bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic analysis of partial resistance to bacterial leaf streak (Xanthomonas campestris pv. cerealis) in wheat
Authors: EL ATTARI H. , SARRAFI A. , ALIZADEH A. , DECHAMP‐GUILLAUME G. , BARRAULT G.
Published: November 2003

Genetic variability of partial resistance to bacterial leaf streak was investigated in hexaploid winter wheat (Triticum aestivum.), using 16 parental genotypes and 48 pure lines (F10) derived from a composite cross programme. Two experiments were undertaken in a controlled growth chamber. Seeds of all genotypes were grown under controlled conditions using a randomized block design with three replications. Each replication consisted of a row of 20 seedlings of each parent and pure line. An Iranian strain of bacterial leaf streak was used for the inoculation of 12‐day‐old seedlings. In a third experiment, eight genotypes from parents and F10 pure lines representing a large variability for partial resistance were inoculated with four other Iranian strains of bacterial leaf streak. A large genetic variability was observed amongst the 64 genotypes for partial resistance to the disease. Partial resistance heritability estimates were rather high (70%), indicating that the resistance factors may be transmitted by crossing. Amongst all genotypes investigated, ‘DC2‐30‐N2’ and ‘IBPT‐66’ displayed the highest partial resistance to the disease. Significant correlations between strains in the third experiment show that a genotype resistant or susceptible to one strain will have similar reactions with other strains. No significant genetic gain was observed for partial resistance in the best pure line of the 48 lines studied, when compared with the best parental line. Increasing the number of pure lines is likely to result in the identification of genotypes that might prove to be more resistant.
Long‐term maintenance of nonculturable apple‐proliferation phytoplasmas in their micropropagated natural host plant
Authors: JARAUSCH W. , LANSAC M. , DOSBA F.
Published: November 2003

Phytoplasmas associated with apple proliferation (AP) disease of apple trees have been maintained in their micropropagated natural host plant Malus pumila since 1985. Different isolates of these nonculturable plant pathogens could thus be studied in vitro. Amplification of a pathogen‐specific DNA fragment by polymerase chain reaction (PCR) confirmed the presence of AP phytoplasmas in the diseased plants even after 10 years of in‐vitro propagation. Restriction fragment length polymorphism analysis of the amplified chromosomal DNA fragments revealed no genetic difference between the AP phytoplasma isolates. Growth parameters, symptom expression and phytoplasma concentration were examined to compare the in‐vitro behaviour of four different AP phytoplasma isolates and to compare different subculture conditions. A comparison of these data obtained after 2 or 8 years of micropropagation revealed no essential differences. Eight years after culture initiation, diseased shoots still exhibited typical symptoms like witches’ broom, small leaves with large stipules and stunted growth. The use of phytoplasma‐diseased micropropagated plants to establish a ‘type culture collection’ of these otherwise nonculturable plant pathogens is discussed.
Prevalence of Plasmodiophora brassicae in a spring oilseed rape growing area in central Sweden and factors influencing soil infestation levels
Authors: WALLENHAMMAR A.‐C.
Published: November 2003

During 1986–87 the presence of clubroot in soils sampled from 190 fields was assessed using a bioassay method, based on baiting the soils with Brassica campestris spp. pekinesis cv. Granaat. Clubroot was detected in 148 (72%) of the fields investigated and, on average, 49.2% of the plants were infected according to the bioassay. Subsequent testing of fields in 1990 and 1992 (54 and 81 fields, respectively) where no further Brassica crops had been grown indicated a significant decrease in the degree of infestation to 7.1% in 1992. Clay soils showed, on average, the highest degree of infestation, and high infestation was recorded for a wide range of pH values (5.2–6.6). The highest degree of infestation was recorded on fields where oilseeds were grown five times during the period 1965–85. The results presented show that, in a field with 100% infestation, the level of infestation declined to below the detection level after a period of 17.3 years. The half‐life of the spore inoculum was determined to be 3.6 years. During the sensitivity testing of different Brassica species and cultivars, it was found that Chinese cabbage showed a low percentage of infestation in two soils, whilst some oilseed rape and spring oilseed turnip rape cultivars showed high degrees of infestation in these soils.
Pathogenic specialization in Melampsora epitea var. epitea on Salix
Authors: PEI M. H. , ROYLE D. J. , HUNTER T.
Published: November 2003

Eighteen isolates of the rust fungus Melampsora from different locations in England were tested for pathogenicity to a large range of willow clones (Salix spp.) in experiments involving inoculation of leaf discs. Seventeen of the isolates were of leaf‐infecting M. epitea var. epitea, 16 of which represented forms which alternated on Larix and one of which alternated on Ribes. The remaining isolate was of uncertain identity. Two experiments were carried out. In the first experiment, 24 willow clones consisting of 20 Salix species and interspecific hybrids were inoculated with eight isolates from clones of S. viminalis. In the other experiment, 77 clones from 57 species or hybrids were inoculated with 10 isolates from several Salix spp. The M. epitea var. epitea isolates from S. viminalis clones were all similarly pathogenic, whilst most of the other isolates expressed distinct host specificity. Eight distinct pathotypes were recognized within M. epitea var. epitea. All except one of these alternated on Larix and could be assigned to three formae speciales which had been reported previously in Europe: four pathotypes to f.sp. larici‐epitea typica, two to f.sp. larici‐retusae, and one to f.sp. larici‐daphnoides. The Ribes‐alternating pathotype of M. epitea var.epitea infected only S. purpurea. Nine differential willow hosts are proposed as reference clones to distinguish between the larch‐alternating pathotypes, the Ribes‐alternating rust and the ‘stem‐infecting’ form. The extent of pathogenic variation encountered amongst sexually reproducing rusts suggests that more pathotypes probably exist and will arise in future in response to selection given by long‐term clonal willow plantings.
A possible role of sexuality in the population structure of Diaporthe adunca, a pathogen of Plantago lanceolata
Authors: LINDERS E. G. A.
Published: November 2003

