bluuebunny/crossref_metadata_2025 huggingface dataset:
Host‐mediated interactions between pathogen genotypes
Authors: CHIN K. M. , WOLFE M. S. , MINCHIN P. N.
Published: April 2007

Barley c ltivars with different resistance genes were inoculated with various sequences of virulent and non‐virulent isolates of Erysiphe graminis f.sp. hordei. The resistance induced in incompatible reactions decreased infection by virulent isolates while, conversely, the degree of susceptibility induced in compatible reactions was sufficient to increase the ability of normally non‐virulent isolates to infect a resistant host. The net effect of interactions was always overall reduction of conidial production when compared with inoculation of a virulent isolate alone.

Each interaction between isolates was dependent on the host cultivar, the pathogen isolates used and on the inoculation sequence. Often, induced resistance was most obvious when a nonvirulent isolate was inoculated prior to a virulent isolate. Induced susceptibility was usually more apparent when the virulent isolate was inoculated first. However, on the cultivar Wing, induced susceptibility was more apparent following prior inoculation of a non‐virulent isolate. On the cultivar Hassan, prior inoculation with a virulent isolate sometimes induced susceptibility, but in some cases more susceptibility was induced by prior inoculation with a non‐virulent isolate. In the latter instances, although relatively little infection developed, the majority of the spores produced were those of the normally non‐virulent isolate.

There was some evidence of non‐virulent isolates acquiring the ability to infect normally incompatible hosts. This effect disappeared after several generations in the absence of the virulent isolate.
Oospores in cultures of Phytophthora infestans resulting from selfing induced by the presence of P. drechsleri isolated from blighted potato foliage
Authors: SKIDMORE D. I. , SHATTOCK R. C. , SHAW D. S.
Published: April 2007

A Phytophthora species isolated from blighted potato foliage was identified as P. drechsleri, mating type A2. The isolate was found to be weakly pathogenic on a range of hosts. Pairings in vitro of P. drechsleri with British isolates of P. infestans mating type A1 when separated by a polycarbonate membrane resulted in selfed oospores of both species. The possibility that A1 P. infestans is induced to self in the field and the genetic consequences of such selfing are discussed.
Differential host‐parasite interactions between oilseed rape and Leptosphaeria macufans, the causal fungus of stem canker
Authors: NEWMAN PAMELA L.
Published: April 2007

Seedlings of 13 cultivars of oilseed rape (Brassica napus) were inoculated with 10 isolates of Leptosphaeria maculans. Three virulent isolates were identified which gave a resistant reaction on some cultivars normally considered susceptible. Further experiments to compare these with standard isolates confirmed the existence of a differential host‐pathogen interaction. The breeding line 78/271, plus the cultivars Quinta, Garant, Norli and possibly Elvira differentiated the isolates tested while Jet Neuf, Rafal, Primor, Doral, Hercules, Rapora, Liraglu and Erra did not. The relevance of these findings to breeding for canker resistance in oilseed rape is discussed.
Biochemical characteristics of sporelings of Puccinia graminis f. sp. tritici and protoplasts from wheat isolines of potential significance in specificity
Authors: HOLDEN D. W. , STRANGE R. N.
Published: April 2007

The affinity of various lectins for protoplasts from isolines of wheat differing in their reaction to Puccinia graminis Pers. f. sp. tritici, Ericks and E. Henn. race 21 and for infection structures of the fungus was studied. Protoplasts of both isolines were agglutinated by concanavalin A and soybean lectin and lysed by wheat germ agglutinin. Pokeweed mitogen and wheat germ agglutinin bound to fungal germ tubes and appressoria but not to uredospore walls, substomatal vesicles or infection hyphae.

Viability of protoplasts from either isoline was not affected when they were incubated with uredospores, germlings with and without infection structures or with an extract of the susceptible line, heavily infected by the fungus. No differences between polypeptide fractions prepared from protoplasts of the isolines were detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis.
The effects of direct harvesting and drying systems on the incidence and control of neck rot (Botrytis allii) in onions
Authors: MAUDE R. B. , SHIPWAY M. R. , PRESLY A. H. , O'CONNOR D.
Published: April 2007

Direct harvesting, with mechanical removal of the foliage (topping), of onion crops followed by post‐harvest drying at ambient temperatures (c. 18°C) resulted in an increase in the incidence of onion neck rot (Botrytis allii).

The disease was substantially reduced if topped onions were dried at 30°C with an airflow of 425 m3 air/h/tonne. The treatment was most effective if the crop was removed from the field for drying within 48 h of topping thus avoiding severe infection of the damaged green tissues of the necks of onions.
Little leaf disease of Piper nigrum in Sri Lanka
Authors: RANDOMBAGE SUNIETHA , BANDARA J. M. R. S.
Published: April 2007

In recent years Black pepper (Piper nigrum) in Sri Lanka has become affected with‘Little leaf’disease. The main symptoms are chlorosis of leaves, shortening of internodes, proliferation of branches, greening and enlargement of floral bracts. Detailed measurements within experimental plots of two improved varieties Panniyur 1 and Kuching, indicated that leaf size, the number of flowers per spike and berry weight were reduced on infected vines. Seeds from infected vines germinated less well than those from healthy vines. In a field trial, disease spread was similar in plots planted with pepper at different spacings and receiving different fertilizer treatments.
Quantitative measurement of vascular flow in petioles of healthy and Verticillium‐infected tomato
Authors: STREET P. F. S. , COOPER R. M.
Published: April 2007

