bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Bacterial Soft Rot of White Flowered Calla Lily Caused by Erwinia chrysanthemi in Taiwan
Authors: Lee Y.-A. , Chen K.-P. , Chang Y.-C.
Published: May 2007

In 2002, soft rot symptoms on white flowered calla lily (Zantedeschia aethiopica) were found in some nurseries in the Yang Ming Shan area, Taipei, Taiwan. The disease was characterized by foul smelling rot and collapse of flower stems. Isolations from diseased flower stems consistently yielded bacterial colonies that were translucent, white, and glistening on nutrient agar. Ten representative isolates were chosen for further characterization. All isolates were gram-negative rods, facultatively anaerobic, sensitive to erythromycin (25 μg/ml), negative for oxidase and arginine dihydrolase, and positive for catalase, phosphatase, tryptophanase (indole production), and lecithinase. They fermented glucose and reduced nitrates to nitrites. The maximum temperature for growth was 37°C. The isolates hydrolyzed gelatin and esculin, produced acids from utilizing D(+)-glucose, melibiose, amygdalin, L(+)-arabinose, D-mannitol, and sucrose, but not from trehalose, lactose, D-sorbitol, or maltose. They degraded pectate and rotted potato, carrot, sweet pepper, and onion slices. Bacterial suspensions (108 CFU/ml) were injected in stems of white flowered calla lily to fulfill Koch's postulates. Control plants were inoculated with sterile distilled water. Inoculated plants were kept in a growth chamber at 30°C. Symptoms developed 1 to 2 days in all four inoculated plants and appeared to be identical to those observed on diseased material in nurseries. The four control plants did not rot. The bacterium was readily reisolated from diseased plants, confirmed to be the inoculated pathogen, and identified as Erwinia chrysanthemi. E. carotovora subsp. carotovora has been reported to cause soft rot of other calla lilies, such as Zantedeschia sp. cvs. Black Magic and Pink Persuasion and Z. elliottiana in Taiwan (1). However, to our knowledge, this is the first report of soft rot caused by E. chrysanthemi on white flowered calla lily in Taiwan.

Reference: (1) S. T. Hsu and K. C. Tzeng. Pages 9–18 in: Proc. Int. Conf. Plant Path. Bact., 5th. J. C. Lozano, ed. CIAT, Cali, Colombia, 1981.
Occurrence of Potato Powdery Scab Caused by Spongospora subterranea f. sp. subterranea in Costa Rica
Authors: Montero-Astúa M. , Vásquez V. , Rivera C.
Published: May 2007

Powdery scab of potatoes, caused by Spongospora subterranea (Wallr.) Lagerheim f. sp. subterranea Tomlinson, is important worldwide due to its effect on tuber quality and transmission of Potato mop-top virus. Although powdery scab-like lesions have been observed on potato in Costa Rica (1), the presence of the pathogen has not been confirmed. During a survey in 2001, powdery scab-on was observed from a field and a greenhouse in the high elevation zone of the main potato-producing area of Costa Rica. Commercial potatoes with scab-like lesions were also obtained at a farmers' market. Scraping the lesions, and observing spore balls or cystosori with a honey-comb-like structure under light microscopy confirmed the identity of S. subterranea. The identity of the pathogen was also confirmed by enzyme-linked immunosorbent assay using monoclonal antibodies specific for S. subterranea (BioReba Ag, Reinach, Switzerland). Pathogenicity of S. subterranea was confirmed by a bioassay on tomato plants grown in nutrient solution culture (2). Tomato cv. Supermarmande plants were grown from seed in pots filled with quartz and watered with nutrient solution. Three weeks after planting, the roots were trimmed to 60 mm, and the plants were transferred to the nutrient solution for additional growth. After growing for 1 week in the nutrient solution, tomato seedlings were inoculated by replacing the nutrient solution with nutrient solution containing cystosori (20 mg/liter, wt/vol) that were scraped from the scab lesions. Zoosporangia of S. subterranea were observed in root hairs and epidermal cells of the seedlings 2 weeks after inoculation. To our knowledge, this is the first report that confirms the presence of S. subterranea on potato in Costa Rica.

References: (1) R. Amador. Invest. Agri. Costa Rica. 1(1):16, 1987. (2) U. Merz. Bull. OEPP 19:585, 1989.
Transmission of Pigeon pea sterility mosaic virus by the Eriophyid Mite, Aceria cajani (Acari: Arthropoda)
Authors: Kulkarni N. K. , Kumar P. Lava , Muniyappa V. , Jones A. Teifion , Reddy D. V. R.
Published: May 2007

