bluuebunny/crossref_metadata_2025 huggingface dataset:
Increase in Cucurbit Aphid–Borne Yellows Virus Concentration by Co–infection with Sap–transmissible Viruses does not Increase its Aphid Transmissibility
Authors: Bourdin D. , Lecoq H.
Published: May 2008

The cucurbit aphid–borne yellows virus (CABYV) is a new tentative member of the luteovirus group which is transmitted persistently by Myzus persicae and Aphis gossypii.

In muskmelon plants, mixed infection with CABYV and zucchini yellow mosaic virus (ZYMV) induced an increase in CABYV concentration estimated by double antibody sandwich–enzyme linked immunosorbent assay (DAS–ELISA), which was maximum after 3 weeks, of co–infection.

Assays, conducted with other cucurbit hosts and sap–transmissible viruses showed that a similar increase occurred with most of the potyviruses tested. However, cucumber mosaic virus (CMV) and squash mosaic virus (SqMV) were inefficient for less efficient than potyviruses) in increasing CABYV concentration.

Aphid transmission experiments were conducted to check whether increased virus multiplication could either enhance transmission rates or modify the mode of CABYV acquisition by aphids. However, when A. gossypii was used, no increases in CABYV, transmissibility nor in its acquisition mode were detected.
Screening for Barley Yellow Dwarf Luteovirus Resistance in Barley on the Basis of Virus Movement
Authors: Makkouk K. M. , Comeau A. , St‐Pierre C. A.
Published: May 2008

The movement of barley yellow dwarf luteovirus (BYDV) was evaluated in susceptible and resistant barley and bread wheat genotypes. After leaf inoculation, the virus infected the root system and the growing point of susceptible earlier than resistant, barley genotypes. No difference in virus movement occurred in resistant and susceptible wheat genotypes. It was possible to reliably differentiate susceptible from resistant genotypes when root extracts of 41 barley genotypes were tested by DAS‐ELISA 3 or 4 days after inoculation at the oneleaf stage. When barley plants inoculated at the two‐ or three‐leaf stage were assayed by tissue‐blot ELISA on nitrocellulose membrane, virus was detected in the phloem vessels of the growing points of the susceptible, but not of the resistant genotype, 4–6 days after inoculation. Our results thus suggest that screening for BYDV resistance in barley could be done quickly and cheaply especially when assays are made by the tissue‐blot test.
PVX MS, a New Strain of Potato Virus that Overcomes the Extreme Resistance Gene Rx
Authors: Tozzini A. C. , Ceriani M. F. , Cramer P. , Palva E. T. , Hopp H. E.
Published: May 2008

A new resistance‐breaking isolate of potato virus X (PVX MS; also called PVX fcaOl) that multiplies in genotypes carrying the Rx gene was detected in Argentina. Enzyme‐linked immunosorbent assay (ELISA) assessment of PVX multiplication in mechanically inoculated micropropagated plantlets revealed that PVX MS is able to replicate in both resistant (Rx) and suceptible plantlets whereas strain PVX cp is able to replicate only in the latter. Immunoblot detection with specific monoclonal an, tibodies showed that PVX MS belongs to the serotype PVXo (common or European strain), whereas PVX HB is included in the serotype PVXA (Andean). SDS polyacrylamide gel electrophoresis followed by immunoblotting of the coat proteins of the PVXst, rains cp, cp4, HB, and MS showed that they differed in mobility with apparent mol. wts of 27.9, 28.8, 29.9, and 29.4 kDa, respectively.
Scanning Electron Microscopy of Sclerotia of Sclerotinia trifoliorum and Related Species
Authors: Arseniuk E. , Macewicz J.
Published: May 2008

The microanatomy of immature ‘white’, ‘slightly pigmented’ and mature, 1‐month‐old ‘black’ sclerotia of Sclerotinia trifoliorum, S. sclerotiorum, and S. minor were studied by scanning electron microscopy (SEM). A surface mycelial network was present over sclerotia at maturity. Also dried exudate on the superficial, sclerotial cells at maturity was observed. At this stage of morphogenesis an outer layer of the wall of medullary hyphae was synthesized. Two zones (i.e., rind and medulla) of hyphal tissue in sections of mature sclerotia were distinguished. The wall of rind cells was thick and one‐layered, whereas the wall of medullary hyphae was thick and bi‐layered.

No lacunac (intercellular spaces) in sclerotial rind were found but the sclerotial medulla appeared to be lacunate in all three species. At the SEM level the structural organization of sclerotia of S. trifoliorum was identical to that one of sclerotia of S. sclerotiorum and S. minor. Thus, in the conducted investigation of the sclerotial stromata, a unique, structural characteristic of taxonomic importance to distinguish S. trifoliorum from the other Sclerotinia species was not found. Observations on the sclerotial morphogenesis in S. trifoliorum and the related species agree with and supplement the light and transmission electron microscope studies of other researchers.
Development and Application of Cloned DNA Probes for Clavibacter xyli subsp. xyli, the Causal Agent of Sugarcane Ratoon Stunting
Authors: Chung C. H. , Lin C. P. , Chen C. T.
Published: May 2008

