bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors determining the severity of epidemics of Mycosphaerella graminicola (Septoria tritici) on winter wheat in the UK
Authors: SHAW M. W. , ROYLE D. J.
Published: April 2007

Epidemics of disease caused by Septoria tritici were studied in detail in 11 crops of winter wheat cv. Longbow over 4 years. Serious damage to the uppermost two leaf layers was caused by splash‐borne infection from lower in the crop early in the life of the leaves, followed by one or rarely two cycles of multiplication within a leaf layer. Infection conditions rarely limited damage, even in a dry year; the timing and, to a lesser extent, amount of initial inoculum movement to an upper leaf layer was of greater importance. Timing of initial infection was determined by when rain splash occurred in relation to emergence of a leaf layer. Occurrence of infections soon after a leaf layer started to emerge allowed more time for multiplication of disease within that layer. These infections tended to be more severe because the leaves were closer to inoculum sources within the crop. Slight differences in phenology between locations explain why initially random disease distributions sometimes become aggregated. Early‐sown crops are at greater risk because they mature more slowly, allowing more disease multiplication and better transfer between leaf layers.
Restriction fragment length polymorphism analysis of variation in Fusarium species causing ear blight of cereals
Authors: NICHOLSON P. , JENKINSON P. , REZANOOR H. N. , PARRY D. W.
Published: April 2007

Genetic variation in Fusarium species on wheat was investigated using restriction fragment length polymorphism (RFLP) analysis. Single‐spore lines (76) of Fusarium were recovered from 24 ears of wheat in a field plot exhibiting severe symptoms of Fusarium ear blight and identified using classical taxonomic criteria. Four Fusarium species were present, of which F. avenaceum and F. culmorum were predominant with F. lateritium and F. poae present in two ears and one ear, respectively. RFLP analysis using rDNA (pTA71) or total genomic DNA from an F. culmorum isolate clearly distinguished the four species. Genetic fingerprints of the isolates generated using DNA of bacteriophage M13 (which contains a mini‐satellite repeat sequence) revealed considerable variation within three of the four species (except F. poae). Generally, only a single clone was recovered from each ear and in all but one case only a single species was obtained from each spikelet. However, in several instances it appeared that more than one clone of a species was present within a single spikelet.
Effects of the mycoparasite Verticillium biguttatum on barley stunt disease caused by Rhizoctonia solani anastomosis group 8 in a model system
Authors: MORRIS R. A. C. , COLEY‐SMITH J. R. , WHIPPS J. M.
Published: April 2007

The height of barley stunted by Rhizoctonia solani anastomosis group 8 was significantly increased by up to 72·8% after incubation for 8 days at 20°C in seedling tray tests following application of the mycoparasite Verticillium biguttatum. The pathogen and mycoparasite were applied at the rate of 1% Perlite maizemeal inoculum (w/w potting mixture) resulting in propagule densities of approximately 24·0 and 6·6 × 105 colony‐forming units (cfu) per g potting mixture, respectively. Sieving (2 mm) R. solani inoculum prior to dilution in potting mixture increased the recovery of propagules from 1·2 × 2·1 × 103 cfu per g inoculum compared with recovery when inoculum was sieved after dilution. Applications of a V. biguttatum isolate from the UK (vbl) and a Dutch isolate (M73) reduced stunting to a similar extent but did not stimulate the growth of healthy plants. The height of stunted plants was significantly increased after application of V. biguttatum inoculum after 6 days if inoculated trays were preincubated for 1 day prior to planting but a similar increase was only detected after 7 days if seeds were planted immediately. The number of stunted plants which emerged after 4 days was significantly increased by treatment with V. biguttatum but preincubation had no additional effect. These results suggested that control of R. solani was effected both before and after the initiation of disease.
Banana bunchy top disease in Pakistan
Authors: KHALID S. , SOOMRO M. H.
Published: April 2007

The cause of a banana disease in the province of Sindh, Pakistan, was attributed to banana bunchy top virus. Identification was based on symptomatology, size/morphology of the virus particles (20‐22 nm) detected in diseased tissue, and serology (DAS‐ELISA).
Host specificity testing and assessment of the pathogenicity of the rust, Puccinia abrupta var. partheniicola, as a biological control agent of Parthenium weed (Parthenium hysterophorus)
Authors: PARKER A. , HOLDEN A. N. G. , TOMLEY A. J.
Published: April 2007

Parthenium hysterophorus, a native of Central America, is a problem weed of Australian rangeland, particularly in Queensland. Following field surveys in Mexico, the rust fungus Puccinia abrupta var. partheniicola was selected as a potential biological control agent. One isolate was chosen for further investigation after infection studies with one Kenyan and five Mexican isolates. Assessment of inoculation conditions showed that temperatures of less than 20° C and dew periods of more than 6 hours were required for abundant pustule production. Infection with the rust hastened leaf senescence, significantly decreased the life span and dry weight of Parthenium plants, and reduced flower production 10‐fold. Subsequent host‐range studies against 120 species and varieties, with further screening against a limited number of species conducted under a range of environmental regimes, indicated the rust to be sufficiently host‐specific to be considered for introduction. Additional host‐range tests against sunflowers demonstrated that resistance to P. abrupta var. partheniicola was not modified by prior inoculation with P. helianthi.
Effects of simulated acid rain and root‐knot nematode on tomato
Authors: KHAN M. R. , KHAN M. W.
Published: April 2007

