bluuebunny/crossref_metadata_2025 huggingface dataset:
Botryosphaeriaand Related Taxa Causing Oak Canker in Southwestern Spain
Authors: Sánchez M. E. , Venegas J. , Romero M. A. , Phillips A. J. L. , Trapero A.
Published: May 2007

Although root disease caused by Phytophthora cinnamomi is considered to be the most frequent and damaging disease associated with Quercus spp. decline in southwestern Spain, cankers commonly are observed on branches of declining Mediterranean Quercus spp. in this region. In surveys carried out in eight declining Quercus forests, strips of necrotic inner bark were common on diseased branches. Botryosphaeria stevensii, B. dothidea, and Diplodia sarmentorum consistently were isolated from these branches. Isolates of all three species caused cankers when inoculated onto excised Quercus branches. Inoculations on healthy branches in the field also induced canker development, but only B. stevensii caused lesions that girdled and killed the branches. The optimum temperature for in vitro growth of B. stevensii and B. dothidea was above 25°C, with slow growth at 35°C. In contrast, D. sarmentorum had an optimum temperature for growth of about 21°C, and did not grow at 35°C. The common occurrence and wide distribution of these pathogens, their association with cankers, and their ability to infect Quercus spp. suggest that they may contribute to the Quercus spp. decline in southwestern Spain.
Genetic Analysis of Adult-Plant Resistance to Leaf Rust in Five Spring Wheat Genotypes
Authors: Navabi A. , Singh R. P. , Tewari J. P. , Briggs K. G.
Published: May 2007

Inheritance of adult-plant resistance to leaf rust, caused by Puccinia triticina, was studied in the progeny of a one-way diallel cross involving five CIMMYT-derived adult-plant resistant wheat (Triticum aestivum) genotypes and a susceptible wheat ‘Avocet-YrA’. F1 progenies, F2 populations, F2-derived F3, and F4-derived F5 lines were field evaluated under artificial epidemics with leaf rust race MCJ/SP. Adult-plant resistance to leaf rust was incompletely dominant in crosses with the susceptible parent and was found to be controlled by additive interactions of Lr34 with at least two to three additional genes. Transgressive segregation giving rise to plants or lines with higher and lower levels of resistance than the parents was observed in all F2 and F5 derivatives of the resistant-parent intercrosses and suggested that, apart from Lr34, some of the other additive genes were nonallelic. Although specific combining ability was significant in some generations, general combining ability was found to be the major component of variation. Among generations, the estimates of the narrow-sense heritability of adult-plant resistance to leaf rust ranged from 0.67 to 0.97.
Evaluation of Inoculation Methods to Determine Resistance Reactions of Wheat to Fusarium graminearum
Authors: Engle Jessica S. , Madden Laurence V. , Lipps Patrick E.
Published: May 2007

Reliable greenhouse assays are needed to differentiate types of resistance in wheat to Fusarium graminearum. Genotypes with known field reactions were evaluated for resistance type using four greenhouse inoculation techniques. Percentage of spikelets with symptoms per spike (severity) and percentage of inoculated spikelets per spike developing symptoms were assessed 7, 10, and 14 days after inoculation (DAI). Genotypes were evaluated using disease assessments 14 DAI and area under the disease progress curve (AUDPC). Significant genotype-inoculation technique interactions for disease assessments indicated that genotypes responded differently to greenhouse inoculation techniques. The central floret injection technique used to assess resistance to spread within the spike (type II resistance) did not indicate a resistant response in genotypes with low field disease severity (putative type II). Atomizing macroconidia onto spikes, used to assess resistance to primary infection (type I resistance), indicated a resistant response in one of five genotypes with low field disease incidence (percentage of spikes with symptomatic spikelets) (putative type I). The inoculation techniques in the greenhouse were unable to differentiate between different types of partial resistance. Results indicated disparity in the ability of greenhouse inoculation methods to identify genotypes with partial resistance as observed in the field. It was concluded that atomizing conidia onto the spikes and assessing disease severity did not differentiate between resistance types. Additionally, a one-time assessment 14 DAI was determined to be as informative as multiple assessments and calculating the AUDPC.
First Report of Bronze Leaf Disease on Hybrid Poplar (Populus × canescens ‘Tower’) Caused by Apioplagiostoma populi in Manitoba, Canada
Authors: Northover P. R. , Desjardins M.
Published: May 2007

Poplars (Populus alba × P. tremula (P. × canescens) (Aiton) Smith cv. Tower) are common ornamental and windbreak trees in Manitoba and across the Canadian prairie provinces because of their rapid growth and columnar growth habit. Bronze leaf disease symptoms have been reported on five poplar species (P. alba, P. canescens, P. grandidentata, P. tremula, and P. tremuloides) (2), and the disease presents a significant barrier to the development and continued use of poplars (1). Elimination of tower poplars would represent a significant loss to the Canadian horticultural industry, and the costs incurred in the replacement of existing windbreaks would be high. In August 2002, we observed symptoms of bronze leaf disease on approximately 20-year-old tower poplars, ranging in height from 8 to 12 m at a tree nursery and golf course near Carman, Manitoba (49°30′N, 98°0′W). The leaf laminae of affected plants were chocolate brown, and the petioles and veins were yellow to light green. In the nursery windbreak, 70 trees had foliar symptoms on 30 to 80% of the canopy. At the golf course, eight trees had foliar symptoms on approximately 5 to 20% of the canopy. No fruiting structures were visible on leaf or shoot tissue, and no staining of vascular tissues was observed. Attempts to isolate the causal fungus of bronze leaf disease on artificial media have been unsuccessful (2). In October 2002, branches with symptomatic leaves were covered with netting, and the trapped leaves were left to overwinter. In March 2003, symptomatic leaves were brought to the laboratory and surface sterilized in 1% NaOCl for 1 min, rinsed with sterile water, and incubated at 18°C in moist chambers. After 2 weeks, dark brown, beaked, single perithecia that were 150 to 200 μm long × 150 μm wide emerged from the upper and lower leaf surfaces. Asci were fusoid clavate with a conspicuous apical ring and contained 4 or 6 spores. The two-celled, hyaline ascospores varied from 10.5 to 14.5 × 2 to 3 μm, the basal cell shorter than the apical cell. Leaf symptoms and microscopic fungal features matched those of Apioplagiostoma populi (Cash & A.M. Waterman) Barr, the cause of bronze leaf disease (1,2). Voucher specimens have been deposited in the U.S. National Fungus Collections (BPI 843385). To our knowledge, this is the first report of this fungus in western Canada, and the first confirmed report of this pathogen on tower poplar in Canada.