In this study, the population structure of the fungal pathogen Diaporthe adunca on its perennial wild host plant Plantago lanceolata was analysed, together with the occurrence of the sexual stage of the fungus. The fungus overwinters on scapes infected in the previous year. In spring, it sporulates asexually on these scapes leading to primary infection sources for an epidemic. From mid‐June onwards, after asexual reproduction has ceased, the sexual stage is formed on the same overwintered scapes. In one location where the sexual stage was prominent, a more diverse fungal population structure was found than in another location where the sexual stage was less frequent and where one clone (with a low female fertility) dominated the same area during three consecutive years. A trade‐off was found between the sexual and asexual reproduction. Female sterile isolates, which have lost the ability to produce the sexual stage, may invest all available nutrients in the scape for asexual reproduction and, therefore, might be selected for under relatively stable regimes. In unstable situations, where there is a lower probability of host plant survival, selection may favour sexual reproduction.
Resistance to Sphaerotheca pannosa in roses induced by 2,6‐dichloroisonicotinic acid
Authors: HIJWEGEN T. , VERHAAR M. A. , ZADOKS J. C.
Published: November 2003

The susceptible rose cv. Madelon and the partially resistant cv. Sonia both responded with reduced development of rose powdery mildew when they were treated with the synthetic inducer 2,6‐dichloroisonicotinic acid (INA). The EC50 for number of colonies cm−2 was approximately 0.4 mg L−1 in both cultivars when treated 4 days prior to inoculation. However, conspicuous differences were observed with respect to number of spores per cm2. For sporulation, the EC50 was 0.37 mg L−1 in cv. Madelon and only 0.08 mg L−1 in cv. Sonia. A comparison with the pathosystems cucumber/Sphaerotheca fuliginea and red cabbage/Peronospora parasitica is made and the importance of the observed phenomenon for the selection of parents in a breeding programme for (partial) resistance is discussed.
Elimination of ornithogalum mosaic virus from chincherinchee (Ornithogalum thyrsoides) by meristem tip culture, and field trials of reinfection
Authors: WANGAI A. W. , BOCK K. R.
Published: November 2003

Meristem domes excised from plantlets of Ornithogalum thyrsoides infected with ornithogalum mosaic virus (OrMV) in Kenya were cultured on basic Murashige and Skoog medium without added growth hormones. Of the resulting plantlets 30% were virus‐free as determined by symptom appearance, mechanical inoculation to virus‐free O. thyrsoides, electron microscopy and serological tests. When healthy plants were placed within a field of diseased O. thyrsoides, 35% became re‐infected within 4 months and 100% infection was reached within 8 months. However, healthy plants placed in isolation, about 2 km downwind of infected commercial plantings, remained healthy over the 12‐month test period.
The role of alternative hosts of Polymyxa betae in transmission of beet necrotic yellow vein virus (BNYVV) in England
Authors: HUGO S. A. , HENRY C. M. , HARJU V.
Published: November 2003

The host range of beet necrotic yellow vein virus (BNYVV) and Polymyxa betae was determined by growing plants in naturally infested soils from rhizomania outbreaks in England. Apart from Beta vulgaris, plant species infected by BNYVV were included in the families Chenopodiaceae (Atriplex patula, Chenopodium bonus‐henricus, C. hybridum, C. polyspermum and Spinacia oleracea), Amaranthaceae (Amaranthus retroflexus) and Caryophyllaceae (Silene alba, S. vulgaris, S. noctiflora and Stellaria graminea). Only P. betae isolates from B. vulgaris, C. polyspermum and S. oleracea were found to be able to transmit BNYVV back to sugar beet. When a range of weed plants from infected fields were tested, none were found to be infected by BNYVV. Therefore, it seems likely that the weed hosts play only a minor role in the spread of rhizomania disease compared to that of sugar beet, other Beta vulgaris crop types or spinach.
Morphological and biochemical characterization of Armillaria isolates from Zimbabwe
Authors: MWENJE E. , RIDE J. P.
Published: November 2003

Variations in cultural and biochemical characteristics have been used to group 20 Armillaria isolates collected from different hosts and regions in Zimbabwe. Morphological features, including colony type and rhizomorph characteristics in vitro, rhizomorph characteristics from inoculum buried in soil, and features of basidiocarps produced in vitro on wood, millet and oranges, divided the Zimbabwean isolates into three morphologically distinct groups, designated I, II and III. Biochemical attributes involving isozyme and protein patterns studied by electrophoresis and isoelectric focusing also indicated three groups which corresponded precisely with the three groups observed for morphological studies. Isozyme analyses of pectin lyase (PL), pectin methylesterase (PME), beta‐1,3‐glucanase, nonspecific esterases and putative suberinases were important in grouping the isolates. Pectin lyase and pectin methylesterase patterns gave the clearest and mostly easily interpreted results. Total protein patterns by SDS–polyacrylamide gel electrophoresis also showed some group‐specific bands. Cluster and principal component analyses of the data confirmed the separation of the Zimbabwean Armillaria isolates into three distinct groups.
Grapevine leafroll‐associated viruses and grapevine virus A in selected Vitis vinifera cultivars in northern Italy
Authors: CREDI R. , GIUNCHEDI L.
Published: November 2003

