bluuebunny/crossref_metadata_2025 huggingface dataset:
Greenhouse and Field Evaluation of Biological Control of Fusarium Head Blight on Durum Wheat
Authors: Schisler D. A. , Khan N. I. , Boehm M. J. , Slininger P. J.
Published: May 2007

Fusarium head blight (FHB) is a devastating disease that causes extensive yield and quality losses to wheat and barley. In durum wheat, the pathogen-produced toxin deoxynivalenol (DON) is retained in semolina at ˜50%, and the causal agent of FHB, Gibberella zeae, has a strong adverse effect on pasta color. Two bacteria and two yeast strains with known efficacy against G. zeae on hexaploid wheats were produced in liquid culture and assayed on two cultivars of durum wheat in greenhouse bioassays. All antagonists reduced FHB severity on cultivar Renville, and three of the four reduced severity on cultivar Ben, with Bacillus subtilis strain AS 43.3 decreasing FHB severity by as much as 90%. In separate greenhouse bioassays, the car-bon:nitrogen ratio of the medium used to produce antagonists did not consistently influence antagonist efficacy. All antagonist/production medium combinations but one were effective in reducing disease on both durum cultivars. Of six antagonists tested at field sites, Cryptococcus sp. OH 71.4 and C. nodaensis OH 182.9 reduced disease severity by as much as 57% in Peoria, IL, while Cryptococcus sp. OH 181.1 reduced disease severity by as much as 59% in a trial at Langdon, ND. Antagonists did not influence the DON content of grain in the Peoria trial. Relative performance indices for four antagonists calculated from greenhouse and field results on the two durum cultivars demonstrated that the bioassay location, but not the cultivar of durum, influenced the relative performance of antagonists. Yeast antagonists OH 71.4, OH 181.1, and OH 182.9 appear to have the highest potential for contributing to the reduction of FHB on du-rum wheat in the field.
Identities and Geographic Distributions ofPhytophthoraspp. Causing Root Rot of Red Raspberry in Chile
Authors: Wilcox W. F. , Latorre B. A.
Published: May 2007

Five identified and two unidentified Phytophthora spp. were isolated from diseased roots of dead or declining red raspberry (Rubus idaeus L.) plants sampled from 18 plantations along a >1,000-km north-south axis in Chile. The array of Phytophthora spp. isolated was strongly associated with geographical location. P. fragariae var. rubi was recovered from 75 and 60% of the plantations in the southern (40°16′ to 40°53′ S latitude) and central (34°35′ to 37°23′ S latitude) production sectors, respectively, but was not recovered from any plantation in the northern sector (32°43′ to 33°45′ S latitude). Similarly, P. megasperma and P. gonopodyides were recovered from multiple plantations in the southern and central sectors but were not recovered in the northern sector. In contrast, P. cryptogea was recovered from 80% of the plantations in both the northern and central sectors but not from any plantation in the south, whereas P. citricolawas isolated from diseased plants in all sectors. In subsequent pathogenicity trials, P. citricola, P. cryptogea, and an unidentified Phytophthora sp. were equally and highly virulent on ‘Heritage’ red raspberry in each of three greenhouse experiments. The other species were less virulent in the experiment when soil temperatures were highest (mean weekly maximum = 27.5°C) relative to the other two experiments when temperatures were more moderate (mean weekly maxima of 19.9 and 23.7°C). Isolates identified as P. cryptogea were very similar to P. cryptogea isolates recovered previously from kiwi fruit in Chile and from deciduous fruit trees in California with respect to morphological characters and electrophoretic banding patterns of soluble mycelial proteins. Using the same criteria, isolates identified as P. gonopodyides were very similar to isolates recovered earlier from deciduous fruit crops in New York, which previously were identified as P. cryptogea sensu lato but are hereby reclassified as P. gonopodyides.
First Report of Fusarium oxysporum f. sp. basilici in Sweet Basil Cultivation in Spain
Authors: Moya M. L. Guirado , Vázquez J. Gómez , Prieto R. Blanco , Marquina J. C. Tello
Published: May 2007

Recently, sweet basil (Ocimum basilicum L.) grown in greenhouses was introduced in Almería, Spain. It is typically cultivated in soil or perlite soilless culture. During the last 6 years, the following symptoms were observed sequentially in basil cultivation: yellowing and wilting of apical tips, wilting and necrosis of leaves and petioles, stunting, black lines along stems and petioles, and discoloration and necrosis of the xylem. Symptoms began at the apex and progressed to the plant base. Within 4 months of planting, symptoms developed in more than 14% of soil-cultivated plants, and in more than 13% of perlite-cultivated plants. Isolations from diseased xylem revealed the presence of Fusarium oxysporum. Inoculations were performed with a fungal suspension (104 CFU/ml) on basil cv. Genovesa, by drenching plants grown in sterile substrate or dipping the roots and transplanting plants into sterile substrate. Of 30 isolates, 80% were pathogenic and resulted in symptoms of the disease described above. The pathogen was reisolated from all inoculated plants. Inoculating Melissa officinalis L., Salvia officinalis L., Origanum majorana L., Mentha piperita L., Satureja hortensis L., and Thymus vulgaris L tested specificity of F. oxysporum. This test utilized the same methods used for basil. None of these species developed symptoms. Results indicated that symptoms of the disease on basil were caused by F. oxysporum f. sp. basilici. Since cultivation of basil is relatively new to Almería, it was necessary to determine the source of the inoculum. Accordingly, 3,200 seeds from Germany and Italy, the primary source of seed in Almería, were analyzed. F. oxysporum was isolated from 0.5% of the seeds. Following methods used earlier, all isolates were inoculated on basil. Fifty percent of the isolates reproduced the disease symptoms. The results suggest that the seeds from Germany and Italy were the source of the inoculum, and to our knowledge, introduced the disease into the growing basil cultures of Almería.
First Report of Pestalotiopsis funerea on Cupressocyparis leylandii in Italy
Authors: Gonthier P. , Nicolotti G.
Published: May 2007

