bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Fusarium oxysporum on Lettuce in Europe
Authors: Garibaldi A. , Gilardi G. , Gullino M. L.
Published: May 2007

In spring 2001, plants of the lettuce cv. Salad Bowl showing symptoms of a wilt disease were observed in several commercial plastic greenhouses near Bergamo, in northern Italy. Wilted plants were first observed during the spring and summer of 2001 when temperatures were between 26 and 35°C. Symptoms were observed in the same area and the same farms in March 2002, in concomitance with a period of high temperatures. Although the distribution of the disease was generally uniform, symptoms were more severe in the central part of the greenhouses where temperatures were warmest. Symptoms were first observed at thinning, when seedlings (30 days old) appeared wilted. Vascular tissues of affected seedlings appeared red or brown. Affected plants were stunted and developed yellow leaves and brown or black streaks in the vascular system. The vascular streaks in the yellow leaves extended from the crown and were continuous with a red-brown discoloration in the vascular system of the crown and upper taproot. Symptoms were typically not visible on the outside of the crowns or roots. Fusarium oxysporum was consistently and readily isolated from symptomatic vascular tissues on a Fusarium-selective medium (2). Seeds of cv. Salad Bowl were planted in steam-sterilized soil artificially infested with 1 × 104 CFU/g soil of each of two isolates of F. oxysporum obtained from infected plants. Plants grown in noninfested soil served as noninoculated control treatments. Plants (25 per treatment) were grown at 25 to 28°C in growth chambers. Wilt symptoms and vascular discoloration of the roots, crown, and veins developed 20 days after seeding for all plants grown in the infested soil, and F. oxysporum was consistently reisolated from infected plants. The pathogenicity test was conducted twice. To our knowledge, this is the first report of F. oxysporum on lettuce in Europe. A wilt of lettuce attributed to F. oxysporum f. sp. lactucae was reported in Japan in 1967 (3) and in the United States in 1993 (1), in the latter case the incitant organism was described as F. oxysporum f. sp. lactucum.

References: (1) J. C. Hubbard and J. S. Gerik. Plant Dis. 77:750, 1993. (2) H. Komada. Rev. Plant Prot. Res. 8:114, 1975. (3) T. Matuo and S. Motohashi. Trans. Mycol. Soc. Jpn. 8:13, 1967.
Interactions Between Rotylenchus reniformis and Pineapple mealybug wilt associated virus-1 in Pineapple
Authors: Sipes B. S. , Sether D. M. , Hu J. S.
Published: May 2007

The individual and combined effects of Pineapple mealybug wilt associated virus-1 (PMWaV-1) infection in pineapple, Ananas comosus, and Rotylenchus reniformis on pineapple growth were evaluated under greenhouse and field conditions. Under greenhouse conditions, no effect of PMWaV-1 infection on pineapple growth or nematode reproduction was observed. Under field conditions, the interaction of PMWaV-1 and nematodes was evaluated in plant and ratoon crops. In the plant crop, pineapple in plots treated with the nematicide 1,3-dichloropropane showed increased vegetative growth, whereas virus infection had no effect on vegetative growth. Nematodes reduced the average fruit weight (P = 0.01), whereas PMWaV-1 infection did not (P > 0.14). However, more fruit in the largest size classes (sizes 7 and 8) were produced in PMWaV-1-free plots than in PMWaV-1-infected plots (P = 0.03). The average fruit weight decreased in the presence of virus or nematodes. The smallest fruits were from PMWaV-1-infected plants infested with R. reniformis. More early-ripening fruit (30%) were produced by plants infected with PMWaV-1 than by PMWaV-free plants (P < 0.05). PMWaV-1 infection may be one of the reasons for asynchronous fruit ripening, which is a top limiting factor for pineapple production in Hawaii. In the ratoon crop, PMWaV-1 infection reduced fruit weight by 9% (P < 0.01), whereas nematode effects were similar across treatments (P > 0.10). More fruit in the three largest size categories were produced in PMWaV-1-free plots than in PMWaV-1-infected plots (P < 0.01). PMWaV-1 infection reduced the number of fruit produced in the ratoon crop (P < 0.02). An interaction (P < 0.03) between R. reniformis and PMWaV-1 infection status was detected in the ratoon crop. The fewest fruit were produced in plots with PMWaV-1-infected plants that were nematode infected.
Relative Incidence of Erwinia carotovora subsp. atroseptica in Stolon End and Peridermal Tissue of Potato Tubers in Canada
Authors: De Boer S. H.
Published: May 2007

An enrichment enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody 4F6, which is specific for the lipopolysaccharide antigen of serogroup I strains of Erwinia carotovora subsp. atroseptica, was used to detect the blackleg pathogen in potato seed lots after having confirmed that this serogroup is still the predominant strain of the pathogen in Canada. E. carotovora subsp. atroseptica was detected on <6% of tubers in most seed lots, but the level of tuber contamination increased with the number of field generations. The incidence of E. carotovora subsp. atroseptica was generally greater in tissue taken from the stolon end of tubers than from peel samples, although there was a positive correlation between the bacterium's presence in the two sample types. The incidence of E. carotovora subsp. atroseptica in seed tuber lots was estimated from the results of tests on multiple composite samples, providing a cost effective approach for indexing seed lots for blackleg risk. The incidence of E. carotovora subsp. atroseptica was two and three times greater for both stolon end and peel samples, respectively, after harvest and storage of seed lots compared with tubers hand dug just before commercial harvesting, which suggests that the process whereby tubers become contaminated has both field and postharvest components.
Selected Soybean Plant Introductions with Partial Resistance to Sclerotinia sclerotiorum
Authors: Hoffman D. D. , Diers B. W. , Hartman G. L. , Nickell C. D. , Nelson R. L. , Pedersen W. L. , Cober E. R. , Graef G. L. , Steadman J. R. , Grau C. R. , Nelson B. D. , del Rio L. E. , Helms T. , Anderson T. , Poysa V. , Rajcan I. , Stienstra W. C.
Published: May 2007

