bluuebunny/crossref_metadata_2025 huggingface dataset:
Plumele Soft Rot Caused by Fusarium equiseti, F. oxysporum, and F. pallidoroseum on Soybean Seedlings in Argentina
Authors: Gally T. , González B. , Sobero y Rojo M. P. , Lori G.
Published: May 2007

Soybean (Glycine max) is an important crop in the northern area of the province of Buenos Aires, Argentina. Phomopsis spp. and Fusarium spp. are the prevalent pathogens in soybean seeds. Infection levels for both pathogens can be greater than 50%. In seedlings growing in sand or soil, both pathogens produce rotten lesions on cotyledons and hypocotyls, but over the past 2 years a plumele soft rot has also been observed associated with detached teguments that was previously demonstrated to be caused by Fusarium spp. (1). In 1996, seeds with a germination level lower than 82% were selected from an assay including 22 cultivars, and examined for the presence of Fusarium spp. The infection level ranged from 2 to 16%, and the Fusarium spp. present were identified as F. equiseti, F. oxysporum, and F. pallidoroseum. After each Fusarium sp. was cultured on potato dextrose agar, a conidial suspension was prepared and adjusted to 1.8 × 106 conidia per ml. This inoculum was sprayed on water-soaked paper, in petri dishes, and good quality soybean seeds were placed on the paper, with 400 seed for each Fusarium sp. The petri dishes were maintained at 26°C for 24 h. Control seeds were plated on water-soaked paper. Inoculated seeds were sown in sand with a water content of 16% wt/wt, covered with polyethylene bags, and incubated for 7 days in a growth chamber at 26°C and a 12-h light period. All the samples inoculated with the three Fusarium spp. exhibited seed rot, seedlings with cotyledon and hypocotyl lesions as described previously (2), but also plumele soft rot. Control seedlings remained symptomless. This is the first report confirming that the characteristic plumele soft rot of soybean seedlings is a nonspecific symptom associated with F. equiseti, F. oxysporum, and F. pallidoroseum.

References: (1) B. González et al. ISTA-PDC Symp., 2nd. 1996. (2) G. S. Saharan and V. K. Gupta. Plant Dis. Rep. 56:693, 1972.
A Vascular Wilt of Turnsole Caused by Fusarium oxysporum
Authors: Trapero-Casas A. , Kaiser W. J.
Published: May 2007

Turnsole (Chrozophora tinctoria) is a common spring-summer weed in chickpea (Cicer arietinum) and other dry-land crop production areas in southern Spain. Under field conditions, this weed often develops a general wilt and eventual death associated with a vascular discoloration of stems and roots. Diseased turnsole plants frequently occurred together with chickpea plants affected by Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris, a major disease of chickpea crops in southern Spain (1). Isolations from roots, stems and leaf petioles of turnsole plants consistently yielded F. oxysporum, and it was morphologically similar to F. oxysporum f. sp. ciceris. To test the pathogenicity of this fungus, germinated and previously surface-sterilized seeds of turnsole and chickpea cultivar Blanco Lechoso were planted in a greenhouse soil mixture artificially infested with four isolates of F. oxysporum from turnsole and two isolates of F. oxysporum f. sp. ciceris, one of them inducing the wilt syndrome and the other causing yellowing (1). Pathogenicity tests were conducted following the standard inoculation method used for F. oxysporum in chickpea (1). Inoculated and control plants were maintained in a greenhouse at 15 to 30°C. Isolates of F. oxysporum from turnsole caused wilt symptoms and death of turnsole plants within 2 months, but chickpea isolates did not affect turnsole. Conversely, chickpea plants were affected only by the two isolates of F. oxysporum f. sp. ciceris from chickpea. All diseased chickpea and turnsole plants exhibited typical vascular discoloration. F. oxysporum was consistently reisolated from the vascular tissues of roots, stems, and leaf petioles of affected plants. Based on these results, the fungus causing wilt of turnsole was identified as a forma specialis of F. oxysporum different from the chickpea wilt pathogen. Since the Fusarium wilt diseases of turnsole and chickpea are caused by different pathogens, the occurrence of F. oxysporum causing wilt of turnsole in the field can not be used to forecast Fusarium wilt of chickpea, but it may be considered as a potential biocontrol agent of this weed under field conditions. This is the first report of F. oxysporum causing wilt of turnsole.

Reference: (1) A. Trapero-Casas and R. M. Jiménez-Díaz. Phytopathology 75:1146, 1985.
First Report of A1 and A2 Mating Types of Phytophthora infestans on Potato and Tomato in Nepal
Authors: Shrestha S. K. , Shrestha K. , Kobayashi K. , Kondo N. , Nishimura R. , Sato K. , Ogoshi A.
Published: May 2007

Late blight caused by Phytophthora infestans (Mont.) de Bary is an important disease of potato and tomato that occurs annually in the hills and occasionally in the terai (plain) of Nepal. In 1996 and 1997, each year, 50 samples of late blight-infected potato and tomato leaves were collected from the hill and terai areas. The pathogen was cultured on Rye A agar. Each isolate was paired on clear V8 agar with reference isolates DN111 (A1 mating type) and DN107 (A2 mating type) received from Hokkaido University, Japan, and examined for oospore formation after 10 to 15 days of incubation at 20°C. The proportion of A2 isolates was 6% in 1996 and 42% in 1997. The A2 isolates were mainly from the high hills (2,000 to 2,500 m) where local and Andean types of potatoes are grown. Analysis of genotypes of isolates at the glucosephosphate isomerase (GPI-1), malic enzyme (ME), and peptidase (PEP-1) (1,2) isozyme loci revealed genetic diversity between A1 and A2 isolates. A1 isolates from potato were either homozygous (100/100) or heterozygous (86/100) for GPI-1, whereas all A1 isolates from tomato were heterozygous (86/100). All A1 isolates were homozygous (100/100) at the ME locus and heterozygous (92/100) at the PEP-1 locus. A2 isolates were homozygous (100/100) at all isozyme loci. The results show that both A1 and A2 mating types of P. infestans are present in Nepal, and that they display different isozyme genotypes. It is speculated that the A1 type may have migrated with potatoes from Europe while the A2 type may have been introduced with Andean potatoes from Latin America more recently. The simultaneous occurrence of both mating types may allow the fungus to increase its pathogenic diversity and to survive by means of oospores.