References: (1) E. K. Cash and A. M. Waterman. Mycologia 49:756, 1957. (2) J. A. Smith et al. Plant Dis. 86:462, 2002.
Expression of Susceptibility to Fusarium Head Blight and Grain Mold in A1 and A2 Cytoplasms of Sorghum bicolor
Authors: Stack James P. , Pedersen Jeffrey F.
Published: May 2007

Panicle diseases are among the major constraints to sorghum (Sorghum bicolor) production in the northern Great Plains; host plant resistance is the primary management option. However, essentially all commercial sorghum hybrids contain A1 cytoplasm, which raises the concern about increased disease risk as a result of cytoplasmic genetic uniformity. To determine the influence of cytoplasmic background on the expression of susceptibility to panicle diseases, F1 hybrids with four nuclear genotypes in each of two cytoplasms (A1 and A2) were planted in three environmentally diverse geographic locations in Nebraska. Fusarium head blight ranged in incidence from 13 to 100% across locations. Grain mold, caused primarily by species of Alternaria, Fusarium, and Cladosporium, ranged in incidence from 5 to 100% across locations. There was a significant effect of nuclear genotype on the incidence and severity of both head blight and grain mold across the three locations. Cytoplasm had no effect on head blight incidence or severity, or on grain mold severity. Cytoplasm had a significant effect on grain mold incidence, with A1 exhibiting slightly lower incidence than A2 (64 versus 70%). Although the cytoplasm effect for grain mold incidence was statistically significant, most of the variation in grain mold incidence was attributable to nuclear genotype. The slight increase in grain mold incidence attributable to A2 cytoplasm should be overcome easily by selection of nuclear genotypes with grain mold resistance. The use of A2 cytoplasm to incorporate genetic diversity into grain sorghum hybrids should not increase the risk of head blight or grain mold in commercial grain production.
Suppression of Powdery Mildew on Greenhouse-Grown Cucumber by Addition of Silicon to Hydroponic Nutrient Solution Is Inhibited at High Temperature
Authors: Schuerger Andrew C. , Hammer William
Published: May 2007

Silicon amendments to hydroponic nutrient solutions have been used successfully in Canada to suppress powdery mildew (PM) caused by Sphaerotheca fuliginea on cucumber (Cucumis sativus). In contrast, preliminary trials in Florida greenhouses failed to achieve the level of disease suppression reported in the literature for Canadian studies. A series of greenhouse experiments were conducted in Florida to determine the factors involved in reducing the effectiveness of silicon amendments for PM suppression on cucumber. Three horticultural practices (cultivar, nutrient solution formula, and rooting medium) and two environmental factors (light intensity and temperature) were tested in combination with silicon amendments for their effects on the suppression of PM on cucumber. When plants were irrigated with a standard nutrient solution amended with potassium silicate at 0 mg/liter, the cucumber cv. Vetomil was found to be resistant and cvs. Corona, Cilla, Farbio, and Toska were found to be susceptible to PM. Susceptible cultivars irrigated with potassium silicate at 100, 150, or 200 mg/liter exhibited a slight but statistically significant reduction in PM over the course of a 49-day trial. Although PM in the cultivar trial was slightly lower in treatments with added silicon, disease suppression with silicon was not commercially useful because it failed to increase fruit yields. Nutrient solution formula, rooting medium, and light intensity had no effects on the levels of PM suppression, regardless of whether plants were irrigated with potassium silicate at 0 or 100 mg/liter. Temperature was found to act in a synergistic manner with silicon. The greatest effect of temperature on PM suppression was observed at 20°C in which cucumber plants, irrigated with silicon at 100 mg/liter, exhibited significant reductions in the numbers of PM colonies per leaf. Disease suppression by silicon was observed at 25 and 30°C, but the magnitude of the disease suppression was significantly lower than when plants were maintained at 20°C. The effect of temperature on PM suppression by silicon may explain the difference in results between previous experiments in Canada, where greenhouse temperatures averaged 20 to 25°C, and the current study in Florida, where greenhouse temperatures averaged 24 to 32°C.
Characterization of Erwinia Populations from Nursery Retention Ponds and Lakes Infecting Ornamental Plants in Florida
Authors: Norman D. J. , Yuen J. M. F. , Resendiz R. , Boswell J.
Published: May 2007