Effects were examined of simulated acid rain and of root‐knot nematode, Meloidogyne incognita race 1, on plant growth, yield, photosynthetic pigments and leaf epidermal characters of tomato (Lycopersicon esculentum cv. Pusa Ruby). Sequential inoculation exposures (pre‐, post‐, and concomitant with nematode inoculation) were carried out in a greenhouse. Intermittent treatments of simulated acid rain at pH 3.2 caused white‐to‐tan irregular lesions on both the upper and lower surfaces of tomato leaves. The foliar symptoms were more pronounced on nematode‐infected plants. Simulated acid rain (pH 3.2) and/or nematode infection suppressed plant growth, yield and pigment synthesis, the effects being greatest in post‐inoculation treatments compared with simulated acid rain at pH 6.8. The total weight of fruits per plant was greatly suppressed owing to simulated acid rain or nematode infection. Chlorophyll a was found to be more sensitive to simulated acid rain or nematode infection than other leaf pigments. Root penetration, galling, egg mass production, and fecundity (number of eggs per egg mass) of M. incognita were enhanced at pH 5.6 and suppressed at pH 3.2 compared with pH 6.8. Nematode infection or simulated acid rain at pH 3.2 suppressed stomata and trichome development (number and size). Simulated acid rain treatments at pH 5.6 had a positive effect on number and size of trichomes, but a negative effect on stomata. The apertures of stomata were wider on tomato leaves exposed to simulated acid rain, especially at pH 3.2, than at pH 6.8.
Dispersal of conidia of Ascochyta fabae f. sp. lentis from infected lentil plants by simulated wind and rain
Authors: PEDERSEN E. A. , MORRALL R. A. A. , McCARTNEY H. A. , FITT B. D. L.
Published: April 2007

Splash was shown to be an effective mechanism for short‐range dispersal of conidia of Ascochyta fabae f. sp. lentis, the cause of ascochyta blight of lentil. The dispersal gradients were well described by the power law model in its linear form, Iny= Ina‐b Inx. In still air the slope of the linearized dispersal gradient, b, ranged from 2.83 to 4.07 and was steeper for 4.9 mm than for 3.9 mm incident drops. Nevertheless, for all drop sizes tested, fewer than 50% of the conidia were splashed more than 15 cm from the source. The pattern of conidium dispersal was similar for both drop sizes when horizontal windspeeds were 2.5 or 5 m/s. Wind significantly decreased the value of b (range 2.35‐2.43 at 2.5 m/s, 1.71–1.91 at 5 m/s) and increased by about 2 m the maximum distance that conidia in ballistic droplets were deposited. In addition, the experiments suggested two other potentially important mechanisms for dispersal of the pathogen over longer distances, namely conidia in small air‐borne droplets and windblown leaflets.
Estimation of the number of loci involved in the inheritance of resistance to Phytophthora palmivora (Butl.) Butl. in the leaves of Theobroma cacao L.
Authors: WARREN J. M. , PETTITT T. R.
Published: April 2007

Comparisons of theoretical and observed distributions indicated that resistance to necrosis caused by Phytophthora palmivora within leaf tissues of Theobroma cacao clone ICSl was influenced by a minimum of five unlinked heterozygous loci. The frequency of infection at the leaf surface was not linked to necrotic spread and did not adequately fit the expected progeny distributions. It is argued that this lack of fit was possibly the result of gene effects of differing magnitude influencing the observed variation in leaf surface infection rate, although other factors such as epistasis may be important.
Detection of grapevine leafroll‐associated closterovirus III by molecular hybridization
Authors: SALDARELLI P. , MINAFRA A. , MARTELLI G. P. , WALTER B.
Published: April 2007

Highly purified double‐stranded (ds) RNA was obtained from cortical scrapings of mature canes of vines infected by grapevine leafroll‐associated closterovirus III (GLRaV III) using phenol‐chloroform extraction, chromatography on CF‐11 cellulose minicolumns and enzymatic digestion. Complementary (c) DNA fragments of various lengths, obtained by random priming denatured dsRNA templates, were cloned into the plasmid pUC‐18 at the Smal site in Escherichia coli strain DH5α. Two 32P‐labelled cDNA clones denoted p16ds (c. 1100 bp) and p23ds (c. 1500 bp) were successfully used as probes for detecting GLRaV III sequences in grapevine extracts from leaves and petioles, or cortical tissues. Probe p23ds was virus‐specific and did not hybridize with total RNA from healthy controls, or from vines infected by grapevine leafroll‐associated closterovirus I (GLRaV I), or with genomic RNA from purified grapevine closterovirus A (GVA) and B (GVB). A riboprobe (pGEM23ds) transcribed from p23ds in transcription vector pGEM3zf specifically recognized GLRaV III sequences, but not GLRaV I or GVA sequences, in extracts from differently infected vines. Moreover, in Northern blots, the same probe hybridized also with smaller dsRNA components, which may be replicative forms of subgenomic RNAs.
Host specialization of Verticillium dahliae, with emphasis on isolates from cocoa (Theobroma cacao)
Authors: RESENDE M. L. V. , FLOOD J. , COOPER R. M.
Published: April 2007

Isolates of Verticillium dahliae from cocoa (four Brazilian and one Ugandan) were screened against cocoa, aubergine, tomato, cotton, and pepper. Isolates originating from hosts other than cocoa were also inoculated. In general, all inoculated crops were systemically invaded by isolates from cocoa. Isolates from each host tended to be more aggressive on their original host. All isolates from cocoa were pathogenic to cocoa, but exhibited various degrees of aggressiveness to other crops. They induced severe symptoms on aubergine, but few symptoms on tomato, although colonization occurred up to the stem apex in both cases. Likewise, symptomless invasion of pepper was found with some Brazilian isolates. The Ugandan isolate was significantly more aggressive on cotton and pepper than the Brazilian isolates.