The occurrence of grapevine leafroll‐associated virus 1 (GLRaV‐1), grapevine leafroll‐associated virus 3 (GLRaV‐3) and grapevine virus A (GVA) was demonstrated in a viticultural region of northern Italy (Emilia‐Romagna) using immunoelectron microscopy. Virus incidence was subsequently assessed using ELISA. A total of 60.6% of the 150 clone selections tested, from 18 local Vitis vinifera cultivars, were found to be infected. ELISA did not reveal the presence of grapevine leafroll‐associated virus 2 (GLRaV‐2) or grapevine leafroll‐associated virus 5 (GLRaV‐5). GLRaV‐1, GLRaV‐3 and GVA were found individually and in various combinations. The most common findings were GLRaV‐1 alone (25.3%) and associated with GVA (33%). Serological data confirmed that the majority (91%) of the clones known to be affected by grapevine leafroll (GLR), on its own or in association with rugose wood (RW), contained viruses. On the other hand, where the RW phenomenon was present on its own, only 40% of these clones were ELISA‐positive. The implications for the biology of GLR and RW are discussed and the complex aetiology of these grapevine diseases is confirmed.
Identification and sensitive endophytic detection of the fire blight pathogen Erwinia amylovora with 23S ribosomal DNA sequences and the polymerase chain reaction
Authors: MAES M. , GARBEVA P. , CREPEL C.
Published: November 2003

Two short sequences, situated in the bacterial 23S rDNA gene, were used as primers for the PCR detection of Erwinia amylovora bacteria. All 34 E. amylovora strains tested, coming from different geographical and host plant origins and of different virulence, produced a 565‐bp PCR fragment. The E. amylovora bacteria could be discriminated from all other phytobacteria with which no PCR product was observed. Only Escherichia coli bacteria were cross‐recognized by the production of a weaker PCR band of similar size to E. amylovora. In a fast PCR protocol, where two temperatures were cycled, E. amylovora in pure culture could be detected on gel at concentrations as low as 3 × 102 cfu mL–1. This corresponds to a detection limit of 1.5 bacteria per PCR. However, reliable PCR detection in woody host plant tissue was only obtained with PVP/PVPP‐treated sample extracts. Using E. amylovora‐spiked plant extracts and extracts of fruit tree shoots artificially infected with E. amylovora, the PCR detection sensitivity was determined to be 6.6 × 102 cfu mL–1 of extract. Starting from the plant samples, the PCR detection results were visualized on gels within 5 h.
Pathogenic variation in Xanthomonas campestris pv. phaseoli, the causal agent of common bacterial blight in Phaseolus beans
Authors: OPIO A. F. , ALLEN D. J. , TERI J. M.
Published: November 2003

A total of 93 isolates of Xanthomonas campestris pv. phaseoli was collected from five countries over a wide range of altitude (500–2320 m above sea level) in eastern Africa. Collections were made from a range of cultivars of the common bean (Phaseolus vulgaris), including known sources of resistance, as well as from wild alternative but symptomless hosts including Senna (Cassia) hirsuta and Digitaria scalarum. From these, 30 isolates were selected for detailed characterization. Although variation was found in parameters including phage type, the production of brown pigment in culture media and in‐vitro growth rate, there was little consistent relationship between these characters and pathogenic variation.

Studies of pathogenic variation among the 30 isolates on 20 genotypes of P. vulgaris revealed quantitative host non‐specific differences (aggressiveness). On tepary bean (P. acutifolius), however, the 30 isolates interacted differentially with the genotypes and eight distinct physiologic races of X. c. pv. phaseoli were defined, suggestive of an underlying gene‐for‐gene relationship.

Despite this apparent gene‐for‐gene interaction, resistance to common bacterial blight in P. vulgaris, derived from earlier use of P. acutifolius, has apparently remained non‐specific and essentially durable. It is suggested that, since levels of resistance already available within P. vulgaris provide adequate protection, bean breeders should resist the temptation to incorporate new complete resistance from P. acutifolius as it would risk destabilizing the host–bacterium relationship by introducing race‐specific resistance that is more likely to prove transient in agriculture.
Application of formulated rhizobacteria against root rot of field pea
Authors: XI K. , STEPHENS J. H. G. , VERMA P. R.
Published: November 2003

Formulations of bacterial biocontrol agents were evaluated for the control of pea root‐rot caused primarily by Pythium ultimum and Rhizoctonia solani, at different levels of disease severity in field trials. Pseudomonas fluorescens (strain PRA25) in a peat‐based formulation increased yield by 17% over the untreated, in a trial with light disease infection, and by 120% in another with moderate infection. Other bacteria including P. cepacia (strain AMMD) and fluorescent pseudomonads increased seedling emergence, and decreased disease incidence and severity, but with variable effects on yield when disease level was light to moderate. Biocontrol agents resulted in only limited control when disease was severe. Control with Captan did not differ significantly from that obtained with bacterial biocontrol agents. The application of Rhizobium granular inoculum together with PRA25 granules did not differ from other treatments in disease control, indicating that Rhizobium is compatible with biocontrol agents. The population dynamics of a fluorescent pseudomonad introduced into the rhizosphere in peat or granular formulation was monitored using an antibiotic‐resistant mutant marker strain. The bacterium in peat formulation established a considerably higher population than that in granular formulation in 1993 trials, and a slightly higher population in 1994 trials. The higher population may have been responsible for the efficiency of root colonization and the effectiveness of disease control.
Morphology, pathogenicity and isozyme variation amongst French isolatesof Leptosphaeria maculans recovered from Brassica juncea cv. Picra
Authors: SOMDA I. , RENARD M. , BRUN H.
Published: November 2003