A Scholander pressure bomb was modified to measure accurately and continuously the flow through excised tomato petioles of sufficient length to contain no open xylem vessels. The contribution of vascular occlusion to water stress induced by Verticillium albo‐atrum was determined by comparing vascular flow through petioles supporting healthy, symptomless or wilted leaves. Invariably, flow was markedly reduced or completely prevented well before visual symptoms were apparent in leaves. In the system described collection of exuded xylem fluids for analysis over extended periods also allows the determination of the fate of fungal products introduced into vessels or the release of products from xylem walls or cells following treatment or infection. The various uses of this system to study xylem occlusion and host‐parasite inter actions in vascular diseases are discussed.
The occurrence and effects of barley yellow dwarf virus in maize in SW England
Authors: PEARSON M. N. , ROBB SHEILA M.
Published: April 2007

During 1975 and 1976 barley yellow dwarf virus was isolated, using the aphid Rhopalosiphum padi (L.) from five maize cultivars in the Exeter area. The isolates produced interveinal flecking, often accompanied by leaf reddening, in the maize cultivar Anjou 210 and several other susceptible cultivars. ln 1976 visual assessment of six commercial maize plantings indicated natural infections ranging from 11 to 14% of plants, whilst infection in a disease observation plot ranged from 0.8 to 27.5%. Population counts for the three aphid vectors Sitobion avenae (F.), Metopolophium dirhodum (W.) and Rhopalosiphum padi (L.), associated with the crop, corresponded closely with the Rothamsted Insect Survey results from Starcross, Devon.

The maize cultivars Anjou 210 and De Kalb 202 were grown in experimental plots with individual rows containing 0, 25, 50, or 100% barley yellow dwarf‐infected plants. Infection caused severe stunting of Anjou 210 but had less effect on De Kalb 202. Dry matter yield losses of 50% for Anjou 210 and 27% for De Kalb 202 were recorded; there were also significant changes (p<0.05) in dry matter content, metabolisable energy, digestible crude protein and water soluble carbohydrate.
Control of red thread, a disease of grasses caused by Laetisaria fuciformis
Authors: HIMS M. J. , DICKINSON C. H. , FLETCHER J. T.
Published: April 2007

A severe outbreak of red thread disease, caused by Laetisaria fuciformis, on reclaimed heathland is described and factors most likely to have favoured this epidemic are discussed. The efficacy of several fungicides and fertilizer treatments for control of the pathogen were examined in experiments which also involved a new method for assessing the distribution and spread of the pathogen at established foci. The most successful fungicides were benodanil and anilazine. Applications of nitrogen had no discernible effects in the 3 weeks following treatment.
Relating disease progress to cumulative numbers of trapped spores: apple powdery mildew and scab epidemics in sprayed and unsprayed orchard plots
Authors: JEGER M. J.
Published: April 2007

A technique for relating the progress of plant diseases caused by airborne fungal pathogens to cumulative numbers of trapped spores is proposed. The relationship involves two epidemiological parameters—a disease asymptote and the infection efficiency (disease units/spore) of inoculum. The technique was evaluated using data on apple powdery mildew and scab epidemics in sprayed and unsprayed apple orchard plots. For powdery mildew, the observed relationships were close to those proposed in the unsprayed plot, but changed after or during the period of fungicide application in sprayed plots. Parameter estimates gave useful comparative information on the epidemics. The technique was not useful for scab because of the discontinuous patterns of infection.
Treatments to control Phoma and Alternaria infections of brassica seeds
Authors: MAUDE R. B. , HUMPHERSON‐JONES F. M. , SHURING CATRJONA G.
Published: April 2007

The screening of chemicals using agar plate tests for activity against cultures of Phoma lingam, Alternaria brassicicola and A. brassicae is described. Most fungicides which were inhibitory to growth at 20 μg/ml or less showed eradicant activity when used as seed treatments. Selected on this basis, thiabendazole, applied as a slurry at 2–5 g a.i./kg seed, showed excellent eradicant activity against seed‐borne Phoma but not Alternaria when tested under laboratory, glasshouse and field conditions. Triarimol, tridemorph and azepine‐A2151, nuarimol, fenarimol and imaza‐lil although effective in agar plate tests against Alternaria and Phoma were phytotoxic when applied to seeds at rates sufficient to eliminate these fungi, Iprodione and fenpropimorph inhi bited the growth of the fungi at concentrations of 0.625 to 4 μg/ml and subsequent treatment of infected seeds at 1.25–2.5 g a.i. fungicide/kg seed with these fungicides proved effective against all three pathogens. Neither chemical adversely affected germination or emergence.
Selection on Erysiphe graminis in pure and mixed stands of barley
Authors: CHIN K. M. , WOLFE M. S.
Published: April 2007

The response of populations of Erysiphe graminis f. sp. hordei to selection by pure and mixed stands of three spring barley cultivars was studied in two field trials. The range of virulence of the pathogen genotypes selected in mixed host stands was dependent on the relative fitness of each genotype over all hosts. Unnecessary virulences were rapidly selected against on some hosts, but were less deleterious or favoured on others. In general there was selection for widely adapted pathogen genotypes in mixed host populations but this selection for flexibility limited the abilitytions in the absolute size of the pathogen population in host mixtures reduced the absolute frequencies of pathogen genotypes with combined virulences in comparison with those in pure stands. It is argued that host mixtures are therefore unlikely to favour rapid pathogen evolution towards races which are both widely adapted and highly virulent on all component cultivars which they can infect his definition docs not conform with conventional usage in population genetics.
Effects of rust and post‐infection drought on photosynthesis, growth and water relations in groundsel
Authors: PAUL N. D. , AYRES P. G.
Published: April 2007