Water shortages in Florida are occurring due to intense utilization of the aquifer system by municipalities and agriculture, and because of continued deficits in annual rainfall. Water districts therefore, are, recommending the use of recycled irrigation water, stormwater runoff, reclaimed municipal sewage water, and lakes for agricultural use. With recycled water, however, there is potential for both introducing and concentrating plant pathogens. In Florida, Erwinia soft-rot bacteria (synonym Pectobacterium) cause extensive crop losses in ornamental plant production. To determine Erwinia spp. population levels, samples were taken monthly for 1 year from four hypereutropic lakes and eight nursery retention ponds. Seventy-seven Erwinia strains were collected by both direct plating and by an enrichment process. With the direct plating method, 0 to 29 CFU/ml were detected on sodium polypectate medium. Significantly higher populations of Erwinia were detected in retention ponds of nurseries that were actively reutilizing their water. Erwinia strains were identified to species by fatty acid analysis and biochemical tests. Strains were further characterized by repetitive element-polymerase chain reaction (rep-PCR) and compared with 120 strains of Erwinia collected from ornamentals over a 17-year period in Florida. Using rep-PCR, most strains were clustered into two heterogeneous populations of E. chrysanthemi and E. carotovora subsp. carotovora in a 1:2 and a 1:4 ratio for isolates from ornamentals and from water, respectively. Within each population of E. chrysanthemi and E. carotovora, genetically different subpopulations could be identified that contained high percentages of Erwinia strains from water sources. Even though genetic differences exist, 99% of the strains from water sources were found to be pathogenic on dieffenbachia. Without water treatment of irrigation and stormwater runoff, there is a potential for both introducing and concentrating Erwinia populations within these water sources.
First Report of a Geminivirus Inducing Yellow Mottle in Okra (Abelmoschus esculentus) in Mexico
Authors: De La Torre-Almaráz R. , Monsalvo-Reyes A. C. , Rivera-Bustamante R. F. , Méndez-Lozano J.
Published: May 2007

Okra is an annual vegetable species native to Africa. In Mexico, the states of Tamaulipas, Guerrero, and Morelos contain the most important okra-producing areas. Viral-like diseases have recently affected the fruit production. In the field, the most common symptoms encountered include yellow streak, distortion of fruits, and foliar yellow mottle. Total DNA extracts from symptomatic okra plants were used as a template for polymerase chain reaction (PCR)-based detection using begomovirus-specific primers. RepMot and CPMot primers (1) were used for the amplification of DNA fragments that included the Rep and coat protein (CP) genes of begomoviruses. PCR results suggested the presence of a begomovirus in symptomatic plants. Southern and dot blot hybridization analysis were performed using a DNA fragment containing the CP gene of Pepper huasteco virus as a probe. Hybridization conducted under low stringency conditions confirmed the presence of a geminivirus. Additionally, transmission by grafting and biolistic (total DNA extracts from symptomatic plants) inoculations induced consistently severe streak fruits and yellow mottle symptoms in okra plants. Cloning of the PCR products (approximately 632-bp fragment) was performed in the PCRTopo vector (Invitrogen, San Diego, CA). Cloned viral inserts were sequenced (Genbank Accession No. AF349113). Nucleotide sequence comparisons were performed using the Clustal Method (MegAlign, DNAStar software, Madison, WI) with the GenBank database. Analysis of the PCR products confirmed the begomovirus nature of the sequence. The first 64 amino acids of the CP had 89% identity with Squash leaf curl virus while the intergenic region had 85% identity with Sida golden mosaic virus. To our knowledge, this is the first report of a begomovirus infecting okra in Mexico.

Reference: 1) J. T. Ascencio et al. Plant Dis. 86:692, 2002.
Tobacco mosaic virus in Jalapeno Pepper in New York
Authors: Murphy J. F. , Zitter T. A. , Erb A.
Published: May 2007

Jalapeno pepper plants (Capsicum annuum cv. Jaladuro) grown in Erie County, New York expressed chlorotic oak-leaf patterns along the primary vein of fully expanded leaves. Fruit had patterns of irregular ripening with a bumpy surface. Symptom expression was most obvious in August 2002, when leaf and fruit abscission occurred. Symptomatic fruit samples were tested by western blot analysis for the presence of Cucumber mosaic virus (CMV), Potato virus Y (PVY), Pepper mottle virus (PepMoV), Tobacco etch virus (TEV), and Tobacco mosaic virus (TMV). A positive reaction for TMV, but none of the other viruses, was observed. Symptomatic leaf samples were tested by Agdia, Inc. (Elkhart, IN) for Alfalfa mosaic virus, CMV, Impatiens necrotic spot virus, Pepper mild mottle virus, PepMoV, PVY, TEV, TMV, Tobacco ringspot virus, Tomato ringspot virus, and TSWV and for potyviruses using a group-specific test. The Agdia test confirmed that the pepper plants were infected with TMV. The pepper field where the original samples were collected was surveyed for TMV-infected plants. Fifty symptomatic plants expressing foliar and fruit symptoms similar to those originally tested, and 50 asymptomatic plants were sampled by collection of three leaves per plant and tested using enzyme-linked immunosorbent assay for the presence of TMV. All symptomatic plants and 18% of asymptomatic plants tested positive for TMV. To our knowledge, this is the first occurrence of TMV causing losses in commercially grown pepper in New York.
First Report of Septoria Leaf Spot on Cornus sericea in Italy
Authors: Garibaldi A. , Bertetti D. , Gullino M. L.
Published: May 2007

