bluuebunny/crossref_metadata_2025 huggingface dataset:
Biological control of southern blight disease of tomato caused by Sclerotium rolfsii with simplified mycelial formulations of Trichoderma koningii
Authors: LATUNDE‐DADA A. O.
Published: April 2007

Two simple formulations of an antagonistic strain of Trichoderma koningii were employed against southern blight disease caused by Sclerotium rolfsii in seedling, potted outdoor and field‐grown tomatoes (cvs. Ife No. 1 and Ibadan Local). Corn cob germling inoculum and mycelium powder of T. koningii significantly controlled (P≤0·05) symptoms of damping off, blight and wilting in both tomato cultivars. The populations of the antagonist increased from an initial 1 × 104 to about 1 × 106 colony‐forming units per g of soil in the protected plants. Moreover, sclerotial counts decreased significantly (P≤0·05) in these soils and those sclerotia found had been parasitized by T. koningii. Trichoderma‐protected plants were more vigorous than those in the other treatment categories. The significance of these results is discussed in relation to the use of Trichoderma in appropriately simplified formulations.
Screening for potential antagonists of Pseudocercosporella herpotrichoides, the causal agent of eyespot disease of cereals
Authors: CLARKSON J. P. , LUCAS J. A.
Published: April 2007

Bacteria isolated from wheat seedlings, plants or straw from several field sites were screened for antagonism towards the cereal eyespot pathogen Pseudocercosporella herpotrichoides on several media of differing nutrient status. Thirteen out of 348 isolates inhibited pathogen growth on low‐nutrient media and several also prevented spore germination or reduced germ tube extension. These were selected for further tests on wheat seedlings inoculated with the eyespot fungus. Twelve known bacterial antagonists of other fungal plant pathogens were tested in vitro using the same methods, and the majority showed some activity towards P. herpotrichoides. Selected isolates were equally inhibitory to both W and R pathotypes of the fungus. Effects of potential antagonists on disease development were assessed by scoring lesions or by counting the number of infection plaques formed by the fungus on leaf sheaths. Two isolates of Pseudomonas fluorescens, along with a commercial strain of Streptomyces griseoviridis, showed activity both in vitro and in subsequent infection trials with plants and may therefore be of potential value as antagonists of P. herpotrichoides.
An ultrastructural study of tomato roots inoculated with pathogenic and non‐pathogenic necrotrophic fungi and a saprophytic fungus
Authors: BESWETHERICK J. T. , BISHOP C. D.
Published: April 2007

Tomato cultivar Moneymaker was independently inoculated with Alternaria alternata, Cunninghamella elegans, Fusarium culmorum, F. oxysporum f.sp. lycopersici, F. oxysporum f.sp. pisi and Stromatinia gladioli and analysed ultrastructurally. The extent and amount of superficial fungal growth on tomato roots was similar but C. elegans, a saprophyte, was exceptional in that hyphae were not closely appressed to plant surfaces and did not adhere to plant cell walls.

In general, the type of plant responses to fungal colonization and infection were similar in all of the interactions studied, with the exception of C. elegans which did not infect tomato root tissue. The failure to penetrate tomato roots by C. elegans may have been associated with the lack of hyphal adhesion to plant cell walls. Migration of cytoplasm and wall apposition/penetration papilla formation were regularly observed in tomato root tissue beneath appressed hyphae and at sites of fungal infection. Specific cellular reactions in the exodermis, namely the formation of wall ‘inclusions’ and appearance of ‘sensitive’ cells, indicated that exodermal cells were particularly responsive to fungal challenge.

Fusarium oxysporum f.sp. lycopersici, a pathogen of tomato, invaded tomato root tissue more extensively than the other fungi inoculated onto tomato roots. Infection of tomato by the other fungi studied was variable, and the extent and success of fungal invasion was tentatively associated with their necrotrophic capability and typical host range.
Bacterial wilt resistance in tomato associated with tolerance of vascular tissues to Pseudomonas solanacearum
Authors: GRIMAULT V. , PRIOR P.
Published: April 2007

High populations of Pseudomonas solanacearum were detected in some, but not all stems of bacterial wilt resistant (‘CRA 66’, ‘Hawaii 7996’ and ‘Caraibo’) and susceptible (‘Floradel’) tomatoes. Latent infection, i.e. spread of P. solanacearum into xylem vessels, was confirmed in Caraibo, Hawaii 7996 and ‘CRA 66’ (the resistant parent of Caraibo). None of the plants within the resistant cultivars wilted and those cultivars were characterized by tolerance of the vascular tissues to high bacterial densities. In contrast, plants of cultivar Floradel showed consistent symptoms and wilted rapidly, with higher mean bacterial density than resistant cultivars. Bacterial wilt resistance was not associated with resistance to bacterial root invasion but with the capability of the plant to limit P. solanacearum colonization in the stem. The extent of bacterial colonization is proposed as a criterion to quantify tolerance, complementary to absence of external wilt symptoms used in breeding programmes for resistance.
Development of disease symptoms and fungal pathogens on shoot bases in continuous winter wheat, and effects of fungicides
Authors: BATEMAN G. L.
Published: April 2007