Pestalotiopsis funerea (Desm.) Steyaert occurs worldwide and is reported as an opportunistic invader of conifers. It can also be have as a primary pathogen. During the spring of 2001, leaf yellowing was observed on mature and young Cupressocyparis leylandii trees in some nurseries in northern Italy. Symptoms were first observed on twig tips and progressed toward the stem during the summer, resulting in twig dieback and death of branches up to 15 mm. Dark acervuli were present in the cankers. Isolations were made from cankers and necrotic twigs by removing the outer tissue and placing wood slivers from affected tissues on potato dextrose agar. P. funerea was isolated from 88 and 72% of cankers and necrotic twigs, respectively. Four isolates were selected for inoculation tests. Inoculations were made in September on the upper part of stems of 4-year-old pot-grown C. leylandii saplings. The outer layer of the bark (5 × 3 mm) was removed, and a 5-mm-diameter mycelial plug on malt extract agar (MEA) was placed on the wound and covered with Parafilm. Sterile MEA plugs served as controls. The experiment included 20 replications for each isolate and the control. After 4 weeks, 80% of inoculated plants showed bark necrosis or small cankers, or both, and 20% died. P. funerea was reisolated. No cankers developed in the controls. P. funerea was previously reported in Italy on Thuja orientalis L. (2) and from France on C. leylandii (1), but to our knowledge, this is the first report of the pathogen on C. leylandii in Italy.

References: (1) M. Morelet. Rev. Hortic. 227:35, 1982. (2) A. Panconesi and G. Vettori. Inf. Fitopatol. 5:37, 1994.
First Report of Orchid fleck virus in Costa Rica
Authors: Freitas-Astúa Juliana , Moreira Lisela , Rivera Carmen , Rodríguez Carlos M. , Kitajima Elliot W.
Published: May 2007

Orchid fleck virus (OFV), a tentative member of the family Rhabdoviridae, infects orchids in several countries. The virus is vectored worldwide by the mite Brevipalpus californicus (Banks) (Acari: Tenuipalpidae). Eleven plants of Oncidium spp. and one plant each of the genera Cymbidium and Maxillaria exhibiting numerous yellow flecks and necrotic ringspot lesions on leaves were collected in two private orchid collections in Costa Rica. Presence of OFV was assessed by plate-trapped antigen enzyme-linked immunosorbent assay (PTA-ELISA) using an antiserum developed against an OFV isolate in Japan (2), analyses of ultrathin sections of the host cell with transmission electron microscopy (TEM), and reverse transcription-polymerase chain reaction (RT-PCR) amplification using specific primers for the viral nucleocapsid gene (1). Eight of eleven Oncidium samples, and both Cymbidium and Maxillaria samples tested positive for OFV with PTA-ELISA having A405 values ranging from 3.9 to 14.6 times higher than negative controls. Thin sections from individual samples of Cymbidium, Oncidium, and Maxillaria revealed electron-lucent intranuclear viroplasm and short, rodlike particles (40 to 50 × 100 nm) in the nucleus or cytoplasm typical of OFV-infected cells. RT-PCR amplifications from one sample of each genera resulted in PCR-product bands of approximately 800 bp. The Cymbidium RT-PCR product was cloned into a pGEM-T-Easy expression vector and sequenced using an ABI 3700 sequencer. The 619-bp nucleocapsid gene consensus sequence had 98% homology with the OFV isolate 0023 identified in Germany (GenBank Accession No. AF343870) (1). However, it had only approximately 85% nucleocapsid gene homology with other OFV isolates available through GenBank, including those from countries geographically closer to Costa Rica, such as Brazil (1). To our knowledge, this is the first report of OFV infecting orchids in Costa Rica.

References: (1) A. L. Blanchfield et al. J. Phytopathol. 149:713, 2001. (2) H. Kondo et al. Bull. Res. Inst. Bioresour. Okayama Univ. 4:149, 1996.
Natural Infestation of Onion Seed by Pantoea ananatis, Causal Agent of Center Rot
Authors: Walcott R. R. , Gitaitis R. D. , Castro A. C. , Sanders F. H. , Diaz-Perez J. C.
Published: May 2007

An immunomagnetic separation and polymerase chain reaction (IMS-PCR) assay was used to detect Pantoea ananatis in naturally infested onion seeds. Using species-specific PCR primers and polyclonal antibodies, IMS-PCR consistently demonstrated detection thresholds of 101 to 103 CFU/ml. There was no significant difference between the numbers of CFU recovered from onion seed wash by IMS (after repeated rinses) and by direct plating, indicating that IMS effectively captured P. ananatis cells from heterogeneous bacterial populations. Using IMS-PCR and IMS followed by plating on nutrient agar, P. ananatis was detected in 19.7% of onion seed samples harvested from two onion fields in which center rot developed naturally in 2000. When planted in germination boxes, 53% of the seed samples that tested positive for P. ananatis produced seedlings with symptoms of center rot. There was no significant difference in germination between infested and noninfested seed samples. This is the first report of natural infestation and transmission of P. ananatis in onion seed.
Laboratory and Growth Chamber Evaluation of Fungicidal Seed Treatments for Maize Seedling Blight Caused by Fusarium Species
Authors: Munkvold G. P. , O'Mara J. K.
Published: May 2007

