bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection and localization of viruses in orchids by tissue‐print hybridization
Authors: CHIA TET‐FATT , CHAN YANG‐SUN , CHUA NAM‐HAI
Published: April 2007

A tissue‐print hybridization assay for the detection and localization of viruses in orchids is described. Orchid leaves were cut transversely and the cut surfaces were printed on to nitrocellulose paper. Because orchid leaves are often succulent, there is excellent transfer of plant sap to the membrane, resulting in clear tissue prints. The nucleic acid on the nitrocellulose membrane was then hybridized to radio‐labelled cDNAs of cymbidium mosaic virus (CyMV) and odontoglossum ringspot virus (ORSV), and the viruses were detected by autoradiography. The assay was able to detect as little as 20 pg of purified virus, which is 2–3 orders of magnitude more sensitive than the enzyme‐linked immunosorbent assay (ELISA) for CyMV. When tissue prints derived from different parts of the plants were used for hybridization, the method was able to show the distribution of viruses within the plants. On the basis of its sensitivity and ease of use, this method should find wide application in the detection and localization of viruses in orchids as well as in other succulent plants.
The use of antioxidants (free radical scavengers) to control grey mould (Botrytis cinerea) and white mould (Sclerotinia sclerotiomm) in various crops
Authors: ELAD Y.
Published: April 2007

Eighteen free radical scavengers (antioxidants) were tested for their ability to control grey mould. Most of the compounds reduced disease significantly in at least one of the test hosts–leaves of tomato, pepper, Senecio sp., bean, eggplant, or rose flowers; however, the effective concentration varied between 0.1 and 100 mm. Selected antioxidants were tested further. Butylated hydroxy toluene (BHT), tannic acid, ascorbic acid and dimethyl sulfoxide (DMSO) at a concentration of 1 .0 mm controlled grey mould of tomato fruits. All these compounds except BHT controlled the disease on cucumber fruits. Antioxidants affected Rhizopus stolonifer on grape berries but not Botrytis cinerea or Aspergillus spp. Some combinations of antioxidants were found to be more effective than either compound alone when tested on pepper or tomato. The synergists ascorbic acid and citric acid improved the control activity of BHT, propyl gallate, benzoic acid and tert‐butylhydroquinone on tomato leaves. Ethylene production was inhibited in tomato leaves treated with propyl gallate, ascorbic acid and benzoic acid, but not in pepper leaves. Ethephon or H2O2 increased the severity of grey mould on leaves of Senecio sp. Their effect was controlled by BHT and benzoic acid or by BHT, respectively. Four to six compounds reduced linear growth of B. cinerea isolates in culture at a concentration of 1.0 mm, and six more compounds were effective at 10.0 mm. However just five compounds inhibited conidial germination at the high concentration alone. Gluconic acid lactone, thiourea and propyl gallate reduced Sclerotinia sclerotiomm on lettuce by 51‐76%. The multiple activity of antioxidants on the host plant interaction is discussed.
Microscopy of invasion of red clover roots by Trichocladium basicola, and effects of benomyl and prochloraz
Authors: NAN Z. B. , LONG P. G. , SKIPP R. A. , HOPCROFT D. H.
Published: April 2007

Roots of red clover seedlings grown on plates of water agar, or water agar containing benomyl or prochloraz, were inoculated with conidia of Trichocladium basicola and examined by light and transmission electron microscopy. Penetration of host epidermal cells occurred from about 16 h after inoculation of untreated or fungicide‐treated seedlings. Intracellular hyphae were constricted at septa and had a beaded appearance. They invaginated the host plasmalemma, but had no obvious deleterious effect on the cytoplasm until they had grown to fill much of the lumen, when host cells degenerated and died. As colonization of the cortex progressed, straight, unconstricted hyphae were formed and from these reproductive hyphae developed, which produced endoconidiophores and chlamydospores on the root surface. Penetration of host cell walls appeared to involve localized action of fungal enzymes. Papillae were often found at sites of penetration, but these rarely obstructed fungal development. Seedlings treated with prochloraz had fewer sites of fungal penetration, and fewer cells in the beaded hyphae than untreated seedlings or those treated with benomyl. Both fungicides caused abnormalities in fungal ultrastructure. Hyphae treated with benomyl were often found to contain lomasomes, while those treated with prochloraz had thickened, fragmented walls, and disorganized cell contents.
The effect of methyl bromide fumigation on rhizomania inoculum in the field
Authors: HENRY C. M. , BELL G. J. , HILL S. A.
Published: April 2007

The first outbreak of rhizomania disease in the UK occurred in 1987 and was limited to a single sugar‐beet crop in Suffolk. In an attempt to prevent the spread of this disease, the crop was first destroyed by herbicide. In 1988, to reduce the level of rhizomania still present in the soil, the field was treated with methyl bromide at a rate of 900 kg/ha prior to seeding for permanent pasture. Levels of methyl bromide were monitored during the fumigation. A mean concentration time product of 5500 mgh/1 was achieved after 72 h at the soil surface and of 3300‐4100 mg‐h/1 at a soil depth of 0.3 m after 24 h. Soil samples were taken from five plots across the field before and after fumigation. In the plot with the highest initial inoculum levels, further samples were taken at three depths down to 0.61 m. Sugar‐beet seedlings were grown in all soil samples as a bait test for rhizomania inoculum. The presence or absence of Polymyxa betae was observed by microscopical examination, and an enzyme‐linked immunoassay was used for the detection of beet necrotic yellow vein virus (BNYVV). The results showed that the methyl bromide treatment had reduced rhizomania inoculum and BNYVV in the soil to levels that were undetectable by the procedures used.
Observations on swimming pattern and morphology of secondary zoospores of Spongospora subterranea
Authors: MERZ U.
Published: April 2007