Cornus sericea (synonym C. stolonifera), family Cornaceae, is becoming widely used in Italy as ground cover in parks and gardens. In spring 2001, severe outbreaks of a previously unknown disease were observed in several gardens located in northern Italy (Biella Province). Infected leaves displayed small, circular, angular, or irregular necrotic lesions measuring 1 to 3 mm in diameter. Lesions were olivaceous to dark brown with a distinct reddish-to-black margin and surrounded by a chlorotic halo. Lesions eventually coalesced. Under favorable conditions, infected leaves become heavily spotted, dulling their appearance; severe infections resulted in premature defoliation. Pycnidia occurred on diseased leaves, and a fungus identified as Septoria cornicola (1) was consistently isolated on potato dextrose agar (PDA). Dark mycelium grew slowly on PDA and produced abundant pycnidia and conidia. Conidia were holoblastic, hyaline, 2 to 6 septate, 22 to 48 µm (average 35) × 2.2 to 3.6 µm (average 2.5). Pathogenicity tests were performed by inoculating leaves of healthy plants of C. sericea (cv. Flaviramea) with a conidial suspension (1 × 106 CFU/ml). Noninoculated plants served as controls. Plants were covered for 72 h with plastic bags and maintained in a growth chamber at 20°C. The first lesions developed on leaves of inoculated plants after 15 days. From such lesions, S. cornicola was consistently reisolated. No symptoms occurred on control plants. The presence of S. cornicola on C. sericea cv. Flaviramea has been reported in the United States (2) and was observed in 1905 in northeastern Italy on Cornus sanguinea (1), but to our knowledge, this is the first report of septoria leaf spot on C. sericea in Italy.

References: (1) D. F. Farr. Mycologia, 83:611, 1991. (2) D. Neely and D. S. Nolte. J. Arboric. 15:263, 1989.
Resistance of Pepper Cultivars and Accessions of Capsicum spp. to Sclerotinia sclerotiorum
Authors: Yanar Y. , Miller S. A.
Published: May 2007

Sclerotinia stem and fruit rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, is a potentially serious disease of bell peppers (Capsicum annuum L.), affecting both seedlings and mature plants. Management options for the disease are limited and information is not available on resistance in Capsicum spp. to this pathogen. The level of resistance of 12 commercial pepper cultivars and 110 Capsicum spp. accessions to Sclerotinia sclerotiorum was determined by using limited-term and ascospore inoculation methods. None of the commercial cultivars tested were resistant to Sclerotinia stem rot. Stem rot incidence among the Capsicum spp. accessions tested by ascospore inoculation ranged from 0 to 100%. Fifty-eight accessions had significantly less stem disease than the susceptible commercial cultivar Marengo. There was no correlation between results of the limited-term and ascospore inoculation tests. These results demonstrate for the first time that a high level of Sclerotinia stem rot resistance exists among the Capsicum spp. accessions. Several accessions may be suitable for use in breeding programs to increase resistance in commercial pepper cultivars.
Incidence of Viruses and Virus like Diseases of Sweetpotato in Uganda
Authors: Mukasa Settumba B. , Rubaihayo Patrick R. , Valkonen Jari P. T.
Published: May 2007

Sweetpotato plants were surveyed for viruslike diseases and viruses in the four major agroecological zones of Uganda. Testing of 1,260 sweetpotato plants, of which 634 had virus-like symptoms, showed that virus disease incidence ranged from 2.7% (Soroti district, short grassland—savannah zone) to 20% (Mukono district, tall grass—forest mosaic zone). Sweet potato chlorotic stunt virus (SPCSV), Sweet potato feathery mottle virus (SPFMV), Sweet potato mild mottle virus (SPMMV), and sweet potato chlorotic fleck virus (SPCFV) were serologically detected and positive results confirmed by immunocapture reverse transcriptase polymerase chain reaction (IC-RT-PCR) and subsequent sequence analyses of the amplified fragments, except SPCFV, which lacked sequence information. SPCSV and SPFMV were detected in all the 14 districts surveyed, whereas SPMMV and SPCFV were detected in 13 and 8 districts, respectively. Logistic regression analysis revealed that SPCSV and SPFMV, SPFMV and SPMMV, and SPFMV and SPCFV more frequently occurred together than any other virus combinations or as single virus infections. Co-infections of SPCSV with SPFMV and/or SPMMV were associated with more severe and persistent symptoms than infections with each of the viruses alone. Several plants (11%) displaying viruslike symptoms did not react with the virus antisera used, suggesting that more viruses or viruslike agents are infecting sweetpotatoes in Uganda.
Appressorium Formation and Tomato Fruit Infection by Colletotrichum coccodes
Authors: Sanogo S. , Stevenson R. E. , Pennypacker S. P.
Published: May 2007

Tomato fruit grown for commercial processing are harvested when the majority of the fruit are at the full, red-ripe stage of development. At this physiological stage, marketable yields often are reduced significantly by Colletotrichum coccodes. Appressorium formation and the infection of tomato fruit by C. coccodes were investigated in controlled-environment experiments. Conidia of C. coccodes were subjected to five temperature treatments (10 to 34°C with 6°C increments), and eight incubation periods (3 to 24 h with 3-h increments). The highest proportion of conidia that formed appressoria occurred at 16 and 22°C. Appressoria were formed within as few as 6 h of incubation at 16, 22, and 28°C. In contrast, incubation periods of at least 15 and 18 h were required for appressoria to form at 34 and 10°C, respectively. Appressorium formation was significantly reduced by 0.1 to 0.2 ppm of the fungicide chlorothalonil, and no appressoria formed at concentrations >0.4 ppm. When tomato fruit were inoculated with C. coccodes at three inoculum densities (2 × 105, 6 × 105, and 10 × 105 conidia/ml) and incubated in dew chambers for 8, 16, and 24 h at 5°C increments from 15 to 35°C, there was no significant interaction among inoculum density, dew period, and temperature. In general, across all inoculum densities and dew periods, anthracnose severity levels were greater for each 5°C increase in temperature from 15°C until its maximum level was observed at 30°C. However, when the fruit were exposed to 35°C, disease development was minimal. At temperatures from 15 to 30°C anthracnose severity increased proportionally as dew-period duration and inoculum density increased.
Peach Rusty Spot Epidemics: Temporal Analysis and Relationship to Fruit Growth
Authors: Furman Laura A. , Lalancette Norman , White James F.
Published: May 2007