The characteristics of 36 isolates of Leptosphaeria maculans originating from cv. Picra were investigated using cultural, pathogenicity and isozyme analyses in comparison with six known isolates of A‐ and B‐groups. Picra‐related isolates were similar to the three known B‐group isolates from Brassica napus using a cultural test. Two known B‐group isolates and 29 of the 36 Picra‐related isolates tested were aggressive on cv. Picra, whereas all the three known A‐group isolates were not. All the 42 isolates tested were aggressive onthe B. napus–B. juncea recombinant line MX and on B. napus cv. Westar. Phosphoglucose isomerase analysis showed two different patterns, separating A‐group known (fast band) from B‐group known isolates (slow band). All cv. Picra isolates displayed the slow band. Considerable differences in isoesterase patterns were found between known A‐ and B‐group isolates. Isolates recovered from cv. Picra displayed six different electrophoretic patterns, including that of the known B‐group isolates. Clusters of the 42 isolates, generated by UPGMA analysis based on similarity coefficients of electrophoretic types, matched the previous classification into A‐ and B‐groups, although two atypical Picra‐related isolates with a singular pattern clustered with the A‐group. The importance of these isolates for blackleg epidemiology and resistance breeding is discussed.
Immigration of the barley mildew pathogen into field plots of barley
Authors: O'Hara R. B. , Brown J. K. M.
Published: November 2003

Immigration of the barley powdery mildew pathogen (Erysiphe graminis f.sp. hordei) into field plots of the spring barley variety Tyra (carrying the resistance allele Mla1) was investigated. Spores were trapped from the top of the plot canopies, as well as from control plots of wheat with no barley nearby. Comparison of the frequencies of virulent and avirulent single‐colony isolates showed that the amount of immigration, relative to the amount of inoculum being produced within the plot, reduced very rapidly, until it could not be detected in the middle of the growing season (mid‐June).
Effects of wetness period and temperature on development of dark pod spot (Alternaria brassicae) on oilseed rape (Brassica napus)
Authors: HONG C. X. , FITT B. D. L. , WELHAM S. J.
Published: November 2003

In controlled environment experiments, when oilseed rape pods or leaves were inoculated with spore suspensions of Alternaria brassicae, the maximum disease incidence (proportion of pods or leaves diseased) increased as wetness period after inoculation increased from 4 to 24 h and as temperature increased to 20°C. There was a clear relationship between disease incidence on pods and incidence on leaves with the same wetness/temperature conditions. Logistic equations described the effects of wetness period after inoculation on disease incidence (number of pods or leaves infected) or disease severity (number of lesions on pods or leaves) using temperature‐dependent and tissue‐dependent parameters. The time from inoculation to the appearance of the first lesions was shorter on pods than on leaves at temperatures ≤15°C and wetness periods ≤12 h. Two‐dimensional response surface equations or simple interpolations from one‐dimensional equations were used to develop contour maps of expected disease incidence and severity, respectively, on leaves or pods to estimate the effects of different combinations of wetness period during infection and temperature on disease development.
Effects of wheat crop debris on the sporulation and survival of Pseudocercosporella herpotrichoides
Authors: JALALUDDIN M. , JENKYN J. F.
Published: November 2003

Three separate experiments showed that wheat tissue infected with the cereal eyespot fungus, Pseudocercosporella herpotrichoides, produced fewer spores in the presence of chopped wheat straw than when it was absent. This provides a possible explanation for earlier observations that there was often less eyespot in plots where straw had been incorporated than where it had been burnt. Sporulation on eyespot infected wheat tissue was not closely correlated with the viability of P. herpotrichoides, which could usually be isolated from infected tissue for some time after it had apparently lost the ability to produce spores. Many of the colonies that were isolated from such tissue also failed to sporulate under the conditions used but non sporulating colonies were less common amongst those isolated from tissue that had been mixed with chopped straw than from tissue that had not.
Splash dispersal of Pseudocercosporella herpotrichoides spores in wheat monocrop and wheat–clover bicrop canopies from simulated rain
Authors: Soleimani M. J. , Deadman M. L. , McCartney H. A.
Published: November 2003

Simulated rain was allowed to fall onto spore suspensions of Pseudocercosporella herpotrichoides. The resulting splash droplets were collected on horizontal traps at the bottom of a canopy and at 12 cm above treatments comprising no‐crop, wheat monocrop and a wheat–clover bicrop. The number of conidia collected on horizontal traps declined exponentially with distance from the inoculum source. The mean number of spores collected in the absence of any crop was twice that in a monocrop; in the monocrop it was twice that in the bicrop. Both splash droplet and spore deposition gradients were steeper in the monocrop treatment than in no‐crop, and shallower in bicrop than in monocrop. Evidence is presented that suggests the clover canopy acts as a secondary source for the redistribution of previously dispersed droplets and spores.
Diallel analysis of partial resistance to an Iranian strain of bacterial leaf streak (Xanthomonascampestris pv. cerealis) in wheat
Authors: EL ATTARI H. , SARRAFI A. , GARRIGUES S. , DECHAMP‐GUILLAUME G. , BARRAULT G.
Published: November 2003