References: (1) A. A. Mosa et al. Plant Pathol. 42:26, 1993. (2) P. W. Tooley et al. J. Hered. 76:431, 1985.
Effects of Long-Wave UV Light on Monilinia Growth and Identification of Species
Authors: Cal A. De , Melgarejo P.
Published: May 2007

The effect of long-wave UV/dark period on mycelial growth of 46 isolates of Monilinia sp. collected in Spain and 16 isolates collected from other parts of the world was investigated. Typical isolates of M. laxa, M. fructigena, and M. fructicola were grown in the dark and identified by morphological characteristics. Long-wave UV/dark conditions reduced the growth rates of M. laxa, M. fructigena, and M. fructicola on potato dextrose agar. All isolates of M. fructigena grew more slowly than those of M. fructicola. Typical and atypical isolates of M. fructigena and M. fructicola were placed in their respective species based on long-wave UV/dark growth rate data. M. laxa isolates were readily distinguished by the short distance from their conidium to the first germ tube branch. The involvement of different photoreceptors in photoresponses by M. fructicola and M. fructigena is discussed. Differences in mycelial growth under long-wave UV may be a useful tool to identify Monilinia spp.
Quantification, Persistence, and Status of Dodine Resistance in New York and Michigan Orchard Populations of Venturia inaequalis
Authors: Köller W. , Wilcox W. F. , Jones A. L.
Published: May 2007

Isolates of Venturia inaequalis were sampled from apple orchards during 1990 to 1996 and isolate sensitivities to dodine were determined by testing the relative growth (RG) of mycelial colonies at a discriminatory dose of 0.2 μg ml-1. Sensitivities were not significantly different for a wild-type population and several populations sampled from orchards never or rarely treated with dodine, and respective data were combined to provide a reference for baseline populations. The baseline sensitivity was compared with sensitivities determined for four orchards with evidence for practical dodine resistance. At these sites, increases of phenotype frequencies were most pronounced for isolates with RG values >90; they had increased from a baseline level of 0.9 to >30% and, therefore, were rated dodine-resistant. For two orchards with confirmed cases of previous dodine resistance, frequencies of resistant isolates had declined to 11 and 14% after dodine use was discontinued for 13 and 4 years, respectively. Sensitivities had not returned to baseline levels, and indirect evidence suggested that practical dodine resistance could recur rapidly in response to resumed dodine usage. Monitoring of commercial orchards in New York and Michigan revealed that dodine sensitivities were not uniform throughout regions where dodine resistance was widespread in the late 1970s. Sensitivities ranged from baseline to dodine-resistant and appeared to reflect the dodine use history at particular sites. Because the history of dodine use is not always known to growers, applications of dodine remain risky when accurate historical records are not available.
First Report of Fusarium solani Canker and Wilt Symptoms on Red Oak (Quercus rubra) in Quebec, Canada
Authors: Vujanovic Vladimir , Cogliastro Alain , St-Arnaud Marc , Neumann Peterjürgen , Gagnon Daniel
Published: May 2007

Fusarium solani (Mart.) Sacc., causing wilt of leaves and twigs in the crown and annual cankers on trunks and branches of red oak (Quercus rubra L.) in the field, was found for the first time in Canada. F. solani is known to occur on red or black oaks of sect. LOBATAE: nuttall oak (Q. nuttallii E. J. Palmer), red oak, willow oak (Q. phellos L.), and water oak (Q. nigra L.) throughout the eastern half of the United States (1,2). In autumn 1997 and summer 1998, the disease was observed in 10-year-old trees at an experimental plantation near Cazaville (45°03′, 74°22′) located 5 km north of New York State in the St. Lawrence Valley of Québec, where 224 of 350 (64%) of the trees were symptomatic. The fungus was isolated on 2% potato dextrose agar from the necrotic bark around the active cankers (0.5 to 32 cm long) or it was obtained as erumpent sporodochia at green bark lenticels initiated from subcortical streaks in a moist chamber (relative humidity >90%). Previously, no fungus had been isolated from brown streaks found in vascular tissues with the use of two trapping techniques, either in a moist chamber or in water. From detached dead bark, other opportunistic fungi such as an Alternaria sp., Cytospora intermedia, a Phoma sp., and a Teichospora sp. were also isolated. Koch's postulates was completed for F. solani by dipping the roots of five 2-year-old Q. rubra seedlings that had their stem collar wounded by removal of a 5 mm2 area of bark, in a conidial suspension (4 × 103 conidia per ml) for 30 min. Five control seedlings were dipped in sterile, distilled water. Plants were potted in a soil mix and incubated in a growth chamber at 22°C. Within 3 weeks, inoculated plants exhibited wilted leaves and necrotic bark symptoms similar to those originally observed. The fungus was reisolated from the leaf petioles and bark tissues of symptomatic plants, but never from the controls. After 1 month all inoculated seedlings were dead. The pathogen could have a significant impact on commercial oak production in Québec.