The transmission characteristics of Pigeon pea sterility mosaic virus (PPSMV) to pigeon pea (Cajanus cajan) by its eriophyid mite vector, Aceria cajani, were studied. Nonviruliferous A. cajani colonies were established on detached healthy leaflets of a PPSMV-immune pigeon pea cultivar floating on water. The transmission efficiency of single A. cajani was up to 53% but was 100% when >5 mites per plant were used. A. cajani acquired PPSMV after a minimum acquisition access period (AAP) of 15 min and inoculated virus after a minimum inoculation access period (IAP) of 90 min. No latent period was observed. Starvation of A. cajani prior to, or following, PPSMV acquisition reduced the minimum AAP and IAP periods to 10 min and 60 min, respectively, and mites retained virus for up to 13 h. None of the mites that developed from eggs taken from PPSMV-infected leaves transmitted the virus, indicating that it is not transmitted transovarially. Taken together, these data suggest a semipersistent mode of transmission of PPSMV by A. cajani.
Resistance of Peanut to Sclerotinia Blight and the Effect of Acibenzolar-S-methyl and Fluazinam on Disease Incidence
Authors: Lemay A. V. , Bailey J. E. , Shew B. B.
Published: May 2007

Sclerotinia minor, a soilborne fungal pathogen of peanut, can cause serious yield loss in North Carolina. A field test was implemented to study genotype reaction, and the effect of aciben-zolar-S-methyl (a plant activator) and the fungicide fluazinam on disease incidence. In all, 13 genotypes in 1997 and 12 genotypes in 1998 were evaluated. Three applications of acibenzolar-S-methyl (0.14 kg a.i./ha) or fluazinam (0.58 kg a.i./ha) were made on a calendar-based schedule. Disease ratings were made weekly in 1997 and every other week in 1998. Fluazinam suppressed disease at all sites and increased yield at two of three locations. Acibenzolar-S-methyl had no effect on disease incidence or yield. The advanced breeding line N92056C and cvs. Tam-run 98 (TX 901417) and Perry (N93112C) had moderate to high levels of resistance to S. minorand produced high yields compared with susceptible cv. NC 7. Lines derived from wild species also demonstrated moderate to high levels of resistance relative to NC 7 and represent potential breeding lines.
Improved PCR Detection of Blackcurrant reversion virus in Ribes and Further Evidence that It Is the Causal Agent of Reversion Disease
Authors: Jones A. Teifion , McGavin Wendy J.
Published: May 2007

Within 5 years of mechanically inoculating blackcurrant cultivars with partially purified preparations of particles of Blackcurrant reversion virus (BRV), infected plants developed leaf and flower bud symptoms typical of reversion disease, demonstrating that BRV is the causal agent of this disease. To improve the erratic immunocapture reverse transcriptase-polymerase chain reaction (RT-PCR) detection of BRV in Ribes plants, various stepwise changes were made to the original protocol. Significant improvement in the reliability and sensitivity of BRV detection was made by extracting RNA from trapped BRV particles using Triton-X 100, the design of new primers with higher annealing temperatures, and the use of ‘Ready-to-go’ RT-PCR beads. These features, combined with other minor changes to the protocol, improved BRV detection in reverted blackcurrant plants from <50% to >90% but the reliability of BRV detection in red currant was always very much less and was possible only using nested PCR that was developed for this purpose.
Effects of Herbicides on Root Rot and Damping-off Caused by Rhizoctonia solani in Glyphosate-Tolerant Soybean
Authors: Harikrishnan R. , Yang X. B.
Published: May 2007

Diseases caused by Rhizoctonia solani are one of many production constraints in soybean-growing regions. Little information is available about the diseases in soybeans tolerant to different herbicides. In 1998 and 1999, studies were conducted to evaluate the plausible interaction between glyphosate-tolerant soybean and herbicides (glyphosate, imazethapyr, lactofen, and pendimethalin) on damping-off and root rot caused by R. solani under greenhouse and field conditions. The herbicides were applied at the product recommended field rate on glyphosate-tolerant (Pioneer 93B01 and Pioneer 9344) and glyphosate-sensitive (BSR 101) soybean grown in soils infested with R. solani (isolate AG-4). Root rot and plant stand was significantly affected by soybean cultivars and herbicide treatments in the greenhouse study. A significant cultivar-treatment interaction was detected in the greenhouse study. The interaction implies that the cultivars responded differently to the various herbicides and especially to the herbicide pendimethalin. Plant stands of both cultivars were reduced by R. solani alone or in combination with different herbicides compared with the noninoculated control, and this was presumed to be due to damping-off. In a 2-year field study, cultivar and treatment main effects differed with respect to plant stand between years. In 1998, analysis of variance revealed a significant treatment effect on root rot severity but not plant stand. In 1999, analysis of variance revealed a significant effect of treatment on root rot severity and plant stand whereas cultivar showed a significant effect on plant stand only. In 1999, plant stands of both cultivars were similarly affected by most treatments. However, in BSR 101, the R. solani + pendimethalin + imazethapyr treatment significantly reduced plant stand compared with the R. solani + pendimethalin treatment. Root rot severity was generally low in both years of the field study. Some differential disease responses were detected between glyphosate-tolerant and glyphosate-sensitive cultivars following the application of certain herbicides in greenhouse and field studies. However, glyphosate-tolerant and glyphosate-sensitive cultivars reacted similarly to most herbicide treatments with respect to root rot and damping off.
Reduction of Landscape Pathogens in Florida by Soil Solarization
Authors: McGovern R. J. , McSorley R. , Bell M. L.
Published: May 2007

