bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Powdery Mildew (Sawadaea bicornis) on Norway Maple (Acer platanoides) in North America
Authors: Nischwitz C. , Newcombe G.
Published: May 2007

Norway maple (Acer platanoides L.) was introduced into the continental United States around 1756 as a street tree (2). It is a widely planted shade tree in the northern United States and Canada due to its fast growth rate when young and its tolerance of pavement and dry soils. Powdery mildew is common on Norway maple in Europe with records from at least 22 countries according to the databases of the U.S. National Fungus Collections. However, there are no North American records. In September 2002, powdery mildew was observed on young Norway maple trees along the Idaho-Washington border in Moscow and Pullman, respectively. Mildew was not observed on older Norway maple trees. The mildew occurred mainly on the upper leaf surface as patches of dense, white mycelium with scattered or gregarious cleistothecia. Mean diameter of the cleistothecia was 146 (± 13.4) μm. Short stalked and subsessile asci averaged 69 (± 4.1) μm × 48 (± 5.4) μm. Ascospores averaged 27 (± 3.2) μm × 12 (±0.9) μm. Appendages were deeply cleft, simple, or one to three times dichotomously branched. This mildew fits the description of the European species Sawadaea bicornis (Wallr:Fr.) Homma (1). Also, conforming to S. bicornis were chains of macroconidia (21 (± 2.7) × 14 (± 1.5) μm) and microconida. Fibrosin bodies were seen in both. Infection of only some young trees and its absence in previous years lead us to believe that the introduction is recent in the Pacific Northwest. The susceptibility of native maples to the Norway maple mildew remains to be determined. Specimens have been deposited in the U.S. National Fungus Collections (BPI 842088).

References: (1) U. Braun. A monograph of the Erysiphales (powdery mildews) J. Cramer, Berlin-Stuttgart, 1987. (2) D. J. Nowak and R. A. Rowntree. J. Arboric. 16:291, 1990.
Screening Cherry Germ Plasm for Resistance to Leaf Spot
Authors: Wharton Phillip S. , Iezzoni Amy , Jones Alan L.
Published: May 2007

A detached leaf disk assay was developed for screening sour cherry (Prunus cerasus) cultivars for resistance to cherry leaf spot (Blumeriella jaapii). This assay was used to characterize the events occurring in cv. Montmorency (susceptible) and cv. GiSelA 6 [GI 148-1] (resistant) host-pathogen interactions, and to develop a disease scoring scheme to categorize disease severity in sour cherry trees. Forty-three seedlings grown from seeds collected in Russia were screened for resistance using the scoring scheme. Cross infection studies were also carried out with leaf spot isolates from four other Prunus species. These studies were made possible by the development of a new method of culturing B. jaapii isolates, using cherry fruit agar. This method enabled large amounts of inoculum to be produced within 2 weeks rather than a couple of months as required previously. In ‘Montmorency’, disease symptoms were first observed 4 days postinoculation (dpi), with the appearance of small white spots on the undersides of inoculated leaves. These spots gradually grew, producing erumpent spore masses in acervuli approximately 7 dpi. In ‘GI 148-1’, disease symptoms were also first observed 4 dpi, with the appearance of small transparent lesions. In the majority of cases, these lesions did not increase in size; however, acervuli occasionally were formed approximately 8 dpi. These contained small cirrhi and were often surrounded by an abscission zone. Of the sour cherry seedlings tested, only ‘Almaz’ open pollinated (o.p.) R1(1) was rated as resistant. ‘Almaz’ o.p. R1(1) and ‘GI 148-1’ were also rated as resistant to leaf spot isolates from other Prunus species. These results and the implications for breeding resistant sour cherry cultivars are discussed.
Effect of Urea, CaCO3, and Dolomite on Pseudothecial Development and Ascospore Production of Mycosphaerella citri
Authors: Mondal S. N. , Timmer L. W.
Published: May 2007

Citrus greasy spot, caused by Mycosphaerella citri, produces lesions on leaves, followed by premature defoliation, and rind blotch on fruit. Ascospores produced in leaf litter represent the major source of inoculum. The effect of treatment of leaf litter with urea, CaCO3, or dolomite on the development of pseudothecia and ascospore production was evaluated. In laboratory experiments, one urea application reduced production of pseudothecia and ascospores by up to 90%, but did not affect time of production of pseudothecia or ascospores or rate of leaf decomposition. Two applications of urea delayed leaf decomposition. As the rates of CaCO3 or dolomite were increased, pseudothecial incidence, density, time to ascospore production, and total numbers of ascospores decreased and the rate of leaf compostion increased. Immature pseudothecia on leaves treated with urea or CaCO3 degenerated and produced fewer ascospores per pseudothecium. The results observed in microplot studies in the field were similar to those observed in laboratory experiments. The number of days to pseudothecia and ascospore production and the pseudothecial incidence and density were negatively related to the rate of CaCO3 or dolomite applied. Application of CaCO3 dolomite, or urea to leaf litter can reduce inoculum and be useful in an integrated program of greasy spot management.
Effects of Temperature and Water Vapor Pressure on Conidial Germination and Lesion Expansion of Sphaerotheca macularis f. sp. fragariae
Authors: Miller T. C. , Gubler W. D. , Geng S. , Rizzo D. M.
Published: May 2007