Secondary zoospores of Spongospora subterranea were observed during and after emergence from sporangia using a light microscope, video equipment and scanning electron microscopy. Freshly discharged zoospores showed rapid movements and sudden changes in direction. Electron micrographs of secondary zoospores showed a lateral insertion of two flagella at an angle of 180o to each other. A biflagellate contaminant appeared to be distinguishable on the basis of its morphology and manner of swimming.
Isolation of mycoparasite Verticillium biguttatum from sclerotia of Rhizoctonia solani in the United Kingdom
Authors: MORRIS R. A. C. , COLEY‐SMITH J. R. , WHIPPS J. M.
Published: April 2007

Verticillium biguttatum was isolated from sclerotia of Rhizoctonia solani removed from black scurf‐infected potato tubers which had been field‐grown in the UK. Two isolates were identified by means of morphological and physiological characteristics, together with their ability to overgrow cultures of R. solani. A Dutch isolate M73 was used for comparison.
Disease‐yield relationship in barley.
Authors: WRIGHT A. C. , GAUNT R. E.
Published: April 2007

The effect of disease on growth and yield of two barley cultivars sown at different times and in different years was investigated in New Zealand. The data were used to develop yield‐loss models based on both disease severity (measured as green leaf area) and yield target (estimated by duration of crop growth). Disease influenced yield differently in Triumph and Sonya barley (spring and winter types, respectively), and yield components were affected to different degrees. Empirical yield‐loss models for individual cultivars, sowing dates and seasons had different slope values, and the best models were based on measurements of disease at different growth stages. Combined models were less significant and explained less variation in yield than the individual models. Models which included the duration of crop growth as an estimate of yield target improved the fit to the data. Empirical models were specific to cultivar, sowing date and season, suggesting that they were not applicable in the varying conditions tested. The inclusion of estimated yield target improved the general applicability of models, and provided a method of using models in crops sown at different times and in different seasons, without measuring yield target directly.
Generation of a ribosomal DNA probe by PCR and its use in identification of fungi within the Gaeumannomyces‐Phialophora complex
Authors: WARD E. , GRAY R.M.
Published: April 2007

The polymerase chain reaction (PCR) was used to amplify a ribosomal DNA fragment from Gaeumannomyces graminis. This fragment was labelled and tested for its usefulness as a probe in restriction fragment length polymorphism (RFLP) studies of fungi within the Gaeumannomyces‐Phialophora complex. When the probe was hybridized to Eco RI digests of DNA from these fungi, there were consistent band pattern differences between the three varieties of G. graminis (tritici, avenae and graminis). This method of probe production, which is more rapid than many others currently used, has considerable potential for use in the identification of these organisms, and may also be applicable to other groups of fungi.
Variation in the resistance of Vicia faba to Ascochyta fabae in relation to disease development in field trials
Authors: MAURIN N. , TIVOLI B.
Published: April 2007

The epidemic development of Ascochyta fabae in artificially infected field trials was studied in order to define resistance criteria and assess the variation in resistance of infected lines of faba bean. Large differences were demonstrated among French winter lines during the 1985/86 and 1986/87 growing seasons. All the scoring systems allowed the differentiation of very susceptible and resistant material, but disease indices, which account for the number and intensity of lesions, were more precise. The different phases of the epidemic are described on the basis of the variation in disease incidence on foliage and on pods during the 1986/87 cropping season in Brittany. There were three phases in disease development: initiation, spread throughout foliage, and pod infection, and these were all influenced by host resistance. On a very susceptible line, the disease spread was seen as an increase in the number and size of lesions and rapidly developed up the plant. Low disease indices observed on the resistant line 29 H were due to the small size and low frequency of lesions, resulting in a reduced area of foliage affected.
Resistance to thiabendazole inFusariumspecies isolated from potato tubers affected by dry rot
Authors: HIDE G. A. , READ P. J. , HALL S. M.
Published: April 2007

Fusariumspecies obtained from stored potato tubers affected with dry rot were grown on agar containing thiabendazole. All 40 isolates of F. coeruleum and 60 isolates of F. avenaceum tested were sensitive to the fungicide, but 68% of the 85 isolates ofF. sulphureumand one isolate ofF. culmorumwere classified as resistant. When isolates were made from dry rots on tubers that had been treated with thiabendazole during loading into store, all 81 isolates ofF. sulphureumwere resistant, whereas all the isolates ofF. coeruleum(25),F. avenaceum(4) andPhoma foveata(10) were sensitive. Resistance was not found in five isolates ofCylindrocarpon destructans.All theFusariumspp. were sensitive to imazalil and were pathogenic when inoculated into potato tubers. Resistant and sensitive isolates ofF. sulphureumcaused rots of similar size.
Botryodiplodia dieback of Mimosa pigra, a noxious weed in northern Australia
Authors: WILSON C. G. , PITKETHLEY R. N.
Published: April 2007

Widespread dieback of the introduced noxious weed Mimosa pigra was observed during the dry months in monsoonal northern Australia. Stems were girdled by reddish‐brown lesions that generally originated from leaf axils. Botryodiplodia theobromae was consistently isolated from the lesions and was shown to cause the symptoms. It is suggested that the occurrence of dieback is linked with the establishment of a stem‐boring moth introduced as a biological control agent for M. pigra.
Barley yellow dwarf viruses in Japanese pasture grasses and lack of correlation with the presence of fungal endophytes
Authors: GUY P. L.
Published: April 2007