EcoRI restriction fragments of genomic DNA from Clavibacter xyli subsp. xyli (CXX) were ligated with plasmid pUC18 and cloned in Escherichia coli JM109. The cloned DNA inserts from recombinant plasmids were EcoRI‐excised and labeled with non‐radioactive digoxigenin and used as probes. Ten specific DNA probes, RSD3, 15, 30, 31, 32, 35, 37, 41, 71, and 73 were selected for disease detection and pathogen differentiation. In the specificity tests, all of the 10 CXX DNA, probes differentiated Clavibacter xyli from other bacteria specifically. Seven out of the 10 CXX probes crossreacted with C. x. subsp. cynodontis (CXC) very weakly under moderate stringency wash conditions of hybridization. In the sensitivity tests, all of the 10 DNA probes detected the homologous DNA of CXX from 0.19 to 0.75 ng. To detect various cell numbers of CXX, the DNA probes detected 104 to 105 cells effectively. In Southern hybridizations, distinctly different band patterns were shown when the probes hybridized with DNA from CXX and CXC. Among these probes, RSD3, 15, 30, 31, 35, 37, and 71, efficiently detected CXX present in the sap collected from symptomless sugarcane.
Antagonism of Chaetomium globosum, Gliocladium virens and Trichoderma viride to four soil‐borne Phytophthora species
Authors: Heller W. E. , Theiler‐Hedtrich R.
Published: May 2008

Chaetomium globosum, Gliocladium virens and Trichoderma viride, isolated from soil samples from the Kivu‐region of Zaire, are antagonistic and mycoparasitic to four soil‐borne Phytophthora spp. Radial growth of Phytophthora cinnamomi, P. cactorum, P. fragariae or P. nicotianae mycelia was inhibited in all antagonist‐pathogen combinations; mycelial mats of Phytophthora colonies were overgrown by the antagonists and hyphae lysed. Samples of mycoparasited mycelium, plated on benlateamended PDA to inhibit the development of antagonists, showed severely reduced vitality after 77 days of dual culture.
Effects of Foliar Sprays of Phosphates on Powdery Mildew (Sphaerotheca pannosa) of Roses
Authors: Reuveni R. , Agapov V. , Reuveni M. , Raviv M.
Published: May 2008

Powdery mildew on plants of a local clone of Rosa indica Major was significantly controlled by a single spray of 25 mM aqueous solutions of K2HPO4, KH2PO4 plus KOH, or NaHCO3, all plus Tween 20 (0.5 ml/l) or bupirimate (Nimrod) at 0.5 ml/l, which was applied 4 days before inoculation with conidial suspension of Sphaerotheca pannosa var. rosae.

Disease incidence was reduced by 79, 71, 54 and 50%, as compared to controls on plants sprayed with KH2PO4 plus KOH, K2HPO4, NaHCO3 or bupirimate, respectively. Phosphates were suppressive and expressed by disappearance of 99% of the pustules and conidia, as early as 2 days after a single spray on mildewed foliage. This treatment was efficient for at least 9 days after the first application when large infected greenhouse‐grown plants were used. Re‐application of these salts on the same plants reduced the lesion area by about 90% from that recorded before the application. Phosphate and bicarbonate were more suppressive than the systemic fungicide bupirimate in the early period (up to 2 days). The suppresion effects of bicarbonate and bupirimate, however, were short‐term and not persistent, while the phosphate treatments remained significantly suppressive for up to 23 days, when the experiment was terminated. The inhibitory and suppressive effectiveness of phosphate salts is discussed in the light of their possible acceptance as ideal foliar fertilizers which should be considered for use in the field for disease control.
Use of the Polymerase Chain Reaction and Sandwich‐Hybridization for Detecting Artichoke Mottled Crinkle Tombusvirus in Artichoke
Authors: Barbarossa L. , Grieco F. , Iosco P. , Gallitelli D.
Published: May 2008

Two non‐radioactive methods were applied for the detection of artichoke mottled crinkle tombusvirus (AMCV) in artichoke plant sap. A sandwich hybridization method was developed using a biotinylated transcript as capture and a digoxigenin‐labelled riboprobe. The hybrid was collected onto Nylon membranes coated with streptavidin using a slot‐blot procedure. The second method was the reverse transcriptional polymerase chain reaction (RT‐PCR) carried out with three different primers obtained from widely, separated sequences of AMCV genome. In artichoke plant sap, RT‐PCR was 20‐fold more sensitive than sandwich‐hybridization and 2.5‐fold less sensitive than dor‐blot hybridization labelled with radioactive reporter groups.
Stenocarpella maydis (Berk.) Sutton Colonization of Maize Ears
Authors: Bensch M. J.
Published: May 2008

A study was undertaken to determine the ramification of maize shank, cob and kernel tissues by Stenocarpella maydis. Trials consisting of inoculated and uninoculated treatments were planted at two localities. Shank, cob and kernels of each treatment were divided into segments and S. maydis colonization was determined. Infection of the pedicel portion of maize kernels was significantly higher than the apical portion. Preferential colonization of the embryo's of kernels was observed. Colonization of cobs occurred primarily at the attachment end of the cob, with sclerenchymatous tissues showing the greatest re‐isolation frequency. Shank segments did not show significant differences in S. maydis re‐isolation frequency, although a tendency for higher re‐isolations was observed at the stalk‐attachment end. It is concluded that S. maydis colonization occurs at the base of the ear with mycelial ramification toward the tip of the ear. The sclerenchyma and placentae were the primary colonized cob tissues. as were the embryos in the kernels.
RAPD Analysis of Pathogenic Variability in Ascochyta rabiei
Authors: Fischer C. , Porta‐Puglia A. , Barz W.
Published: May 2008