Conidial germination in vitro and foliar lesion expansion were studied for Sphaerotheca macularis f. sp. fragariae. Detached strawberry (Fragaria × ananassa) leaves were inoculated, then held in controlled environments of constant temperatures (4 to 36°C) and relative humidity (RH, 32 to 100%) representing the range of these variables observed under California commercial production conditions. Percent germination and lesion expansion rate were determined by destructive subsampling over time. Conidia germinated at all temperatures by 6 h and reached a maximum by 48 h, with the optimum near 20°C. Lesions were marked with the aid of a microscope and measured by computer-assisted image-analysis to determine expansion rate. Maximal rates occurred at 25°C. Several growth models were fit to the expansion rate data with high significance. Predicted optima from these models ranged from 22 to 27°C and/or 17 to 27 mm Hg VPwater@100%RH. Neither RH, partial vapor pressure of water (VPwater), nor vapor pressure deficit (VPD) correlated with lesion expansion rate, adding to studies minimizing the importance of RH and VPD as determinants of asexual phase powdery mildew growth other than specifically at spore germination.
First Detection ofRupestris stem pitting associated virusParticles by Antibody to a Recombinant Coat Protein
Authors: Petrovic Natasa , Meng Baozhong , Ravnikar Maja , Mavric Irena , Gonsalves Dennis
Published: May 2007

Rupestris stem pitting associated virus (RSPaV), a member of the genus Foveavirus, is associated with the Rupestris stem pitting component of the Rugose wood (RW) disease complex of grapevines. Heretofore, particles of RSPaV have not been visualized. In this work, flexuous rod particles approximately 723 nm in length were detected in the sap of infected grapevines by immunosorbent electron microscopy (ISEM), using a polyclonal antiserum produced to a recombinant coat protein of RSPaV. Particles of RSPaV were detected in tissue culture-, greenhouse-, and field-grown grapevines infected with RSPaV, but not in healthy control plants. Detection of virus particles by ISEM corresponded with detection of RSPaV by Western blot, enzyme-linked immunosorbent assay, and reverse transcription-polymerase chain reaction. Virus particles were decorated with the antibodies specific to RSPaV but not with antibodies to Grapevine virus A or Grapevine virus B, two other viruses believed to be associated with RW. This definitive identification of RSPaV particles will help define the etiology of RW.
Epidemic Development of Hawthorn Leaf Blight (Monilinia johnsonii) on Mayhaw (Crataegus aestivalisandC. opaca) in Georgia
Authors: Scherm H. , Savelle A. T.
Published: May 2007

Mayhaws are small trees and shrubs in the hawthorn genus, Crataegus. They are native to the southern United States, where their fruit is highly valued for use in jellies and preserves. Since 1997, symptoms of hawthorn leaf blight, caused by Monilinia johnsonii, have been observed in mayhaw orchards in southwestern Georgia. We studied epidemic development of the disease in a mixed planting of Crataegus aestivalis (eastern mayhaw) and C. opaca (western mayhaw) between 2000 and 2002. Apothecia of M. johnsonii were first observed in early to mid-February on overwintered, mummified fruit of C. aestivalis; no apothecia were detected in plots underneath C. opaca trees. Both mayhaw species exhibited moderate to severe leaf blighting beginning in early March, although some genotypes within each species apparently escaped primary infection via delayed leaf bud break or a slower rate of leaf expansion. On a per-tree basis, leaf blight incidence was positively correlated with mean leaf length during the period when apothecia were most numerous (r = 0.7225, P = 0.0003, n = 20). Fruit mummification, which results from secondary infection of open flowers by conidia, was widespread by late March to early April and was significantly (P < 0.05) more severe on C. aestivalis, most likely because trees of this species were at an earlier bloom stage when conidia-bearing blighted leaves were first observed. By contrast, C. opaca advanced through bloom earlier, thereby partly escaping secondary infection. On a per-tree basis, there was no relationship between incidence levels of leaf blight and fruit infection for either species; indeed, some trees with the lowest incidence of leaf blight had the greatest incidence of fruit mummification and vice versa. Thus, in a mixed planting of different mayhaw genotypes, conidia appear to be dispersed readily from heavily blighted trees, leading to high levels of fruit infection even in trees with negligible incidence of leaf blight. There are genotypes within both mayhaw species that almost completely avoid either primary infection or secondary infection; therefore, planting such genotypes in pure stands may aid in minimizing losses due to the disease.
A First Assessment of the Cranberry Fruit Rot Complex in Michigan
Authors: Olatinwo R. O. , Hanson E. J. , Schilder A. M. C.
Published: May 2007

Samples of ripe fruit were taken at harvest from all eight commercial cranberry farms in Michigan over a 3-year period to determine the distribution and incidence of fruit rot diseases and the fungal pathogens associated with rotted fruit. Totals of 23, 33, and 28 beds were sampled in 1999, 2000, and 2001, respectively. Fruit rot incidence varied widely among beds and farms and ranged from 5 to 97% (mean 33.4%) in 1999, 1 to 91% (mean 26.3%) in 2000, and 1 to 67% (mean 12.8%) in 2001. Differences in fruit rot incidence were observed among cultivars, but rankings differed among farms. In general, cultivars Ben Lear, Bergman, and Pilgrim tended to have lower and Beckwith and WSU61 higher fruit rot incidence than other cultivars grown in the same location. Colletotrichum acutatum, Pestalotia vaccinii, and Phyllosticta vaccinii were the fungi most frequently recovered from rotted fruit. Fusicoccum putrefaciens, Phomopsis vaccinii, Physalospora vaccinii, Allantophomopsis lycopodina, Coleophoma empetri, and Botrytis cinerea were isolated occasionally in 1999. The isolation frequency of Physalospora vaccinii, Phomopsis vaccinii, and C. empetri increased markedly in 2000. Glomerella cingulata was first detected in 2001. Fusicoccum putrefaciens was most common in the northern and Glomerella cingulata in the southern growing areas. A comparison of sound and rotted fruit from selected beds showed that Phyllosticta elongata predominated in sound fruit, whereas G. cingulata predominated in rotted fruit.
First Report of Burkholderia cepacia as a Pathogen of Banana Finger-Tip Rot in Taiwan
Authors: Lee Y.-A. , Shiao Y.-Y. , Chao C.-P.
Published: May 2007