The performance of seed treatment products for maize usually is evaluated in field experiments, where it is difficult to assess their effects on specific important pathogens such as fungi in the genus Fusarium. To evaluate three fungicidal seed treatments (captan, difenoconazole, and fludioxonil) against six Fusarium species that infect maize seed or seedlings, we conducted experiments in the laboratory and in growth chambers. In the laboratory experiments, treated and nontreated seeds of two maize hybrids were incubated on the surface of an agar medium colonized by each of 12 Fusarium isolates. The fungi did not reduce seed germination, but most Fusarium isolates caused decay of the seed and radicle, and arrested the development of the radicle. All three fungicides significantly reduced the colonization and decay of the seeds and radicles by Fusarium isolates and resulted in greater radicle lengths, but there were significant interactions between the effects of fungicide treatments and Fusarium isolates. Overall, difenoconazole was the most effective fungicide for the prevention of seed colonization and decay. Fludioxonil was overall the most effective fungicide in terms of increased radicle length, particularly when seed was exposed to isolates of F. graminearum, which were among the most aggressive isolates in the experiments. In the growth chamber experiments, seeds were planted in a Fusarium-infested potting medium, which resulted in lower emergence, shoot length, root length, and dry weight of seedlings compared to the noninfested control. Some isolates also caused root rot symptoms. All three fungicides significantly improved shoot and root length and root health, difenoconazole and fludioxonil significantly improved emergence, and only difeno-conazole significantly improved dry weight compared to the nontreated control. There were significant rank correlations between the results of the laboratory and growth chamber experiments in terms of relative aggressiveness of the isolates and relative efficacy of the fungicides. The laboratory experiments were more sensitive in terms of detecting differences in fungicide performance. These results indicate that all three fungicides were effective against Fusarium, but difenoconazole and fludioxonil generally were more effective than captan; the fungicides also differed in efficacy against different Fusarium species.
Model to Enhance Site-Specific Estimation of Leaf Wetness Duration
Authors: Kim K. S. , Taylor S. E. , Gleason M. L. , Koehler K. J.
Published: May 2007

The ability of empirical models to enhance accuracy of site-specific estimates of leaf wetness duration (LWD) was assessed for 15 sites in Iowa, Nebraska, and Illinois during May to September of 1997, 1998, and 1999. Enhanced estimation of LWD was obtained by applying a 0.3-m height correction to SkyBit wind-speed estimates for input to the classification and regression tree/stepwise linear discriminant (CART/SLD) model (CART/SLD/Wind model), compared to either a proprietary model (SkyBit wetness) or to the CART/SLD model using wind speed estimates for a 10-m height. The CART/SLD/Wind model estimated LWD more accurately than the other models during dew-eligible (20:00 to 9:00) as well as dew-ineligible (10:00 to 19:00) periods, and for the period 20:00 to 9:00 regardless of rain events. Improvement of LWD estimation accuracy was ascribed to both the hierarchical structure of decision-making in the CART procedure and wind speed correction. Accuracy of the CART/SLD/Wind model identifying hours as wet or dry varied little among the 15 sites, suggesting that this model may be desirable for estimating LWD from site-specific data throughout the midwestern United States.
Characterization of Powdery Mildew Caused by Leveillula taurica on Calla Lily in California
Authors: Koike S. T. , Beckman P.
Published: May 2007

Spring calla lily (Zantedeschia spp.), also known as colored or miniature calla, has markedly increased in popularity in recent years, and the production acreage in the central coast counties of California (Monterey, Santa Cruz, and San Benito), therefore, has significantly increased. Commercial plantings of calla lily (Z. albo maculata and Z. rehmannii hybrids) in California have been infected with a powdery mildew for several years, with the disease particularly evident in late summer and fall. In 2001, powdery mildew was again prevalent, and the pathogen was examined in detail. Initial symptoms consisted of chlorotic, circular-to-oval leaf lesions with diffuse margins. As the disease progressed, white sporulation became visible on lesions. In advanced stages of the disease, the center tissue of lesions turned necrotic. For any such lesion, both the corresponding adaxial and abaxial sides of the leaf always exhibited the symptoms of the disease and developed sporulation of the pathogen. Epidermal strips from both sides of leaves and leaf cross sections were mounted in drops of lactophenol and aniline blue and examined with a light microscope. These preparations showed that epiphytic mycelium was absent and all conidiophores developed from endophytic mycelium and emerged through stomata. Conidiophores carried single or sometimes two conidia and were sometimes branched. Hyaline, single-celled conidia were dimorphic. Primary (terminal) conidia were lanceolate with distinct apical points and measured (58-) 67 to 78 (-81) × 14 to 22 μm. Secondary conidia were ellipsoid-cylindric and measured (56-) 58 to 72 × 17 to 22 μm. For both conidial types, length to width ratios were greater than three. Based on these characters, the pathogen was identified as Leveillula taurica (anamorph Oidiopsis taurica). Cleistothecia were not observed. To test whether the calla lily pathogen could infect another known host of L. taurica, diseased calla lily leaves were gently pressed against leaves of potted tomato (Lycopersicon esculentum) plants (2). Inoculated tomato plants were kept in a humidity chamber for 48 h and maintained in a greenhouse (24 to 26°C). After 12 days, chlorotic lesions appeared on inoculated tomato leaves, and sporulation of L. taurica was observed on the lesions. Uninoculated control tomato plants did not develop powdery mildew. To our knowledge, this is the first report of powdery mildew, caused by L. taurica, on calla lily in North America. This disease has been reported on calla lily in South Africa, Spain, Taiwan, Turkey, and Zimbabwe (1,3,4).