A Brazilian isolate from cocoa from the State of Bahia was also used to inoculate 12 common weed species from the same geographical area. Four species showed wilt symptoms, while V. dahliae was readily recovered from the stems of a further four species. The role of alternative hosts on disease spread in cocoa growing areas is discussed.
Relationships between temperature and latent periods of rust and leaf‐spot diseases of groundnut
Authors: WADIA K. D. R. , BUTLER D. R.
Published: April 2007

The effect of temperature on the latent periods of rust, late leaf spot and early leaf spot diseases of groundnut caused by Puccinia arachidis, Phaeoisariopsis personata and Cercospora arachidicola, respectively, was studied. The latent periods (LP) of rust, late leaf spot and early leaf spot ranged from 12–49 days, 13–38 days and 13–39 days, respectively, between 12°C and 33°C An equation relating the rate of pathogen development (1/LP) to temperature was fitted using daily mean temperatures to provide three cardinal temperatures: the minimum (Tmln), optimum (Topl), and maximum (Tmax), Tmln was about 12°C for rust and about 10°C for the two leaf‐spot diseases. Topt, for all three diseases was close to 25°C. Tmax was 31°C for early leaf spot, and extrapolated values for late leaf spot and rust were about 35 and 40°C, respectively.

For P. personata, a temperature response curve was fitted using data only from controlled environment experiments. This curve was used to simulate latent periods from both mean daily and mean hourly temperatures in the field. There was substantially better agreement between observed and simulated latent period with hourly temperatures, provided the developmental rate of the pathogen was determined at a constant temperature.
Biological characterisation of various geographical isolates of potato virus Y inducing superficial necrosis on potato tubers
Authors: ROMANCER M. Le , KERLAN C. , NEDELLEC† M.
Published: April 2007

A range of selected PVY isolates that induce superficial necrosis on potato tubers, originating from several countries, were compared with standard strains of PVA, PVV and PVY. Biological properties (e.g., host range, aphid transmissibility and relationships based on cross‐protection between virus isolates) were studied. PVYNN isolates differ from the normal PVYC, PVYN and PVO strains by their ability to infect Capsicum annuum but not Chenopodium amaranticolor and C. quinoa. All PVYNN isolates are transmissible by Myzus persicae, without any significant differences from one standard strain. These additional data confirm that these tuber‐necrosing isolates belong to PVY. However, they could be ranged in a homogeneous and distinct group inside the PVYN group, based on the differences revealed in the host range, in addition to the specific ability naturally to induce necrosis on tubers.
Interactions among maize streak virus disease, leafhopper vector populations and maize cultivars in forest and savanna zones of Nigeria
Authors: ASANZI C. M. , BOSQUE‐PEREZ N. A. , BUDDENHAGEN I. W. , GORDON D. T. , NAULT L. R.
Published: April 2007

Monthly plantings of three maize cultivars with differing resistance/susceptibility to maize streak geminivirus (MSV) and samplings of Cicadulina leafhopper vectors were made from December 1988 to April 1990 in the humid forest and from May to November 1989 in the Guinea savanna zones of Nigeria. High MSV disease incidences (43–56%) were recorded on susceptible cultivar TZB‐Gusau in late‐season (July‐October) plantings. Hybrid 8321‐21 showed significantly lower MSV disease incidence and severity than the other two cultivars, TZB‐Gusau and 8329‐15. Cicadulina species population peaks (5.2‐13.5 leafhoppers/m2) were observed before the rains ended in savanna locations and after the end of the rains in the forest zone. Cicadulina mbila was the predominant species, whereas C. storeyi (syn. C. triangula), C. arachidis, C. similis and C. ghaurii were less common. The proportion of viruliferous leafhoppers increased as the season progressed, reaching maxima of 15–25% at the end of the growing season. Interactions between disease incidence, Cicadulina populations, maize cultivars and rainfall are discussed.
Interactions between Erysiphe graminis and Septoria nodorum on wheat
Authors: WEBER G. E. , GÜLEC S. , KRANZ J.
Published: April 2007

Interactions between Erysiphe graminis f.sp. tritici and Septoria nodorum on wheat were studied in the greenhouse and in a 2‐year field experiment using artificial inoculation. The integrated form of the logistic growth model dy/dt = ry (1 ‐y/K), with infection rate r and final accumulated disease K, was fitted to the disease progress data. Septoria nodorum substantially reduced the disease severities of E. graminis, and caused significant reductions of at least 60% in final accumulated disease K of E. graminis. In the field trials, E. graminis increased the final accumulated disease K of S. nodorum. Owing to the extremely low severity of E. graminis, the increase of S. nodorum severity was small, and significance was given in one of the two years only, with an increase in K of roughly 30%. In the pot experiment, final accumulated disease K of S. nodorum remained unchanged, but there was a significant 30% increase in the infection rate r of S. nodorum. The difference between field and pot trials was explained by the climatic conditions in the greenhouse which excluded secondary infections of 5. nodorum, and which are important factors for disease progress in the field.
Effect of root‐knot nematodes on cajanol accumulation in the vascular tissues of pigeonpea after stem inoculation with Fusarium udum
Authors: MARLEY P. S. , HILLOCKS R. J.
Published: April 2007

