bluuebunny/crossref_metadata_2025 huggingface dataset:
Microscopical studies of resistance to powdery mildew disease in the hop cultivar Wye Target
Authors: GODWIN J. R. , MANSFIELD J. W. , DARBY P.
Published: April 2007

Microscopical studies of fungal development and host responses during infection of the hop cultivars Northern Brewer (susceptible) and Wye Target (resistant) with a Zenith isolate of Sphaerotheca humuli are described. Resistance to powdery mildew disease in cv. Wye Target is principally determined by the R2 major gene. Fungal growth was typically restricted in cv. Wye Target following formation of a single haustorial initial or haustorium which failed to develop the characteristic lobes found in susceptible cells. The hypersensitive reaction of penetrated epidermal cells was associated with death of haustorial initials but the associated appressorium remained alive during the first 2 days after inoculation. In leaves expressing resistance, histochemical staining revealed deposition of lignin‐like material and callose in penetrated cells and to a lesser extent in underlying palisade mesophyll cells. Transmission electron microscopy and enzymic digestion clearly demonstrated extensive paramural deposition of β‐1.3 glucans (callose) in reacting mesophyll cells. Plant cell death, lignification and widespread callose deposition were rarely observed at infection sites in cv. Northern Brewer but collars of callose were deposited around the necks of all haustoria formed.
The inheritance of mechanisms of partial resistance to Erysiphe graminis in spring barley
Authors: ASHER M. J. C. , THOMAS C. E.
Published: April 2007

The response of epidermal cells to attempted penetration by Erysiphe graminis was examined in the fifth leaf of 13 barley lines selected for partial resistance. In leaf segments fixed and stained 72 h after inoculation cell reactions were classified as susceptible or as exhibiting non‐hypersensitive or hypersensitive resistance. The proportion of cells with each type of reaction varied in a continuous manner among the lines and there were significant differences between lines in the levels of non‐hypersensitive and hypersensitive resistance. Crosses were made between lines exhibiting high and low levels of each resistance mechanism. Fifty challenged epidermal cells per duplicate leaf segment were examined on 45‐50 F2 plants derived from two such crosses. The frequency distribution of each of the three types of cell reaction in the fifth leaf was found to be continuous and, in general, normally distributed and in no case was there a significant difference between parent and progeny mean values, suggesting that the two resistance mechanisms were under the control of several genes showing predominantly additive gene action.
A new disease of cardamom (Elettaria cardamomum) caused by Erwinia chrysanthemi in Papua New Guinea
Authors: TOMLINSON D. L. , COX P. G.
Published: April 2007

A serious disease of cardamom in East New Britain Province of Papua New Guinea was shown by pathogenicity and biochemical tests to be caused by Erwinia chrysanthemi. The bacterium was repeatedly isolated from blackened roots, soft discoloured rhizome tissue and rhizosphere soil, but not from field soil in the immediate neighbourhood of diseased plants.
Studies of the distribution of yellowing viruses in the sugar beet root crop from 1981 to 1984
Authors: SMITH HELEN G. , HINCKES JENNIFER A.
Published: April 2007

Two viruses, beet yellows virus (BYV) and beet mild yellowing virus (BMW), cause yellowing of sugar beet, their principal vector being Myzus persicae. Although the viruses have different properties which are likely to influence their spread within root crops, for the purpose of control they have been treated in the past as one disease. This paper describes the results of a crop survey carried out in co‐operation with agricultural staff of British Sugar plc from 1981 to 1984 in which leaves from plants with symptoms of virus yellows were tested by enzyme‐linked immunosorbent assay (ELISA) for BYV and BMW. The two viruses differed in their incidence and distribution within the national sugar beet root crop; BMW was the main cause of yellowing and occurred in all parts of the growing region while BYV, which has the more severe effect on yield, was more limited in distribution. The survey located areas in southern East Anglia which are at greatest risk from BYV infection. The possible need to modify control measures depending on which virus threatens to invade the crops is discusssed. A high proportion of leaves visually identified as infected was found to contain neither BYV nor BMYV, emphasizing the difficulties of identifying virus‐infected plants by field symptoms.
Genetic variability and the inheritance of resistance to cedar‐apple rust in apple
Authors: CHEN H. , KORBAN S. S.
Published: April 2007

Thirteen apple cultivars and selections were evaluated in a greenhouse for their reaction to cedar‐apple rust inoculation Five of the cultivars selections developed aecial lesions on their leaves whereas the sixth cultivar Jonathan, showed only pycnial lesions. The responses of the remaining seven resistant cultivars selections ranged from a lack of any visible symptoms to the presence of discrete flecks or continuous chlorotic mottles Quantitative parameters were used for statistical analysis; these included the highest number of pycnial lesions on a leaf/plant (N). the largest diameter of pycnial lesions on any leaf/plant (D)), and the calculated infection rating (IR = ND). Significant differences were observed among cultivars selections for variables N. D. and IR. Segregation ratios among progenies derived from 16 controlled crosses indicated that resistance to cedar‐apple rust was conditioned by two major genes, and both were required in dominant form to confer resistance. However, in three crosses the dual‐gene hypothesis was inadequate to explain the reaction of seedlings.
Epidemiological studies on cercospora leaf spot of sugar beet
Authors: PUNDHIR V. S. , MUKHOPADHYAY A. N.
Published: April 2007