Pasture grasses from temperate Japan were tested for infection with barley yellow dwarf viruses (BYDVs) and fungal endophytes. BYDVs from both the MAV and RPV subgroups were detected, but no symptoms attributable to BYDV infection were observed. Not all isolates from the MAV subgroup could be clearly discriminated as MAV or PAV solely on ELISA results, and may have been intermediate serotypes or mixed infections. BYDVs were found to infect fescue (Festuca arundinacea: 17%), ryegrass (Lolium perenne: 41%), timothy (Phleum pratense: 94%) and Poa spp. (20%). Fescue and ryegrass were predominantly infected with RPV and PAV, respectively. The small collections of Poa spp. were only infected with PAV, while timothy was only tested for MAV subgroup viruses. In fescue 26% of tillers were infected with Acremonium coenophialum, and 60% of ryegrass tillers from an ecotype collection were infected with Acremonium lolii. There was no correlation between BYDV infection and the presence of endophytes for the above species or for Epichloe typhina‐infected (50%) timothy. An ELISA test for A. lolii did not detect A. coenophialum in fescue or E. typhina in timothy but showed good agreement with epidermal staining of A. lolii in ryegrass leaf sheaths.
Effect of intercropping beans with maize on the severity of angular leaf spot of beans in Kenya
Authors: BOUDREAU M. A.
Published: April 2007

Angular leaf spot severity was evaluated on Phaseolus beans which had been planted alone (monocrop) and also simultaneously with maize (intercrop) at Kabete, Kenya, in November 1986 (short rains), and at Kabete and Thika in April 1987 (long rains). Intercropping reduced the area under the disease progress curve (AUDPC) in the short rains at Kabete and at Thika in the long rains by 23–33% at bean: maize proportions of 2:1 for some leaf positions, but did not reduce AUDPC significantly at Kabete in the long rains. Additional treatments to evaluate bean density and planting pattern (row against random) conducted in the short rains had no effect on AUDPC, although disease was reduced by 12–17% at higher bean densities when maize was not present. Fertilization increased AUDPC by 135–205% in the long rains at both sites. Microclimatological observations made at Kabete during the long rains indicated reductions in leaf temperature and air temperature, and increases in relative humidity, in most plots. These changes were small, averaging 0·6°C, 0·2°C, and 1·8%, respectively. Wind velocity was reduced by 55–63% in the intercrop in relation to the monocrop. The results reflect the variable response of angular leaf spot to maize intercrops seen in other studies.
Separation and interference of strains from a citrus tristeza virus isolate evidenced by biological activity and double‐stranded RNA (dsRNA) analysis
Authors: MORENO P. , GUERRI J. , BALLESTER‐OLMOS J. F. , ALBIACH R. , MARTÍNEZ M. E.
Published: April 2007

Separation of strains of citrus tristeza virus (CTV), differentiated by their double‐stranded RNA (dsRNA) profiles, was obtained by graft‐inoculating citron plants from a Mexican lime that had been recently aphid‐ or graft‐inoculated with a mild CTV isolate (T‐385). Up to 24 sub‐isolates with differing dsRNA profiles were obtained from the aphid‐inoculated lime. Some of these sub‐isolates induced stronger symptoms in several citrus species than the original T‐385 isolate. One sub‐isolate, T‐385‐33, was mild in Mexican lime, but induced stem pitting on sweet orange. Inoculation of this isolate on Mexican lime, sour orange and Eureka lemon induced mild or no symptoms when inoculum was taken from citron, but very severe symptoms when the inoculum was from sweet orange. Mexican lime and sweet orange plants co‐inoculated with T‐385‐33 from sweet orange in combination with the other 23 sub‐isolates showed mild symptoms. The results obtained suggest that there is natural cross‐protection among sub‐isolates in the original T‐385 isolate.
Classification of a world‐wide collection of isolates of Pseudocercosporella herpotrichoides by RFLP analysis of mitochondrial and ribosomal DNA and host range
Authors: NICHOLSON P. , REZANOOR H. N. , HOLLINS T. W.
Published: April 2007

Two profiles of mitochondrial DNA (mtDNA) were detected among 59 isolates of Pseudocercosporella herpotrichoides from diverse geographical sources. One profile (type II) was present only among isolates pathogenic on rye (R‐type), and a second profile (type I) was present in W, C and S‐pathotypes of the fungus. Mitochondrial DNA from P. herpotrichoides hybridized strongly to DNA of P. anguioides, but very weakly to DNA from P. aestiva, suggesting that the latter is not closely related to P. herpotrichoides. Fifteen profiles of ribosomal DNA (rDNA) were observed among isolates with type I mtDNA, and five of these were only found among seven isolates from Ireland. The other profiles present among type‐I isolates appeared to be largely independent of geographic origin. Three rDNA profiles were observed among R‐type (type II mtDNA) isolates.
Viral inclusions in monocotyledons infected by maize streak and related geminiviruses
Authors: PINNER M. S. , MEDINA V. , PLASKITT K. A. , MARKHAM P. G.
Published: April 2007