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a major soybean (Glycine max) disease in north-central regions of the United States and throughout the world. Current sources of resistance to Sclerotinia stem rot express partial resistance, and are limited in number within soybean germ plasm. A total of 6,520 maturity group (MG) 0 to IV plant introductions (PIs) were evaluated for Sclerotinia stem rot resistance in the United States and Canada in small plots or in the greenhouse from 1995 to 1997. Selected PIs with the most resistance were evaluated for resistance in the United States and Canada in replicated large plots from 1998 to 2000. The PIs in the MG I to III tests in Urbana, IL were evaluated for agronomic traits from 1998 to 2000. The selected PIs also were evaluated with an excised leaf inoculation and petiole inoculation technique. After the 1995 to 1997 evaluations, all but 68 PIs were eliminated because of their susceptibility to Sclerotinia stem rot. In field tests in Urbana, higher disease severity in selected MG I to III PIs was significantly (P< 0.05) associated with taller plant heights and greater canopy closure. All other agronomic traits evaluated were not associated or were inconsistently associated with disease severity. MG I to III PIs 153.282, 189.931, 196.157, 398.637, 417.201, 423.818, and 561.331 had high levels of resistance and had canopies similar to the resistant checks. The resistance ratings from the petiole inoculation technique had a high and significant (P< 0.01) correlation with disease severity in the MG I and II field tests. The partially resistant PIs identified in this study can be valuable in incorporating Sclerotinia stem rot resistance into elite germ plasm.
Ralstonia solanacearum Race 3, Biovar 2 Strains Isolated from Geranium Are Pathogenic on Potato
Authors: Williamson Lynn , Nakaho Kazuhiro , Hudelson Brian , Allen Caitilyn
Published: May 2007

Ralstonia solanacearum race 3, biovar 2 is a soilborne bacterium that causes potato brown rot disease in temperate and subtropical climates. Recent outbreaks of this disease in Europe have caused serious losses, but the pathogen had not been identified in the United States. However, in 1999, strains of R. solanacearum were isolated from wilting geraniums growing in Wisconsin greenhouses. Physiological and biochemical tests of the Wisconsin strains and a similar strain from South Dakota demonstrated that the strains belong to R. solanacearum subgroup biovar 2, which is largely synonymous with the race 3 subgroup, a classification based on host range. These results were confirmed by polymerase chain reaction analyses in which race 3, biovar 2-specific primers amplified a fragment of the expected size. This is the first report of race 3, biovar 2 in the United States, and it is the first known occurrence of race 3, biovar 2 in Wiscon-sin. The geranium strains were highly pathogenic on both geranium and potato. The presence of R. solanacearum race 3, biovar 2 in the United States raises concern that the bacterium could move from ornamental plants into potato fields, where it could cause both direct economic damage and quarantine problems. A commercial indirect enzyme-linked immunosorbent assay for R. solanacearum produced some false negatives for these strains, indicating that current indexing may not be sufficient to identify this destructive pathogen.
Bean common mosaic virus and Bean common mosaic necrosis virus in Mexico
Authors: Flores-Estévez N. , Acosta-Gallegos J. A. , Silva-Rosales L.
Published: May 2007

A survey was performed in Mexico to study the distribution of Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) using a set of primers directed to the coat protein gene (CP) that were designed to detect and characterize the two viral species. Both viral species were present in different locations in the country. BCMV was predominant in the central states of the country, whereas BCMNV proliferated toward the eastern tropical states. The alignment of nine nucleotide sequences for each viral species at the amino region of the CP gene confirmed the identities of the viruses and set the basis to assign them tentatively to pathogroups I, II, and VI.
Development of Real-Time PCR for the Rapid Detection of Episomal Banana streak virus (BSV)
Authors: Delanoy M. , Salmon M. , Kummert J. , Frison E. , Lepoivre P.
Published: May 2007

A real-time assay for the detection of episomal Banana streak virus (BSV; strain OL) in banana and plantains that carry integrated BSV sequences is described. Primers specific to the viral DNA were designed using the viral sequence integrated into the cv. Obino l'Ewai genome and the sequence of the genomic DNA of the infecting virus strain OL. They amplify a sequence of 1,336 bp that is detected in real-time by a short fluorogenic 3' minor groove binder DNA probe. This method enables reproducible and specific detection of episomal BSV from purified DNA as well as from crude extracts from infected plants. The assay is rapid, adaptable for large-scale experiments, and circumvents carryover problems.
Pre- and Post-harvest Harpin Treatments of Apples Induce Resistance to Blue Mold
Authors: de Capdeville Guy , Beer Steven V. , Watkins Christopher B. , Wilson Charles L. , Tedeschi Luís O. , Aist James R.
Published: May 2007

Harpin was studied for its ability to induce resistance in apple fruit to blue mold caused by Penicillium expansum after harvest. Red Delicious fruit were harvested and sprayed with harpin at 0, 40, 80, and 160 mg/liter applied as a commercial formulation. At 48, 96, and 144 h after treatment, fruit were wound inoculated with spore suspensions of P. expansum at 103, 5 × 103, or 104 spores/ml. The diameters of the resulting lesions were directly proportional to the inoculum concentration. Fewer fruit treated with harpin became infected relative to the controls, and disease progress was considerably reduced. In a second experiment, apple trees of the cultivars McIntosh, Empire, and Red Delicious were sprayed with different concentrations of harpin 8 or 4 days before harvest. Fruit were harvested, wounded, inoculated with the fungus, and stored in a commercial cold room. Fewer fruit treated with harpin became infected compared with the controls. Greater control resulted from the higher concentrations of harpin, but no difference in control occurred as a function of interval between the spray time and harvest. Spraying apple trees with harpin a few days before harvest is a promising strategy for reducing blue mold decay in storage.
Assessment of Resistance of Tubers of Potato Cultivars to Phytophthora erythroseptica and Pythium ultimum
Authors: Salas Bacilio , Secor Gary A. , Taylor R. J. , Gudmestad Neil C.
Published: May 2007