Exchanges of CO2and water vapour were examined in groundsel,Senecio vulgaris, grown and infected with rust,Puccinia lagenophorae, under laboratory conditions. The effects of drought were examined by withholding water from plants from 2 days until approximately 10 days after infection, after which further daily water losses were restored. Net photosynthesis was inhibited and dark respiration was stimulated in rust‐infected leaves but, in young healthy leaves on the same plant, gross and net photosynthesis were stimulated and photorespiration was inhibited. The growth of plants was stunted 15 days after infection because the growth of leaf area was inhibited and, thereby, the photosynthetic capacity of the plant was reduced. Drought inhibited the growth of leaf area in both healthy and infected plants and, when combined with rust, had additive deleterious effects on net photosynthesis per plant and on growth. After sporulation, rusted plants transpired more rapidly than did healthy controls and leaf water potential fell to reach ‐ 0.95 and‐1.92 MPa in well‐watered and drought‐stressed plants respectively, compared with ‐0.18 and ‐ 1.2 MPa in healthy controls, 20 days after infection. Rust impaired the normal increase in Water‐Use Efficiency in response to drought.
Methods of measuring rhizoctonia patch of cereals in Western Australia
Authors: MACNISH G. C. , LEWIS SUSAN
Published: April 2007

Methods of measuring rhizoctonia patch in cereals are compared. Included are mapping and determination of area with a leaf area planimeter, aerial photography and determination of area by a grid overlay, a patch scoring technique, sampling and assessing for rhizoctonia root rot, and determination of yield. Mapping, aerial photography, and patch scoring were all highly correlated. Of these methods, the patch scoring technique was the quickest and most convenient. Yield within a patch was about 8% of yield immediately outside the patch.
Mapping rhizoctonia patch in consecutive cereal crops in Western Australia
Authors: MACNISH G. C.
Published: April 2007

Rhizoctonia patches in a field were mapped during consecutive seasons of cropping with wheat, oats or barley sown directly without tillage into the previous season's stubble. Distribution, size, shape and number of patches varied considerably between seasons. Less than a quarter of patches were circular and the others tended to be elongated parallel to seed‐rows. Barley was most severely affected, followed by wheat and then oats.

It is proposed that changes in patch distribution, configuration and number between seasons is due to shifts in a balance of suppressive or conducive soil factors interacting with Rhizoctonia solani inoculum.
Effect of fungal pathogens on digestibility and chemical composition of Italian ryegrass (Lolium multiflorum) and tall fescue (Festuca arundinacea)
Authors: LAM A.
Published: April 2007

Slight infection by Drechslera siccans or Rhynchosporium spp. significantly reduced in vitro dry matter digestibility, water‐soluble carbohydrate and the total amino acid content of Italian ryegrass (Lolium multiflorum) foliage. The concentration of all 15 amino acids detected was reduced, with arginine reduced significantly more than the others. Total nitrogen was either increased or not changed, and the amino acid composition was not altered. Limited work with Drechslera festucae on tall fescue (Festuca arundinacea) gave similar results. Small samples of healthy and diseased grass leaves at three different physiological stages were used to detect these changes.

Limited leaf spotting by D. siccans caused metabolic changes of the same magnitude as extensive leaf blotching by Rhynchosporium. Impaired photosynthesis and growth of the fungi within the leaf tissues are possible causes of these changes. Decreased digestibility and increased dry matter content of diseased grass foliage could be of great practical importance.
Effects of Pyrenophora teres on dry matter production and yield components of winter barley
Authors: JORDAN V. W. L. , BEST G. R. , ALLEN E. C.
Published: April 2007

Inoculation of winter barley plants in a glasshouse with Pyrenophora teres at three different growth stages (GS 11, 13 or 30) greatly decreased root and shoot dry matter production and the size of healthy leaves produced subsequently, but there was no significant yield loss with a single inoculation at GS 11 or 30. Inoculation at GS 13, GS 31 or GS 39 decreased grain yield by 12,17 and 20% respectively, and also straw yield. Larger yield losses resulted from repeated inoculations on five successive occasions (GS 11, 13, 30, 31 and 39) which caused much disease on all leaves throughout the life of the plant. All components of yield measured were decreased by the cumulative effect of successive inoculations; ear number by 15%), grain sites per ear by 20%, grain yield by 48% and straw yield by 32%.
The effect of copper sprays on bacterial blight and coffee berry disease in Kenya
Authors: KAIRU G. M. , NYANGENA C. M. S. , CROSSE J. E.
Published: April 2007

In field trials four different copper formulations, Kocide 101, Perenox, copper oxychloride and Procida Bordeaux Mixture effectively controlled bacterial blight and coffee berry disease and significantly increased yields of clean coffee. Under a severe incidence of the two diseases, Kocide 101 sprays were superior in performance. Copper sprays induced phytotoxic symptoms on light soils with low organic matter, but not on heavy, loamy soils. Residual effects of copper sprays in one year increased the susceptibility of trees to infection in the next. Cumulative copper sprays in 2 years had a significant effect on the control of both diseases and on yield response but gave an indication of long‐term problems that could arise from excessive use of copper.
A study of populations of Pseudomonas syringae pv. syringae on stonefruits in Victoria
Authors: WIMALAJEEWA D. L. S. , FLETT J. D.
Published: April 2007

In a survey of the major stonefruit nurseries in Victoria during winter 1978 and 1979, Pseudomonas syringae pv. syringae, the causal organism of bacterial canker, was found to be present on most of the stonefruit material in all nurseries but was detected most frequently on apricot.

