bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial patterns of spear rot in oil palm plantations in Surinam
Authors: Van de Lande  , Zadoks
Published: March 2003

As the aetiology of spear rot of oil palm is unknown, indirect methods were applied to study its putative infectiousness by analysing data from commercial oil palm plantations in Surinam. Geostatistics and gradient analysis were used to examine the spatial variation of spear rot disease in 13 blocks at two plantations. In two blocks, which had low spear rot incidence initially, the variogram indicated that affected trees were not spatially related, suggesting that infection came from various distant sources. Later, the semivariances in one of these two blocks and in seven others, calculated for successive dates, showed a linear increase with distance. The variograms for four blocks showed a nonlinear increase in variance. Over the years, the variograms suggested that the variation in spear rot was anisotropic, with more spatial dependence in a westerly direction. Classical analysis of disease gradients over time confirmed that there was a preferential direction of disease spread. The data are compatible with the following hypotheses: (1) spear rot is an infectious disease; (2) the causal agent of spear rot is vector‐borne, the vector being displaceable by wind; and (3) spear rot appears in two distinct phases, phase 1 being characterized by few randomly scattered trees, phase 2 by focal spread of disease starting from such scattered trees. The trigger of the change from phase 1 to phase 2 remains unknown.
Postulation of virulence groups and resistance factors in the quinoa/downy mildew pathosystem using material from Ecuador
Authors: Ochoa  , Frinking  , Jacobs Th.
Published: March 2003

Twenty downy mildew isolates were collected in south, central and north Ecuador and inoculated on seedlings of 60 quinoa lines. A scale for scoring quinoa downy mildew infections was developed. Four virulence groups and three resistance factors were identified. In southern Ecuador only isolates of virulence group 2 were collected, while in the central region only virulence group 4 was found. In the north of Ecuador isolates of all four virulence groups were collected. Resistance factor R3 was found most frequently in seedlings of 13 high‐yielding Ecuadorian quinoa lines. No effective resistance against group 4, the most virulent group, was observed. Lines ECU‐288 (susceptible), ECU‐291(R1), ECU‐470 (R2) and ECU‐379 (R3) could be used as a preliminary quinoa differential set for identifying downy mildew virulence groups.
Occurrence of watermark disease of willows in Japan
Authors: Sakamoto  , Takikawa  , Sasaki
Published: March 2003

The watermark disease of willows was recently identified in Japan for the first time, in the northern island of Hokkaido. During spring and summer, the leaves and branches of affected trees suddenly wilted and some trees died. When affected branches or trunks were cut, a distinct, watery, reddish‐brown or brownish‐black stained zone (watermark) was seen in the sapwood. The causal bacterium was isolated from the watermark and identified as Erwinia salicis by its bacteriological characteristics. Inoculation tests confirmed its pathogenicity to willows.
Histology of Sclerotium cepivorum infection of onion roots and the spatial relationships of pectinases in the infection process
Authors: Metcalf  , Wilson
Published: March 2003

Sclerotium cepivorum (isolate Sc4) hyphae penetrated the epidermis and hypodermis of onion roots and grew into the cortex. Immediately following penetration only the cells through which S. cepivorum grew were lysed, but subsequently cells were killed and cell walls disintegrated ahead of the infection hyphae. Sclerotium cepivorum produced two polygalacturonases (PG) and two pectinesterases (PE) in culture. These isozymes were also found in infected onion root tissues and another PG and a PE were occasionally detected. Two isozymes of PG and three isozymes of PE diffused ahead of the infection hyphae. The spatial distribution of these enzymes was associated with cell death and cell wall degradation. The epidermis, hypodermis, endodermis and vascular tissues were more resistant to hydrolysis than the cortex, but only the endodermis and cells within it retained nuclei following hydrolysis of the surrounding cortical tissues. The cavity within the root cortex became filled with swollen, vacuolate S. cepivorum hyphae.
Relationship between natural occurrence of banana streak badnavirus and symptom expression, relative concentration of viral antigen, and yield characteristics of some micropropagated Musa spp.
Authors: Dahal  , Ortiz  , Tenkouano  , Hughes  , Thottappilly  , Vuylsteke  , Lockhart
Published: March 2003

Micropropagated plants of 36 Musa genotypes with diverse genetic backgrounds, including 14 tetraploid plantain (TMPx) and banana (TMBx) hybrids, were evaluated for their response to banana streak badnavirus (BSV) infection under three environments from 1995 to 1997 in Nigeria. The characteristics evaluated were the natural incidence of BSV based on symptoms and virus indexing, relative concentration of BSV antigens in leaf tissues determined by ELISA, and some growth and yield descriptors. Virus occurrence and symptom expression, as well as the relative concentration of BSV antigens, fluctuated greatly between seasons during the cropping cycle, being high during the rainy season and low or negligible during the hot dry season. The natural incidence of plants with symptoms and BSV‐infected plants varied between genotypes. Incidence of BSV on most International Institute of Tropical Agriculture (IITA) TMPx hybrids and three Fundación Hondureòa de Investigación Agrìcola (FHIA) hybrids was high in the three environments, with some variation. Most landraces and some FHIA or Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA) hybrids were not BSV‐infected under either environment at Onne. However, a few expressed some foliar symptoms at Ibadan and indexed BSV positive. The relative concentration of BSV antigens in leaf samples was also high in most TMPx and some FHIA hybrids, but low in most landraces. While BSV infection had no significant effect on most growth characteristics, it had a highly variable effect on bunch weight loss among the genotypes. There was no relationship between the natural incidence of BSV, concentration of viral antigen and bunch weight loss among the 11 TMPx hybrids, three FHIA hybrids and three plantain landraces. Despite the high natural BSV incidence and the high relative antigen concentration in their leaf tissue, TMPx 548‐9, TMPx 2637‐49, TMPx 7002‐1 and FHIA 21 suffered less than 15% bunch weight loss, and TMPx 548‐4 and FHIA 22 suffered no loss. These results suggest that under the conditions specified in this study, these hybrids could be tentatively classified as ‘field tolerant’ to BSV.
Host range and symptomatology of a graft‐transmissible pathogen causing bud union crease of citrus on trifoliate rootstocks
Authors: Galipienso L. , Navarro L. , Ballester‐Olmos J.F. , Pina J.A. , Moreno P. , Guerri J.
Published: March 2003