Banana finger-tip rot is an endemic minor disease in Taiwan. Diseased fingers are recognized externally by their distorted shape, often being narrow at the tip, smaller, and curved out of line with the other fingers. Parts of the pulp within the finger appear slightly gelatinous and yellow. Frequently, a brown discoloration is evident at the tip of the flower end. Although Pseudomonas sp. was reported to be a causal pathogen, the identity of the species was not determined (1). Isolations from diseased fingers consistently yielded bacterial colonies that were whitish-yellow on Luria-Bertani agar and did not produce fluorescent pigment on King's medium B. Three isolates were selected for further characterization. All isolates were gram negative, aerobic, and grew at 42°C, positive for oxidase, lysine decarboxylase, and ornithine decarboxylase, but negative for arginine dihydrolase and tryptophanase (indole production). The isolates hydrolyzed gelatin and esculin, produced acids by utilizing d (+)-glucose, mannose, sucrose, maltose, d-mannitol, d-sorbitol, and dulcitol, but not melibiose, or rhamnose. The isolates caused rotting symptom on onion that was more severe than on potato and carrot slices. The bacterium was identified as Burkholderia cepacia. Almost complete 16S rDNA sequence (1,489 bp; GenBank Accession No. AY207313) of one isolate (strain B9) was determined and compared with available 16S rDNA sequences of members of B. cepacia complex. The sequence was similar (99.87%) to that of B. cepacia genomovar III LMG 12614 (GenBank Accession No. AF097532). Bacterial suspensions (108 CFU/ml) were injected through the center of the stigma, and the fingers were enclosed in a plastic bag to maintain high humidity. Twenty fingers (three to four fingers in each hand) were inoculated totally. A majority (80%) of the wound inoculations were successful, and typical symptoms appeared in 10 to 14 days. Control plants were inoculated with sterile distilled water. A small amount (2 to 5%) of control plants also showed symptoms. This may result from finger infestation with epiphytic or endophytic B. cepacia. Young fruits were more susceptible than older fruits. The bacterium was readily reisolated from diseased fingers and confirmed as B. cepacia. To our knowledge, this is the first report of B. cepacia as a causal pathogen of banana finger-tip rot.

Reference: (1) I. W. Buddenhagen. Plant Prot. Bull. 16:17, 1968.
First Report of Sclerotinia sclerotiorum on Niger (Guizotia abyssinica)
Authors: Bradley C. A. , Río L. E. del , Johnson B. L.
Published: May 2007

Niger is a new crop being grown in North Dakota and Minnesota for the commercial birdseed market. In 2002, approximately 60 and 150 ha of niger were grown in North Dakota and Minnesota, respectively. In September 2002, niger plants in a field located near Prosper, ND showed the following symptoms and signs: bleached, shredded, and broken stems at the basal area, and presence of white mycelium and black sclerotia (2.2 ± 0.8 mm diameter) inside the pith cavity. Approximately 40% of plants in that field showed signs or symptoms of infection. Sclerotia were collected from the pith cavity, soaked in a 0.53% NaOCL solution for 30 s, air dried, and placed in petri dishes containing potato dextrose agar (PDA). A fungal colony grew out from the plated sclerotia that subsequently produced aerial white mycelium and black sclerotia characteristic of Sclerotinia sclerotiorum (Lib.) de Bary. To confirm pathogenicity, 2 groups of 10 30-day-old niger seedlings each were inoculated using the straw test method (2) or petiole inoculation test method (1) with mycelium from a S. sclerotiorum isolate obtained from an infected niger plant; 20 seedlings served as a noninoculated control. At the time of inoculation, seedlings were healthy and approximately 14 cm high. Three days after inoculation using either method, tissue at the inoculated area turned gray. The gray lesions progressed across the majority of the seedling tissue and 1 week after inoculation, all inoculated plants were wilted and dead. S. sclerotiorum was reisolated from infected tissue that was placed on PDA. To our knowledge, this is the first report of S. sclerotiorum causing a stem rot disease of niger or any species in the Guizotia genus. Several of the major crops grown in North Dakota and Minnesota, such as canola, dry edible bean, soybean, and sunflower are susceptible to S. sclerotiorum. Growing niger in rotation with these or other susceptible crops could increase S. sclerotiorum inoculum levels and lead to severe disease outbreaks if conditions are favorable.

References: (1) L. E. del Río et al. (Abstr.) Phytopathology 90(Suppl.):S176, 2000. (2) R. Petzoldt and M. H. Dickson, Annu. Rep. Bean Improv. Coop. 39:142, 1996.
First Report of Ascochyta Blight of Chickpea Caused by Ascochyta rabiei in Chile
Authors: Galdames R. , Mera M.
Published: May 2007

Chickpea (Cicer arietinum L.) plants with foliar and stem lesions fitting the description of Ascochyta blight were observed in October 2002 in four chickpea crops located in the La Araucania Region (38°S, 72°24′W) in southern Chile. Large, circular foliar and stem lesions containing pycnidia arranged in concentric circles were observed (1). Stem breakage also was observed. Isolates were obtained from mature pycnidia developed on stems by culturing a spore suspension on potato dextrose agar (PDA) and chickpea seed meal agar. A pathogenicity test was performed by inoculating 25 plants with a suspension of 1.2 × 105 conidia ml-1 and incubating at 22°C and 75% relative humidity. Foliar and stem lesions were observed 5 and 7 days after inoculation, respectively. Four check plants sprayed with sterile distilled water showed no symptoms. Fungal colonies obtained from inoculated plants showed the same cultural characteristics as the original isolates. Cultural morphology was consistent with the description of Ascochyta rabiei (Pass.) Labrousse (teleomorph Didymella rabiei (Kovacheski) v. Arx (= Mycosphaerella rabiei Kovacheski)) (3). Conidia produced on PDA were predominantly aseptate, 3.90 to 5.85 μm wide, and 9.75 to 11.7 μm long. Affected plants (cv. Kaniva) originated from seed introduced at commercial volumes (69 ton) from Victoria, Australia in August 2002. A. Rabiei can be disseminated via infected seed (1). Ascochyta blight symptoms also have been observed in small patches in several crops near Temuco, the capital of the La Araucania Region. Chickpea production is currently, relatively small in southern Chile, however, plans to promote its cultivation may be hindered by this outbreak. Previously, the only other country to report Ascochyta blight of chickpea in South America was Bolivia (2).

