bluuebunny/crossref_metadata_2025 huggingface dataset:
Some properties of alfalfa mosaic virus isolated from Buddleia davidii in the UK
Authors: PERKINS C. J. , HICKS R. G. T.
Published: April 2007

Alfalfa mosaic virus (AMV) and cucumber mosaic virus (CMV) were isolated from clones of Buddleia davidii collected at Long Ashton Research Station for assessment of horticultural characteristics. The AMV isolate investigated in this study (AMV‐B) infected 18 species and cultivars of herbaceous test plants. The in vitro properties of AMV‐B were determined. The virus was purified by permeation chromatography on controlled‐pore glass beads and an antiserum prepared. AMV‐B appeared to be serologically indistinguishable from AMV isolate 15/64. The sizes and shapes of the virus particles were those of classical AMV components. The capsid protein was a single polypeptide of Mr 24 375. Buddleia seedlings inoculated with AMV‐B showed only mild chlorosis and slight distortion of leaves.
China and the origins of Dutch elm disease: an appraisal
Authors: BRASIER C. M.
Published: April 2007

Circumstantial evidence has led to the widespread assumption that Dutch elm disease (caused by Ophiostoma ulmi) spread to Europe and North America from China. The author's recent surveys indicate that the disease is probably absent from China, and only a relatively recent arrival in the Soviet Tien Shan mountain region on the western Chinese border. Alternative origins for the disease include introduction from the Himalayas, and recent rapid evolution within Europe from a fungus such as Ophiostoma piceae. Elucidation of the various possibilities is complicated by the need to account for the spread of at least three genetically divergent subgroups of the pathogen.
The production and release of ascospores of Pyrenopeziza brassicae on oilseed rape
Authors: MCCARTNEY H. A. , LACEY MAUREEN E.
Published: April 2007

The results of observation for three seasons in oilseed rape crops of the production and release of ascopores of Pyrenopeziza brassicae, the cause of light leaf spot disease of brassicas, are presented. Large apothecia (1–2 mm in diameter) take at least 3 weeks to develop on leaf petioles after infected leaves die, but small apothecia (50–200 um) may form on leaf lamellae after about 15 days. Apothecia were found on all 12 oilseed rape varieties examined. Spore trapping experiments in infected crops show that ascospore release is associated with rain, but most ascospores are released after rainfall when the crop debris bearing apothecia are wet. Ascospores can be released for up to 5 days after rain. Laboratory measurements show that apothecia can continue to release ascospores for up to 3 weeks even when they are subjected to wet and dry cycles. The consequences of the widespread occurrence of the sexual stage of P. brassicae are discussed and possible cycles of disease and spore production in oilseed crops are suggested.
First record of Tapesia yallundae as the teleomorph of Pseudocercosporella herpotrichoides var. acuformis, and its occurrence in the field in the Federal Republic of Germany
Authors: KING AMBER C.
Published: April 2007

Tapesia yallundae is reported for the first time in the Federal Republic of Germany. Apothecia were found on wheat and rye stubble at two sites in the north of the country and one in the centre, in April 1988. Isolates of Pseudocercosporella herpotrichoides var. acuformis were obtained from germinating single ascospores, identified on the basis of colony morphology, mode of conidial production and pathogenicity to wheat and rye.
Long‐term survival of sclerotia of Sclerotium cepivorum and Stromatinia gladioli
Authors: COLEY‐SMITH J. R. , MITCHELL CHRISTINE M. , SANSFORD CLAIRE E.
Published: April 2007

In an experiment with pure‐culture sclerotia of Sclerotium cepivorum and Stromatinia gladioli a large proportion of the sclerotia survived burial for 20 years in the field in the absence of host plants. Some evidence for metabolic activity or leakage leading to the gradual erosion of the sclerotial contents was obtained with S. cepivorum. The results of other experiments suggested that, for unknown reasons, a variable proportion of sclerotia formed naturally on infected plants may decay shortly after their formation, but those which survive beyond this limited period are likely to remain viable for many years. The viability of sclerotia was also reduced by prolonged flooding, but the period for which land would have to be under water excludes this as a method of eliminating sclerotia from infested land in the UK. Treatment with the mycoparasite Teratosperma oligocladum did not affect the survival or infectivity of sclerotia of S. cepivorum or S. gladioli.
Pathogenicity of four Pythium species to wheat, barley, peas and lentils
Authors: INGRAM D. M. , COOK R. J.
Published: April 2007

Pythium heterothallicum, P. irregulare, P. torulosum and P. ultimum var. sporangiiferum were compared for pathogenicity to seedlings of winter wheat, spring barley, lentils and peas in growth chambers at 5, 10, 15, 20 and 25 C. These four fungi are among the most commonly isolated Pythium species from wheat roots and wheat‐field soils in eastern Washington and northern Idaho, USA, where wheat, spring barley, lentils and peas are grown in various rotations. Pathogenicity was determined in artificially infested soils (500 propagules per g) based on ability to cause pre‐emergence death and post‐emergence stunting of seedlings. P. ultimum var. sporangiiferum caused significant pre‐emergence death of the wheat at 15–25 C, lentils at 10–25 C. and peas at 5 25 C. P. irregulare caused pre‐emergence death only of peas and only at 5 C. With the possible exception of lentils at 25 C, P. heterothallcum and P. torulosum caused no pre‐emergence death of any of the four plant species. None of the species caused pre‐emergence death of spring barley. P. ultimum var. sporangiiferum caused the most post‐emergence stunting of wheat, peas and lentils at 10 C and above. Pythium irregulare caused as much or more stunting than P. ultimum var. sporangiiferum on wheat, lentils and peas at 5 C, and was the most pathogenic species on barley at 10, 20 and 25 C. P. irregulare caused significantly more post‐emergence stunting of wheat at 5 C with than without chaff (added as a food base for the pathogen); this was not offset by adding ammonium sulphate with the chaff.
Studies on resistance to beet western yellows virus in lettuce (Lactuca sativa) and the occurrence of field sources of the virus
Authors: WALKEY D. G. A. , PINK D. A. C.
Published: April 2007