A graft‐transmissible pathogen causing bud union crease of Nagami kumquat SRA–153 on Troyer citrange was characterized for host range and symptomatology. Buds of Marsh grapefruit, Nules clementine, Eureka lemon and Pineapple sweet orange preinoculated with kumquat SRA–153 were propagated on citrange rootstocks. Some plants of Nules clementine and Eureka lemon had developed bud union crease six months after propagation, whereas all Marsh grapefruit and Pineapple sweet orange plants still showed normal bud union after one year. On indexing these preinoculated species, Nules clementine and Eureka lemon caused vein clearing in Pineapple sweet orange and Dweet tangor, chlorotic blotching in Dweet tangor and stem pitting in Etrog citron, whereas Marsh grapefruit and Pineapple sweet orange caused only chlorotic blotching in Dweet tangor and stem pitting in Etrog citron. Following shoot‐tip grafting in vitro of kumquat SRA–153, kumquats 38–1 and 497–2 obtained from it caused chlorotic blotching in Dweet tangor and stem pitting in Etrog citron, but not vein clearing in Pineapple sweet orange and Dweet tangor or bud union crease when propagated on citrange. These results suggest the presence of at least two pathogens or pathogen strains in kumquat SRA–153 and the elimination of one of them after shoot‐tip grafting in vitro or inoculation on Marsh grapefruit or Pineapple sweet orange. They also indicate that the pathogens in kumquat SRA–153 can be detected by indexing on Dweet tangor or Etrog citron.
Evidence for differential host preference in Microdochium nivale var. majus and Microdochiumnivale var. nivale
Authors: Simpson D.R. , Rezanoor H.N. , Parry D.W. , Nicholson P.
Published: March 2003

The pathogenicity of Microdochium nivale var. majus and var. nivale was tested on wheat, rye and oat seedlings using both visual disease scoring and quantitative PCR measurements. In an individual inoculation trial at 10°C var. majus and var. nivale were strongly pathogenic towards wheat and rye, with var. nivale causing slightly greater disease in rye. At this temperature only var. nivale caused significant disease of oats. In a further experiment M. nivale was inoculated as a series of mixtures of the two varieties and incubated at 15°C. The ratio of the varieties present in the inoculum and present at harvest was analysed by quantitative PCR and this enabled a coefficient of selection to be calculated for the varieties on each host. M. nivale var. majus showed a weak selective advantage over var. nivale on wheat (0.33 ± 0.08) and oat seedlings (0.35 ± 0.016) and M. nivale var. nivale showed a strong selective advantage over var. majus on rye seedlings (0.92 ± 0.26). The isolates were also compared for sensitivity to benzoxazolinone (BOA), a hydroxamic acid compound derived from rye leaves. M. nivale var majus was found to be significantly more sensitive to BOA than M. nivale var. nivale, indicating a possible mechanism for the selective advantage of var. nivale growing on rye. This is the first substantiated indication of a significant difference in host preference between Microdochium nivale var. majus and var. nivale.
Association of ‘Candidatus Phytoplasma australiense’ with green petal and lethal yellows diseases in strawberry
Authors: Padovan A. , Gibb K. , Persley D.
Published: March 2003

The identity of phytoplasmas detected in strawberry plants with green petal (SGP) and lethal yellows (SLY) diseases was determined by RFLP analysis of the 16S rRNA gene and adjacent spacer region (SR). RFLP and sequence comparisons indicated that the phytoplasmas associated with SGP and SLY were indistinguishable and were most closely related to ‘Candidatus Phytoplasma australiense’, the phytoplasma associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases. This taxon lies within the aster yellows strain cluster. Primers based on the phytoplasma tuf gene, which amplify only members of the AY strain cluster, amplified a DNA product from the SGP and SLY phytoplasmas. Primers deduced from the 16S rRNA/SR of P. australiense that amplify only members of this taxon amplified rDNA sequences from the SGP and SLY phytoplasmas. Primers that selectively amplify members of the faba bean phyllody (FBP) phytoplasma group, the most commonly occurring phytoplasma group in Australia, did not amplify rDNA from the SGP and SLY phytoplasmas.
Effects of stem canker (Leptosphaeria maculans) and light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus) in southern England
Authors: Zhou Y. , Fitt B. D. L. , Welham S. J. , Evans N. , Gladders P.
Published: March 2003