References: (1) W. J. Kaiser. Epidemiology of Ascochyta rabiei. Pages 117–134 in: Disease-resistance Breeding in Chickpea. K. B. Singh and M. C. Saxena, eds. ICARDA, Aleppo, Syria, 1992. (2) W. J. Kaiser et al. Plant Dis. 84:102, 2000. (3) E. Punithalingam and P. Holliday. No. 337 in: CMI Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1972.
Tissue Blot Immunoassay for Detection of Tomato spotted wilt virus in Ranunculus asiaticus and Other Ornamentals
Authors: Whitfield A. E. , Campbell L. R. , Sherwood J. L. , Ullman D. E.
Published: May 2007

A tissue blot immunoassay (TBIA) was developed to detect Tomato spotted wilt virus (TSWV) in Ranunculus asiaticus tubers and other ornamentals. TBIA was comparable to double-antibody sandwich enzyme-linked immunosorbent assay for accuracy and reliability. A nondestructive sampling method was used with R. asiaticus tubers to determine: (i) the relationship between tuber infection and size; (ii) the distribution of TSWV in tubers; and (iii) the relationship between tuber infection and tuber germination. Small tubers had a higher percentage (44%) of infection than large tubers (19%). When destructive sampling was acceptable, the central stem tissue was the most reliable to test. TSWV infection was associated with a significant reduction of tuber germination. Among the tubers that tested positive for TSWV infection, 48% of those that germinated produced foliage in which TSWV was detected. The remaining 52% of the infected tubers planted that germinated developed into plants that were asymptomatic and in which TSWV was not detectable after germination. Only 4% of tubers that tested negative produced infected plants after germination. Our results indicate that TBIA can be used in TSWV management programs to identify infected plants and to index tuber crops.
Response of Soybean Sudden Death Syndrome to Subsoil Tillage
Authors: Vick C. M. , Chong S. K. , Bond J. P. , Russin J. S.
Published: May 2007

The soilborne pathogen Fusarium solani f. sp. glycines causes sudden death syndrome (SDS) of soybean. Previous research indicated that soil compaction related directly to disease foliar symptoms. Therefore, we hypothesized that decreasing soil compaction would increase soil porosity and provide a more aerated root zone that would hinder root infection by the fungus and decrease SDS foliar symptom severity. Two experimental areas (110 by 120 m) were established to evaluate the relationship between soil variables and SDS. Across the experimental area, strips (9.14 m wide) were subsoiled perpendicular to soybean rows to a depth of 40 to 45 cm, which alternated with strips that were not tilled. In both 1999 and 2000, subsoiling dramatically reduced foliar symptoms of SDS. Compared with no-till plots, subsoiled plots had lower soil bulk density, greater soil porosity, and less soil moisture. In areas where SDS occurs and soil compaction exists, the use of subsoiling can be used to reduce severity of foliar symptoms of SDS.
Changes in the Sensitivity of Erwinia amylovora Populations to Streptomycin and Oxolinic Acid in Israel
Authors: Manulis S. , Kleitman F. , Shtienberg D. , Shwartz H. , Oppenheim D. , Zilberstaine M. , Shabi E.
Published: May 2007

A survey of streptomycin resistance in the fire blight pathogen, Erwinia amylovora, conducted in pear, apple, and quince orchards in Israel during 1998 to 2001 revealed a decrease in the frequency of locations with streptomycin-resistant strains, from 57% in 1998 to 15% in 2001. In 2001, streptomycin-resistant strains were detected in only five locations in two restricted areas in western Galilee and the Golan Heights, compared with 16 locations found in 1998 throughout the northern part of the country. Since the use of streptomycin for fire blight control was terminated in 1997, this antibiotic has been replaced with oxolinic acid (Starner) in commercial orchards. Strains resistant to oxolinic acid were isolated from two pear orchards in the northern part of Israel in 1999. In a nationwide survey conducted during the spring and winter of 2000 and 2001, 51 and 47 pome fruit orchards, respectively, were sampled. Oxolinic acid-resistant strains were detected in several orchards located in two restricted areas in northern Galilee. Strains with resistance to both streptomycin and oxolinic acid were not found during 2000 to 2001. Results of this survey are used in managing fire blight with bactericides.
Heterodera glycines Infection Increases Incidence and Severity of Brown Stem Rot in Both Resistant and Susceptible Soybean
Authors: Tabor G. M. , Tylka G. L. , Behm J. E. , Bronson C. R.
Published: May 2007

Growth chamber experiments were conducted to investigate whether parasitism by Heterodera glycines, the soybean cyst nematode, increases incidence and severity of brown stem rot (BSR) of soybean, caused by Phialophora gregata, in both resistant and susceptible soybean cultivars. Soybean genotypes with various combinations of resistance and susceptibility to both pathogens were inoculated with P. gregata alone or P. gregata plus H. glycines. In most tests of H. glycines-susceptible genotypes, incidence and severity of internal stem discoloration, characteristic of BSR, was greater in the presence than in the absence of H. glycines, regardless of susceptibility or resistance to BSR. There was less of an increasing effect of H. glycines on stem symptoms in genotypes resistant to both BSR and H. glycines; however, P. gregata colonization of these genotypes was increased. Stems of both a BSR-resistant and a BSR-susceptible genotype were colonized earlier by P. gregata in the presence than in the absence of H. glycines. Our findings indicate that H. glycines can increase the incidence and severity of BSR in soybean regardless of resistance or susceptibility to either pathogen.
Transmission of Pantoea ananatis, Causal Agent of Center Rot of Onion, by Tobacco Thrips, Frankliniella fusca
Authors: Gitaitis R. D. , Walcott R. R. , Wells M. L. , Perez J. C. Diaz , Sanders F. H.
Published: May 2007