Field plots in three consecutive crops of winter wheat were sampled at approximately 2‐week intervals from April to July in 1989, 1990 and 1991. Culm and stem bases were examined for symptoms of eyespot, sharp eyespot and brown foot rot. The W‐type and R‐type of Pseudocercosporella herpotrichoides, P. anguioides, Fusarium culmorum, F. avenaceum and Microdochium nivale grown from this plant material on agar were identified. Eyespot was most severe in 1991, when plant development was least rapid following cool weather in late winter and the summer was relatively cool and wet. Sharp eyespot was most severe in 1990, which had a warm summer with moderate rainfall. The other warm summer, 1989, was drier and these conditions favoured late development of brown foot rot, associated mainly with F. culmorum which was scarce at other times. Sharp eyespot sometimes increased where prochloraz, which decreased eyespot, was applied. Distinct symptoms of more than one disease occurred less frequently on the same stem than expected from the individual total occurrences, but co‐occurrences of different fungi were often more frequent than expected. In July 1990, Fusarium spp. co‐occurred with R‐type, but not W‐type, P. herpotrichoides more frequently than expected, and in July 1990 and 1991 M. nivale and both W‐type and R‐type co‐occurred more frequently than expected. Fusarium spp. and M. nivale were more frequent, especially in the earlier samples, on nodes than on internodes, whilst P. herpotrichoides normally infected at the internodes. The results suggest that stems weakened or altered by a primary colonizer are often a suitable substrate for a secondary colonizer, often a Fusarium sp., which may begin infection at a distance from the original lesion and often not cause distinct symptoms itself.
Variation for virulence in Erysiphe fischeri from Senecio vulgaris
Authors: BEVAN J. R. , CRUTE I. R. , CLARKE D. D.
Published: April 2007

Variation for virulence was investigated in two populations of Erysiphe fischeri, the cause of powdery mildew of the common annual weed Senecio vulgaris (groundsel). Infection types were recorded on detached leaf segments from 50 inbred lines of S. vulgaris following inoculation with 24 single‐conidial‐chain isolates of E. fischeri (12 each from two UK sites; one, at Glasgow, located about 480 km north of the other, at Wellesbourne). Mean infection types for each isolate/line combination were categorized by applying several upper limits below which combinations were considered to be incompatible. Regardless of the limit applied, numerous specific virulence and resistance phenotypes could be discriminated. Virulence phenotypes were complex and all isolates were capable of colonizing and reproducing on the majority of groundsel lines. However, all isolates were completely avirulent (no reproduction) on at least one groundsel line, so no isolate was universally virulent. Plants of several groundsel lines exhibiting different resistance phenotypes were exposed to natural infection at Wellesbourne to act as mildew traps, to examine the virulence characteristics of the pathogen population. Common components of the fungus population colonized groundsel lines exhibiting resistance to only a few or none of the single‐conidial‐chain isolates. Rarer components of the pathogen population colonized groundsel lines with resistance to the majority or all of the isolates previously tested. These latter components of the fungus population also detected resistance in groundsel lines previously recorded as susceptible to all isolates.
Resistance to Erysiphe fischeri in two populations of Senecio vulgaris
Authors: BEVAN J. R. , CLARKE D. D. , CRUTE I. R.
Published: April 2007

The frequency and distribution of different specific phenotypes for resistance to Erysiphe fischeri was studied in two populations of the annual weed Senecio vulgaris (groundsel) one located in Glasgow, Scotland the other located about 480 km south at Wellesbourne, England. Progeny of individual plants from the two host populations were tested for their response to up to 10 different isolates of E. fischeri, five from each location; each isolate had a different specific virulence phenotype. Most plants in each sample were susceptible to all 10 isolates. The proportion of plants whose progeny were resistant to a particular isolate ranged from 1% to 10% with the exception of resistance to one isolate that occurred with a frequency of 37% at Wellesbourne. Overall, resistance to one or more of the 10 isolates appeared to be more common in the plant population sampled at Wellesbourne than at Glasgow. Of the total number of groundsel line/isolate combinations tested, 10% involving Wellesbourne plants and 2% involving Glasgow plants were incompatible, i.e. resistant/avirulent. Both groundsel populations tended to be dominated by one or two resistance phenotypes but they were nevertheless highly heterogeneous when less frequent resistance phenotypes were considered. This was particularly evident at Wellesbourne where 10 different resistance phenotypes were recorded amongst a total of 75 plants growing within an area of 1 m2.
Soil‐borne spores as a source of inoculum for wheat bunt (Tilletia caries)
Authors: YARHAM D.
Published: April 2007

Wheat bunt (Tilletia caries) has previously been controlled in the UK by routine seed treatment with organomercury. Recent examples are presented of unusual levels of infection due to soil‐borne inoculum. The recent infections may be due to unusually dry weather, favouring the survival of spores in the soil, or to the presence of a more persistent strain of T. caries.
Yellow mottle of tomatillo (Physalis ixocarpa) caused by physalis mottle virus
Authors: VALVERDE R. A. , CAN F. , RUSH M. C.
Published: April 2007

Tomatillo (Physalis ixocarpa) is being evaluated as a food crop in Louisiana. Preliminary studies indicate that virus diseases may be the major factor limiting production. A foliar mosaic and yellow mottle disease was found commonly affecting plants in experimental plots. The cause of the disease was identified as physalis mottle virus (PhyMV). The virus was identified by host reaction, serology and dsRNA analysis. Other viruses found less frequently included cucumber mosaic virus and tomato spotted wilt virus. The flea beetle, Epitrix cucumeris, transmitted PhyMV experimentally. The annual weed Physalis pubescens was found naturally infected with PhyMV near infected tomatillo.
First report of the canker pathogen Endothia gyrosa on Eucalyptus in South Africa
Authors: Van der WESTHUIZEN I. P. , WINGFIELD M. J. , KEMP G. H. J. , SWART W. J.
Published: April 2007