Two experiments were conducted during autumn 1997 and 1998 in west-central Florida to evaluate the effectiveness of soil solarization alone and in combination with the biological control agents Streptomyces lydicus (Actinovate) and Pseudomonas chlororaphis (syn. P. aureofasciens, AtEze) and the reduced-risk fungicide fludioxonil (Medallion) in managing soilborne pathogens of impatiens (Impatiens × wallerana, ‘Accent Burgundy’). Naturally infested soil was solarized for 47 or 48 days during September and October using two layers of 25-μm clear, low-density polyethylene mulch, separated by an air space of up to 7.5 cm. Solarization decreased the final incidence and progress of Rhizoctonia crown rot and blight, incidence of Pythium spp. in roots, and root discoloration, and increased shoot biomass in both experiments. The technique also consistently reduced root-knot severity and population densities of Meloidogyne incognita, Dolichodorus heterocephalus, Paratrichodorus minor, and Criconemella spp. The incidence of Rhizoctonia crown rot and blight was reduced by fludioxonil, but not by the biological control agents.
Biplot Analysis of Host-by-Pathogen Data
Authors: Yan Weikai , Falk Duane E.
Published: May 2007

Effective breeding for disease resistance relies on a thorough understanding of host-by-pathogen relations. Achieving such understanding can be difficult and challenging, particularly for large data sets with complex host genotype-by-pathogen strain interactions. This paper presents a biplot approach that facilitates visual analysis of host-by-pathogen data. A biplot displays both host genotypes and pathogen isolates in a single scatter plot; each genotype or isolate is displayed as a point defined by its scores on the first two principal components derived from subjecting genotype- or strain-centered data to singular value decomposition. From a biplot, clusters of host genotypes and clusters of pathogen strains can be simultaneously visualized. Moreover, the basis for genotype and strain classifications, i.e., interactions between individual genotypes and strains, can be visualized at the same time. A biplot based on genotype-centered data and that based on strain-centered data are appropriate for visual evaluation of susceptibility/resistance of genotypes and virulence/avirulence of strains, respectively. Biplot analysis of genotype-by-strain is illustrated with published response scores of 13 barley line groups to 8 net blotch isolate groups.
Identification of Root-Knot Nematode Species Occurring on Tomatoes in Tanzania and Resistant Lines for Their Control
Authors: Nono-Womdim R. , Swai I. S. , Mrosso L. K. , Chadha M. L. , Opeña R. T.
Published: May 2007

This was a 5-year study that included surveys during the first 2 years, followed by field evaluations of improved tomato lines over the next 3-year period. Surveys were conducted in 12 regions of Tanzania from 1993 to 1995 to identify the causal nematodes of tomato root-knots. Eighty-seven samples were collected and assayed for presence of Meloidogyne spp. M. hapla, M. incognita, and M. javanica were detected at incidences of 1, 19, and 89%, respectively. Species mixtures were common within samples. Results indicated the presence of races 1 and 2 of M. incognita in tomato-growing regions of Tanzania. Reactions of eight advanced tomato breeding lines to the three species in greenhouse and field tests indicated that three lines, namely ARP 365-2, 367-1, and 367-2, were resistant to M. incognita races 1 and 2 and to M. javanica, but all lines were susceptible to M. hapla.
Volatile Fingerprinting (SPME-GC-FID) to Detect and Discriminate Diseases of Potato Tubers
Authors: Kushalappa A. C. , Lui L. H. , Chen C. R. , Lee B.
Published: May 2007

Volatiles from Russet Burbank potatoes inoculated with Erwinia carotovora subsp. carotovora, E. carotovora subsp. atroseptica, Pythium ultimum, Phytophthora infestans, or Fusarium sambucinum were monitored by sampling the head space 3, 4, and 5 days after inoculation, using a solid phase microextraction (SPME) fiber to trap and gas chromatography with flame ionization detector (GC-FID) to fingerprint volatiles. Noninoculated (NON) potatoes served as the control. Volatile fingerprints varied among diseases. Within a disease, the fingerprints varied with time since inoculation and among blocks. In general, more volatiles were observed on the fourth and fifth day after inoculation than on the third day. The amount of volatile compounds produced (peak area) within a disease group increased with incubation time; however, the variation among blocks was much higher. The amount of volatiles produced, in general, was associated with disease severity. Disease-specific volatiles were observed. The F. sambucinum chromatogram had two unique peaks at retention time (RT) = 14.1 and 17.3 min. P. infestans produced few peaks and the profile was quite similar to NON. In contrast, E. carotovora subsp. carotovora, E. carotovora subsp. atroseptica, and Pythium ultimum produced many peaks, and the P. ultimum was different from the bacteria, in that the chromatogram peaks at RT = 4.04 and 8.76 min were absent. Instead, it produced a distinct peak at RT = 1.71 min. E. carotovora subsp. carotovora and E. carotovora subsp. atroseptica couldn't be discriminated based on unique peaks; however, they varied in concentration of volatiles produced. E. carotovora subsp. carotovora produced more of RT = 2.0 min and less of RT = 2.3 and 2.44 min than E. carotovora subsp. atroseptica. A back-propagation network (using neural networks) was developed to classify volatile profiles into six disease-groups. Cross-validation classification probabilities were NON = 71, E. carotovora subsp. carotovora = 71, E. carotovora subsp. atroseptica = 71, P. ultimum = 67, Phytophthora infestans = 46, and F. sambucinum = 75%.
Investigation of Seed Treatments for Management of Bacterial Leaf Spot of Lettuce
Authors: Pernezny Ken , Nagata Russell , Raid Richard N. , Collins Janice , Carroll Amanda
Published: May 2007