Thirty Italian isolates of the phytopathogenic fungus Ascochyta rabiei (Pass.) Labr., the causal organism of Ascochyta blight on chickpea (Cicer arietinum L.), were analysed by a random oligonucleotide primer dependent polymerase chain, reaction (PCR) technique called random amplified polymorphic DNA analysis (RAPD) using three decamer primers. In previous investigations these isolates had been differentiated in six pathogenic groups. RAPD results were summarized in an analysis using the program PAUP. With each of the primers several amplification products were observed which were common to all isolates. The results of the RAPD analyses also showed that all isolates could be identified by a unique RAPD pattern. No correlation between RAPD patterns and the division of the isolates in pathogenic groups could be established. The application of the RAPD technique for cataloguing isolates and to obtain specific genetic markers for all isolates of the species Ascochyta rabiei is discussed.
Changes in Carbohydrate, Protein and Chlorophyll Content, and Enzyme Activity During the Switch from Uredinio‐ to Teliospore Sporulation in the Bean‐rust Fungus Uromyces appendiculatus (Pers.) Link
Authors: Wagner S. , Boyle C.
Published: May 2008

Changes in carbohydrate metabolism and senescence during the development of the bean‐rust fungus Uromyces appendiculatus (Pers.) Link were investigated. At different stages of uredinio‐ and teliospore production, samples were taken from infected and non‐infected bean leaves, beginnig with the flecking stage. The unsoluble‐carbohydrate, sucrose, glucose and fructose content, as well as fluctuations in soluble acidinvertase activity and parameters of leaf senescence were determined.

While fructose remained constant without significant differences between infected leaf sections and the control, differences in the other carbohydrates and in soluble‐invertase activity could be detected. Parameters indicating leaf senescence were retarded and decreased with age, except for peroxidase activity, which was enhanced and increasd with age in infected tissue to a higher degree than in the control. The results are discussed in relation to their significance for fungal development.
Growth of Agrostis palustris in Response to Adventitious Root Infection by Curvularia lunata
Authors: Hodges C. F. , Campbell D. A.
Published: May 2008

Curvularia lunata is reported as a minor pathogen of adventitious roots of Agrostis palustris. C. lunata isolates from roots of A. palustris were evaluated for their ability to infect adventitious roots at temperatures ranging from 23 to 48°C. All isolates of C. lunata decreased both the shoot and root growth of root‐inoculated plants during a 10‐week observation period, but failed to produce the foliar symptoms observed in the field. Shoot and root weights of inoculated, plants were 47–66% and 55–69% of their respective controls. Infected roots were light tan in colour without lesions or rot, and infections were restricted to root hairs and cortical tissue. These observations are discussed relative to the nature of the pathogenicity of C. hunata as a root pathogen and its potential function in a root disease complex.
Occurrence of Phytoplasma Infection in European Plums (Prunus domestica)
Authors: Pollini C. Poggi , Bissani R. , Giunchedi L. , Vindimian E.
Published: May 2008

Phytoplasmas were constantly detected by the DAPI technique and by PCR amplification of DNA from European plums (Prunus domestica) cv ‘Susina di Dro’ with symptoms similar to those reported for Japanese plum leptonecrosis. These symptoms included upward rolling of the leaves, which also became bronzed‐reddish, thick and brittle, growth of normally dormant axillary buds, off‐scason growth during November January and phloem necrosis. Trees with symptoms showed progressive decline. RFLP analysis, revealed that the phytoplasma isolated from the affected plum trees is closely related to the other phytoplasmas present in Prunus species in Europe and can be included in the apple proliferation cluster. Although Japanese plum leptonecrosis is common in Europe. this is the first report of a wide‐spread phytoplasma‐induced decline in a cultivar of European plum.
PMTV‐Like Particles Inside Resting Spores of Spongospora subterranea
Authors: Merz U.
Published: May 2008

Rod‐shaped particles were found in cysts of a Spongospora subterranea cystosorus after freeze‐fracturing with a mean diameter of 20.5 nm and a maximum length of 500 nm. Their possible identity is discussed.
Isolation and Characterization of a Pseudomonas fluorescens Strain Suppressive to Bipolaris maydis
Authors: Mohamed S. , Caunter I. G.
Published: May 2008

Strain PJ0210, identified as Pseudomonas fluorescens, inhibited Bipolaris maydis both in vitro. The absence of detectable inhibitory substances assayed by a variety of methods indicated nutrient competition as the operative component of antagonism. This was further supported by observations of reduced inhibition by addition of glucose both in vitro and in vivo. Strain PJ0210 was adaptecd to the phyllosphere showing good survivability and colonizing ability both inplant house and field trials. Disease suppression was generally correlated with population sizes of strain PJ0210. Population sizes in the field were lower than those recorded in the plant house with a concomitant reduction in disease suppressive ability, of strain PJ0210.
Peroxidase Activity and Isoperoxidase Pattern in Tobacco Leaves Infected with Tobacco Necrosis Virus and Other Viruses Inducing Necrotic and Non‐Necrotic Alterations
Authors: Montalbini P. , Buonaurio R. , Kumar N. N. Umesh
Published: May 2008

