bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulations of Fungicide Runoff Following Applications for Turfgrass Disease Control
Authors: Vincelli P.
Published: May 2007

Computer simulations of fungicide loading in surface water runoff were conducted with fungicides commonly used in golf course fairways and lawns in Kentucky. For all fungicides, values for degradation half-life and organic carbon partition coefficient were obtained from published sources; other input parameters were selected to simulate conditions typical in local swards. Spray programs were tested using a 21-year period of weather data for Lexington, KY. Predicted amounts of fungicide in runoff were determined, and predicted fungicide concentrations in runoff (mg/liter) were compared with 50% lethal concentration (LC50) values for rainbow trout and Daphnia magna. All simulated chlorothalonil applications produced runoff with concentrations that greatly exceeded the LC50 values for both indicator species. For some applications, concentrations of azoxystrobin, iprodione, and pentachloronitrobenzene exceeded LC50 values of at least one indicator species. Under the conditions simulated, runoff concentrations of metalaxyl, propiconazole, thiophanate methyl, and triadimefon were well below LC50 values of the indicator species. Although actual amounts of fungicide loaded into runoff were relatively low, these simulations suggest that turfgrass applications of fungicides with high intrinsic toxicity to indicator species could pose a risk to populations of primary and secondary consumers in aquatic ecosystems.
Photosynthesis of Blueberry Leaves as Affected by Septoria Leaf Spot and Abiotic Leaf Damage
Authors: Roloff I. , Scherm H. , van Iersel M. W.
Published: May 2007

Leaf spots caused by fungal pathogens or abiotic factors can be prevalent on southern blueberries after harvest during the summer and fall, yet little is known about how they affect physiological processes that determine yield potential for the following year. In this study, we measured CO2assimilation and leaf conductance on field-grown blueberry plants affected by Septoria leaf spot (caused by Septoria albopunctata) or by edema-like abiotic leaf blotching. Net assimilation rate (NAR) on healthy leaves varied between 6.9 and 12.4 μmol m-2s-1across cultivars and measurement dates. Infection by S. albopunctata had a significant negative effect on photosynthesis, with NAR decreasing exponentially as disease severity increased (R2≥0.726, P < 0.0001). NAR was reduced by approximately one-half at 20% disease severity, and values approached zero for leaves with >50% necrotic leaf area. There was a positive, linear correlation between NAR and leaf conductance (R2≥ 0.622, P < 0.0001), suggesting that the disease may have reduced photosynthesis via decreased CO2diffusion into affected leaves. Estimates of virtual lesion size associated with infection by S. albopunctata ranged from 2.8 to 3.1, indicating that the leaf area in which photosynthesis was impaired was about three times as large as the area covered by necrosis. For leaves afflicted by edema-like damage, there also was a significant negative relationship between NAR and affected leaf area, but the scatter about the regression was more pronounced than in the NAR-disease severity relationships for S. albopunctata (R2= 0.548, P < 0.0001). No significant correlation was observed between leaf conductance and affected area on these leaves (P = 0.145), and the virtual lesion size associated with abiotic damage was significantly smaller than that caused by S. albopunctata. Adequate carbohydrate supply during the fall is critical for optimal flower bud set in blueberry; therefore, these results document the potential for marked yield losses due to biotic and abiotic leaf spots.
First Report of Chickpea Chlorotic Dwarf Virus Infecting Spring Chickpea in Syria
Authors: Kumari S. G. , Makkouk K. M. , Attar N. , Ghulam W. , Lesemann D.-E.
Published: May 2007

During May 2003, a high incidence of symptoms suggestive of virus infection in spring chickpea were observed in many fields in Al-Ghab Valley, Syria, the ICARDA farm (near Aleppo, Syria), as well as in other locations in northern Syria, including the Idleb governorate. Symptoms observed were yellowing, stunting, and necrosis. A total of 1,345 chickpea samples with these symptoms (331 from Al-Ghab Valley, 269 from the ICARDA farm, and 745 from the Idleb governorate) were collected and tested for the presence of five viruses with tissue-blot immunoassay (TBIA) (4) at the Virology Laboratory of ICARDA, using the following antisera: monoclonal antibodies for Faba bean necrotic yellows virus (FBNYV, genus Nanovirus) (1); Bean leafroll virus (BLRV, family Luteoviridae) (4B10) (3); Beet western yellows virus (BWYV, genus Polerovirus, family Luteoviridae [ATCC PVAS-647, American Type Culture Collection, Manassas, VA]); and Soybean dwarf virus (SbDV, family Luteoviridae, [ATCC PVAS-650]) and polyclonal antibodies for Chickpea chlorotic dwarf virus (CpCDV, genus Mastrevirus, family Geminiviridae, provided by H. J. Vetten, BBA, Braunschweig, Germany). The most common virus present was BWYV (detected in 54.1% of samples tested), followed by CpCDV (19.2%), BLRV (10.2%), and FBNYV (5.5%). SbDV was not detected in any of the samples tested. Using immunosorbent electron microscopy, infected chickpea samples revealed low numbers of geminivirus-like particles after 15 min of incubation on CpCDV antiserum-coated grids. When CpCDV was purified from infected chickpea plants, the virus coat protein was 32 kDa with sodium dodecyl sulfate-polyacrylamide gel electrophoresis typical of CpCDV coat protein (2) and reacted strongly with CpCDV antiserum in western blots. The CpCDV vector in Syria was found to be Orosius albicinctus Distant, and is thought to be similar to Orosius orientalis (Matsumura), the reported vector of CpCDV (2). FBNYV, BWYV, and BLRV infection of chickpea have been previously reported from Syria, but to our knowledge, this is the first report of CpCDV infecting chickpea in Syria.