In the glasshouse, inoculation of sugar beet with Cercospora beticola followed by 16 h of high humidity produced visible disease only with at least four conidia per cm2 of leaf area. Disease became more severe after increasing periods of high humidity in the range of 0–24 h. In the field, spraying plants with water enhanced disease spread from a focus. Disease progress curves were sigmoid. Apparent infection rate declined towards the end of the season, possibly because of high temperature. In approximate agreement with prediction, epidemic development was delayed when initial inoculum was reduced. Reduced infection, resulting from either reduced initial inoculum or delayed inoculation, decreased the adverse effect of disease on sugar yield.
Differential stimulation of germination of sclerotia of Sclerotium cepivorum by cultivars of onion and its effect on white rot disease
Authors: COLEY‐SMITH J R. , REESE R A. , GEORGY N. I.
Published: April 2007

Differences were found in the ability of onion cultivars to stimulate the germination of sclerotia of Sclerotium cepivorum under UK conditions. The differences between European and Egyptian cultivars were particularly marked. Differences also occurred in the development of white rot disease in European and Egyptian cultivars. These differences were related to the pattern of growth of the cultivars and not to levels or types of flavour and odour compounds. The effect of the pattern of growth of plants on germination of sclerotia was confirmed in experiments with different types of planting material. Germination beneath plants grown from sets was particularly rapid, but very slow beneath plants produced by direct seeding. An experiment with plants grown under different levels of sulphate nutrition showed that low levels of flavour and odour compounds were associated with a weak capacity to stimulate the germination of sclerotia. No evidence was found to suggest that control of white rot disease by selection for growth features or for differences in flavour and odour characteristics would be a practicable proposition for the foreseeable future.
Assessment of resistance to Plasmodiophora brassicae in swedes
Authors: WILLIAMSON CYNTHIA J.
Published: April 2007

A method is described in which swede seedlings inoculated with standardized concentrations of resting spores of specific populations of Plasmodiophora brassicae can be evaluated for resistance in different environments. Similar ranking for resistance of four swede cultivars inoculated with one pathogen population was obtained from seedling tests in a glasshouse, from young plants in a polythene tunnel, and from mature plants in field trials. Differential resistance of the four cultivars to two pathogen populations evident in glasshouse seedling tests was more clearly demonstrated in the field where there was a highly significant cuitivar × pathogen population interaction (p<0 001) for both root fresh weight and mean disease category.

The inclusion of uninoculated control plants in field trials enabled a direct comparison of yield with that from inoculated plants. Cultivars were defined as resistant in terms of yield if they did not suffer any crop loss in comparison with uninoculated plants, even though some plants showed restricted gall development. The distribution of fresh weight to galls, roots and shoots could be used to characterize the relative resistance of cultivars; in the most susceptible cultivars there was rapid gall development but little increase in root or shoot fresh weight between 6 and 12 weeks after inoculation. Differential response was determined during the 6 weeks following inoculation; the implications of this observation are discussed in relation to growth stage and rate of development of host and pathogen.
Sensitivity of Pseudoeevcosporella herpotriehoides to the fungicide prochloraz
Authors: GALLIMORE K. , KNIGHTS I. K. , BARNES G.
Published: April 2007

In a survey carried out in 1984, isolates of the eyespot fungus, Pseudocercosporella herpotrichoides, from cereals in the UK, Denmark and West Germany were tested in vitro for sensitivity to the fungicide prochloraz. Of 194 isolates tested, 191 showed no growth on agar amended with prochloraz at 2 μg/ml or more. The mean concentration of prochloraz calculated to inhibit colony growth by 50% (IG50) was 0 44+0−010 μg/ml. The three isolates that grew at 2 μg/ml displayed weak colony development and were clearly disrupted by the presence of the fungicide. R‐type isolates appeared more sensitive to prochloraz than W‐type isolates. Comparisons with similar data for isolates obtained from other years revealed no consistent change with time in sensitivity to prochloraz.
Vertical distribution of root damage caused by Rhizoctonia solani in wheat
Authors: MACNISH G. C. , DODMAN R. L.
Published: April 2007

Vertical distribution of root damage caused by Rhizoctonia solani within a rhizoctonia patch was examined on five occasions during the growing season using a soil core technique. The effect of depth on root damage was assessed by determining root growth of wheat seedlings grown in cores of undisturbed soil taken at depths 0−2−5, 2−5−5−0, 5−0−7−5 and 7−5−10 cm from both inside and outside a patch. Within the patch most of the damage occurred in the top 5 0 cm of soil with less in the next 2−5 cm and least in the 7−5−10 cm zone. Outside the patch, soil depth had little or no effect on root growth.
Screening for resistance to canker (Leptosphaeria maculans) in winter oilseed rape (Brassica napus ssp. oleifera)
Authors: NEWMAN PAMELA L. , BAILEY D. J.
Published: April 2007

A test involving infection of seedlings in a glasshouse was evaluated for potential use in screening breeding material by comparing the results with those of field tests. The two tests correlated well for some resistant selections, particularly those closely related to Jet Neuf, and for very susceptible selections. However, two small groups of selections were resistant in the field but consistently susceptible in the glasshouse. Inoculation of mature plants in the glasshouse resulted in similar discrepancies and therefore gave no advantage over the seedling test. These discrepancies limit the usefulness of glasshouse techniques for routine resistance screening. A very high correlation was found overall between internal and external canker symptoms of the crown in nine field trials. Significant differences were found, however, between selections and cultivars in the relative severity of these two symptoms. Upper stem canker and crown canker were found to be very poorly correlated for individual plants, but highly correlated for eultivar means. The significance of these observations is discussed with respect to scoring canker in the field.
Chemical control of vascular‐streak dieback disease of cocoa in Papua New Guinea
Authors: PRIOR C.
Published: April 2007