Isolates of maize streak virus (MSV) were examined by thin‐section electron microscopy in plants, assessed for characteristic features of infection and compared with other related geminiviruses infecting monocotyledons from Africa, islands in the Indian Ocean, and the Pacific Island of Vanuatu. Arrays of virus particles, often crystalline, were most often seen in the nucleus. The morphology of the nuclear crystalline arrays was characteristic of certain isolates or groups of isolates (strains). Infected nuclei could be seen in cells from the phloem parenchyma, vascular bundle sheath and mesophyll tissue, and also in epidermal guard cells of plants infected with the maize strain of MSV. The particle arrays varied in morphology from regular rows of virions forming distinctive blocks, to randomly arranged aggregates in certain areas of the nucleus. We consistently failed to find viral crystalline arrays associated with infection of panicum streak virus (PSV) and sugar cane streak virus (SSV) isolates either in these hosts or in maize. Occasionally arrays of MSV particles were found outside the nuclear envelope in physiologically active cells. Accumulations or sheets of MSV particles were seen lining the walls of some phloem companion cells. Crystalline aggregates of particles were frequently observed in the cell vacuole, after lysis of the nuclear membrane of dead cells which made up the chlorotic lesions, the typical symptom of virus infection. Virus preparations from all hosts contained typical geminate particles regardless of the morphology of the virion arrays. The effect on chloroplasts appeared to vary between isolates and this is discussed in relation to lesion colour. The arrangement of virions in the nucleus as a taxonomic character is diagnostic for MSV. Inclusions with crystalline structure found in sieve elements of infected plants were not immunogold labelled when thin sections were probed using antiserum to the virus particles.
The partial characterization of melon vein‐banding mosaic virus, a newly recognized virus infecting cucurbits in Taiwan
Authors: HUANG C. H. , CHANG L. , TSAI J. H.
Published: April 2007

A potyvirus (designated as no. 656) causing mosaic or vein‐banding symptoms on melons was isolated and characterized. The virus was mechanically transmitted to 14 herbaceous plant species, and induced mosaic symptoms in most cucurbitaceous plants. Aphis gossypii transmitted the virus non‐persistently, and flexuous filamentous virus particles c. 755 nm in length were consistently observed in extracts of the infected pumpkin leaf tissues. Pinwheel and tubular inclusions were observed in the cytoplasm of infected zucchini leaf tissues. The virus was purified from infected pumpkin leaves by isopycnic centrifugation (Cs2SO4). The molecular weights of purified capsid and cylindrical inclusion proteins as estimated by SDS‐PAGE were 32·5 and 73 KDa, respectively. In SDS‐immunodiffusion tests, antiserum to virus particles from isolate 656 was serologically unrelated to ZYMV, WMV‐2, PRV‐W and a type W variant of PRV, but antiserum to its cylindrical inclusion protein did produce spur precipitin bands between homologous and WMV‐2 antigen wells. However, neither WMV‐2 virus particle nor cylindrical inclusion antisera reacted with this virus. Furthermore, this virus was not serologically related to BCMV, BYMV, CYVV, SMV, WMV‐M or ZYFV. Based on test results and symptomatology, this virus appears to be a new potyvirus, for which the name melon vein‐banding mosaic virus (MVbMV) is proposed.
Adaptation of barley powdery mildew populations in England to varieties with two resistance genes
Authors: BROWN J. K. M. , SIMPSON C. G. , WOLFE M. S.
Published: April 2007

In 1986, two spring barley cultivars were widely grown in the UK for the first time: Klaxon, which carries the powdery mildew resistance alleles Mla7, Mlk and Ml(La), and Natasha (Mla12 + Ml(Ab)). Significant amounts of a third cultivar, Doublet (Mla7+ Ml(La)), were grown for the first time in 1986. The individual resistance genes, and the combination Mla7+Mlk, had previously been used separately in different varieties. Isolates of the mildew pathogen Erysiphe graminis f.sp. hordei, which were virulent on Doublet and Klaxon, were rare up to June 1986. One clone of E. g. f.sp. hordei, virulent on Doublet and Klaxon, increased in frequency from < 1% to 36% from June to October 1986, in samples from the airborne population in Cambridge, UK. This consisted of isolates with apparently identical virulences, responses to fungicides and genetic fingerprints. It also formed the majority of Doublet‐virulent mildew sampled from a field of Doublet near Cambridge in 1987. By contrast, isolates virulent on Natasha were already common and genetically diverse in 1985:22 of 100 isolates sampled in October 1985, belonging to 13 races, were virulent. Natasha appeared not to influence the E. g. f.sp. hordei population greatly, as the frequency of Natasha‐virulent isolates fell slightly, from 15·5% to 11·7% between June and October 1986. No single clone predominated in the Natasha‐virulent population. These results support the view that new epidemics of barley powdery mildew in the UK arise by highly stochastic evolution of E. g. f.sp. hordei populations. They also indicate that varieties with new combinations of previously exposed resistance genes do not necessarily provide durable control of mildew, because the frequency of a virulent clone may rise rapidly.
Vanilla viruses in the South Pacific
Authors: PEARSON M. N. , JACKSON G. V. H. , PONE S. P. , HOWITT R. L. J.
Published: April 2007

Surveys for viruses affecting Vanilla fragrans and V. tahitensis carried out in Cook Islands, Fiji, Niue, Tonga and Vanuatu detected cymbidium mosaic potexvirus and odontoglossum ringspot tobamovirus in all countries; vanilla necrosis potyvirus in Fiji, Tonga and Vanuatu; and vanilla mosaic potyvirus in Cook Islands, Fiji and Vanuatu. For all these viruses the surveys extended the previously known distribution in the South Pacific. Other, unreported potyviruses and rhabdovirus‐like particles were detected from Fiji and Vanuatu. Symptoms associated with potyvirus infection (leaf distortion, sunken chlorotic patches, stem necrosis and vine die‐back) were found in a majority of plantings in Fiji, Tonga and Vanuatu; in Fiji and Tonga there were instances where up to 50% of the plants in farmers’ plots were affected.
A geminivirus causing vein yellowing of Ageratum conyzoides in Singapore
Authors: SWANSON M. M. , HARRISON B. D. , WONG S. M.
Published: April 2007