Tubers of 34 potato cultivars were examined for their susceptibility to infection by zoospores of Phytophthora erythroseptica and mycelia of Pythium ultimum. Incidence of infected tubers (%) and penetration of rot (mm) were the parameters used to determine the susceptibility of each cultivar. Tubers of cv. Atlantic appeared to have some resistance to infection and colonization by Phytophthora erythroseptica. Cvs. Russet Norkotah and Snowden were the most susceptible to infection by P. erythroseptica. Snowden was found to be highly susceptible to P. erythroseptica, but it was the most resistant to Pythium ultimum. Cvs. FL-1625 and FL-1867 also were less susceptible to P. ultimum than the other cultivars. Cvs. Superior, Itasca, and Dark Red Norland were the most susceptible to P. ultimum. Cultivar susceptibility should be considered when making disease management decisions, particularly in fields where these soilborne diseases are a recurring problem.
First Report of a Disease of Peony Caused by Alfalfa mosaic virus
Authors: Bellardi M. G. , Rubies-Autonell C. , Bianchi A.
Published: May 2007

During the summers of 2001 and 2002, Japanese peony (Paeonia albiflora Pall., synonym P. lactiflora, family Paeoniaceae) plants, cultivated in the Botanical Garden of the University of Parma (Emilia Romagna Region of northern Italy), were found affected by a disease with virus-like symptoms. The oldest leaves showed yellow, mosaic, oak-like arabesques and line-patterns; the remaining leaves and pink flowers were symptomless. A disease of peony, known as peony ring spot disease, has been reported worldwide (Europe, United States, Japan, and New Zeland) for several years and is associated with strains of Tobacco rattle virus (TRV) (1). Electron microscopic observations of peony leaf sap (leaf dip preparations stained with uranyl acetate and phospotungstic acid) did not show the presence of any rod-shaped virus particles, including TRV. Mechanical inoculations of sap from symptomatic leaves caused symptoms typical of Alfalfa mosaic virus (AMV) on Chenopodium amaranticolor Coste & Reyn. (local chlorotic and necrotic lesions and systemic periveinal line-patterns), Ocimum basilicum L. (yellow mosaic), Vigna unguiculata (L.) Walp. (red, local necrotic lesions), and Nicotiana tabacum cv. Samsun (white, necrotic lesions, systemic leaf malformation, and mosaic), and N. glutinosa L. (systemic leaf variegation). Symptomatic leaves of peony and infected herbaceous plants were analyzed for virus presence by protein A sandwich enzyme-linked immunosorbent assay (PAS-ELISA). The polyclonal antisera tested were those to AMV (PVAS 92, American Type Culture Collection, Manassas, VA), AMV-Vinca minor L. (DiSTA collection, Italy), and the nepoviruses Strawberry latent ringspot virus, Tomato ringspot virus, and Cherry leaf roll virus. PAS-ELISA revealed only the presence of AMV. Immunoelectron microscopy and gold-labeled decoration confirmed the identity of the virus. In 2001, five symptomless peony plants (provided by a commercial grower and previously analyzed for AMV and TRV presence) were grafted with shoots from peony showing yellow mosaic on the leaves and maintained in a greenhouse under aphid-proof cage. During the summer of 2002, one of the grafted plants showed a mild mosaic on the leaves; PAS-ELISA revealed this peony was infected by AMV. To our knowledge, this is the first report of AMV in peony.

Reference: (1) Chang et al. Ann. Phytopathol. Soc. Jpn. 42:325, 1976.
Interactions Between Beet necrotic yellow vein virus and Beet soilborne mosaic virus in Sugar Beet
Authors: Wisler G. C. , Lewellen R. T. , Sears J. L. , Wasson J. W. , Liu H.-Y. , Wintermantel W. M.
Published: May 2007

Soils naturally infested with cultures of aviruliferous Polymyxa betae and viruliferous P. betae carrying two sugar beet benyviruses, Beet necrotic yellow vein virus (BNYVV) and Beet soilborne mosaic virus (BSBMV), alone and in combination, were compared with noninfested soil for their effects on seedling emergence, plant fresh weight, and virus content as measured by enzyme-linked immunosorbent assay (ELISA). Studies examined sugar beet with and without resistance to the disease rhizomania, caused by BNYVV. The Rz gene, conferring resistance to BNYVV, did not confer resistance to BSBMV. BSBMV ELISA values were significantly higher in single infections than in mixed infections with BNYVV, in both the rhizomania-resistant and -susceptible cultivars. In contrast, ELISA values of BNYVV were high (8 to 14 times the healthy mean) in single and mixed infections in the rhizomania-susceptible cultivar, but were low (approximately three times the healthy mean) in the rhizomania-resistant cultivar. Results indicate BNYVV may suppress BSBMV in mixed infections, even in rhizomania-resistant cultivars in which ELISA values for BNYVV are extremely low. Soils infested with P. betae, and with one or both viruses, showed significantly reduced fresh weight of seedlings, and aviruliferous P. betae significantly decreased sugar beet growth in assays.
Efficacy of Chlorine on Multiple Species ofPhytophthorain Recycled Nursery Irrigation Water
Authors: Hong C. X. , Richardson P. A. , Kong P. , Bush E. A.
Published: May 2007

