bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in phenylalanine ammonia‐lyase and peroxidase activities in wheat cultivars expressing resistance to the leaf‐rust fungus
Authors: SOUTHERTON S. G. , DEVERALL B. J.
Published: April 2007

Phenylalanine ammonia‐lyase (PAL) and peroxidase activities increased slightly during pre‐haustorial stages of development of the leaf‐rust fungus (Puccinia recondita f. sp. tritici) in each combination of rust strain and wheat line used. Activity of both enzymes greatly increased during the formation of the first haustoria by avirulent and virulent strains in an Lr28‐bearing line but not in an Lr20‐bearing line. PAL increased markedly in activity at the time when an avirulent strain was known to cause hypersensitivity in the Lr28‐bearing line and when another avirulent strain was known to cause cellular changes that preceded the expression of resistance in the Lr20‐bearing line. PAL increased less markedly and not at all at corresponding times when virulent strains developed in the Lr28 and Lr20 lines, respectively. Increases in peroxidase activity occurred after the increases in PAL activity and were greater during resistance expression than in leaves infected with virulent strains. Cytochemical tests revealed enhancements of peroxidase activity in epidermal and guard cells in response to avirulent and virulent strains and in mesophyll cells that were becoming necrotic in response to avirulent strains only. The implications of the changes are that aromatic and phenylpropanoid synthesis and peroxidations may be enhanced in wheat by infection and particularly during resistance expression. The products of these processes may play roles in both Lr28‐ and Lr20‐based expression of resistance.
Differences in cerato‐ulmin production between the EAN, NAN and non‐aggressive subgroups of Ophiostoma ulmi
Authors: BRASIER C. M. , TAKAI S. , NORDIN J. H. , RICHARDS W. C.
Published: April 2007

A test of comparative in vitro cerato‐ulmin wilt toxin production in the aggressive and non‐aggressive subgroups of the Dutch elm disease pathogen Ophiostoma ulmi was carried out by turbidity and ELISA methods. Ten non‐aggressive, ten EAN aggressive and ten NAN aggressive isolates were tested from a range of geographical sources. In liquid shake cultures the non‐aggressive isolates produced the greatest and the NAN aggressives the least mean biomass. Despite considerable variation in cerato‐ulmin production by individual isolates in three separate experiments, both the turbidity and ELISA methods showed a clear separation of the non‐aggressive and aggressive subgroups. Non‐aggressive isolates produced little or no cerato‐ulmin (ELISA range of means 0–56.0 ng/ml) and EAN and NAN aggressive isolates moderate to high levels (EAN 1.6–89.0 × 104 ng/ml and NAN 0.2–300 × 104 ng/ml). In the aggressive isolates no correlation was detected between cerato‐ulmin production and either biomass or pathogenicity to clonal Commelin elm. The role of cerato‐ulmin in the pathogenicity of O. ulmi is discussed.
Effects of temperature, leaf wetness and cultivar on the latent period of Mycosphaerella graminicola on winter wheat
Authors: SHAW M. W.
Published: April 2007

After inoculation of winter wheat cv. Longbow at a single time, lesions of M. graminicola were produced over a long interval starting 15–35 days after inoculation, dependent on temperature. There was no evidence that a single infection gave rise to more than one lesion. After the initial infection period at 100% relative humidity (r.h.), keeping leaves wet for c. 10 h per day did not shorten latent period on seedlings. Experiments in controlled‐environment chambers demonstrated a minimum latent period at approximately 17°C Variation in the latent period of individual lesions was also minimum at this temperature. The latent period varied among the cultivars tested, cv. Longbow having the shortest, cv. Avalon having almost the longest. Field observations broadly confirmed the results of experiments in constant‐environment chambers.
Diseases of Myrica faya (firetree, Myricaceae) in the Azores, Madeira and the Canary Islands
Authors: GARDNER D. E. , HODGES C. S.
Published: April 2007

Myrica faya, native to the Azores, Madeira, and the Canary Islands, was introduced to Hawaii where it has become a noxious weed. Exploration of the native habitats for potential biocontrol agents yielded several new or noteworthy disease records: cankers caused by Nectria galligena and Cryphonectria sp., dieback caused by Ramularia destructiva and Botryosphaeria ribis, and root rot caused by Armillaria me Ilea.
Root colonization by Phymatotrichum omnivorum and symptom expression of Phymatotrichum root rot in cotton in relation to planting date, soil temperature and soil water potential
Authors: KENERLEY C. M. , JEGER M. J.
Published: April 2007

Cotton was grown in containers of soil with sclerotia of Phymatotrichum omnivorum. Plants were grown for 3 weeks in the greenhouse and then transferred to field plots. Foliar and stem symptoms of Phymatotrichum root rot occurred 15–50 days after field placement. Mean incubation periods (defined as time from field placement to symptoms) were about 24 days for placements made in June and July and about 35 days for placements made in August and September 1984. Colonization of roots was more advanced in the top 24 cm of soil. The time taken for symptoms to appear was not related to the amount of root colonization at the time plants were transferred to the field. In the later two planting dates a drop in soil water potential to approximately −25 bars after 20–24 days was associated with the delay in symptom expression. There were significant linear relationships between the length of the incubation period (days), or its inverse (day−1), and the independent variables: mean maximum daily temperature (°C) in the top 12 cm layer of soil, soil water potential in the 31–60 cm layer of soil and their product (representing the interaction of these two variables). In general, symptom expression was faster at higher temperatures and with wetter conditions. Newly‐formed sclerotia were found most frequently in containers some 5–6 weeks after plant death when soil temperatures had decreased and soils were close to saturation (September and October).
Hypersensitive reaction in alfalfa (Medicago sativa) induced by alfalfa mosaic virus
Authors: ESBROECK Z. PESIC‐VAN , HIRUKI C.
Published: April 2007