An effective method based on glasshouse and field procedures was developed for screening commercial cultivars and other lettuce types for resistance to beet western yellows virus (BWYV). Field experiments in 1985, 1986 and 1987 showed that lettuce cultivars varied in their reaction to BWYV, but no high levels of resistance were identified in the main commercial types. Crisp types generally showed milder symptoms than butterhead or cos types, but individual butterhead cultivars were identified with resistance equal to the best crisp types. The highest levels of resistance were identified in Batavian type cultivars and extreme resistance or possible immunity was found in Lactuca perennis and L. muralis. BWYV caused yield reductions in some cultivars as high as 63% and reduced maturation by up to 38%, in others. There was no correlation between chlorotic leaf symptom severity and yield reduction.

BWYV was isolated from a range of weed and non‐lettuce host species growing near affected lettuce crops. Isolates of BWYV obtained from infected lettuce and brassicas appeared to be similar. They infected sugar beet with difficulty but caused no symptoms, and could only be detected by ELISA serology.
Analysis of the effects of selected gronomic factors on the dynamics of the take‐ all disease of wheat in field plots
Authors: WERKER A.R. , N C. A. GILLIG
Published: April 2007

Linear models were used to investigate the effects and interactions of treatments for the control of disease in multifactorial experiments on the dynamics of the take‐ al disease of wheat. Analyses were based on repeated measures of disease on second successive winter wheat crops in three successive se sons. The treatments were date of sowing, presence or absence of triadimenol‐containing seed treatment, autumn nitrogen and chloride applications, timing of early spring nitrogen and total spring nitrogen applications. The effects of treatments were investigated on line and quadratic trends of disease increase and on the integral amount of disease over time. Different disease variables were used to express disease relative to the total and diseased plant populations. The effects of treatments on absolute and relative numbers of diseased roots per plant were also analysed. During three se sons when disease was never severe, the effects of the treatments were shown to be variable. Late sowing consistently reduced disease during the early stages of the epidemic (in the winter months). The effect of late sowing in reducing disease, however, persisted through to the end of the growing se son in only one of the 3 years of the study. autumn nitrogen application and Baytan seed treatment (containing triadimenol) also reduced disease in some seasons. The presence of an effect for either was dependent on sowing date and was most evident on the proportion of diseased roots relative to the diseased plant rather than the total plant population.
Isozyme polymorphism in pathotypes of Pseudocercosporella herpotrichoides and related species from cereals
Authors: JULIAN ANGELA M. , LUCAS J. A.
Published: April 2007

Isolates of Pseudocercosporella herpotrichoides, causal agent of the eyespot disease of cereals, are usually classified as W‐type or R‐type on the basis of differential pathogenicity towards wheat and rye hosts, a distinction often correlated with cultural morphology. Polyacrylamide gel electrophoresis (PAGE) of soluble proteins was used to compare 101 isolates of Pseudocercosporella spp. including both W‐types and R‐types, and the related species P. anguioides and P. aestiva. Of 16 enzyme activities detected, seven were differential for the pathotypes. Isozyme polymorphisms for five enzymes clearly differentiated W‐type from R‐type isolates, a result confirmed by pathogenicity tests. Within each pathotype, isozyme patterns were similar for isolates of diverse geographical origins, including Europe, North America, South Africa and New Zealand. Isolates of P. anguioides and P. aestiva could also be distinguished on the basis of isozyme patterns. The mechanisms maintaining these polymorphisms, and the value of PAGE for population studies of this pathogen, are discussed.
Rhizoctonia leaf spot of tobacco in South Africa
Authors: MEYER J. C. , VAN WYK R. J. , PHILLIPS A. J. L.
Published: April 2007

Leaf spot of tobacco caused by Rhizoctonia solani isreported forthe first time from South Africa. All the leaf spot isolates anastomosed with the AG‐3 tester strain.
Sources, survival and transmission of Cladosporium allii and C. allii‐cepae, leaf blotch pathogens of leek and onion
Authors: JORDAN MARY M. , MAUDE R. B. , BURCHILL R. T.
Published: April 2007

Neither Cladosporium allii nor C. allii‐cepae was detected in seed samples of 46 commercial cultivars of leek and nine of onion.

In glasshouse tests where flower inflorescences of onions and leeks were dusted with conidia of C. alliicepae and C. allii, respectively, few onion seeds and no leek seeds became contaminated. In field crops of leeks some spathes and inflorescences became diseased and gave 0 002%C. allii contaminated seeds. No infected onion seeds were obtained from naturally‐infected plants in the field.

Conidia of both fungi survived for less than 6 weeks in sterile and non‐sterile soil (during which time the temperature varied from ‐8 to +11 C); pseudothecial bodies survived longer.