A vein‐yellowing disease of Ageratum conyzoides in Singapore was shown to be caused by a geminivirus, here named ageratum yellow vein virus (AYVV), which was transmitted by the whitefly Bemisia tabaci but not by inoculation with sap or through seed. AYVV particles (30 × 20 nm) are serologically related to those of other whitefly‐transmitted geminiviruses, and reacted with some monoclonal antibodies elicited by particles of African cassava mosaic or Indian cassava mosaic geminiviruses. However, the epitope profile of AYVV differed from the profiles of these viruses, and from those of geminiviruses from vein yellowing‐affected A. conyzoides from India and from yellow leaf curl‐affected tomato from either Singapore or India. The results provide further evidence of antigenic differences among geminiviruses that cause similar diseases in the same plant species in different geographical regions.
Evidence for Phytophthora cinnamomi involvement in Iberian oak decline
Authors: BRASIER C. M. , ROBREDO F. , FERRAZ J. F. P.
Published: April 2007

Rapid and sometimes extensive mortality and decline of oak, principally Quercus suber and Q. ilex, has occurred in parts of southern Spain and Portugal in recent decades. We report here isolation of the aggressive root pathogen Phytophthora cinnamomi from roots of diseased oaks or from soil at eleven out of thirteen decline foci examined. It is proposed that the introduction and spread of P. cinnamomi may be a major factor in the Iberian oak decline, interacting with drought and other site factors, and leading to stress‐related attacks by insects and other fungi. By analogy, it may also be involved in the similar oak declines occurring elsewhere on the Mediterranean.
Association of mycoplasma‐like organisms with tomato big bud disease in Greece
Authors: ALIVIZATOS A. S.
Published: April 2007

The big bud disease of tomato is described in Greece for the first time. Its identity and aetiology were ascertained by electron microscopy, fluorescence and bright‐field microscopy, transmission tests and antibiotic treatments. Pleomorphic mycoplasma‐like organisms (MLOs) were detected in the sieve tubes of infected leaf tissues by thin‐section electron microscopy and also by fluorescence and bright‐field microscopy after staining with the DNA‐binding fluorescent stain Hoechst 33258, and with toluidine blue. Infected tomato plants showed remission of symptoms when treated with tetracycline‐HCl, but not with benzylpenicillin, while healthy plants developed big bud symptoms when graft inoculated with diseased tomato shoots. The occurrence of natural spread of big bud disease in Greece indicates that one or more vector species are present in the country.
Effect of Heterodera cajani on biomass and grain yield of pigeon pea on vertisol in pot and field experiments
Authors: SHARMA S. B. , NENE Y. L. , REDDY M. V. , McDONALD D.
Published: April 2007

Glasshouse and field trials were conducted to determine the effects of the cyst nematode, Heterodera cajani on biomass and grain yield of pigeon pea, Cajanus cajan. Shoot length, fresh and dry shoot masses, leaf area and pod yields of pigeon pea were significantly reduced by H. cajani. In glasshouse pot experiments, an initial density of 1.0 juveniles per cm3 soil caused 14 to 24% reduction in plant height, root and shoot mass and leaf area. Application of carbofuran 3G (1·5, 3·0 and 6·0 kg a.i./ha) in H. autoclaved soil in pots did not improve growth of pigeon pea; however, its application (6 kg a.i./ha) in H. cajani‐infested fields reduced the nematode density (P < 0·05) and improved plant growth and yield. The densities of eggs and juveniles of H. cajani were 72 and 48% lower in the carbofuran‐treated plots than in the control plots 35 and 52 days, respectively, after sowing. No such differences were observed at 70 days after sowing. The tolerance limit for pod yield in field experiments was 2·6 eggs and juveniles of H. cajani per cm3 soil at sowing time. Grain yield was 20 to 25% higher in the carbofuran‐treated plots than in the control plots. Application of carbofuran protected the roots from nematode damage during the early stages of plant growth and resulted in good plant growth and yield.
Detection of spore balls of Spongospora subterranea on potato tubers by enzyme‐linked immunosorbent assay
Authors: HARRISON J. G. , REES E. A. , BARKER H. , LOWE R.
Published: April 2007

A rabbit was immunized with a homogenate of spore balls (cystosori) of Spongospora subterranea which also contained some potato tuber debris. The resultant polyclonal antiserum contained antibodies which reacted against extracts of spore balls and healthy tubers. Antibodies to the tuber debris were removed by incubating the blood serum with an extract from a S. subterranea‐free tuber. In enzyme‐linked immunosorbent assay (ELISA), the γ‐globulin fraction of the absorbed antiserum reacted with dilute tuber extracts containing the equivalent of as little as 0·08 spore balls per ml. The reaction with spore balls was inhibited in high concentrations of tuber sap. Extracts of peel from symptomless tubers which had been stored in contact with scabbed tubers also reacted with the γ‐globulin, presumably because the symptomless tubers became contaminated with spore balls. However, spore balls in soil were only weakly detected when high numbers were present. The γ‐globulin did not react with the plasmodial stage of the pathogen, or with 15 other micro‐organisms tested, including resting spores of Plasmodiophora brassicae.
Effects of barley genotype on induced resistance to powdery mildew
Authors: MARTINELLI J. A. , BROWN J. K. M. , WOLFE M. S.
Published: April 2007