References: (1) A. Franz et al. Ann. Appl. Biol. 128:255, 1996. (2) N. M. Horn et al. Ann. Appl. Biol. 122:467, 1993. (3) L. Katul. Characterization by serology and molecular biology of bean leaf roll virus and faba bean necrotic yellows virus. Ph.D. thesis. University of Gottingen, Germany, 1992. (4) K. M. Makkouk and A. Comeau. Eur. J. Plant Pathol. 100:71, 1994.
First Report of Powdery Mildew Caused by Erysiphe viburni on Viburnum tinus in California
Authors: Koike S. T. , Shishkoff N.
Published: May 2007

In June 2003, landscape and potted nursery plants of laurustinus (Viburnum tinus) in Monterey County, California, were found to be infected with a powdery mildew. White, ectophytic mycelial and conidial growth were present primarily on adaxial leaf sides with only sparse growth on abaxial surfaces. Severely infected leaves were buckled and slightly twisted. Affected leaf tissue exhibited slight purple-to-brown discoloration. Appressoria were opposite and lobed. Conidia were produced singly, cylindrical in shape, and measured 31 to 42 × 14 to 19 μm. No fibrosin bodies were observed in the conidia, and the conidia germinated at the ends. Ascomata were not observed. The fungus was identified as Erysiphe (section Microsphaera) viburni Duby (= Microsphaera sparsa Howe = Microsphaera penicillata [M. sparsa is not completely synonymous with M. penicillata because M. sparsa is defined as only those mildews that attack viburnum, whereas M. penicillata was defined as attacking dogwood, alder, etc.]) (1,2). Pathogenicity was demonstrated by gently pressing infected leaves with abundant sporulation onto recently expanded leaves of four, large, potted laurustinus in standard 5-gallon nursery containers (19 liters). Twelve leaves per plant were inoculated. The plants were incubated in a greenhouse (23 to 25°C). After 9 to 10 days, powdery mildew colonies developed on approximately 50% of the inoculated leaves. Such colonies were morphologically similar to the original fungus. Uninoculated control plants did not develop powdery mildew. Using the same technique, inoculating fully mature leaves of the same plants did not result in disease. To our knowledge, this is the first report of Erysiphe viburni infecting V. tinus in California. At some landscaped areas the powdery mildew was extremely severe, causing plants to take on a whitish appearance and resulting in all new foliage being misshapen. E. viburni has also been reported to infect V. japonicum in California.

References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustave Fischer. New York, 1995. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000.
Sudden Death of Citrus in Brazil: A Graft-Transmissible Bud Union Disease
Authors: Román M. P. , Cambra M. , Juárez J. , Moreno P. , Duran-Vila N. , Tanaka F. A. O. , Alves E. , Kitajima E. W. , Yamamoto P. T. , Bassanezi R. B. , Teixeira D. C. , Jesus W. C. , Ayres A. J. , Gimenes-Fernandes N. , Rabenstein F. , Girotto L. F. , Bové J. M.
Published: May 2007

Citrus Sudden Death (CSD), a new, graft-transmissible disease of sweet orange and mandarin trees grafted on Rangpur lime rootstock, was first seen in 1999 in Brazil, where it is present in the southern Triângulo Mineiro and northwestern São Paulo State. The disease is a serious threat to the citrus industry, as 85% of 200 million sweet orange trees in the State of São Paulo are grafted on Rangpur lime. After showing general decline symptoms, affected trees suddenly collapse and die, in a manner similar to trees grafted on sour orange rootstock when affected by tristeza decline caused by infection with Citrus tristeza virus (CTV). In tristeza-affected trees, the sour orange bark near the bud union undergoes profound anatomical changes. Light and electron microscopic studies showed very similar changes in the Rangpur lime bark below the bud union of CSD-affected trees: size reduction of phloem cells, collapse and necrosis of sieve tubes, overproduction and degradation of phloem, accumulation of nonfunctioning phloem (NFP), and invasion of the cortex by old NFP. In both diseases, the sweet orange bark near the bud union was also affected by necrosis of sieve tubes, and the phloem parenchyma contained characteristic “chromatic” cells. In CSD-affected trees, these cells were seen not only in the sweet orange phloem, but also in the Rangpur lime phloem. Recent observations indicated that CSD affected not only citrus trees grafted on Rangpur lime but also those on Volkamer lemon, with anatomical symptoms similar to those seen in Rangpur lime bark. Trees on alternative rootstocks, such as Cleopatra mandarin and Swingle citrumelo, showed no symptoms of CSD. CSD-affected trees did recover when they were inarched with seedlings of these rootstocks, but not when inarched with Rangpur lime seedlings. These results indicate that CSD is a bud union disease. In addition, the bark of inarched Rangpur lime and Volkamer lemon seedlings showed, near the approach-graft union, the same anatomical alterations as the bud union bark from the Rangpur lime rootstock in CSD-affected trees. The dsRNA patterns from CSD-affected trees and unaffected trees were similar and indicative of CTV. CSD-affected trees did not react by immunoprinting-ELISA using monoclonal antibodies against 11 viruses. No evidence supported the involvement of viroids in CSD. The potential involvement of CTV and other viruses in CSD is discussed.
Timing of Preharvest Infection of Pear Fruit byBotrytis cinereaand the Relationship to Postharvest Decay
Authors: Lennox C. L. , Spotts R. A.
Published: May 2007