Six wheat genotypes with wide genetic variability for resistance to bacterial leaf streak were crossed in diallel fashion to determine the inheritance of resistance to this disease. Parental genotypes and their F1 hybrids were inoculated at the second leaf stage with an Iranian isolate of Xanthomonas campestris pv. cerealis. Two experiments were undertaken in a controlled environment chamber. Results showed that the genotypes IBPT66, IBPT84 and IBPT34 had a high level of partial resistance to the disease. General and specific combining abilities presented several significant positive or negative values, showing the importance of both additive and dominant genetic control for partial resistance to this bacterial disease. The resistant line IBPT66 could be a good donor of partial resistance to bacterial leaf streak in wheat.
Response of foreign barley cultivars to barley yellow mosaic virus at different sites in China
Authors: CHEN J. P. , ADAMS M. J. , ZHU F. T. , WANG Z. Q. , CHEN J. , HUANG S. Z. , ZHANG Z. C.
Published: November 2003

About 90 barley cultivars mostly of European or Japanese origin, were grown for 2–5 years at eight sites in China where barley yellow mosaic virus was known to occur. The sites were selected because they had previously been used to screen breeding lines and some differences between them in cultivar response had been suspected. ELISA tests showed that symptomless plants were not infected by the virus and the proportions of plants with symptoms were therefore recorded as a measure of susceptibility. European cultivars carrying the ym4 gene, which confers resistance to the common European strain, were usually resistant at two sites but susceptible at the others, but one (cv. Energy) was resistant at all sites. Eleven of the Japanese cultivars showed differential responses between sites but there was no correspondence with strains recognized in Japan. There are probably several distinct Chinese strains but further experiments would be needed to identify them. The Japanese cultivars Chosen, Hagane Mugi, Iwate Mensury 2 and Mokusekko 3 seem to be resistant to all known virus strains and are probably the most useful for plant breeders.
Bioassays of glucosinolate‐derived isothiocyanates against postharvest pear pathogens
Authors: MARI M. , IORI R. , LEONI O. , MARCHI A.
Published: November 2003

The present study assayed the effect of six isothiocyanates (ITCs), produced by the enzymatic hydrolysis of glucosinolates, on fungal pathogens of pear. Sample pear fruits were artificially inoculated through induced wounds with conidial suspensions of Botrytis cinereaRhizopus stoloniferMonilinia laxaMucor piriformis or Penicillium expansum and were then treated with ITCs. Of the six ITCs tested, the ITC from glucoraphenin showed the highest effectiveness after 6 days at 20°C, against M. laxaB. cinerea and M. piriformis. The effectiveness of the ITC from glucoraphenin against M. laxa was assayed in two further trials to test the effect of ITC concentration on different concentrations of inoculum and to determine the duration of the curative effect of this ITC. ITC concentration directly affected fungus control capacity. The highest ITC concentration (3.6 mg mL−1) afforded pathogen control at the highest level of pathogen concentration (106 conidia mL−1) after 6 days at 20°C. Its curative effect was evident up to 40 h after inoculation.
Albugo candida staghead formation in Brassica juncea in relation to plant age, inoculation sites, and incubation conditions
Authors: GOYAL B. K. , VERMA P. R. , SPURR D. T. , REDDY M. S.
Published: November 2003

Maximum staghead formation was obtained in 26‐day‐old (growth stage [GS] 3.1) Brassica juncea plants by inoculating differentiating flower buds with a zoospore suspension of Albugo candida race 2 V; exposing apical meristem tissues by opening the flower buds with forceps proved more conducive to staghead formation. Inoculation of 35‐ and 45‐day‐old plants (GSs 4.1 and 5.0, respectively) produced fewer hypertrophies, mainly in isolated flowers. Inoculation of 7‐ and 13‐day‐old plants (GSs 1.0 and 2.1, respectively) did not produce any hypertrophied flowers, but did result in the production of hypertrophied branches at the first node on the main stem. In general, hypertrophies were initiated more readily under greenhouse conditions than in the growth chamber. Other Brassica hosts inoculated with A. candida race 2 V or 7 V at GS 31 showed similar rankings for staghead formation and leaf infection. The technique should prove useful in screening breeding lines for disease resistance, particularly staghead formation, the most damaging phase as far as yield loss is concerned.
Effect of split applications of fenpropimorph‐containing fungicides on sensitivity of Erysiphe graminis f.sp. tritici
Authors: ENGELS A. J. G. , MANTEL B. C. , DE WAARD M. A.
Published: November 2003