The relationships between yield loss and incidence or severity of stem canker and light leaf spot in winter oilseed rape were analysed by correlation and regression analyses, using data from experiments at Rothamsted, England in 1992/93, 1994/95 and 1995/96. Growth stages (GS) 6,3/6,4 and 4,0/4,5 were identified as the critical points for relating percentage yield loss to stem canker and light leaf spot (on stems), respectively. Critical point (CP) and area under disease progress curve (AUDPC) models relating percentage yield loss to combined incidence or severity of stem canker and light leaf spot (stems) in each experiment were constructed by linear regression. There were no differences in the CP models for incidence between 1992/93, 1994/95 and 1995/96 experiments, or in the AUDPC models for incidence between 1992/93 and 1994/95 experiments. Therefore, a general CP model relating percentage yield loss (ΔY) to combined incidence of stem canker (Si) at GS 6,3/6,4 and light leaf spot (stems) (Li) at GS 4,0/4,5 was constructed using data from the three experiments: ΔY = 0·85 + 0·079Si + 0·065Li(R2 = 43·7%,P < 0·001, 92 df). A general AUDPC model relating ΔYto the AUDPC of combined incidence of stem canker (Sia) from GS 5·7 to GS 6·5 and light leaf spot (stems) (Lia) from GS 4·0 to GS 6·3 was constructed using data from the 1992/93 and 1994/95 experiments: ΔY = 0·07 + 0·00096Sia + 0·0026Lia(R2 = 43·6%,P < 0·001, 68 df). These two general yield‐loss models were tested with data from Rothamsted in 1993/94 and Boxworth in 1992/93. The predictive accuracy of the CP model based on combined incidence of stem canker and light leaf spot (stems) was better than that of the AUDPC model. Yield losses predicted by summing the estimates from individual models for incidence of stem canker alone (GS 6,3/6,4) and light leaf spot alone (on leaves at GS 3,3) were greater than observed yield losses in experiments at Rothamsted in 1992/93, 1993/94, 1994/95 and 1995/96 and at Boxworth in 1992/93.
Identification of crop and weed hosts of Ralstonia solanacearum biovar 2 in the hills of Nepal
Authors: Pradhanang P. M. , Elphinstone J. G. , Fox R. T. V.
Published: March 2003

Common agricultural weeds and crops that grow in the high hills of Nepal were examined after artificial inoculation and under natural conditions in the UK and Nepal to determine whether such plant species could act as hosts to biovar 2 of Ralstonia solanacearum. Bacterial populations in the roots were determined 1 and 2 months after inoculation, and at various intervals after harvesting infected potato crops under natural conditions. Inoculated roots of the summer weeds Drymaria cordata and Polygonum capitata and the winter weeds Cerastium glomeratum and Stellaria media yielded 102−107 colony‐forming units per g root. High populations of the bacterium were recovered from these plants even after partial surface sterilization, indicating that systemic infection had occurred. Ralstonia solanacearum populations were recovered from root extracts of 75% of naturally growing D. cordata plants when sampled 3 months after harvest of a potato crop with bacterial wilt. Similarly, root extracts of 25% of P. capitata plants carried the bacterium. No potential winter weed hosts were infected under natural conditions when sampled 5 and 6 months after harvest of infected potato, indicating that winter conditions in the high hills of Nepal are not conducive to infection. Among crops, mustard (Brassica juncea cv. Fine White) developed typical wilt symptoms after artificial inoculation in warm glasshouse conditions (20–28°C). Mustard and barley are winter crops in Nepal. However, neither mustard (Brassica juncea var. Lumle Tori) nor barley (Hordeum vulgare cv. Bonus) was infected when planted into heavily infested plots under natural conditions. The results indicated that the role of nonsolanaceous summer weeds in the persistence of biovar 2 of R. solanacearum in the environment may have been previously underestimated.
Involvement of soilborne Phytophthora species in Central European oak decline and the effect of site factors on the disease
Authors: Jung T. , Blaschke H. , Oßwald W.
Published: March 2003

A survey was made on the occurrence of soilborne Phytophthora species in 35 oak stands on a range of geologically different sites in Bavaria. The most widespread species were P. quercina, P. cambivora and P. citricola. Seven other Phytophthora species were isolated infrequently. The fine root systems of 106 healthy and 111 declining mature trees of Quercus robur and Q. petraea were intensively investigated. The results indicate that, depending on the site conditions, at least two different complex diseases are referred to under the name ‘oak decline’. On sites with a mean soil pH (CaCl2)  3·5 and sandy‐loamy to clayey soil texture Phytophthora spp. were commonly isolated from rhizosphere soil, and highly significant correlations existed between crown transparency and various root parameters. Oaks with P. quercina or other Phytophthora spp. in their rhizosphere had markedly higher levels of fine root damage than oaks without Phytophthora spp., and were subject to a relative risk of severe crown symptoms of 2·1 and 2·8, respectively. In contrast, in stands with sandy to sandy‐loamy soils and a mean soil pH  3·9, Phytophthora spp. were not found. In these stands, correlations between crown transparency and various root parameters were either less significant or not significant. It is concluded that Phytophthora species are strongly involved in oak decline on sandy‐loamy to clayey sites with a mean soil‐pH (CaCl2)  3·5.
Sexual recombination in Phytophthora cinnamomi in vitro and aggressiveness of single‐oospore progeny to Eucalyptus
Authors: Linde C. , Soo S. H. , Drenth A.
Published: March 2003