Botrytis cinerea causes significant levels of postharvest decay in the winter pear cultivar d'Anjou. The objectives of this study were to determine the timing of B. cinerea infection of pear stems and calyxes in the orchard during the growing season, to investigate the development of gray mold in storage, and to determine whether preharvest levels of B. cinerea in pear stems and calyxes can be used as predictors of gray mold levels observed in storage. Very low levels of B. cinerea were isolated from stem tissue prior to harvest. In a single year repeat experiment, stems sampled at harvest had higher levels of infection than those sampled earlier in the season. Little or no stem end gray mold was detected in fruit after 3 months in air-storage; however, incidence increased between 6 and 8 months. Calyx end gray mold was detected at low levels in fruit stored for up to 8 months. The mean incidence of stem end gray mold was 3.6 and 2.0%, and incidence of calyx end gray mold was 1.2 and 0.2%, in 1996 and 1997, respectively. Calyxes were susceptible to infection soon after full bloom; however, inoculation of calyxes in April or May did not result in higher levels of calyx end gray mold in storage. Therefore, preharvest level of calyx infection is a poor predictor of calyx end gray mold in storage. In addition, application of benomyl in the orchard reduced the level of B. cinerea in blossoms but had no effect on levels of calyx end gray mold of fruit in storage. Packing and shipping fruit within 3 to 6 months of harvest may mitigate economic losses due to gray mold.
Host Range of Phytophthora capsici from Pumpkin and Pathogenicity of Isolates
Authors: Tian D. , Babadoost M.
Published: May 2007

This study was conducted to determine the host range of Phytophthora capsici isolates from pumpkin and virulence of the isolates on pumpkin cultivars. The pathogenicity of P. capsici isolates from pumpkin was evaluated on 45 species of herbaceous plants, including 36 species of crops grown in rotation sequences with pumpkin and nine species of weeds that commonly grow in pumpkin fields in Illinois. Plants were grown in the greenhouse, and 4-week-old seedlings were inoculated by adding 5 ml of a zoospore suspension (2 × 105 spores per ml of water) onto the soil surface around the stem of each plant in the pot. Twenty-two crop species and two weed species became infected with P. capsici and developed symptoms. P. capsici was reisolated from all of the symptomatic plants by culturing tissues onto a semiselective medium (PARP). Also, P. capsici was detected in 87.5% of symptomatic plants by a polymerase chain reaction (PCR) method using PCAP and IT5 primers. Cucurbits and pepper were the most susceptible hosts of P. capsici. Five crop species or varieties, beet (Beta vulgaris), Swiss-chard (Beta vulgaris var. cicla), lima beans (Phaseolus lunatus), turnip (Brassica rapa), and spinach (Spinacia oleracea), and one weed species, velvet-leaf (Abutilon theophrasti), were found to be hosts of P. capsici for the first time. Six isolates of P. capsici were inoculated onto six pumpkin cultivars (three processing and three jack-o-lantern pumpkins) in the greenhouse and resulted in significant interactions between pathogen isolates and pumpkin types. P. capsici isolates were more virulent on jack-o-lantern pumpkins than on processing pumpkins.
Dose Curves of Disinfestants Applied to Plant Production Surfaces to ControlBotrytis cinerea
Authors: Copes W. E.
Published: May 2007

Lethal dose curves were calculated using probit analysis for six disinfestants (chlorazene hydrosol, hydrogen dioxide, hydrogen peroxide, iodine, quaternary ammonium chloride, sodium hypochlorite) when applied on seven substrates (galvanized metal, stainless steel, polyethylene ground fabric, polyethylene pot plastic, pressure-treated pine, exterior latex-painted pine, raw pine) that had been inoculated with Botrytis cinerea conidia. Mortality was determined by percentage of ungerminated versus germinated conidia that had been rubbed off of a substrate onto half-strength potato dextrose agar (hPDA) 16 to 24 h previously. Based on overlapping confidence limits (95% CL) of the lethal doses resulting in 90 and 50% mortality (LD90and LD50, respectively) and significance of slopes, differences occurred between substrates with all six disinfestants. LD90values ranged from 0.21 to 4.54 g a.i./liter for chlorazene hydrosol, 4.99 to 40.3 g a.i./liter for hydrogen dioxide, 63.0 to 233.1 g a.i./liter for hydrogen peroxide, 0.42 to 2.45 g a.i./liter for iodine, 0.64 to 6.46 g a.i./liter for quaternary ammonium chloride, and 0.87 to 6.84 g a.i./liter for sodium hypochlorite. For hydrogen dioxide, quaternary ammonium chloride, and sodium hypochlorite, a binomial lethal dose (LDb) was calculated by plating the inverted inoculated substrates on hPDA, then recording the presence or absence of B. cinerea mycelial growth over 7 days. Lethal doses resulting in the absence of mycelial growth (LDb100) were equal to or greater than the LD90values for most disinfestants and substrates. Results demonstrate for the six disinfestants that dose should be selected based on the substrate being disinfested of B. cinerea conidia.
A Two-Phase Resistance Response of Venturia inaequalis Populations to the QoI Fungicides Kresoxim-Methyl and Trifloxystrobin
Authors: Köller Wolfram , Parker D. M. , Turechek W. W. , Avila-Adame Cruz , Cronshaw Keith
Published: May 2007