Infection of barley by an avirulent isolate of Erysiphe graminis f.sp. hordei reduces the development of powdery mildew disease by a virulent isolate, inoculated subsequently. This phenomenon, known as induced resistance, was studied in three sets of near‐isogenic lines of barley, each of which included varieties with four different race‐specific resistance genes. The extent of induced resistance, expressed as a reduction in the number of colonies formed, differed in lines carrying different race‐specific resistance genes, being most effective in lines with Mla7, followed by Mth, then Mla6 and Mla13. These differences may be related to the extent of the hypersensitive response to infection by avirulent spores. A further effect of induced resistance in reducing sporulation, taking the number of colonies into account, was least effective in Mth lines, with the other lines ranking as they did when induced resistance was expressed as colony numbers. By contrast, the genetic backgrounds of the three near‐isogenic sets had similar effects on the fractional reduction of colony number by induced resistance. The effect of induced resistance on sporulation was strongest in the most resistant background, and weakest in the most susceptible.
Biological diversity of citrus tristeza virus (CTV) isolates in Spain
Authors: BALLESTER‐OLMOS J. F. , PINA J. A. , CARBONELL E. A. , MORENO P. , DE MENDOZA A. HERMOSO , CAMBRA M. , NAVARRO L.
Published: April 2007

A survey of citrus tristeza virus (CTV) isolates was carried out in most citrus‐growing areas in Spain. Twenty‐two isolates were selected by geographical origin, cultivar of source tree, and symptoms observed on the host or in preliminary tests, and were biologically characterized.

A wide range of variation in transmissibility by aphids and symptom intensity on nine different indicator species or scion‐rootstock combinations was observed among CTV isolates. Mexican lime. Citrus macrophylla, and to a lesser extent citron were the most useful hosts for characterizing these isolates, and leaf symptoms and stem pitting were the most discriminating traits. Positive correlation was observed between symptoms induced on Mexican lime and C. macrophylla, but not between the symptoms induced on these indicators under greenhouse conditions and the homologous symptoms on plants grown in the screenhouse. Some of the traits studied enabled us to establish relatively well‐defined groups of isolates, but in most cases a continuous range of variation was obtained and no clear group could be defined.
Quantification of Sclerospora graminicola in tissues of Pennisetum glaucum using an enzyme‐linked immunosorbent assay
Authors: KUMAR VASANTHI U. , MEERA M. S. , SHISHUPALA S. , SHETTY H. S.
Published: April 2007

Antibodies raised against whole sporangia of Sclerospora graminicola reacted specifically with sporangia and mycelium of this fungus. Agglutination studies localized the antigen on the cell‐wall surfaces. Using this antibody, an indirect enzyme‐linked immunosorbent assay (ELISA) with a biotin‐avidin amplification system was developed for the quantification of S. graminicola in the host tissues of Pennisetum glaucum. This sensitive assay system, which could detect 3·1–5·5 μg dry weight of fungal biomass, was used to monitor the increase in fungal biomass during disease progression.
Tamusred mosaic virus, a potexvirus from black bryony (Tamus communis)
Authors: CACIAGLI P. , BOCCARDO G. , LISA V. , LOVISOLO O.
Published: April 2007

A virus was isolated in Italy from Tamus communis in which it caused symptoms of red mosaic and leaf distortion. The virus, for which the name tamus red mosaic virus (TRMV) is suggested, was differentiated from other potexviruses or possible potexviruses on the basis of host range, particle properties and serology. In crude preparations, TRMV had elongated particles of modal length 550–560 nm and diameter of 13 nm. TRMV was easily purified from Chenopodium quinoa and had a buoyant density of 1·34 g/cm3 in CsCl and 1·27 g/cm‐3 in Cs2SO4. An antiserum to TRMV was obtained with a titre of 1/1024 in slide precipitin tests. TRMV was related to, but distinct from, tamus latent virus, a potexvirus isolated from Tamus communis in the UK, and more distantly related to potato virus X, cactus virus X and commelina virus X. Polyacrylamide gel electrophoresis (PAGE) indicated that the virus particles contained a single protein species of estimated molecular weight 25·2 kDa. Enzymatic digestions, agarose gel electrophoresis and infectivity of the isolated nucleic acid indicated that the virus has a single major molecule of single‐stranded positive‐sense RNA of estimated molecular weight 2120 kDa (ca. 6·4 kb).
Use of phages for identifying the citrus canker bacterium Xanthomonas campestris pv. citri in Taiwan
Authors: WU W. C. , LEE S. T. , KUO H. F. , WANG L. Y.
Published: April 2007

Phages CP115 and CP122, which were isolated from canker lesions on grapefruit and Liucheng sweet orange, respectively, showed a high degree of specificity with respect to lysis of test bacterial strains. When used jointly, they lysed 135 (97·8%) out of 138 Xanthomonas campestris pv. citri strains isolated from the canker lesions on leaves, twigs, and fruits of various citrus species, cultivars, and hybrids grown throughout Taiwan, but they did not lyse other X. campestris pathovars and other phytopathogenic bacteria, nor other bacteria isolated from soil, clinical or environmental samples. Of 252 CP115/CP122‐sensitive and 78 CP115/CP122‐resistant bacterial strains with colony characteristics typical of or similar to those of X. campestris pv. citri, isolated from canker lesions of various citrus plants in diverse growing regions in Taiwan, 250 (99·2%) and 76 (97·4%) strains were pathogenic and non‐pathogenic, respectively, when inoculated into Liucheng sweet orange or Mexican lime. Thus, phages CP115 and CP122, when used jointly, appear to be applicable for identifying X. campestris pv. citri in Taiwan.
Antibody production and identity of MLOs associated with sugar‐cane whiteleaf disease and bermuda‐grass whiteleaf disease from Thailand
Authors: SARINDU N. , CLARK M. F.
Published: April 2007