References: (1) W. A. Sinclair et al. 1993. Diseases of Trees and Shrubs. 3th ed. Cornell University Press, Ithaca, NY. (2) E. R. Toole. Plant Dis. Rep. 50:160, 1966.
Reduced Sensitivity in Monilinia fructicola to Propiconazole Following Prolonged Exposure in Peach Orchards
Authors: Zehr Eldon I. , Luszcz Lynn A. , Olien William C. , Newall W. C. , Toler Joe E.
Published: May 2007

The baseline sensitivity of Monilinia fructicola in a peach orchard not previously exposed to demethylation-inhibiting (DMI) fungicides was determined for propiconazole, using the concentration in an agar medium required to suppress radial growth of mycelium by 50% (EC50) The baseline sensitivity was found to be approximately 0.03 μg/ml. Prolonged, regular exposure of the natural population of M. fructicola to propiconazole in the test orchard over a 3-year period (29 total applications) resulted in a wider range of sensitivity (EC50 of 0.02 to 2.16μg/ml) among isolates than was observed in the initial population (EC50 of 0.02 to 0.15 μg/ml). Comparisons with isolates from commercial orchards where DMI fungicides were used regularly showed that sensitivities were comparable to, or less than, those of isolates from the population in the test orchard that had been exposed to propiconazole for the 3-year period. M. fructicola in South Carolina peach orchards might now be less sensitive to DMI fungicides than when those fungicides were first introduced for brown rot control, although effective disease control in the field has been maintained.
Surface Colonization, Penetration, and Lesion Formation on Grapes Inoculated Fresh or After Cold Storage with Single Airborne Conidia ofBotrytis cinerea
Authors: Coertze Sonja , Holz Gustav
Published: May 2007

Infection of grapes by different densities of airborne conidia of Botrytis cinerea was investigated on table grapes (cultivar Dauphine) harvested ripe (16°Brix) and inoculated fresh, or after SO2treatment and 8-week storage at -0.5°C. Berries were detached at each inoculation and dusted with dry conidia in a settling tower. Following inoculation, the fresh berries were incubated for 24 h at high relative humidity (≥93%), or were overlaid with wet sterile paper towels. Cold-stored berries were incubated at high relative humidity. The effect of conidial density on surface colonization, penetration, and lesion formation was determined by surface sterilization, isolation, and freezing studies on fresh berries. Only symptom expression was determined on cold-stored berries. Fluorescence microscopy of skin segments showed that conidia were consistently deposited as single cells, and not in pairs or groups, on berry surfaces. Individual conidia, at all densities tested, readily infected the cold-stored berries and formed separate lesions after 2 days. Although the cold-stored berries were highly susceptible, lesion numbers were not related to conidial density at low inoculum dosages (0.67 to 2.60 conidia per mm2berry surface). Lesion numbers tended to increase exponentially at higher dosages (3.24 to 3.88 conidia per mm2berry surface). Individual conidia, however, did not induce any disease symptoms on fresh berries. Removal of the pathogen after 24-h incubation from the surface of fresh berries by ethanol, and subsequent incubation of excised skin segments revealed that, irrespective of the conidial density or the wetness regime, less than 2% of skin segments were penetrated. Furthermore, increasing densities of conidia did not lead to higher rates of surface colonization and skin penetration. The low incidence of disease caused on fresh berries and high disease incidence induced after prolonged cold storage indicated that infection was not governed by conidial density on berry surfaces, but by the level of host resistance.
Possible Role of Trichothecene Mycotoxins in Virulence of Fusarium graminearum on Maize
Authors: Harris L. J. , Desjardins A. E. , Plattner R. D. , Nicholson P. , Butler G. , Young J. C. , Weston G. , Proctor R. H. , Hohn T. M.
Published: May 2007

Trichothecene-producing and -nonproducing Fusarium graminearum strains were tested for their ability to cause Gibberella ear rot in field trials at two locations—Ottawa, Ontario, and Peoria, Illinois—in 1996. Maize ears were inoculated with wild-type or transgenic F. graminearum strains in which the trichothecene biosynthetic pathway had been disabled by the specific disruption of the trichodiene synthase gene and with a derivative revertant strain in which trichothecene production had been restored through recombination. A silk channel inoculation method was employed at both locations. In addition, a kernel puncture inoculation method was used at the Ontario location. Harvested maize ears were analyzed for visual disease severity, grain yield, deoxynivalenol (DON) concentration, and fungal biomass by quantitative polymerase chain reaction (PCR) and/or ergosterol quantitation. There was a significant correlation (r= 0.86) between data obtained from the two different methods of quantifying fungal biomass. The trichothecene-nonproducing strains were still pathogenic but appeared less virulent on maize than the trichothecene-producing progenitor and revertant strains, as assayed by most parameters. This suggests that the trichothecenes may act as virulence factors to enhance the spread of F. graminearum on maize.
First Report of Copper-Tolerant Pseudomonas syringae pv. tomato in Virginia
Authors: Alexander S. A. , Kim S. H. , Waldenmaier C. M.
Published: May 2007

Bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, is an important disease of fresh-market tomatoes along the Eastern Shore of Virginia. P. syringae pv. tomato was first identified in Northampton County on 17 May 1993, using the Biolog software program. During the spring of 1998, a field of tomato plants showed symptoms of bacterial speck. Three isolations on tryptic soy agar were made from symptomatic leaves and fruit tissues taken from young transplanted tomato plants, cv. Sunpride. The isolates were identified as P. syringae pv. tomato, using Biolog. A representative isolate was sent to the Pennsylvania Department of Agriculture, Plant Disease Diagnostic Laboratory, Harrisburg, for confirmation. The Virginia isolate was transferred to King's medium B, and identification of P. syringae pv. tomato was confirmed by fulfilling Koch's postulates, matching with the Biolog database, and testing for levan production (+), oxidase reaction (-), potato soft rot (-), arginine dihydrolase production (-), and tobacco hypersensitivity (+). In vitro growth inhibition of the 1998 Virginia P. syringae pv. tomato isolate required anhydrous cupric sulfate at 368 μg/ml compared with only 175 μg/ml for a known copper-sensitive 1998 Pennsylvania isolate. Therefore, the 1998 Virginia isolate was considered a copper-tolerant strain of P. syringae pv. tomato. For field evaluation, three copper treatments and two noncopper treatments were established in a randomized complete block design replicated four times. Treatments were initiated on 19 May and reapplied every 7 days for a total of 10 applications. Three disease ratings were taken every 7 days beginning on 30 June. For copper hydroxide (2.24 kg/ha; Kocide DF) plus mancozeb (2.24 kg/ha; Dithane); chlorothalonil (2.34 liters/ha; Bravo) plus copper salts of fatty and rosin acids (2.34 liters/ha; Tenncop); 2% maneb plus 66% copper sulfate (6.72 kg/ha; Cuprofix); and an untreated control, area under the disease progress curve (AUDPC) values were 319, 468, 478, and 438, respectively. There was no significant difference (P = 0.05) between the copper treatments and untreated control, confirming laboratory findings. In contrast, noncopper treatments of acibenzolar (21g/ha; Actigard), and acibenzolar (21 g/ha) plus mancozeb (2.24 kg/ha) (Actigard plus Dithane) were significantly different (P = 0.05) from the untreated control and copper treatments with AUDPC values of 116 and 160, respectively. This is the first report of copper-tolerant P. syringae pv. tomato in Virginia.
Bacterial Blight, a New Disease of Lobelia ricardii Caused by Pseudomonas cichorii
Authors: Putnam M. L.
Published: May 2007

Lobelia ricardii is a small perennial bedding plant grown for its abundant purple flowers. During April 1998, young lobelia plants with severe leaf blight were observed in a commercial nursery in Washington State. Symptoms consisted primarily of watersoaking of leaves, followed by collapse of leaves, watersoaking of stems, and eventual dieback of all foliage. Isolations from affected tissues were made on King's medium B (KMB). A fluorescent, gram-negative, oxidase-positive, arginine dihydrolase- and potato rot-negative, levan-producing bacterium was recovered that produced a hypersensitive response in tobacco. The bacterium was identified as Pseudomonas cichorii by carbohydrate utilization profiling (Biolog, Hayward, CA). A single-colony isolate of the bacterium was raised on KMB. A bacterial suspension was made from a 24-h agar culture of the isolate, using 0.1 M phosphate buffer, pH 6.2, with 0.2% gelatin (PBG). The suspension concentration was adjusted to 1 × 107 cells per ml by direct enumeration. The suspension (3 ml) was atomized onto leaves of five potted 5-month-old lobelia plants that were then bagged in plastic and maintained at 22°C. Bags were removed after 2 days. Eight days after inoculation, foliage was extensively watersoaked, and plants showed symptoms similar to those observed in the nursery. The plants later died. P. cichorii was reisolated from all inoculated plants. Control plants, which were treated with PBG, did not develop any symptoms nor was P. cichorii isolated from them. This is the first report of P. cichorii as a pathogen of L. ricardii.
First Report of Natural Infection of Peanut (Groundnut) by Impatiens Necrotic Spot Tospovirus (Family Bunyaviridae)
Authors: Pappu S. S. , Black M. C. , Pappu H. R. , Brenneman T. B. , Culbreath A. K. , Todd J. W.
Published: May 2007

Impatiens necrotic spot tospovirus (INSV) of the family Bunyaviridae is an important viral pathogen of ornamentals and a major constraint in the greenhouse industry (2). Evidence of natural infection of peanut (groundnut, Arachis hypogaea L.) by INSV was found in samples collected from three sites in Frio County, TX, and one site each in Mitchell and Tift counties, GA, during October 1998. Roots from several plants were tested by enzyme-linked immunosorbent assay for tomato spotted wilt tospovirus (TSWV) and INSV. Symptoms on individual mature plants positive for INSV were the same as those associated with late-season TSWV infections: plants appeared yellow and wilted, internal taproot and crown were necrotic, and plant death resulted (1). At one Texas site, three of five composite samples were positive only for INSV. One composite sample at a second Texas site was positive for both TSWV and INSV. Double infections were found in three of four TSWV-positive samples at a third Texas site. In Mitchell County, GA, three of four samples tested were positive only for TSWV, and one was positive for both TSWV and INSV. In Tift County, GA, 11 of 23 samples tested were positive only for INSV, whereas 4 were positive only for TSWV. Double infections were found in 5 of 23 samples. The presence of INSV in the sample from Mitchell County was verified by immunocapture-polymerase chain reaction (PCR) (4). The apparently low titer of INSV in the doubly infected plant necessitated two cycles of PCR for detection of INSV sequences. A primer pair that can amplify most tospoviruses was used for the first PCR cycle (3). Using the PCR product obtained, a second PCR cycle was performed with one tospovirus-specific and one INSV-specific primer. This approach resulted in a product of the expected size (≈298 bp). The PCR product was cloned in a pGEM-T vector and sequenced. Comparisons indicated the sequence obtained from the infected peanut sample from Georgia was 99% identical to the respective S RNA region from known INSV isolates. Serological and molecular sequence data suggest the peanut samples were infected by INSV. Future surveys and screenings of peanut plants for spotted wilt disease should include a test for INSV.