Center rot of onion, caused by Pantoea ananatis, was first reported on onion in Georgia in 1997 and has continued to reduce yields and cause postharvest losses. In a previous study, we developed a nondestructive assay that demonstrated an association between P. ananatis and approximately 10% of the tobacco thrips, Frankliniella fusca, surveyed. In this study, we report that all strains of P. ananatis, isolated from surface-sterilized, crushed thrips, were pathogenic when inoculated onto greenhouse-grown onion plants. Furthermore, when 6 to 12 thrips harboring populations of P. ananatis of 1 × 103 CFU ml-1 or greater were placed on healthy onion seedlings to feed, disease transmission occurred in 52% of the plants challenged. Incubation periods ranged from 4 to 9 days. Bacteria isolated from symptoms typical of those associated with center rot were characterized and identified as P. ananatis. In contrast, an equal number of plants remained healthy for up to 28 days after being exposed to the same number of tobacco thrips that were identified as being free of P. ananatis.
Identification of Resistance to Potato yellow mosaic virus-Trinidad Isolate (PYMV-TT) Among Lycopersicon Species
Authors: Rampersad S. N. , Umaharan P.
Published: May 2007

Three studies were carried out with the objective of identifying resistance to Potato yellow mosaic virus-Trinidad isolate (PYMV-TT) among Lycopersicon species through field screening and using field-inoculated infector rows. The presence of PYMV-TT was confirmed using dot blot hybridization assays. In the first study, eight commercial cultivars of tomato were tested for resistance. In a subsequent study, 11 breeding lines showing high levels of resistance to Tomato mottle virus (ToMoV-Florida) and six lines resistant to Tomato yellow leaf curl virus (TYLCV-Old World Begomovirus) were screened for resistance to PYMV-TT. All breeding lines and the commercial cultivars tested were susceptible to PYMV-TT infection. The third study involved screening 92 accessions from a representative core collection of wild Lycopersicon germ plasm. PYMV-TT was not detected in individuals of 22 accessions.
Races and Inoculum Density ofFusarium oxysporumf. sp.niveumin Commercial Watermelon Fields in Maryland and Delaware
Authors: Zhou X. G. , Everts K. L.
Published: May 2007

A survey was conducted to determine races and inoculum density of Fusarium oxysporum f. sp. niveum, the causal agent of Fusarium wilt of watermelon in Maryland and Delaware. Virulence on six differential cultivars was tested for each of 63 isolates of F. oxysporum f. sp. niveum, obtained from 25 commercial watermelon fields. Thirteen isolates (21%) were identified as race 0, 36 isolates (57%) as race 1, and 14 isolates (22%) as race 2. Races 0 and 1 were present in 12 (48%) and 10 (40%) of the fields, respectively. The highly aggressive race 2 was identified from five fields in two counties in Maryland and from one field in Delaware, representing 24% of the fields. Race 2 was copresent with one or two other races. Race 2 (19 isolates) predominated among the 25 isolates obtained from a research field in Maryland. Nineteen commercial fields had inoculum densities of F. oxysporum f. sp. niveum ranging from 100 to 1,200 CFU/g of soil at harvest. Within this range of inoculum densities, >20% incidence of wilt was observed when the susceptible watermelon cv. Sugar Baby was planted in samples of soil collected from these fields. The relationship (P < 0.0001) between inoculum density of F. oxysporum f. sp. niveum (X) and incidence of Fusarium wilt (Y) on Sugar Baby was best described using the monomolecular equation, Y = 1 - exp[-0.0013 (X + 166)]. The ratio of pathogenic to total population of F. oxysporum in the fields linearly increased with increasing inoculum density of F. oxysporum f. sp. niveum (R2= 0.4; P < 0.0009).
Improved Detection of Tilletia indica Teliospores in Seed or Soil by Elimination of Contaminating Microorganisms with Acidic Electrolyzed Water
Authors: Bonde M. R. , Nester S. E. , Schaad N. W. , Frederick R. D. , Luster D. G.
Published: May 2007

Acidic electrolyzed water (AEW) is a germicidal product of electrolysis of a dilute solution (e.g., 0.4% vol/vol) of sodium chloride. This solution can be used to disinfest wheat seed or soil samples being tested for teliospores of Tilletia indica, causal agent of Karnal bunt, without risk of damaging the teliospores. The AEW used in this study had a pH of 2.5 to 2.8 and oxidation-reduction potential of approximately 1,130 mV. In simulations of routine extractions of wheat seed to detect teliospores of T. indica, the effectiveness of a 30-min AEW treatment was compared with a 2-min 0.4% sodium hypochlorite (NaOCl) treatment to eradicate bacteria and nonsmut fungi. Each treatment reduced bacterial and fungal populations in wheat seed extracts by 6 to 7 log10 units when determined on 2% water agar with antibiotics. Reductions of 5 log10 units or more were observed on other media. NaOCl and AEW also were very effective at eliminating bacteria and fungi from soil extracts. In studies to detect and quantitate T. indica teliospores in soil, AEW was nearly 100% effective at eliminating all nonsmut organisms. Free chlorine levels in AEW were very low, suggesting that compounds other than those with chlorine play a significant role in sanitation by AEW. The low pH of AEW was shown to contribute substantially to the effectiveness of AEW to reduce microorganisms. A standardized protocol is described for a 30-min AEW treatment of wheat seed washes or soil extracts to eliminate contaminating microorganisms. A significant advantage of the use of AEW over NaOCl is that, with AEW, teliospore germination is not reduced and usually is stimulated, whereas teliospore germination declines after contact with NaOCl. The protocol facilitates detection and enumeration of viable teliospores of T. indica in wheat seed or soil and the isolation of pure cultures for identification by polymerase chain reaction. The germicidal effects of AEW, as demonstrated in this study, illustrate the potential of AEW as an alternative to presently used seed disinfestants.
Evaluation of Virulence to Adlays of Korean Isolates of Bipolaris coicis Using a Disease Rating Scale
Authors: Chang Seog Won , Hwang Byung Kook
Published: May 2007