The level of peroxidase activity was greatly enhanced in tobacco leaves infected by tobacco necrosis virus (TNV) and other viruses which induce necrotic symptoms (TMV, ToMV and PVYN). The intensity was related to the age of the leaves infected: absent or neglible in mature leaves and very pronounced in young growing infected leaves. On the contrary, changes in peroxidase activity were negligible when the infection was provoked by viruses which do not produce necrotic reactions (TMV and PVYO). Analysis of the peroxidase isoenzymes, pattern in tobacco leaves infected by TNV and other necrosis‐inducing viruses revealed in all cases, a slight increase in anionic (pl 3.5–3.7) and a considerable increase in moderately anionic isoenzymes particularly the pl 4.6 isoenzyme which in TNV and PVYN‐infected leaves reached levels up to 21 and 72 times the healthy control values. A considerable increase in the cationic (pl9.3–8.8) isoenzymes and the appearance of one moderately cationic isoenzyme (pl 8.2) was also detected. In leaf extracts from‐virus‐infected tobacco leaves with nonnecrotic response, no, or negligible alterations on the isoenzyme pattern were detected. However, infection by a fungal parasite (Erisyphe cichoracearum), which established a fully compatible, non‐necrotic, interaction with tobacco leaves, like the necrosis‐inducing viruses, changed the isoperoxidase pattern. The data suggest the necrotic alterations and associated changes in the peroxidase activity and isoperoxidase pattern in virus‐infected leaves are not clearly related.
A Monogenic Dominant Resistance of Tomato to Bacterial Wilt in Hawaii 7996 is Associated with Plant Colonization by Pseudomonas solanacearum
Authors: Grimault V. , Prior P. , Anaïs G.
Published: May 2008

Hawaii 7996, a tomato cultivar resistant to bacterial wilt caused by P. solanacearum was crossed with Floradel, a susceptible cultivar and the F1 and F2 seeds were obtained. Inoculated plants were tested in the field for bacterial wilt resistance and colonization by P. solanacearum. The F1 did not wilt and a significant 3:1 segregation for non wilting: wilting was observed in the F2, indicating a monogenic dominant resistance in Hawaii 7996. In the F2 and in Hawaii 7996, resistance was, associated to the limitation of bacterial spread in the stem. The degree of resistance of Floradel, the F2 and Hawaï 7996 was correlated to colonization at midstem. The usefulness of plant colonization criteria for breeding programs is discussed.
Polyploidy Among Isolates of Phytophthora infestans from Eastern Germany
Authors: Daggett S. S. , Knighton J. E. , Therrien C. D.
Published: May 2008

The ploidy of 101 isolates of Phytophihora infestans from the eastern states of the Federal Republic of Germany (formerly the German Democratic Republic) was determined by Feulgen DNA microdensitometry. The isolates used in this investigation were collected during 11 growing seasons between 1976 and 1990. Fifty hyphal nuclei per isolate were used for DNA measurements. Polyploids predominated throughout the 15‐year sampling period. Four of the isolates collected during 1989 were diploid. Based on the results of this investigation, there appears to have been no trend towards a diploid. sexual population during the sampling period.
The Influences of Epicuticular Wax Disruption and Cutinase Resistance on Penetration of Tomatoes by Colletotrichum gloeosporioides
Authors: Cruickshank R. H.
Published: May 2008

Conidia of Colletotrichum gloeosporioides germinated on green and ripe tomato fruit with intact epicuticular wax, and formed penetration pegs below melanized appressoria. If the delicate layer of epicuticular wax was distupted by abrasion or removed by solvents before inoculation, apparent increased diffusion of fruit substances into the inoculum stimulated fungal growth, hyphal anastomosis and the production of penetration pegs from hyaline appressoria. This was followed by cutlcle erosion centred on the penetration pegs in green fruit allowing sec‐ondary growth of infection hyphae. Due to the development of cutinase resistance when the cuticle became yellow at ripening, no cuticle erosion occurred at penetrations on ripe fruit Since cuticle erosion followed penetration of the cutinase‐susceptible cuticle and since penetration peg formation was not hindered by the cutinase cuticle, the process of primary penetration is regarded as mechanical.
The Natural Occurrence of Chickpea Chlorotic Dwarf Geminivirus in Chickpea and Faba Bean in the Sudan
Authors: Makkouk K. M. , Dafalla G. , Hussein M. , Kumari S. G.
Published: May 2008

A survey of faba bean and chickpea for virus infection, conducted during February 1994 in the Sudan, showed that bean yellow mosaic potyvirus and broad bean mottle bromovirus occurred commonly in both crops. Chickpea chlorotic dwarf geminivirus (CCDV) was detected for the first time in naturally infected chickpeas and faba beans. This is the first report of natural CCDV infection of chickpeas outside India and the first record of chickpea and faba bean infection in West Asia and North Africa (WANA).
In vitro Antagonism of Phytophthora cinnamomi and P. citricola by Isolates of Trichoderma spp. and Gliocladium virens
Authors: Chambers S. M. , Scott E. S.
Published: May 2008

Three fungi, isolated from soil from which Phytophthora was not obtained, were evaluated for antagonism of Phytophthora spp. shown to cause root rot of chestnut in South Australia. Trichoderma hamatum and T. pseudokoningii appeared to inhibit P. cinnamomi by mycoparasitism. with evidence of parallel growth and coiling, and both Trichoderma spp. and Gliocladium virens grew over P. cinnamomi in vitro, preventing further growth of this pathogen. Antibiotics produced by young T. hamatum cultures and G. virens in culture filtrate experiments inhibited growth of P. cinnamomi and P. citricola. with filtrate from 4‐day‐old cultures of G. virens showing the greatest potential for biocontrol. All three antagonists prevented P. cinnamomi and P. citricola from causing infection symptoms on micropropagated shoots of chestnut cvs Goldsworthy and Buffalo Queen in an in vitro excised shoot bioassay for biocontrol.
European Stone Fruit Yellows Phytoplasma as the Cause of Peach Vein Enlargement and other Yellows and Decline Diseases of Stone Fruits in Southern Italy
Authors: Marcone C. , Ragozzino A. , Seemüller E.
Published: May 2008