References: (1) Y.-K. Chen et al. Ann. Phytopathol. Soc. Jpn. 62:580, 1996. (2) J. C. Correll et al. Plant Dis. 71:248, 1987. (3) K. A. Hirata. Host Range and Geographic Distribution of the Powdery Mildew Fungi. Japan Scientific Society Press, Tokyo, 1986. (4) E. Sezgin et al. J. Turkish Phytopathol. 13:111, 1984.
First Report of Beet soil-borne virus on Sugar Beet in Iran
Authors: Farzadfar Sh. , Pourrahim R. , Golnaraghi A. R. , Shahraeen N.
Published: May 2007

Sugar beet is a main field crop in Iran and is cultivated in 186,000 ha. During the summer of 2001, sugar beet (Beta vulgaris) plants with pale, often upright, narrow, and rolled leaves were collected from the six main beet cultivation provinces of Iran (Fars, Ghazvin, Kermanshah, Khorasan, Semnan, and Isfahan). Roots of symptomatic plants were small, often with constriction, and exhibited warty outgrowth, proliferation of fibrous roots, and vascular necrosis. Beet soil-borne virus (BSBV) and Beet necrotic yellow vein (BNYVV, genus Benyvirus) were detected in sugar beet root samples by tissue-blot immunoassay (TBIA) using BSBV- and BNYVV-specific monoclonal antibodies (As-0576.1 and As-0799.1/CG6-F4, respectively; DSMZ Plant Virus Collection, Germany). Root extracts of sugar beet plants infected with BSBV, were infective by mechanical inoculation to Chenopodium quinoa causing necrotic ring spots. BSBV was detected in inoculated plants by TBIA. Laboratory tests using TBIA on 2,387 randomly collected samples showed that BSBV was present in 406 plants (17%) and BNYVV was present in 1,347 plants (56.43%). BSBV resembles BNYVV, the causal agent of sugar beet rhizomania, morphologically and in its transmission by Polymyxa betae (1). BNYVV has been reported previously from Iran (2). To our knowledge, this is the first report of BSBV occurring on sugar beet in Iran.

References: (1) M. Ivanovic and I. Macfarlane. Annu. Rep. Rothamsted Exp. Stn. Page 190, 1982. (2) K. Izadpanah et al. Iran. J. Plant Pathol. 32:155, 1996.
Effects of Cultural Practices and Temperature on Fusarium Root and Crown Rot of Container-Grown Hostas
Authors: Wang B. , Jeffers S. N.
Published: May 2007

Fusarium root and crown rot of hosta plants grown in containers is caused primarily by Fusarium hostae. In an effort to develop an integrated strategy for managing this disease at nurseries, the effects of wounding, container mix content, watering schedule, and temperature on disease development were investigated. Plants were not wounded or were wounded by severing the roots, severing the roots and making incisions in the crown, or severing the roots and removing a small piece of the crown. Plants were inoculated by dipping roots and crowns into a suspension of conidia from one of two isolates of F. hostae. In addition, some plants were inoculated by wounding crowns with a scalpel dipped in a conidium suspension. Disease development was examined on plants grown at different temperatures (18, 25, or 32°C), grown in different container mixes (100% Canadian sphagnum peat, 100% aged and processed pine bark, or a mixture of 50% peat and 50% bark), and watered on different schedules (which kept the container mix wet, moist, or dry). Significant levels of disease occurred only on plants that were wounded when inoculated. Fusarium root and crown rot was more severe when both the roots and crowns were wounded than when only the roots were wounded. Disease symptoms developed when crowns of plants were wounded with a scalpel infested with conidia, suggesting that contaminated tools used for vegetative propagation may transfer F. hostae. Disease development also was affected significantly by container mix content, watering schedule, and temperature. In separate experiments, disease was most severe on plants grown in 100% aged pine bark, in dry container mix, or at 18 to 25°C. Disease development was significantly less when plants were grown in 100% peat, in wet container mix, or at 32°C. These results suggest that altering or manipulating cultural practices used to produce hostas in containers at nurseries can reduce the impact from Fusarium root and crown rot.
Resistance to QoI (Strobilurin-like) Fungicides in Isolates of Pyricularia grisea from Perennial Ryegrass
Authors: Vincelli P. , Dixon E.
Published: May 2007

In August 2000, azoxystrobin was ineffective in controlling gray leaf spot of perennial ryegrass at a golf course in Lexington, KY and at two golf courses in Illinois. Isolates suspected of being fungicide-resistant (“suspect isolates”) were compared to “baseline” isolates obtained from sites with no known use of quinol-oxidizing inhibitor (QoI) fungicides. Conidial germination of Pyricularia grisea was tested in vitro with 100 μg of salicylhydroxamic acid per ml. For baseline isolates, 50% effective concentration (EC50) values for azoxystrobin and trifloxystrobin were 0.015 to 0.064 and 0.013 to 0.078 μg/ml, respectively; EC50 values for suspect isolates were 2.39 to 44.8 and 0.31 to 111, respectively. All suspect isolates exhibited significantly (P = 0.05) lower sensitivity to QoI fungicides than all baseline isolates. The mean EC50 values for suspect isolates for azoxystrobin and trifloxystrobin were 690 and 827 times higher, respectively, than the means for baseline isolates. In the laboratory, azoxystrobin and trifloxystrobin provided essentially complete control of disease induced by nine baseline isolates in vivo. Azoxystrobin and trifloxystrobin provided poor to no control of disease induced by six of eight suspect isolates; control of disease induced by the remaining two isolates was partial for azoxystrobin and complete for trifloxystrobin. We conclude that one or more biotypes of perennial ryegrass-infecting strains of P. grisea with resistance to QoI fungicides have emerged. This is the first report of resistance to QoI fungicides in P. grisea. Furthermore, this is one of two QoIresistant fungal pathogens collected in the United States during the 2000 growing season, the first instances reported for North America.
Virulence Phenotypes of Puccinia triticina in the South Atlantic States in 1999
Authors: Kolmer J. A.
Published: May 2007