Chemical seed treatments were evaluated for efficacy of disinfestation of lettuce seed that had been inoculated with Xanthomonas campestris pv. vitians. Three concentrations of each chemical were evaluated by treating seed lots for 5 or 15 min. In addition, the effects of each seed treatment on seed germination and early plant growth were examined by observing seed germination rates. Bacteria were not detected when seed were treated with 3 or 5% hydrogen peroxide for 5 or 15 min. Treatment of seed with 0.52% sodium hypochlorite was relatively ineffective at 5 and 15 min. When sodium hypochlorite was used at a 1% concentration for 15 min, the level of bacterial infestation was reduced to 2%. Suspensions of copper hydroxide plus mancozeb also reduced seedborne inoculum to ≤2%. Treatment of seed with copper hydroxide alone, benzoyl peroxide, or calcium peroxide did not reduce seed infestation levels significantly. Seed germination rates were 90% or greater for the majority of seed treatments tested in laboratory assays. Hydrogen peroxide treatments at a concentration of 5% reduced seed germination up to 28% compared with controls. However, no significant differences in germination were observed among control treatments (noninoculated, nontreated seed and inoculated, nontreated seed) and any of the chemical seed treatments when seed were sown in a pasteurized soil mix in the greenhouse.
Effect of Compost Amendments on Disease Severity and Yield of Tomato in Conventional and Organic Production Systems
Authors: Abbasi P. A. , Al-Dahmani J. , Sahin F. , Hoitink H. A. J. , Miller S. A.
Published: May 2007

Field trials were conducted over 2 years to assess the effects of compost amendments on disease development in organic and conventional processing tomato (Lycopersicon esculentum L.) production systems. The incidence of anthracnose fruit rot was reduced in organic tomato plots amended with a high rate of composted cannery wastes compared with the incidence in nonamended control plots in 1998 when disease incidence was high. Marketable yield was increased by 33% in compost-amended organic plots. Plots amended with a high compost rate had more ripe fruit than the nonamended control. The incidence of anthracnose and of total disease on fruit was less on the cultivar OH 8245 than on Peto 696. Total fruit yield of OH 8245 but not Peto 696 in organic plots was increased by amendment with composted cannery wastes. In conventional tomato production, composted yard wastes increased disease severity on foliage both years but reduced bacterial spot incidence on fruit in 1997, when disease pressure was high. The incidence of anthracnose was not affected by composted yard wastes. Marketable and total fruit yields of Peto 696 were not increased in compost-amended conventional plots. The plant activator Actigard reduced foliar disease severity and the incidence of bacterial spot and anthracnose on fruit, while increasing yield of marketable fruit.
Report of Bacterial Leaf Spot on Collards and Turnip Leaves in Ohio
Authors: Ivey M. L. Lewis , Wright S. , Miller S. A.
Published: May 2007

In 2000, circular water-soaked lesions typical of bacterial leaf spot were observed on leaves of collards (Brassica oleracea L. var. viridis) throughout commercial fields in northwest Ohio. Light brown, rectangular, water-soaked lesions were observed on turnip leaves (Brassica rapa L.). Bacterial streaming from lesions on both crops was observed microscopically. Cream colored, fluorescent colonies were isolated from diseased tissues on Pseudomonas F medium, and eight representative colonies (four from collards and four from turnip) were selected and purified. Fatty acid methyl ester analysis was performed on all of the isolates. Two from collards and two from turnip were identified as Pseudomonas syringae pv. maculicola (mean similarity index = 0.82 [MIDI Inc., Newark, DE]). DNA extracts from pure cultures of the P. syringae pv. maculicola strains were used as template in a polymerase chain reaction (PCR) assay with primers derived from the region of the coronatine gene cluster controlling synthesis of the coronafacic acid moiety found in P. syringae pv. tomato and P. syringae pv. maculicola (CorR and CorF2) (D. Cuppels, personal communication). DNA from P. syringae pv. tomato strain DC3000 and P. syringae pv. maculicola strain 88–10 (2) served as positive controls, while water and DNA from Xanthomonas campestris pv. vesicatoria strain Xcv 767 were used as negative controls. The expected 0.65-kb PCR product was amplified from three of four strains (two from turnip and one from collards) and the positive control DNA, but not from the negative controls. Pathogenicity tests were performed twice on 6-week-old turnip (‘Forage Star’, ‘Turnip Topper’, ‘Turnip Alamo’, ‘Turnip 7’), collard (‘Champion’) and mustard (Brassica juncea L. ‘Southern Giant Curl’) seedlings using the three PCR-positive strains. Premisted seedlings were spray-inoculated separately with each of the three strains (2 × 108 CFU/ml, 5 ml per plant) and a water control. Greenhouse temperatures were maintained at 20 ± 1°C. For both tests, all strains caused characteristic lesions on all of the crucifer cultivars within 5 days after inoculation; the control plants did not develop symptoms. To satisfy Koch's postulates, one of the turnip strains was reisolated from ‘Turnip Topper’ plants, and the collard strain was reisolated from ‘Champion’ plants. The three original and two reisolated strains induced a hypersensitive response in Mirabilis jalapa L. and Nicotiana tabacum L. var. xanthia plants 24 h after inoculation with a bacterial suspension (1 × 108 CFU/ml). The original and reisolated strains were compared using rep-PCR with the primer BOXA1R (1). The DNA fingerprints of the reisolated strains were identical to those of the original strains. To our knowledge, this is the first report of bacterial leaf spot on commercially grown collards and turnip greens in Ohio.