High‐volume foliage sprays of 18 compounds including 13 systemic fungicides in field trials at 4‐week intervals did not control vascular‐streak dieback (VSD) of cocoa caused by Oncobasidium theobromae in Papua New Guinea. Soil drenching with carbendazim and other systemics was also ineffective, possibly because insufficient carbendazim may have been taken up into the xylem to inhibit the fungus. Stem paints with four systemic fungicides in aqueous formulations were also ineffective, but 4‐weekly stem painting of the hardened bark of young seedlings with 10 g/l propiconazole in 25% white oil caused a highly significant reduction in VSD incidence under field conditions. The treatment had no curative effect. Some phytotoxicity was observed but this was not apparent when the concentration of propiconazole was doubled and the treatment interval lengthened to 8 weeks. The ineffectiveness of systemic fungicides as soil drenches and foliage applications was probably due to failure of these compounds to accumulate at the shoot apex where infection occurs. A stable and non‐toxic formulation containing surfactants was developed which may improve control by aiding bark penetration by propiconazole or related compounds.
Studies of the epidemiology and control of tomato stem rot caused by Didymella lycopersici
Authors: FAGG J. , FLETCHER J. T.
Published: April 2007

Pycnidiospores of Didymella lycopersici were capable of inducing stem lesions when used at concentrations as low as two spores per 15‐μl droplet, provided the inoculum was placed on wounded tissue and the relative humidity maintained at more than 90%. At c. 75% RH, lesions were not produced even at high spore concentrations and with pre‐inoculation stem wounding. Pycnidiospores remained viable when stored for 17 weeks in sterile water and 14 weeks in nutrient solution. Detailed examination of tomato stems with a single lesion indicated that, in some cases, the pathogen may be widely distributed as it was isolated at distances of up to 1000 mm above the lesion and 750 mm below. Experiments on the transmission of D. lycopersici using sciarid flies demonstrated that, although this may be possible, it is probably infrequent in occurrence. None of the fungicides tested for the control of stem lesions were better than the standard benomyl in Actipron, but benomyl in medical‐grade liquid paraffin was as good.
Frequency of virulence phenotypes of Phytophthora fragariae in the field
Authors: KENNEDY DIANA M. , DUNCAN J. M.
Published: April 2007

The virulences of 102 single‐zoospore cultures of Phytophthora fragariae from one field site were determined on a range of strawberry differentials, and used to assign the cultures to four clusters (I, II A, IIB, IIC) using cluster analysis. On cv. Favourite, which is susceptible to all known races of the pathogen, isolates in cluster I were recovered most frequently and had the narrowest spectrum of virulence. On cv. Saladin isolates in cluster IIB were more common and were pathogenic to this cultivar. However, c. 30% of the single zoospores from field isolates from Saladin were avirulent on this cultivar and belonged to cluster I. Hyphal‐tip and single‐zoospore cultures from selected field isolates in cluster IIB did not always have the same virulence phenotype as the parent isolates. One hyphal‐tip culture from a field isolate in cluster IIB had a virulence phenotype (IID) which had not been recorded before in Europe, and it attacked some cultivars not previously affected by red core. When cultivars such as Saladin were inoculated with mixtures of zoospores from two isolates from different clusters, with and without the corresponding virulence factors, the isolate with the corresponding virulence factor was selected. However, on the universally susceptible cv. Favourite the results depended on the relative competitiveness of the isolates and not on virulence factors.
Detection of the leaf curl pathogen of anemones in corms by enzyme‐linked immunosorbent assay (ELISA)
Authors: BARKER I. , PITT D.
Published: April 2007

Colletotrichum sp., the cause of leaf‐curl disease of cultivated anemones in south‐west England, was detected in anemone tissue by means of an indirect enzyme‐linked immunosorbent assay (ELISA). The method had a lower detection limit of less than 100 ng/ml (dry weight pure mycelium) and was specific enough for the detection of the pathogen in host tissue. The potential of the method in indexing anemone corms and also in the detection of a new disease of strawberries is discussed.
Methods of testing potato cultivars for resistance to soft rot of tubers caused by Erwinia carotovora subsp. atroseptica
Authors: BAIN R. A. , PÉROMBELON M. C. M.
Published: April 2007

The resistance of eight potato cultivars to tuber soft rot caused by E. carotovora subsp. atroseptica was assessed in 2 years using three different test methods. Similar cultivar resistance rankings were obtained for any one method within a year and between years for two methods (single site, infectivity titration), but not for the third (vacuum infiltration). However, the ranking of cultivars differed for the three methods. Ranking was not affected by inoculating the cortex or the more susceptible medullary tissue, or by assessing rotting in terms of infection frequency or lesion size, but it was affected by oxygen concentration during incubation. Differences among cultivars were greater when inoculated tubers were incubated anaerobically than when incubated with 5% oxygen. There was no relationship between the relative susceptibilities of cultivars to tuber soft rot in storage in January/February and those of mother tubers after planting.
Sensitivity of Crinipellis perniciosa to two triazole fungicides in vitro and their effect on development of the fungus in cocoa
Authors: McQUILKEN M. P. , SUPRIADI  , RUDGARD S. A.
Published: April 2007