The epiphytic populations of P.s. pv. syringae on leaves, buds and shoots of apricot and cherry were assessed periodically between 1979 and 1983 by determining the proportion of trees bearing the bacterium or by counting numbers of bacteria. Populations consistently reached peak levels during spring and late autumn, with highest levels in spring. Populations were lowest during mid‐ to late summer. High proportions of tree contamination and high populations coincided with periods when maximum temperatures ranged from 19° to 25°C, and when rainfall was moderately high. The significance of these findings in the light of information from other studies on the seasonal variability of host susceptibility, and in relation to chemical control, is discussed.

There was no evidence of occurrence of P.s. pv. morsprunorum in Victoria.
The effect of homoeologous group 7 chromosomes upon adult plant resistance of wheat to yellow rust (Puccinia striiformis)
Authors: PINK D. A. C. , LAW C. N.
Published: April 2007

Aneuploid and intervarietal chromosome substitution lines of wheat ev. Chinese Spring were used to study the effects of homoeologous chromosomes 7A, 7B and 7D upon adult plant resistance to yellow rust (Puccinia striiformis). Chromosomes 7B and 7D carry factors upon their short arms which interact to influence resistance. The results can be explained if there is a single locus determining resistance upon the short arms of chromosomes 7B and 7D. These loci may be homoeo‐allelic; however, no evidence was found for a corresponding locus upon the short arm of chromosome 7A. Three homologous variants of the factor on 7DS were found but no variation was found for the factor on 7BS.
Variation amongst isozymes of Rhynchosporium secalis
Authors: NEWMAN PAMELA L.
Published: April 2007

Mycelial extracts of 288 single‐spore isolates of Rhynchosporium secalis. derived from infected leaves collected from seven barley cultivars at nine sampling sites, were subjected to horizontal slab polyacrylamide gel electrophoresis. A total of 28 patterns for α‐esterase, four for β‐glucosidase and one for β‐galactosidase were obtained. One probable isozyme polymorphism, for α‐esterase, was identified. There was no correlation between any particular band or pattern and either host cultivar or site.
Evidence of asexual recombination in Rhynchosporium secalis
Authors: NEWMAN PAMELA L. , OWEN H.
Published: April 2007

Three single‐spore isolates of Rhynchosporium secalis that differed in their α‐esterase and β‐glucosidase isozyme patterns were inoculated as two mixtures, each of two isolates, on to seedlings of the susceptible barley cultivar Maris Mink. Approximately 100 single‐spore isolates were taken from mature lesions produced by each mixture. These were subjected to polyacrylamide gel electrophoresis and the gels were stained for α‐esterase and β‐glucosidase. Parental types only were produced by one of the isolate mixtures. However, one of the 10 lesions examined for the second mixture produced nine isolates with a novel combination of isozymes, indicating that some form of asexual recombination had occurred. The use of isozymes as a natural marker system for the detection in vivo of asexual recombination in pathogenic fungi is discussed.
Genotypic influences on the incidence of infection by Ascochyta fabae in winter‐hardy faba beans (Vicia faba)
Authors: LOCKWOOD G. , JELLIS G. J. , AUBURY R. G.
Published: April 2007

Variation in resistance to Ascochyta fabae among winter‐hardy genotypes of faba bean was demonstrated in artificially inoculated field trials. The incidence of seed infection after harvest was strongly correlated with both foliar and pod infection. Joint regression of the incidence of pod infection on flowering date and length of straw accounted for 33–56% of the variance but this largely reflected the behaviour of the entries with a determinate habit which were very susceptible and sensitive to infection by A. fabae. Two indeterminate lines which were similar to each other in flowering date and straw length contrasted greatly in the incidence of foliar and pod infection.
Methods for the production and use of sclerotia of Sclerotium cepivorum in field germination studies
Authors: COLEY‐SMITH J. R.
Published: April 2007

Methods are described for maintaining isolates of Sclerotium cepivorum and for producing large numbers of sclerotia of this organism for field studies. Techniques for testing the viability of sclerotia and for measuring their germination in response to host plants are also described together with other aspects of field studies.
The incidence of Alternaria spp. and Leptosphaeria maculans in commercial brassica seed in the United Kingdom
Authors: HUMPHERSON‐JONES F. M.
Published: April 2007