References: (1) B. Martin et al. Nucleic Acids Res. 20:3479, 1992. (2) R. A. Moore et al. Can. J. Microbiol. 35:910, 1989.
First Report of Pepper mottle virus in Tomato
Authors: Verhoeven J. Th. J. , Willemen T. M. , Roenhorst J. W.
Published: May 2007

In 2000, a breeding company submitted a tomato (Lycopersicon esculentum) sample from Guatemala for diagnosis. The plants showed necrotic lesions on leaves surrounded by some chlorosis, necrotic streaks on stems, and large superficial necrotic lesions on fruits. By mechanical inoculation of plant sap to different plant species, symptoms appeared in Capsicum annuum ‘Westlandse Grote Zoete’, Lycopersicon esculentum ‘Money-maker’, Nicotiana benthamiana, N. bigelovii, N. glutinosa, N. hesperis-67A, N. occidentalis-P1, N. tabacum ‘White Burley’, and Physalis floridana. Systemically infected leaves from N. occidentalis-P1 were used for all further experiments. Leaf dip preparations were analyzed by transmission electron microscopy and revealed the presence of filamentous virus particles typical of a potyvirus. Double-antibody sandwich enzyme-linked immunosorbent assay tests for Potato virus A, V, and Y, Tobacco etch virus, and Wild potato mosaic virus were negative. An antiserum (PepMoV/DSMZ As 0186) to Pepper mottle virus (PepMoV), however, gave a positive reaction. To obtain further evidence for the presence of this virus, the nucleotide sequence of the complete 3′ nontranslated region (3NTR) and the 3′ terminal part of the coat protein gene (3CPG) was determined using the set of degenerate primers P9502/CPUP (1). The obtained nucleotide sequence (approximately 700 bp) was deposited in GenBank under Accession No. AF440801. It showed 93 to 94% 3NTR and 90 to 93% 3CPG homology with the three sequences of PepMoV from pepper already present in GenBank. The two viruses with the next closest nucleotide sequence homology were Potato virus V and Potato virus Y showing up to 80 and 75% homology with the 3CPG and up to 53 and 48% homology with the 3NTR, respectively. Based on these results, we concluded that the virus isolated from the symptomatic tomato plants was PepMoV. Because of the relatively low homologies with the pepper isolates of PepMoV, this tomato isolate might be a separate strain of the virus. To our knowledge, this is the first report of the occurrence of PepMoV in tomato.

Reference: (1) R. A. A. van der Vlugt et al. Phytopathology 89:148, 1999.
Phytophthora ramorum as the Cause of Extensive Mortality of Quercus spp. and Lithocarpus densiflorus in California
Authors: Rizzo D. M. , Garbelotto M. , Davidson J. M. , Slaughter G. W. , Koike S. T.
Published: May 2007

A new canker disease, commonly known as sudden oak death, of Lithocarpus densiflorus, Quercus agrifolia, Q. kelloggii, and Q. parvula var. shrevei in California is shown to be caused by Phytophthora ramorum. The pathogen is a recently described species that previously was known only from Germany and the Netherlands on Rhododendron spp. and a Viburnum sp. This disease has reached epidemic proportions in forests along approximately 300 km of the central coast of California. The most consistent and diagnostic symptoms on trees are cankers that develop before foliage symptoms become evident. Cankers have brown or black discolored outer bark and seep dark red sap. Cankers occur on the trunk at the root crown up to 20 m above the ground, but do not enlarge below the soil line into the roots. Individual cankers are delimited by thin black lines in the inner bark and can be over 2 m in length. In L. densiflorus saplings, P. ramorum was isolated from branches as small as 5 mm in diameter. L. densiflorus and Q. agrifolia were inoculated with P. ramorum in the field and greenhouse, and symptoms similar to those of naturally infected trees developed. The pathogen was reisolated from the inoculated plants, which confirmed pathogenicity.
Evaluation of Corn Inbreds and Advanced Breeding Lines for Resistance to Aflatoxin Contamination in the Field
Authors: Windham G. L. , Williams W. P.
Published: May 2007