During country‐wide surveys of Eucalyptus plantations for Cryphonectria canker, cankers distinctly different from those usually associated with Cryphonectria cubensis were observed. These cankers were less severe and were exemplified by cracked and slightly swollen areas on the bark. Endothia gyrosa, a well‐known pathogen of woody plants including Eucalyptus spp., was consistently associated with these cankers. The pathogen is easily distinguished from C. cubensis by the presence of orange‐brown stromata and non‐septate ascospores. Inoculations on Eucalyptus grandis resulted in lesions similar to those observed on naturally infected trees. The disease associated with E. gyrosa is widespread in South Africa, and research is required to establish control strategies.
In vitro effects of temperature and wet periods on infection of oilseed rape by Alternaria brassicae
Authors: MRIDHA M. A. U. , WHEELER B. E. J.
Published: April 2007

The influence of temperature and duration of wet periods on infection of oilseed rape by Alternaria brassicae was studied on detached leaves and pods, leaf disks and intact seedlings. Infections increased with age of leaf and the interaction between temperature and leaf age was highly significant. On older leaves infection was optimal at 25°C. There were many infections also at 15, 20 and 29 C but relatively few infections at 10°C. On pods most infections were observed at 20 C, the highest temperature studied. Infection at each temperature increased progressively with duration of surface wetness. The minimum wet periods for infection of leaves were 3 h at 20–25°C, 4 h at 15°C, 6–9 h at 10 C and 12–24 h at 5 C and for infection of pods, between 6 h and 9 h at 10°C and 6 h (or less) at 15°C and 20 C. On leaves, dry periods interrupting wet periods limited lesion development to that obtained with the initial wet period only; on pods some further infections developed when pods were re‐wetted. Dry periods of 3 h and 6 h following the inoculation of pods reduced subsequent infection but there was no further reduction by longer periods of drying to 48 h.
Disease assessment of pea lines with resistance to foot rot pathogens: protocols for in vitro selection
Authors: GRETENKORT M. A. , HELSPER J. P. F. G.
Published: April 2007

Cultural conditions were optimized so that disease reactions of plantlets and callus tissue from partially resistant and susceptible genotypes of Pisum sativum could be differentiated when inoculated with Fusarium solani f.sp. pisi. Disease was assessed using both semi‐quantitative (disease score/fungal diameter) and quantitative methods (ergosterol assay).

After optimization of inoculum concentration and incubation period it was possible to differentiate the disease reactions of plantlets using disease scores and amount of ergosterol in the tissues.

Incubation period, temperature and the auxin added to the media were important in allowing differentiation of callus tissue cultures. These differences were visible by measurement of the diameter of fungal growth on the callus and the amount of ergosterol in the tissues, but not with disease scores.

The plantlet test was also applicable to the other foot rot pathogens Phoma medicaginis var. pinodella and Aphanomyces euteiches, allowing differentiation of the disease reactions of a partially resistant and susceptible genotype using disease scores. The ergosterol assay could be used to quantify infection caused by P. medicaginis var. pinodella, but this sterol was not detectable in mycelium of A. euteiches. In this fungus the presence of cholesterol was detected, which may be used to quantify infection.
Effects of Alternaria macrospora on the yield components of Pima cotton in Israel
Authors: SHTIENBERG D.
Published: April 2007

Effects of Alternaria leaf spot (caused by Alternaria macrospora) on the yield components of Pima cotton (Gossypium barbadense) were examined in four field trials, for the lower (< 30–50 cm), middle (30–50 to 70–90 cm) and upper (>70–90 cm) layers of the canopy. The influence of the disease on yield was determined by comparing measurements taken in fungicide‐treated plots with those taken in untreated plots. Alternaria‐induced defoliation was most severe in the lower canopy layer and gradually decreased towards the upper canopy layers. Significantly fewer bolls (26·0%) were picked in untreated plots than in fungicide‐treated plots, but differences in average boll size (reduction of 1·07%) among the treatments were non‐significant. The relationship between disease intensity and the loss of bolls was linear. Of the differences in yield between fungicide‐treated and untreated plots, 43·5% was observed in the lower canopy layer, 37·6% in the middle canopy layer and only 18·9% in the upper canopy layer.
Development of resistance to thiabendazole in Helminthosporium solani (silver scurf) as a result of potato seed tuber treatment
Authors: HIDE G. A. , HALL S. M.
Published: April 2007

Applying thiabendazole to potato seed tubers affected with silver scurf caused by Helminthosporium solani sensitive to thiabendazole decreased the severity of disease on progeny tubers at harvest, but about 50% of the isolates from these were resistant to the fungicide. The disease was not decreased when samples of the progeny tubers were treated with thiabendazole and planted in the following year, and the incidence of resistant isolates increased. Resistant isolates continued to be present when tubers were planted in the next 2 years without fungicide treatment. Treatment with a mixture of thiabendazole and imazalil also decreased the disease and fewer isolates were resistant than when treated with thiabendazole alone, although the proportion increased after treatment with the mixture in the following year. When seed tubers were infected with thiabendazole‐resistant H. solani, silver scurf on progeny tubers was not affected by thiabendazole applied to the seed tubers but was decreased by the mixture of thiabendazole and imazalil. Imazalil was equally effective against H. solani sensitive or resistant to thiabendazole.