Tests on samples of oilseed rape seed (Brassica napus) sown in the UK between 1981 and 1984 indicated that on average 25% of samples were infected with Alternaria brassicae and 61% with Leptosphaeria maculans, with maximum incidences of infection of 19 and 4.2% respectively. Much infection by Alternaria spp. occurred on vegetable and forage brassica seed produced in the UK between 1979 and 1983. In B. oleracea types A. brassicicola occurred most frequently, affecting 88% of samples and up to 55% of seeds. A. brassicae was detected in 44% of B. oleracea samples and in up to 13% of seeds. Little Alternaria infection occurred in swede or forage rape samples (B. napus), but A. brassicae affected up to 8–5% of seeds in turnip samples (B. campestris). L. maculans occurred in 44% of samples of vegetable and forage brassica seed produced in the UK, with a maximum of 4–6% infected seeds. A. brassicicola was present in 73% of samples of imported B. oleracea seed, affecting up to 25.5% of seeds. A. brassicae was absent from these samples and little L. maculans was detected. Pathogenicity tests on isolates of L. maculans from infected seeds indicated that virulent pathotypes were present in 16 rape seed samples but in only one sample (swede) of vegetable or forage brassica seed. The high incidence of seed infection by these pathogens emphasizes the importance of applying fungicide treatments to all types of brassica seed.
Botrytis cinerea in stored cabbage: the use of germ‐tube growth on leaf discs as an indicator of potential head rot
Authors: DAVIES R. M. , HEALE L. B.
Published: April 2007

The growth of germ‐tubes of Botrytis cinerea at 24°C on leaf discs of six cabbage cultivars taken from heads prior to storage, was directly related to the proportion of whole heads developing rots caused by Botrytis during storage for 6 months at 1–2°C. Dipping heads in iprodione before cold storage substantially reduced losses, particularly in the most susceptible cultivar (Decema Extra). Both leaf disc assays of germ‐tube growth and studies of whole heads in store indicated significant and similarly ranked differences in cultivar susceptibility.
A comparison of fungicide seed treatments to improve sugar beet seedling establishment
Authors: BYFORD W. J.
Published: April 2007

In a series of field trials from 1977 to 1979, steeping sugar beet seed in thiram gave slightly better plant establishment than the ethyl mercury phosphate (EMP) steep currently applied to all sugar beet seed used in England. Steeping in a phenyl mercury acetate solution gave establishment close enough to EMP steep to show that it could be used as a replacement for EMP if the latter were unavailable for agricultural use. TCMTB steep and maneb slurry were clearly inferior to EMP steep, particularly when the incidence of seed‐borne Phoma betae was high.
Detection of two viruses infecting Narcissus by enzyme‐linked immunosorbent assay
Authors: HILL S. A. , BLUNT SARAH
Published: April 2007

The enzyme‐linked immunosorbent assay (ELISA) proved sufficiently reliable to detect narcissus tip necrosis virus (NTNV) and arabis mosaic virus (AMV) in Narcissus leaf material provided it was of the right age. Similar trends in virus concentration in leaf samples were indicated by ELISA reactions for both viruses, with highest levels at the start of growth, a decrease during flowering, followed by an increase before levels fell as leaves died. Leaf tip samples consistently provided the highest ELISA reactions at all stages and testing was more reliable from outer, older leaves than inner, younger ones. Best samples for ELISA detection of both viruses were from the tips of older leaves early in the growing season.
Methods for visualizing hyaline fungi for the detection of antifungal compounds on thin‐layer chromatograms
Authors: WOODWARD S. , PEARCE R. B.
Published: April 2007

Two methods facilitating the use of hyaline fungi for the detection of antifungal compounds on thin‐layer chromatograms are described. Fungal growth was visualized under ultraviolet light either by the metabolic release of fluorescein from the esterase substrate fluorescein diacetate, or by the binding of a fluorescent brightener (Calcofluor White M2R New, or Tinopal‐CBS) to the mycelium on the TLC plate.

These methods were used to demonstrate compounds inhibitory to the wood‐decay fungus Heterobasidion annosum in bark extracts of Sitka spruce (Picea sitchensis).
Association of a xylem‐limited bacterium with Sumatra disease of cloves in Indonesia
Authors: BENNETT CHRIS P. A. , HUNT PETER , ASMAN ARIFUL
Published: April 2007

Sumatra disease is highly destructive in most clove‐growing areas of Sumatra and in western parts of Java. Symptoms of leaf‐fall and twig die‐back, starting in the upper branches, and often associated with wilting, lead to tree death in 6–18 months. Normally, only seedlings and young trees survive. Symptoms are usually more severe and disease spread is more rapid at higher elevations. Patterns of jump‐spread suggest that the disease agent is carried via an airborne pathway, possibly by insect vectors. Small, Gram‐negative, non‐motile, rod‐shaped bacteria are consistently associated with the disease. Initial attempts to culture the bacteria in vitro did not succeed. The bacteria are confined within xylem vessels and are found throughout diseased trees. Greyish‐brown streaks are present in wood of heavily infected tissues which release a bacterial ooze from cut surfaces; in such tissues many of the vessels are occluded by bacteria embedded in a gelatinous matrix. At the time of first above‐ground symptoms, bacteria are already well established in roots and the trunk base, from where they appear to spread upwards in newly formed wood into the crown of the tree. Symptoms are thought to result from root dysfunction and mechanical blockage of the vascular system. All known clove varieties appear equally susceptible.
The relationship between brown and corky root rot caused by Pyrenochaeta lycopersici and yield loss in tomatoes established by the use of artificially infested soils
Authors: POLLEY R. W.
Published: April 2007

In an experiment conducted in a commercial glasshouse, tomato plants were grown in pots containing soils infested with a range of levels of Pyrenochaeta lycopersici in a randomized block design. There was found to be a negative correlation (r= ‐0.93) between total yield in kg per plant (y) and % disease severity (x) recorded 8 weeks after planting when the disease data were exponentiated; the best fit was obtained by the equation v = 45.7–42.3x0.006 Fruit number was reduced by 0.2% for each 1% increase in the disease, but a stronger correlation was obtained by the equation y (fruit number) = 417–368x 0.006