Collections of Puccinia triticina were made from rust-infected wheat leaves in Georgia, South Carolina, North Carolina, and Virginia in 1999 to examine if these states can be considered as a single epidemiological unit for virulence phenotypes of the wheat leaf rust pathogen. Singleuredinial isolates derived from the leaf rust collections were processed for identification of virulence phenotypes on seedling plants in greenhouse tests. Twenty-one virulence phenotypes from 253 isolates were described based on infection type to 16 Thatcher wheat lines near-isogenic for leaf rust resistance genes. Virulence phenotype MBRK (virulent to leaf rust resistance genes Lr1, Lr3, Lr3ka, Lr11, Lr30, Lr10, Lr14a, and Lr18) was the most common phenotype in the region, at 38.7% of all isolates. Phenotype TLGF (virulent to Lr1, Lr2a, Lr2c, Lr3, Lr9, Lr11, Lr14a, and Lr18) was the second most common phenotype overall, at 33.8% of isolates. Twenty-nine isolates selected on the basis of seedling virulence phenotypes also were tested for virulence to adult wheat plants with the resistance genes Lr12, Lr13, Lr22b, and Lr34. In all, 23 isolates were avirulent to Lr12 and 26 isolates were virulent to Lr13. All isolates had fewer and smaller uredinia on the Thatcher line with Lr34 compared with Thatcher. The widespread occurrence of the predominant P. triticina virulence phenotypes throughout the region indicated that the South Atlantic states should be considered as a single epidemiological area for wheat leaf rust. Some virulence phenotypes which occurred at lower frequencies were found primarily in the Coastal Plain and mountains of North Carolina or in breeding plots in southern Georgia. Localized populations of P. triticina may develop in the South Atlantic region due to overwintering of leaf rust infections or specific selection by leaf rust resistance genes in wheat cultivars.
Suppression of Phytophthora Root and Crown Rot on Pepper Plants Treated with Acibenzolar-S-Methyl
Authors: Matheron M. E. , Porchas M.
Published: May 2007

The fungicide mefenoxam is registered for the control of Phytophthora blight of peppers caused by Phytophthora capsici. Isolates of the pathogen that are insensitive to mefenoxam, however, have been detected in some locations. Consequently, alternative methods are needed to control Phytophthora blight of peppers. Acibenzolar-S-methyl (ABM, Actigard) is a chemical activator of plant disease resistance that has potential for the management of Phytophthora blight of peppers. The effect of foliar applications of ABM on the development of root and crown rot on pepper plants grown in the greenhouse and inoculated with Phytophthora capsici or in soil naturally infested with the pathogen was evaluated. Inhibition of stem canker development on pepper cvs. Bell Tower and AZ9 after four treatments with ABM (75 μg/ml) was significantly greater than on plants receiving a single application of the chemical. Stem canker length on Bell Tower or AZ9 peppers was inhibited by 93.2 to 97.2% and 87.4 to 92.4% when plants were inoculated with P. capsici at 1 or 5 weeks, respectively, after the fourth application of ABM. Survival of chile pepper plants grown in field soil naturally infested with P. capsici was significantly increased by three foliar applications of ABM (75 μg/ml) compared with nontreated plants in all three trials when pots were watered daily and in two of three trials when pots were flooded for 48 h every 2 weeks. When soil was flooded every 2 weeks to establish conditions highly favorable for disease development, plants treated once with mefenoxam (100 μg/ml) survived significantly longer than those treated with ABM. On the other hand, when water was provided daily without periodic flooding to establish conditions less favorable for disease development, plant survival between the two chemicals was not different in two of three trials. Length of survival among chile pepper plants treated twice with 25, 50, or 75 μg/ml of ABM and grown in soil infested with P. capsici was not different. This work indicates that ABM could be an important management tool for Phytophthora root and crown rot on pepper plants.
Evaluation of Generalized Linear Mixed Models for Analyzing Disease Incidence Data Obtained in Designed Experiments
Authors: Madden L. V. , Turechek W. W. , Nita M.
Published: May 2007

Diseased individuals (e.g., leaves, plants) typically are clustered in nature, resulting in greater heterogeneity or variability of disease incidence than would be expected for a random pattern. To account for this variability, as well as the binary nature of disease incidence and the multiple sources of variation in designed experiments, a generalized linear mixed model (GLMM) can be used to analyze collected data. GLMMs are becoming more common in many disciplines and may be preferred over analysis of variance for non-normally distributed data. We evaluated several GLMMs for analyzing the incidence of Phomopsis leaf blight of strawberry in relation to fungicide treatments in five experiments which varied greatly in mean incidence and the differences in incidence between treatments. The first model form accounted for heterogeneity through the residual variance (i.e., the overdispersion parameter), which was assumed to be either fixed for the experiment, or dependent on either treatment or incidence. The second model form accounted for heterogeneity explicitly through a within-plot sampling variance, which was assumed to be either constant or dependent on treatment. All GLMMs could be successfully fitted to the data in each experiment, but there was weak evidence based on the conditional deviance and residual plots that the residual-variance models were more appropriate than the sampling-variance models. Model choice had only a minor effect on F tests for treatment effects and significant differences between treatment means. Based on ease of use and evaluation results, we recommend that the simplest (fixed residual variance) model be used as the first choice in analyzing disease incidence data using GLMMs.
Occurrence of Bacterial Stripe of Pearl Millet in Georgia
Authors: Gitaitis R. , Wilson J. , Walcott R. , Sanders H. , Hanna W.
Published: May 2007