Recycled irrigation water is a primary source of inoculum for Phytophthora spp. and is capable of spreading propagules throughout nursery production. Chlorination commonly is used by the industry to disinfest recycled irrigation water; however, chlorine has not been fully researched as a disinfestant for this purpose. In this study, zoospores of seven species and eight isolates of Phytophthora were exposed for 2 min to free available chlorine at 0.25, 0.5, 1.0, 2.0, and 4.0 mg/liter. Zoospores, mycelial fragments, and culture plugs of P. nicotianae also were exposed to chlorine concentrations ranging from 0.25 to 8.0 mg/liter for periods ranging from 15 s to 8 min. In addition, chlorinated water was assayed monthly in 2000 and 2001 at two commercial nurseries, and quarterly in the first year at four other nurseries in Virginia, for chlorine and survival of pythiaceous species using a selective medium. No zoospores of any species tested survived endpoint free chlorine at 2 mg/liter, while limited mycelial fragments of P. nicotianae survived at 8 mg/liter, and mycelial plugs treated at the same level of chlorine were able to produce few sporangia. Phytophthora spp. were recovered only from nursery irrigation water with levels of free chlorine at 0.77 mg/liter or lower. The results of this study are essential for improving current chlorination protocols.
Sources of Partial Resistance to Fusarium Root Rot in the Pisum Core Collection
Authors: Grünwald N. J. , Coffman V. A. , Kraft J. M.
Published: May 2007

Fusarium root rot, caused by Fusarium solani f. sp. pisi, is one of the most important fungal diseases of pea and is found in most pea-growing areas around the world. Currently, no commercial cultivars are resistant to this pathogen. Availability of new sources of partial resistance could provide another tool for managing Fusarium root rot. In all, 387 accessions from the Pisum core collection were evaluated for resistance to Fusarium root rot in two independent experiments. Nonparametric analysis of variance conducted on ranks of disease severity for each accession indicated that the two experiments corresponded well. Forty-four plant introduction lines with a disease severity rating of 2.5 or less on a 0-to-5 scale (where 5 = completely rotted) were selected as being partially resistant to root rot. Immunity to Fusarium root rot was not found. Comparison of disease resistance data for Aphanomyces root rot and Fusarium root rot showed a weak, but significant and positive correlation. A complete listing of the data for the partial resistance of all accessions tested can be found at the National Plant Germplasm System website, United States Department of Agriculture-Agricultural Research Service.
Effect of Inoculation with Selected Isolates of Stagonospora nodorum on Field Evaluations of Host Resistance in Winter Wheat
Authors: Fraser D. E. , Murphy J. P. , Leath S. , Van Sanford D. A.
Published: May 2007

Although Stagonospora nodorum blotch occurs annually in North Carolina, selection for resistance in wheat (Triticum aestivum) breeding nurseries is hampered by the infrequent occurrence of heavy and timely disease pressure. The objective of this study was to compare estimates of host resistance in a population of 147 random winter wheat lines evaluated in epidemics produced by natural infection versus epidemics supplemented by inoculation with selected isolates. Two isolates were chosen from a set of 43 collected in North Carolina based on their aggressiveness on four wheat cultivars in a controlled environment test. Field experiments utilized a split-plot design with three replications. The main plots were inoculation treatments and the subplots were the 147 wheat genotypes. The inoculation treatments were (i) selected isolate A (more aggressive) alone, (ii) selected isolate B (less aggressive) alone, (iii) a combination of isolates A plus B, and (iv) natural infection. Selected isolate treatments were applied at Feekes growth stage 9 to 10.1, and disease intensity was measured two or three times at 14-day intervals postinoculation. The study was conducted at one location in the 1996-97 season and two locations in the 1997-98 season. High levels of natural infection occurred, and no differences were observed among the four inoculation treatments for mean disease intensity in any of the three environments. Within environments, genotype-by-inoculation treatment variance was significant in the two environments inoculated with selected isolates at growth stage 9 but not in the environment inoculated at growth stage 10.1. Magnitudes of genetic variation and heritability for Stagonospora nodorum blotch resistance were not consistently associated with main plot treatments, and inoculation with selected isolates masked genetic variation for resistance in two treatments in one environment. Genotype rank correlations for Stagonospora nodorum blotch resistance between inoculation treatments varied from zero to 0.69 within environments, but only a single correlation between inoculation treatments in different environments was observed. Estimates of host resistance in epidemics supplemented with selected isolates did not consistently agree with estimates in epidemics produced by natural infection. Our results did not support the routine use of supplemental inoculation of wheat breeding nurseries with selected isolates of S. nodorum as a means of increasing genetic gain for host resistance.
Properties of Strains of Sweet potato feathery mottle virus and Two Newly Recognized Potyviruses Infecting Sweet Potato in the United States
Authors: Souto E. R. , Sim J. , Chen J. , Valverde R. A. , Clark C. A.
Published: May 2007