Alfalfa (Medicago sativa) cv. Beaver was screened for resistance to alfalfa mosaic virus (AIMV). A1MV infection in clonal plants was tested by double‐antibody sandwich ELISA 4 and 8 weeks after inoculation with purified A1MV (1 mg/ml in 0025 M phosphate buffer, pH 7 0). Twelve clones showed a hypersensitive reaction 3–4 days after inoculation and the infection was restricted to the inoculated leaves. All the plants of hypersensitive clones consistently produced local lesions when inoculated with purified AIM V. In contrast, plants inoculated with AIMV in crude sap remained symptomless, although AIMV was detectable in inoculated leaves. The remaining 16 clones were susceptible to AIMV and showed systemic infection.
The natural occurrence of bean yellow mosaic, cucumber mosaic and tobacco mosaic viruses in lisianthus in Israel
Authors: GERA A. , COHEN J.
Published: April 2007

Mosaic on leaves, necrosis, stunting and flower symptoms were observed in lisianthus (Eustoma russellianum) raised from seed. Three viruses, bean yellow mosaic (BYMV), cucumber mosaic (CMV) and tobacco mosaic (TMV), were isolated. Virus identification was based on electron microscopy, host range, aphid transmission and serology.
Detection of components of partial resistance to mildew (Erysiphe graminis f.sp. hordei) incorporated into advanced breeding lines of barley using measurement of fungal cell wall sterol
Authors: NEWTON A. C.
Published: April 2007

Characters for partial resistance to mildew (Erysiphe graminis f.sp. hordei) derived from primitive barley lines were tested and found to have been transmitted to F9 progeny of crosses with the susceptible cultivar Golden Promise with varying degrees of efficiency, and putative transgressive segregation was observed. Derived sterol extracts from mildew cell walls were used, in conjunction with infection frequency data, to quantify the mildew present, and this sterol was characterized as being of MW 470, probably (3.beta)‐ergosta‐5,24(28)dienol (C31.H54.0.SI SILANE).
Occurrence of a viroid in chrysanthemum in Brazil
Authors: DUSI A. N. , FONSECA M. E. N. , DE ÁVILA A. C.
Published: April 2007

A viroid was detected in Chrysanthemum plants showing symptotns of stunting in a commercial field in Brazil. Analysis by return polyacrylamide gel electrophoresis (R‐PAGE) of the nucleic acid preparations of leaves and flowers revealed the presence of a nucleic acid of low molecular weight with mobility within the range of viroids. The viroid‐like band was completely eliminated by ribonuclease treatment or alkaline hydrolysis. The Chrysanthemum viroid was readily transmissible to Chrysathemum, tomnato and Gynura, which suggests that it may be an isolate of chrysanthemum stunt viroid.
Gametic disequilibria between virulence genes in barley powdery mildew populations in relation to selection and recombination. II. Danish observations
Authors: HOVMøLLER MOGENS S. , øSTERGÅRD HANNE
Published: April 2007

Analyses of gametic disequilibria (linkage disequilibria) between virulence genes were carried out on 14 samples of Erysiphe graminis f.sp. hordei collected from the aerial population at six Danish localities from 1985 to 1988. In most samples, the virulence genotypes Va7 Va12, Va9 Va12, VarV(la). Vk V(la) and VhV(La) were significantly less frequent than the product of the corresponding gene frequencies (negative gametic disequilibrium), while the virulence genotypes VaVk,Va9VnVh, VvVn and VkVh and were significantly more frequent than the product of the corresponding gene frequencies (positive gametic disequilibrium). These results could largely be explained by the distribution of powdery mildew resistance genes in the barley varieties grown in Denmark. Selection forces induced by two resistance genes present mainly in different varieties were likely to generate negative gametic disequilibrium between the corresponding virulence genes, whereas selection forces induced by two resistance genes present mainly in the same variety were likely to generate positive gametic disequilibrium between the corresponding virulence genes. This pattern was in accordance with that predicted from two‐ and three‐locuS models comprising recombination and selection induced by host resistance genes (Øsstergård & Hovmøller, 1991). It was concluded that such a model system is necessary for designing an ideal strategy for the deployment of varieties (resistance genes), and that the signs of gametic disequilibria do not provide adequate information for that purpose.
Effect of growth media, storage environment, soil temperature and delivery to soil on binucleate Rhizoctonia AG‐G for protection of potato from Rhizoctonia canker
Authors: ESCANDE A. R. , ECHANDI E.
Published: April 2007