Incidence and severity of peach rusty spot were monitored throughout the growing seasons of 1999 to 2001. Graphical and statistical analysis revealed that disease increased from the shuckoff stage of fruit development until 60 days after full bloom; epidemics typically lasted from 17 to 30 days. An analysis of fruit growth indicated that the early-season epidemic coincided with the first stage of stone fruit development, physiologically characterized as the period of cell division. During this period, as fruit growth slowed and approached initiation of pit-hardening, the rate of disease increase slowed. Since fruit infection was greatest during the period of fruit growth, disease progression was modeled as a function of plant growth instead of time. Temporal analysis revealed that the logistic function was appropriate for describing both growth processes, and a synchronous logistic/logistic composite disease progression/fruit growth model was fit to all data sets. No change in disease levels occurred during midseason, which coincided with the second stage of fruit development, a period of slow growth. Subsequently, disease incidence and severity significantly declined on average by 26% and 1.3 lesions per fruit, respectively, during the 20 to 30 days prior to harvest. This decline phase coincided with the third stage of fruit growth, the period of cell enlargement and coloration. These disease reductions may be related to physical changes in fruit size and pigmentation, as opposed to resistance development, causing younger, less established lesions to become undetectable.
The Detection and Variation of Strawberry mottle virus
Authors: Thompson J. R. , Jelkmann W.
Published: May 2007

Strawberry mottle virus (SMoV) is probably the most important virus to infect strawberry (Fragaria spp.). All species of strawberry are susceptible to SMoV, resulting in severe losses both in fruit and runner yield. However, due to the absence of definitive symptoms in commercial varieties, the only effective means of detecting SMoV is by transmission to susceptible indicator plants. In this study, we describe a reverse transcription-polymerase chain reaction (RT-PCR) method for the detection of SMoV in Fragaria spp. with the use of primers specific for the noncoding regions (NCR) of both RNA1 and RNA2 of the virus. Using this method, all of 16 isolates from various geographical origins were positive for SMoV. Partial sequences of a 327-nt long coding region were obtained for the putative large coat protein of all isolates by RT-PCR using degenerate primers. Nucleotide identities between isolates ranged from 72.8 to 99.7%. A 546-nt sequence of the putative polymerase gene of nine isolates was obtained by RT-PCR and compared. Nucleotide identities ranged from 73.4 to 100%. There was a clear tendency for isolates to group according to their geographical origin. Sequence data obtained of the NCR show four completely conserved regions of 20 or more bases.
Isothiocyanates Produced by Brassicaceae Species as Inhibitors of Fusarium oxysporum
Authors: Smolinska U. , Morra M. J. , Knudsen G. R. , James R. L.
Published: May 2007

Glucosinolates contained in members of the Brassicaceae release isothiocyanates potentially useful in controlling Fusarium oxysporum pathogens in conifer seedling nursery soils. Our objective was to determine the toxicity of individual isothiocyanates to different growth stages of the fungus. Bioassays with four F. oxysporum isolates were conducted using sealed containers in which 0.3 μl of 2-propenyl, ethyl, buty, phenylethyl, benzyl, or phenyl isothiocyanate was allowed to volatilize. Propenyl and ethyl isothiocyanates were the most fungistatic of those compounds tested. The same concentrations of propenyl and ethyl isothiocyanates that inhibited mycelial growth completely suppressed conidial and chlamydospore germination of all isolates. Other isothiocyanates including ethyl, benzyl, and phenethyl were also fungitoxic to F. oxysporum conidia and chlamydospores. Reduction in pathogen populations resulting from a green-manure crop are likely achievable since chlamydospores are sensitive to isothiocyanate. Pathogenic F. oxysporum isolates infesting nursery soils would likely be most suppressed by species of plants such as Brassica carinata, B. nigra, and B. juncea, which contain glucosi-nolates that release high concentrations of propenyl isothiocyanate.
Mating Type Distribution and Fertility Status in Magnaporthe grisea Populations from Turfgrasses in Georgia
Authors: Tredway L. P. , Stevenson K. L. , Burpee L. L.
Published: May 2007

Populations of Magnaporthe grisea associated with tall fescue and St. Augustinegrass in Georgia were analyzed for mating type distribution and fertility status in 1999 and 2000. A polymerase chain reaction based assay for mating type was developed to facilitate population analysis. M. grisea populations from St. Augustinegrass in Georgia were dominated by the Mat1-1 mating type, whereas populations from tall fescue were dominated by Mat1-2. The opposite mating type was found in low frequency (0 to 5.7%) associated with each host. The fertility status of isolates from two populations was determined using controlled crosses in vitro. Seventy-eight Mat1-1 isolates from St. Augustinegrass were sterile in test crosses, but a single Mat1-2 isolate from St. Augustinegrass was male fertile. Of 87 Mat1-2 isolates from tall fescue, 47 were male fertile in test crosses, but 19 produced perithecia that were barren. All Mat1-1 isolates from tall fescue were sterile. Although both mating types exist in M. grisea populations from turfgrasses in Georgia, no female fertile isolates were identified in sample populations. The predominance of one mating type in eight sample populations and absence of female fertile isolates in two sample populations indicates that sexual reproduction may not occur with significant frequency in M. grisea populations associated with turfgrasses in Georgia.
Effects of Light, Temperature, and Leaf Wetness Duration on Daylily Rust
Authors: Mueller D. S. , Buck J. W.
Published: May 2007