The class of fungicides acting as respiration inhibitors by binding to the Qo center of cyto-chrome b (QoIs) are in wide use for the management of apple scab caused by Venturia inaequalis. In order to assess responses of V. inaequalis populations to treatments with QoIs, sensitivities of isolates were determined for germinating conidia or for mycelial colonies developing from germinating conidia. Under both test conditions, inhibitory potencies of kresoxim-methyl and trifloxystrobin were largely equivalent. V. inaequalis populations treated with QoIs in a commercial and an experimental orchard both responded with significant shifts toward declining QoI sensitivities. However, the population responses were quantitative in nature, and highly resistant isolates indicative of a cytochrome b target site mutation were not detected. V. inaequalis populations from both orchards investigated also were fully resistant to sterol de-methylation-inhibiting fungicides (DMIs) such as fenarimol and myclobutanil, but isolate sensitivities to QoIs and DMIs were largely unrelated. Performance tests with kresoxim-methyl and trifloxystrobin at the experimental orchard diagnosed as DMI-resistant revealed that the quantitative shift toward declining QoI sensitivities did not constitute the status of practical QoI resistance. In contrast to these quantitative responses, emergence of qualitative QoI resistance was documented for V. inaequalis in an orchard in North Germany, which had been treated intensively with a total of 25 QoI applications over four consecutive seasons. Isolates retrieved from the orchard were highly resistant to both kresoxim-methyl and trifloxystrobin and were characterized as G143A cytochrome b mutants. The results indicated that the paths of QoI resistance can be both quantitative and qualitative in nature. A similar phenomenon has not been described before. Circumstantial evidence suggests that the quantitative phase of V. inaequalis population responses to QoIs might be succeeded by a quantitative selection of highly resistant G143A target-site mutants.
First Report of White Mold Caused by Sclerotinia sclerotiorum on Blue Marguerite (Felicia amelloides) in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Felicia amelloides (Asteraceae family), also known as blue marguerite, is cultivated as a potted plant in Italy and increasingly used for ornamental purposes. In winter 2002, plants grown outdoors in 14-cm-diameter pots (2 liters) in commercial farms near Albenga (northern Italy) showed leaf yellowing. At the soil level, soft and watery tissues covered with whitish mycelium were evident. Later, dark brown sclerotia differentiated from the mycelium. As necrosis progressed, infected plants wilted and died. Sclerotinia sclerotiorum (1) was consistently recovered from infected stem pieces of F. amelloides that were disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotia produced on PDA were ellipsoid and measured 1.3 to 6.1 × 1.1 to 3.3 mm (average 2.9 × 2.3 mm) (2). Pathogenicity of three isolates (used as a mixture and obtained from infected plants from the same farm) was confirmed by inoculating 90-day-old plants grown in 14-cm-diameter pots. Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate was placed on the soil surface around the base of each of 20 plants. Ten noninoculated plants served as controls. The inoculation trial was repeated. All plants were kept outdoors at temperatures ranging between 5 and 26°C and watered as needed. All inoculated plants developed symptoms of leaf yellowing, followed by the appearance of white mycelium within 15 days, and then eventually wilted. Control plants remained symptomless. White mycelium and sclerotia developed on infected tissues, and S. sclerotiorum was reisolated from inoculated plants. To our knowledge, this is the first report of white mold of F. amelloides caused by S. sclerotiorum in Italy as well as elsewhere in the world.

References: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 32:75, 1949. (2) C. M. Messiaen et al. Les Maladies des Plantes Maraichères. INRA, Paris, 1991.
Effect of Moisture and Temperature on Disease of Green Foxtail Caused by Drechslera gigantea and Pyricularia setariae
Authors: Green S. , Peng G. , Connolly T. , Boyetchko S. M.
Published: May 2007

Leaf wetness duration, temperature, intermittent leaf wetness, and delayed leaf wetness were investigated for their influence on disease of green foxtail caused by Drechslera gigantea and Pyricularia setariae to determine the potential of these two fungi as bioherbicide agents in the Canadian prairies. For both fungi, disease severity increased with increasing leaf wetness duration at 15, 20, 25, 30, and 32°C. At 10°C, conidia of both fungi showed minimal germination, regardless of leaf wetness duration; however, an increase in conidial germination, appressoria formation, and disease occurred at 15°C. Conidia of both species showed 80% or greater germination at all temperatures above 15°C, whereas the optimum temperatures for appressoria formation by D. gigantea and P. setariae were 23 and 25°C, respectively. Maximum disease occurred after 48 h of leaf wetness at 32°C for D. gigantea and at 25°C for P. setariae. Disease caused by both fungi decreased when 4 h of continuous leaf wetness was followed by a 20-h dry period, and after an 8-h delay in leaf wetness following inoculation. Both fungi required immediate and prolonged periods of leaf wetness at temperatures of 15°C and above to cause severe disease on green foxtail. The moisture requirements of these fungi may limit their effectiveness as bioherbicide agents in the semi-arid Canadian prairies.
Species of Pythium from Greenhouses in Pennsylvania Exhibit Resistance to Propamocarb and Mefenoxam
Authors: Moorman G. W. , Kim S. H.
Published: May 2007