Eighteen corn inbred lines and advanced breeding lines were evaluated for resistance to aflatoxin contamination when artificially inoculated with Aspergillus flavus in 1998, 1999 (two tests), and 2000 at Mississippi State, MS, in field studies. The top ear of each plant was inoculated with the A. flavus isolate NRRL 3357 seven days after midsilk (50% of the plants in a plot had silks emerged) using the side-needle technique. Ears were harvested at kernel maturity approximately 63 days after midsilk and aflatoxin levels were measured using the Vicam AflaTest. Aflatoxin contamination in the inbreds was extremely high in 1998. Levels ranged from 139 to 21,090 ng/g. In 1999, aflatoxin contamination ranged from 17 to 1,070 ng/g in one test and 14 to 1,278 ng/g in another test. In 2000, aflatoxin levels ranged from 237 to 7,503 ng/g. Lines that supported lowest levels of aflatoxin contamination included Mp81:112, Mp92:673, Mp92:679, and Mp494. These lines provide potential new sources of resistance that can be used to move aflatoxin resistance into commercial corn hybrids.
Establishment and Dispersal of Puccinia thlaspeos in Field Populations of Dyer's Woad
Authors: Kropp Bradley R. , Hansen Dane R. , Thomson Sherman V.
Published: May 2007

Dyer's woad rust is being intensively studied as a biocontrol agent for the noxious weed dyer's woad. These studies report on methods to establish this fungus in woad populations and to obtain information about disease incidence and dispersal of the rust subsequent to establishment. Inoculum dosages as low as 1 mg/plant established disease in dyer's woad rosettes. Dosages higher than 1 mg/plant resulted in better levels of infection, and inoculation was equally effective when the inoculum was placed directly on the plants or on the soil adjacent to the plants. The highest incidence of infection occurred when plants were inoculated in the spring, whereas summer or fall inoculations did not result in infections. Large-scale inoculation of woad was effective and resulted in significant levels of disease. However, it was not clear if artificial inoculation was effective in changing disease incidence in populations of woad where the rust was present prior to treatment because there were no significant differences between inoculated and check plots. Woad rust is systemic but apparently it is not seed dispersed, even though some infected plants occasionally produce seed. Two years after inoculation, dyer's woad rust had dispersed an average of 14.6 m from the focus of inoculation. After 3 years, the dispersal distance had not increased and infected plants averaged only 10 m from the point of inoculation. Disease was maintained naturally in woad populations after treatment, but the overall percent infection in the treated plots decreased by 3 years after inoculation.
Optimization of Sample Size and DNA Extraction Methods to Improve PCR Detection of Different Propagules of Phytophthora infestans
Authors: Wangsomboondee T. , Ristaino J. B.
Published: May 2007

The plant pathogen Phytophthora infestans causes a destructive blight of potato tubers and foliage. A rapid polymerase chain reaction (PCR) assay has been developed for detection of P. infestans in potato tubers. In this study, the effect of method of DNA extraction on different propagule types and the minimal number of propagules of P. infestans detectable by PCR were assessed using the PINF and internal transcribed spacer (ITS)5 primers. Sensitivity of the primers for PCR was high, and DNA was detectable at concentrations as low as 10 pg/ml. Zoospores and oospores responded differently to different extraction methods, whereas all extraction methods worked equally well for sporangia. Freeze-thaw DNA lysis, in which propagules were frozen at -80°C and thawed at 65°C three times for 15 min each, or direct PCR, in which propagules were placed directly in the reaction mix, were effective methods for PCR detection of sporangia or zoospores but were not effective methods for PCR detection of DNA in oospores of P. infestans. DNA from a single sporangium or oospore could be amplified by PCR after hexadecyltrimethyl-ammonium bromide (CTAB) or NaOH lysis extraction methods, whereas DNA from a single zoospore could be amplified by CTAB or direct PCR methods. “IsoCode” Stixs, used in forensic applications, were used to collect the pathogen from leaf and tuber lesions and provided another simple method to extract template DNA. PCR detection of the pathogen in infected tubers using PINF and ITS5 primers was compared to tissue isolation or visual observation. The probability of detection of P. infestans in infected tubers at 7 days post inoculation using the PCR assay, tissue isolation, or visual observation was 0.90, 0.80, and 0.75, respectively. The PINF and ITS5 primers provide a powerful tool for rapid and sensitive detection of zoospores, sporangia, and oospores of P. infestans when used with appropriate extraction methods, and could easily be deployed to reduce spread of the pathogen in potato tubers.
Influence of Timing of Harvest in Relation to Haulm Killing and Planting Date on Potato Tuber Rot Caused by Phytophthora infestans
Authors: Miller J. S. , Cummings T. F. , Mikitzel L. J. , Johnson D. A.
Published: May 2007