Some isolates of H. solani had grey aerial mycelium and of 516 of these isolates obtained in 4 years 29% were resistant to the fungicide. Other isolates produced small, black colonies and their frequency increased with thiabendazole treatment of seed tubers. Of 244 of these isolates, 62% were resistant.
Variation in pathogenicity among single‐oospore isolates of Sclerospora graminicola, the causal organism of downy mildew in pearl millet*
Authors: THAKUR R. P. , SHETTY K. G.
Published: April 2007

Variation in pathogenicity (virulence and aggressiveness) of various single‐oospore isolates of Sclerospora graminicola, the causal organism of downy mildew in pearl millet, was studied. Oospore isolates were maintained as sporangial progenies on the susceptible pearl millet genotype 7042‐S through asexual generations. Twenty single‐oospore isolates obtained from samples of oospore inocula from three locations (the ICRISAT Centre, Coimbatore, and Hisar) in India, were tested for pathogenicity on 7042‐S. All the isolates were virulent on 7042‐S and they varied considerably, between and within locations, in infection efficiency (11–44% infection). The S. graminicola populations from the ICRISAT Centre and Hisar were significantly more aggressive than those from Coimbatore. Considerable variation was found among the 10 single‐oospore isolates from the ICRISAT Centre in infection efficiency and for latent period on a set of resistant and susceptible genotypes. Seven representative isolates, two each from the ICRISAT Centre (ICOS) and Coimbatore (CBOS), and three from Hisar (HSOS), exhibited variation in infection efficiency, sporangial production capacity, and oospore production rating on the susceptible genotypes 7042‐S and NHB 3. A pathogenic fitness index (PFI) was calculated for these isolates as the product of the reciprocal of the latent period × percentage infected seedlings × log10 sporangia per cm2 leaf area × oospore production rating. Aggressiveness of these isolates, measured as PFI, varied greatly. CBOS‐1 was the least aggressive with a PFI of 8·5 on NHB 3 and 69·6 on 7042‐S; the PFI of the other isolates ranged from 81·1 to 370·5. Downy mildew resistance in three of the five known resistant lines (700651, P7‐4 and 7042‐R) was consistently effective against all 10 ICOS isolates, indicating that the resistance of these three lines is likely to be more stable, at least at the ICRISAT location, than that of the other two resistant lines.
The histology of processes associated with the infection of resistant and susceptible wheat cultivars with Septoria tritici
Authors: COHEN L. , EYAL Z.
Published: April 2007

The development of Septoria tritici blotch on seedling leaves of the wheat cultivars Shafir (susceptible) and KVZ‐K4500 L.6.A.4 (resistant) was studied by light and fluorescence microscopy. Appressoria were usually located above a stomatal opening. Percentage germination, formation of appressoria and the pattern of invasion of the substomatal chamber were the same in the susceptible and resistant cultivars. Growth of hyphae was observed in the intercellular spaces of the leaf tissue of both cultivars.

Autofluorescence was more commonly observed in the resistant accession, as was the affinity for trypan blue dye. Some lignification of cell walls and sparse deposition of callosic materials occurred in the resistant line. Leaves of KVZ‐K4500 L.6.A.4, which macroscopically appeared pycnidia‐free, revealed microscopically the presence of arrested, immature, pycnidia‐like aggregations that did not progress further under prolonged environmental conditions conducive for pycnidial induction.
Genetic diversity of Pseudomonas solanacearum biovars 2 and N2 assessed using restriction endonuclease analysis of total genomic DNA
Authors: GILLINGS M. , FAHY P.
Published: April 2007

Biovars 2 and N2 of Pseudomonas solanacearum differ in their distribution and metabolic properties, the former generally being recovered from areas of cool climate (highland strains), whereas the latter is widespread in the tropical Amazon basin (lowland strains), and is metabolically more versatile. The relationships between 53 isolates of P. solanacearum conforming to biovar 2 or N2 were assessed using analysis of total genomic DNA digested with Hae III. Separation of these digests on 5% polyacrylamide gels and subsequent silver‐staining was shown to be a rapid and sensitive method of distinguishing between biovar 2 and N2 strains. Five restriction fragment length polymorphism (RFLP) groups could be identified which were further divisible into a total of 11 clonal lines. The majority of isolates examined were biovar 2 and of one clonal type (RFLP 26A), which was found in South America and is also a world‐wide pathogen of potato. All other RFLP groups were found only in South America, where they only occurred east of the Andes, with the exception of RFLP group 27 which was only found west of the Andes. The confinement of these closely related groups to South America supports the hypothesis that this continent was the source of the common potato bacterial wilt pathogen (RFLP 26A). The genomic DNA analysis clearly separated the highland (biovar 2) strains of P. solanacearum into the two subgroups previously recognized on the basis of nutritional and DNA hybridization data (RFLP groups 26 and 27), although these subgroups were shown to be closely related, having a similarity coefficient of 85%. The metabolically more versatile lowland strains (biovar N2) exhibited considerable diversity at the DNA level, which is at odds with reports of their uniform phenotype. To demonstrate the general utility of the total genomic DNA analysis, restriction patterns of a limited number of other biovars (1, 3 and 4) are also presented.
The effects of white clover mosaic virus on vegetative growth and yield of clones of S.100 white clover
Authors: POTTER L. R.
Published: April 2007

Ramet of eight clones of cultivar S.100 white clover were infected with white clover mosaic virus (WCMV) and compared with uninfected ramets. Infection reduced herbage yield over two cuts by between 25 and 75%, with a mean of 40% at both. Petiole length was reduced significantly by 8% at the first cut, but not at the second. There was an overall reduction of about 6% in mid‐rib length. The mean length of the longest stolon was reduced by about 20% at both cuts, but this did not reflect the reaction of whole plants as total stolon length was reduced by a mean of 43%, within a range of 25–75%. The mean dry weight of stolon was reduced by 47%, while stolon specific weight (weight per unit length) was reduced by 7%. The reduced leaf yield in WCMV‐infected plants was caused mainly by a reduction in stolon growth and not by a reduction in leaf size. Virus infection reduced the total number of growing points per plant by over 30%, but the number per metre of stolon was increased by over 20%. The total acid‐soluble carbohydrate content of stolons was unaffected.