Experiments in controlled environments were completed to determine the influence of light intensity, temperature, and leaf wetness duration on daylily rust caused by Puccinia hemerocallidis. As light intensity increased, there was a significant decrease in urediniospore germination (R2 = 0.88 and Y = 96 - 0.6x). Urediniospores germinated in vitro between 7 and 34°C with an optimal temperature of 22 to 24°C. To test the effect of temperature on infection efficiency, plants were inoculated with urediniospores, incubated under high relative humidity at 4, 10, 22, 30, or 36°C, and then transferred to a greenhouse at 23°C for 15 days. Plants incubated at 22°C had an average of 13 lesions cm leaf-1. Incubation temperatures of 4, 10, 30, or 36°C resulted in less than 1.5 lesions cm leaf-1. Plants were inoculated, incubated at 22°C for 24 h, and then incubated at different temperatures for 15 days to test the effect of temperature on disease development. There were no significant differences in disease development at 22 and 30°C; however, there were significantly fewer lesions at 10°C and no lesions developed at 36°C within 15 days. Five to six h of leaf wetness were required for lesion development and as the duration of leaf wetness increased, there was a significant increase in the number of lesions that developed. These studies indicate that for disease development of P. hemerocallidis on daylily, temperatures around 22°C and 5 h of leaf wetness are required during infection. However, once a daylily is infected, disease development is not as sensitive to environmental conditions.
First Report of Root Rot on Asparagus Caused by Phytophthora megasperma in Canada
Authors: Vujanovic V. , Hamel C. , Jabaji-Hare S. , St-Arnaud M.
Published: May 2007

In August 2002, Phytophthora megasperma Drechs. was isolated from wilted plants of Asparagus officinalis L. cv. Guelph Millenium displaying spear and crown rot. Six affected plants were sampled in a commercial asparagus field located in the Saguenay-Lac-Saint-Jean Region (300 km northeast of Montreal, Quebec, Canada). The fungus was isolated from asparagus fern stalks, crown tissue, and spears after a rainy period and identified using morphological and cultural characteristics (2). In pinkish 4-week-old cultures, unbranched stalks bore abundant sporangia, which were ovoid to obpyriform in shape, 15 to 45 m long, and 10 to 30 m in diameter. Characteristic circular oospores >30 m in diameter were produced on V8 juice agar at 25°C in darkness after 1 month. Pathogenicity was tested on asparagus cvs. Guelph Millenium and Jersey Knight. A mycelium suspension (3 ml at 106 CFU/ml) prepared from 1-week-old shaken potato dextrose (PD) broth was sprayed on 30 1-week-old seedlings grown in petri plates filled with sterilized, moist, sandy soil and held at 20°C (day/night). Controls received sterile PD broth. Within 3 weeks of incubation in the dark, inoculated seedlings exhibited necrotic symptoms similar to those observed initially, while controls remained healthy. The pathogen was isolated from 75% of the ‘Guelph Millenium’ and 98% of the ‘Jersey Knight’ symptomatic seedlings, but not isolated from the control seedlings. In North America, disease caused by P. megasperma resulting in yield loss has been reported in California and New York (1,3). In Canada, the etiology of asparagus diseases is not well characterized. To our knowledge, this is the first report of P. megasperma on asparagus plants in Canada.

References: (1) P. A. Ark and J. T. Barrett. Phytopathology 28:754, 1938. (2) D. C. Erwin et al. Phytophthora: Its Biology, Taxonomy, Ecology, and Pathology. The American Phytopathological Society, St Paul, MN, 1983. (3) T-L. Kuan and D. C. Erwin. Phytopathology 70:333, 1980.
Occurrence of Pseudoperonospora cubensis Pathotype 5 on Squash in Italy
Authors: Cappelli C. , Buonaurio R. , Stravato V. M.
Published: May 2007

During the period of May to August 2002, typical symptoms of downy mildew were observed on squash (Cucurbita pepo L.) in both tunnel and open field cultivation in central Italy (Latium and Umbria). The disease spread rapidly and because the control measures used were not effective, growers suffered severe yield losses. Infected plants showed yellow spots on the upper leaf surface. Based on morphological features observed at ×10 to ×40 magnification, the pathogen was identified as Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev. To verify the pathogenicity of the fungus, a sporangial suspension (1 × 104 sporangia per ml) was sprayed on leaves of squash plants with two expanded leaves, which were held in dark moist chambers at 20 ± 2°C for 48 h. Control plants were sprayed with sterile water. Inoculated and control plants were kept in a growth chamber at 24 ± 2°C with 14/10 h day/night cycles. Chlorotic spots and sporulation were observed on inoculated plants. The morphological features of the fungus obtained from the inoculated plants were identical to those from the original diseased plant. Previous observations of downy mildew in Italy suggested that squash was not susceptible (1). The physiological specialization among isolates of P. cubensis based on the compatibility of different cucurbit hosts (2) was not tested previously in Italy. To determine the pathotype of four fungal isolates obtained from squash cultivated in different localities, 10 plants per species of the cucurbit species (2) were inoculated with each isolate using the same procedure described for the pathogenicity test. Disease symptoms were detected on all inoculated hosts, including squash, suggesting that all the fungal isolates obtained from squash are pathotype 5. Only pathotype 5 is a common causal agent of downy mildew of squash and other cucurbit hosts. During the period of our observations, climatic conditions were unusually wet because frequent storms occurred during the summer providing favorable environmental conditions for the development of secondary spread. Today, it appears there are no commercially acceptable cultivars of squash resistant to downy mildew available to growers in Italy.