Binucleate Rhizoctonia (BNR) isolates propagated for 20 days at 24°C on oat kernels and for 30 days on vermiculite amended with potato broth were recovered from an average of 62% of whole kernels, 100% of chopped kernels and 71 % of vermiculite particles within the cultures, respectively. Viability of BNR isolates 232‐CG and JF‐3S4‐3 was higher when stored at 5 than at 24°C, and was slightly affected by the vacuum used to reduce the O2 level. After 17 weeks of storage at 5°C in air, BNR isolates 232‐CG and JF‐3S4‐3 maintained similar viability (75% viability on whole oat kernels and 100% viability on chopped oat kernels), but in vermiculite amended with potato broth, viability of isolate 232‐CG remained at 100% while that of JF‐3S4‐3 was 28%. In the glasshouse, BNR isolates 232‐CG and JF‐3S4‐3 protected potato plants from Rhizoctonia canker caused by R. solani in soil maintained at 11, 17 and 23°C. Protection from Rhizoctonia canker was greater when BNR was delivered to soil than when placed on seed pieces. BNR‐colonized‐whole oat kernels placed in soil (15 g m of row) gave the greatest protection from Rhizoctonia canker in all experiments. In two field experiments in soil naturally infested with R. solani AG‐3. the amount of BNR‐colonized oat kernels was reduced from 15 g/m of row to 1‐9 g m of row without affecting protection of potato plants from Rhizoctonia canker.
PANCRIN, a prototype model of the pandemic cultivar‐race interaction of yellow rust on wheat in China
Authors: SHI‐MAI ZENG
Published: April 2007

The pandemic of yellow rust on wheat in China, including cultivar‐race interactions at the population level, is described by a prototype model (PANCRIN). As the framework of this model, the main epidemic system of wheat yellow rust in China was divided into 11 epidemiological regions. The major parameters are R, the rate of epidemic progress of each region in each month, determined by regional climatological factors and cultivar‐race interactions; DIL, the dilution coefficient of inter‐regional longdistance dissemination of this disease, determined mainly by distance; and F, fitness values of the pathogen on different cultivar‐race combinations. With cultivar deployment, initial disease amount, and initial race frequency as inputs, this model can output the disease amount on each cultivar and the race frequencies of each region. Results of preliminary simulation experiments tallied with some historical situations such as the breakdown of disease resistance of some important cultivars Weak points of this model are also discussed.
Effects of temperature and humidity on diseases caused by Phoma medicaginis and Leptosphaerulina trifolixs in lucerne (Medicago sativa)
Authors: BARBETTI M. J.
Published: April 2007

The post‐inoculation temperature and humidity conditions most favourable for development of Phoma black stem and leaf spot (Phoma medicaginis) and Leptosphaerulina leaf spot (Leptosphaerulina trifolii) diseases on lucerne (Medicago sativa) were determined using controlled‐environment cabinets. P. medicaginis caused more severe leaf disease at day/night temperatures of 21/16 and 18/13°C compared with 15/10°C; petiole disease was most severe at 21/16°C compared with 18/13°C, and least severe at 15/ 10°C. L. trifolii generally caused more severe leaf disease at 18/13°C compared with 21/16°C or 15/10°C, but the most severe petiole disease occurred at 21/16°C with least at 15/10°C Leaf disease caused by either P. medicaginis or L. trifolii was always more severe with the longest period (168 h) of high‐humidity incubation and, generally, increased with increasing periods of high humidity. The severity of petiole disease was much less affected than that of leaf disease by an increase in the period of high‐humidity incubation.
Requirements of leaf wetness and temperature for infection of groundnut by rust
Authors: BUTLER D. R. , JADHAV D. R.
Published: April 2007

Experiments are described to quantify the effects of temperature and duration of leaf wetness on infection of groundnut by Puccinia arachidis. After inoculation, a minimum period of leaf wetness, m. was necessary for infection. When leaf wetness duration was greater than m, lesion density increased with increasing wetness duration to an asymptote, Dmax. The principal effects of temperature were on m and Dmax‐ The value of m decreased linearly from 6 h, as temperature increased from 15 to 25 C and increased slightly at temperatures greater than 25 C Dmax increased with temperature from zero at 8 C to a maximum at 22 C. and decreased to zero again at about 30 C. The experimental results were used to produce a set of curves relating an infection index to leaf wetness duration at different temperatures. The implications for infection of groundnut crops are discussed in relation to the climate at Patancheru in southern India.
A second world‐wide migration and population displacement of Phytophthora infestans?
Authors: SPIELMAN L J. , DRENTH A. , DAVIDSE L. C. , SUJKOWSKI L. J. , GU W. , TOOLEY P. W. , FRY W. E.
Published: April 2007

The appearance of the A2 mating type (previously restricted to central Mexico) in Europe during the 1980s prompted an investigation of the genetic make‐up of European populations using allozyme loci as genetic markers. The investigation shows that major genetic changes have occurred in populations of Phytophthora infestans in the Netherlands, Poland, and the British Isles. It now appears that a new type of population has been introduced into several locations, and has displaced or is displacing the original populations in these locations. The new and old population types are characterized by unique allozyme alleles and genotypes. The mechanism for displacement of the‘old’by the‘new’population is not yet known.
Virulent and fungicide‐tolerant races of loose smut (Ustilago nuda and U. tritici) in Ireland
Authors: DHITAPHICHIT P. , JONES P
Published: April 2007

Following the severe outbreaks of loose smut in the early 1980s, a survey was carried out over the period l984‐86of the Ustilago nuda and U. tritici populations in the Republic of Ireland. U. tritici was very rare, only one infected wheat plant being reported in the 3 years of the survey. This fungus was represented by a virulent race distinct from those identified in Britain in the 1950s. U. nuda was widespread, and two races were identified in 1984. A virulent race, capable of overcoming the recessive resistance gene present in differential variety Missouri Early Beardless, was isolated from a single crop grown from imported seed. Several crops grown from seed treated with Vitavax (active ingredient carboxin), which had been imported from France, contained a carboxin‐tolerant race of U. nuda. Subsequent surveys in 1985 and 1986 failed to recover these U. nuda races. The role of imported infected seed in the introduction of new races of the loose smut fungi is discussed.
Effects of Rhynchosporium secalis at specific growth stages on barley grown in a controlled environment
Authors: MAYFIELD A. H. , CLARE B. G.
Published: April 2007

