNA and amplified by cloning into E. coli plasmid pBR322. This DNA hybridizes with PVX‐RNA and not at all to RNA of potato virus Y. A low amount of cross‐hybridization was observed with strain‐group 2 of PVX (PVX2). However, by hybridization of PVX2‐RNA to restriction endonuclease fragments of PVX3‐cDNA, it was demonstrated that cross‐homology was not present in all regions of the PVX genome.

The cloned PVX3‐cDNA was hybridized to viral RNA in crude sap samples which had been spotted on to nitrocellulose membrane. The signal, which was assayed by autoradiography, allowed the detection of 50 pg of viral RNA. This value was not adversely affected by encapsidation of the RNA, nor by components of crude sap. The sap spot hybridization was as effective as enzyme‐linked immunosorbent assay both in detection of small quantities of purified PVX3, and in screening of plants from a breeding programme for immunity to PVX3 infection.