Fifty single oospore progeny were established from an in vitro mating of A1 and A2 mating type isolates of Phytophthora cinnamomi from South Africa. Forty‐nine progeny were identified as F1 hybrids using seven random amplified polymorphic DNA (RAPD) primers, and one was a selfed isolate of the A1 mating type parent. Among the hybrid progeny, 24 and 25 were A1 and A2 mating type, respectively. Aggressiveness of progeny and parental isolates was assessed on 1‐year‐old seedlings of Eucalyptus smithii. The mean aggressiveness of hybrid oosporic isolates, expressed as lesion length, was significantly (P = 0·0001) lower than that of the parental isolates. No significant difference in aggressiveness of A1 and A2 mating type F1 hybrid isolates was observed. This is the first report demonstrating sexual recombination in vitro in P. cinnamomi.
Effect of early infection on pathotype frequencies in barley powdery mildew (Blumeria graminis f.sp. hordei) populations in field plots
Authors: Bousset L. , Schaeffer B. , De Vallavieille‐Pope C.
Published: March 2003

A field experiment with barley powdery mildew (Blumeria graminis f.sp. hordei) was designed in order to study how the time of arrival of inoculum in the field influenced pathotype frequencies in the resulting populations. Three isolates belonging to pathotypes that were absent or rare in the local aerial inoculum were used to inoculate field plots of winter barley cv. Plaisant. Two successive inoculations with different combinations of the three isolates were performed with an approximately two‐generation delay, and frequencies of inoculated pathotypes were assessed four and nine generations after the first inoculation. Pathotypes of the first inoculated isolates generally persisted throughout the period of sampling; this is described as an ‘early arrival’ effect. During the epidemics the inoculated isolates were not replaced by isolates from the natural airborne inoculum. Pathotype frequencies depended mainly on the time of arrival of inoculum in the plot, but frequencies also depended on the isolate that had been inoculated. The most frequent isolate, GL1, belonged to the clonal lineage dominant in powdery mildew populations on winter barley in the north of France. These results confirmed that the composition of a powdery mildew population in a field is largely determined by the composition of the initial inoculum.
Assessment of biological and molecular variability between and within field isolates of Plasmodiophora brassicae
Authors: Manzanares‐Dauleux M. J. , Divaret I. , Baron F. , Thomas G.
Published: March 2003

Plasmodiophora brassicae is an obligate biotroph that causes clubroot, one of the most damaging diseases of crucifers. Differential cultivars and random amplified polymorphic DNA markers were used to assess the extent of genetic diversity among nine single‐gall populations of P. brassicae and 37 single‐spore isolates (SSI) derived from four of those field samples. Isolates were classified into eight pathotypes, and each isolate was associated with a unique molecular genotype. Virulence and DNA polymorphisms were detected within and between field isolates, and among SSIs from different pathotypes, hosts and geographical origins. The relatively high level of genetic diversity among field isolates was similar to that among SSIs derived from a single‐club field isolate. Molecular and pathogenicity‐based classifications were not clearly correlated, but isolates belonging to pathotype P1 were clustered. Two RAPD markers were specific to pathotype P1. The finding that genetic differences can occur in P. brassicae field isolates will be an important consideration in resistance genetic studies and in choosing breeding strategies to develop durable clubroot resistance.
Molecular and morphological characterization of Colletotrichum gloeosporioides from native Mexican Stylosanthes species
Authors: Munaut F. , Hamaide N. , Maraite H.
Published: March 2003

A total of 264 Stylosanthes spp. plants collected from 78 Stylosanthes spp. populations in seven southern Mexican states were analysed for the presence of Colletotrichum spp. Isolates were obtained from 64 plants collected from 36 Stylosanthes populations; 198 isolates produced straight conidia, while 72 isolates produced falcate conidia. Molecular identification was performed to confirm the identity of C. gloeosporioides for the straight‐spored isolates. PCR amplifications using the primer CgInt, synthesized from an ITS1 fragment specific to C. gloeosporioides, and the universal primer ITS4 generated the target fragment for 120 Mexican isolates with straight conidia. The endonucleases Ava II and Sma I were used for restriction of the entire amplified ITS1 region of these 120 isolates. The tree constructed from the restriction data grouped 118 Mexican C. gloeosporioides isolates into three clusters containing reference isolates from Africa and Australia, and generated two additional clusters for two Mexican isolates. Conidial shape and growth rate on solid medium were used as the major morphological criteria for distinguishing types A and B. On the basis of 32 other morphological characteristics, a phenogram grouped the colonies into three main clusters. These clusters were partially related to the Stylosanthes species from which they were isolated, and to the molecular groups.
Factors affecting diseases of winter wheat in England and Wales, 1989–98
Authors: Hardwick N. V. , Jones D. R. , Slough J. E.
Published: March 2003

Samples from 360 to 450 randomly selected winter wheat crops in England and Wales were collected annually during the milky ripe development stages (GS 73–75) from 1989 to 1998. The number of samples from each region was proportional to the area of winter wheat grown. The percentage area affected by disease was assessed on the top two leaves and the ear, and the incidence and severity of stem base diseases were also recorded. An estimate of the percentage area of the crop affected by barley yellow dwarf virus (BYDV) and take‐all (Gaeumannomyces graminis) was made in the field. Septoria leaf blotch (Septoria tritici, teleomorph Mycosphaerella graminicola) was the major foliar disease recorded, with an average maximum severity of 7·8% of the area of leaf 2 affected in 1998. Eyespot (Tapesia spp.) was the major stem base disease, with the highest incidence of stems falling into the damaging moderate plus severe categories (18·9%) in 1998. Levels of powdery mildew (Blumeria graminis) showed a decline from 0·4% of the area of leaf 2 in 1989 to 0·1% in 1998. This fall was associated with a reduction in the proportion of disease‐susceptible cultivars grown. There were significant regional differences in levels of septoria leaf blotch, brown rust (Puccinia recondita), eyespot, sharp eyespot (Rhizoctonia cerealis) and BYDV. The percentage of crops treated with a fungicide rose from 96% in 1989 to 98% in 1998 and the mean number of spray applications per crop rose during this period from 2·1 to 2·5. A higher proportion of crops was treated with fungicides between the end of tillering and fifth node detectable (GS 24–35) than around flag leaf emergence (GS 36–48) or ear emergence (GS 49–71). Prior to 1994, the majority of late fungicide sprays was applied at, or after, ear emergence, but from 1994, the majority was applied around flag leaf emergence. The value and socioeconomic implications of the results are discussed.
Development of conventional and quantitative real‐time PCR assays for the detection and identification of Rhizoctonia solani AG‐3 in potato and soil
Authors: Lees A. K. , Cullen D. W. , Sullivan L. , Nicolson M. J.
Published: March 2003