Pythium isolates from commercial greenhouses in Pennsylvania were tested in vitro and in vivo for sensitivity to propamocarb. Isolates of Pythium aphanidermatum, P. irregulare, and P. ultimum consistently infected geranium seedlings that had been treated with propamocarb. P. ultimum and P. irregulare isolates exhibited dual fungicide resistance by overcoming propamocarb, mefenoxam, and a mixture of propamocarb and mefenoxam to infect seedlings. The sensitivity of isolates to propamocarb in vitro was not a good predictor of in vivo sensitivity. This is the first report of Pythium spp. resistance to propamocarb and dual resistance to propamocarb and mefenoxam.
Characterization of Fusarium oxysporum Isolates Obtained from Cucumber in China by Pathogenicity, VCG, and RAPD
Authors: Vakalounakis D. J. , Wang Z. , Fragkiadakis G. A. , Skaracis G. N. , Li D.-B.
Published: May 2007

Thirty-four isolates of Fusarium oxysporum, obtained in China from cucumber plants showing either Fusarium wilt (F. oxysporum f. sp. cucumerinum) or root and stem rot (F. oxysporum f. sp. radicis-cucumerinum) symptoms, were characterized by pathogenicity, vegetative compatibility, and random amplified polymorphic DNA (RAPD). Of these, 23 isolates were identified by pathogenicity as F. oxysporum f. sp. cucumerinum, and one as F. oxysporum f. sp. radicis-cucumerinum, while 10 isolates were avirulent on cucumber, melon, sponge gourd, and pumpkin. The Chinese isolates of F. oxysporum f. sp. cucumerinum were assigned to RAPD groups III and XXI and to vegetative compatibility group (VCG) 0183, four new VCGs, 0184 to 0187, and a single-member VCG included in the artificial VCG 018-. The Chinese isolate of F. oxysporum f. sp. radicis-cucumerinum was assigned to RAPD group I and bridging VCG 0260/0261. The occurrence of F. oxysporum f. sp. radicis-cucumerinum on cucumber is reported for the first time in China.
Susceptibility of the Stem Pull Area of Mechanically Harvested Apples to Blue Mold Decay and Its Control with a Biocontrol Agent
Authors: Janisiewicz W. J. , Peterson D. L.
Published: May 2007

A new harvester, which uses a rapid displacement actuator on the main scaffolds to remove apples from trees with narrow-inclined trellises, has shown good potential. With this technique, stem loss (stempulls) during harvest ranges from 20 to 57%, depending on the cultivar. This can create a potential point of entry for pathogens. We evaluated the susceptibility of the stem cavity area, with and without stems, to blue mold decay (Penicillium expansum) on three cultivars of mechanically harvested apples, and tested the effectiveness of the antagonist Pseudomonas syringae (used in BioSave 110) in controlling decay. Fruit with stempulls were more susceptible to blue mold decay than fruit with stems. On fruit with stempulls inoculated with P. expansum and stored for 2 months at 1°C, decay incidence was 0% on ‘Pink Lady’, 8.3% on ‘Ace Spur Delicious’, and 41% on ‘Empire’. On fruit with stems, there was no decay on all three cultivars. P. syringae reduced decay on ‘Empire’ with stempulls to 3.3%, and no decay occurred on the other two cultivars. Similar trends were observed on fruit stored at 22°C for 14 days, but the incidence of decay was higher, and only ‘Pink Lady’ had no decay on the antagonist-treated fruit. Although mechanical harvesting can predispose the stem cavity to decay in some cultivars, this problem can be alleviated using biological control without resorting to the use of synthetic pesticides.
Occurrence of Turnip Scab Caused by Phytotoxin-Producing Streptomyces spp.
Authors: Embleton Jean , King Russell R. , Lawrence Harold C.
Published: May 2007

Turnips (Brassica rapa L var. rapifera) purchased from a New Brunswick supermarket in the winter of 2003 contained discernable corky scab-like lesions on their surfaces. The turnips were surface-disinfested with a warm-water rinse, and microorganisms from excised lesions were isolated with methodologies developed for the specific isolation of Streptomyces spp. (1). Nine isolates morphologically characteristic of Streptomyces scabies strains (2) were subsequently examined for pathogenicity on potato mini-tubers and production of the scab phytotoxin, thaxtomin A (1). Four of the nine isolates proved pathogenic on potato mini-tubers. When grown on an oatmeal broth medium, only the pathogenic isolates generated thin-layer chromatographic detectable quantities of the requisite phytotoxin, thaxtomin A (1). Previous greenhouse studies have demonstrated the ability of pathogenic Streptomyces spp. isolated from scab lesions on potatoes to infect turnips (2). To our knowledge, this is the first investigation to confirm the presence of thaxtomin A producing isolates on field-grown turnips.