Both pathogens survived for 3 months in debris of onion or leek on the surface of soil in pots under similar conditions. In debris buried at a depth of 7 cm in sterile or unsterile soil they survived for 2 months. Although C. allii survived only 1 month in debris on the soil surfaces following a leek crop, conidia of the fungus were trapped from the air above the area for at least 6 months and healthy leeks transplanted into this area developed the disease. No leaf blotch developed in leeks grown on land which had not previously borne that crop.
Phenotypes of Phytophthora infestans collected in England and Wales from 1985 to 1988: mating type, response to metalaxyl and isoenzyme analysis
Authors: SHATTOCK R. C. , SHAW D. S. , FYFE A. M. , DUNN J. R. , LONEY K. H. , SHATTOCK J. A.
Published: April 2007

In a survey of 1864 isolates derived from samples of Phytophthora infestans obtained from potato and tomato collected in England and Wales between 1985 and 1988, the A2 mating type was identified in approximately 10% of samples. There was no evidence for an overall increase in the frequency of the A2 mating type over this period. In agar culture, A2 isolates exhibited a distinct lumpy‐colony morphology. Lumps were made up of intensely dichotomously branched hyphae. The incidence of resistance to metalaxyl among samples increased from 41 to 60% between 1986 and 1988. Some of the A2 isolates were resistant to metalaxyl and like other A2 isolates gave rise to progeny from in vitro matings with Al isolates. Except in one case, Al and A2 isolates were uniformly homozygous at an isoenzyme locus for glucosephosphate isomerase but isolates exhibited some variation at a peptidase locus. The source of the A2 isolates could not be established from these data.
Control of grey mould (Botrytis cinerea) with film‐forming polymers
Authors: ELAD Y. , AYISH N. , KATAN J.
Published: April 2007

Several film‐forming polymers reduced the amount of grey mould on various crops in a dew chamber and in a plastic house under natural conditions. The polymers Wilt Pruf, Biofilm and Colfix reduced germination of conidia and germ tube length of Botrytis cinerea. The most effective inhibition of linear growth of the pathogen on potato dextrose agar was obtained by Safe Pack and Biofilm. All polymers significantly reduced grey mould on detached leaves of Capsicum, Phaseolus, tomato, cucumber, rose and pelargonium. Grey mould on rose flowers was not controlled, apparently due to latent infection. The substances Biofilm and Vapor Gard were applied either alone or with chlorothalonil fungicide on cucumber plants in a commercial greenhouse. The polymers had no harmful effect to the host. Disease on senescing female fruits of cucumber was reduced by 46–67% with no additive effect to the mixture with fungicides. Stem infection also was reduced.
Pathogenicity of Gaeumannomyces graminis isolates to wheat and rye seedlings
Authors: HOLLINS T. W. , SCOTT P. R.
Published: April 2007

A total of 187 isolates of Gaeumannomyces graminis, obtained from diseased cereal roots between 1979 and 1983, mostly from the UK, were compared for their ability to produce disease on wheat and rye seedlings in the glasshouse. Isolates varied continuously in pathogenic adaptation to rye. from those infecting wheat substantially and rye slightly (designated normal or N‐isolates) to those infecting both wheat and rye substantially (designated R‐isolates). The degree of adaptation to rye was a consistent characteristic of individual isolates. All were morphologically similar toG. graminis var. tritici R‐isolates were obtained from all the areas sampled, they did not appear to predominate on a particular host species and occurred together with N‐isolates and intermediates in a single field.
Distinguishing pathovars of Pseudomonas syringae on peas: nutritional, pathogenicity and serological tests
Authors: MAZAREI MITRA , KERR A.
Published: April 2007

Of the published methods to distinguish Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. pisi, inoculation of susceptible cultivars was the most reliable. Results were confirmed by inoculation of lemon fruit.

A much more rapid and convenient serological method was developed to distinguish the two pathovars. Antisera against glutaraldehyde‐fixed cells had a high level of specificity in Ouchterlony gel double‐diffusion tests and, after cross‐absorption with heterologous antigens, in indirect ELISA. Antiserum to P. syringae pv. pisi has considerable potential to detect pea seed infected with this pathogen.
Control of vascular‐streak dieback of cocoa with triazole fungicides and the problem of phytotoxicity
Authors: HOLDERNESS M.
Published: April 2007

The effectiveness of a range of systemic fungicides against vascular‐streak dieback of cocoa, caused by Oncobasidium theobromae, was evaluated over 2 years in Papua New Guinea. Monthly foliar sprays of the triazole fungicides hexaconazole, tebuconazole and triadimenol all gave good protection against the disease. The relative efficacy of these chemicals was, in order, tebuconazole (EC50 0–90 mg a.i. per plant), hexaconazole (EC50 2.35 mg a.i. per plant), triadimenol (EC50 4.17 mg a.i. per plant). However, the relative severity of plant growth inhibition induced by these compounds had the same ranking. Growth inhibition was reduced by extending the interval between treatments, but this also reduced the efficacy of disease control. Propiconazole stem paints (EC50 2502 mg a.i. per plant) were markedly less effective than these sprays. Neutralized phosphorous acid sprays and paints showed no activity against the disease.
Biological control of fire blight of hawthorn (Crataegus monogyna) with Erwinia herbicola under protected conditions
Authors: WILSON M. , EPTON H. A. S. , SIGEE D. C.
Published: April 2007

Isolates of Erwinia herbicola, obtained from flowers and leaves of hawthorn (Crataegus monogyna), were screened as potential control agents of fire blight disease (caused by Erwinia amylovora) using an immature pear fruit assay. Selected isolates were subsequently tested for disease control by infection of hawthorn blossom in the laboratory, and by shoot infection of hawthorn plants grown under controlled (glasshouse) and fluctuating (polythene tunnel) environmental conditions.