A specific and sensitive PCR assay was developed for the detection and identification of Rhizoctonia solani AG‐3, the main causal pathogen of stem canker and black scurf of potato. A conventional primer set (Rs1F2 and Rs2R1) was designed from the nuclear ribosomal internal transcribed spacer (ITS1 and ITS2) regions of R. solani. Following PCR amplification, a 0·5‐kb product was amplified from DNA of all isolates of AG‐3 using primers Rs1F2 and Rs2R1. No product was amplified when DNA from isolates belonging to a range of other R. solani anastomosis groups or from a selection of other potato pathogens was tested, confirming the specificity of the primers for AG‐3 only. Rhizoctonia solani AG‐3 was also detected in potato tissue with varying black scurf severity, and in soil inoculated with sclerotia of R. solani to a minimum detection level of 5 × 10−4 g sclerotia/g soil. In addition, specific primers RsTqF1 (based on the Rs1F2 sequence) and RsTqR1, and a TaqMan™ fluorogenic probe RQP1, were designed to perform real‐time quantitative (TaqMan) PCR. The conventional PCR and real‐time PCR assays were compared and combined with direct DNA extraction from soil and a seed‐baiting method to determine the most reliable method for the detection and quantification of AG‐3 in both artificially inoculated field soil and naturally infested soils. It was shown that direct DNA extractions from soil could be problematic, although AG‐3 was detectable using this method combined with the real‐time PCR assay. The amplification of Rhizoctonia solani by seed baiting increased the sensitivity of the assay compared with direct extraction of DNA from the soil, and AG‐3 was detectable in artificially inoculated and naturally infested soils when seed baiting was combined with either the conventional PCR or the real‐time PCR assay. The potential for using these rapid and quantitative AG‐3‐specific assays to address epidemiological questions and as tools for decision‐making in disease management is discussed.
Detection of Strawberry crinkle virus in plants and aphids by RT‐PCR using conserved L gene sequences
Authors: Posthuma K. I. , Adams A. N. , Hong Y. , Kirby M. J.
Published: March 2003

About 10% of the large (L) protein gene of Strawberry crinkle virus (SCV) was sequenced after amplification with degenerate primers designed to conserved regions of the rhabdovirus L protein. The virus sequence was extended to 1362 nucleotides through rapid amplification of cDNA ends. One pair of degenerate L gene primers amplified a 683‐bp fragment from four different isolates of SCV cultured in the experimental host Physalis pubescens; the nucleotide sequences of these fragments differed by < 1% to 10% indicating the suitability of this region as a diagnostic target. This information enabled the development of a reverse transcription polymerase chain reaction (RT‐PCR) detection method for SCV using primers designed to the L gene sequence. SCV was amplified from infected P. pubescens (573 bp fragment) and from infected Chaetosiphon fragaefolii aphids (770 bp fragment). SCV was also detected by RT‐PCR in total RNA extracts from three strawberry plants showing symptoms typical of SCV infection but failed when the intensity of the disease symptoms decreased. However, both SCV positive‐sense RNA, and negative‐sense genomic RNA, were detected by nested PCR in chronically infected strawberry plants sampled in September.
Potato latent virus: a proposed new species in the genus Carlavirus
Authors: Brattey C. , Badge J. L. , Burns R. , Foster G. D. , George E. , Goodfellow H. A. , Mulholland V. , McDonald J. G. , Jeffries C. J.
Published: March 2003

A previously undescribed carlavirus, potato latent virus (PotLV), was found infecting the potato cultivar Red La Soda imported from the USA. The particles were filamentous and slightly curved, with modal lengths of 530 and 670 nm. The 11 kDa protein encoded downstream from the coat protein contained a ‘zinc‐finger’ motif characteristic of carlaviruses, and RT–PCR using a carlavirus‐specific primer gave a PCR product of 857 bp. Antibodies produced to PotLV did not detect other carlaviruses when used in ELISA and the coat‐protein nucleic acid sequence of PotLV showed < 67% similarity with the other carlaviruses tested. The closest similarity was with the Andean strain of potato virus S. Unusually for a carlavirus, PotLV systemically infected Nicotiana bigelovii, N. glutinosa, N. rustica, N. tabacum and Physalis floridana.
Movement of Xanthomonas campestris pv. vitians in the stems of lettuce and seed contamination
Authors: Barak J. D. , Koike S. T. , Gilbertson R. L.
Published: March 2003