Killing potato haulms 2 to 3 weeks prior to harvesting tubers is recommended for the management of potato late blight to eliminate the foliage as a source of tuber blight inoculum. Some potato growers in the Columbia Basin of Washington and Oregon, however, harvest tubers within days of killing potato haulms or harvest tubers without killing potato haulms. The susceptibility of potato tubers harvested from green haulms to late blight is unknown. From 1996 to 1998, Russet Burbank and Ranger Russet seed tuber pieces were planted on three different dates and then harvested simultaneously to obtain daughter tubers at different levels of maturity as determined by physiological degree day (P-day) accumulation. Tubers from two trials in 1996 were harvested within 1 to 4 days of haulm killing, tubers from a single trial in 1997 were harvested 16 days after haulm killing, and tubers from two trials in 1998 were harvested 1 and 21 days after haulm killing. Tubers from each plot were divided into two samples; one sample was inoculated the day after harvest and the other sample was inoculated 6 months after harvest on the buds and periderm tissue with a US-8 isolate of Phytophthora infestans. Severity of tuber blight on tuber surfaces and internal tuber tissue was highly correlated. When tubers were harvested within 1 to 4 days after haulm kill, the youngest tubers had the highest percentage of skinning and the lowest percentage of tuber blight. These tests, however, were not designed to test the hypothesis that increased tuber skinning resulted in increased tuber rot. Severity of tuber blight was greater for Ranger Russet tubers than for Russet Burbank tubers. The correlation between the severity of tuber blight at harvest and after 6 months in storage was significant. In some cases, differences in susceptibility to tuber blight due to planting date were observed after 6 months in storage. When tubers were harvested within 1 to 4 days after vine killing, tubers from plants that had been growing longer were more susceptible to late blight tuber rot than tubers from plants that had been growing for a shorter period of time.
Effect of Placement of Inoculum of Gaeumannomyces graminis var. tritici on Severity of Take-all in Winter Wheat
Authors: Kabbage Mehdi , Bockus William W.
Published: May 2007

Take-all, caused by Gaeumannomyces graminis var. tritici, is one of the most important root diseases of wheat worldwide. Because of the lack of highly effective chemical control, cultural practices, such as crop rotation, play a major role in managing disease severity. In Kansas, many producers do not use these measures and continue to suffer losses from take-all. Greenhouse and field experiments were established to assess the effect of horizontal versus vertical distribution of G. graminis var. tritici inoculum on disease severity. Oat kernel inoculum was placed at 0 (seed level), 5, 10, or 15 cm below the wheat seed or 5, 10, or 15 cm to the side of the wheat seed at a depth of 5 cm. Inoculum spatial location and distance greatly influenced take-all. Experiments showed more severe losses due to take-all when inoculum was placed below the seed than to the side of the seed. Regression analyses were used to develop take-all risk models relating inoculum distance from the seed to yield loss. Quadratic models were a better fit for data from experiments where inoculum was placed to the side of the seed, whereas linear models significantly fit data from experiments where inoculum was positioned below the seed. Within the same direction, take-all decreased as the inoculum was placed at greater distances from the seed, often to insignificant levels at 10 to 15 cm. According to the regression models, significant reduction (≥50%) in take-all might be achieved by plowing under the infested residues (crowns) to depths greater than 15 cm, or placing seed >6.0 cm to the side of inoculum. Therefore, under no-till conditions, sowing parallel to and exactly between the previous years' stubble rows (inoculum) might help manage take-all. These possibilities need to be investigated under field conditions.
First Report of Gray Leaf Spot Caused by Cercospora zeae-maydis on Corn in Ontario, Canada
Authors: Zhu X. , Reid L. M. , Woldemariam T. , Tenuta A. , Schaafsma A. W.
Published: May 2007

During an annual corn disease survey in mid-September 2001, sporadic symptoms typical of gray leaf spot (causal agent Cercospora zeae-maydis Tehon & E.Y. Daniels) (4), consisting of long, narrow, rectangular, 0.3 to 0.5 × 2 to 5 cm, tan or gray-to-tan spots, were found in nine fields in southern Ontario. Leaf samples with symptoms were placed in petri dishes containing moistened filter paper to maintain high humidity and stored at room temperature for 48 h. Clustered conidiophores arose from stomata on both leaf surfaces. Slightly curved, hyaline conidia, 4 to 8 × 25 to 88 µm long with 3 to 5 septa appeared on the tops of conidiophores, similar to those described by Kingsland (3). When single-spore isolates were cultured on carrot leaf decoction agar (2) at room temperature, aerial mycelia were rare, but slightly larger conidia were produced in 3 weeks. When single-spore isolates were cultured on V8 agar (1) at room temperature, aerial mycelia were abundant, and conidiophores and conidia were produced on the tops of mycelia in 1 to 2 weeks, but conidia were slightly smaller. Greenhouse-grown plants of two commercial corn hybrids (Pioneer 32Y52 and Zimmerman NX7208) were inoculated at the 8- to 10-leaf stage by injecting a suspension of 5 × 103 conidia per ml (washed from a V8 agar culture with sterile water) into the whorl and by spraying the suspension on the leaves. High moisture was maintained in the greenhouse by a misting system. After 14 to 21 days, typical symptoms of gray leaf spot and typical conidiophores and conidia were observed. Gray leaf was reisolated from inoculated plants, fulfilling Koch's postulates. We have suspected that gray leaf spot has been present in Ontario for a few years based on unconfirmed reports from the seed corn industry, but to our knowledge, this is the first confirmed report of this pathogen in Canada. Voucher specimens of field material, dried cultures, and greenhouse-inoculated leaves have been deposited in the National Mycological Herbarium (DAOM 229597 to 229600) in Ottawa, ON, Canada; and the isolate has been deposited with the Canadian Collection of Fungal Cultures (CCFC).