Under controlled environmental conditions, inoculation of barley at five growth stages with Rhynchosporium secalis reduced grain yield by up to 30%. Greater yield losses resulted from inoculations carried out after tillering than from those during or before tillering. Most of the yield loss was due to a reduction in the number of heads per plant. The number of grains per head was reduced only when plants were inoculated at mid‐ or late‐tillering growth stages. The mean weight of individual grains was not reduced significantly by any treatment. Inoculation at stem elongation also resulted in less leaf area and water use, and delayed anthesis. Inoculation affected root dry weight more than shoot dry weight and all inoculations reduced root dry weight at the boot growth stage
The effect of climatic factors on Colletotrichum gloeosporioides, causal agent of mango anthracnose, in the Philippines
Authors: DODD J. C. , ESTRADA A. B. , MATCHAM J. , JEFFRIES P. , JEGER M. J.
Published: April 2007

The epidemiology of the anthracnose pathogen of mango, Colletotrichum gloeosporioides, was studied over two growing seasons in the Philippines. This pathogen spreads within tree canopies as water‐borne conidia during rainfall, and causes symptoms on young flush leaves, flowers and fruit. Infection studies with leaves and fruit incubated at different temperatures and humidities led to the derivation of a logistic regression model of the percentage of conidia forming appressoria. This model was compared with a similarly derived model from work in Australia; it appeared that the Philippine isolates of C. gloeosporioides were adapted to the higher mean temperatures of the Philippines. Conidia were observed to germinate and form appressoria at relative humidities (RH) between 95 and 100%, even though free surface moisture was only visible at 100% RH. This model was used retrospectively to estimate infection levels in two field trials which had been established to compare pre‐ and post‐harvest practices in the control of the disease. Using this information to plan applications of a curative fungicide might have resulted in four fewer sprays in the first trial and one less in the second, compared with the standard protective spray programme employed.
Induction of myceliogenic germination of sclerotia of Sclerotinia sclerotiorum by exposure to sub‐freezing temperatures
Authors: HUANG H. C.
Published: April 2007

When sclerotia of a Canadian isolate of Sclerotinia sclerotiorum were exposed to temperatures of – 10 or– 20 C for 4 weeks, their germination behaviour changed from carpogenic to myceliogenic type. Mycelial growth from sclerotia exposed to– 20 C was more vigorous than that from sclerotia exposed to– 10 C. The mode of germination in sclerotia treated with above‐freezing temperatures of 0 5, 10. 15. 25 or 30 C did not change: they retained the capacity for carpogenic germination. The possible epidemiological impact of this low‐temperature induction of myceliogenic germination on the development of sclerotinia wilt of sunflower seedlings in western Canada is discussed.
Effects of cultivation, conditioning and isolate on sclerotium germination in Sclerotium cepivorum
Authors: BRIX H. D. , ZINKERNAGEL V.
Published: April 2007

Sclerotium germination in various isolates of S. cepivorum was studied following different cultivation and conditioning treatments. A simple and rapid laboratory test was developed to trigger sclerotial germination under unsterile conditions. In most isolates, sclerotia produced under sterile and unsterile conditions showed a constitutive dormancy immediately after maturing. In contrast to this, the sclerotia of some isolates germinated quite well as soon as they were mature. The dormancy of sclerotia from axenic cultures broke down after storage in soil for 12 weeks. In a few cases sclerotia produced under unsterile conditions germinated remarkably well. Freezing and thawing of sclerotia decreased the ability of most isolates to germinate.
Incidence of Acremonium lolii and lack of correlation with barley yellow dwarf viruses in Tasmanian perennial ryegrass pastures
Authors: GUY P. L.
Published: April 2007

The perennial ryegrass endophyte Acremonium lolii occurred in all ryegrass (Lolium perenne) pastures sampled in Tasmania. Cultivars tested included Ellett, Martlet, Tasdale, Tasmanian No. 1 and Victorian. The range in incidence was 4–94% (average 66%). Many pastures more than 4 years old caused perennial ryegrass staggers syndrome in livestock, and the range in incidence in these pastures was 79–94%. There was no correlation, positive or negative, between barley yellow dwarf virus infection and the incidence of A. lolii. There was good agreement between ELISA and microscopic examination of epidermal strips. However unlike previous studies, the ELISA test was specific for A. lolii and did not detect Acremonium coenophialum, the endophyte of tall fescue.
Multiple fungicide resistance to benzimidazoles, dicarboximides and diethofencarb in field isolates of Botrytis cinerea in Israel
Authors: ELAD Y. , YUNIS H. , KATAN T.
Published: April 2007