For all growth parameters measured, there was considerable variation between the eight clones in their reaction to WCMV infection, most clones being affected detrimentally. In one clone, however, leaf dry weight yield of infected plants at the first cut was double that of healthy plants. At the second cut, both leaf and total stolon dry weights were greater by 40%, the total number of growing points by 80%, and the growing points per metre of stolon by 30%.
Natural infection of cucumber mosaic virus on Dianthus barbatus in India
Authors: RAJ AMINUDDIN S. K. , SRIVASTAVA K. M. , SINGH B. P.
Published: April 2007

Cucumber mosaic virus (serologically closely related to strains CMV‐C and CMV‐D) is reported for the first time as a natural infection of Dianthus barbatus causing leaf crinkle and stunting of plants. It was mechanically transmitted to healthy D. barbatus and Vaccaria pyramidata (Caryophyllaceae) and to other herbaceous test plants, and was also aphid‐transmissible from D. barbatus to D. barbatus. A convenient host for multiplication and purification of the virus was Nicotiana rustica. The presence of CMV was confirmed in D. barbatus and also in V. pyramidata by Western immunoblotting, but the concentration was too low in both the hosts to detect the virus by agar double diffusion tests.
Root rot of tree lucerne caused by Phytophthora nicotianae
Authors: BOTHA W. J.
Published: April 2007

Phytophthora nicotianae Breda de Haan was consistently isolated from rotted roots and discoloured vascular tissues of tree lucerne (Chamaecytisus palmensis). It was identified with the aid of total DNA restriction fragment length polymorphisms and morphological characters. Pathogenicity was demonstrated by inoculation. This is the first record of P. nicotianae on tree lucerne in South Africa.
The occurrence of a new genetic variant of Fusarium oxysporum f.sp. pisi
Authors: BØDKER L. , LEWIS B. G. , CODDINGTON A.
Published: April 2007

During a survey of root diseases of pea in Denmark, a new genetic variant of Fusarium oxysporum f.sp. pisi was isolated from vining peas in two widely separated geographical regions. In terms of pathogenicity on a set of differential pea lines, the Danish isolated closely resembled a race 6 isolate from the United States, DNA extracts of the isolates, restricted with the endonuclease HindIII, then probed with a homologous repetitive genomic fragment from the plasmid pDG106 by the Southern hybridization technique, gave a unique‘fingerprint’pattern distinctly different from the American race 6 and all other known races. When probed with pDG312, containing a homologous ribosomal repeat unit, the pattern obtained for the Danish isolates was indistinguishable from races 1, 5 and 6 but distinctly different from 2A and 2B. The Danish isolates represent a separate vegetative compatibility group because they are compatible with each other but incompatible with the other known races. In pigmentation the new variant resembled races 1, 5 and 6 for the first 8‐12 days, after which it began to secrete a dark purple pigment resembling that of race 2A and 2B. Until an additional line in the host differentials can separate the new genetic variant it should be considered a subgroup of F. oxysporum f. sp. pisi race 6.
Restriction fragment length polymorphisms in Fusarium oxysporum f.sp. dianthi and other fusaria from Dianthus species
Authors: MANICOM B. Q. , BAAYEN R. P.
Published: April 2007

DNA restriction fragment length polymorphisms (RFLPs) among 46 isolates of Fusarium oxysporum from Dianthus spp., representing the known range of pathogenicity in carnation, were determined using total DNA digested with the restriction enzyme HindIII and a previously described probe, D4. Distinct multiple band RFLP patterns were found, which delineated RFLP groups as follows: (i) F. oxysporum f.sp. dianthi races I and 8; (ii) F. oxysporum f.sp. dianthi races 2, 5 and 6; (iii) F. oxysporum f.sp. dianthi race 4; (iv) a recently described race of F. oxysporum f.sp. dianthi (wilt‐causing isolates from D. caryophyllus formerly classified as F. redolens); (v) wilt‐causing isolates from D. barbatus formerly classified as F. redolens and (vi), (vii) and (viii), three further recently described races of F. oxysporum f.sp. dianthi. Isolate groups derived from analysis of RFLPs were consistent with existing and recently described vegetative compatibility groups (VCGs) in F. oxysporum f.sp. dianthi, but not in all cases with races. Isolates of F. oxysporum and F. proliferatum not associated with wilt disease had simpler RFLP patterns (with one exception) that were not associated with VCGs.
The effect of elevated CO2 levels on the symptom expression of Colletotrichum gloeosporioides on avocado fruits
Authors: PRUSKY D. , PLUMBLEY R. A. , KOBILER I. , ZAUBERMAN G. , FUCHS Y.
Published: April 2007