Although the immature pear fruit assay provided a general screen for the selection of antagonists for the control of both blossom and shoot blight, it had two major limitations when quantitatively applied. Firstly there were inconsistencies in the relative effects of different isolates on the pear‐slice surface, with some isolates being more suppressive than the standard antagonist Eh252 in the first screening and less in the second. Secondly the assay was not able to predict accurately the level of control in the intact plant‐as no correlation occurred between the level of control in the pear fruit assay and the percentage control of either blossom blight or shoot blight.

Two isolates of E. herbicola, WL9 and WL40, reduced both blossom‐ and shoot‐blight. WL9 provided over 80% control of blossom blight, equivalent to that provided by chemical agents, and also gave total control of shoot blight when applied at a WL9: pathogen ratio of 10:1.
Normal germling development by Erysiphe graminis on cereal leaves freed of epicuticular wax
Authors: CARVER T. L. W. , THOMAS B. J.
Published: April 2007

Experiments were conducted to test the hypothesis that recognition of the physical structure of epicuticular leaf waxes by Erysiphe graminis may be important to the development of normal germlings and the formation of functional appressoria. Comparisons of germination rates and characteristics of germling development by E. graminis f.sp. avenae, and in one experiment by f.sp. hordei, were made between intact cereal leaves and leaves from which the epicuticular waxes had been stripped away.

Overall, fungal development was very similar on intact and wax‐free leaves: although germination rates were slightly, but significantly, lower, and lengths of appressorial germ tubes slightly greater, on stripped than intact leaves, a very similar proportion of germlings formed apparently normal appressoria in both cases. This was true for f.sp. avenae on first‐ and fifth‐formed leaves of susceptible and adult plant resistant oats, and on barley and wheat first leaves, and for f.sp. hordei on first leaves of barley, oat and wheat. The appressoria formed on stripped leaves not only appeared normal, but also formed haustoria with at least the same frequency as on intact leaves; in several experiments, a higher proportion formed haustoria in stripped than intact leaves. Wax removal did not affect the adult plant resistance of oat cv. Maldwyn, which limits haustorium formation by appressoria, indicating that epicuticular wax was not involved in this resistance. It is concluded that the physical structure of epicuticular wax is not involved in the recognition processes leading to normal germling development.
Structure and evolution of a population of Erysiphe graminis f.sp. hordei
Authors: BROWN J. K. M. , WOLFE M. S.
Published: April 2007

Samples of single colony isolates of Erysiphe graminis f.sp. hordei were collected in Cambridge on three dates in 1985, and tested for the presence of 12 virulence alleles and resistance to two fungicides, triadimenol and ethirimol. The frequency of the virulence V‐(La) fell during 1985, while the frequency of V‐h. virulence on cv. Triumph and higher levels of resistance to each fungicide and combined resistance to both fungicides rose. Two phenotypes, both of which possessed virulence on cv. Triumph and three unnecessary virulence alleles and had similar sensitivities to ethirimol, but differed in their level of resistance to triadimenol, accounted for 35.9% of all isolates. The high frequency of these phenotypes accounted for most of the observed gametic phase disequilibria between pathogenicity characters. Most individuals with these two phenotypes may be members of the same clone. It was estimated that 25% of the spore population which initiated the autumn epidemic of E.g. f.sp. hordei originated from ascospores formed by sexual reproduction in the summer. It is proposed that genetic drift followed by hitch‐hiking selection, due to intense selection for a clone virulent on a newly‐introduced cultivar, is a major factor influencing the frequency of unnecessary virulence alleles.
The use of DNA polymorphisms to test hypotheses about a population of Erysiphe graminis f.sp. hordei
Authors: BROWN J. K. M. , O'DELL M. , SIMPSON C. G. , WOLFE M. S.
Published: April 2007

The distribution of restriction‐fragment‐length polymorphisms (RFLPs) among isolates of Erysiphe graminis f.sp. hordei was used to test hypotheses about the structure of the pathogen population. There was a large diversity in the lengths of DNA restriction fragments homologous to E9, a chromosomal fragment of unknown function. It was shown that a large group of isolates, which shared identical or very similar virulence phenotypes, including virulence on the barley cv. Triumph, were members of a single clone. Several other clones were identified, including a second group of identical isolates which were virulent on cv. Triumph but were highly distinct from the more common clone of Triumph‐virulent isolates. Isolates which shared the same level of resistance to the triazole fungicide triadimenol were genetically diverse. Such diversity is consistent with triadimenol resistance being under oligogenic, rather than polygenic, control. Conclusions obtained from analysis of the most easily identifiable subset of fragment lengths were very similar to those obtained from analysis of the complete set.
The role of temperature and rainfall in the epidemiology of Puccinia striiformis f.sp. tritici in the summer rainfall area of eastern Australia
Authors: PARK R. F.
Published: April 2007