References: (1) A. K. Culbreath et al. Plant Dis. 75:863, 1991. (2) M. Daughtrey et al. Plant Dis. 81:1220, 1997. (3) R. Dewey et al. Virus Genes 13:255, 1996. (4). R. K. Jain et al. Plant Dis. 82:900, 1998.
Additional Ornamental Species as Hosts of Impatiens Necrotic Spot Tospovirus in Italy
Authors: Roggero P. , Ciuffo M. , Dellavalle G. , Gotta P. , Gallo S. , Peters D.
Published: May 2007

Impatiens necrotic spot (INSV) and tomato spotted wilt (TSWV) tospoviruses are among the most important viral pathogens of glasshouse ornamental plants worldwide (1). Tospovirus infections drastically reduce the market value of plants and create certification problems for international traders. As with TSWV, the number of natural host species recorded for INSV is steadily increasing (2). In 1998, severe INSV infections were found on different ornamental plants in glasshouses in the Piedmont Region of northwestern Italy, together with heavy infestations of the thrips Frankliniella occidentalis. A high proportion of plants were infected with INSV, as shown by enzyme-linked immunosorbent assay (ELISA) with polyclonal antisera and monoclonal antibodies against its nucleocapsid protein. Results were confirmed by sap-inoculation to indicator hosts. Some species were already known to be susceptible to INSV, but others are apparently new hosts (2): Ageratum houstonianum (Asteraceae), showing small necrotic rings and leaf malformation; Cordyline terminalis (Agavaceae), showing chlorotic-necrotic ringspots and leaf malformation; Dianthus chinensis (Caryophyllaceae), showing stunting, mosaic, and leaf malformation (some plants had symptomless infections); Episcia capreata (Gesneriaceae), showing necrotic spots on stems and leaves; Godetia grandiflora (Onagraceae), showing necrotic rings; Maranta leuconeura (Marantaceae), showing chlorotic-necrotic spots and apical malformation; Peperomia obtusifolia (Piperaceae), showing necrotic ringspots and leaf malformations; Scindapsus aureus (Araceae), showing necrotic spots and rings; Torenia fournieri (Scrophulariaceae), showing necrosis on stems and apexes. Thrips feeding damage was high on some species, particularly those showing necrotic ringspot symptoms. It often was difficult to distinguish between true systemic symptoms and local INSV infection at thrips feeding sites. Capsicum sp., Coleus blumei, and Dahlia sp., which also were infected in our study, are species known to be infrequent hosts of INSV (2).

References: (1) M. L. Daughtrey et al. Plant Dis. 81:1220, 1997. (2) D. Peters. 1998. Pages 107–110 in: Abstr. 4th Int. Symp. Tospovirus Thrips Floral Vegetable Crops. University of Wageningen, The Netherlands.
First Report of Clover Proliferation Phytoplasma in Strawberry
Authors: Jomantiene R. , Maas J. L. , Dally E. L. , Davis R. E. , Postman J. D.
Published: May 2007

In 1996, diseased plants of Fragaria virginiana Duchesne were collected from a native population in Quebec, Canada, and sent to the National Clonal Germplasm Repository in Corvallis, OR, where grafting onto disease-free plants of F. chiloensis (L.) Duchesne (4) was performed. Plants of both species were sent to Beltsville, MD, for identification of a phytoplasma possibly associated with the disease symptoms of dwarfing and multibranching crowns. A phytoplasma was found in both species and characterized as the strawberry “multicipita” (SM) phytoplasma, which is representative of subgroup 16SrVI-B, a new subgroup of the clover proliferation (CP) group (2). In 1999, we observed commercial strawberry (Fragaria × ananassa Duchesne) plants collected in California and Maryland that were stunted and chlorotic or exhibited these symptoms in addition to small, distorted leaves. Infected F. × ananassa plants, as well as diseased F. virginiana and grafted F. chiloensis plants previously infected by the SM phytoplasma, were assessed for phytoplasma infection by nested polymerase chain reactions primed by phytoplasma universal primer pairs R16mF2/R1 and F2n/R2 (1) or P1/P7 (3) and F2n/R2 for amplification of phytoplasma 16S rDNA (16S rRNA gene) sequences. Phytoplasma-characteristic 1.2-kbp DNA sequences were amplified from all diseased plants. No DNA sequences were amplified from healthy plants. Restriction fragment length polymorphism patterns of rDNA digested with AluI, KpnI, HhaI, HaeIII, HinfI, HpaII, MseI, RsaI, and Sau3A1 endonucleases indicated that all plants were infected by a phytoplasma that belonged to subgroup 16SrVI-A (CP phytoplasma subgroup) and that diseased F. virginiana and grafted F. chiloensis plants were infected by both SM and CP. This is the first report of the CP phytoplasma, subgroup 16SrVI-A, infecting strawberry. This report also indicates that the occurrence of the CP phytoplasma in strawberry may be widespread in North America and that F. chiloensis, F. virginiana, and F. × ananassa plants are susceptible to infection by the CP phytoplasma.