Bacterial stripe, caused by Acidovorax avenae subsp. avenae, was observed on breeding lines of pearl millet (Pennisetum glaucum (L.) R. Br.) in Georgia in 1999 and 2001. A gram-negative, oxidase-positive, rod-shaped bacterium that produced circular, cream-colored, nonfluorescent, butyrous colonies with entire margins on King's medium B was consistently isolated from leaf lesions. The bacterium was identified as A. avenae subsp. avenae by gas-chromatography of extracted, whole-cell, fatty acid methyl esters using the Sherlock Microbial Identification System (MIDI, Newark, DE) and by substrate utilization patterns using the Biolog Identification System (Biolog Inc., Hayward, CA). Isolates from pearl millet produced amplicons of expected size (360 bp) from 16S rDNA after conducting polymerase chain reaction (PCR) with primers WFB1 and WFB2, which are specific for A. avenae. When bacterial suspensions of 1 × 108 CFU/ml were infiltrated into the intercellular spaces of leaves of pearl millet seedlings in the greenhouse, typical water-soaked, reddish-brown stripes developed and were identical to those observed in the field. In contrast to previous reports (1), the pearl millet strains produced atypical symptoms on sweet corn (cvs. Merit and Primetime). Necroses were restricted, lacked customary water-soaking, and were similar to symptoms produced by the watermelon pathogen, A. avenae subsp. citrulli, which was used as a negative control. In contrast, three strains of A. avenae subsp. avenae previously isolated from corn in Georgia produced typical water-soaked stripes in both millet and the sweet corn ‘Merit’. However, like the millet strains, A. avenae subsp. avenae strains from corn produced atypical symptoms on the sweet corn ‘Primetime’. Using immunomagnetic separation and PCR (2), A. avenae subsp. avenae was detected in remaining samples of pearl millet seed planted in Georgia in 2001, as well as in remnant samples of seed sent to Puerto Rico for increase in 2000. The A. avenae subsp. avenae strain recovered from seed was identified by the methods listed above, and in the greenhouse it was identified by the production of typical water-soaked stripes after inoculation of pearl millet. This is the first report of A. avenae subsp. avenae infecting pearl millet in the United States. The detection and distribution of seedborne inoculum in breeding lines is significant since the program at Tifton represents a major effort by the U.S. Department of Agriculture to develop higher-yielding, disease-resistant pearl millet hybrids. Furthermore, the strains from pearl millet appear to be different from previous A. avenae subsp. avenae strains isolated from corn in Georgia, because they did not produce typical disease symptoms when infiltrated in corn leaves.

References: (1) L. E. Claflin et al. Plant Dis. 73:1010, 1989. (2) R. R. Walcott and R. D. Gitaitis. Plant Dis. 84:470, 2000.
First Report of Peanut stunt virus in Perennial Peanut in North Florida and Southern Georgia
Authors: Blount A. R. , Pittman R. N. , Smith B. A. , Morgan R. N. , Dankers W. , Sprenkel R. K. , Momol M. T.
Published: May 2007

In spring 2001, symptoms similar to aphid-vectored peanut stunt disease caused by Peanut stunt virus (PSV) were observed on perennial peanut (Arachis glabrata) cv. Floragraze in Jackson and Gulf counties, FL and Lowndes County, GA. Symptoms observed in commercial hay fields and at the North Florida Research and Education Center in Marianna and Quincy included malformed leaves, plant chlorosis, leaf mottling, and stunted plants, which resulted in reduced foliage yield. Leaf symptoms were visible throughout the growing season. Stunting was more common in spring and early summer. No symptoms were seen on rhizomes. Diagnosis of PSV (genus Cucumovirus) from symptomatic leaves and rhizome materials of 12 plants was confirmed by a direct antigen-coated enzyme-linked immunosorbent assay (DAC-ELISA). ELISA tests were repeated three times. Antibodies specific to the Clemson isolate, serotype E, were obtained from Clemson University, Clemson, SC. DAC-ELISA (1) values of 0.1 A405 above the healthy control for perennial peanut were considered positive for foliage and rhizome material tested. ELISA values ranged from 0.4 to 2.1. The mean ELISA value of the positive controls was 2.65. Symptomatic plants were also tested with ELISA using available antibodies from Agdia Inc., Elkart, IN, for Tomato spotted wilt virus, from ATCC for Peanut stripe virus, and from Clemson University (Cowpea isolate) for Cucumber mosaic virus, but all results were negative. To our knowledge, this is the first report of PSV on perennial peanut in Florida and southern Georgia. At this time, it is not known what role perennial peanut may play as a reservoir of the virus in the vicinity of peanut fields. Little is known about the potential for forage production loss and stand longevity. Next season, molecular detection techniques and epidemiological studies on peanut and perennial peanut will be conducted to ascertain the incidence and possible impact of PSV in Georgia and Florida.

Reference: (1) A. G. Gillaspie, Jr. et al. Plant Dis. 79:388, 1995.
First Report of Mixed Infection of Hop stunt viroid and Peach latent mosaic viroid on Peach
Authors: Tessitori M. , Reina A. , Rosa R. La
Published: May 2007

Hop stunt viroid (HSVd), belonging to the family Pospiviroidae, was first reported in hop, but infects several plant species, including herbaceous and woody hosts (e.g., grapevine, pear, peach, plum [2], apricot, almond, and pomegranate). In grapevine and apricot, the viroid appears to be latent. However, in other species, the viroid is associated with specific disorders: hop stunt, dapple fruit disease of plum and peach (2), and citrus cachexia. During spring 2000, stunted trees exhibiting delayed budbreak were observed in peach, cv. Redhaven, orchards in Sicily. In the summer of 2000, peach leaves were collected from symptomatic trees, triturated, and used to purify total nucleic acids by phenol extraction followed by CF-11 cellulose-chromatography. Viroid RNAs were detected by sequential polyacrylamide gel electrophoresis (sPAGE) and silver staining. Citrus exocortis viroid (371 nt) and Citrus viroid IIIb (294 nt) were used as standards. Nonradioactive hybridizations with digoxigenin (DIG)-labeled, Peach latent mosaic viroid (PLMVd) and HSVd RNA probes were used in viroid detection and identification. Predicted sizes of the viroid RNAs calculated in sPAGE and DIG probe hybridization demonstrated that ‘Redhaven’ peach trees were infected with PLMVd and HSVd. These results provide the first evidence of the contemporary presence of HSVd and PLMVd in peach trees. To our knowledge, this is the first report of HSVd in peach trees in Italy. Molecular characterization of this HSVd isolate is in progress to determine the nucleotide sequence of some of the variants in the population and to decide to which of the five proposed HSVd groups (1) this isolate should be assigned.