During the period January‐March 1989, 15 greenhouses at 12 sites in Israel were surveyed for the presence of fungicide‐resistant strains of Botrytis cinerea, using a fungicide‐amended Botrytis‐selective medium. Resistance to benzimidazoles (BenR) and to dicarboximides (DicR) was frequent in most sites. Resistance to carbendazim + diethofencarb (BenR NPCR) was found in all eight sites in which a mixture of these fungicides had been used against grey mould, but not in other sites. A new phenotype of multiple fungicide resistance was found among these isolates. The new phenotype, designated BenR DicR NPCR, combines the three previously described characteristics of resistance to benzimidazole, dicarboximide and N‐phenylcarbamate fungicides. It was found only in cucumber greenhouses that had been sprayed with the fungicide mixture carbendazim + diethofencarb against grey mould. Isolates of this phenotype were pathogenic in artificial inoculation of cucumber cotyledons treated with carbendazim, iprodione or carbendazim + diethofencarb.
New host records for Puccinia allii Rud.
Authors: BECKETT A. , HOUSTON L. , FROST L. C.
Published: April 2007

Uredinia and telia of Puccinia allii were found on leaves of Allium sphaerocephalon, but uredinia only were found on A. carinatum, A. roseum and Nectaroscordum siculum. Each combination represents a new record for Britain, and N. siculum has not been recorded previously as a host for this fungus.
Axenic culture of Peridermium pini from single aeciospores
Authors: PEI M. H. , GIBBS J. N.
Published: April 2007

For the first time with a rust fungus, continuously growing axenic cultures have been obtained from single spores. This was achieved with aeciospore sources of the pine stem rust Peridermium pini (Pers.) Lev. from Thetford Forest, East Anglia, but not with sources from north‐east Scotland. Approximately 30% of the single spores of two East Anglian sources out of the three tested developed into transferable and subculturable colonies on modified Harvey & Grasham's medium.
Effect of soil moisture on the transmission of pea bacterial blight (Pseudomonas syringae pv. pisi) from seed to seedling
Authors: ROBERTS S. J.
Published: April 2007

Controlled‐environment studies in which pea seed cv. Solara, inoculated with Pseudomonas syringae pv. pisi, was sown in pots of compost maintained at different moisture contents showed that soil moisture had a considerable influence on the transmission of the disease from seed to seedling. An equation was derived from this data which described the relationship between the proportion of seedlings infected (p) and the soil water stress (s) in MPa: ‐In(‐In(1 −p)) = 0.64 In(s) + 4.5. This equation was used to produce predicted transmission rates for each year from 1987 to 1990, which were compared with measured transmission rates in field experiments at Wellesbourne in the same years. Although agreement between the observed and predicted transmission rates was poor, years of severe and slight disease transmission were successfully predicted.
Association of stomatal frequency and morphology in Lycopersicon species with resistance to Xanthomonas campestris pv. vesicatoria
Authors: RAMOS L. J. , NARAYANAN K. R. , MCMILLAN R. T.
Published: April 2007

Study of the stomata and leaf epidermis of eight Lycopersicon species has revealed a relationship between frequency of stomata, stomatal size and some morphological leaf characteristics, and resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vesicatoria. Significant correlations were found between the stomatal frequency in both adaxial and abaxial leaf epidermis and the number of bacterial lesions per leaf area (r= 0.70 and 0.68, respectively) and the frequency of stomata in both adaxial and abaxial epidermis and disease incidence (percentage of diseased plants) (r=0.87 and 0.80, respectively) for all the Lycopersicon species and one hybrid tested. A correlation was also found between disease incidence and number of bacterial lesions per leaf area (r= 0.85). The length and width of stomata were correlated with frequency of stomata in adaxial and abaxial epidermis (r= 0.85, 0.75, 0.89 and 0.90, respectively). The stomatal width was correlated with the number of bacterial lesions per cm2 (r=0.82; P= 0.0065). Scanning electron microscopic studies of the leaf surface and stomata indicated that other morphological features such as the raised stomatal complex in L. hirsutum and persistent, hydrophobic waxy coating of the epidermis in L. peruvianum may also be relevant in disease response.
Temporal variation in the racial structure of flax rust (Melampsora lini) populations growing on natural stands of wild flax (Linum marginale): local versus metapopulation dynamics*
Authors: BURDON J. J. , JAROSZ A. M.
Published: April 2007

A total of 567 isolates of the rust fungusMelampsora liniwere collected from nine populations of the Australian endemic host,Linum marginale, growing over a distance of 100 km within the Kosciusko National Park, New South Wales, Australia, Collections at each site were made over 2–4 consecutive years and races were identified using a set of 12 lines ofL. marginalecarrying different resistances. Four races dominated the combined metapopulation: three were widespread and common, while the fourth (with the largest range of virulence of the four) was widespread but, with the exception of one population, rarely occurred at a frequency of greater than 15%. This general pattern was maintained over all years. Individual populations were generally composed of one or two dominant races plus a variable number of others represented by only a few isolates. The diversity of populations (Shannon‐Weaver index) showed little variation either within populations across years or between populations within years. At the individual population level, significant year‐to‐year variation was detected in the racial structure of four populations. However, when compared in terms of virulence on individual members of the differential set, significant year‐to‐year variation occurred in only two of these populations. Analysis of the data suggested that the pathogen exists as an overall metapopulation (a set of local populations) with high levels of migration occurring between individual populations.
Parry's disease of pears is similar to pear decline and is associated with mycoplasma‐like organisms transmitted by Cacopsylla pyricola
Authors: DAVIES D. L. , GUISE C. M. , CLARK M. F. , ADAMS A. N.
Published: April 2007