References: (1) D. E. Gunderson and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (2) R. Jomantiene et al. HortScience 33:1069, 1998. (3) R. Jomantiene et al. Int. J. Syst. Bacteriol. 48:269, 1998. (4) J. D. Postman et al. Acta Hortic. 471:25, 1998.
Effects of Calcium Salts on Apple Bitter Rot Caused by Two Colletotrichum spp.
Authors: Biggs Alan R.
Published: May 2007

The effects of three calcium salts on conidial germination, germ tube elongation, growth in vitro, and infectivity in the laboratory and field were studied for the apple bitter rot pathogens, Colletotrichum gloeosporioides and C. acutatum. Calcium chloride, calcium propionate, and calcium silicate at 1,000 μg of calcium per ml had no effect on conidial germination; however, calcium chloride and calcium propionate inhibited germ tube growth by 41 and 50% relative to the control, respectively. All three calcium salts reduced fungal dry weight in liquid culture media. When calcium salt solutions were applied to wounded apples prior to inoculation, fruit treated with calcium chloride and calcium propionate exhibited 30% smaller lesions than those treated with calcium silicate or the control, which were similar. Fruit treated with calcium chloride and calcium propionate exhibited delayed formation of acervuli relative to the control and calcium silicate, which were similar. When fruit were inoculated with varying concentrations of conidia, from 1 × 103 to 1 × 105 conidia per ml, fruit treated with calcium chloride exhibited reduced incidence of infection after inoculations with 1 × 103 conidia per ml. In all tests at 1 ×104 and 1 × 105 conidia per ml, the control and calcium salt treatments resulted in similar incidences of infection after inoculations. In six field trials, where fruit received three weekly dilute applications of calcium solutions, fruit treated with calcium salts and then inoculated with conidia of either C. gloeosporioides or C. acutatum exhibited lower incidences of infection when compared with control fruit. These experiments demonstrate that calcium salts have suppressive activity against the bitter rot pathogens and could be used as part of a disease management program.
Seedling Blight Development and Control in Spring Wheat Damaged by Fusarium graminearum Group 2
Authors: Jones R. K.
Published: May 2007

Aspects of seedborne infection in Fusarium-damaged and undamaged seed lots of hard red spring wheat were studied. In a 22°C environment, seedling blight developed from plantings of Fusarium-damaged seed that were characterized by both reduction and delay in emergence and postemergence seedling death. After 28 days, stand counts from the Fusarium-damaged seed lot averaged 46%, compared with 98% from the undamaged seed lot. However, the mean dry weight of surviving seedlings from the Fusarium-damaged lot was not statistically different from that of seedlings from the undamaged seed lot. Surface-sterilization reduced recovery of Fusarium graminearum group 2 from the damaged lot by 7% and increased germination by 32%, suggesting that seed are both infected and contaminated with viable propagules of the fungus. In field experiments, seed treatment with maneb- or thiabendazole-containing fungicide combinations significantly reduced seedling blight and improved stands derived from the Fusarium-damaged seed lot. Triazole fungicides, including difenoconazole, fenbuconazole, and tetraconazole, were less effective. Triazole fungicides and carboxin-containing fungicide combinations controlled loose smut in these trials, while maneb seed treatments did not. In four field tests, seedling blight incidence in plantings of Fusarium-damaged seed increased as soil temperatures during emergence increased. The distribution of blighted seedlings was random and not clustered. Seedling blight did not develop in field plantings of the undamaged seed lot.
Relationship of Developmental Stage of Cantaloupe Fruit to Black Rot Susceptibility and Enzyme Production byDidymella bryoniae
Authors: Zhang J. X. , Bruton B. D. , Miller M. E. , Isakeit T.
Published: May 2007

Black rot of cantaloupe fruit, caused by Didymella bryoniae, can be severe when environmental conditions and fruit developmental stages are favorable for infection. Symptoms of black rot on cantaloupe fruit varied greatly depending on fruit age. The black rot phase was observed only on mature fruit. Inoculation of cantaloupe fruit at different developmental stages with five D. bryoniae isolates resulted in the greatest amount of decay on 10-day-old fruit compared with 20-, 30-, 40-, or 50-day-old fruit. There was no difference in lesion size among 20-, 30-, 40-, or 50-day-old fruit, although there was variation in lesion size among fungal isolates. Five fungal isolates all produced the greatest polygalacturonase (PG) activity in inoculated 10-day-old fruit compared with 20-, 30-, 40- or 50-day-old fruit. There was a positive correlation between lesion size and total fungal PG activity in decayed tissue. Using a representative D. bryoniae isolate (OK 963096), multiple PG isozymes were detected in both fungal shake culture and decayed fruit. Eleven PG isozymes (pI 4.7 to 7.9) were detected from fungal shake culture using pectin or polygalacturonic acid as the sole carbon source. Twelve PG isozymes (pI 4.7 to 8.7) were detected from decayed tissue of 10-day-old fruit, and 13 PG isozymes (pI 4.2 to 8.7) were observed from decayed tissue of 50-day-old fruit. The activity of D. bryoniae PG produced in vitro and in vivo was optimum at pH 5.0 and 5.5, respectively. The activity of the fungal PG produced in vitro exhibited primarily an endo-mode of action. In contrast, PG extracted from decayed tissue was predominately exo-PG. Thus, PG may play an important role in pathogenesis of D. bryoniae during cantaloupe fruit decay.
Organic Material Soil Amendment Effects on Root Rot and Sugarcane Growth and Characterization of the Materials
Authors: Dissanayake N. , Hoy J. W.
Published: May 2007