References: (1) R. R. King et al. Am. Potato J. 68:675, 1991. (2) R. Loria et al. Plant Dis. 81:836, 1997.
Witches'-broom of Bakraee (Citrus reticulata hybrid) in Iran
Authors: Djavaheri M. , Rahimian H.
Published: May 2007

Symptoms, resembling those of witches'-broom disease of lime (WBDL), consisting of proliferation and growth of spindly shoots, rosetting, development of stunted, pale green, cupped leaves, and long thin thorns were observed on some bakraee (Citrus reticulata hybrid) trees, the major rootstock species in Ghazi-Ghale (Hormozgan Province) and Kahnouj (Kerman Province) in southern Iran. Vein clearing, mottling, and mild to severe yellowing of leaves was evident on some rosetted flushes. The disease occurred sporadically, and only some branches of the tree displayed the symptoms. Sour lime (Citrus aurantifolia) trees with symptoms of WBDL were also encountered in adjacent citrus groves in the area where an association of “Candidatus Phytoplasma aurantifolia” with diseased trees was previously established. Total nucleic acids were extracted from symptomatic as well as apparently healthy bakraee (1). The nucleic acids were subjected to nested polymerase chain reaction (PCR) amplification with the universal primers R16mF2/R16mR1, followed by R16F2n/R16R2 (2). The PCR program consisted of an initial denaturation at 94°C for 2 min, followed by 40 cycles of 1 min at 94°C, 2 min at 55°C, and 3 min at 72°C. After a final extension of 10 min at 72°C, the samples were electrophoresed on agarose gels, and the DNA fragments were stained with ethidium bromide and visualized under ultraviolet light. An expected 1.2-kb product was amplified in DNA preparations from broomed bakraee and WBDL-affected sour lime trees. No such amplicon was detected in similar DNA extracts of asymptomatic trees. These results demonstrated an association of a phytoplasma with witches'-broom disease of bakraee. However, its relationship with “Candidatus Phytoplasma aurantifolia” remains to be determined.

References: (1) S. L. Dellaporta et al. Plant Mol. Biol. Rep.1:19, 1983. (2) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.
First Report of Tomato mosaic virus on Hibiscus rosa-sinensis in China
Authors: Huang J. G. , Fan Z. F. , Li H. F. , Tian G. Z. , Hu J. S.
Published: May 2007

Hibiscus rosa-sinensis Linn., family Malvaceae, is an attractive horticultural plant originating from China. Five viruses infecting H. rosa-sinensis that have been characterized previously are Hibiscus chlorotic ringspot virus (HCRSV, genus Carmovirus), Hibiscus latent ringspot virus (HLRSV, genus Nepovirus), Hibiscus yellow mosaic virus (genus Tobamovirus), Eggplant mottled dwarf virus (EMDV, genus Nucleorhabdovirus), and Okra mosaic virus (OkMV, genus Tymovirus) (2). Recently, two novel tobamoviruses infecting H. rosa-sinensis were characterized in Singapore and Florida (1). In this study, viral symptoms were observed on H. rosa-sinensis in Nanyang City in Henan Province, China. The systemic symptoms included dark and light green mosaic in young leaves, leaf puckering and malformation on older leaves, and significant stunting. Rod-shaped virus particles were isolated from H. rosa-sinensis expressing systemic symptoms. The virus was transmitted mechanically to 10 species from three families. Symptoms expressed on these plants included systemic leaf chlorosis and distortion on Lycopersicum esculentum, systemic mosaic on Capsicum annuum, Nicotiana tabacum, and Physalis floridana, and systemic chlorosis on Glycine max. N. tabacum-Xanthi nc and Datura stramonium were asymptomatic. The virus also produced chlorotic and necrotic local lesions on Chenopodium quinoa, C. amaranticolor, and C. murale. The virus was propagated in L. esculentum, N. tabacum, and P. floridana. Virions purified from systemically infected N. tabacum contained a single-stranded RNA of approximately 6.4 kb and a coat protein (CP) of approximately 17.6 kDa. The double-stranded RNA profile revealed a single band of approximately 6.4 kb. Sap extracted from virus-infected plants reacted positive with an antiserum prepared against Tobacco mosaic virus (TMV) using an antigen-coated plate enzyme-linked immunosorbent assay. The CP gene was amplified by reverse transcription-polymerase chain reaction with primers specific to Tomato mosaic virus (ToMV) and sequence data obtained from the resulting amplification product. The CP gene consisting of 159 amino acids (GenBank Accession No. AY313136) shared 99.37% identity with the ToMV Queensland isolate (GenBank Accession No. AF332868). On the basis of biology, serology, properties of virions, and the sequence of the CP gene, we conclude that the virus isolated from H. rosa-sinensis in China is Tomato mosaic virus(ToMV).

References: (1) S. Adkins et al. Plant Dis. 87:1190, 2003. (2) M. H. V. van Regenmortel et al., eds. Virus Taxonomy. 7th Report of the ICTV, Academic Press, NY, 2000.
Long-Term Effect of Biological Soil Disinfestation on Verticillium Wilt
Authors: Goud Jan-Kees C. , Termorshuizen Aad J. , Blok Wim J. , van Bruggen Ariena H. C.
Published: May 2007