In a separate trial, the relationship between disease severity 8 weeks after planting and yield loss was shown to be affected by soil type. Early‐season loss of potential yield was found to be lower in sandy soil than in peat and clay. By the end of the season, loss in total potential yield was greater in peat soil than in clay. The effect that soil conditions can have in modifying the relationship between disease severity and yield loss is discussed.
Pelleting of seed with the antagonist Pythium oligandrum for biological control of damping‐off
Authors: LUTCHMEAH R. S. , COOKE R. C.
Published: April 2007

Pythium oligandrum oospores, incorporated in clay carrier, survived a commercial seed‐pelleting process to give protection against damping‐off in sugar beet and cress induced by Pythium ultimum, together with damping‐off in carrot caused by Mycocentrospora acerina.

It is suggested that field scale evaluation of P. oligandrum as a biocontrol of fungally incited seedling diseases is now both feasible and desirable.
In vitro responses of different Armillaria taxa to gallic acid, tannic acid and ethanol
Authors: SHAW CHARLES G.
Published: April 2007

Twenty‐one isolates from four Northern Hemisphere species of Armillaria (A. mellea, A. ostoyae, A. bulbosa. and the unnamed North American Group V) and two Southern Hemisphere species (A. luteobubalina and A. novae‐zelandiae) were grown on media with or without ethanol. gallic acid, or tannic acid. Ethanol increased dry weights for all isolates except one of A. bulbosa and colony diameters for all isolates of the Northern Hemisphere species except one of North American Group V. Ethanol decreased colony diameters for some isolates of the Southern Hemisphere species. Rhizomorph production increased for most isolates of Northern Hemisphere species on medium amended with tannic acid rather than gallic acid and on ethanol‐amended medium with or without gallic acid. Both Southern Hemisphere species formed rhizomorphs in abundance, regardless of the medium. For most isolates colony diameters and dry weights were reduced by gallic acid, with or without ethanol. but were increased by tannic acid, with or without ethanol.

Acid and ethanol effects on colony weights and diameters were not consistent, however, and variation among isolates within each species was great enough for these media to be of little value in distinguishing among the species. Newly defined species of Armillaria have thus retained the attribute of extensive variation in cultural characteristics that is a feature of A. mellea, sensu lato, which necessitates evaluating the responses of several isolates before determining effects of any compound on growth of any species.
Use of fungicides to control chocolate spot (Botrytis fabae) on winter field beans (Vicia faba)
Authors: BAINBRIDGE A. , FITT B. D. L. , CREIGHTON N. F. , CAYLEY G. R.
Published: April 2007

Less chocolate spot (% leaf area affected) developed on winter–sown field beans sprayed with benomyl than on untreated beans or beans sprayed with iprodione, prochloraz or thiabendazole. A single benomyl spray during flowering reduced disease development and increased yield by 20% in 1982 when a severe chocolate spot epidemic developed in untreated plots during flowering. Benomyl sprays at flowering also increased yield in 1980 when there was less disease at flowering than in 1982, but did not increase yield in 1981 when there was little disease at flowering. In 1981 a severe chocolate spot epidemic developed early in the season and less chocolate spot developed on lower leaves of beans grown from seed treated with benomyl plus thiram than on beans grown from untreated seed. Treated plots yielded 70% more than untreated plots, although by early flowering there was no difference in chocolate spot between them. Seed treatment did not increase bean yields in 1982 and 1983, when chocolate spot did not develop early in the season. In the glasshouse, benomyl seed treatment prevented the development of aggressive lesions on lower leaves but thiram did not.
The use of associations of nematode species to aid the detection of small numbers of virus–vector nematodes
Authors: BOAG B. , TOPHAM P. B.
Published: April 2007

Information from a large data bank of the most commonly occurring plant–parasitic nematodes within the British Isles was used to assess the frequency of joint occurrences of pairs of species. Analysis of the results showed that many of the virus–vector species had significant positive relationships with non–vector species, while only a few significant negative relationships were observed. A comprehensive table of joint occurrences enables the likely presence of virus–vector species to be predicted from the presence or absence of another species in a soil sample. This information is particularly valuable when the detection of very small numbers of virus–vector nematodes is required.
The nature of virulence in isolates of Bremia lactucae from South Devon
Authors: CORNFORD C. A. , PITT D.
Published: April 2007

Nine isolates of Bremia lactucae from South Devon showed the presence of virulence factors against all 11 resistance factors available in lettuce, but no insensitivity to metalaxyl. The virulence phenotype of a single–sporangium isolate of the fungus changed from VI, 3, 4 and 7 to 1, 2, 3, 4, 6 and 7 after it was maintained on Lobjoit Green Cos (RO) for 10 months.
Survey of fungi associated with subterranean clover leaves and petioles in Western Australia
Authors: BARBETTI MARTIN J.
Published: April 2007