Soil amendment with different organic materials was evaluated in greenhouse experiments for effects on root rot and growth of sugarcane. Materials included composts prepared from cotton gin trash, cottonwood bark, mixed hardwood bark, municipal solid waste, and municipal yard waste; municipal biosolids; and a sugar mill by-product, filterpress cake. Field soil, steam-treated field soil, and steam-treated soil infested with Pythium arrhenomanes were amended with nonsterile or steam-treated organic materials. A metalaxyl fungicide treatment was included for comparison. When added in nonsterile form, cotton gin trash compost, filterpress cake, and biosolids suppressed disease and increased plant growth in field soil and soil infested with P. arrhenomanes, but this ability was reduced after steam treatment. Bark composts were capable of suppressing root rot and increasing plant growth in field soil and Pythium-infested soil when added in either nonsterile or steam-treated forms. Plant growth in steam-treated soil was not promoted by nonsterile or steam-treated materials. Disease suppression provided by organic materials resulted in plant growth increases generally lower than those resulting from metalaxyl treatment in steam-treated soil infested with P. arrhenomanes, but some amendments resulted in growth increases comparable to those obtained with the metalaxyl treatment in field soil. Municipal waste composts had no effect or were detrimental to sugarcane growth. Differences in microbial community composition and chemical properties, including N content, C:N ratio, and other mineral nutrient levels, distinguished organic materials that may suppress disease and promote plant growth by different mechanisms. Microbial activity level of a material was an indicator of potential for disease suppression. The study results suggest that the severity of root rot in sugarcane may be reduced by amending soil with some organic materials.
Pathogenicity of Fungi Associated with Stem Cankers of Eucalypts in Tasmania, Australia
Authors: Yuan Z. Q. , Mohammed C.
Published: May 2007

Thirteen stem-infecting fungal species, 11 from Tasmania and 2 from other parts of southeast Australia, were tested for their pathogenicity on 12-month-old seedlings of Eucalyptus nitens and E. globulus. They were classified into three groups based on their ability to cause stem canker lesions following artificial inoculation: pathogenic species (Phoma sp., Endothia gyrosa, and Seiridium eucalypti), intermediate or weakly pathogenic species (Botryosphaeria sp., Seiridium papillatum, Pestalotiopsis neglecta, Zythiostroma sp., Ceuthospora innumera, Cytospora eucalypticola, and Wuestneia epispora), and nonpathogenic species (Dinemasporium strigosum, Seiridium unicorne, and Harknessia aff. eucalypti). The potential threat of canker fungi, especially Endothia gyrosa, to plantation forestry in Australia is discussed.
First Report of Pepper Powdery Mildew Caused by Leveillula taurica in Oklahoma
Authors: Damicone J. P. , Sutherland A. J.
Published: May 2007

During April 1999, bell peppers (Capsicum annuum L.) from a commercial hydroponics greenhouse in Oklahoma County, OK, were severely affected by powdery mildew caused by Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica (Lév.) Salmon). Defoliation levels (50 to 75%) were similar for cvs. Valencia, Lavender Islander, Sweet Chocolate, Aladdin, Purple Beauty, Golden Summer, Chocolate Beauty, Early Sunsation, Fat N'Sassy, Lilac, Sweet Rainbow Mix, and Ivory. Fruit from infected plants were small and unmarketable. Newly infected leaves exhibited light powdery colonies that were visible on abaxial leaf surfaces. On older leaves, abaxial leaf surfaces were completely covered by powdery mildew. Severely infected leaves developed chlorotic and necrotic patches on adaxial leaf surfaces prior to leaf drop. L. taurica was identified by the presence of endophytic mycelia, often-branched conidiophores, and dimorphic conidia borne singly or in short chains (1). In 50 measurements of each type, pyriform conidia averaged 67.8 ± 5.3 × 17.9 ± 2.2 μm and cylindrical conidia averaged 62.7 ± 6.2 × 15.7 ± 2.0 μm. Although conidia were slightly longer and narrower than those reported for isolates of L. taurica from pepper in California (2), dimensions were within the range reported for the species (1). The teleomorph of this powdery mildew pathogen was not observed. Peppers were grown from seed on the site. The source of L. taurica for the outbreak and the potential impact of powdery mildew on field production of peppers are unknown. Tomatoes in another hydroponics greenhouse within 100 m were not affected. This is the first report of L. taurica in Oklahoma.

References: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980. (2) J. C. Correll et al. Plant Dis. 71:248, 1987.
First Report of Clover Yellow Edge and STRAWB2 Phytoplasmas in Strawberry in Maryland
Authors: Jomantiene R. , Maas J. L. , Dally E. L. , Davis R. E.
Published: May 2007

Commercial strawberry (Fragaria × ananassa Duchesne) plants that were either chlorotic and severely stunted or exhibiting fruit phyllody were collected in Maryland. The plants were assessed for phytoplasma infection by nested polymerase chain reactions primed by phytoplasma universal primer pairs R16mF2/R1 and F2n/R2 (2) or P1/P7 (3) and F2n/R2 for amplification of phytoplasma 16S ribosomal (r) DNA (16S rRNA gene) sequences. Phytoplasma-characteristic 1.2-kbp DNA sequences were amplified from all diseased plants. No phytoplasma-characteristic DNAs were amplified from healthy plants. Restriction fragment length polymorphism patterns of rDNA digested with AluI, KpnI, HhaI, HaeIII, HpaII, MseI, RsaI, and Sau3A1 endonucleases indicated that chlorotic and stunted plants were infected by a phytoplasma that belonged to subgroup 16SrIII-B (clover yellow edge [CYE] subgroup) and that the plant exhibiting fruit phyllody was infected by a phytoplasma that belonged to subgroup 16SrI-K (STRAWB2 subgroup). The STRAWB2 phytoplasma was first reported from strawberry plants grown in Florida and characterized as representative of a new subgroup of the aster yellows group, 16SrI (3); this is the first report of this phytoplasma occurring in strawberry outside of Florida. A STRAWB2-infected plant produced phylloid fruits in two consecutive years of observation in the greenhouse; the plant previously had been field-grown in a breeder's evaluation plots in Beltsville, MD. The CYE phytoplasma was first experimentally transmitted by leafhopper to commercial strawberry and F. virginiana Duchesne in Ontario Canada (1); this is the first report of natural CYE phytoplasma infection of strawberry in Maryland. CYE phytoplasma-infected plants, representing ≈5% of the total number of plants of one advanced sselection, were located in a breeder's evaluation plots in Beltsville.