Exposure of freshly harvested avocado fruits to different concentrations of CO2 (11, 16 and 30%) for different lengths of time (4, 17 and 26 h) affected the decay development caused by Colletotrichum gloeosporioides. The delay in symptom development depended on the treatment given, the temperature regime of the fruit and time after harvest for treatment application. The most appropriate treatment was the application of 30% CO2 for 24 h at a temperature of 20‐25 C on the day of harvest. Treatment for shorter time periods, at lower temperatures or 50 h after harvest, resulted in a reduced response and, in some cases, enhanced symptom expression. Concentrations of 11 or 16% CO2 were less effective than 30% CO2 as the fruits became more mature. It is concluded that treatment of avocado fruits with high levels of CO: for a short period has the potential to provide an alternative means of controlling anthracnose.
Glasshouse and field evaluation of cowpea lines for partial resistance to Phytophthora vignae
Authors: DAVIS R. I. , IRWIN J. A. G. , IMRIE B. C.
Published: April 2007

The reaction of cowpea lines to naturally occurring Phytophthora vignae in the field was studied in three trials over the period 1987–89 with the aim of identifying and characterizing lines with partial resistance. Seven lines (CPI 84853, CPI 84851, CPI 65393, CPI 77359, CPI 78209. CPI 78213 and cultivar Blackeye 5) were found to be partially resistant. Partial resistance was assessed by calculating disease incidence, disease severity, time lag before onset of disease, relative area under the disease progress curve and apparent mortality and infection rates. Significant differences in some of the characters further divided the partially resistant lines into different groups. It was concluded that the characters found to be most useful in the differentiation of relative levels of partial resistance were final percentage infection, and final percentage of plants with non‐killing lesions. There were also significant correlations between these variables within and between years, although the relative rankings of some of the lines changed between years. Overall, CPI 84853 and CPI 65393 showed higher levels of partial resistance in the field than the remaining lines. In general, the partially resistant lines gave variable reactions following hypocotyl inoculation with P. vignae. There were clear indications of host‐isolate interactions, suggesting that partial resistance may be no more durable than complete resistance for this particular host‐pathogen interaction.
Susceptibility to ergot in Zimbabwe of sorghums that remained uninfected in their native climates in Ethiopia and Rwanda
Authors: FREDERICKSON D. E. , MANTLE P. G. , DE MILLIANO W. A. J.
Published: April 2007

Forty‐four local Ethiopian and Rwandan sorghums (Sorghum bicolor) were observed to remain free of ergot, or had only low incidence, in their natural equatorial latitudes and were potentially of interest, in the design of male‐sterile lines for F1 hybrid breeding, if they possessed a physiologically based resistance mechanism. These sorghums were therefore also investigated under natural and artificial disease pressures in Zimbabwe where unadapted development and inappropriate long daylength prevented flowering in 18 accessions. Of the remaining 16 Ethiopian and 10 Rwandan accessions which flowered, only one from each country remained free of ergot. The susceptibility expressed was ascribed to observed asynchrony of stigma exsertion with anthesis. In the Rwandan accession that persistently remained free of ergot in Zimbabwe, histology of ovules showed pollination before floret gaping, so that a general principle of disease escape due to efficient pollination is proposed for the Ethiopian and Rwandan sorghums in their native climates. The findings emphasize that cleistogamy is a desirable character for avoiding ergot infection in self‐fertile sorghums and suggest that the Ethiopian and Rwandan sorghums may not generally be useful for breeding ergot‐resistant male‐sterile female lines. However, a few accessions deserve more detailed study as a potential genetic resource, before a firm conclusion that all apparent resistance is disease escape owing to efficient pollination.
Restriction fragment length polymorphisms (RFLPs) and the relationships of some host‐adapted isolates of Verticillium dahliae
Authors: OKOLI C. A. N. , CARDER J. H. , BARBARA D. J.
Published: April 2007

The relationships of two host‐adapted pathotypes of Verticillium dahliae have been examined at the molecular level using restriction fragment length polymorphisms. Isolates obtained from and adapted to Mentha×piperita (peppermint), which were presumed to be haploid, formed a distinct subspecific group (referred to as M) related to the previously described non‐host‐adapted subspecific group A of V. dahliae. The limited molecular variation found among the four group M isolates was not related to geographic origin. Isolates from several cruciferous hosts (and one from Beta vulgaris (sugar beet)), which are thought to be natural, stable diploids, formed another distinct group (referred to as D) that was markedly different from all previously described subspecific groupings in both V. dahliae and V. alboatrum. This group of isolates might better be regarded as a separate species. Again, only limited variation was found within the D group. Polymorphisms revealed by two probes distinguished two isolates derived from Brassica rapa (Chinese cabbage) from the six other isolates (four from Brassica napus (oilseed rape) and one each from Raphanus raphanistrum (wild radish) and Beta vulgaris).
Changes in morphology and measurement of cytokinin levels during the development of witches' brooms on cocoa
Authors: ORCHARD J. , COLLIN H. A. , HARDWICK K. , ISAAC SUSAN
Published: April 2007

The anatomy of diseased stems from brooms induced on cocoa (Theobroma cacao) by the fungus Crinipellis perniciosa was examined using the scanning electron microscope, and the amounts of selected cytokinins were measured by immunoassay.

Although the diseased stems were wider in diameter with a lower dry weight:fresh weight ratio than stems of healthy plants, the overall internal organization of tissues remained unchanged, and all the cell types were present. However, the vascular tissue was less differentiated in diseased stems since xylem vessels were absent and the ratio of phloem fibres and sieve tubes to phloem parenchyma was reduced. Cell sizes in diseased stems were larger for all tissues but cell numbers were unchanged except for xylem where fewer cells were seen.