Xanthomonas campestris pv. vitians, the causal agent of bacterial leaf spot of lettuce (BLS), can be seedborne, but the mechanism by which the bacteria contaminates and/or infects lettuce seed is not known. In this study, the capacity of X. campestris pv. vitians to enter and translocate within the vascular system of lettuce plants was examined. The stems of 8‐ to 11‐week‐old lettuce plants were stab‐inoculated, and movement of X. campestris pv. vitians was monitored at various intervals. At 4, 8, 12 and 16 h post‐inoculation (hpi), X. campestris pv. vitians was recovered from 2 to 10 cm above (depending on stem length) and 2 cm below the inoculation site. Xanthomonas campestris pv. vitians was also recovered from surface‐disinfested stem sections of spray‐inoculated plants. Together, these results are consistent with X. campestris pv. vitians invading and moving systemically within the vascular system of lettuce plants. To investigate the mechanism of seed contamination, lettuce plants at the vegetative stage of growth were spray‐inoculated with X. campestris pv. vitians and allowed to develop BLS. Seed collected from these plants had a 2% incidence of X. campestris pv. vitians external colonization, but no bacteria were recovered from within the seed.
Role of wild Prunus species in the epidemiology of European stone fruit yellows
Authors: Carraro L. , Ferrini F. , Ermacora P. , Loi N.
Published: March 2003

Several uncultivated trees of the species Prunus spinosa, P. cerasifera and P. domestica, sampled both adjacent to European stone fruit yellows (ESFY)‐infected orchards and in isolation from cultivated stone fruit plants, were found to be infected by ESFY phytoplasma. These species were also colonized by Cacopsylla pruni, vector of the ESFY agent. In contrast, uncultivated species of Prunus avium, P. cerasus and P. mahaleb hosted neither the pathogen nor the vector. Insect‐ and graft‐transmission trials of ESFY phytoplasma conducted under controlled conditions confirmed the data obtained in the field. The role played by the wild Prunus species is discussed and appears to be fundamental in the epidemic cycle of the disease.
Pathogenicity and race characterization of Fusarium oxysporum f. sp. phaseoli isolates from Spain and Greece
Authors: Alves‐Santos F. M. , Cordeiro‐Rodrigues L. , Sayagués J. M. , Martín‐Domínguez R. , García‐Benavides P. , Crespo M. C. , Díaz‐Mínguez J. M. , Eslava A. P.
Published: March 2003

Virulence (≡ severity of disease) and physiological specialization of nine isolates of Fusarium oxysporum f. sp. phaseoli recovered in El Barco de Avila (Castilla y León, west‐central Spain) and of two isolates from Chryssoupolis (Greece) were determined. The susceptibility/resistance response showed by a differential set of common bean cultivars (Phaseolus vulgaris) selected at the Centro Internacional de Agricultura Tropical (CIAT) delineated the isolates into two new races: races 6 and 7. The results of pathogenicity tests did not show any significant differences in virulence among the isolates. However, the reactions of several Spanish common bean cultivars indicated the presence of two groups of isolates, highly virulent and weakly virulent, among the Spanish isolates analysed. These results indicate that isolates classified in the same race are not homogeneous with respect to virulence, and suggests that race analysis using the CIAT differential cultivars is insufficient to describe the physiological specialization of F. oxysporum f. sp. phaseoli.
Mechanisms involved in control of Blumeria graminis f.sp. hordei in barley treated with mycelial extracts from cultured fungi
Authors: Haugaard H. , Collinge D. B. , Lyngkjær M. F.
Published: March 2003

Treatment with mycelial extracts, prepared from liquid cultures of Bipolaris oryzae, Pythium ultimum and Rhizopus stolonifer, protected barley (Hordeum vulgare) against powdery mildew disease caused by the fungus Blumeria graminis f.sp. hordei. The mechanisms of this protection were studied using histopathological methods and molecular analysis. Germination and appressorial formation of B. graminis were generally reduced after treatment with mycelial extracts. Although this reduction (between 12 and 62% depending on treatment and experiment) was inconsistent and only occasionally significantly different from the water‐treated control, it indicated a direct antifungal effect of the extracts. In situations where the fungus succeeded in forming an appressorium, penetration efficiency and haustorium formation from these appressoria was not affected – no enhanced penetration resistance associated with papilla formation was detected. However, a post‐penetration effect was observed, as B. graminis colonies on mycelial extract‐treated leaves produced 50% fewer hyphae than on controls. Northern blot analyses showed earlier accumulation of defence‐related gene transcripts following treatment with B. oryzae and P. ultimum mycelial extracts, and to a lesser extent R. stolonifer mycelial extract, compared with water‐treated leaves. It is suggested that the protection mechanism of the mycelial extracts involves direct antifungal effects and possible induced resistance for the B. oryzae and P. ultimum mycelial extracts.
Black dot (Colletotrichum coccodes): an increasingly important disease of potato
Authors: Lees A. K. , Hilton A. J.
Published: March 2003

In recent years black dot (Colletotrichum coccodes) has become an economically important disease problem in potato (Solanum tuberosum). It is characterized by silvery lesions on the tuber surface which result in a deterioration in skin quality. In addition to causing tuber blemish symptoms, C. coccodes also causes symptoms on stems and foliage, resulting in crop losses in some countries, and is implicated as a factor in the potato early dying disease complex. In the past, the incidence and severity of black dot might have been underestimated, as tuber symptoms were often mistaken for silver scurf (Helminthosporium solani). Inoculum of C. coccodes can be both seed tuber‐ and soilborne, and disease control is difficult as there are few chemical control methods and little resistance in commercial cultivars. Cultural control options offer the only potential means to control this disease at present. Current developments in rapid and specific PCR‐based detection methods are being used to address epidemiological questions.
Taxonomy of Wisteria vein mosaic virus and extensions to its host range and geographical distribution
Authors: Clover G. R. G. , Tang Z. , Smales T. E. , Pearson M. N.
Published: March 2003