References: (1) L. N. Chiykowski. Can. J. Bot. 54:1171, 1976. (2) D. E. Gunderson and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) R. Jomantiene et al. Int. J. Syst. Bacteriol. 48:269, 1998.
First Report of Gray Leaf Spot (Pyricularia grisea) on Perennial Ryegrass (Lolium perenne) in New England
Authors: Schumann G. L. , Jackson N.
Published: May 2007

Pyricularia grisea (Cooke) Sacc. causing significant damage in perennial ryegrass (Lolium perenne L.) was first observed on a golf course in eastern Maryland in 1985 by P. H. Dernoeden, but there is no published account. The first published report of the problem was from southeastern Pennsylvania in 1991 (1). There were scattered reports of gray leaf spot in several other states in 1991. A more severe and widespread epidemic occurred under similar environmental conditions throughout the mid-Atlantic region in 1995 and has reoccurred to some extent annually since then in an expanding area throughout the United States. This report documents the expansion of the northern range of the epidemic into New England. Samples of perennial rye-grass with gray leaf spot from golf courses in three towns in Connecticut (Norwich, Stratford, and Willamantic) and one in Rhode Island (West Warwick) were submitted to the diagnostic labs at the universities of Massachusetts and Rhode Island beginning on 22 September 1998. Severe gray leaf spot was observed in perennial ryegrass fairways and roughs, especially where new seedlings were present, causing turf loss exceeding 50% in some areas. Diagnosis of this now familiar disease is based on the presence of abundant sporulation of the pathogen on infected tissue, distinctive leaf symptoms, and rapid foliar blighting of only perennial ryegrass in plantings of mixed turfgrass species. Golf course superintendents in New England with perennial ryegrass may have to extend their late-season fungicide applications to accommodate this new and destructive late-summer and fall disease.

Reference: (1) P. J. Landschoot and B. F. Hoyland. Plant Dis. 76:1280, 1992.
Introduction of Tomato Yellow Leaf Curl Virus in Florida and Implications for the Spread of This and Other Geminiviruses of Tomato
Authors: Polston J. E. , McGovern R. J. , Brown L. G.
Published: May 2007

In July 1997, symptoms characteristic of tomato yellow leaf curl virus (TYLCV-Is) were observed on one tomato plant in a field in Collier County, Florida, and on several tomato plants in a retail garden center in Sarasota, Florida. Amplification with three sets of primers, analysis of amplified fragments using restriction enzyme digestion, and hybridization with a clone of TYLCV-Is indicated that TYLCV-Is was present in symptomatic plants. The sequence of a 1,300-bp amplified fragment was 99% identical to TYLCV-Is from the Dominican Republic and 98% identical to an isolate from Israel. It appears that TYLCV-Is entered the United States in Dade County, Florida, in late 1996 or early 1997. Subsequently, infected tomato transplants produced for retail sale at two Dade County facilities were rapidly distributed via retail garden centers throughout the state. Infected plants purchased by homeowners and placed in and around homes appeared to be the source of TYLCV-Is for nearby commercial nurseries and production fields. It appears that transplants have played a role in the movement of this and probably other geminiviruses. A number of regulatory procedures, as well as field management practices, were implemented in the 1997-98 production season to minimize the movement of TYLCV-Is within and out of the state.
Detection of Clavibacter michiganensis subsp. sepedonicus in Potato Tubers by BIO-PCR and an Automated Real-Time Fluorescence Detection System
Authors: Schaad N. W. , Berthier-Schaad Y. , Sechler A. , Knorr D.
Published: May 2007

Ring rot of potato, caused by Clavibacter michiganensis subsp. sepedonicus, is one of the most regulated diseases of potatoes world wide. The organism is often difficult to detect in symptomless tubers because of low populations and slow competitive growth on available media. Polymerase chain reaction (PCR) primers and a fluorescent probe for use in the Perkin Elmer 7700 automated real time PCR detection system (TaqMan) were designed from a C. michiganensis subsp. sepedonicus-specific genomic DNA fragment for development of a BIO-PCR assay for C. michiganensis subsp. sepedonicus in potato tubers. Results of screening the primers with strains of C. michiganensis subsp. sepedonicus and other bacteria showed the primers to be specific. A total of 30 naturally infected ring rot suspect tubers were sampled by the core extract, shaker incubation procedure and assayed by (i) plating aliquots onto agar media, (ii) classical PCR, and (iii) BIO-PCR. In all, 4 tubers were positive by agar plating and pathogenicity tests, 8 by classical TaqMan PCR, and 26 by TaqMan BIO-PCR. We conclude that BIO-PCR combined with the TaqMan automated closed detection system is a rapid, reliable method of assaying large numbers of potato tuber extracts for C. michiganensis subsp. sepedonicus. Furthermore, for a large central laboratory running large numbers of PCR assays, the high-throughput TaqMan system can reduce costs per sample over the more labor-intensive classical PCR.