The effect of root‐knot nematodes (Meloidogyne javanica and M. incognita) on production of the isoflavonoid phytolexin, cajanol, was investigated in pigeonpea (Cajanus cajan) plants infected with Fusarium udum, the causal organism of Fusarium wilt. Seven‐day‐old seedlings of a wilt‐resistant pigeonpea cultivar, ICP 9145 and a wilt‐susceptible cultivar, Malawi Local, both of which were moderately susceptible to the nematode, were grown in soil infested with 2000 Meloidogyne juyeniles per plant. A duplicate set of plants remained free from nematodes. Twenty‐one days later, all the plants were inoculated with F. udum by stem puncture. Quantitative estimates of cajanol in the vascular tissues were made at intervals up to 15 days after inoculation with the fungus. No external symptoms of wilt appeared in any plants of the wilt‐resistant cultivar in the absence of the nematode. However, when inoculated with the nematode, two thirds of the plants developed wilt symptoms. Cajanol levels were lower in both the wilt‐resistant and wilt‐susceptible plants in the presence of the nematode than in its absence, although this effect was considerably more marked in the wilt‐resistant cultivar. These results indicate that the root‐knot nematode is capable of breaking resistance of ICP 9145 to Fusarium wilt and that at least part of the mechanism of this effect is retarded cajanol accumulation.
Occurrence of powdery mildew on aubergine in West Sussex
Authors: WHIPPS J. M. , HELYER N. L.
Published: April 2007

A powdery mildew (Erysiphe sp.) was found on the upper surfaces of leaves of a glasshouse‐grown aubergine (Solanum melongena) crop in West Sussex during Autumn 1992. It could be readily transferred to tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum), but produced restricted growth and sporulation on cucumber (Cucumis sativus). Sweet pepper (Capsicum annuum), Chinese cabbage (Brassica campestris var. chinensis), lettuce (Lactuca sativa), chrysanthemum (Dendranthema x grandiflorum) and Nicotiana benthamiana did not show symptoms. When transferred to tomato and cucumber, the morphology of aubergine powdery mildew resembled the natural glasshouse powdery mildew on the two crops, respectively, rather than powdery mildew on aubergine. Powdery mildew from naturally infected tomato could infect aubergine directly, and also after one, but not two, generations on cucumber.
Selection of pathotypes of Erysiphe graminis f.sp. hordei in pure and mixed stands of spring barley
Authors: HUANG R. , KRANZ J. , WELZ H. G.
Published: April 2007

Pathotypes of Erysiphe graminis f.sp. hordei were monitored at fortnightly intervals in pure and mixed stands of spring barley during the course of mildew epidemics in two field trials. Mixtures were composed of cultivars with Arabische (gene Mla12), Laevigatum (Ml(La)), and Monte Cristo (Mla9) resistance, respectively. The three‐way mixtures were either random or, in 1989, laid out as one‐row mixtures (i.e., regularly alternating rows of different genotypes) or three‐row mixtures (i.e., regularly alternating three‐row strips of different genotypes), respectively. In 1990 only random mixtures and six‐row mixtures were compared with pure stands. The virulence complexity (i.e., the average number of virulence factors per isolate with reference to Mla12, Ml(La), and Mla9) was always maximal in the random mixtures. In 1989, linear regression of complexity on mildew generations gave significant b‐values (slopes) of 0·049, 0·031, and 0·025 in the random mixture, one‐row mixture, and three‐row mixture, respectively; the b‐value from pure stands was not significant. In 1990, another sampling technique allowed selection to be observed on each genotype in the mixtures separately. In the random mixture b‐values were 0·048, 0·064 and 0·017 (not significant) on Mla12, Ml(La), and Mla9 cultivars respectively. In six‐row mixtures and in pure stands, there was no significant increase in complexity (b > 0) on any of the mixture components. Although the frequency and relative fitness of complex pathotypes were higher in all types of mixtures than in pure stands, selection towards complex races was much less intense in row mixtures than in random mixtures in both field trials.
Assessment of Andean bean diseases using visual keys
Authors: STONEHOUSE J.
Published: April 2007

Pictorial keys are given for the visual assessment of damage to bean (Phaseolus vulgaris) leaves of diseases found in the Colombian Andes. There are keys for anthracnose, rust, ascochyta blight, web blight and angular leaf spot, and also for necrotic tissue and damage to leaves by adult chrysomelid beetles. Unusual features of the keys are discussed. Their evaluation by a group of untrained assessors demonstrated that the average deviation from the correct values was ‐0.171 of one unit on a scale of 0 to 9. Statistically significant differences existed between assessors, and there were interactions with other variables. These findings suggest that care should be taken to minimize the effects of likely differences among assessors, and the implications of this are discussed.
Partial characterization of reovirus‐like particles associated with garlic dwarf disease
Authors: LOT H. , DELECOLLE B. , BOCCARDO G. , MARZACHI C. , MILNE R. G.
Published: April 2007

A dwarfing disease of garlic (Allium sativum) has recently been noted in southern France. Affected plants were stunted and had thickened leaves that sometimes developed vein swellings or enations and a darker green colour; leaves often had purple tips and an abnormal phyllotaxy. The root system was poor and the bulb spongy, containing few normal cloves. A previously undescribed virus, here named garlic dwarf virus (GDV), was associated with the syndrome and has been partially purified. The particle morphology, electrophoretic pattern of dsRNA segments and cytopathology were similar to those of Fijiviruses (Reoviridae). Limited serological and nucleic acid hybridization tests did not, however, reveal any relationship with members of the Reoviridae. Apart from one preliminary Australian report of a reo‐like virus in lilies from Japan, this is the first description of a reo‐like virus affecting a monocotyledonous host outside the Gramineae.
Biological control of peach twig blight (Monilinia laxa) with Epicoccum nigrum
Authors: MADRIGAL C. , PASCUAL S. , MELGAREJO P.
Published: April 2007