Infection of wheat seedlings by Puccinia striiformis f.sp. tritici was investigated under both laboratory (constant temperature) and field conditions using a 15‐h period of 100% r.h. In laboratory studies, infection decreased from 100% at 15 4 C to 0.8% at 20.5 C, and it was estimated that no infection would occur at or above 20.8 + 0.2 C. In contrast, high levels of infection occurred under field conditions even when temperatures fluctuated within the range 19–30°C. Overnight infection experiments conducted at Toowoomba over an 18‐month period demonstrated that periods of moisture and temperature favouring infection by P. striiformis f.sp. tritici occurred regularly, even during summer, and that high temperature was a limiting factor on only 3% of the nights tested. This indicates that stripe rust could oversummer readily in this region of the eastern Australian wheat belt, at least in sheltered areas, given a susceptible host. Regression equations relating mean temperature to infection and minimum temperature to infection identified mid to late autumn as an important period in the epidemic development of the disease in this region. The amount of rain recorded during this period was closely associated with subsequent levels of stripe rust observed in commercial crops over the years 1983–87.
Studies on the chemical control of chrysanthemum white rust caused by Puccinia horiana
Authors: DICKENS J. S. W.
Published: April 2007

Experiments evaluating the curative and protective effect of sprays of benodanil, bitertanol, oxycarboxin, triadimefon, triforine and propiconazole, and intensive oxycarboxin fog and triforine spray regimes, against chrysanthemum white rust are described. All treatments reduced the disease when applied before symptoms developed but only propiconazole completely prevented disease development. A single spray of propiconazole applied 4–8 days after inoculation was sufficient to eradicate infection. This fungicide was also found to eliminate symptomless infection from cuttings when used as a dip prior to planting, or as two sprays after planting. When sporulation had occurred, three sprays of propiconazole or benodanil killed the telia, but viable telia were still present after three sprays of oxycarboxin, triadimefon or triforine. When applied as single protective sprays none of these fungicides consistently prevented infection, although levels were considerably reduced when application was made 2–3 days before exposure to the disease. Observational trials indicate that although propiconazole has some growth retardant effect it does not appear to present any significant phytotoxicity problems, either as a spray or as soil residue. As a result of this work propiconazole has been successfully used in a statutory eradication campaign against this rust. To avoid the possible development of resistance, it is suggested that its use should be confined to actual outbreaks, or when it is suspected that plants or cuttings may have become infected.
Assessing resistance to Crinipellis perniciosa using cocoa callus
Authors: FONSECA S. E. A. , WHEELER B. E. J.
Published: April 2007

Callus cultures from cocoa clones reported to have different susceptibilities to Brazilian isolates of Crinipellis perniciosa, causal fungus of witches' broom disease, including Catongo (susceptible). Scavina‐6, CAB 64 and CAB 67 (resistant) were inoculated with basidiospores of C. perniciosa and the subsequent development of mycelia was assessed. Generally, on Catongo callus, mycelium similar to that found in green brooms (parasitic type), developed abundantly but on callus from Scavina‐6 and the two CAB clones, mycelial growth was relatively poor and tended to be similar to that in dry brooms and on agar media (saprotrophic type). There was often considerable variation in fungal development on individual callus cultures from the same clone, but there was an overall consistency between successive experiments in ranking the callus material in terms of fungal development. However, growth of isolates from Colombia and Trinidad was similar on callus from Scavina‐6 which in the field is known to reac differentially to these two isolates. Experiments with isolates from Colombia indicated that inoculum from basidiocarps produced on brooms which were kept for long periods in cabinets to induce fruiting had a decreased ability to colonize callus.
Separation of citrus viroids by shoot‐tip grafting in vitro
Authors: JUÁREZ J. , MOLINS M. I. , NAVARRO L. , DURAN‐VILA N.
Published: April 2007

Arizona 861‐S1 citron (Citrus media L.) infected with a severe exocortis isolate containing four citrus viroids was used as source of tissue for shoot‐tip grafting in vitro. Out of 51 attempts, 25 successful grafts were obtained. Only 16 plants survived transplanting and of these 12 were viroid‐free. The viroid profile of the other four plants showed fewer viroids than the original field source. The significance of these results, as compared with previous reports on the recovery of viroid‐free plants, is discussed. The results show the usefulness of shoot‐tip grafting in vitro as a tool to recover single viroid isolates from complex field sources.
The seed‐borne fungi of Chinese cabbage (Brassica pekinensis), their pathogenicity and control
Authors: VALKONEN J. P. T. , KOPONEN H.
Published: April 2007

The pathogenicity and control of seed‐borne fungi of Chinese cabbage (Brassica pekinensis) were studied to evaluate the quality of imported seed lots on the Finnish market and to develop practical methods for seed health testing. Amongst the numerous fungal species in the seed lots, nine were found to be pathogenic on B. pekinensis seedlings, Alternaria raphani and A. brassicicola being the most common and the most pathogenic. A. brassicicola was effectively controlled by dressing seed with thiram or powdered Streptomyces griseoviridis. unlike A. raphani which was mostly located in the inner parts of the seed. Water agar was successfully used as an incubation medium for seed health testing. Surface sterilization of the seeds with sodium hypochlorite was used to determine the internal infection of A. raphani. A linear relationship between the incidence of A. brassicicola and A. raphani was demonstrated. Ten per cent of the seed lots were excluded from seedling production because of high infection with A. raphani.
Association of double‐stranded RNA with whitefly‐mediated silvering in squash
Authors: BHARATHAN N. , GRAVES W. R. , NARAYANAN K. R. , SCHUSTER D. J. , BRYAN H. H. , McMILLAN R. T.
Published: April 2007