Biological soil disinfestation (BSD), involving incorporation of grass combined with plastic mulching, eliminates many soilborne pests and diseases through the creation of anaerobic conditions. BSD was compared at two locations with a nontreated control, Italian ryegrass amendment alone, and plastic mulch alone. After the soil treatments, plots were cropped with Acer platanoides and Catalpa bignonioides and grown for 4 years. Relative to the control, soil inoculum levels of Verticillium dahliae were reduced by 85% after BSD and did not increase for 4 years. Populations of Pratylenchus fallax, known for their interaction with V. dahliae, in the soil and in roots were reduced by 95 to 99%. The incidence of infection by V. dahliae was reduced by 80 to 90%. Verticillium wilt severity was significantly reduced in A. platanoides in all 4 years at one location and in the first 2 years at the other location, and significantly fewer plants died at one location. Shoot length and trunk width were larger after BSD compared with the control at one location. Market value of the crop in BSD plots was up to € 140,000 ha-1 higher for A. platanoides and up to € 190,000 ha-1 higher for C. bignonioides than in the untreated control. BSD is an effective, economically profitable, and environmentally friendly control method for tree nurseries.
Development of MILIONCAST, an Improved Model for Predicting Downy Mildew Sporulation on Onions
Authors: Gilles Tijs , Phelps Kath , Clarkson John P. , Kennedy Roy
Published: May 2007

The effects of temperature and relative humidity on Peronospora destructor sporulation on onion (Allium cepa) leaves were studied under controlled environmental conditions. Sporangia were produced most rapidly at 8 to 12°C after 5 h of high humidity during dark periods. The greatest number of sporangia was produced at 100% relative humidity (RH), and sporulation decreased to almost nil when humidity decreased to 93% RH. A model, named MILIONCAST (an acronym for MILdew on onION foreCAST), was developed based on the data from these controlled environment studies to predict the rate of sporulation in relation to temperature and relative humidity. The accuracy of prediction of sporulation was evaluated by comparing predictions with observations of sporulation on infected plants in pots outdoors. The accuracy of MILIONCAST was compared with the accuracy of existing models based on DOWNCAST. MILIONCAST gave more correct predictions of sporulation than the DOWNCAST models and a random model. All models based on DOWNCAST were more accurate than the random model when compared on the basis of all predictions (including positive and negative predictions), but they gave fewer correct predictions of sporulation than the random model. De Visser's DOWNCAST and ONIMIL improved their accuracy of prediction of sporulation events when the threshold humidity for sporulation was reduced to 92% RH. The temporal pattern of predicted sporulation by MILIONCAST generally corresponded well to the pattern of sporulation observed on the outdoor potted plants at Wellesbourne, UK.
Occurrence and Impact of a New Leaf Rust Race on Durum Wheat in Northwestern Mexico from 2001 to 2003
Authors: Singh R. P. , Huerta-Espino J. , Pfeiffer W. , Figueroa-Lopez P.
Published: May 2007

Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000-2001, 2001-2002, and 2002-2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT's durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses.
Finger Imprint of Poncirus trifoliata: A Specific Interaction of a Viroid, a Host, and Irrigation
Authors: Vidalakis G. , Gumpf D. J. , Bash J. A. , Semancik J. S.
Published: May 2007

The unusual symptom, “finger imprint”, described exclusively on Poncirus trifoliata, has been reported in only a single field trial investigating the effects of citrus viroids on crop performance. With this, the question has persisted whether the observed growth abnormality was a disease symptom induced by Citrus viroid IIIb (CVd-IIIb) or a consequence of mechanical damage caused by the handling of young trees during propagation or cultural practices in the field. The recurrence of finger imprint symptoms on trees after 5 years in the field in which no abnormal growth features were previously noted now supports the proposition of a viroid-induced disease. The symptom expression results from an unusual etiology of a complex relationship of the specific viroid CVd-IIIb on the specific rootstock P. trifoliata only when supplemental water is applied by sprinkler irrigation.
Management of Tomato Bacterial Spot in the Field by Foliar Applications of Bacteriophages and SAR Inducers
Authors: Obradovic A. , Jones J. B. , Momol M. T. , Balogh B. , Olson S. M.
Published: May 2007

Various combinations of the harpin protein, acibenzolar-S-methyl, and bacteriophages were compared for controlling tomato bacterial spot in field experiments. Harpin protein and aciben-zolar-S-methyl were applied every 14 days beginning twice before transplanting and then an additional four applications throughout the season. Formulated bacteriophages were applied prior to inoculation followed by twice a week at dusk. A standard bactericide treatment, consisting of copper hydroxide plus mancozeb, was applied once prior to inoculation and then every 7 days, while untreated plants served as an untreated control. Experiments were conducted in north and central Florida fields during fall 2001, spring 2002, and fall 2002. In three consecutive seasons, acibenzolar-S-methyl applied in combination with bacteriophage or bacteriophage and harpin significantly reduced bacterial spot compared with the other treatments. However, it did not significantly affect the total yield compared with the standard or untreated control. Application of host-specific bacteriophages was effective against the bacterial spot pathogen in all three experiments, providing better disease control than copper-mancozeb or untreated control. When results of the disease severity assessments or harvested yield from the bacteriophage-treated plots were grouped and compared with the results of the corresponding nonbacteriophage group, the former provided significantly better disease control and yield of total marketable fruit.
Resistance of Eucalyptus Clones to Ceratocystis fimbriata
Authors: Zauza E. A. V. , Alfenas A. C. , Harrington T. C. , Mizubuti E. S. , Silvai J. F.
Published: May 2007