In the Campania region of southern Italy, peach trees showing vein enlargement and decline symptoms, as well as apricot and Japanese plum trees showing symptoms similar to that of apricot chlorotic leaf roll and plum leptonecrosis, respectively, were examined for phytoplasma infection using PCR technology. From diseased apricot and plum trees, the target DNA could be amplified with both universal phytoplasma primers and primers that are specific for fruit tree phytoplasmas of the apple proliferation group. However, from samples from diseased peach trees, detectable amplification products were only obtained by nested PCR, in which amplification with universal phytoplasma primers was followed by amplification with primers specific for the apple proliferation group. Following digestion of the amplification products with suitable restriction enzymes, all strains from apricot, plum, and peach showed the same restriction profiles that were identical to those of the European stone fruit yellows phytoplasma, a member of the apple proliferation group.
Alternaria alternata f. sp. helianthina: a New Pathotype of the Fungus Causing Alternaria Leaf Spot to Sunflower
Authors: Lagopodi A. L. , Thanassoulopoulos C. C.
Published: May 2008

Pathogenicity tests of Alternaria alternata pathogenic on sunflower were effected on various plants in order to determine the host range of the fungus. Twenty‐five plant species, including members of four botanical families of cultivated plants and seven families of weeds were tested in greenhouse experiments for susceptibility to the fungus by artificial inoculations. Among all plants tested sunflower was found to be the only species highly susceptible to this pathogen. To distinguish this A. alternata which attacks sunflower among other known formae speciales of the fungus we propose for it to be named as Alternaria alternata f. sp. helianthina f. sp. nova.
Barley Yellow Striate Mosaic Rhabdovirus Naturally Infects Cereal Crops in the Anatolian Plateau of Turkey
Authors: Makkouk K. M. , Bertschinger L. , Conti M. , Bolay N. , Dusunceli F.
Published: May 2008

Field surveys of cereal crops in the Anatolian Plateau of Turkey revealed that bread wheat, durum wheat, barley, triticale and oats are naturally itifected with barley yellow striate mosaic rhabdovirus. Identification was based on symptomatology, double antibody sandwich ELISA (DAS‐ELISA), tissue‐blot immunoassay (TBIA) and immunoelectron microscopy (IEM). BYSMV was identified in cereal fields near Ankara, Eskisehir, Konya, Karaman and in an area 70km north east of Isparta. Virus incidence in all the fields surveyed was less than 1%. This is the first report where evidence is presented on the natural occurrence of BYSMV on cereals in Turkey.
The Probability of Detecting Clavibacter michiganensis subsp. sepedonicus by Indexing Seed Potato Lots with Serological Tests
Authors: De Boer S. H. , Hall J. W.
Published: May 2008

Detection of the bacterial ring pot pathogen (Clavibacter michiganensis subsp. spedonicus) in seed potato lots by laboratory indexing complements visual inspection. The probability of detecting symptomless infections is a function of sample size and incidence of infection. We determined the incidence of asymptomatic stem and tuber infections in four potato cultivars at three levels of inoculum. At the high inoculum level, 51–93% of stems were infected at 80 days after planting, and 10–59% of the tubers were infected at harvest. The effect of the different percentages of infected stems and tubers on the probability of detection for simple random sampling was calculated for a constant sample size. The actual detection levels for two cultivars planted in field plots with predetermined incidence levels of ring rot infected plants were reasonably close to predicted probabilities.
The Spread of Epiphytic Populations of Xanthomonas campestris pv. vesicatoria on Pepper in the Field
Authors: Bernal R. F. , Berger R. D.
Published: May 2008

The spread of the epiphytic population of Xanthomonas campestris pv. vesicatoria and the disease it causes, bacterial leaf spot, were studied in field plots of pepper near Gainesville, Florida. In the summer of 1989, the epiphytic population of X. campestris pv. vesicatoria was dispersed to the west‐northwest from point sources of diseased plants. Winds from the southeast during rainstorms were essential for the spread of bacteria in the field. In the autumn of 1989, a focus of bacterial leaf spot developed naturally near the centre of the experimental plot. The epiphytic population of X, campestris pv. vesicatoria increased sharply after a 2‐day rain accompanied with strong wind. The wind was believed to be responsible for the transport of bacteria to distances 32 m from the focus. Initially in both seasons, the epiphytic populations occurred as distinct gradients from the focal sources of diseased plants. These gradients flattened over time and the disease incidence increased to near 100%, The increase in the epiphytic populations of the pathogen to > 3.0 log10 (cfu cm−2) on healthy plants away from the foci preceded disease appearance by several weeks. Applications of cupric hydroxide plus mancozeb significantly reduced the epiphytic population of X. campestris pv. vesicatoria on pepper leaves and slowed the spread of disease in the plots.
Location of the 5′ Termini of Tobacco Necrosis Virus Strain D Subgenomic mRNAs
Authors: Offel S. K. , Coutts R. H. A.
Published: May 2008