A disorder of unknown aetiology appearing as silvering on squash (Cucurbita pepo) leaves has become prevalent in south Florida. Typical symptoms, observed after 2 weeks of exposure to adults of Bemisia tabaci, the sweet potato whitefly (SPWF) include vein clearing followed by silvering of whole leaves. Fruits from affected plants are blanched or streaked longitudinally. The silverleaf syndrome was not mechanically transmissible when crude extracts of symptomatic leaves were used as inoculum. Two sizes of double‐stranded RNA (dsRNA) of c. 4.6 and 4.2 kilobase pairs (kbp) were consistently observed in leaf extracts of caged, whitefly‐infested, symptomatic plants. In contrast, caged plants not exposed to whiteflies showed no symptoms and contained no detectable dsRN A. In addition, squash plants exposed to SPWF colonies from California neither developed silverleaf symptoms nor contained any dsRNA. Double‐stranded RNA could also be readily detected in whitefly‐infested yellow summer squash and zucchini from the field. However, asymptomatic eggplant and watermelon infested with SPWF from nearby fields did not contain detectable dsRNA. Dot‐spot hybridization assays using an RNA‐specific probe detected homologous sequences in both adults and nymphs of SPWF that induced silverleaf symptoms but not in adults and nymphs of SPWF that could not induce silverleaf symptoms. These results, along with the non‐endogenous nature of the detected dsRNA suggest that the dsRNA is or is associated with the causal agent of whitefly‐mediated leaf silvering in squash.
Alfalfa mosaic virus in lucerne seed during seed maturation and storage, and in seedlings
Authors: BAILISS K. W. , OFFEI S.K.
Published: April 2007

The incidence of alfalfa mosaic virus (AMV) in lucerne seed and pods during maturation, when monitored by sap transmission to Phaseolus (infective virus) and ELISA (AMV antigen), showed that infective virus incidence decreased rapidly with maturation, whereas antigen incidence declined slowly and was always higher than infective virus. Infective virus and antigen incidence were higher in mature seed of cv. Maris Kabul than cv. Europe because virus inactivation/degradation were more rapid in cv. Europe. Seed infection with virus originating from pollen, ovules or both was found in pods and seeds 12–15 days after pollination between healthy or AMV‐infected plants; this was before maturation‐associated virus inactivation. Ovule transmission was more frequent than pollen transmission. AMV antigen was present in embryos and testas of mature seed; infective virus only in embryos. Non‐infective but ELISA‐positive antigen in testa extracts accounted for the higher incidence of ‘seed‐borne AMV’ compared with embryo‐associated seed transmission to seedlings. Tests with dry mature seed either underestimated (infectivity tests) or overestimated (ELISA) eventual seedling infection. Infectivity and ELISA tests gave identical incidence values for 17 to 29‐day‐old seedlings.
Influence of site factors on yield response of winter wheat to fungicide programmes in England and Wales, 1979–1987
Authors: COOK R. J. , THOMAS M. R.
Published: April 2007

Results of 460 field experiments between 1979 and 1987 incorporating one, two and three fungicide sprays, with a range of active ingredients, were analysed according to site factors including previous crop, sowing date and geographical area. The average untreated yield was 7–48 t/ha, although this fluctuated widely from 6 15 t/ha in 1985 to 9 411 ha in 1984. A single spray at flag‐leaf emergence gave an average yield increment of 0 59 t/ha over plots receiving no fungicide. The addition of a second spray at the first‐node growth stage gave an extra benefit of 0.22 t/ha, while an additional third spray at ear emergence gave a further 0.28t/ha. The effects on yield of different spray timings were modified by other factors, of which sowing date and previous crop were most important to the first‐node spray, and cultivar and geographical area to the ear emergence spray. The data suggest that all crops would benefit economically from a broad‐spectrum fungicide applied at flag‐leaf emergence. Additionally, crops sown in September, those following winter wheat and those in regions bordering the North Sea respond well at the first‐node stage to a fungicide active against eyespot.
Effect of plant age, leaf position and leaf segment on infection of leek by leek rust, Puccinia allii
Authors: JENNINGS D. M. , FORD‐LLOYD B.V. , BUTLER G. M.
Published: April 2007

Potted plants of leek, Allium porrum cv. Musselburgh, were inoculated with urediniospores of leek rust, Puccinia alliii, and maintained for 21 days in a controlled‐environment cabinet. Mean pustule density, mean pustule length and mean colony length all decreased with increasing plant age, from 2 to 8 months old, and there was a tendency for latent period to increase with increasing plant age. On 8‐month‐old plants pustule development continued over 21 days post‐inoculation but the proportion of flecks developing into pustules remained below 50%. In non‐tip portions of inoculated leaves, mean pustule density increased and mean pustule length decreased from upper to lower leaves in the standing crop. Tip portions of leaves either varied less in resistance with leaf position or showed random variation.
The incidence of Fusarium spp. in stem bases of selected crops of winter wheat in the Midlands, UK
Authors: PARRY D. W.
Published: April 2007