Reference: (1) S. A. Kofalvi et al. J. Gen. Virol. 78:3177, 1997. (2) T. Sano et al. J. Gen. Virol. 70:1311, 1989.
Influence of Wound Type and Storage Duration on Susceptibility of Sweetpotatoes to Rhizopus Soft Rot
Authors: Holmes Gerald J. , Stange Richard R.
Published: May 2007

Susceptibility of stored sweetpotato roots (cvs. Beauregard and Hernandez) to Rhizopus soft rot caused by Rhizopus stolonifer was tested at 4- to 6-week intervals over a storage period of 335 days in 1998-1999 (year 1) and 1999-2000 (year 2). In each experiment, roots were wounded by four methods (puncture, bruise, broken, and scrape), inoculated with freshly harvested spores from 4- to 10-day-old cultures, and compared with a nonwounded but inoculated control for their susceptibility to decay. Roots were totally resistant to infection after harvest for 60 days in year 1 and 30 days in year 2. The bruise wound type was most commonly associated with infection, with disease incidence peaking 100 and 175 days after harvest in years 1 and 2, respectively. Inoculation by the puncture method followed a similar pattern in Hernandez but was ineffective in Beauregard. Following the peak in disease incidence at 100 or 175 days, susceptibility of roots declined to levels comparable to that of freshly harvested roots. This period of heightened susceptibility was longer in Hernandez than in Beauregard. The effects of injury types broken and scrape were more variable and did not show the same trend in both years.
Management of Late Leaf Spot of Peanut with Benomyl and Chlorothalonil: A Study in Preserving Fungicide Utility
Authors: Culbreath A. K. , Stevenson K. L. , Brenneman T. B.
Published: May 2007

Recent registration of sterol biosynthesis inhibitor and strobilurin fungicides for control of early (Cercospora arachidicola) and late (Cercosporidium personatum) leaf spot diseases of peanut (Arachis hypogaea) has renewed interest in the potential for loss of disease control due to fungicide resistance. The objectives of this study were to use the systemic fungicide benomyl, the protectant fungicide chlorothalonil, and late leaf spot of peanut as a model system to compare fungicide application strategies for fungicide resistance management. Field experiments were conducted at Tifton and Plains, GA, in 1995 and 1996 to determine the effects of alternate applications, mixtures, and alternating block applications of chlorothalonil and benomyl compared with full-season applications of two rates of chlorothalonil and two rates of benomyl alone on late leaf spot of peanut and on the proportion of the pathogen population resistant to benomyl following the various regimes. Tank mix combinations of half rates of the two fungicides and alternations of the full rates of the two fungicides provided better (P ≤ 0.05) control of late leaf spot than full-season applications of either rate of benomyl alone, and were comparable to full rates of chlorothalonil alone. Neither tank mixes nor alternating sprays prevented an increase in the relative frequency of benomyl-resistant isolates compared with other treatments in which benomyl was used. Both mixtures and alternate applications of chlorothalonil and benomyl were effective for management of leaf spot in fields where benomyl alone did not provide season-long leaf spot control.
Influence of Inoculum Density of Fusarium oxysporum f. sp. cyclaminis and Sodium Chloride on Cyclamen and the Development of Fusarium Wilt
Authors: Elmer Wade H.
Published: May 2007

The influence of soil densities of Fusarium oxysporum f. sp. cyclaminis on development of Fusarium wilt of cyclamen (Cyclamen persicum) was evaluated by adding increasing amounts of F. oxysporum f. sp. cyclaminis-colonized millet inoculum to potting mix planted to cyclamen. Additions of inoculum resulted in an increase in the CFU of F. oxysporum f. sp. cyclaminis per ml of potting mix and an increase in vascular discoloration of the corm of cyclamens after 10 weeks. A threshold of 5 × 104 CFU/ml of potting mix was needed to consistently cause vascular discoloration in the corms. Final fresh leaf weights declined to 30% of the leaf weights of the control when inoculum was added at 105 CFU/ml of potting mix. The effect of NaCl on Fusarium wilt was also examined, as anecdotal reports from cyclamen producers suggest that NaCl applications may improve plant growth. When NaCl was applied to potting mix at rates of 0.25 and 0.50 g/liter of potting mix, final fresh weights were greater and the area under the disease progress curve values were less than those of control plants. However, final disease severity was not affected. In the absence of the pathogen, leaf weights were greater when NaCl was added at 0.25 g/liter of potting mix. Disease development and the effectiveness of NaCl on disease were not affected by potting mix pH 5.1 to 7.2. Cyclamens grown in potting mix with a pH of 7.2 had chlorotic leaves, but with the addition of NaCl, the chlorosis was not observed. Leaf analyses showed that the addition of NaCl increased foliar levels of Na, Cl, and Mn, but decreased foliar levels of P, Ca, Mg, S, and B. Sodium chloride applied at 0.25 to 0.50 g/liter of potting mix had growth benefits, but disease suppression was marginal.
Sensitivity to Azoxystrobin Among Isolates of Uncinula necator: Baseline Distribution and Relationship to Myclobutanil Sensitivity
Authors: Wong Francis P. , Wilcox Wayne F.
Published: May 2007