Northern blot analysis of double‐stranded (ds) RNA from bean‐leaf tissue infected with tobacco necrosis virus strain D (TNV‐D) detected the 4 kb genomic RNA and two subgenomic RNAs of about 1.5 kb and 1.2 kb; RNA extracted from virus particles only contained the genomic species. Blotting and probing with a range of probes indicated the approximate locations of the 5’ends of subgenomic RNA so that primers to fine‐map the ends could be designed. When both singlestranded and ds RNA, extracted from TNV‐D infected and healthy bean leaves were used as templates for primer extension using primers complementary to sequences at, or upstream of, the initiation codons of, respectively, the coat protein and the p7a genes, major infectionspecific products were detected. Both subgenomic RNAs start at G residues. The larger subgenomic RNA is 1547 nucleotides in length with a leader sequences of 36 nucleotides upstream of the p7a gene, and the smaller subgenomic RNA has a 90 nucleotide leader upstream of the coat protein AUG and is 1202 nucteotides long. An analysis of the 5’terminal locations of both subgenomic RNAs and the previously mapped analogous subgenomic RNAs associated with infection with the related TNV‐A isolate, revealed a marked degree of homology downstream of the initiation sites for each RNA. This homology was maintained at the 5’termini of both virion RNAs and could be extended to another isolate of TNV for which partial sequence data, but not subgenomic mapping RNA data are available.
The Natural Occurrence of Eggplant Mottled Dwarf Rhabdovirus in Tobacco in Italy
Authors: Polverari A. , Marte M. , Castellano M. A.
Published: May 2008

The natural occurrence of eggplant mottled dwarf rhabdovirus (EMDV) in field‐grown tobacco plants iti Italy is reported. The virus was identified by the differential reactions of herbaceous hosts, electron microscopy and serology. This seems to be the first record of natural itifection of tobacco by EMDV.
Characterization of Xanthomonas campestris pv. pruni strains from different hosts by pathogenicity tests and analysis of whole‐cell fatty acids and whole‐cell proteins
Authors: Scortichini M. , Janse J. D. , Rossi M. P. , Derks J. H. J.
Published: May 2008

Strains of Xanthomonas campestris pv. pruni obtained from Prunus armeniaca. P. domestica, P. persica and P. salicina in different geographical areas were compared for pathogenicity, fatty acid and wholecell protein analysis. Four strains, one per each host plant, were inoculated at the same time, on the foliage of P. armeniaca, P. avium, P. persica and P. salicina cultivars. Mean content of fatty acids of X.c. pv. pruni strains were also compared with those of many strains of X.c. pv. campestris, pv. graminis, pv. hyacinthii, pv. pelargonii and pv. vasculorum. Strains showed a remarkable homogeneity in fatty acids content and whole‐cell protein profiles and principal component and cluster analysis did not reveal any grouping according to original host or geographical origin. However, X.c. pv. pruni strains can be grouped apart from the other X. campestris pathovars. There appears to be no pathogenic specialization among the strains tested, however, they varied in aggressiveness to host plants and host plant in susceptibility. The most of the strains were able to cross‐infect species other that from where they were originally isolated, although, P. avium did not show any symptom of disease. P. persica cv. Sentry and P. salicina cv. Globe Sun, recently licensed as resistant to X.c. pv. pruni. were infected, although to a lesser extent, by some strains.
First Report of Phytoplasma Infection in Olive Trees (Olea Europea L.)
Authors: Pollini C. Poggi , Bissani R. , Giunchedi L. , Vindimian E.
Published: May 2008

In the Sarca valley (Trento, north Italy) the presence of olive trees (Olea Europea L.) with yellow symptoms in a few branches was observed. Some leaves showed diffuse chlorotic mottling affecting almost all the blade, while others showed mottling with green and yellow areas: leaf deformation was also sometimes present. Phytoplasmas were only detected in olive trees with yellow leaves by polymerase chain reaction (PCR) amplification and subsequent restriction fragment length polymorphism (RFLP) analysis. The results obtained suggested a high similarity between this phytoplasma and the elm yellows phytoplasma. This is the first time that a phytoplasma has been reported in the genus Olea.
The Role of Infective Plant Debris, and its Concentration in Soil, in the Ecology of Tomato Mosaic Tobamovirus—a Non‐vectored Plant Virus
Authors: Pares R. D. , Gunn L. V. , Keskula E. N.
Published: May 2008

Only a few plants in a crop are generally thought to become infected by abiotic soil transmission. In glasshouse experiments we have induced almost total infection in tomatoes growing in soil with infective debris, but levels of infection are dependent upon certain conditions. We found that as the inoculum concentration decreased (i) a greater percentage of the infections were either latent (symptomless) or restricted to roots and (ii) infection levels decreased. Thus, apparent infection (based on symptoms) of 0. 10% was in reality 0 60–70% based on enzyme‐linked immunosorbent assay and immunoelectron microscopy testing of roots and leaves. This occurred whether seedlings or seed were planted into infected mix. Under conditions in which minimal root damage was caused (planting seed) or roots were mechanically inoculated only once, almost all systemically infected plants were symptomless.
Effects of Plant Contact, Inoculation Pattern, Leaf Wetness Regime, and Nitrogen Supply on Inoculum Efficiency in Rice Sheath Blight
Authors: Castilla N. P. , Leaño R. M. , Elazhour F. A. , Teng P. S. , Savary S.
Published: May 2008