Various preparations of spores and mycelium of the antagonist Epicoccum nigrum, alone or in combination with Captan, were applied in four different field trials to peach trees inoculated with Monilinia laxa, the cause of twig blight. Biocontrol obtained after application of E. nigrum was variable each year, depending on the releative disease severity in the first 2–3 weeks after infection and the climatic conditions. In three out of four trials, treatments with E. nigrum were comparable with Captan in reducing disease severity and combinations of E. nigrum and Captan gave a level of disease suppression similar to that given by the antagonist or chemical alone. In the remaining trial, combinations of E. nigrum and Captan were necessary to obtain successful disease suppression.
Biocontrol of post‐harvest fungal diseases on Dutch white cabbage by Pseudomonas and Serratia antagonists in storage trials
Authors: STANLEY R. , BROWN M. , POOLE N. , ROGERSON M. , SIGEE D. C. , KNIGHT C. , IVIN C. C. , EPTON H. A. S. , LEIFERT C.
Published: April 2007

Post‐harvest rotting of Dutch white cabbage was reduced by post‐harvest treatment with Pseudomonas fluorescens strains CL42, CL66, CL82, Serratia plymuthica strain CL43 or Serratia liquefaciens CL80, in three storage trials carried out in an experimental cold store at Manchester University, Manchester, UK and in a commercial cold store at L.W. van Geest Farms Ltd, Spalding, UK. The amount of surface area covered by fungal growth was assessed at 6‐week intervals during storage and the trimming losses were determined after 8 to 10 months. Only strains CL80 and CL82 were found to reduce fungal spoilage significantly in all three trials, and control by strain CL82 was similar to that achieved by post‐harvest treatment with fungicides. In the commercial cold store, CL42 showed better results than any of the other bacterial strains.
Distribution of Pseudomonas solanacearum in the stem tissues of tomato plants with different levels of resistance to bacterial wilt
Authors: GRIMAULT V. , ANAIS G. , PRIOR P.
Published: April 2007

Ten tomato cultivars, from the USA, Taiwan and French Antilles, were compared for resistance to bacterial wilt as measured by disease and pathogen population invasiveness and density in the stem at the collar and midstem regions. On the basis of disease incidence, cultivars ranked from highly susceptible to totally resistant. By contrast, no significant difference was observed in bacterial population in wilting plants, regardless of the cultivar. All symptomless plants were latently infected at the collar level. Percentage of symptomless plants with bacteria at the midstem level was significantly correlated with the degree of resistance; the more resistant, the lower the stem colonization. Restriction of Pseudomonas solanacearum invasiveness in the vascular tissues of the stem is associated with resistance properties in tomato. This observation may be useful in developing improved criteria for selecting stable resistance to the disease.
The effect of using a Horsfall‐Barratt scale on precision and accuracy of visual estimation of potato late blight severity in the field
Authors: FORBES G. A. , KORVA J. T.
Published: April 2007

Assessments of potato late blight severity by eleven people using directly estimated percentage severity (EPS) of potato late blight caused by Phytophthora infestans were compared with the assessments of another group of ten people using a Horsfall‐Barratt scale with wider intervals in the mid range of severity (25‐75% infection). This scale is frequently used at the International Potato Center (CIP) to select for resistant germplasm. EPS readings had greater variability among assessors at mid range of severity than at extremes, as predicted by Horsfall and Barratt (1945). Transformation of EPS to CIP scale units or logits corrected uneven variances. Direct utilization of the CIP scale in the field, however, did not correct uneven variances. This may have been due in part to subconscious linearization of scale intervals, which are based on logarithms. Direct comparisons made by converting EPS to CIP scale levels demonstrated that precision and accuracy were greater among assessors using EPS.
A rapid test to evaluate in vitro sensitivity of Septoria tritici to flutriafol, using a microtitre plate reader
Authors: PIJLS C. F. N. , SHAW M. W. , PARKER A.
Published: April 2007

The sensitivity of Septoria tritici to the sterol biosynthesis inhibiting fungicide flutriafol was assessed using a quick and objective technique based on light absorbance to measure fungal growth. Microtitre plates were inoculated with suspensions of pycnidiospores taken directly from single pycnidia on leaves, after which glucose peptone broth containing different fungicide concentrations was added. After 10 days’ incubation in the dark at 17°C, growth was measured using a spectrophotometer at 405 nm. A dose‐response curve fitted to the absorbance data was used to estimate the fungicide concentration reducing absorbance by one half (EC50). The method was precise, quick, reproducible and objective, with substantial advantages over conventional techniques.
Giant calyx: a disease of eggplant (Solanum melongena) associated with a mycoplasma‐like organism in Brazil
Authors: BOITEUX L. S. , LIMA M. ISABEL , KITAJIMA E. W.
Published: April 2007

A disease of eggplant (Solanum melongena) associated with a mycoplasma‐like organism (MLO) was found in the Federal District, Brazil. Symptoms were characterized by teratological changes in the flowering structure, reduction and malformation of leaves, proliferation of lateral buds, and an overall plant stunting. Evidence for the association between MLO infection and disease symptoms was obtained through graft‐transmission experiments and electron microscopy. This is the first record of an eggplant disease associated with MLOs in Brazil.
The incidence and distribution of races of Verticillium dahliae in Crete
Authors: LIGOXIGAKIS E. K. , VAKALOUNAKIS D. J.
Published: April 2007