Two triazole fungicides, hexaconazole and triadimenol, were evaluated for their effects on the growth of Crinipellis perniciosa in vitro, and for their ability to prevent broom formation on cocoa seedlings. Amounts of both fungicides required to reduce fungal growth, germ tube extension and basidiospore germination by 50% were found respectively to be less than 1, 10‐150 and more than 200 mg/l. Reductions in germ tube length were associated with slower rates of cell growth, whereas growth of dikaryotic mycelium was reduced due to shorter cell lengths. Isolates of C. perniciosa showed different sensitivities to the fungicides, variation between collections from different localities being greater than between collections from the same locality. Hexaconazole gave good control of the disease applied as a spray to cocoa seedlings both before and after inoculation. Triadimenol showed good activity when used as a preinoculation soil drench and in some treatments where plants became infected no necrosis of host tissue was observed. Activity was greatly reduced by drench treatments applied 10 days after inoculation, and most infected plants formed necrotic cankers.
Suppression of septoria tritici blotch and leaf rust on wheat seedling leaves by pseudomonads
Authors: LEVY EDNA , EYAL Z. , CHET I.
Published: April 2007

Application of cells of two isolates of fluorescent pseudomonads from soil to wheat seedlings prior to inoculation with Mycosphaerella graminicola (anamorph, Septoria tritici) or Puccinia recondita f.sp. tritici markedly reduced symptom expression. These Pseudomonas isolates, LEC 1 and LEC 2. also reduced in vitro growth of Geotrichum candidum. Rhizoctonia solani. Sclerotium rolfsii and S. tritici. Growth of the melanin‐producing isolate ISR398 of S. tritici was inhibited on silica gel thin‐layer chromatograms by compound(s) extracted with diethyl ether from King's Medium B colonized by Pseudomonas isolate LEC 1. The growth of the antagonistic pseudomonads on defined medium was not affected by the following commercial fungicides: benomyl, captafol, chlorothalonil, fenarimol, mancozeb, maneb, metalaxyl, prochloraz, propiconazole, triadimefon, and the herbicides 2,4‐D and diclofop‐methyl at the recommended concentrations
Tomato powdery mildew
Authors: FLETCHER J. T. , SMEWIN BELINDA J. , COOK R. T. A.
Published: April 2007

A powdery mildew (Erysiphe sp.) occurred on greenhouse‐grown tomato crops in southern England in 1987. White pustules appeared on the upper surfaces of leaves of affected crops and only rarely on the under surfaces. In greenhouse experiments, stems were very severely affected. In host range studies 19 tomato cultivars and six breeders' lines were susceptible as well as Nicotiana tabacum. N. xanthi. Solanium melongena, S. pseudocapsicum, S. tuberosum, Datura stramonium and Petunia hybrida. Conidia germinated readily at 15, 20 and 25 C and were viable for 2 days in the laboratory and at least 6 days in the greenhouse. The disease was well controlled by a range of fungicides including benomyl, bupirimate, carbendazim, chlorothalonil, fenarimol and pyrazophos. All of these except pyrazophos are approved for use on tomatoes in the UK. The pathogen was very sensitive to low concentrations of benomyl and fenarimol but less so to bupirimate.
Survival of the lettuce anthracnose fungus (Microdochium panattonianum) in Victoria
Authors: GALEA V. J. , PRICE T. V.
Published: April 2007

Soils from anthracnose‐infected lettuce fields at Keilor, Werribee South and La Trobe University caused lesions of Microdochium panattonianum to develop when inoculated on to lettuce leaves. Under field conditions conidia lost infectivity within 10 weeks in pasteurized and 6 weeks in non‐pasteurized Werribee South soil, 2 weeks in Keilor red and immediately in Keilor black non‐pasteurized soils. Soils remained infective for 18 weeks in non‐pasteurized and pasteurized Werribee South soils inoculated with conidia and for Hand 16 weeks respectively when the same soils were inoculated with infected leaf discs.

In 1983 and 1984 M. panattonianum survived for 14 and 16 weeks respectively on infected Cos Verdi debris on the soil surface, for 10 and 20 weeks respectively on debris buried at 10 cm depth and for 70 and 58 weeks respectively on debris suspended in the air. The fungus survived for similar periods on infected Winterlake debris on the soil surface and buried at 10 cm depth. In soil the decline of infectivity was primarily influenced by duration of exposure and soil moisture, and in debris by duration of exposure and rainfall that occurred over the 2 weeks preceding each sample. The disease was not transmitted on seed produced on infected plants. Seedlings grown from healthy seed inoculated with conidia did not develop anthracnose after the seed had been stored for 24 days at 5 or 20°C. The significance of these results to the management of lettuce anthracnose in Victoria is discussed.
Leptosphaeria nodorum on wheat in Ireland
Authors: O'REILLY P. , BANNON ENDA , DOWNES M. J.
Published: April 2007

Symptomless leaves of young wheat crops collected in January and February produced, after surface‐sterilization and incubation on an agar medium, perithecia typical of Leptosphaeria nodorum. Single‐ascospore cultures produced pycnidia typical of Septoria nodorum, whose conidia caused necrotic lesions to develop when sprayed on wheat seedlings.
Fungitoxicity of plant growth regulators (PGRs) and PGR/fungicide mixtures in soak treatments to Septoria apiicola pycnidiospores
Authors: GOTT KATHLEEN A. , MAUDE R. B. , THOMAS T. H.
Published: April 2007