An experimental design was developed which allowed the measurement of inoculum efficiency (IE) represented by lesions of a leaf‐borne disease such as rice sheath blight. In this design. IE is measured as the ratio of newly established lesions on trap plants relative to the inoculum present in a canopy, i.e. lesions artificially established on source plants, IE of the rice sheath blight pathogen, Rhizoctonia solani, was studied under semi‐controlled conditions in which the effects of the following factors were measured; contact frequency among host tissues, amount and location of inoculum in the canopy, leaf wetness regime, and nitrogen content of the host plant. The conduciveness of these factors to sheath blight infection was measured in terms of IE which was expressed as the ratio of the density of daughter lesions on trap rice hills to the density of mother lesions on the inoculated quadrat hills. IE generally declined with the three successive batches of trap hills used in the experiments. It was significantly higher at closer plant spacings and under interrupted leaf wetness regimes. IE was not affected by the amount, nor by the location, of inoculum (mother lesions) in the canopy, but was significantly lower in hills with high total nitrogen content.
Systemic Migration of Pseudomonas syringae pv. avellanae in Twigs and Young Trees of Hazelnut and Symptom Development
Authors: Scortichini M. , Lazzari M.
Published: May 2008

At the beginning of October 1992 and 1993, healthy adult and young trees of hazelnut, cultivars Tonda Gentile Romana and Nocchione, were inoculated with a Pseudomonas syringae pv. avellanae strain through leaf scars located midway from the tip of the twig. In adult trees, the systemic migration and the population level of the pathogen were monitored during autumn and winter by means of weekly to monthly isolation and countings. In young plants, the possible displacement of the bacterium was checked in May by sampling different sites of the plant. At each sampling, the presence of internal and external symptoms was carefully assessed. During the 2‐year study, the results on migration and symptom development were consistent between the cultivars. Until the end of February. P.s. pv. avellanae colonized for approximately 45 mm, only the trait of the twig below the site of inoculation. At that time the population level ranged, in the farthest point reached by the pathogen, from 4.1 to 5.6 = 104 cfu/3 mm of twigportion. During March the pathogen was recovered from the tip of the twig. The first sign of disease was noticed in November as brown discolouration of the epidermis near the site of inoculation as well as internal necrosis of the vascular tissue. In young trees. P.s. pv. avellanae from the twig reached the branches, collar and roots from where it also colonized the branch which did not carry an inoculated leaf scar. Extensive twig dieback was noticed during April, whereas in June, most of the adult trees inoculated in autumn with approximately 25000 cells of the pathogen, randomly distributed in 25 sites of the crown, wilted completely. The role of leaf scars as a favourite site of penetration exploited by the pathogen as well as phytosanitary measures are discussed.
Differentiation of Yam Virus Isolates Using Symptomatology, Western Blot Assay, and Monoclonal Antibodies
Authors: Goudou‐Urbino C. , Givord L. , Quiot J. B. , Boeglin M. , Konate G. , Dubern J.
Published: May 2008

Monoclonal antibodies (mAbs) were prepared against a yam mosaic virus (YMV) isolate from the Côte d'Ivoire. Symptomatology, Western immunoblotting, and ELISA were used to discriminate 69 isolates of YMV originating from different Dioscorea species and from various yam producing areas. These isolates induced two types of symptoms, were of four different electrophoretic mobilities and formed two serogroups. These results suggest that at least six differetit groups of isolates exist, three of which infect the main cultivated species in various geographical areas while two others were from unusual samples in our collection. An isolate from ‘Pilimpikou Yam’ from Central Burkina Faso was serologically distinct. It is concluded that there is a significant variability among yam virus isolates which is unrelated to the origin of the isolate (geographic or host species). It is suggested that precautions should be taken in order to avoid international exchange of infected material.
Infection of Adventitious Roots of Agrostis palustris by Idriella bolleyi1
Authors: Hodges C. F. , Campbell D. A.
Published: May 2008

Seven isolates of Idriella bolleyi obtained from adventitious roots of Agrostis palustris displaying symptoms of thinning, low vigor, and death of turf in a random, nondescript pattern were evaluated for their ability to infect adventitious roots of A. palustris under high and low temperature regimes and to affect plant growth and symptom expression. All isolates of I. bolleyi infected roots under high and low temperature regimes and all but one isolate decreased shoot and root dry weight. Isolate IB‐2 decreased dry weight under low temperatures, but not under high temperatures. Stolon growth of root‐inoculated plants increased or remained unchanged among plants subjected to high temperature; stolon growth decreased on plants subjected to low temperature. Most isolates of I. bolleyi decreased the chlorophyll content of leaves of plants subjected to high temperature; chlorophyll content of leaves of inoculated plants subjected to low temperature remained unchanged. Hyphal growth was observed on inoculated adventitious roots and was accompanied by dark clusters of fungal cells and chlamydospores on the epidermis and cessation structures within the cortex. Vascular tissues were not penetrated by I. bolleyi. It was concluded that I. bolleyi can infect adventitious roots of A. palustris as a minor root pathogen and alter root and shoot growth.
Barley Yellow Dwarf Luteovirus (BYDV) Infectivity of Alate Aphid Vectors in Northeast Spain
Authors: Comas J. , Pons X. , Albajes R. , Plumb R. T.
Published: May 2008

Rhopalosiphum padi and Sitobion avenae alates were collected from colonised winter cereals and maize in N.E. Spain and fed on young wheat plants for 7–10 days in the glasshouse. Then, aphids were killed and the plants on which aphids reproduced were kept in the glasshouse for 30–40 days. ELISA of infested plants was made using polyclonal and monoclonal antisera against PAV‐, RPV‐ and MAV‐like isolates. In autumn and spring, MAV serotypes were transmitted by S. avenae and R. padi, mainly in mixed infections with PAV serotypes. This possibly explains the high frequency of MAV‐like isolates and their previously recorded year‐to‐year stability in maize, grain and forage winter cereals and cereal volunteers. PAV‐like isolates were rarely transmitted by S. avenae and its spread thus depends almost exclusively on R. padi. These results confirm the importance of forage cereals and cereal volunteers as virus sources for winter cereal infection in the autumn, and the latter as a source of BYDV for maize in spring.
Root Colonization by Bipolaris sorokiniana in Different Cereals and Relations to Lesion Development and Natural Root Cortical Cell Death
Authors: LIUEROTH E. , Franzon‐Almgren I. , Gunnarsson T.
Published: May 2008