Some biological and molecular properties of six potyvirus isolates (LSU-1, -2, -3, and -5; 95-2; and 95-6) from sweet potato (Ipomoea batatas) were evaluated. Isolates LSU-1 and -3 and 95-2 were transmitted by Aphis gossypii and Myzus persicae while LSU-2 and -5 were not transmitted by either aphid. The partial nucleotide sequence of the nuclear inclusion b (NIb) and the coat protein (CP) genes of these six isolates were compared with the corresponding sequences of 17 Sweet potato feathery mottle virus (SPFMV) strains and 18 other potyviruses. LSU-1 and -3 had high sequence similarity to the published sequences for Sweet potato virus G (SPVG), did not react with antisera to other known sweet potato viruses, and caused distinct symptoms. We propose to designate these two isolates as SPVG. This report documents the occurrence of this virus in the United States and provides the first characterization of its biological properties. LSU-2 and -5 were distinct in symptomatology; partial Nib, CP nucleotide, and derived amino acid sequence; and serology to other viruses. We propose to call this virus (LSU isolates 2 and 5) Ipomoea vein mosaic virus. The present study revealed a high degree of sequence similarity between 95-6 and the common strain of SPFMV, and between 95-2 and the russet crack strain of SPFMV. Results from this study suggest not only that at least two strains of SPFMV occur in the United States, but that two other potyviruses also are present.
Effects of Rate and Time of Application of Poultry Litter on Hoplolaimus columbus on Cotton
Authors: Koenning S. R. , Edmisten K. L. , Barker K. R. , Bowman D. T. , Morrison D. E.
Published: May 2007

Field experiments were conducted to evaluate the effect of soil-incorporated poultry litter on the population dynamics of Hoplolaimus columbus and cotton lint yield. Rates of poultry litter applied varied from 0.0 to 27.0 t/ha and were applied in December, February, or March. Time of application did not influence population densities of this nematode or cotton yield. The rate of poultry litter applied was negatively related to the population density of H. columbus at midseason, but not at other sampling dates. The lower midseason levels of this nematode corresponded with increases in cotton lint yield in all experiments. Cotton yield increases generally were linear with respect to the rate of litter applied, although the highest rates of litter applied did not always result in the greatest cotton yield. Poultry litter can be used effectively to supply nutrients to the crop and suppress damaging levels of H. columbus. Optimal rates of litter application were from 6.0 to 13.4 t/ha. Application of poultry litter at these rates, however, may exceed nutrient levels required for best management practices.
Cultivar Preference and Genotype Distribution of the Brown Stem Rot Pathogen Phialophora gregata in the Midwestern United States
Authors: Malvick D. K. , Chen W. , Kurle J. E. , Grau C. R.
Published: May 2007

Brown stem rot (BSR), caused by Phialophora gregata f. sp. sojae, is an important yield-limiting disease of soybean (Glycine max) in the midwestern United States. Midwestern populations of P. gregata are separated into genotypes A and B based on intergenic spacer sequences of nuclear ribosomal DNA. Genotype A causes both leaf and stem symptoms, and genotype B typically causes internal stem symptoms only. Data are limited on the geographic distribution of genotypes A and B. It is not well understood whether cultivars may be infected preferentially by a genotype. Field plots were established at five sites in Illinois, three sites in Wisconsin, and two sites in Minnesota in two different years. Soybean cvs. Bell, BSR101, Dwight, Sturdy, Williams 82, LN92-12033, and LN92-12054 were sown with two to four replications at each field site. From each plot, 5 to 10 stems were harvested arbitrarily at the R8 growth stage and assayed by polymerase chain reaction to detect the A and B genotypes. Both pathogen genotypes were detected at all locations except Urbana, where only genotype A was detected, and St. Paul, where only B was detected. Genotype A was the predominant genotype detected in susceptible cvs. Williams 82 and LN92-12054, with 70 and 78% of infected stems, respectively, positive for A. The other susceptible cultivar, Sturdy, yielded predominantly genotype A at four of the seven Illinois and Wisconsin locations where both pathogen genotypes were present, but yielded predominantly B at the Minnesota location where both genotypes were detected. Genotype B was the predominant type detected in partially resistant cvs. Dwight, LN92-12033, and Bell, with 56, 85, and 99% of the infected stems, respectively, testing positive for B.
Sclerotinia Stem and Crown Rot of Corn-Salad Caused by Sclerotinia minor in California
Authors: Koike S. T.
Published: May 2007

Corn-salad or lamb's lettuce (Valerianella locusta) is a specialty leafy green vegetable that is grown commercially in California and is harvested fresh for use in salads. In 2001, field plantings of corn-salad in coastal California showed symptoms and signs of a previously undescribed disease. Initial symptoms consisted of a light tan discoloration at the crown and lower leaf attachment areas. Once this discoloration was observed, the crown rapidly developed a soft rot, attached leaves wilted, and the entire plant collapsed. White mycelium and small (0.5 to 3.0 mm in diameter), irregularly shaped, black sclerotia formed on the crowns and lower leaves. Isolations from symptomatic crowns, mycelium, and sclerotia produced colonies of Sclerotinia minor (1). Seven-week-old corn-salad plants grown in a peat moss-based rooting medium in pots were used to test pathogenicity. Sclerotia from six corn-salad isolates from the Salinas Valley were inserted into slots made in the potting mix adjacent to the crowns of plants. Sclerotia were not placed in slots for control corn-salad. All test plants were incubated in a greenhouse at 21 to 23°C. After 4 weeks, inoculated corn-salad plants wilted and collapsed, and S. minor was reisolated from necrotic crown and stem tissues. Uninoculated plants were asymptomatic. Using the same method, sclerotia from one lettuce (Lactuca sativa) isolate were used to inoculate corn-salad plants that produced similar symptoms. All experiments were repeated and results were similar. To our knowledge, this is the first report of corn-salad as a host of S. minor in California and the United States. The susceptibility of corn-salad to S. minor from lettuce indicates that this crop might contribute to inoculum levels and lettuce drop incidence for the extensive lettuce plantings in the Salinas Valley.