Wisteria mosaic, a serious disease of Wisteria spp. in horticultural production in many parts of the world, is caused by a virus, Wisteria vein mosaic virus (WVMV). This paper reports the presence of the virus in a new host, Wisteria venusta, and a new geographical distribution, New South Wales, Australia. A partial sequence (1329 nucleotides) of this isolate of WVMV was obtained, which represents the first available sequence data for the virus. Alignment of the nucleotide and predicted amino acid sequences with those of members of the Potyviridae showed closest identity with viruses of the Potyvirus genus. The predicted amino acid sequence has one open reading frame, open at the 5′ end, corresponding to part of the nuclear inclusion b protein and the capsid protein, followed by a 251‐nucleotide untranslated region and a polyadenylated tail at the 3′ end.
Association of HLA B27 with Benign Clinical Course of Nephropathia Epidemica Caused by Puumala Hantavirus
Authors: Mustonen  , Partanen  , Kanerva  , Pietilä  , Vapalahti  , Pasternack  , Vaheri
Published: March 2003

Both the severe course of nephropathia epidemica (NE) caused by Puumala hantavirus, and the fast progression of human immunodeficiency virus (HIV) disease, are associated with the HLA B8 DRB1*0301 haplotype. As HLA B27, on the contrary, is associated with the slow progression of HIV disease, we wanted to test whether the same is true for NE. Only six (8%) NE patients, half the figure expected, had the HLA B27 allele in 74 randomly selected hospital‐treated patients. All six had a benign overall clinical course of NE; none had any severe complications, the severity of renal failure was also mild, and the treatment time at the hospital was half that needed for HLA B27− patients (P = 0.004). Patients who were HLA B27− had maximal blood leucocyte count > 10.000 × 109/L (P = 0.020) more often, probably reflecting differences in immune response. Thus, similar HLA associations can be found in both HIV infection and NE caused by Puumala virus.
CD4− CD8− C.B‐17 SCID Thymocytes Enter the CD4+ CD8+ Stage in the Presence of Neonatally Grafted T Cells
Authors: Schneider  , Grönvik
Published: March 2003

The aim of this work was to study the selection of donor T cells and their influence on thymic development in C.B‐17 scid/scid (severe combined immunodeficient; SCID) mice during chronic graft‐versus‐host disease (GVHD). Recipient SCID mice (H‐2d), neonatally grafted with allogeneic peripheral T cells from CBA/J strain (H‐2k) of mice, only developed a mild acute GVHD, and were, at the chronic stage, devoid of pathological symptoms. Thymic cell numbers of injected mice differed from 105 to 1.2 × 107 at 2–3 weeks post‐injection (p.i.), and from 4 × 105 to 8.5 × 107 at 2 months p.i. In these mice, the thymus size was correlated to the CD4− CD8− (double negative; DN) to CD4+ CD8+ (double positive; DP) cell ratio, where at 2 months p.i, 8 out of 16 treated SCID mice contained 5 × 106 cells or more and also possessed the highest frequencies of endogenous DP cells (25–95%). In contrast to previous findings, peripheral donor T cells from allogeneic and syngeneic mice, infiltrating the host thymus, had a positive effect on the development of endogenous DP thymocytes. Furthermore, these thymocytes were developmentally blocked at the DP stage, occasionally in combination with the expression of CD25, CD44 and CD117 but in the absence of T‐cell receptor (TCR) expression. Also, at this time‐point, the CBA/J donor TCR Vβ repertoire was equal to that of normal CBA/J mice, but purified responding donor cells were proliferatively inhibited against H‐2d stimulators in ex vivo mixed lymphocyte cultures. In contrast, the same responders showed a pronounced proliferation against syngeneic H‐2Kk stimulators, suggesting either a reversion from anergy of autoreactive CBA/J T cells or a vast expansion of multiple self‐reactive T‐cell clones, when parked in a milieu with a lower concentration of self‐antigens.
Differential Adhesion Molecule Expression on Porcine Mononuclear Cell Populations
Authors: Arriëns  , Summerfield  , Mccullough
Published: March 2003

Adhesion molecule expression was analysed on porcine blood and lymphoid organ CD4+ CD8− naïve T helper (Th) lymphocytes, CD4+ CD8+ memory Th lymphocytes (particular to the pig), CD4− CD8high cytotoxic T (Tc) lymphocytes, CD4− CD8low NK cells (CD3− in the pig), CD4− CD8− T‐cell receptor‐γδ‐positive (TCRγδ+) lymphocytes, B lymphocytes and monocytes. While CD44 expression was relatively homogeneous amongst mononuclear cells, differences were noted for the integrins. Blood naïve Th lymphocytes were CD49dlow CD11alow, as were splenic naïve Th cells; blood memory Th lymphocytes were CD49dhigh CD11alow, splenic memory Th cells were CD49dhigh CD11ahigh with a CD49dhigh CD11alow subpopulation; blood Tc lymphocytes were mainly CD49dlow CD11alow, and splenic cells were CD49dhigh CD11ahigh. Lymph node lymphocytes were more homogeneous in their integrin expression. These were relatively CD49dlow CD11alow, except the memory Th lymphocytes which had higher integrin expression. B lymphocytes related to the majority of integrinlow T cells, while monocytes and NK cells were CD49dhigh CD11ahigh; γδ T lymphocytes showed variable CD49d expression but a CD11ahigh phenotype. CD49dhigh CD11ahigh co‐expression was found, and this phenotype was typical of, but not exclusive to, CD25+ (activated) lymphocytes. These results demonstrated that porcine memory Th lymphocytes and NK cells, as well as activated cells, would have increased integrin‐dependent activities compared with naïve Th lymphocytes, and integrin‐dependent reactions would probably vary between blood and lymphoid organ cells.
Dendritic Cells Enhance the Differentiation of Naïve B Cells into Plasma Cells In Vitro
Authors: Fayette  , Durand  , Bridon  , Arpin  , Dubois  , Caux  , Liu  , Banchereau  , BriÈre
Published: March 2003