In a survey of verticillium wilt of cultivated and weed hosts in Crete in 1988–89, Verticillium dahliae was the only species isolated. The pathogen was found in 84 out of 231 vegetable crops, and six out of 14 olive orchards. It was also found in two locations on the weed Solanum nigrum. Hosts belonged to 12 plant species in six different botanical families. Natural infection of Vicia faba by V. dahliae is reported for the first time. The physiological races of 92 isolates of V. dahliae were identified using two differential tomato cultivars. Of these isolates, 89 were race 1, one was race 2, and the remaining two were non‐pathogenic. Virulence of the various isolates to tomato varied from slightly to highly pathogenic and was independent of the hosts from which they originated.
A potyvirus isolated from Senna occidentalis
Authors: WALKEY D. G. A. , SPENCE N. J. , CLAY C. M. , MILLER A.
Published: April 2007

A potyvirus causing severe mosaic symptoms was isolated from Senna occidentalis (syn. Cassia occidentalis) in the Yemen Republic and Ethiopia. It was transmitted mechanically and by Myzus persicae in a non‐persistent manner. The flexuous, rod‐shaped particles had a mean length of 830 nm, and pinwheels and scrolls were observed by electron microscopy of thin sections of infected Nicotiana clevelandii leaves. Its host range was narrow with only a few legume species, Nicotiana clevelandii and N. benthamiana susceptible to experimental infection. This virus was purified from N. clevelandii and the coat protein had a molecular mass of 34‐5 kDa. It reacted positively in ELISA with monoclonal antibody 197 that is specific for potyviruses, but was not decorated by antibodies to any other potyvirus tested when examined by electron microscopy. The virus has been tentatively named cassia severe mosaic potyvirus.
Infection efficiency of Phaeoisariopsis personata and the influence of different wetness patterns on germ‐tube growth of the pathogen
Authors: WADIA K. D. R. , BUTLER D. R.
Published: April 2007

Controlled environment studies with Phaeoisariopsis personata, the causal agent of late leaf spot disease of groundnut (Arachis hypogaea), have shown that infection is enhanced if leaves are exposed to alternate wet and dry periods (intermittent wetness) compared with continuous wetness. Detailed investigations to elucidate this phenomenon revealed more germ tubes per conidium and more branching of germ tubes with intermittent wetness than with continuous wetness. With intermittent wetness there was clear evidence of tropic growth of germ tubes and branches towards stomata and subsequent penetration. With continuous wetness, germ tube growth did not appear to be directional and germ tubes commonly passed over the stomatal guard cells, therefore leading to relatively few stomatal penetrations. For both wetness regimes, stomatal penetrations continued to increase with increased leaf wetness for at least 6 days after inoculation and there was a linear relationship between the number of stomatal penetrations and the number of resultant lesions. Infection efficiency was markedly increased when the spore load was reduced to 0.1 conidia per cm2 (about one spore per leaflet).
Species spectrum, host range and distribution of powdery mildews on Cucurbitaceae in Crete
Authors: VAKALOUNAKIS D. J. , KLIRONOMOU E. , PAPADAKIS A.
Published: April 2007

Examination of mycelial and conidial features of 436 samples of cucurbit powdery mildews in Crete during 1991‐92 revealed the presence of three species: Erysiphe sp., Sphaerotheca fusca and Leveillula taurica. S. fusca predominated both in the field and in the greenhouse. Characteristics of the three pathogens are compared.
Maintenance of mycoplasma‐like organisms occurring in Pyrus species by micropropagation and their elimination by tetracycline therapy
Authors: DA VIES D. L. , CLARK M. F.
Published: April 2007

Pear explants (Pyrus communis cv. Pine) infected with mycoplasma‐like organisms (MLOs) were maintained for more than 3 years by micropropagation on Murashige and Skoog medium supplemented with gibberellic acid, indole butyric acid and benzyl amino purine. MLOs reached consistently higher concentrations in micropropagated explants than in samples from field‐grown plants, although explants remained free from symptoms. MLOs could be eliminated by incorporation of 100/μg/ml oxytetracycline into the growth medium for a period of 4 weeks. These results have implications for plant propagation schemes of symptomless MLO‐infected explants raised by micropropagation.
Development of a polyclonal antibody‐based immunoassay for the early detection of Sclerotinia sclerotiorum in rapeseed petals
Authors: JAMAUX I. , SPIRE D.
Published: April 2007

A serological test has been developed that allows the early detection of infection of young petals by Sclerotinia sclerotiorum, an important pathogen of rapeseed. Two steps were required to obtain an antiserum sufficiently specific for S. sclerotiorum. Soluble mycelial extracts of S. sclerotiorum were used to produce the first generation polyclonal antiserum. This was not specific for S. sclerotiorum in double antibody sandwich enzyme‐linked immunosorbent assay (DAS‐ELISA) and allowed the screening of cross‐reacting fungal species such as Botrytis cinerea, a pathogen commonly present on rapeseed petals. Using a polyclonal anti‐B. cinerea serum enabled the absorption, by serial cycles, of S. sclerotiorum antigens common to B. cinerea. Residual antigens were then used as immunogens for the production of two second generation antisera (S1 and S2) which were then tested by DAS‐ELISA. Cross‐reactions with B. cinerea decreased with purification cycles of the immunogen whereas Cross‐reactions with some unrelated fungi slightly increased. S. sclerotiorum and B. cinerea were distinguishable using antiserum S2.
The effect of fungicides on fungal antagonists of onion white rot and selection of dicarboximide‐resistant biotypes
Authors: KAY S. J. , STEWART A.
Published: April 2007