Mycoplasma‐like organisms (MLOs) were detected by fluorescence microscopy in a number of pear cultivars and pear seedlings growing under a range of different conditions. In the cultivar Conference, MLOs were consistently associated with symptoms of Parry's disease, a decline‐like disease of young trees with quince rootstocks. MLO‐free pear seedlings rapidly became infected when they were planted outside. Experimental transmission of MLOs to pear seedlings and Conference trees was achieved using pear psyllids, caught outside or raised on infected plants under controlled conditions. Conference trees in an orchard trial remained free from the severe spring symptoms of Parry's disease when they were protected from feeding insects during spring of the previous year. MLOs were graft transmissible, but were not perpetuated by the standard propagation practices of budding or grafting when quince rootstocks were used. Parry's disease appears to be similar to pear decline, an MLO‐induced disease well established in several other parts of the world. It is suggested that Parry's disease should be referred to as pear decline.
Influence of the amount of blackgram mottle virus in different tissues on transmission through the seeds of Vigna mungo
Authors: VARMA A. , KRISHNAREDDY M. , MALATHI V. G.
Published: April 2007

Blackgram mottle virus (BMoV) was transmitted via up to 16% of seeds of different cultivars of blackgram, as determined by seedling symptom tests. The percentage of seed infection by BMoV as determined by EL1SA was even higher. Seed transmission was highest in cv. PLU‐277 (15.9%), followed by cvs T‐9 (11.8%), PLU‐213 (7.0%) and UH‐81‐7 (1.3%). Seed transmission was correlated with the amount of virus present in the embryonic axis and later in primary leaves. The presence of virus in the testa alone did not result in its transmission through seeds. Virus concentration in different tissues varied; the mean amount of virus in the three cultivars was found to be 48–1234 ng per embryonic axis, 15–24 ng per cotyledon, and 12–20 ng per testa. The infection of primary leaves through the seed also resulted in systemic infection if the amount of virus in primary leaves exceeded 100 ng/100 mg of tissue. Close agreement was found between the percentage of seedlings with systemic infection and the percentage of seeds and embryonic axes containing more than 100 ng virus. The cultivars that resisted seed transmission contained relatively small amounts of the virus in embryonic axes.
Relationships among measurements of fitness and disease severity in Phytophthora infestans
Authors: SPIELMAN L. J. , McMASTER B. J. , FRY W. E.
Published: April 2007

Several methods of estimating pathogen fitness and disease severity in the Phytophthora infestans Solanum tuberosum pathosystem were investigated. Components of fitness measured in a growth chamber were compared with area under the disease progress curve (AUDPC) measured in small field plots. The closest relationship with AUDPC was for sporulation capacity (coefficient of determination, r2= 0.86)and the least close relationship was with infection frequency (r2= 001). Two different methods were compared for calculating the relative fitnesses of two isolates: (i) apparent infection rates and (ii) changes in frequency in mixed epidemics. The values obtained by the two methods were not contradictory (0.98 and 0.93 units per day for the less fit isolate, against 1 for the more fit isolate), but had wide and overlapping confidence intervals.
Purification, characterization and serological properties of two virus isolates associated with the maize stripe disease in Mauritius
Authors: DE DOYLE M. M. ROCA , AUTREY L. J. C. , JONES P.
Published: April 2007

Two virus isolates associated respectively with the maize stripe and the maize chlorotic stripe syndromes in Mauritius, denoted MSM and MCS, have been purified and characterized. A single nucleoprotein band of buoyant density 1.289 g/ml was recovered from both MSM and MCS extracts after isopycnic centrifugation in CsC1 gradients. Rate zonal centrifugation in 10–40% sucrose gradients of extracts of leaves infected by each isolate resulted in five light‐scattering zones. The highest absorbency at 254 nm was associated with the third fraction from the top. Analysis of purified proteins by SDS‐PAGE revealed a single capsid protein of Mr 34000 in preparations of each isolate. Large quantities of a non‐capsid protein ofMr 23000 were extracted from both MSM‐ and MCS‐infected material with a concentration of 1 75 and 2.35 mg/g of infected tissue, respectively. No such bands were detected in preparations from healthy leaves or leaves infected with maize streak virus (MSV). Both the 34000 and 23 000 proteins could be recovered from partially purified virus extracts. The property of the non‐capsid protein to solubilize above and crystallize below pH 60 was used as the basis for a rapid diagnostic test. Electron microscopy of purified preparations of both isolates showed filamentous particles less than 5 nm in diameter and of different lengths. Several particle configurations, including circular, coiled and unfolded structures, were present, and were typical of a tenuivirus. Antisera raised in rabbits against the two nucleoproteins, each had titres of 1/32 both in homologous and reciprocal Ouchterlony double‐diffusion tests. Sap extracts of both MSM‐ and MCS‐infected plants gave strong reactions with antisera to maize stripe virus (MSpV) from Reunion, Kenya and the USA. The most sensitive diagnosis was achieved using F(ab′)2 ELISA. Both MSM and MCS should be considered isolates of maize stripe virus (MSpV). Although MSM and MCS induce different symptoms, they were indistinguishable in our tests; we propose that they are the same and that symptom differences arise as a result of late and early infection, respectively.
Occurrence of Melampsora euphorbiae on Euphorbia lagascae in south‐east Spain
Authors: VILLALOBOS M. J. PASCUAL , JELLIS G. J.
Published: April 2007

Melampsora euphorbiae (Schub.) Castagne is reported for the first time on Euphorbia lagascae, a spurge which is a native of south‐east Spain and has seed oil rich in vernolic acid. In Spanish trials, rust caused by M. euphorbiae was the major disease of this potential crop.
Splash dispersal of Colletotrichum acutatum and Phytophthora cactorum by short‐duration simulated rains
Authors: MADDEN L. V. , WILSON L. L. , YANG X. , ELLIS M. A.
Published: April 2007