A field trial was conducted in the south of the Netherlands over a period of 3 years (1992–94) in order to test the effect of fenpropimorph‐containing fungicides on the sensitivity of Erysiphe graminis f.sp. tritici to fenpropimorph. In general, use of split applications resulted in a better protection against wheat powdery mildew than use of normal applications. This is ascribed to a better timing of the split applications. The sensitivity to fenpropimorph of the mildew population in plots treated with normal applications of both fungicides did not change during the growing seasons of the years investigated. In contrast, the sensitivity of the mildew population from plots treated with split applications of Corbel became significantly lower. A significantly lower sensitivity was also found in the mildew population from plots treated with split applications of Tilt Top in 1993 and 1994. These results indicate that split applications can increase the rate at which E. graminis f.sp. tritici can become less sensitive to fenpropimorph. Because maintenance of sensitivity of the pathogen population is valued highly, the split application strategy of fenpropimorph‐containing fungicides is not recommended for wheat powdery mildew control.
Association of Pythium coloratum and Pythium sulcatum with cavity spot disease of carrots in Western Australia
Authors: EL‐TARABILY K. A. , ST. J. HARDY G. E. , SIVASITHAMPARAM K.
Published: November 2003

All 170 Pythium isolates from carrot cavity spot lesions from a field in Western Australia were found to belong to either P. coloratum or P. sulcatum. All isolates of P. coloratum produced large, brownish‐black, water‐soaked and depressed lesions on mature carrots inoculated with agar plugs colonized by the pathogen. In comparison, only a few isolates of P. sulcatum produced lesions and these were small. In glasshouse trials, P. coloratum produced substantial and numerous lesions at an inoculum density of 0.5% (weight of millet seed‐based inoculum/weight of soil), whilst P. sulcatum produced few and small lesions at inoculum densities of 0.8 and 1% and none at 0.5%. This is the first record of P. coloratum as a causal agent of cavity spot of carrots.
Transmission and overseasoning of Diaporthe adunca on Plantago lanceolata
Authors: LINDERS E. G. A. , VAN DAMME J. M. M. , ZADOKS J. C.
Published: November 2003

To obtain a better understanding of the onset and the progress of epidemics caused by Diaporthe adunca on Plantago lanceolata we investigated the role of the asexual phase of the fungus not only in the transmission of the disease from season to season, but also in the spread of the fungus within the same season. Splash dispersal of conidia during rain episodes proved to be an effective method for the spread of the fungus. Conidial production by pycnidia present on scapes left on the ground during winter was delayed in comparison to that of pycnidia produced on greenhouse infected scapes, indicating that the fungus overwinters with immature pycnidia. Latent infections occurred in 8.3% of the seedlings which emerged from seeds originating from infected spikes. A scenario for the transmission and spread of the fungus is proposed.
Epidemics of Diaporthe adunca in experimental and in natural populations of Plantago lanceolata and the effect of partial resistance on disease development
Authors: LINDERS E. G. A. , VAN DAMME J. M. M. , ZADOKS J. C.
Published: November 2003

Epidemics of the splash‐dispersed pathogenic fungus Diaporthe adunca on its host, the perennial herb Plantago lanceolata, were followed during two consecutive years in transects at roadsides in the Netherlands. Epidemics of D. adunca were also studied on clones of a susceptible and a partially resistant genotype of P. lanceolata grown either in a pure stand or in a 1:1 mixture in small plots in the garden. The epidemics in the natural and experimental populations could be adequately described by logistic and Gompertz models, but large differences were found in final disease levels and relative growth rates. The effect of partial resistance on the epidemic in the mixture was less than in a pure stand, probably due to the provision of inoculum from the highly diseased susceptible genotype to the partially resistant genotype. In the garden focal and wind‐direction effects were seen. In the natural populations the epidemics developed from numerous primary infected scapes making foci and wind‐directions effects less conspicuous.
Factors affecting the susceptibility of six cocoa clones to Phytophthora palmivora (Butl.) Butler bark canker in Trinidad
Authors: OKEY E. N. , DUNCAN E. J. , SIRJU‐CHARRAN G. , SREENIVASAN T. N.
Published: November 2003

An assessment of canker incidence in six cocoa clones revealed IMC 67 to be least susceptible and TSH 1076 most susceptible among the clones tested (ICS 1, IMC 67, P 18, SCA 6, TSH 1076 and TSH 1188). These results were confirmed by greenhouse studies on budded plants using artificial inoculation. IMC 67 with the smallest canker lesion size was found to have the highest value (3.75 N/m2) for extra‐xylary tissue hardness while TSH 1076 with the largest lesion size had the lowest value (1.9 N/m2). Bark moisture content determination also showed lowest values for IMC 67 and highest for TSH 1076. Bark hardness and moisture content were highly correlated with canker resistance.
The use of the random amplified polymorphic DNA technique to identify mating groups in the Fusarium section Liseola
Authors: AMOAH B. K. , MACDONALD M. V. , REZANOOR N. , NICHOLSON P.
Published: November 2003

The random amplified polymorphic DNA (RAPD) technique was used to determine the mating groups of several members of the Fusarium section Liseola recovered from maize, rice and sorghum collected from different locations in Ghana. Three mating groups were identified, A, D and F, of which all A and F isolates were confirmed by mating studies. Fertile crosses were also obtained in crosses involving two of the isolates identified as belonging to the D population. Variability within the A population isolated from seeds and stem‐bases of maize was investigated to determine whether the sub‐structuring of this population was related to the host tissue from which the isolates were obtained. The relative merits of the RAPD procedure, compared to the mating procedure, for determining the mating affiliations of isolates and for more detailed analyses of isolates within a population, as well as its possible advantages over established RFLP methodologies are discussed.
Detection and identification of seed‐borne viruses from cowpea (Vigna unguiculata (L.) Walp.) germplasm
Authors: BASHIR M. , HAMPTON R. O.
Published: November 2003