We have shown previously that in vitro‐generated human dendritic cells have an effect on the response of B cells at various stages of their differentiation. In a culture system described for the in vitro induction of plasma‐cell differentiation, it was reported that naïve B cells have a poor propensity to differentiate into plasma cells. In such a culture system, 12% of naïve B cells differentiated into plasma cells in the presence of IL‐2 and IL‐10, despite the interruption of CD40 signalling which is necessary for plasma‐cell differentiation. However, as reported herein, naïve B cells differentiated fully into plasma cells in response to dendritic cells. Addition of dendritic cells enhanced this differentiation strikingly by recruiting 57% of B cells as plasma cells producing IgM, but also IgG and IgA. In this model, dendritic cells act in synergy with IL‐2 at an early stage of CD40‐dependent B‐cell differentiation, while IL‐2 and IL‐10 act together, at a later stage, in the generation of plasma cells in a CD40‐independent manner. Thus, in addition to the key role played by dendritic cells in the initiation of T‐cell responses, our results suggest that dendritic cells regulate humoral responses.
Efficient Presentation of House Dust Mite Allergen Der p 2 by Monocyte‐Derived Dendritic Cells and the Role of β2 Integrins
Authors: SUNG  , TAKETOMI  , SMITH  , PLATTS‐MILLS  , FU
Published: March 2003

Monocyte‐derived dendritic cells (MDDC) are potent antigen‐presenting cells (APC). The APC functions of MDDC in allergy were examined. MDDC presentation of the major house dust mite allergen Der p 2 resulted in 4–12‐fold higher T‐cell proliferation and markedly higher IFN‐γ and IL‐5 production than PBMC cultures. Comparable T‐cell proliferation was obtained with 10‐fold fewer MDDC than purified monocytes. MDDC cultured from adherent cells, or CD14+, CD11b+ or Percoll‐purified monocytes were comparable in presenting soluble Ag, and in stimulating allogeneic MLR. Importantly, MDDC presentation of Der p 2 resulted in both Th1 and Th2 stimulation, although MDDC are known to produce high levels of IL‐12 and stimulate biased Th1 responses. The basis for the potent APC function of MDDC was further examined. MDDC were found to be highly phagocytic. Immunoprecipitation studies showed markedly elevated ICAM‐1 expression but > 10‐fold reduction in LFA‐1 expression on MDDC compared with monocytes. Monoclonal antibody (MoAb)‐blocking experiments showed that ICAM–LFA‐1 interaction was essential for MDDC stimulation of Der p 2‐specific T‐cell proliferative responses. These results show that the use of MDDC as APC provides a simple, sensitive and versatile method for detecting T‐cell responses to allergens and that the strong phagocytic capability and the increased ICAM‐1 expression of MDDC contribute significantly to their Ag presentation potency.
Methyl‐Prednisolone Up‐Regulates Monocyte Interleukin‐10 Production in Stimulated Whole Blood
Authors: Hodge  , Hodge  , Flower  , Han
Published: March 2003

Glucocorticosteroids (GCS) have been used successfully in the treatment of inflammatory conditions such as asthma and acute graft‐vs‐host disease, but their mode of action remains unclear. There have been numerous reports of the in‐vitro suppression of cytokine production by GCS based on quantitation of cytokines by ELISA on bulk supernatants from isolated cell culture systems. We report the use of a whole‐blood intracellular cytokine assay which is more representative of an in‐vivo environment. We examined the effects of GCS, prednisolone and dexamethasone, on cytokine production by individual cells (monocytes, T lymphocytes and natural killer or NK cells) in heterogenous cell populations. Cells in whole blood were activated with various stimuli: phorbol ester and calcium ionophore for T cells, Escherichia coli lipopolysaccharide (LPS) for monocytes, and phytohaemagglutinin (PHA) plus interleukin (IL)‐12 for NK cells. Brefeldin A was used as an intracellular transport inhibitor to enhance the detection of intracellular cytokine production. The effects of various concentrations (10−5, 10−7, 10−9 and 10−11 m) of GCS on cytokine production were studied using multiparameter flow cytometry. After surface staining with fluorescently‐conjugated monoclonal antibodies (MoAbs) to identify cell type, cells were fixed and permeabilised. Intracellular cytokines interferon (IFN)‐γ, IL‐10, IL‐1α and β, IL‐2, tumour necrosis factor (TNF)‐α, and IL‐12 were stained with their respective conjugated MoAbs. The GCS both caused a dose‐dependent modulation of cytokine production by T cells, monocytes and NK cells. After 4 h, a decrease in the MFI (amount of cytokine produced per cell) was noted for all cell types. After 24 h a decrease in both MFI and the percentage of cells producing cytokine was observed for all cell types. The exception was monocyte production of IL‐10 which was enhanced at low concentrations of GCS (10−9 and 10−11 m). Our findings thus suggest that one anti‐inflammatory mechanism of GCS action may be through inhibition of the release of pro‐inflammatory cytokines IL‐1α and β, IL‐2, IFN‐γ and TNF‐α, and up‐regulation of the anti‐inflammatory cytokine IL‐10.