Reference: (1) C. L. Patterson and R. G. Grogan. Plant Dis. 72:1046, 1988.
Variations in the Sensitivity of Phytophthora infestans Isolates from Different Genetic Backgrounds to Dimethomorph
Authors: Stein J. M. , Kirk W. W.
Published: May 2007

The sensitivities of 11 isolates of Phytophthora infestans to dimethomorph were examined at all stages of the asexual life cycle and when inoculated onto potato leaf discs. In vitro zoospore encystment and cyst germination were highly sensitive to dimethomorph with 50% reduction of mycelial growth and cyst germination (EC50) values for most isolates <0.20 μg/ml, whereas direct sporangia germination and in vitro hyphal growth and sporulation were less sensitive (means of 0.45 and 0.22 μg/ml, respectively). Zoosporogenesis was not significantly inhibited at the maximum dimethomorph concentration examined, 10 μg/ml. Significant differences (Fisher's least significant difference, P = 0.05) in the EC50 values were present between isolates for all stages of the asexual life cycle, except direct sporangia germination and zoosporogenesis. Sensitivity ratios between the least- and most-sensitive isolates were 6.11, 12.14, 12.36, and 10.56 for hyphal growth, in vitro sporulation, zoospore encystment, and cyst germination, respectively. Application of dimethomorph at 1,000 μg/ml to potato leaf discs at 24 or 48 h before inoculation completely inhibited symptom incidence for most isolates, whereas application after inoculation generally was not significantly different from the untreated control, regardless of concentration. Sporulation from leaf discs treated with dimethomorph at 24 or 48 h after inoculation was completely inhibited for all isolates with dimethomorph at 1,000 μg/ml, even when symptom incidence was not significantly reduced.
Biological and Phylogenetic Analyses Suggest that Two Cryphonectria spp. Cause Cankers of Eucalyptus in Africa
Authors: Roux J. , Myburg H. , Wingfield B. D. , Wingfield M. J.
Published: May 2007

Cryphonectria cubensis is an economically important pathogen of commercial Eucalyptus spp. Differences have been reported for disease symptoms associated with Cryphonectria canker in South Africa and other parts of the world, and recent DNA-based comparisons have confirmed that the fungus in South Africa is different from that in South America and Australasia. During a disease survey in the Republic of Congo, Cryphonectria canker was identified as an important disease on Eucalyptus grandis and E. urophylla. In this study, we compared Congolese and South African isolates of C. cubensis using DNA sequence data and pathogenicity under greenhouse conditions. The β-tubulin and internal transcribed spacer (ITS) region sequences show that C. cubensis in Congo is different from the fungus in South Africa and that Congolese isolates group most closely with South American isolates. Furthermore, pathogenicity tests showed that a South African isolate was more aggressive than two Congolese isolates. We conclude that two distinct Cryphonectria spp. occur in Africa and hypothesize that the fungus in the Congo probably was introduced into Africa from South America. Both fungi are important pathogens causing disease and death of economically important plantation trees. However, they apparently have different origins and must be treated separately in terms of disease management and quarantine considerations.
Development of Real-Time RT-PCR Assay for Detection of Prunus necrotic ringspot virus in Fruit Trees
Authors: Marbot S. , Salmon M. , Vendrame M. , Huwaert A. , Kummert J. , Dutrecq O. , Lepoivre P.
Published: May 2007

A real-time fluorescent reverse-transcriptase polymerase chain reaction (RT-PCR) assay using a short fluorogenic 3′ minor groove binder (MGB) DNA hydrolysis probe was developed for the detection of Prunus necrotic ringspot virus (PNRSV) in stone fruit trees. The covalent attachment of the minor groove binder moiety at the 3′ end of the probe increased the probe target duplex stability and raised the melting temperature to a range suitable for real-time analysis. The real-time RT-PCR assay correlated well with conventional RT-PCR results for the detection of PNRSV. This assay reliably detects PNRSV in bark tissues of dormant cherry and plum trees. Furthermore, it is well adapted for the routine detection of PNRSV because it eliminates one risk of contamination by performing the whole test in a single closed tube. This system may replace the commonly used diagnostic techniques (e.g., woody indicators and immunological tests) to detect this virus.
Mycofumigation with Muscodor albus and Muscodor roseus for Control of Seedling Diseases of Sugar Beet and Verticillium Wilt of Eggplant
Authors: Stinson A. M. , Zidack N. K. , Strobel G. A. , Jacobsen B. J.
Published: May 2007

Mycofumigation is the use of antimicrobial volatiles produced by fungi such as Muscodor albusitalic and M. roseus for the control of other organisms. Sugar beet (Beta vulgaris L.) stand establishment was increased and disease severity decreased by mycofumigation with M. roseus and M. albus in autoclaved soil infested with Rhizoctonia solani, Pythium ultimum, or Aphanomyces cochlioides. Eggplant seedlings (Solanum melongena L.) transplanted into autoclaved soil infested with Verticillium dahliae and mycofumigated with M. albus and M. roseus had significantly less disease (P < 0.05) after 4 and 5 weeks compared with nonmycofumigated Verticillium-infested soil. The effect of formulation on efficacy of mycofumigation with M. roseus was tested using potato dextrose agar strips, alginate capsules, ground barley, pesta granules, and stabileze granules. The stabileze and ground barley formulations of M. roseus resulted in the best control of P. ultimum damping-off. The best control of A. cochlioides damping-off was with the stabileze formulation, and the stabileze, ground barley, and agar strip formulations provided similar control of R. solani damping-off. In soil infested with P. ultimum, mycofumigation with M. albus stabileze formulation resulted in stand establishment similar to that in the autoclaved soil. Mycofumigation was ineffective in controlling Fusarium wilt of sugar beet. Neither M. albus nor M. roseus affected sugar beet or eggplant growth or appearance except in the stabileze formulation, where stunting was noticed. Mycofumigation with M. albus and M. roseus shows promise for control of soilborne diseases caused by P. ultimum, A. cochlioides, R. solani, and V. dahliae.
Broad-Spectrum Protection Against Several Pathogens by PGPR Mixtures Under Field Conditions in Thailand
Authors: Jetiyanon Kanchalee , Fowler William D. , Kloepper Joseph W.
Published: May 2007