The effect of short rain durations (≤ 16 min) on splash dispersal of Colletotrichum acutatum, the cause of strawberry anthracnose, and Phytophthora cactorum, the cause of strawberry leather rot. was investigated using a rain simulator. Potted strawberry plants were held in two concentric circles, of radius 30 and 60 cm, respectively, surrounded by soil in an area that was uniformly exposed to simulated rain falling at 15 mm/h. Infected fruit with sporulating lesions (source fruit) were placed in the centre and healthy (target) fruit were placed in front of each circle of plants. Dispersal was measured as the proportion of fruit infected (disease incidence). Disease incidence increased with increasing rain duration. The incidence of anthracnose 30 cm from the inoculum source increased from c. 25% after 30s of rain to 99% after 16 min. The incidence of leather rot increased from 1% after 2 min to 26% after 16 min. In other experiments, source fruit and the entire target area were first exposed to 4 or 8 min of rain (pre‐rain treatments), source fruit were then removed, and target fruit were placed on the soil and exposed to 4 or 16 min of rain. Splash dispersal still occurred, although there was a significant effect on disease incidence of a pre‐rain on the source fruit. The incidence of C. acutatum infection was 68 and 98% for the 4‐ and 8‐min pre‐rain treatments, respectively, after 16 min of rain at 30 cm from the source. The incidence of P. cactorum infection was 15 and 36% for the 4‐ and 8‐min pre‐rain treatments, respectively, after 16 min of rain at 30 cm from the source. High disease incidence with pre‐rain treatments was probably due to the rapid removal of spores by rain. Between 44 and 50% of spores of both pathogens were removed from the source fruit after 4 min of rain. When plants and fruit were arranged on a slope of 7° inclination, there was greater dispersal of C. acutatum downhill than uphill. These results indicate that very short rains can result in high levels of disease if subsequent conditions are favourable for infection.
Development of a monoclonal antibody‐based immunodetection assay for Botrytis cinerea
Authors: BOSSI R. , DEWEY F. M.
Published: April 2007

Three hybridoma cell lines secreting antibodies that specifically recognize Botrytis cinerea and B.fabae, but not B. allii, have been raised from splenocytes of mice immunized with a low molecular‐weight fraction (30 kDa) from surface washings of B. cinerea. Antibodies from these cell lines have been used to develop an antigen‐based elisa test that will detect B. cinerea in strawberries. This monoclonal antibody immunoassay detection assay should prove useful to both the cut‐flower and wine industries. Supernatants from the three specific cell lines recognize mycelial fragments, saline extracts of mycelia and germinating conidia by both ELISA and immunofluorescence. Recognition of non‐germinating spores is poor. Supernatants from the specific cell lines did not recognize other fungi normally involved in post‐harvest spoilage of fruits and vegetables. Supernatants from KH4 gave the lowest background values with healthy tissue. Indirect evidence from heat, protease and periodate treatment of the antigens indicates that antibodies from all three specific cell lines are recognizing carbohydrate epitopes on a glycoprotein.
Erysiphe pisi var. pisi on faba beans and other legumes in Britain
Authors: COOK R. T. A. , FOX R. T. V.
Published: April 2007

The powdery mildew Erysiphe pisi var. pisi, complete with its teleomorph, has been observed on faba beans (Vicia faba cultivars) for the first time in Britain. It appeared in a glasshouse on Syrian lines of fodder bean and English cultivars of broad bean. It also infected tare (Vicia sativa) and sweet pea (Lathyrus odoratus), but not edible pea (Pisum sativum), ornamental lupin (Lupinus polyphyllus), French bean (Phaseolus vulgaris) or sainfoin (Onobrychis viciaefolia). Inoculations in a glasshouse showed that another strain of E. pisi var. pisi found on outdoor everlasting pea (Lathyrus latifolius) was also capable of affecting faba bean, and was distinguished by its ability to infect edible pea. A third strain found on outdoor ornamental lupin infected only lupin. E. pisi var. pisi was shown to be morphologically and pathogenically distinct from the Erysiphe sp. newly affecting tomatoes in Britain.
Interaction between phyllosphere yeasts, aphid honeydew and fungicide effectiveness in wheat under field conditions
Authors: DIK A. J. , VAN PELT J. A.
Published: April 2007

Aphid honeydew can reduce fungicide effectiveness against necrotrophic pathogens of wheat under controlled conditions. In 1988 and 1989, field experiments were carried out at different locations in The Netherlands, to assess the interference of honeydew with fungicide effectiveness under field conditions, and to establish whether honeydew consumption by naturally occurring saprophytes could prevent this effect. Different combinations of chemicals were used to create differences in saprophytic population densities and aphid populations, which were expected to result in differences in the amount of honeydew and other nutrients on the leaves. In two of the experiments, Septoria nodorum was the only necrotrophic pathogen present; in the other two the only necrotroph was S. tritici. On several sampling dates, the effect of the fungicides was significantly enhanced by addition of insecticide, most often when the saprophytes were reduced by maneb/anilazine. This effect of insecticide is ascribed to prevention of interference of honeydew with fungicide activity, and not to a direct effect of insecticide, as insecticide alone had no effect on necrosis. On the basis of the fact that interference of honeydew with fungicide activity was most apparent when saprophytic population densities were reduced, it is concluded that the naturally occurring saprophytes can generally prevent the effect of honeydew. The same interactions are likely to occur between other nutrients and fungicides, and it is therefore argued that the naturally occurring saprophytes should be protected by elimination of harmful chemicals.
Stilbene glucoside levels and the resistance of Sitka spruce (Picea sitchensis) tissues to colonization by root‐ and butt‐rotting fungi
Authors: UNDERWOOD C. D. TOSCANO , PEARCE R. B.
Published: April 2007