Seedlings from 182 cowpea (Vigna unguiculata) pre‐introductions/germplasm accessions from 12 countries were tested under greenhouse conditions for six seed‐borne viruses. Twenty‐one (13.3%) accessions from eight countries were found to be seed‐infected with one of the three following viruses: blackeye cowpea mosaic (BlCMV) and cowpea aphid‐borne mosaic (CABMV) potyviruses, and cucumber mosaic cucumovirus (CMV). Natural seed transmission incidence of 0–6.9%, 0–13.3%, and 0–2.0% were determined for BlCMV, CABMV and CMV respectively.  Another set of 2930 cowpea germplasm accessions, mostly from Botswana and Senegal (Africa), were examined under field conditions for detection and identification of seed‐borne viruses. Only CABMV was detected in this material. Most of the lines were free from other viruses reported in cowpea seed. Eight isolates of BlCMV and 28 isolates of CABMV were derived from cowpea pre‐introductions/germplasm accessions evaluated under greenhouse and field conditions.
Occurrence of barley yellow dwarf viruses in some common grasses (Gramineae) in south west England
Authors: KENDALL D. A. , GEORGE S. , SMITH B. D.
Published: November 2003

The incidence and distribution of aphid transmitted barley yellow dwarf (BYD) viruses (PAV‐, RPV‐ and MAV‐like isolates) are described in 14 species of common pasture and hedgerow grasses from five localities of south‐west England during 1987 and 1988. Isolates were identified by indirect ‘sandwich‘ ELISA using the monoclonal antibodies MAC91, MAC92 and MAFF2. More infection was detected in 1987 than in 1988 but this was mainly due to a sharp decline at one site. Intensity of infection was greater in Poa annua and Lolium perenne populations than in most other species. BYD was not detected in Arrhenatherum elatiusElymus repensAgrostis canina and A. stolonifera. All three isolates of BYD were widespread. MAV was associated more with localities further north and RPV more with those further south. PAV was common only at the southern‐most site. This geographical distribution was reasonably consistent in both years. Given these trends, susceptible grass species fell broadly into three groups with respect to isolate frequency, those predominently infected by RPV and MAV (seven spp.), those equally infected by all isolates (two spp.) and a single species, Poa annua, infected mainly by PAV. Some implications of these findings for the epidemiology and control of BYD viruses are briefly considered.
Prestorage heat treatment reduces pathogenicity of Penicillium expansum in apple fruit
Authors: FALLIK E. , GRINBERG S. , GAMBOURG M. , KLEIN J. D. , LURIE S.
Published: November 2003

Penicillium expansum is one of the main postharvest pathogens of apples in Israel. Heating apple fruit inoculated with P. expansum for 96 h at 38°C completely inhibited decay development. Fruit held for 24 h at 42°C or 12 h at 46°C had significantly reduced decay after an additional 14 days incubation at 20°C, compared with unheated inoculated control fruit. Mycelial growth and percentage spore germination in vitro were inversely proportional to length of time of exposure to various temperatures. The ET50 for spore germination was 42, 34 and 20 h at 38, 42 and 46°C, respectively, while the ET50 for mycelial growth was 48, 44 and 36 h at those temperatures. When Penicillium spores were incubated on crude extract prepared from the peel of apple fruits held 4 days at 38°C, germ tube elongation was significantly reduced, while the walls of the tubes were thicker, compared with germ tubes from spores incubated on crude extract prepared from peel of non‐heated fruit. The evidence presented here supports the hypothesis that the effect of heating on the decay of apples caused by P. expansum is not only the result of direct inhibition of fungal germination and growth by high temperature, but is also partly due to the formation of an inhibitory substance in the heated peel.
Virulence spectrum in populations of the barley powdery mildew pathogen, Erysiphe graminis f. sp. hordei in Tunisia and Morocco in 1992
Authors: YAHYAOUI A. H. , REINHOLD M. , SCHAREN A. L.
Published: November 2003

The virulence of 57 single colonies of Erysiphe graminis f. sp. hordei from Tunisia and Morocco was investigated using the Pallas near‐isogenic differential set. Virulence patterns in general were similar in both countries. Va8, Va10+Du2, V41/145, VLa and VRu2 appear to be common in the region. The resistance alleles Mla7 and Mla9, in combination with other resistances, were highly effective against the isolates tested. No virulence against mlo and Mla9 + k was detected in Tunisia. No virulence on Mla7 and Mla9 was detected in Morocco. The frequency of virulence against several resistances was significantly higher in Morocco than in Tunisia. On the other hand, virulence against other resistances was higher in Tunisia than in Morocco. Three isolates from Morocco infected mlo to an extent greater than previously described. All pathotypes were unique. An attempt is made to interpret the results by comparison with pathotype evolution in Europe.
The occurrence of bean common mosaic necrosis virus in wild and forage legumes in Uganda
Authors: SENGOOBA T. N. , SPENCE N. J. , WALKEY D. G. A. , ALLEN D. J. , FEMI LANA A.
Published: November 2003

Bean common mosaic necrosis virus (BCMNV) was isolated from Centrosema pubescens, Crotalaria incana, Lablab purpureus, Phaseolus lunatus, Senna bicapsularis, S. sophera, Vigna vexillata and an unidentified Crotalaria species growing in Uganda. Thirteen distinct isolates were characterized using symptoms, pathogenicity in differential bean cultivars, serology, immunosorbent electron microscopy, and seed and aphid transmission. Some isolates conformed with the characteristics of previously described strains of BCMNV but others showed novel properties. All isolates reinfected the natural host from which they were obtained. The origin and ecological significance of these isolates is discussed.
Mycelial compatibility groups in Sclerotium cepivorum
Authors: EARNSHAW D. , BOLAND G. J.
Published: November 2003