Two hundred fifty-six single-conidial chain isolates of Uncinula necator were assayed for their sensitivity to azoxystrobin and myclobutanil. These isolates were collected from two sites in New York in 1999: an “organic” vineyard where no synthetic fungicides have been used (baseline population) and a commercial vineyard having a history of compromised powdery mildew control with myclobutanil (demethylation inhibitor [DMI]-resistant population). Mean coefficients of variance for a leaf disk assay used to test fungicide sensitivities were 31% for azoxystrobin and 41% for myclobutanil. Baseline ED50 values ranged from 0.0037 to 0.028 μg/ml (mean 0.0097μg/ml) for azoxystrobin and from 0.0049 to 0.69 μg/ml (mean 0.075 μg/ml) for myclobutanil. A shift in the mean ED50 value for azoxystrobin to 0.018 μg/ml was observed in the DMI-resistant population; with the strongest shift observed for isolates collected from vines treated exclusively with myclobutanil (0.024 μg/ml). For the 256 tested isolates, there was a moderate, but statistically significant, correlation between azoxystrobin and myclobutanil sensitivities (R2 = 0.36, P < 0.001). Tests with three other strobilurin fungicides (kresoxim-methyl, pyraclostrobin, and trifloxystrobin) indicate clear differences in the intrinsic activity of these compounds against U. necator, and the applicability of the methods developed with azoxystrobin for assays with pyraclostrobin and trifloxystrobin. Isolates from the high and low ends of the azoxystrobin sensitivity distribution (15× difference in mean ED50 values) were equally controlled in planta by protectant or postinfection treatment with azoxystrobin at 250 μg a.i./ml, but postinfection application at lower rates (2.5 and 25 μg a.i./ml) resulted in a 41 and 44% decrease, respectively, in the control of the low-sensitivity isolates versus high-sensitivity isolates. The results of this study document the baseline sensitivity distribution of U. necator to azoxystrobin, provide evidence of partial cross-sensitivity between azoxystrobin and myclobutanil, and illustrate the potential selection for individuals with reduced sensitivity (quantitative range) to azoxystrobin by postinfection application and reduced rates of this fungicide.
Different Reactions to the Wheat Curl Mite andWheat streak mosaic virusin Various Wheat-Haynaldia villosa6V and 6VS Lines
Authors: Li Hongjie , Conner R. L. , Chen Qin , Jia Xu , Li Hui , Graf R. J. , Laroche A. , Kuzyk A. D.
Published: May 2007

Wheat curl mite (WCM), Aceria tosichella, is the vector of Wheat streak mosaic virus (WSMV), a destructive viral pathogen in wheat (Triticum aestivum). Genetic resistance to WCM colonization can reduce the incidence of wheat streak mosaic. Chromosome 6V in Hay-naldia villosa is a new source of WCM resistance. We compared variation in resistance among different sources of H. villosa chromosome 6V and 6VS lines to WCM and WSMV and their effectiveness in controlling the incidence of WSMV following exposure to viruliferous WCM. WCM resistance varied among the 6V and 6VS lines depending on the H. villosa parent. The 6V substitution lines Yi80928, GN21, and GN22 derived from an accession of H. villosa from China, and the 6VS translocation lines 92R137, 92R178, and Sub6V from an H. villosa accession collected from the United Kingdom were uniformly resistant to WCM colonization. In contrast, the 6V substitution line RW15 and a 6VS translocation line Pm33 developed from an H. villosa collection from the former Union of Soviet Socialist Republics were susceptible to WCM. All 6V and 6VS lines were susceptible to WSMV when manually inoculated. However, symptom expression was delayed in the WCM-resistant 6V and 6VS lines after exposure to viruliferous WCM. The 6V and 6VS lines differed in their ability to control WSMV infection. WCM-susceptible lines RW15 and Pm33 had no effect on controlling the infection by WSMV. Lines GN21 and GN22 were the most effective of the three H. villosa sources in limiting the spread of WSMV. Their high yield potential and protein content, in combination with resistance to stripe rust (Puccinia striiformis f. sp. tritici) and powdery mildew (Erysiphe graminis f. sp. tritici), make GN21 and GN22 promising sources of WCM resistance.
Screening Common Bean (Phaseolus vulgaris) for Resistance to Tomato yellow leaf curl virus
Authors: Lapidot Moshe
Published: May 2007

Commercial cultivars of common bean (Phaseolus vulgaris) were screened for resistance to Tomato yellow leaf curl virus (TYLCV). Fourteen-day-old bean plants were inoculated with TYLCV by means of the whitefly vector (Bemisia tabaci). Following inoculation, plants were sprayed with an insecticide, kept in an insect-proof greenhouse for 4 weeks, and monitored for disease symptom development. The presence of viral DNA in the inoculated plants was assayed by dot blot hybridization and by polymerase chain reaction. Out of the 42 cultivars that were tested, 24 were found to be susceptible: the plants exhibited severe symptoms and accumulated high levels of viral DNA. In all, 18 cultivars were found to be resistant to the virus: 1 cultivar showed mild symptoms while the other 17 showed no symptoms following inoculation. From the 17 symptomless cultivars, plants of 3 cultivars contained viral DNA while no viral DNA was detected in the plants of the other 14 cultivars. When the effect of bean plant age on viral inoculation by whiteflies was assayed, it was found that the success rate of TYLCV infection was highly dependent on bean plant age. When 14-day-old susceptible bean plants were inoculated, nearly 100% infection was achieved but, when 26- or 12-day-old plants of the same cultivar were inoculated, the infection rates were only 34 and 40%, respectively.