Cytokinins (zeatin, zeatin riboside, isopentenyl adenine and isopentenyl adenosine) were measured in healthy plants and diseased stems at specific stages of disease development. Of these cytokinins only zeatin riboside was present in significantly greater amounts in diseased tissue. The likely role of plant growth regulator balance in stem enlargement and proliferation in witches' broom disease of cocoa is discussed.
Characterization of Spanish isolates of Pseudomonas corrugata from tomato and pepper
Authors: LOPEZ M. M. , SIVERIO F , ALBIACH M. R. , GARCIA F , RODRIGUEZ R.
Published: April 2007

Pseudomonas was isolated from tomato plants with pith necrosis collected from different areas in Spain and from pepper plants with pith necrosis in Tenerife (Canary Islands). Cultural, biochemical and physiological characteristics of isolates from both hosts were similar to those of the type strain of P. corrugata. Serological heterogeneity was observed among isolates of P. corrugata in immunofluorescence tests. A plasmid of more than 273 MDa was detected in all the isolates. Inoculation of pepper and tomato plants with isolates from both hosts caused similar pith necrosis. This is apparently the first report of P. corrugata on pepper.
The effect of leaf age on infection of Coffea genotypes by Hemileia vastatrix
Authors: COUTINHO T. A. , RIJKENBERG F. H. J. , van ASCH M. A. J.
Published: April 2007

The age of a leaf at the time of inoculation affected both development of infection structures on the leaf surface and subsequent sporulation. In the case of the susceptible genotypes, cv. Caturra and line NC‐169, there was a decrease in the number of appressoria formed, with an increase in age of fully expanded leaves. On the selected resistant line, NP‐547, significantly fewer appressoria were formed on the fourth leaf pair than on younger or older leaf pairs. Appressoria were formed significantly more readily over stomata of leaf pairs one, two, three, four and six than over five and seven of the susceptible selections. On the youngest leaf pair a significantly large percentage of appressoria formed away from stomata compared with the percentages obtained for older leaf pairs, where a large proportion of germinated uredospores did not form appressoria. The reaction type of the susceptible genotypes was a greater value on younger than older leaf pairs, and the reverse was true of the resistant genotype. The latent period (inoculation to sporulation) was shorter on NC‐169 than on cv. Caturra. No uredospores formed on NP‐547. Uredosorus density decreased with an increase in leaf age on the susceptible genotypes.
Effects of leaf wetness and temperature on late leaf‐spot infection of groundnut
Authors: BUTLER D. R. , WADIA K. D. R. , JADHAV D. R.
Published: April 2007

Experiments are described to quantify the effects of temperature and leaf wetness duration on infection of groundnut by Phaeoisariopsis personata. Temperature response curves for conidial germination and infection were similar, with optima close to 20°C and minimum and maximum temperatures of about 8°C and 34 C, respectively. The effect of temperature on infection between 15°C and 26°C was slight. Lesions developed only if the leaf wetness period exceeded about 20 h, and the total wetness period necessary for maximum infection exceeded 160 h. The number of lesions resulting from a fixed amount of inoculum was several times greater if leaves were exposed to alternate wet and dry periods (intermittent wetness), compared with continuous wetness. With intermittent wetness the length of the dry period had little effect on the number of lesions, providing it exceeded 2 h. The response curve relating total wetness periods to lesion density was an exponential asymptote.
The biological characteristics of dicarboximide‐resistant isolates of Monilinia fructicola from New Zealand stone‐fruit orchards
Authors: ELMER P A. G. , GAUNT R. E.
Published: April 2007

Dicarboximide‐resistant isolates of Monilinia fructicola were detected in New Zealand stone fruit orchards in 1985. The EC50 values of resistant isolates ranged from 3 to 217 mg a.i./l iprodione, compared with 0‐3 to 0‐7 mg a.i./l for sensitive isolates. The degree of dicarboximide resistance was maintained over nine generations in fruit tissues in most isolates, but in four isolates there was a significant decline. Three resistant and two sensitive isolates were selected for further study on agar and host tissues. Resistant isolates caused disease, grew and sporulated as well as sensitive isolates on flowers not amended with dicarboximide fungicides, but some were less fit on fruit. The pathogenicity and spore production of a resistant strain on flowers was reduced significantly by dicarboximide applied prior to pathogen inoculation. Fitness of isolates on flowers and on fruit was poorly correlated. Resistant isolates were significantly less competitive than sensitive isolates when mixed inocula were applied to flowers and fruit. The relative performance on flowers and fruit was not a reliable indicator of competitive ability.
Differentiation of Mediterranean plum pox virus isolates by coat protein analysis
Authors: LÓPEZ‐MOYA J. J. , CANTO T. , LÓPEZ‐ABELLA D. , DÍAZ‐RUÍZ J. R.
Published: April 2007

Six isolates of plum pox potyvirus from different Mediterranean countries were compared by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), peptide mapping and Western blotting after improved purification of virions using a protease inhibitor cocktail that reduced coat protein degradation. One isolate (Spanish isolate 3.3 from plum) differed from the others in possessing a smaller coat protein (approximately 34 instead 36 kDa) with a possible deletion in the surface‐exposed amino‐terminal region. Infectivity of the viruses after proteolysis, assessed using a local lesion host, was significantly reduced. Protease digestion conditions were established to generate a 28 kDa resistant core of the viral coat protein. Such conditions (longer incubation times or an increase in the enzyme concentration) differed from the milder ones reported for other potyviruses. Implications of the results in relation to the production and screening of virus‐specific monoclonal antibodies are discussed.
Population dynamics of Fusarium species on oil palm seeds following chemical and heat treatments
Authors: FLOOD J. , MEPSTED R. , COOPER R. M.
Published: April 2007