Isolates of Sclerotium cepivorum from the Holland–Bradford Marsh, Ontario, Canada (n = 146) and other locations (n =23) were evaluated for mycelial compatibility in agar culture and by transmitted light microscopy. In compatible interactions, hyphae of paired colonies anastomosed without cell deterioration or death at the point of fusion. In some incompatible interactions, hyphae of paired colonies were initially similar to those of compatible interactions but were later followed by deterioration or death of the fused cells. Incompatible interactions were associated with a red–brown colour that, in mass, produced a dark line at the junction of the two colonies. In other incompatible interactions, hyphae were observed to bypass or repel each other without fusing. Compatible and incompatible reactions were used to define nine mycelial compatibility groups (MCGs) among the isolates examined. Among isolates from Ontario, no incompatibility responses were observed among isolates from individual fields (e.g. no intrafield variability) but two MCGs were found among isolates from different fields (e.g. interfield variability). Among isolates from other regions, seven additional MCGs were detected that consisted of one to eight isolates. Two isolates were variable in reaction and were not assigned to any MCG. Three isolates from Switzerland were compatible with MCG‐1 isolates from Ontario; and one isolate from Switzerland, two from England, two from New Zealand, and two from Australia were all intercompatible. The results establish that mycelial compatibility can be used to reflect genetic heterogeneity among isolates of S. cepivorum.
The response of different celery genotypes to infection by septoria apiicola
Authors: EDWARDS S. J. , COLLIN H. A. , ISAAC S.
Published: November 2003

A rapid and useful method of disease assessment, based on a visual key, was developed for leaf spot of celery, caused by Septoria apiicola. Details were provided by an assessment of percentage infection, number and type of lesions per plant and number of pycnidia per lesion. The lesion response was graded from 0 (resistant with no lesions) to 3 (susceptible with grey lesions, leaf chlorosis and numerous pycnidia). Assessments were performed on leaves attached to the plants as well as on detached leaves incubated in sealed Petri dishes, after inoculation with a standard spore suspension. Tests were carried out on currently popular celery varieties, lines of wild celery, hybrids of celery × wild celery and celery × parsley. Lesion response 0 was found on some lines of wild celery, lovage and parsley; response 1 on lines of wild celery; response 2 on hybrid celery × wild celery and on the commercial celery Giant Red; and response 3 on all of the remaining celery varieties tested (Monarch, Fenlander, Tall Utah and Galaxy). Detached leaves from the individual genotypes showed responses in an order similar to that of the attached leaves but the onset of the response in detached leaves was always more rapid, with fewer lesions and pycnidia. Analysis of leaf chlorophyll content from the different sources was made to establish any relationship between chlorophyll and resistance but none was found.
Production of cell‐wall polysaccharide degrading enzymes in carrot root tissues infected by Mycocentrospora acerina.
Authors: LE CAM B. , LEBRETON L. , MASSIOT P. , ROUXEL F.
Published: November 2003

Mycocentrospora acerina, the causal agent of liquorice rot of carrot roots, produces several cell‐wall polysaccharide degrading enzymes in vitro. To assess the involvement of these enzymes in tissue invasion, the production and localization of pectin methylesterases, polygalacturonases, pectate lyases and endoglucanases were measured in root tissue infected by M. acerina. Isoelectrofocusing studies demonstrated the production of three isoforms of pectin methylesterase in healthy tissue. In infected tissue, two isoforms already observed in the culture filtrate and two novel isoforms were detected. Tissue maceration was associated with in vivo production of pectin methylesterase and polygalacturonase, which were first detected on the second day whereas pectate lyase and endoglucanase activities were detected only from the fourth day after infection. Maceration was always detected ahead of the mycelium, indicating diffusion of these enzymes.
Biocontrol of seedborne Botrytis cinerea in chickpea with Gliocladium roseum
Authors: BURGESS D. R. , BRETAG T. , KEANE P. J.
Published: November 2003

An isolate of Gliocladium roseum proved highly antagonistic to Botrytis cinerea. Sporulation of B. cinerea on chickpea seed naturally infected or inoculated with B. cinerea was suppressed by seed treatment with conidial suspensions of G. roseum at 107 and 108 conidia/mL, respectively. Establishment of healthy seedlings in punnets (small trays) 5 weeks after sowing with inoculated seed was increased from 29.2% to 59.7% by treatment with G. roseum at 3×107 conidia/mL, and from 1.4% to 69.4% with G. roseum at 3×108 conidia/mL, the latter being equivalent to disease control by Thiram. There was no significant effect of Rhizobium on disease suppression by G. roseum, and treatment with G. roseum at 108 conidia/mL did not reduce nodulation. Amendment with culture filtrates of G. roseum did not affect the growth rate of B. cinerea on potato dextrose agar, indicating that constitutive production of an antibiotic is not involved in biocontrol. A selective medium was developed to enumerate propagules of G. roseum on seed recovered from soil. There was no significant change in the population of G. roseum on seed after incubation for 4 weeks in soil to which the isolate of G. roseum was indigenous.