The incidence of pathogenic Fusarium and Microdochium species in stem bases of winter wheat was investigated in a total of nine crops in 3 years, i.e. 1987, 1988 and 1989. Four Fusarium species were isolated: F. nivale (= Microdochium nivale),F. avenaceum, F. culmorum and F. graminearum. The predominant species was F. nivale followed by F. avenaceum and F. culmorum. Isolations of F. graminearum were made only from shoots collected during August 1989. The highest incidence of F. nivale occurred during April 1989 in the cultivar Brock when the fungus was isolated from 65% of the shoots sampled. The highest incidence of F. avenaceum was 60% (August 1988, cv. Slejpner) and F. culmorum 37% (August 1989, cv. Mercia). A delay in the isolation of Fusarium spp. during 1987 was attributed to the low January temperatures, and an upsurge ofF. culmorum and F. graminearum during 1989 to the warm dry summer. The incidence of F. nivale fluctuated during the 1988 and 1989 seasons, particularly during spring. The effects of fungicide spray programmes and the growth and development of the wheat crop are discussed as possible contributory factors to this.
Comparison between ELISA and bio tin‐la belled probes from cloned cDNA of potato virus X for the detection of virus in crude tuber extracts
Authors: EWEIDA M. , XU H. , SINGH R. P. , ABOUHAIDAR M. G.
Published: April 2007

Diseases caused by potato virus X (PVX) are of significant agronomic importance, and early detection is vital. Biotinylated DNA probes were prepared by random‐primed labelling from cDNA inserts and used for the detection of PVX in crude extracts of infected tubers. The minimum detection level in these extracts is in the order of femtograms of PVX RNA. Comparison with ELISA showed that the hybridization method is 100–250 times more sensitive. Probes prepared by this method are highly specific for target RNA even in crude tuber extracts.
The occurrence of beet pseudo‐yellows virus in England
Authors: COFFIN R. S. , COUTTS R. H. A.
Published: April 2007

Beet pseudo‐yellows virus (BPYV) has been identified in England for the first titne, in lettuce, following transmission by the greenhouse whitefly (Trialeurodes vaporariorum) to healthy plants. Infected plants had leaves with severe interveinal chlorosis and slight downward curling, and were gerterally smaller than healthy plants. Indirect ELISAs with an antiserum raised against the Californian isolate of BPYV were positive with extracts produced from infected plants. Infected but not healthy plants contained a single species of double‐stranded RNA of about 7.5 × lO6Da, a size similar to that found with beet yellows virus, the type member of the closterovirus group.
Regeneration of healthy banana plantlets from banana bunchy top virus‐infected tissues cultured at high temperature
Authors: WU R. Y. , SU H. J.
Published: April 2007

Exposure of banana bunchy top virus (BBTV)‐infected plantlets of Cavendish banana to 40°C for 16 h daily for periods of up to 5 weeks did not free them from BBTV. However, BBTV was less readily transmitted by aphids from treated plants than from untreated controls. The same heat treatment applied for up to 12 weeks also failed to eliminate the virus from BBTV‐infected tissue. When similar BBTV‐infected tissue was cultured for 3 months at 35°C some of the buds started to produce healthy looking plantlets. Five out of 11 cultures produced healthy‐looking plantlets in 6 months. Crude extracts from the leaves of these plantlets did not react with a monoclonal antibody prepared against BBTV. When heat‐treated, healthy‐looking plantlets were inoculated with viruliferous aphids all plants developed bunchy top symptoms indicating that they were not resistant to BBTV. The results suggest that the uneven distribution and low concentration of virus after treatment at high temperature leads to BBTV‐free primordial cells which in turn may develop into healthy plantlets.
Variability among Spanish citrus tristeza virus isolates revealed by double‐stranded RNA analysis
Authors: GUERRI J. , MORENO P. , MUÑOZ N. , MARTINEZ M. E.
Published: April 2007

A survey for citrus tristeza virus (CTV) strains, based on double‐stranded RNA (dsRNA) analysis, was carried out in five locations on the eastern citrus‐growing area of Spain. CTV was recovered from 137 trees of different ages, citrus species and varieties, sampled in 53 orchards. The best months for dsRNA recovery were April, May, September, October, and November, and the highest dsRNA yield was obtained from sweet orange cultivars. Sixteen dsRNA profiles differing by the number and/or position of subgenomic bands were detected. One of these profiles was detected in more than half the trees analysed. Maximum diversity of dsRNA patterns was found in the location with the oldest citrus orchards and the highest CTV incidence (Alzira‐Carcaixent). In many instances, several dsRNA profiles were detected in neighbouring trees of the same orchard, notably in Alzira‐Carcaixent, where 70% of the plots sampled contained more than one profile. The possible causes for the diversity of CTV isolates found in this specific area are discussed.
The distribution of barley yellow mosaic virus (BaYMV) and barley mild mosaic virus (BaMMV) in UK winter barley samples, 1987‐1990
Authors: ADAMS M. J.
Published: April 2007

Improved diagnosis of barley yellow mosaic (BaYMV) and barley mild mosaic (BaMMV) viruses was obtained by adjusting the buffers used in immunospecific electron microscopy (ISEM) to ensure a pH ≥ 7‐0 and in ELISA by replacing ovalbumin with 10 g/l full cream milk powder.