The virulence of 33 isolates of Bipolaris coicis from diverse geographic origins in Korea was evaluated on six adlay cultivars or lines under controlled environmental conditions. To evaluate infection levels of B. coicis isolates in adlay plants, a 10-class disease rating scale was developed based on the qualitative and quantitative differences of lesions on adlay leaves infected. There were significant differences in virulence among isolates of B. coicis, although the differences were quantitative rather than qualitative. Significant differences also were observed among cultivar-isolate interactions in the analysis of variance. All isolates of B. coicis, except KG-9515, were pathogenic on adlay plants. BC-20136, the most virulent isolate, was capable of causing highly susceptible reactions on the adlay cultivars or lines. Significant differences in levels of resistance were found among six adlay cultivars or lines tested. The disease rating scale may be a reliable criterion to evaluate a large number of adlays for resistance to leaf blight or B. coicis isolates for virulence to adlays.
Control of Fusarium Crown and Root Rot of Tomato with Hypovirulent Binucleate Rhizoctonia in Soil and Rock Wool Systems
Authors: Muslim A. , Horinouchi H. , Hyakumachi M.
Published: May 2007

Hypovirulent binucleate Rhizoctonia (HBNR) isolates L2, W1, W7, and Rhv7 were studied as potential antagonists of Fusarium crown and root rot of tomato (FCRR) caused by Fusarium oxysporum f. sp. radicis-lycopersici, in either soil or hydroponic rock wool systems. Reduction of FCRR on tomato by HBNR isolates was different depending on the isolate, days after inoculation of pathogen, and experiments. In the greenhouse soil system, HBNR isolates significantly (P = 0.01) reduced vascular discoloration and discoloration of total roots systems by 90 to 100% and by 73 to 89%, respectively, in three experiments. Under field soil conditions, HBNR W1 provided significant (P = 0.05) reduction of vascular discoloration by 71%. In the rock wool system, all HBNR isolates except L2 in experiment 1 significantly reduced (P = 0.05) vascular discoloration by 18 to 100% in four experiments. Plants treated with all HBNR isolates had foliar symptoms reduced by 41 to 100% in four experiments under the rock wool system. Application of HBNR also resulted in increases of marketable and total yields of tomatoes as much as 70 and 73%, respectively, over the untreated plants. The number of colony forming units of F. oxysporum f. sp. radicis-lycopersici per gram fresh weight of roots and stems was significantly reduced (P = 0.05) in plants treated with HBNR in both soil and rock wool systems. HBNR was re-isolated at a high frequency from roots grown inside paper pots containing soil infested with HBNR, but rarely isolated from the roots grown in soil infested with only F. oxysporum f. sp. radicis-lycopersici outside the paper pots. HBNR was not re-isolated from the tomato stems. Stem extracts from HBNR-treated and pathogen-challenged plants in the rock wool system inhibited germination and production of budding cells of F. oxysporum f. sp. radicis-lycopersici.
First Report of Plectosporium Blight on Pumpkin Caused by Plectosporium tabacinum in Alabama
Authors: Mullen J. M. , Sikora E. J.
Published: May 2007

In October of 2001, Plectosporium tabacinum (van Beyma) M.E. Palm, W. Gams, & H.I. Nirenberg (formerly known as Microdochium tabacinum (von Arx, 1984) and Fusarium tabacinum (Gams & Gerlagh, 1968)) was observed in field plantings of pumpkin (Cucurbita pepo L.) in Cullman and Jackson counties in north Alabama. Symptoms were white or tan, spindle-shaped lesions on the stems and leaf petioles and slightly raised, corky, white or light brown lesions on pumpkin fruit and fruit stems. Pumpkin symptoms were identical to a previous description of P. tabacinum (published as M. tabacinum) on pumpkin, zucchini, and yellow summer squash (1). Disease severity ranged from less than 10% stem tissue damage on pumpkins in Cullman County to 40 to 45% stem tissue damage on pumpkins in Jackson County. A field section of pumpkins in Jackson County sprayed with azoxystrobin (Quadris 2.08F, 0.20 kg a.i./ha) alternated weekly with chlorothalonil (Bravo Ultrex, 2.44 kg a.i./ha) beginning at vine-run had stem damage of approximately 5% compared to approximately 45% stem damage on pumpkins in an unsprayed field section. A 50% reduction in marketable fruit due to P. tabacinum was observed in the unsprayed field section compared to the section sprayed weekly with fungicides. When thin slices of lesions were taken from stem and fruit surfaces using a scalpel and examined microscopically, one- or two-celled, hyaline, bilaterally symmetric spores, 7.0 to 8.5 × 2.8 to 3.0 μm were observed. The ends of the spores were slightly narrowed and rounded. Spore characteristics were identical to previous descriptions of P. tabacinum produced in culture and on diseased pumpkins and squash (2,3). Surface-sterilized tissue from fruit lesion margins was plated on potato dextrose agar and incubated under light (Sylvania Gro-Lux, 40w) with a light/dark cycle of 12 h at 23°C. After 10 days, spores were observed that were similar to those from fruit except they were multiguttulate and had a phialide arrangement. The fungal mycelium was pale pink to pale orange and closely appressed to the agar. Fungal characteristics in culture agree with a previous description of P. tabacinum in culture (2). To our knowledge, this is the first report of P. tabacinum in Alabama.