References: (1) F. Ciccarese et al. Phytopathol. Mediterr. 29:14, 1990. (2) C. E. Thomas et al. Phytopathology 77:1621, 1987.
First Report of Powdery Mildew (Microsphaera palczewskii) on Siberian Pea Tree (Caragana arborescens) in North America
Authors: Nischwitz C. , Newcombe G.
Published: May 2007

Caragana arborescens Lam. is an exotic ornamental that can also be somewhat invasive. In July 2002, powdery mildew was observed on C. arborescens along the Idaho-Washington border in Moscow and Pullman, respectively. Leaves were colonized as soon as they emerged, and entire plants were affected. The fungus covered both leaf surfaces, but cleistothecia were more abundant on abaxial surfaces. The mean diameter of the cleistothecia was 91 (± 9.8) μm. Short-stalked asci averaged 67 (± 7.1) μm × 37 (± 5.2) μm, and the ascospores were 21 (± 2.0) μm × 13 (± 0.8) μm. There are records of four species of Microsphaera on C. arborescens in Europe and Asia. The measurements fit the description of Microsphaera palczewskii Jacz. (1), and the identification was confirmed by comparison with specimens of this fungus on C. arborescens from Sweden (U.S. National Fungus Collections: BPI 749057 and 749058). Specimens of M. grossulariae (Wallr. ex Fr.) Lev. on Ribes divaricatum Dougl. from California (BPI 558266) were also examined, but the cleistothecial appendages were distinctly different from those of the Idaho specimens. To our knowledge, this is the first reported occurrence in North America of powdery mildew on C. arborescens and the first report of M. palczewskii. The latter may have been introduced recently into North America because there are areas in southern Canada and the northern United States in which C. arborescens is unaffected by powdery mildew. Interestingly, it is only in recent decades that M. palczewskii has spread from Asia into Europe (2). Now, host and parasite have been reunited in North America as well. Specimens have been deposited in the U.S. National Fungus Collections (BPI).

References: (1) U. Braun. A monograph of the Erysiphales (powdery mildews) J. Cramer, Berlin-Stuttgarg, 1987. (2) S. Huhtinen et al. Karstenia 41:31, 2001.
First Report of Phytophthora cinnamomi on High-Bush Blueberry in Italy
Authors: Tamietti G.
Published: May 2007

Beginning in the summer of 1996, a disease of high-bush blueberry (Vaccinium corymbosum L.) appeared on cvs. Sparta and Berkeley in commercial plantings near Cuneo and in a nursery in Pinerolo (northwest Italy). In the field, the disease became evident 5 to 8 months after planting. Symptoms included stunting, pale green-to-reddish leaves, premature defoliation, and root and crown rot. The root system was reduced, with few feeder roots and a dark discoloration of the root cortex. Root, crown, and basal stem rot led to death of the plants. Pieces of the discolored organs were surface-sterilized in sodium hypochlorite (2%) for 5 min, rinsed in sterile water, dried on sterile filter paper, and plated on acidified malt extract agar (pH 4.6) (MEA) and a selective medium for oomycetes (2). Slow-growing colonies developed on MEA, whereas colonies characteristic of Phytophthora spp. grew on the selective medium for oomycetes. Six isolates from plants collected from the field and the nursery were inoculated as V8 juice culture homogenate on the roots of blueberry cv. Berkeley, azalea, and 1-year-old chestnut plants in pots. All six isolates reproduced the symptoms in blueberry and caused root and foot rot in the other hosts. The original fungus was reisolated from all inoculated hosts. The isolates were examined and compared with strain 0229 of P. cinnamomi Rands from the International Mycological Institute. They were identified as P. cinnamomi on the basis of morphological characteristics and total mycelial soluble protein patterns on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In Italy, blueberry is a new host for this pathogen that was previously observed in rhododendron (1), and recently in chestnut (3) and other forest species. Because of the high risk of spreading the pathogen to areas where susceptible plants are grown, it is recommended that high-bush blueberry nursery stock be tested for the pathogen.

References: (1) G. Gullino and A. Garibaldi. La difesa delle piante 10:273, 1987; (2) H. Masago et al. Phytopathology 67:425, 1977. (3) A. M. Vettraino et al. Plant Pathol. 50:90, 2001.
Comparison of Seasonal Infection of Citrus Roots byPhytophthora citrophthoraandP. nicotianaevar.parasitica
Authors: Dirac Monica F. , Menge John A. , Madore Monica A.
Published: May 2007