Mixtures of the plant growth regulators (PGRs) gibberellins A4 and A7 (GA 4/7) and ethephon (2‐chloroethylphosphonic acid), applied as soak treatments at 20° C for 24 h, were toxic to pycnidiospores of Septoria apiicola on agar, apparently as a result of low pH of their solutions. Ultraviolet spectroscopy showed that the aqueous solubility of the fungicides benomyl and carbendazim increased significantly when buffered at low pH or mixed with aqueous solutions of GA 4/7 and ethephon. This resulted in greater quantities of 14C‐labelled fungicides entering celery seeds imbibed in PGR/fungicide mixtures in comparison with fungicides alone.

A 24‐h seed soak at 20° C in a mixture of aqueous benomyl, GA 4/7 and ethephon eliminated S. apiicola in infected celery seeds. A thiram soak was also effective but PGR mixtures alone did not completely eliminate the pathogen.
A model of the evolution of polygenically controlled fungicide resistance
Authors: SHAW M. W.
Published: April 2007

A simple model of the evolution of polygenically controlled fungicide resistance is presented. The basic model contains four parameters, all of which are experimentally measurable. The first, β, describes how much a given change in fungicide sensitivity alters the fitness of a clone of the organism in the presence of fungicide. The second, γ, describes the strength of stabilizing selection, which tends to restore sensitivity to an optimal value. The third, σ2, specifies the variance in fungicide sensitivity existing among genotypes in the population. The fourth parameter is the heritability, h2. of fungicide sensitivity; it applies only to pathogens reproducing sexually. The model suggests that changes in sensitivity of populations to fungicide will only be weakly dependent on the concentration applied, but will be mainly controlled by the slope of the graph for fungicide sensitivity against fitness in the presence of fungicide. Unless stabilizing selection is very strong, it will only slightly modify the rate at which sensitivity changes. Loss of resistance in the absence of the fungicide will be, at most, half as fast as its initial gain. If the heritability, h2, is close to 1, annual sexual reproduction will scarcely affect the conclusions drawn above; if h2, is small, long‐term changes will be substantially slowed down and a cycle in population fungicide sensitivity may occur within each year. In suitable fungi, limits could be placed on the strength of stabilizing selection by looking for changes in variance in fungicide sensitivity between clones before and after sexual reproduction. Data to test the model are sparse, but do not contradict it.
Vertical dispersal of plant pathogens by splashing. Part I: the theoretical relationship between rainfall and upward rain splash
Authors: WALKLATE P. J.
Published: April 2007

The theoretical relationship between rainfall intensity, raindrop size distribution and the upward transport of splash droplets is examined to establish a better understanding of the natural rainfall characteristics that can cause upward movement of plant pathogens in a crop. The theory suggests that splash transport is determined by the rain splash intensity index, which is defined as the intensity of the rainfall with raindrops greater than a threshold size. Ulbrich's (1983) empirical model of the size distribution of raindrops is used to calculate the relationship between rainfall intensity and rain splash intensity index. The calculations show that rainfall intensity is not a reliable indicator of the rain splash intensity index, particularly in convective showers. Therefore, a correlation between rainfall volume and upward disease progress is unlikely to provide a reliable basis for forecasting sudden disease outbreaks associated with short‐duration convective showers during the summer. Finally, we consider the instruments that have the capability to measure the rain splash intensity index.
Glomerella cingulata on camellia
Authors: DICKENS J. S. W. , COOK R. T. A.
Published: April 2007

Glomerella cingulata was shown to be associated with a leaf blotch, canker and dieback of imported camellia plants. It was particularly damaging on hybrids of Camellia saluenensis such as C. x williamsii cv. Donation. Pathogenicity tests, using whole plants and detached leaves of cv. Donation, distinguished between virulent and a virulent strains of the fungus. The virulent strain did not cause severe damage when inoculated into a range of other woody ornamentals. Conversely, Colletotrichum spp., including G. cingulata, isolated from other hosts were not virulent to Camellia cv. Donation. Apart from a loss of virulence associated with a mutation to paleness of colonies in culture, virulent isolates with dark‐grey colony centres were morphologically identical to avirulent isolates from camellia, including tea plant (Camellia sinensis), and to some isolates from other hosts. A form of Colletotrichum acutatum isolated from camellia and readily distinguished from G. cingulata by bright pink colonies and conidial shape was shown to be avirulent on Camellia cv. Donation. It is proposed that the virulent form on ornamental camellia be described as Glomerella cingulata f.sp. camelliae.
Resistance to diethofencarb (NPC) in benomyl‐resistant field isolates of Botrytis cinerea
Authors: KATAN TALMA , ELAD Y. , YUNIS H.
Published: April 2007