Prior greenhouse experiments showed that four mixtures of plant growth-promoting rhizobacteria (PGPR) strains (all Bacillus spp.) elicited induced systemic resistance in several plants against different plant pathogens. Based on these findings, we sought to determine if systemic resistance induced by these PGPR would lead to broad-spectrum protection against several pathogens under field conditions in Thailand. Experiments were conducted during the rainy season (July to October 2001) and winter season (November 2001 to February 2002) on the campus of Naresuan University, Phitsanulok, Thailand. The specific diseases and hosts tested were southern blight of tomato (Lycopersicon esculentum) caused by Sclerotium rolfsii, anthracnose of long cayenne pepper (Capsicum annuum var. acuminatum) caused by Colletotrichum gloeosporioides, and mosaic disease of cucumber (Cucumis sativus) caused by Cucumber mosaic virus (CMV). Results showed that some PGPR mixtures suppressed disease more consistently than the individual PGPR strain IN937a. One PGPR mixture, Bacillus amyloliquefaciens strain IN937a + B. pumilus strain IN937b, significantly protected (P = 0.05) plants against all tested diseases in both seasons. Further, cumulative marketable yields were positively correlated with some treatments.
Fruit Distortion Mosaic Disease of Okra in India
Authors: Krishnareddy M. , Jalali Salil , Samuel D. K.
Published: May 2007

Okra (Abelmoscus esculentus (L.) Moench) is an important vegetable crop of India and other subropical and tropical countries. In 2000 and 2001, in the states of Karnataka and Tamil Nadu, okra was severely affected by a new disease. Since that time, the disease has spread to other states: Andhra Pradesh, Madhya Pradesh, Haryana, and Maharashtra. Chlorotic spots, chlorotic leaf blotches, distortion of leaves, chlorotic streaking, distortion of fruits, and severe yield losses as much as 63% characterize the disease. The causal virus induces local and systemic chlorotic and necrotic lesions on Vigna unguiculata (L.) Walp. cv. C-152 and Chenopodium amaranticolor Coste & Reyne., chlorotic local lesions and mosaic on Cucumis sativus L., necrotic local lesions on Gossypium hirsutum L. and black gram (Vigna mungo L.), and chlorotic local lesions and systemic necrosis on sunflower (Helianthus annuus L.). Host reactions on these species are similar to those described for the ilarvirus Tobacco streak virus (TSV) (3). Electron microscopic observation of leafdip preparations from field samples and partially purified virus preparations revealed the presence of isometric virus particles measuring 25 to 30 nm in diameter. The virus was purified from mechanically inoculated okra by differential and sucrose density gradient centrifugation, and disease symptoms were reproduced in okra mechanically inoculated with the purified virus. In direct antigen coated enzyme-linked immunosorbent assay and immunosorbent electron microscopy tests, the purified virus and sap extracts reacted positively with polyclonal antibodies to TSV, the ilarvirus associated with sunflower necrosis and peanut stem necrosis diseases (1,2), but did not react positively to Turnip mosaic virus and Okra mosaic virus that are previously reported to infect okra. In reverse transcription-polymerase chain reaction (RT-PCR), using oligonucleotide primers designed to amplify the entire coat protein region of TSV, an approximately 800-bp DNA fragment was obtained from purified virus and okra displaying fruit distortion mosaic disease (OFDM) but not from healthy okra. On the basis of host range, serological relationship, electron microscopy, and RTPCR amplification, the virus causing OFDM is an ilarvirus closely related to TSV. To our knowledge, this is the first report of the occurrence of an ilarvirus in okra, and is the third and most recent report of an ilarvirus related to TSV causing disease in crops on the Indian subcontinent (1,2).

References:(1). A. I. Bhat et al. Arch. Virol. 147:651, 2002. (2). A. S. Reddy et al. Plant Dis. 86:173, 2002. (3). S. W. Scott. Tobacco streak virus. No 381 in: Descriptions of Plant Viruses. CMI/AAB, Surrey, U.K., 2001.
First Report of Arceuthobium vaginatum subsp. cryptopodum on Pinus mugo
Authors: Mathiasen R. , Haefeli M. , Leatherman D.
Published: May 2007

Southwestern dwarf mistletoe (Arceuthobium vaginatum (Willd.) Presl subsp. cryptopodum (Engelm.) Hawksw. & Wiens, family Viscaceae) is a serious and common pathogen of ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson) in Colorado, Utah, Arizona, New Mexico, and northern Mexico (1). In July 2002, this dwarf mistletoe was observed parasitizing a 1.4-m tall mugo pine (P. mugo Turra) in the Black Forest north of Colorado Springs, CO (39°02.118′N, 104°36.028′W, elevation 2,250 m). The infected mugo pine was planted as an ornamental approximately 6 m from a ponderosa pine infected with A vaginatum subsp. cryptopodum. Dwarf mistletoe shoots were produced on the only infected branch observed but this was sufficient for a positive identification of the dwarf mistletoe. Although J. Weir successfully inoculated mugo pine with western dwarf mistletoe (A. campylopodum Engelm.) and lodgepole pine dwarf mistletoe (A. americanum Nutt. ex Engelm.) (2), to our knowledge, this is the first report of a dwarf mistletoe occurring naturally on P. mugo, as well as the first report of A vaginatum subsp. cryptopodum on P. mugo (1). Specimens of A vaginatum subsp. cryptopodum from P. mugo have been deposited in the Deaver Herbarium, Northern Arizona University, Flagstaff (Accession No. 73761).