Ceratocystis fimbriata, the inciting agent of wilt, canker, and dieback in eucalyptus plantations, was first reported in Brazil in 1998. There is no information regarding the resistance of Eucalyptus spp. to this pathogen. We determined the reaction of 18 Brazilian, commercial clones of the hybrid Eucalyptus grandis × E. urophylla to inoculation by two isolates of the pathogen in two experiments. Container-grown, 8-month-old rooted cuttings of each clone were wound-inoculated with a conidial suspension (2.5 × 106/ml). Plants similarly injected with sterile distilled water served as controls. The plants were evaluated after 30 days for length of xylem discoloration. There was a significant isolate by clone interaction, but most clones reacted similarly to the two isolates. Six clones, including one observed to be highly susceptible under field conditions, were highly susceptible (>20 cm discoloration) to one or both isolates of the pathogen. Four clones showed no more discoloration with either isolate than with the control inoculations, and the other eight clones were intermediate in susceptibility. Thus, highly resistant clones are available to manage this disease.
Borage (Borago officinalis) is a New Host of Pseudomonas cichorii in the Ebro Valley of Spain
Authors: Cambra M. A. , Palacio-Bielsa A. , López M. M.
Published: May 2007

Borage (Borago officinalis L.) is an important vegetable crop for consumption in the Ebro Valley of northeastern Spain. During the autumn and spring of the last 10 years, black necrotic lesions were observed in leaf petioles of white-flowered borage plants in greenhouses and seedbeds in Zaragoza, Spain. These lesions developed from the soil line and spread upward to the central vein of leaves. Severely infected leaves of mature and occasionally young plants become rotted. Longitudinal sections through the crown revealed severely necrotic cortical, vascular, and pith tissues. Isolations from infected roots, petioles, and leaves onto King's B medium yielded a gram-negative, rod-shaped bacterium with colonies that were fluorescent under UV light. Bacterial colonies were purified and characterized. The isolates were strictly aerobic, negative for levan production, soft rot of potato, and arginine dihydrolase activity, oxidase positive, and induced hypersensitive reaction in tobacco leaves (2). The bacteria were further identified as Pseudomonas cichorii by comparison of the 49 carbohydrate utilization profiles, API 50 CH (bioMérieux, Marcy l'Etoile, France), with the reference strain ICPPB 2827. Ten lettuce plants used as indicators and borage plants were inoculated by root and petiole injections of bacterial suspensions (108 CFU/ml) of the borage strains and the P. cichorii reference strain ICPPB 2827. Inoculated plants and controls were maintained in a growth chamber at 20 to 25°C with nearly 100% relative humidity. Symptoms of varnish spot, described in lettuce (1), and the black lesions initially observed in borage roots, petioles, and leaves were evident on all inoculated plants at 7 and 5 days after inoculation, respectively. No symptoms developed on control plants. A bacterium with identical characteristics to those described above was reisolated from the black lesions on inoculated plants. To our knowledge, this is the first report of P. cichorii as a pathogen of B. officinalis. Successful infection of borage plants was dependent on high humidity conditions, which is present because of the greater density of mature crops.

References: (1) R. G. Grogan et al. Phytopathology 67:957, 1977. (2) R. A. Lelliot et al. J. Appl. Bacteriol. 29:470, 1966.
Southern Blight of Jerusalem Artichoke Caused by Sclerotium rolfsii in California
Authors: Koike S. T.
Published: May 2007

Jerusalem artichoke or sunchoke (Helianthus tuberosus) is a specialty vegetable that is grown commercially in California. The fleshy tubers are harvested and used as a fresh salad ingredient or cooked vegetable. During 2003, field plantings of Jerusalem artichoke in coastal California (Santa Cruz County) showed symptoms of an unfamiliar disease. Initial symptoms consisted of wilting of new shoots and leaves followed by browning and collapse of all foliage. Crown and lower stem tissues turned tan to brown. In advanced stages of the disease, crown and stem tissues were colonized internally and externally by white, cottony mycelium. Tan, spherical sclerotia that measured approximately 1 mm in diameter formed on the surfaces of the affected crowns and stems. Mycelia and sclerotia also grew on the soil adjacent to infected plants. Isolations from symptomatic crowns, mycelia, and sclerotia produced colonies that were identified as Sclerotium rolfsii. Pathogenicity was tested using two methods that included sclerotial inocula collected from five isolates grown on potato dextrose agar plates. With the first method, sclerotia of each isolate were applied to sets of tubers (10 tubers per isolate) prior to planting tubers into a soilless, peat moss-based medium in pots. With the second method, 3-week-old potted plants were inoculated by placing sclerotia of each isolate adjacent to stem tissue that was 3 cm below the surface of the soilless medium. Noninoculated controls were included for both methods. All plants were incubated in a greenhouse at 21 to 24°C. For the first method, by the third week after planting, 10 to 40% of plants did not emerge because the tubers were rotted and decayed. For the plants that did emerge, wilting of foliage and browning of crown and stem tissue occurred approximately 6 weeks after planting and by 10 weeks, all plants were diseased. S. rolfsii was reisolated from all necrotic tuber, crown, and stem tissues. For the second method, disease symptoms and signs of the pathogen occurred 5 weeks after inoculation and by week 10, 75% of test plants were symptomatic. S. rolfsii was again reisolated from all necrotic tuber, crown, and stem tissues. Symptoms were not observed on any of the noninoculated plants. To my knowledge, this is the first report of southern blight of Jerusalem artichoke in California. This disease has been reported on Jerusalem artichoke in several southern U.S. states (1,2). The two inoculation methods demonstrated that the pathogen could infect propagation organs (tubers) and also emergent stems of this host.

References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) S. M. McCarter and S. J. Kays. Plant Dis. 68:299, 1984.