Based on the ‘negative cross‐resistance’ phenomenon between N‐phenylcarbamates and benzimidazole fungicides, the fungicidal mixture of carbendazim + diethofencarb (MBC + NPC) was introduced, to control Botrytis cinerea phenotypes which are either sensitive to benzimidazoles and resistant to NPC (wild‐type: BenS NPCR). or resistant to benzimidazoles and sensitive to NPC(BenR NPCS). At one out of four sites where the MBC + NPC mixture was used in commercial cucumber greenhouses, grey mould control failed and a new phenotype of B. cinerea was found. The new phenotype was resistant to benzimidazoles, as was 100% of the population screened in the four sites, but retained resistance to NPC. Accordingly, the new phenotype was designated BenR NPCR. It was pathogenic on cucumber seedlings.
Occurrence of tan spot of wheat caused by Pyrenophoratritici‐repentison wheat in England and Wales in 1987
Authors: COOK R. J. , YARHAM D. J.
Published: April 2007

Drechslera tritici‐repentis, anamorph ofPyrenophora tritici‐repentis, was found in diamond‐shaped, dark‐brown lesions on leaves of several winter wheat crops in England and Wales. Lesions were darker than the otherwise similar lesions caused bySeptoria nodorum.
A comparison of controlled environment and field trials for detection of resistance in cereal cultivars to root rot caused by Rhizoctonia solani
Authors: NEATE S. M.
Published: April 2007

A screening test was developed to study the effect of different quantities of inoculum of Rhizoctonia solani on root rot and growth of cultivars of wheat, barley, oats, rye and triticale in a controlled environment and the field in two seasons. The ranking of relative susceptibility to disease of cultivars within a cereal differed between the controlled environment and field experiments, and between seasons in the field. The ranking of relative susceptibility between cereals also differed between experiments. In the controlled‐environment experiment, wheat had the highest disease rating, followed by oats, barley, triticale and rye, but in the field barley had the highest rating followed by wheat and then oats. The overall differences between the cereals were small.
Measuring the sterol content of barley leaves infected with powdery mildew as a means of assessing partial resistance to Erysiphe graminis f.sp. hordei
Authors: NEWTON A. C.
Published: April 2007

Barley leaf segments of several partially resistant cultivars were inoculated with different strains and combinations of strains of Erysiphe graminis. Infection level was assessed by counting colony number, by measuring sporulating area using an image analyser, and by extracting and quantifying sterols. Good correlations were obtained between data from all three methods. One cultivar contained less sterol than expected from the number of colonies present but some of the resistance in that cultivar was known to be due to reduced colony size. Image analysis was unable to discern the reduced colony size component of resistance. Scanning electron microscopy revealed that single colonies may originate from more than one conidial infection. Sterol analysis was the most representative method of comparing the reaction of diverse host genotypes to mildew infection.
Scanning electron microscopy study of infection structure formation of Puccinia graminis f.sp. tritici in host and non‐host cereal species
Authors: LENNOX C. L. , RIJKENBERG F. H. J.
Published: April 2007

The development of uredospore‐derived infection structures of Puccinia graminis f.sp. tritici in wheat, barley, sorghum and maize was examined by scanning electron microscopy (SEM). Germ tubes grew over the leaf surface until a stoma was located. An appressorium formed over the stoma and the leaf was penetrated by an infection peg. Within the substomatal chamber of all species the infection peg developed a substomatal vesicle by 6 h post‐inoculation (hpi). from which a primary infection hypha developed parallel to the long axis of the leaf. In wheat, barley and maize, when a primary infection hypha abutted onto a host cell, a septum was laid down between the tip of the hypha and the substomatal vesicle, delimiting a haustorial mother cell by 12 hpi; haustorial mother cells did not form in sorghum. Secondary infection hyphae arose on the substomatal vesicle side of the septum; infection did not progress further in maize, but in wheat and barley secondary infection hyphae branched, and proliferated intercellularly forming the fungal thallus. A haustorial mother cell was delimited when an intercellular hypha abutted onto a host cell. Infection sites with haustorial mother cells were observed at 12 hpi in barley and 24 hpi in wheat. In all four plant species, some atypical substomatal vesicle initials, substomatal vesicles and primary infection hyphae were observed.
Infection of the pearl millet (Pennisetum americanum) inflorescence by the downy mildew fungus (Sclerospora graminicola)
Authors: SEMISI S. T. , BALL S. F. L.
Published: April 2007

Different developmental stages of the inflorescence of pearl millet (Pennisetum americanum) were inoculated with zoospores of the downy mildew fungus (Sclerospora graminicola). Individual florets within a panicle were infected, with resultant malformation of any floral organs that were not fully differentiated at the time of infection. ‘Green‐ear’ symptoms resulting from hyperplasia and hypertrophy of the host tissues were accompanied by both sexual and asexual sporulation of the fungus on the malformed plant parts. No grain set occurred in affected florets, indicating that secondary inoculum was able to cause yield reductions even at late stages in the host development. Infection of differentiated stigmas led to rapid dissolution and necrosis of tissue and prevented colonization by the pathogen. This failure suggests that seeds are unlikely to be infected internally.
Comparative morphology of Phytophthora species on rubber
Authors: LIYANAGE N. I S. , WHEELER B. E. J.
Published: April 2007

Eighty‐nine Phytophthora isolates from rubber throughout the world were examined critically. Five species were distinguished: P. palmivora morphological form I (MF1), P. meadii, P. botryosa, P. citricola, P. citrophthora and one currently designated P. palmivora (MF4). P. citrophthora is reported for the first time from rubber in the Ivory Coast and Indonesia, and mating types are given.
Airborne spores of Tilletia caries as a source of wheat bunt through soil contamination
Authors: YARHAM D. J. , McKEOWN B. M.
Published: April 2007