Fusarium oxysporum f.sp. elaeidis may be present naturally on or within oil palm seeds, thus there is a risk of introducing the disease into previously wilt‐free regions. A low proportion of infested seed was shown to give rise to infected plants. Populations of Fusarium spp. on seeds significantly declined after routine processing to induce seed germination, but the pathogen was not eradicated. However, vacuum infiltration and soaking for 7 days with captafol effectively eradicated the pathogen. The significance of F. oxysporum on oil palm seed as a potential inoculum source is discussed.
Sensitivity of Fusarium oxysporum f. sp. cubense to phosphonate
Authors: DAVIS A. J. , SAY M. , SNOW A. J. , GRANT B. R.
Published: April 2007

Phosphonate (0.1 mM) significantly reduced growth of Fusarium oxysporum f. sp. cubense (Foc) race 4 grown at an optimal phosphate concentration of 0.3 mM in vitro. At higher phosphate concentrations, closer to physiological conditions within the plant, the sensitivity of Foc race 4 to phosphonate was greatly reduced, with 25 mM phosphonate required to reduce growth by 50% at 1 mM phosphate. Two isolates of Fusarium oxysporum f. sp. dianthi and another race of Foc, race 1, were shown to be similar to Foc race 4 in their sensitivity to phosphonate, while another species of Fusarium, F. avenaceum, was more sensitive to phosphonate in vitro.
Comparison of disease progress curves for yam anthracnose (Colletotrichum gloeosporioides)
Authors: SWEETMORE A. , SIMONS S. A. , KENWARD M.
Published: April 2007

The incidence and severity of foliar anthracnose, caused by Colletotrichum gloeosporioides, were recorded for seven fields of yams (Dioscorea alata var. White Lisbon) in Barbados over a complete growing season. A scoring system was developed to estimate severity, placing the emphasis on the earliest, least visible stages of the disease. Disease progress curves were described in terms of the logistic model and the effects of site and leaf age on the parameters as well as on disease at tuber bulking were analysed. Differences between sites indicated that disease was more severe in areas of higher rainfall. In severe epidemics, disease predominated on young leaves. Fungicides applied sufficiently early can delay the onset of disease and slow the rate of disease progress.
Pseudomonas syringae pv. syringae on pepper seedlings in Italy
Authors: BUONAURIO R. , SCORTICHINI M.
Published: April 2007

Pseudomonas syringae pv. syringae causing leaf spot on pepper seedlings grown in a plant bed is reported in Italy for the first time. The pathogen was identified by means of biochemical, physiological and pathogenicity tests as well as by SDS‐polyacrylamide gel electrophoresis of whole‐cell proteins. The bacterial isolates showed positive for ice nucleation and biocide production.
A further record of the New Zealand flatworm Artioposthia triangulata (Dendy) in England
Authors: BOAG B. , NEILSON R. , PALMER L. F. , JONES H. D.
Published: April 2007

Studies have shown the New Zealand flatworm to be a predator of earthworms and to be widely distributed throughout most of Ireland and Scotland. Except for one record in 1965, it had not been found in England until, in December 1992, it was positively identified from a garden centre near Manchester. Viable and empty egg capsules were also found suggesting that it had reproduced and become established in that nursery. During 1993 other confirmed reports were received from Yorkshire and East Anglia, indicating that it may be able to survive and multiply across large areas of England.
Occurrence of oat stem rust in west Wales
Authors: RODERICK H. W. , CLIFFORD B. C. , JONES J. E.
Published: April 2007

The first significant occurrence of stem rust (Puccinia graminis Pers, ssp, graminis var, stakmanii Guyot, Massenot & Saccas ex, Urban) on spring oats (Avena sativa L.) in west Wales, UK is reported.
Choanephora blight and alternaria leaf spot of Amaranth in Tanzania
Authors: TERI J. M. , MLASANI D. K.
Published: April 2007

A leaf blight incited by Choanephora cucurbitarum and a leaf spot incited by Alternaria amaranthi on cultivated amaranth, Amaranthus cruentus, are described. This is a new host record for C. cucurbitarum, and A. amaranthi is a new record for Tanzania. Additional hosts of C. cucurbitarum are listed.
Appropriate bacterial identification systems for small plant‐pathology laboratories overseas incorporating the Biolog method
Authors: BLACK R. , SWEETMORE A.
Published: April 2007

Diagnostic services in developing countries are severely limited by the availability of funding and trained personnel. While common fungal pathogens can be identified with minimal equipment and media, the conventional methods for identification of bacterial pathogens are time‐consuming and require a wide range of costly media and reagents. In addition, excessive time and resources are often devoted to the identification of contaminating saprophytic bacteria. The Biolog system for identifying bacteria by metabolic profiles has been evaluated and adapted for use in routine diagnosis in small plant pathology laboratories overseas. Although Biolog is costly, it can be combined with a system for the preliminary identification and elimination of non‐pathogens using a limited number of conventional tests. The database of Gram‐negative profiles supplied by Biolog needs to be supplemented by user‐defined database(s). Bacterial Identifier software (Blackwell Scientific Publications) is advocated as a cost‐effective alternative.