A wide range of fungi was recorded from leaves and petioles of subterranean clover (Trifolium subterraneum L.), with and without symptoms of disease, in Western Australia. Leptosphaerulina trifolii (Rostrup) Petrak and Phoma medicaginis Malb. & Roum. were the two most frequently isolated fungi. Ascochyta caulicola Lamb., Colletotrichum truncatum (Schw.) Andus & Moore, Curvularia trifolii (Kauffm.) Boedijn., Fusarium avenaceum (FR.) Sacc, Myrothecium verrucaria (Fr.) Sacc, Phoma medicaginis, and Stemphylium globuliferum (Vestergr.) Simmons were new records on subterranean clover foliage in Western Australia. Phoma medicaginis was demonstrated to be pathogenic and this is the first record as a pathogen on subterranean clover foliage in Western Australia, M. verrucaria and F. avenaceum caused leaf spotting or more extensive lesions as a consequence of undetermined phytotoxic products produced on agar plate cultures.
Components of partial resistance to Puccinia striiformis in barley
Authors: OSMAN–GHANI N. , MANNERS J. G.
Published: April 2007

Substantial differences in the rates of mycelial growth and sporulation of different isolates of Puccinia striiformis were observed when seedling and upper leaves of five barley cultivars with susceptible reaction types were inoculated. The highest rate of mycelial growth was usually on cv. Sultan, followed by Proctor, Astrix, Senta and Zephyr in that order, but more spores were produced on Senta and Astrix than on Proctor, Zephyr or seedlings of Sultan. Host‐specific differences between isolates were slight, but some isolates were more aggressive than others, with generally higher mycelial growth and sporulation rates and shorter latent periods. The effect of temperature on sporulation varied little between cultivars or isolates, but there was some evidence of high temperature resistance in Senta and Zephyr. Latent periods were longer on flag leaves than on seedling leaves, and spore production per unit area of leaf infected was lower on the flag leaf of all cultivars except Sultan. Low sporulation rates seemed due to adult plant resistance in Astrix and Senta, and overall resistance, more strongly expressed in adult plants than in seedlings, in Proctor and Zephyr. Sultan exhibited slight seedling resistance, but lacked the adult plant resistance of other cultivars.
Cytology of the host‐pathogen interactions between Lolium perenne and Drechslera dictyoides
Authors: CROMEY M. G. , COLE A. L. J.
Published: April 2007

The interactions between Drechslera dictyoides and Lolium perenne resulting in the development of the net blotch lesion were examined using light and electron microscopy. Following appressorium formation a reorganization of the network of cytoplasmic strands in underlying epidermal cells resulted in the accumulation of cytoplasm and the migration of the nucleus towards the appressorium. Successful penetration was followed by extensive colonization of the invaded epidermal cell. Abortive penetration attempts often resulted in the formation of hyphae within the epidermal cell wall. During lesion development, advancing hyphae came into contact with unmodified host cells which responded with the production of wall appositions. Hyphae were sparsely distributed within the developing lesions and their sparingly branched, predominantly linear pattern of growth resulted in the formation of discrete net lesions. Prior to the commencement of sporulation, the density of hyphae increased and the invasion of moribund cells of the senescent host tissue was observed.
The potential value of British wild Solanum spp. as trap crops for potato cyst–nematodes, Globodera rostochiensis and G. pallida
Authors: WHITEHEAD A. G.
Published: April 2007

Two forms of Solanum nigrum subsp. nigrum, two forms of S. nigrum subsp. schultesii, S. americanum, S. chenopodioides, S. sarrachoides, S. scabrum, S. villosum subsp. villosum and S. villosum subsp. puniceum were grown in pots for over 4 months to measure their effect on numbers of potato cyst–nematodes, Globodera rostochiensis and G. pallida, in the soil. No Solanum tested significantly reduced numbers of G. rostochiensis or G. pallida. Solanum americanum, S. sarrachoides and S. villosum puniceum increased numbers of G. pallida slightly.
Evaluation of soil solarization for control of root diseases of row crops in Victoria
Authors: FORTER I. J. , MERRIMAN P. R.
Published: April 2007

The effect of soil solarization on the viability of plant pathogens and disease was evaluated in Victoria. The treatment was tested in NW and S Victoria with natural soil inoculated with high inoculum levels of Eusarium oxysporum, Plasmodiophora brassicae, Sclerotium cepivorum, Sclerotinia minor, Sclerotinia sclerotiorum, Verticillium dahliae and the nematodes Meloidogyne javanica and Pratylenchus penetrans. Other experiments were established at sites with a previous history of disease.

Solarization of artificially inoculated soils reduced inoculum levels to at least a depth of 10 cm and effectively controlled diseases caused by P. brassicae on broccoli, and S. minor and S. sclerotiorum on lettuce. The treatment reduced inoculum levels but not disease of carnations and watermelons affected by E. oxysporum, tomatoes affected by M. javanica, celery affected by P. penetrans, and onions affected by S. cepivorum. Results were inconclusive for tomatoes affected by V. dahliae.

Experiments in naturally infested soils established that solarization reduced disease and increased yields of Chinese cabbage affected by P. brassicae, celery affected by P. penetrans, lettuce affected by S. minor and watermelon affected by root rot.