In 1985 severe bunt was encountered in a crop of wheat grown from organomercury‐treated seed. Circumstantial evidence suggested that the soil had been contaminated by airborne spores of the fungus from a nearby crop which was being harvested at the same time as the affected crop was being sown.
A plant rhabdovirus associated with peanut veinal chlorosis disease in India
Authors: NAIDU R. A. , MANOHAR S. K. , REDDY D. V. R. , REDDY A. S.
Published: April 2007

A disease of peanut characterized by stunting of plants, veinal chlorosis, outward bending of leaflets, and proliferation of axillary buds has been observed in several parts of Peninsular India since 1977. The disease was restricted to peanut crops raised during the post‐rainy season. A rhabdovirus was associated with this disease. This appears to be the first record of natural occurrence of a rhabdovirus in peanut.
The effect of waterlogging on Phytophthora root rot of red raspberry
Authors: DUNCAN J. M. , KENNEDY DIANA M.
Published: April 2007

Red raspberry plants were subjected to waterlogging after inoculation with different species of Phytophthora isolated from field outbreaks of root rot. The commonest species, a form of P. megasperma, was highly pathogenic to raspberry whether the plants had been waterlogged or not, but waterlogging increased the severity of disease caused by other species. P. cambivora and P. drechsleri were moderately pathogenic and non‐pathogenic respectively in non‐waterlogged conditions but killed plants that had been waterlogged for 4 days. P. megasperma var. megasperma required longer periods of waterlogging to cause severe symptoms and did not kill plants. Root rotting of waterlogged and non‐waterlogged plants was controlled with a metalaxyl and copper mixture. The results indicated that several species of Phytophthora may contribute to poor growth and death of raspberries grown in poorly drained sites.
Properties of a hordeivirus from Anthoxanthum odoratum
Authors: EDWARDS M. L. , KELLEY S. E. , ARNOLD M. K. , COOPER J. I.
Published: April 2007

A virus having tubular particles (124, 142 and 167 nm) was manually transmitted from and to Anthoxanthum odoratum (sweet vernal grass). Other experimental hosts were Chenopodium quinoa, C. amaranticolor, Zea mays, Avena sativa and Hordeum vulgare (barley); winter cultivars of barley were more often infected than spring cultivars. In tests which simulated mechanical injury, the virus was transmitted from infected to healthy A. odoratum but not to healthy barley. The virus particles, which were seen as aggregates in the cytoplasm of A. odoratum leaf cells and in anther walls, reacted strongly in immunosorbent electron microscopy tests with antisera to strains of barley stripe mosaic hordeivirus. Nevertheless, the virus could be distinguished from the Type strain of barley stripe mosaic virus by reciprocal serological tests and by symptoms in infected barley cv. Black Hulless. Using an antiserum produced against the virus, a survey of A. odoratum in the field revealed one of 72 tested plants to be naturally infected. The virus is probably that described by Catherall & Chamberlain (1980) and named anthoxanthum latent blanching virus.
RNA/cDNA hybridization studies of UK isolates of barley yellow mosaic virus
Authors: BATISTA M. F. , ANTONIW J. F. , SWABY A. G. , JONES P. , ADAMS M. J.
Published: April 2007

The RNA components of two isolates of BaYMV from Streatley and Wiltshire were analysed by agarose gel electrophoresis. Northern blots of extracts of both isolates analysed with random‐primed cDNA probes to RNA1 and 2 of the Streatley isolate showed little or no sequence homologies between the two isolates, confirming other evidence that they should be considered as different viruses.
Population dynamics of metalaxyl‐sensitive and metalaxyl‐resistant isolates of Phytophthora infestans in untreated crops of potato
Authors: KADISH D. , COHEN Y.
Published: April 2007

Each of six pairs of metalaxyl‐sensitive (MS) and metalaxyl‐resistant (MR) field isolates of Phytophthora infestans was inoculated as a mixture of 90% MS sporangia with 10% MR sporangia onto fungicide‐free potato plants (cv. Alpha) in six walk‐in plastic tunnels in each of 2 years. In both experiments, late blight killed the crops in 26‐31 days. In all tunnels, the frequency of MR sporangia increased during the logarithmic phase of the epidemic to 70‐85% of the population. Later, however, the frequency of M R sporangia decreased to 7‐38% in six tunnels but continued to increase to 94‐100% in the other six. The increased frequency of MR during the logarithmic phase was attributed to the shorter latent period and larger lesion size of MR compared to MS isolates and to the unlimited availability of uninfected host tissue. The later decrease in the frequency of MR in six tunnels was attributed to the lower sporulation capacity and the shorter infectious period of MR compared to MS isolates, and to the limitation of uninfected host tissue. The data showed that the population dynamics of P. infestans was dependent not only on fitness components of isolates, but also on the availability of uninfected host tissue.
Selection for metalaxyl resistance in potato crops infected with Phytophthora infestans: effects of fungicides and initial frequency of resistant sporangia
Authors: COHEN Y. , SAMOUCHA Y.
Published: April 2007