References: (1) F. Hawksworth and D. Wiens. Dwarf mistletoes: biology, pathology, and systematics. USDA Agric. Handb. 709, 1996. (2) J. Weir. Bot. Gaz. 56:1, 1918.
First Report of a Geminivirus Associated with Leaf Curl in Baja California Peninsula Tomato Fields
Authors: Holguín-Peña R. J. , Vázquez Juárez R. , Rivera-Bustamante R. F.
Published: May 2007

Since November 2001, geminivirus-like symptoms (stunting, reduced leaf size, and leaf curling “chino”) have been observed in tomato (Lycopersicon esculentum Mill.) plantings in Baja California Sur, Mexico. Samples of symptomatic plants were collected from commercial fields and analyzed by traditional and molecular methods for the presence of geminiviruses. Inocula prepared from infected plants were experimentally transmitted to tomato seedlings and Datura stramonium by mechanical inoculation and whitefly transmission. Leaf curling and interveinal chlorosis symptoms similar to those found in the field were observed in inoculated tomato and D. stramonium. DNA from infected plants was extracted and analyzed by polymerase chain reaction (PCR) and electrophoresis using degenerate primers PALIv1978/PARIc494 (1). PCR fragments of the expected size (1.1 kb) for the common region (CR) were obtained from 28 of 64 plants, cloned and sequenced (GenBank Accession No. AY336088). Comparisons of CR sequences with the NCBI database by using BLAST and MegAlign (DNASTAR, London) indicated that the Baja Californian isolates were New World bipartite begomoviruses sharing the highest nucleotide sequence identity (93%) with a partially characterized geminivirus (Tomato severe leaf curl virus (ToSLCV); GenBank Accession No. AF130415) from Guatemala.

References: (1) M. R. Rojas et al. Plant Dis. 77:340, 1993.
First Report of Beet pseudo yellows virus in Strawberry in the United States: A Second Crinivirus Able to Cause Pallidosis Disease
Authors: Tzanetakis I. E. , Wintermantel W. M. , Martin R. R.
Published: May 2007

During efforts to characterize strawberry pallidosis disease, we identified a single strawberry plant that indexed positive for pallidosis disease by grafting but it was not infected with the Strawberry pallidosis associated virus (SPaV) based on reverse transcription-polymerase chain reaction (1). Leaves of this plant were grafted onto Fragaria vesca UC-4 and UC-5 and F. virginiana UC-10 and UC-11 indicator plants. The F. vesca plants remained asymptomatic, while the F. virginiana plants gave typical pallidosis symptoms that included marginal leaf chlorosis and epinasty. The combination of these symptoms on F. virginiana and lack of symptoms on F. vesca is used to define pallidosis disease (1). We extracted dsRNA from the original plant, and synthesized and cloned cDNA as previously described (2). Sequence analysis revealed several clones that corresponded to the published sequence of the Beet pseudo yellows virus (BPYV) heat shock protein 70 homolog gene (HSP70h). We transferred the isolate to Nicotiana benthamiana by using the whitefly vector, Trialeuroides vaporariorum, and then reisolated and cloned dsRNA from the infected N. benthamiana. Here we present the complete sequence of the HSP70h and minor coat protein (CPm) genes of the strawberry isolate of BPYV (GenBank Accession Nos. AY 267369 and AY 268107, respectively). Oligonucleotide primers BP CPm F (5′ TTCATATTAAGGATGCGCAGA 3′) and BP CPm R (5′ TGAAAG- ATGTCCACTAATGATA 3′) were designed to amplify a 334-nucleotide fragment of the CPm gene of the strawberry isolate of BPYV. Using this primer set, we were able to verify the presence of BPYV in 1- to 3-year-old plants from the major strawberry producing areas of the United States, including California, Oregon, and the Mid-Atlantic States. Infection rates were highest near Watsonville, CA where more than 20% of plants tested were infected with BPYV. To our knowledge, this is the first report of BPYV infecting strawberry. BPYV and the closely related SPaV (2) pose new concerns for the U.S. strawberry industry. Studies are currently underway to determine the effects of these two viruses on strawberry vigor and productivity.

References: (1) N. W. Frazier and L. L. Stubbs. Plant Dis. Rep. 53:524, 1969. (2) I. E. Tzanetakis et al. (Abstr.) Phytopathology 92:S82, 2002.
Fluctuations of Phytophthora and Pythium spp. in Components of a Recycling Irrigation System
Authors: Bush Elizabeth A. , Hong Chuanxue , Stromberg Erik L.
Published: May 2007

Stringent standards of water quality have prompted many horticultural enterprises to limit pollutant discharge associated with nutrient and pesticide applications. Collecting and recycling effluent is a method that has been implemented by many operations to contain pollutants; however, plant pathogens may be spread through recycled effluent. In this study, Phytophthora and Pythium spp. present in a water-recycling irrigation system at a perennial container nursery in southwestern Virginia were characterized using filtering and baiting techniques with two selective media. Members of Phytophthora were identified to species, whereas Pythium spp. were identified to genus only. Pythium spp. were recovered more frequently and in greater numbers than Phytophthora spp. Phytophthora capsici, P. citricola, P. citrophthora, P. cryptogea, P. drechsleri, and P. nicotianae were recovered in filtering assays. Only P. cryptogea and P. drechsleri were identified from baits placed on the surface of the irrigation reservoir, whereas P. cactorum, P. capsici, P. citricola, P. citrophthora, P. cryptogea, and P. drechsleri were recovered at depths, specifically at 1 and 1.5 m. This research provides data for development of detection technology and management practices for plant pathogens in irrigation water and may lead to improvements in conventional assay protocols.