Over 70% of samples of winter barley with symptoms of mosaic received from different sites in the UK during 1987‐90 had BaYMV and 37% had BaMMV, with 11% containing both viruses. BaMMV was much more common on malting cultivars than on those grown for feed and this resulted in an easterly bias to the geographical distribution of the virus. Both viruses were, however, widely distributed in areas where winter barley is grown intensively. A small number of BaYMV records were from cultivars previously regarded as resistant and these are probably a distinct strain of the virus.
The isolation and characterization of polyclonal and monoclonal antibodies to anastomosis group 8 of Rhizoctonia solani
Authors: MATTHEW J. S. , BROOKER J. D.
Published: April 2007

Polyclonal and monoclonal antibodies were raised against secreted proteins from an anastomosis group 8 isolate of Rhizoctonia solani and tested for reactivity to field isolates from anastomosis groups 2‐1, 3,4 and 8. Polyclonal antibodies raised against total secreted proteins cross‐reacted in immunoblotting experiments with all R. solani isolates. However, immunoreactive proteins specific to Ag‐8 isolates were evident. Monoclonal antibodies to secreted proteins were raised which reacted with fewer proteins and showed a greater degree of specificity for AG‐8 isolates. Two monoclonals were selected for further study. One, an IgM monoclonal antibody, reacted with all R. solani isolates, recognizing a 40‐kDa protein specific to AG‐8 isolates and proteins of lower molecular weight in isolates from other anastomosis groups. The other, an IgG monoclonal antibody, was more specific, reacting with 38, 40 and 55‐kDa proteins from AG‐8 isolates and cross‐reacting with few isolates from other anastomosis groups. Preliminary results on the induction of antigens recognized by the monoclonal antibodies are presented. The monoclonal antibodies characterized here are useful for the identification of isolates of R. solani and may also be used as probes to clarify the relationships between anastomosis groups.
Fusarium crown and root rot of tomatoes in the UK
Authors: HARTMAN J. R. , FLETCHER J. T.
Published: April 2007

Fusarium crown and root rot caused by Fusarium oxysporum f. sp. radicis‐lycopersici was found in the UK in 1988 and 1989 mainly in rockwool‐grown tomato crops. Up to 14% of plants were affected in individual crops. In experiments, leaf and stem symptoms did not appear until the time of first fruit harvest even when the plants were inoculated at planting, first flowers or fruit set. Conidial inoculum at 106 spores/plant applied at seed sowing killed 70–83% of tomato seedlings, whereas similar levels of inoculum applied to young plants caused root and basal stem decay, and eventually death but only after fruit harvest began. Disease incidence and symptom severity increased with inoculum concentration. Experimentally, the disease was more severe in peat‐ or compost‐grown plants than in rockwool. Disease spread was only a few centimetres in 50 days in experimental rockwool‐grown plants. All tomato cultivars tested were highly susceptible. Prochloraz‐Mn was highly effective against the pathogen in vitro and controlled the disease in the glasshouse, but only when applied preventively. Non‐pathogenic Fusarium oxysporum isolates and Trichoderma harzianum also reduced FCRR disease levels.
Forecasting the national incidence of sugar‐beet powdery mildew from weather data in Britain
Authors: ASHER M. J. C. , WILLIAMS G. E.
Published: April 2007

In a national survey of the incidence of powdery mildew (Erysiphe betae) in sugar beet in Britain, between 1980 and 1989, in which between 335 and 717 fields were inspected at the end of August each year, the average crop area infected ranged from 2% in 1986 to 68% in 1989. The effect of various climatic factors that might be expected to influence powdery mildew development over this period was examined, using meteorological records from Broom's Barn Experimental Station, Using simple linear regression analyses, a significant association was found between disease incidence and both air temperature and rainfall incidence in the period April‐August, However, air temperature and frost incidence in some winter months were also closely associated with the incidence of powdery mildew in the following crop.

Combinations of these variables were examined in stepwise multiple‐regression analyses, The model of best fit, incorporating winter frost incidence with summer temperature and rainfall incidence, accounted for 95% of the variation. Model validation procedures demonstrated the superiority of this model over those involving single variables. Nevertheless, for forecasting purposes, the best correlation was found between the crop area infected at the end of August each year and the number of days with a ground frost in the preceding February and March. This single climatic variable accounted for 82% of the variation and its potential use to forecast powdery mildew incidence in the national sugar‐beet crop is discussed.
Induction of pear blossom blast caused by Pseudomonas syringae pv. syringae
Authors: WHITESIDES S. K. , SPOTTS R A.
Published: April 2007

Conditions were established for inducing pear blossom blast caused by Pseudomonas syringae pv. syringae on both attached and detached shoots. The incidence of blossom blast was proportional to the logarithm of the P.s. pv. syringae population under optimal temperature, moisture, and bloom developmental stage. Highest incidence of blossom infection followed occurrence of a major exotherm (an increase in temperature caused by the heat of fusion from ice formation within blossom tissue) in the presence of P. s. pv. syringae. The exotherm was detected inside ovary tissue at temperatures ranging from –1.8 to –3.5 C. Wetness duration following the thawing process was less important than wetness during and immediately after the freeze event. Blossoms inoculated, then air‐dried or removed from low‐temperature treatment prior to occurrence of an exotherm, had a low incidence of infection, The full bloom stage of blossom development was more susceptible to blossom blast than either the open cluster or tight cluster stages of development.
Occurrence of Penicillium corymbiferum on saffron in Italy
Authors: CAPPELLI C. , BUONAURIO R. , POLVERARI A.
Published: April 2007

Penicillium corymbiferum causing disease on saffron in Italy is reported for the first time.