The relationship between constitutive stilbene glucoside (astringin and isorhapontin) levels in Sitka spruce (Picea sitchensis) bark and resistance of these tissues to colonization by the root‐ and butt‐rot fungi Heterobasidion annosum and Phaeolus schweinitzii was determined in vitro in excised bark tissues. Two experimental systems were developed. In one, 15‐mm‐diameter bark discs taken from mature forest trees were challenged with mycelial cultures of the fungi; in the other, 70‐ or 100‐mm lengths of stem, up to c. 30 mm diameter, were similarly challenged at the lower cut end. The extent of fungal colonization or necrosis in the challenged tissues was determined. The results indicated that both systems were capable of detecting differences in bark susceptibility to colonization between individual trees. No consistent correlation between stilbene levels and resistance to colonization by either fungus was found.
Isoenzyme polymorphism and segregation in isolates of Phytophthora infestans from Japan
Authors: MOSA A. , KOBAYASHI K. , OGOSHI A. , KATO M. , SATO N.
Published: April 2007

Isoenzyme variation of 198 isolates of Phytophthora infestans collected from many locations in Japan during 1987–90, and of four pre‐1987 isolates, was examined using starch gel electrophoresis. A previously unreported allele at malic isoenzyme locus/ME (90) was observed. An association between mating types and isoenzyme genotypes at three isoenzyme loci, glucosephosphate isomerase (GPI‐1), peptidase (PEP‐1) and ME, was found. At PEP‐1, the A2 isolates from Japan had a previously unreported genotype (96/96). Normal segregation at the malic isoenzyme locus occurred in a cross of Japanese and Mexican parents. The results provide evidence of a change in the population genetic structure of P. infestans in Japan.
The relative importance of Colletotrichum musae as a crown‐rot pathogen on Windward Island bananas
Authors: FINLAY A. R. , BROWN A. E.
Published: April 2007

Low numbers of conidia of Colletotrichum musae (10–50) applied directly to the surface of freshly cut banana crowns caused extensive rot development. At least 20 times more conidia of Fusarium pallidoroseum were required to cause comparable levels of crown rot. Examination of the relative pathogenicity of the major fungal species involved in development of crown rot, C. musae, F. pallidoroseum, Fusarium moniliforme, F. moniliforme var. subglutinans, and Botryodiplodia theobromae, using a standard inoculum of 2 × 103 conidia per crown, showed C. musae to be the most aggressive species. C. musae produced a distinctive soft, dry fibrous rot while the fruit was still green, and on ripening further rotting, softening and blackening of crown tissues occurred. The other crown‐rot pathogens tested did not rot green fruit.

Fruit inoculated with C. musae and held for 0, 1, 2 and 3 days at ambient temperature before ripening sustained increasingly more severe crown rot. C. musae was isolated with increasing frequency from rotting tissue the longer the period under ambient conditions. Crowns which had been inoculated with F. pallidoroseum and held for a comparable period did not display such extensive rot development although the pathogen was very frequently isolated from the tissue.
Histology of the infection of tritordeum and its parents by cereal brown rusts
Authors: RUBIALES D. , NIKS R. E. , DEKENS R. G. , MARTÍN A.
Published: April 2007

The reactions of tritordeum lines and their Hordeum chilense and Triticum spp. parents to infection by Puccinia recondita f.sp. tritici, P. recondita f.sp. agropyri and P. hordei were studied at the seedling stage. The histological observations indicated that tritordeum behaves as the wheat parent, whatever the H. chilense parental line reaction. Tritordeum is to be considered a host of wheat brown rust where genes for hypersensitive resistance may occur; these are apparently contributed by the wheat parent. Both H. chilense and wheat are highly resistant to barley brown rust, and the reaction of tritordeum is that of the wheat parent with respect to the levels of necrosis associated with the early aborted infection units. The tritordeum reaction is also that of the wheat parent to a rust collected on H. jubatum (putatively P. recondita f.sp. agropyri), with the susceptibility or resistance of H. chilense being overruled by the wheat parent reaction.
Biochemical defence responses in primary roots of Scots pine challenged in vitro with Cylindrocarpon destructans
Authors: BONELLO P , PEARCE R. B.
Published: April 2007

The occurrence of constitutive and induced antifungal compounds in primary roots of Pinus sylvestris seedlings was investigated, and total soluble phenols and lignification estimated, following challenge with the root pathogen Cylindrocarpon destructans. No reliably detectable phytoalexins were found, but the mean content of constitutive, antifungal diterpenic resin acids of the abietic acid group increased in the roots following infection. No diffuse lignitication was detected, but the content of cell‐wall‐bound phenolics increased with a concurrent decrease in the content of soluble phenols, although these changes were not statistically significant. The inhibitory effect of a commercial preparation of abietic acid on the germination of C. destructans spores was evaluated, and the significance of this class of compounds to defence in Scots pine seedlings is discussed.