The sensitivity of four fungal antagonists (Chaetomium globosum, Trichoderma harzianum, T. viride, Trichoderma sp.) to six fungicides was evaluated. The fungi were insensitive to captan, mancozeb and thiram but were sensitive to benomyl (EC50 < 0 3/μg/ml) and the two dicarboximides iprodione and procymidone (EC50 < 3 3/μg/ml). Conidia and mycelia of the four fungi were exposed to a series of ultraviolet irradiations in order to select biotypes resistant to benomyl and iprodione. Resistance to benomyl was not induced but a number of biotypes of each fungus were isolated from irradiated cultures that showed resistance to iprodione (EC50 values of up to 56·4, 177·8, 171·5 and 216·4/μg/ml for Chaetomium globosum, Trichoderma harzianum, T. viride and Trichoderma sp., respectively). With three exceptions, all selected biotypes retained their fungicide‐resistance after being extensively cultured on fungicide‐free medium. In general, growth of the fungicide resistant biotypes on MEA plates and in MYE liquid medium was equal to that of the corresponding wild‐type strains. One resistant biotype of Trichoderma sp. (C62UV3) grew significantly (P < 0·05) better both on solid and in liquid medium. This resistant biotype was also observed to have greatly enhanced conidial production on agar plates. All fungicide resistant‐biotypes retained the ability to antagonize the pathogen Sclerotium cepivorum in dual culture and, in two instances (A53UV1, A53UV5), exhibited greater antagonism as evidenced by the production of larger inhibition zones. Similarly, with two exceptions, the resistant biotypes retained the ability to control onion white rot disease caused by S. cepivorum in the glasshouse. In particular, two fungicide‐resistant biotypes (Trichoderma sp. C62UV3 and Chaetomium globosum A53UV1) reduced white rot of onion more effectively than did their respective wild‐type parents.
Immunodetection of elicitins from Phytophthora spp. using monoclonal antibodies
Authors: DEVERGNE J. C. , FORT M. A. , BONNET P. , RICCI P. , VERGNET C. , DELAUNAY T. , GROSCLAUDE J.
Published: April 2007

Ten monoclonal antibodies were selected from mice immunized with a highly purified elicitin secreted by Phytophthora cryptogea, termed cryptogein. These antibodies could be classified into five groups according to their cross‐reactivity to heterologous elicitins from other Phytophthora species, from strict specificity (reacting solely with cryptogein) to broad reactivity (reacting with all four elicitins under study). When examined on BIA core (a real‐time biospecific interaction analyser), these monoclonal antibodies were found to recognize at least three different epitopes on the cryptogein molecule. Their use in elicitin detection and quantification was optimized in several ELISA protocols. A mixed monoclonal‐polyclonal antibody, indirect DAS‐ELISA procedure detected as little as 20 pg of purified elicitin per well (100 μl). The four elicitins could be detected with the aid of one of couple of polyvalent reagents, whilst each one could be detected separately using appropriate monoclonal antibodies. These protocols have been used to detect elicitins secreted by Phytophthora spp. into culture medium as well as in planta following plant inoculation.
Number of Heterobasidion annosum vegetative compatibility groups in roots of basidiospore‐infected stumps
Authors: MORRISON D. J. , MACASKILL G. A. , GREGORY S. C. , REDFERN D. B.
Published: April 2007

Heterobasidion annosum was isolated from colonized parts of Sitka spruce stumps in Dundeugh Forest, Scotland and amabilis fir stumps in River Jordan, Vancouver Island, British Columbia. Isolates from each stump were paired in all combinations on malt extract agar and their interactions were scored according to established criteria. As many as ten vegetative compatibility (VC) groups were detected among isolates from the roots of a single stump. In four stumps that were intensively studied, about one‐half of the VC groups in the roots were not detected in the upper part of the stump. Transfer of VC groups of H. annosum from stump roots to tree roots was observed.
Double‐stranded RNA comprising the putative avocado virus 1 has a high degree of sequence homology to the avocado genome
Authors: COOK G. , KOTZÉ J. M. , NEL L. H.
Published: April 2007

The hypothesis that the double‐stranded (ds) RNA isolated from avocado is indicative of infection by RNA plant viruses has never been proven. However, it has not been disproven and the different dsRNAs are still known as putative avocado viruses (AV) 1, 2 and 3. We have probed restriction fragments of avocado cellular DNA with cloned 32P‐labelled AV1‐specific cDNA and discovered that the dsRNA nucleotide sequences are also present on plant DNA. Our evidence contradicts the hypothesis that viruses are responsible for the formation of the dsRNA species in avocado.
Effect of wheat cultivar mixtures on populations of Puccinia striiformis races*
Authors: DILEONE J. A. , MUNDT C. C.
Published: April 2007

This study quantifies the frequency of simple and complex races (races that can infect two or more components) of Puccinia striiformis in mixtures of wheat cultivars possessing different race‐specific resistance genes. Treatments were designed so that the complex race changed depending on the host mixture, thus enabling us to observe the influence of pathogen complexity in different genetic backgrounds. Six cultivar mixtures and one pure stand of winter wheat were inoculated with three races of P. striiformis at two locations for two seasons. Potted plants of three winter wheat cultivars, each susceptible to one of the three races of the pathogen, were used to sample the pathogen during the field epidemics. Disease incidence on the differential cultivars was used to calculate the proportion of the three races in each treatment. The specific cultivars included in the mixtures influenced the frequencies of the three races. Increasing the number of virulent races in a mixture reduced the frequency of the complex race relative to the other two races. The results suggest that genetic background of the pathogen race, host composition, and interaction among pathogen races may be as important as cost of virulence in determining race frequencies in mixtures.
Control ofPhytophthoraroot rot of irrigated subterranean clover with potassium phosphonate in Victoria, Australia
Authors: GREENHALGH F. C. , de BOER R. F. , MERRIMAN P. R. , HEPWORTH G. , KEANE P. J.
Published: April 2007