Cuttings from sugar‐cane plants with symptoms of whiteleaf disease and bermuda‐grass plants also showing whiteleaf symptoms were collected in Thailand and transferred to a glasshouse at East Mailing. Using these plants as source material, procedures were devised for the partial purification of MLO‐associated immunogens. Antisera were raised separately to the sugar‐cane whiteleaf and bermuda‐grass whiteleaf immunogens. These antisera exhibited specificity for their homologous MLO antigens in F(ab′)2 indirect enzyme immunosorbent assays (ELISA). Detection of MLO infection was possible in crude tissue extracts diluted several hundredfold. No cross‐reactions were observed in reciprocal tests between these two MLO sources and their antisera, nor were there reactions between either antiserum and extracts of other graminaceous hosts showing symptoms of natural whiteleaf infection. No cross‐reactions were obtained in reciprocal tests with Spiroplasma citri or aster yellows MLO and their homologous antibodies.
Development of a monoclonal antibody immunoassay for the eyespot pathogen Pseudocercosporella herpotrichoides
Authors: PRIESTLEY R. A. , DEWEY F. M.
Published: April 2007

A double‐antibody‐sandwich ELISA test has been developed for the detection of Pseudocercosporella herpotrichoides using a highly specific monoclonal antibody PH‐10 as the capture antibody and genus‐specific rabbit polyclonal antiserum as the detector antibody. The assay recognizes extracts from plants both artificially and naturally infected with P. herpotrichoides giving at least three‐fold higher absorbance values with extracts from Pseudocercosporella‐infected tissue than with extracts from healthy tissues or from tissues naturally infected with Microdochium nivale, Rhizoctonia cerealis or material artificially inoculated with P. anguioides. The assay tested positively against all isolates of P. herpotrichoides, including both W‐type and R‐type isolates. In this assay system, extraction of the antigen from the stem bases of infected plants is a one‐step process not requiring any dilution procedures. The assay can be used to detect the pathogen in presymptomatic infected seedlings. The immunogen used to generate the specific monoclonal antibody and the rabbit antiserum was a mycelial extract from which the high‐molecular‐weight proteins and glycoproteins had been removed by ammonium sulphate precipitation. The high‐molecular‐weight fraction was shown to contain cross‐reactive antigens; it induced antiserum in mice that cross‐reacted with the other stem‐base fungi even at high dilutions. The monoclonal antibody PH‐10 is an IgM antibody. Heat and periodate treatment of the antigen indicate that it is a glycoprotein and that the epitope recognized by the antibody is a protein.
Factors affecting UV‐induced resistance in grapefruit against the green mould decay caused by Penicillium digitatum
Authors: DROBY S. , CHALUTZ E. , HOREV B. , COHEN L. , GABA V. , WILSON C. L. , WISNIEWSKI M.
Published: April 2007

Exposure of harvested grapefruit to ultraviolet (UV) light induced resistance against the green mould decay caused by Penicillium digitatum. Grapefruit picked at various times during the harvest season responded differently to UV treatments. The UV dose required for development of maximum resistance increased as the season progressed. The initial UV dose required in November‐picked fruit for maximum response was 4·8 kJ/m2. It declined to 1·6 and 3·2 kJ/m2 in December‐ and January‐picked fruit, respectively, and increased to 8 kJ/m2 in February‐picked fruit. Correspondingly, the minimum percentage infection developing after UV treatment increased throughout the season from 0 to 35%. Resistance in UV‐treated fruit developed to its maximum extent at 24–48 h following exposure to UV light and then decreased. Development of induced resistance in grapefruit peel was affected by the temperature at which the fruit was stored 24 h after UV treatment and before infection with P. digitatum. In the UV‐treated fruit, the fungus developed a sporadic mycelium with marked inhibition of sporulation. The activity of phenylalanine ammonia‐lyase and peroxidase markedly increased in the peel following exposure of the fruit to UV light.
Take‐all in autumn‐sown wheat, barley, triticale and rye grown with high and low inputs
Authors: GUTTERIDGE R. J. , HORNBY D. , HOLLINS T. W. , PREW R. D.
Published: April 2007

Winter cultivars of wheat, barley, triticale and rye were grown under two contrasting husbandry systems (low and high inputs) at two locations (Woburn and Rothamsted) known to be infested with the take‐all fungus. The sandy loam at Woburn is less fertile than the silty clay loam at Rothamsted. Root infection in these crops was assessed in spring and summer.