Solarization reduced disease of onions affected by S. cepivorum but did not significantly increase yield. At all sites the treatment reduced the number of viable propagules of the pathogens to at least a depth of 10 cm.
Infection of roots of Dieffenbachia maculata by the foliar blight and soft rot pathogen, Erwinia chrysanthemi
Authors: NIEVES–BRUN CARMEN
Published: April 2007

Erwinia chrysanthemi, the organism causing foliage blight, leaf spotting, basal stem rot and root rot of Dieffenbachia maculata, was shown to be capable of infecting via roots. Inoculated plants were sectioned and internal spread of the pathogen determined by ‘sandwich’ plating between two layers of Miller's selective medium. Light microscopy and SEM confirmed that the pathogen was present throughout the plant in the xylem. Resin ducts, previously claimed as being the route for systemic infection, were not found. Initially confined to the xylem, the pathogen spread intercellularly to the neighbouring parenchyma and, after about 8 days, pockets of infection, often surrounded by periderm–like tissues, were seen.
The effect of powdery mildew (Erysiphe graminis f. sp. hordei) and leaf rust (Puccinia hordei) on spring barley in New Zealand. II. Apical development and yield potential
Authors: LIM L. G. , GAUNT R. E.
Published: April 2007

Reduced yields caused by powdery mildew and leaf rust in two seasons were associated with reduced plant growth. Combinations of early, late and full epidemics in one season, and 12 epidemic combinations in the second, were designed to identify crop sensitivity to disease by comparing growth and development with healthy plants. Early epidemics reduced ear number by increasing tiller death, and reduced grain number by effects on spikelet, floret or grain abortion, depending on the type of epidemic. Epidemics later in crop growth increased floret and grain abortion and also reduced grain weight.

There was no compensation by later‐determined components for reduced growth and delayed development at earlier growth stages. Plants infected at early growth stages were more sensitive to late infections, seen as effects on the later‐determined components, than plants which were healthy initially. Interactions occurred between epidemics at different times and are likely to occur between diseases and other constraints.
Control of take‐all of wheat in the field with benzimidazole and triazole fungicides applied at seeding
Authors: BALLINGER D. J. , KOLLMORGEN J. F.
Published: April 2007

Control of take‐all (Gaeumannomyces graminis var. tritici) of wheat, with fungicides applied at seeding, was investigated at three naturally infested field sites. Fungicides were applied with seed either as granules or as pellets at rates ranging from 1‐5 to 140 kg a.i./ha. Treatment with benzimidazole and triazole fungicides resulted in lower disease severity on seminal roots, up to 100% fewer deadheads and more than 200% greater yields.
Influence of rootstock on the susceptibility of sweet cherry scions to bacterial canker, caused by Pseudomonas syringae pvs morsprunorum and syringae
Authors: GARRETT CONSTANCE M. E.
Published: April 2007

In a field trial to determine whether the rootstock influenced the susceptibility of cherry cultivars to bacterial canker three cultivars (Napoleon, Roundel and JI 14039), each grafted on two rootstocks (F 12/1 and Colt), were subjected to natural infectionand to inoculation with three bacterial canker pathogens (Pseudomonas syringae pv. morsprunorum races 1 and 2 and P. syringae pv. syringae). Inoculations were made through leaf scars and through wounds. The high susceptibility of Napoleon and high resistance of JI 14039 were confirmed. Napoleon was more susceptible to inoculation through branches when on F12/1 than when on Colt but the reverse was true for leaf scar inoculations. JI14039 was more susceptible to race 1 inoculated through leaf scars when grown on F12/1 than when on Colt. No rootstock/scion interaction was detected with Roundel.

The complexity of the relationships between the pseudomonad pathogens and their cherry hosts is briefly discussed.
Effects of fungicides on Drechslera spp. and leaf surface filamentous saprophytic fungi on Lolium perenne
Authors: THOMAS M. R. , SHATTOCK R. C.
Published: April 2007

Small plots of Lolium perenne were treated between February and September 1979 with benomyl, triadimefon and chlorothalonil and the incidence and relative abundance of sporulating filamentous fungi measured on distinct lesions and senescent areas of leaves.

Benomyl reduced the levels of most saprophytes but increased the levels of the two Drechslera species present. Triadimefon reduced levels of Drechslera species but allowed an increase in levels of Phoma and Epicoccum and in the number of naturally senescing leaves devoid of obvious filamentous fungal growth. In chlorothalonil‐treated plots, levels of all filamentous fungi except Epicoccum were reduced and, by controlling Drechslera species, the number of healthy leaves increased.
Testing for heterothallism and mating‐type in plant pathogenic fungi
Authors: BARRETT JOHN A.
Published: April 2007

When attempts are made to cross two strains of a heterothallic obligately parasitic fungus, the absence of any evidence of sexual processes can be caused either by mating‐type incompatibility or failure to achieve simultaneous infection by both strains. A simple statistical test is described to discriminate between these alternatives when the number of replicates of each cross is small or not all plants are successfully infected.
Multiplication and spread of pathovars of Xanthomonas campestris in host and non‐host plants
Authors: ROBINSON J. N. , CALLOW J. A.
Published: April 2007

Multiplication and spread of respresentative strains of three pathovars of Xanthomonas campestris were monitored by maceration and plating from inoculated leaves of the host and non‐host plant species Oryza sativa, Poa trivialis, Brassica oleracea and Phleum pratense.

Homologous interactions were characterized by higher multiplication rates and larger population increases than heterologous interactions, except for pv. oryzae which increased as much as pv. poae in leaves of Poa. Spread of heterologous pathovars was limited, but homologous pathovars were distributed throughout host leaves soon after inoculation. Pvs poae and oryzae (from Poaceae) demonstrated considerably greater population increases and higher initial multiplication rates than pv. campestris in leaves of all non‐host Poaceae. Pv. poae spread further into leaves of Oryza and pv. oryzae further into leaves of Poa and Phleum than did pv. campestris. Numbers of pv. poae declined in Brassica as did those of pv. oryzae, which was localized within 2 mm of the point of inoculation.