References: (1) S. C. Bost and C. A. Mullins. Plant Dis. 76:861, 1992. (2) M. E. Palm et al. Mycologia 87(3):397, 1995; (3) T. A. Zitter. Microdochium blight. Page 28 in: Compendium of Cucurbit Diseases. T. A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. The American Phytopathological Society, St. Paul, MN, 1996.
First Report of Resistance to Metalaxyl in Downy Mildew of Sunflower Caused by Plasmopara halstedii in Spain
Authors: Molinero-Ruiz M. L. , Melero-Vara J. M. , Gulya T. J. , Dominguez J.
Published: May 2007

Fifty-two isolates of Plasmopara halstedii Farl. Berl. & de Toni (causal agent of sunflower downy mildew) collected from sunflower (Helianthus annuus L.) in Spain from 1994 to 2000 were evaluated for metalaxyl resistance. The pathogen was identified on the basis of the morphology of the sporangiophores and zoosporangia recovered on the underside of the leaves (2). Metalaxyl (Apron 20% LS) at 2.0 g a.i./kg of seed (labeled European rate) was applied as seed dressing to the susceptible sunflower ‘Peredovik’. There were two replications of 40 plants, and the test was repeated three times. Inoculum (sporangia bearing zoospores) was produced on artificially inoculated plants. Seed were germinated in a humidity chamber at 28°C for 24 to 48 h. When the radicle was 0.5 to 1.0 cm long, untreated and treated seedlings were inoculated by dipping the entire plant in an aqueous suspension of 6.0 × 104 sporangia per ml for 4 h, planted in a sand/perlite mixture (2:3 vol/vol), and grown at 16 to 21°C with a 12-h photoperiod. Plants were incubated for 24 to 48 h at 100% relative humidity and 15°C in the dark to enhance sporulation. After 12 days, disease incidence (DI) of inoculated plants was determined as a percentage of plants displaying sporulation of the fungus on the cotyledons and/or true leaves (3). DI was 95 to 100% for the untreated seedlings, but mildew did not develop on seedlings treated with metalaxyl for 51 of the isolates. The remaining isolate caused symptoms on 67% of the treated plants. This isolate was tested in another experiment in which ‘Peredovik’ seed was treated with metalaxyl at 0, 0.5, 2.0, 3.5, and 5 g a.i./kg of seed. There were four replications of 12 seedlings per treatment, and seedlings were inoculated as described previously. DI in the untreated control was 77%, which was not significantly different from the DI for seed treated with metalaxyl at 0.5, 2.0, and 3.5 g a.i./kg of seed (97, 73, and 96%, respectively). DI for seed treated with metalaxyl at 5.0 g a.i./kg of seed was 37%, which was significantly lower than the other treatments. Although resistance of P. halstedii to metalaxyl has been reported in France (1), to our knowledge, this is the first report of resistance of sunflower downy mildew to metalaxyl in Spain.

References: (1) J. M. Albourie et al. Eur. J. Plant Pathol. 104:235, 1998. (2) G. Hall, Mycopathologia 106:205, 1989. (3) M.L. Molinero-Ruiz et al. Plant Disease 86:736, 2002.
First Report of Phaeomoniella chlamydospora on Vitis vinifera, Vitis labrusca, and French American Hybrids in Pennsylvania and New York
Authors: Stewart E. L. , Wenner N. G. , Hed B. E.
Published: May 2007

Phaeomoniella chlamydospora (W. Gams, Crous, M.J. Wingfield. & L. Mugnai) Crous & Gams (= Phaeoacremonium chlamydosporum) was isolated during the growing seasons of 2001 and 2002 from roots, trunks, and cordons of grapevines including cultivars Concord, Niagara, Steuben, Catawba, Dutchess, DeChaunac, Vidal, Seyval, Chambourcin, Chardonnay, Riesling, Sangiovese, Dolcetto, Baco Noir, Merlot, Villard, Pinot Gris, GR7, and 3309C root stock representing 18 locations in Eastern, Central, and Lake Erie regions of Pennsylvania as well as the Lake Erie and Finger Lakes regions of New York. P. chlamydospora was isolated from 89% of samples from vines 3 to 45 years old showing decline symptoms in the field. Isolates were identified based on a previous description (1) and by internal transcribed spacer (ITS1-5.8S-ITS2) rDNA sequences identical to those of P. chlamydospora isolated from Vitis vinifera from Italy (ex-type culture CBS229.95, GenBank Accession No. AF197973). P. chlamydospora is firmly established as a member of the petri and esca disease complex and as a pathogen of grapevines (2,3). To test pathogenicity of our isolates, approximately 30 μl of a 106 conidia/ml suspension, obtained from six isolates, was injected into the pith of 60 single-node, dormant, unrooted cuttings of ‘3309C’ and ‘Concord’. Ten control cuttings of ‘Concord’ and ‘3309C’ were injected with an equal volume of sterile distilled water. From 24 to 32 weeks after inoculations, all P. chlamydospora-inoculated cuttings exhibited dark streaking of the vascular tissue extending 45 to 50 mm from the point of inoculation. The vascular streaking observed in inoculated plants was identical to symptoms observed in declining vines in the vineyard. Vascular streaking was absent in the controls. P. chlamydospora was isolated as a monoculture from regions of vascular streaking in 89% of inoculated cuttings. P. chlamydospora was not isolated from the water-treated controls. P. chlamydospora is widespread and readily isolated from declining grapevines in Pennsylvania, New York, and other national and international grape growing regions. To our knowledge, this is the first report of P. chlamydospora from the cultivars cited above in Pennsylvania and New York.