Phosphonic acid was more effective in inhibiting the production of sporangia ofPhytophthora clandestinain sterile pond water (ED50= 1·4 p.p.m.) than it was in inhibiting the growth of mycelium of the fungus on either corn meal agar (ED50= 13·8p.p.m.) or lima bean agar (ED50= 236 p.p.m.). Experiments under controlled environmental conditions showed that better control of tap root rot of subterranean clover caused byP. clandestinawas achieved by application of potassium phosphonate to a pasteurized soil mixture than by a spray on the foliage alone. However, in a soil from a pasture, foliar sprays were more effective than soil treatments. Application of superphosphate at a rate of 250 kg/ha or higher to the soil reduced the effectiveness of sprays. In three experiments in irrigated pastures a spray of potassium phosphonate at 300 or 313 ml/ha, applied to cotyledons of subterranean clover and to soil, reduced severity ofPhytophthoraroot rot and increased the annual production of dry matter of the legume by 1·96 to 5·11 t/ha in comparison with untreated controls.
Clasterosporium flexum(T. Matsush.) comb. nov. on dying cuttings ofChamaecyparis lawsonianain UK
Authors: SUTTON B. C. , COOK R. T. A. , SANSFORD C. E.
Published: April 2007

A dematiaceous fungus forming a network of hyphopodiate hyphae over foliage ofChamaecyparis lawsonianacuttings dying under mist propagation has been identified asClasterosporium flexum(T. Matsush.) comb. nov. The concept of the genusClasterosporiumin relation to the generaSporidesmiumandCeratophorumis discussed.
Prevalence and pathogenicity of spinach root pathogens of the genus Pythium in Sweden
Authors: LARSSON M.
Published: April 2007

Several pathogenic Pythium spp. were isolated from spinach roots in a 4‐year disease survey in commercial spinach fields in southern Sweden. Heterothallic and zoospore‐producing isolates belonging to the filamentous, non‐inflated zoosporangia (F) group of van der Plaats‐Niterink were most abundant, followed by P. sylvaticum, P. ultimum var. ultimum and P. heterothallicum. The heterothallic hyphal swelling (HS) group and P. tracheiphilum were found in a few plants. Two types of pathogenicity tests were performed, to measure the effects of seedling infection and of root infection of older plants. These tests showed P. ultimum var. ultimum to be the most severe spinach pathogen inducing pre‐ and post‐emergence damping off as well as root rot of older plants. Also P. heterothallicum and P. tracheiphilum damaged both seedlings and older plants, Pythium sylvaticum, Pythium‘group HS’ and Pythium‘group F’were pathogenic only to seedlings, P. ultimum var. ultimum and Pythium group F were isolated in significantly higher frequencies from spinach grown in the autumn season than in the spring. No clear relationships were found between Pythium prevalence and disease severity index of surveyed field plants, between Pythium prevalence and plant developmental stage, or between prevalence of Pythium and other pathogens isolated. This is the first report of P. heterothallicum and P. sylvaticum being pathogenic on spinach.
Effects of inoculation of barley inflorescences with Drechslera teres upon the location of seed‐borne inoculum and its transmission to seedlings as modified by temperature and soil moisture
Authors: YOUCEF‐BENKADA M. , BENDAHMANE B. S. , SY A. A. , BARRAULT G. , ALBERTINI L.
Published: April 2007

An investigation of the location of Drechslera teres on barley (cv. Thibaut) seeds showed that, when artificial contamination was carried out at the time of flowering, all parts of the caryopsis. including the embryo, were infected by the two forms (f. teres and f. maculata) of the pathogen. An assessment was made of the possible role of abiotic factors, including the effects of temperature and soil moisture, on the expression of the primary symptoms caused by the two forms of the pathogen. The most severe damage was observed in dry soils (pF 3‐4) at temperatures off. 12°C. On young barley seedlings, the seed‐borne inoculum caused coleoptile symptoms in the case of the form maculata, whereas the form teres induced mostly foliar symptoms. Foliar necroses may result from systemic invasion by the pathogen located in the seed.
Restriction fragment length polymorphisms, races and vegetative compatibility groups within a worldwide collection of Fusarium oxysporum f.sp. gladioli
Authors: MES J. J. , VAN DOORN J. , ROEBROECK E. J. A. , VAN EGMOND E. , VAN AARTRIJK J. , BOONEKAMP P. M.
Published: April 2007

Isolates of Fusarium oxysporum f.sp. gladioli were collected from widely different geographic areas. These isolates were characterized by pathogenicity to two differential gladiolus cultivars, vegetative compatibility, and total genomic DNA restriction fragment length polymorphisms (RFLPs). RFLPs were used to estimate the genetic divergence and relationship among isolates of F. oxysporum. RFLPs were detected by Southern blot hybridization of total genomic DNA with a 3‐4 kb DNA probe generated from total DNA off. oxysporum f.sp. dianthi. Cluster analysis allowed the division of pathogenic strains into three main RFLP groups, each group containing strains with similarity coefficients ranging from 78 to 100%. RFLP groups correlated with vegetative compatibility groups, not with races. Two single pathogenic isolates which could not be assigned to any of the three main vegetative compatibility groups also had distinctive RFLP patterns. Little genetic polymorphism was observed within vegetative compatibility groups, whereas the majority of RFLPs occurred between vegetative compatibility groups, suggesting a common ancestry for strains within a specific vegetative compatibility group and a polyphyletic origin for the present special form gladioli.