Potato crops (cv. Alpha) were grown in walk‐in plastic tunnels (33 m2) in winter 1987 and spring 1988. Crops were left untreated or treated (four sprays at intervals of 2 weeks) with either metalaxyl, Ridomil‐MZ (metalaxyl+ mancozeb) or Ridocym (metalaxyl +mancozeb+cymoxanil). Crops were inoculated with sporangial suspensions of Phytophthora infestans containing 01, 1 or 10% metalaxyl‐resistant sporangia. Disease progress and percentage resistant sporangia in tunnels were estimated for a period of 50 days. In the treated crops cumulative disease, rate of disease progress and increase in frequency of resistant phenotypes (selection coefficient) were higher in metalaxyl‐treated crops than in Ridomil‐MZ or Ridocym‐treated crops. Cumulative disease, rate of disease progress and increase in frequency of resistant phenotypes were unaffected by the frequency of resistant sporangia in the original inoculum. Metalaxyl, Ridomil‐MZ and Ridocym speeded up the selection for resistance by 92, 29 and 17%, respectively, relative to untreated crops. The time interval required for the resistant subpopulation to predominate in treated crops was inversely related to initial resistance. It was longest in crops inoculated with 0.1 % resistant sporangia and treated with Ridocym. Results indicated that metalaxyl mixtures were advantageous over metalaxyl alone, both in delaying the buildup of resistance and in improving disease control, but did not prevent resistant subpopulations increasing from 01 to 100% in a single season.
The host range of isolates of downy mildew, Peronospora parasitica, from Brassica crop species
Authors: SHERRIFF CHRISTINE , LUCAS J. A.
Published: April 2007

The host ranges of 33 isolates of the downy mildew fungus Peronospora parasitica from different Brassica hosts and diverse geographic origins were assessed on a standard set of Brassica accessions Isolates from each host species had a distinct host range, and in some cases isolates from the same host species but different geographic origins differed in host range. Most isolates were capable of infecting hosts other than their species of origin. These results are discussed in relation to species specificity and the conservation of certain virulence gene combinations. The epidemiological implications for cross‐infection of Brassica hosts by P. parasitica isolates in the field are also considered.
Genotypic frequencies of phosphoglucose isomerase allozymes in bean rust (Uromyces appendiculatus) populations estimated by densitometry
Authors: LINDE D. C. , GROTH J. V. , ROELFS A. P.
Published: April 2007

Phosphoglucose isomerase (PGI) is a dimeric enzyme in germinating urediniospores of Uromyces appendiculatus. Three distinct bands occur in heterozygous isolates after starch gel electrophoresis. Transmission densitometry was used to estimate the frequency of the homozygous slow (S), homozygous fast (F), and heterozygous (H) individuals in mixed preparations of urediniospores. Areas under each band peak were transformed to genotypic frequencies by comparison with standard 1:1 (F:S)and 100% H preparations. Estimated genotypic and allelic frequencies in prepared mixtures were linearly related to the actual frequencies. Correspondence of estimated with actual frequencies was high, generally differing by 10% or less. Three of 10 field collections examined were polymorphic for PGI allozymes, and two of these were apparently in Hardy‐Weinberg equilibrium.
Variation for virulence among Scandinavian isolates of Peronospora viciae f.sp. pisi (pea downy mildew) and responses of pea genotypes
Authors: STEGMARK R
Published: April 2007

Variation for virulence among Scandinavian isolates of Peronospora viciae f.sp. pisi (downy mildew) on different pea genotypes was investigated. Variation for virulence was found within and between mass‐conidial isolates which were originally obtained from oospore populations. Virulence towards pea cultivars that have not been commerically cultivated in Scandinavia was observed. The specific resistance of the pea cultivars Puget, Cobri, Gastro, Starcovert and Starnain was confirmed. One pea breeding line showed a stable partial resistance to different isolates of the fungus and it was also highly resistant to race 8’from The Netherlands which is considered to be virulent on most pea genotypes carrying known specific resistance factors.
Blackleg development and tuber yield in relation to numbers of Erwinia carotovora subsp. atroseptica on seed potatoes
Authors: BAIN R. A. , PÉROMBELON M. C. M. , TSROR L. , NACHMIAS A.
Published: April 2007

The relationship between number of viable cells of Erwinia carotovora subsp. atroseptica on inoculated potato seed tubers and blackleg development was investigated in 2 years for five cultivars grown in the contrasting climates of Scotland and Israel. Blackleg, and to a lesser extent non‐emergence, increased with higher numbers of bacteria on the seed tubers at planting. This relationship was also found for several commercial seed stocks of one cultivar naturally contaminated with different numbers of E. carotovora subsp. atroseptica.The threshold number of bacteria necessary for the development of blackleg declined during the growing season and was also higher for the cultivar Pentland Crown in comparison with the others. In general, yield declined linearly with blackleg incidence and there was a 0.8% reduction in yield for every 1 % blackleg at 13 weeks after planting. Yield loss was positively related to the incidence of blackleg late in the season, whereas the relationship between yield loss and the incidence of non‐emergence was poor.
A serious attack by Spermospora avenae on oats—a disease new to Western Europe
Authors: CUNNINGHAM P. C.
Published: April 2007

Symptoms of red leather leaf of oats were widespread and severe in spring 1988 on autumn‐sown oat crops in the south and east of Ireland. The disease was characterized by grey‐brown elliptical lesions, developing into light‐grey eyespots surrounded by dark borders. Plants were stunted and showed reddish‐brown foliar pigmentation extending beyond the lesions. Spermospora avenae was isolated and shown to be pathogenic to oats. Cultural characteristics of the pathogen on several agar media are described. The disease has previously been reported only from the USA, Turkey and Australia.