Excised feeder roots from mature citrus trees located in climatically different regions were infected with zoospores of Phytophthora citrophthora and P. nicotianae var. parasitica at different times of the year under identical laboratory conditions. Zoospores encysted on and caused infection in roots from all locations year round. Both pathogens had the most encysted zoospores on roots from November to January and the least from March to May. Infection by P. nicotianae var. parasitica was consistently higher than P. citrophthora in the excised summer roots (May to September) and lower in January 1998 and November 1997. Infection by both species of Phytophthora dropped to a minimum in March when carbohydrate levels in roots were lowest. Temperature was not solely responsible for determining seasonal fluctuations of P. nicotianae var. parasitica and P. citrophthora. Root carbohydrate content also could not be correlated with seasonal infection. Other physiological or microbial factors associated with citrus roots may cause seasonal Phytophthora infection fluctuations. Infection of citrus seedling roots by P. citrophthora at 16°C reduced root starch content but not glucose compared to P. nicotianae var. parasitica, whereas infection at 30°C by P. nicotianae var. parasitica lowered root glucose but not starch content compared to P. citrophthora.
Antiserum to Recombinant Virus Coat Protein DetectsRupestris stem pitting associated virusin Grapevines
Authors: Meng Baozhong , Credi Rino , Petrovic Natasa , Tomazic Irma , Gonsalves Dennis
Published: May 2007

Rupestris stem pitting (RSP) is the most widespread virus disease of grapevines. The genome of Rupestris stem pitting associated virus (RSPaV), the putative causal agent of RSP, was recently sequenced. Until recently, the only method to diagnose RSP was biological indexing on woody indicator plants, a process that takes 2 to 3 years to complete. This study reports on the production of a polyclonal antiserum to a recombinant coat protein of RSPaV. The antiserum was used effectively to detect RSPaV from various genotypes and tissues of grapevines by Western blot and indirect enzyme-linked immunosorbent assay. Virus antigens were consistently detected in the cambium of dormant canes and in actively growing leaves of grapevines. Moreover, plants of Vitis rupestris ‘St. George’, the standard biological indicator for RSP, tested positive for RSPaV. The serological methods developed in this study are advantageous as compared with biological indexing because they are more rapid, less expensive, as reliable, and more suitable for assays of a large number of samples.
Reactions in the Annual Medicago spp. Core Germ Plasm Collection to Phoma medicaginis
Authors: O'Neill Nichole R. , Bauchan Gary R. , Samac Deborah A.
Published: May 2007

The annual Medicago spp. core collection, consisting of 201 accessions, represents the genetic diversity inherent in 3,159 accessions from 36 annual Medicago spp. This germ plasm was evaluated for resistance to spring black stem and leaf spot caused by Phoma medicaginis. Spring black stem and leaf spot is a major destructive disease in perennial alfalfa (Medicago sativa) grown in North America, Europe, and other temperate regions. Disease control is based principally on the use of cultivars with moderate levels of resistance. Evaluation of the core collection was conducted using standardized environmental conditions in growth chambers, and included the M. sativa standard reference cultivars Ramsey (resistant) and Ranger (susceptible). The degree of resistance found among accessions within species was variable, but most annual species and accessions were susceptible. Most accessions from 10 species exhibited high disease resistance. These included accessions of M. constricta, M. doliata, M. heyniana, M. laciniata, M. lesinsii, M. murex, M. orbicularis, M. praecox, M. soleirolii, and M. tenoreana. Most of the accessions within M. arabica, M. minima, M. lanigera, M. rotata, M. rugosa, M. sauvagei, and M. scutellata were highly susceptible. Disease reactions among some accessions within species were highly variable. On a 0-to-5 disease severity scale, ratings ranged from 0.67 (PI 566873) to 4.29 (PI 566883) within accessions of M. polymorpha. Most of the M. truncatula accessions were susceptible, with a mean of 3.74. Resistant reactions were similar to those found in incompatible interactions with P. medicaginis and alfalfa, which have been associated with specific genes leading to the production of isoflavonoid phytoalexins. The large genetic variability in annual Medicago spp. offers potential for locating and utilizing disease resistance genes through breeding or genetic engineering that will enhance the utilization of Medicago spp. as a forage crop.
Relative Longevity of Macrophomina phaseolina and Associated Mycobiota on Residual Soybean Roots in Soil
Authors: Baird Richard E. , Watson Clarence E. , Scruggs Mary
Published: May 2007

Survival of the charcoal rot pathogen (Macrophomina phaseolina) in soybean (Glycine max) on residual root systems was studied over a 2-year period. Root segments colonized by M. phaseolina were placed into fiberglass-mesh bags and buried at depths of 0, 7.6, and 25.4 cm in a Marietta fine sandy loam soil in field microplots. Samples for year 1 and year 2 were buried in October 1999 and 2000, respectively, and sampled every 2 months over a 14-month period. Mean percent frequencies from both years for M. phaseolina showed a decreased linear trend over time from 91% before burial to 24.7% 2 months later, 10.3% at 6 months, and 0.3% after 14 months. Tissues were degraded in the June samplings of both years and this degradation was believed to be partially responsible for the reduced survival of M. phaseolina. Mean isolation frequencies were significantly (P ≤ 0.05) greater at the 0-cm depth than at 7.6 and 25.4 cm across all sampling dates. Other fungi which were present in the preliminary assay, including Fusarium spp. and those in the Phomopsis/Diaporthe complex, also declined by the end of the study. Trichoderma spp. was isolated at significantly (P ≤ 0.05) greater frequencies and a significant positive linear trend over time. It is possible that Trichoderma spp. were involved in direct tissue degradation and nutrient depletion of the root segments, or may have acted as a mycoparasite, reducing the survival of the pathogen M. phaseolina and other associated fungi. Results from this study indicate that farm practices which increase residue destruction immediately after harvest or those that enhance Trichoderma spp. populations may directly or indirectly lower the relative longevity of soilborne pathogens, including M. phaseolina.