References: (1) M. Groenewald et al. Mycol. Res. 105:651, 2001. (2) Phytopathol. Mediterr. 39(1), 2000. (3) Phytopathol. Mediterr. 40, Supplement 2001.
First Report of the Rust Miyagia pseudosphaeria on Sonchus oleraceus in the Americas
Authors: Hernández J. R. , Koike S. T. , Scheck H. J. , Hernández M. E. Palm
Published: May 2007

In January 2002, a rust was observed on leaves and stems of the weed Sonchus oleraceus L. (annual sowthistle) in Santa Barbara, CA. Infected plants were collected in Santa Barbara and Monterey counties, CA. Specimens were examined microscopically and compared with a published description (1) and herbarium specimens at the USDA National Fungus Collection, Beltsville, Maryland. The fungus was identified as Miyagia pseudosphaeria (Mont.) Jorst. based on characteristics of the uredinia and urediniospores. The uredinial sori were subepidermal, erumpent, and single or in groups. Sori were surrounded by peripheral, laterally connected, chestnut brown paraphyses that initially enclosed the developing urediniospores and eventually opened partially at the apex, breaking the host epidermis and remaining as a wall surrounding the spores. The urediniospores were ellipsoid, ovoid, or pyriform with yellowish, often granular, contents and measured 21.5 to 43 × 17 to 26.5 μm. The urediniospore walls were hyaline and finely echinulate and 2.5 to 3.5 μm thick with germ pores sometimes evident in median view. The paraphyses were 70 to 140 × 6 to 8 μm, thick-walled, hyaline below, chestnut brown above, and often somewhat wider or dichotomously branched at the apex. To test pathogenicity, a spore suspension (4.7 × 104 spores/ml) was sprayed onto 7-week-old annual sowthistle plants. Plants were incubated in a dew chamber for 48 h and maintained in a greenhouse at 22 to 24°C. Signs of rust were observed after 2 weeks, and microscopic examination confirmed that the same fungus was present. Uninoculated control plants did not develop rust. Using the same method, plants of prickly sowthistle (S. asper (L.) Hill) were inoculated and also developed the disease. All inoculation experiments were conducted two times and the results were the same. The rust was found on almost all annual sowthistle plants examined in Santa Barbara County, especially well-nourished specimens growing as weeds in irrigated landscapes, vegetable fields, or in container nurseries. Diseased plants were found in and around vegetable fields in Monterey County. M. pseudosphaeria is macrocyclic, autoecious, and known only on Sonchus spp. It has been reported from northern Africa, China, Europe, Japan, New Zealand, and the former Soviet Union. To our knowledge, this is the first report of M. pseudosphaeria in the Americas. Voucher specimens have been deposited in the U.S. National Fungus Collection (BPI 842025, 842055 to 842060, and 842230). Images can be viewed at nt.ars-grin.gov .

References: (1) M. Wilson and D. M. Henderson. British Rust Fungi. Cambridge University Press, Cambridge, 1966.
Screening and Field Trials of Virus Resistant Sources in Capsicum spp.
Authors: Suzuki Kazumi , Kuroda Tomohisa , Miura Yoshio , Murai Jun
Published: May 2007

Thirty-seven Capsicum accessions containing cultivated and wild species were screened for resistance to Cucumber mosaic virus (CMV), and were also investigated for their response to Tomato aspermy virus (TAV), Tomato mosaic virus (ToMV), Pepper mild mottle virus (PMMoV), and Tomato spotted wilt virus (TSWV). C. baccatum PI 439381-1-3 (PI 439381-1-3), C. frutescens LS 1839-2-4 (LS 1839-2-4), and C. frutescens cv. Tabasco (cv. Tabasco) showed a hypersensitive reaction against CMV-Y, and thus were not systemically infected. Only inoculated leaves of C. annuum cv. Sapporo-oonaga and cv. Nanbu-oonaga were infected with CMV-Y, and viral infection did not spread systemically. These five accessions (PI 439381-1-3, LS 1839-2-4, cv. Tabasco, cv. Sapporo-oonaga, and cv. Nanbu-oonaga) were considered resistant to CMV-Y. These accessions were also resistant to other CMV isolates, but not to the TAV isolate. PI 439381-1-3, LS1839-2-4, cv. Sapporo-oonaga, and cv. Nanbu-oonaga were susceptible to PMMoV, while PI 439381-1-3 and LS1839-2-4 showed systemic necrosis. All CMV-resistant accessions were susceptible to TSWV. Field tests of eight Capsicum accessions, including CMV, PMMoV, and/or TSWV-resistant accessions, demonstrated that most of the PI 439381-1-3 plants were not infected with CMV and PMMoV among the virus-infested fields. As occurred with mechanical inoculation, LS 1839-2-4, cv. Tabasco, cv. Sapporo-oonaga, and cv. Nanbu-oonaga were hard to infect with CMV in the field.
Effects of Plant Age, Leaf Position, Inoculum Density, and Wetness Period on Bipolaris coicis Infection in Adlays of Differing Resistance
Authors: Chang Seog Won , Hwang Byung Kook
Published: May 2007

The effects of plant age, leaf position, inoculum density, and wetness period on the development of adlay leaf blight caused by Bipolaris coicis were evaluated using six adlay cultivars or lines of differing resistance in field plots and in the greenhouse. Levels of resistance to leaf blight among the six cultivars or lines were consistent between the 1998 and 1999 field experiments. With the aging of adlay plants, leaf blight development gradually increased in all cultivars or lines tested. Leaf blight severity was significantly greater on the lower (older) leaves than on the upper (younger) leaves. As inoculum density increased from 103 to 106 conidia per ml, the development of leaf blight increased. Disease severity also increased as the time of leaf wetness duration increased from 0 to 60 h. Wetness duration above 48 h and a high inoculum density at 106 conidia per ml caused severe leaf blight symptoms in adlay seedlings. The data from the greenhouse experiments consistently revealed the same trends in relative levels of susceptibility of adlay cultivars to leaf blight as those seen at late plant growth stages under field conditions.