A GUS‐transformed strain of B. sorokiniana was used to study the relationship between fungal growth, lesion development and natural root cortical cell death (RCD) in roots of different cereals. Roots of 10‐day‐old seedlings, grown on filter paper, were inoculated with the fungus and at different time intervals lesion size and GUS‐activity in the roots were determined. A significant, positive correlation was found between GUS‐activity and ergosterol content in barley roots infected with this transformed strain and these results indicate that GUS can be used as a marker to study fungal growth in plant tissue. The fungus had a slower growth rate in resistant barley varieties, i.e., those producing smaller lesions, than in more susceptible varieties.

In wheat and triticale, the fungal growth was faster than in barley, despite the smaller and lighter coloured lesions in these species. This may be explained by the fact that wheat and triticale have a faster rate of root cortical senescence than barley. Presumably, dying cortex cells cannot respond to the fungal invasion by producing phenolic compounds that cause browning of the tissue. Among seven investigated cereal species, there was a positive correlation between the degree of RCD and fungal biomass increase in roots after inoculation.
Interaction Of Barley Yellow Dwarf Virus and Fusarium culmorum (W. G. Sm.) Sacc. in Winter Wheat
Authors: Koch N. , Huth W.
Published: May 2008

The barley yellow dwarf virus (BYDV) epidemics, which occurred predominantly in northern Germany in 1988–90 and caused unusual yield losses of wheat, prompted our study on interactions of BYDV and Fusarium culmorum. At the late stages of plant development (EC 55/65) infections with BYDV resulted in a lower yield reduction of wheat plants than infections with F. culmorum. Combined infections at flowering resulted in severer yield reduction, indicating additive effects of the two pathogens. However, if wheat infected by BYDV at stage EC 25/35 was secondarily inoculated with the fungus at EC 55/65 the yield was less reduced than in combined infections at EC 55/65. Our results proved that the susceptibility of wheat plants to F. culmorum is increased when infection by BYDV takes place during the late stages of growth. These results correspond to observations during 3 years of the epidemic in Germany. In these years BYDV was spread mainly during the late spring, resulting in a severe secondary infection by the fungus. From the results of these investigations it may be concluded that during the years of BYDV epidemic the yield of wheat was reduced to an economically important extent because of the fungal infection, which was favoured by the virus infection.
Effect of Toxic Compounds of Exserohilum turcicum on Chlorophyll Content, Callus Growth and Cell Viability of Susceptible and Resistant Inbred Lines of Maize
Authors: Chauhan R. S. , Singh B. M. , Develash R. K.
Published: May 2008

Toxicity of toxic compounds in the culture filtrates of Exserohilum turcicum towards seed germination, inhibition of shoot and root growth, callus growth and on reduction in chlorophyll content and cell viability of maize was studied. There was no germination in unautoclaved extracts at 100% (undiluted) and 50% concentrations, whereas germination was normal at all the concentrations of autoclaved toxic compounds. Inhibition of root growth was higher compared with that of shoot growth in all the test preparations of toxic compounds. Reduction in total chlorophyll and also chlorophyll a and b contents of disease resistant (KWTC‐17) and susceptible (DK‐4) inbreds occurred at 50, 25 and 10% concentrations of toxic compounds, with maximum reduction in the susceptible compared with the resistant inbred. Chlorophyll a was found to be more sensitive, showing 7.2% reduction in content in susceptible inbred even at 5% toxin concentration. Callus cultures/cell suspensions derived from coleotible nodes of DK‐4 were more sensitive compared with that of KWTC‐17 in all the test concentrations of toxic compounds. Callus growth of susceptible inbred DK‐4 was inhibited by 32.7% compared with 15.31% of resistant inbred KWTC‐17 at 5% concentration of toxic compounds. Cell viability of resistant and susceptible inbreds was 62.0% and 20.2% at 10% toxic concentration, respectively. Spore germination assay with four fungal species or leaf puncture assay were not found useful.
PAL Activity and Differential Ozone Sensitivity in Tobacco, Bean and Poplar
Authors: Biagioni M. , Nali C. , Heimler D. , Lorenzini G.
Published: May 2008

Two cultivars of tobacco and bean and two clones of poplar differing in their phenomenological response to ozone were exposed to a single ozone pulse. The first visible foliar injury appeared after 24–48 h in the sensitive material only. The constitutive levels of PAL activity of ozone resistant and sensitive cultivars/clones were similar. In sensitive material, ozone induced a marked, but transient, increase in PAL activity, which in tobacco cv. Bel‐W3 and Pinto bean was associated with necrosis development. In the resistant material ozone stimulated PAL activity, but the levels remained lower than those observed in the sensitive material. Quantitative and qualitative determinations of phenolic compounds were carried out in the poplar clones. In the sensitive clone only the behaviour of caffeic acid was different, an increase being observed a week after the treatment. The resistant clone exhibited marked increase of all compounds assayed. The results are discussed in relation to the possible role of PAL and secondary metabolites to ozone toxicity mechanisms.