Rye was least infected by the take‐all fungus, wheat the most infected and barley and triticale had intermediate levels of infection. Barley yields were less affected by take‐all than those of wheat or triticale, because barley was at a later growth stage by the time severe infection occurred. Yields of wheat and barley responded most to the high‐input husbandry on the less fertile soil at Woburn. On the basis of quantity of grain, triticale would appear to be a good substitute for wheat on the less fertile soil when inputs are low, but not where they are high. At Rothamsted, yields of wheat and triticale were similar in both input systems. There was no strong support, at either site, for the contention that triticale could be a useful substitute for barley where low or high inputs are used. A total of 177 isolates of Gaeumannomyces graminis var. tritici (the causal fungus of take‐all) were obtained from infected roots in these experiments and tested for their pathogenicity on wheat and rye seedlings. These tests revealed a range of pathotypes with varying pathogenicities to wheat and rye, but pathogenicities were not correlated with the host plant from which the fungi were isolated.
The effect of fungicide sprays on the incidence of apple canker (Nectria galligena) in Bramley's Seedling
Authors: COOKE L. R. , WATTERS B. S. , BROWN A. E.
Published: April 2007

In two trials established between 1983 and 1990, copper oxychloride and prochloraz‐manganese applied at 5 and 50% leaf‐fall were as effective as phenylmercury nitrate, formerly used (but now banned) for the control of leaf‐scar infection by Nectria galligena. However, prochloraz‐manganese has not been developed for use on fruit. Autumn application of carbendazim gave inadequate control and thiophanate‐methyl, bitertanol and fenpropimorph were ineffective. Carbendazim applied as a spring‐summer treatment reduced canker development to a similar level to a spring‐summer dodine scab programme plus autumn copper oxychloride. Summer carbendazim + captafol was an outstandingly effective treatment, but since this trial the use of captafol as a fungicide in the UK has been prohibited. In the absence of an effective autumn treatment, penconazole alone or with captan, and myclobutanil preblossom with myclobutanil alone or with mancozeb post‐blossom tended to be less effictive than the standard programme (dodine pre‐ and dithianon post‐blossom). Carbendazim mixed with an effective scab fungicide such as dithianon therefore remains the recommended treatment in an orchard with a serious canker problem. In orchards where there is a limited risk of canker, a spring‐summer scab fungicide programme should prevent N. galligena infection at this time of year, with copper oxychloride applied at leaf‐fall, particularly after wet weather, to prevent leaf‐scar infection.
Racial diversity and complexity in regional populations of Erysiphe graminis f.sp. hordei in France over a 5‐year period
Authors: ANDRIVON D. , DE VALLAVIEILLE‐POPE C.
Published: April 2007

The evolution of race patterns in three French regional populations of the barley powdery mildew pathogen Erysiphe graminis f.sp. hordei over a 5‐year period showed rapid adaptation to newly introduced host resistance genes. In all three regions, the main change consisted of the replacement of initially abundant races by pathotypes differing markedly from them by their virulence gene combinations. This explained the increase in diversity during the first 3 years of the survey, when the second group of pathotypes became more common in the populations, and its subsequent decrease due to the decline of the first group of races. The mean number of virulence genes per isolate did not vary noticeably over time in the three populations, remaining at about four out of 12 genes tested. However, the distribution of the isolates into virulence complexity classes was greatly modified, fitting a binomial distribution by the end of the study, although significant deviations were apparent in the first 2 years (1986 and 1987). The data indicate that selection, migration and recombination are the most important factors shaping race structure and evolution in powdery mildew populations, and that mutation is of limited significance. No convincing evidence was obtained for the existence of stabilizing selection sensu Vanderplank as the mechanism limiting virulence complexity. Implications regarding spatial and temporal deployment of race‐specific resistance genes to control powdery mildew are discussed.
A third cryptic virus in beet (Beta vulgaris)
Authors: XIE W. S. , ANTONIW J. F. , WHITE R. F. , WOODS R. D.
Published: April 2007

Japanese leaf beet Beta vulgaris var. cicla cv. Fudanso plants were found to contain four double‐stranded RNA (dsRNA) components in apparently healthy beet plants. Two were identified as from beet cryptic virus 1 (BCV1), but the other two showed different mobilities on gel electrophoresis and were transcribed into complementary DNA (cDNA) and cloned. Hybridization analysis showed no significant sequence homology between these two dsRNAs and the dsRNA components of BCV1 or the other known cryptic virus of beet, BCV2. Slot‐ and dot‐blot hybridization were used with cDNA clones as probes to identify plants containing these two dsRNA components. Virus particles were purified from these plants and were shown to contain the two new dsRNA components, thus demonstrating the existence of a new beet cryptic virus, which we have called BCV3.
Variability in the reaction of squash (Cucurbita pepo) to inoculation with Sphaerotheca fuliginea and methodology of breeding for resistance
Authors: COHEN R. , LEIBOVICH G. , SHTIENBERG D. , PARIS H. S.
Published: April 2007

Reaction to inoculation with powdery mildew caused by Sphaerotheca fuliginea was observed on leaf discs and young plants of eleven representatives of seven edible cultivar groups of Cucurbita pepo. Disease intensity (i.e. number of infections per leaf) was highly correlated (r2=0·863, P<0·0001) with spore yield per leaf. Spore yield per leaf and frequency of sporulation on leaf disks were moderately (r2=0·505), but significantly correlated (P<0·01), suggesting that frequency of sporulation can be used for initial screening against susceptibility in a breeding programme. Spore yield per leaf and spore yield per artificially inoculated leaf disc were highly correlated (r2=0·87, P<0·0001); this suggests that counting of spores on leaf discs, a laborious but accurate procedure, could be used on the remaining plants as a second step in selection for resistance of the variation in the response of edible C. pepo to the pathogen, 85·8% was attributed to differences between the edible groups and only 14·2% to individual cultivars within a group. Cultivars of the cocozelle and vegetable marrow groups were the most susceptible, whereas relatively resistant cultivars were found in the scallop and straightneck groups.