References: (1) S. T. Coates et al. Plant Dis. 78:1153, 1994. (2) O. D. Dhingra and J. B. Sinclair. Page 287 in: Basic Plant Pathology Methods. CRC Press, Inc., Boca Raton, FL, 1985. (3) G. C. Kingsland. Plant Dis. Rep. 47:724, 1963. (4) G. P. Munkvold and C. A. Martinson. Page 6 in: Iowa State University Extension Publication Pm-596, Iowa State University Press, Ames, 1994.
First Report of Bean pod mottle virus in Soybean in Canada
Authors: Michelutti R. , Tu J. C. , Hunt D. W. A. , Gagnier D. , Anderson T. R. , Welacky T. W. , Tenuta A. U.
Published: May 2007

In 2001, soybean fields were surveyed to determine the incidence of viruses because soybean aphids (Aphis glycines Matsamura), known to transmit Soybean mosaic virus (SMV) (2), were found in Ontario. In addition, bean leaf beetle (Cerotoma trifurcata Forster) was found during 2000 to be contaminated with Bean pod mottle virus (BPMV), although soybean plants, on which the beetles were feeding, tested negative (3). In the current survey, young soybean leaves were selected at random in July and August from 20 plants per site at growth stages R4 to R5 (1) from 415 sites representing the entire soybean-producing area in Ontario. Samples were maintained under cool conditions until received at the laboratory, where they were promptly processed. A combined sub-sample was obtained from the 20 plants per site. The 415 sub-samples were tested for SMV, BPMV, Tobacco ringspot virus (TRSV), and Tobacco streak virus (TSV) using polyclonal antibody kits for double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) (Agdia Inc., Elkart, IN). The ELISA plates were read with a plate reader (MRX, Dynex Technologies Inc., Chantilly, VA), and results were analyzed using ELISA software (Leading Edge Research, Merrickville, Ontario) and compared positive and negative controls (Agdia). TRSV was detected in one sample from Essex County and another sample from Middlesex County. SMV, BPMV, and TSV were not found in commercial soybean fields. However, SMV and BPMV were found in samples originating from two soybean breeding nurseries, one in Essex County and one in Kent County. Seedlings of soybean cv. Williams 82 were inoculated in the greenhouse with sap from leaf samples that tested positive for BPMV. Leaves of plants that developed mosaic symptoms were retested using ELISA and confirmed to be positive for BPMV. SMV and TRSV have been found previously in commercial soybean fields in Ontario (4). To our knowledge, this is the first report of BPMV on soybean plants in Canada.

References: (1) W. R. Fehr et al. Merr. Crop. Sci. 11:929, 1971. (2) J. H. Hill et al. Plant Dis. 85:561, 2001. (3) A. U. Tenuta. Crop Pest. 5 (11):8, 2000. (4) J. C. Tu. Can. J. Plant Sci. 66:491, 1986.
Relative Competitiveness and Virulence of Four Clonal Lineages of Cephalosporium maydis from Egypt Toward Greenhouse-Grown Maize
Authors: Zeller Kurt A. , Ismael Abou-Serie M. , El-Assiuty Elhamy M. , Fahmy Zeinab M. , Bekheet Fawzia M. , Leslie John F.
Published: May 2007

Four clonal lineages of Cephalosporium maydis, a soilborne vascular wilt pathogen that causes late wilt of maize, were differentiated previously with molecular markers. In Egypt, this fungus can cause significant losses in infected susceptible plants. In greenhouse tests of individual isolates we found that these lineages differ in their virulence toward a series of maize accessions commonly used in Egyptian maize breeding programs. We also determined the relative competitiveness of representatives of the four lineages when incorporated into the soil as a mixed inoculum. The lineage (IV) with greatest mean disease incidence (virulence), when tested alone, was the least competitive on susceptible maize accessions when coinoculated as a component of mixed inocula of all four lineages. In these coinoculation experiments, one of the less-virulent lineages (II) dominated (70% of infections) and appeared to be the most competitive. These results suggest that virulence and competitive ability are not the same in this host-pathogen system. These results also suggest that standard protocols that rely on mixed inocula for resistance screening need to be altered, and that the relative proportion of the different lineages of the pathogen recovered in a field may be influenced by the maize variety/hybrid planted.
First Record of Meloidogyne partityla on Pecan in Georgia
Authors: Nyczepir A. P. , Reilly C. C. , Wood B. W. , Thomas S. H.
Published: May 2007

In July 2000, tree decline was observed in a commercial pecan (Carya illinoensis (Wang.) K. Koch) orchard in Crisp County, GA. Most affected trees exhibited dead branches in the upper canopy, stunted growth, and feeder roots with small galls and associated egg masses typical of root-knot nematode infection. All declining trees that were examined had root systems infected with a Meloidogyne sp. Efforts to culture the nematode on tomato (Lycopersicon esculentum Mill. ‘Rutgers’) were unsuccessful. Identification of the nematode was determined by two laboratory procedures in March 2001. Female nematodes were teased from fresh pecan root galls of declining trees in Georgia, and identified by determining the esterase phenotype from replicate samples of single females compared with standard root-knot nematode species, including a population of M. partityla (3). Galled roots also were sent to New Mexico State University in Las Cruces, where mitochondrial DNA from specimens was extracted and compared with that from standard root-knot nematode species and known populations of M. partityla (2). Specimens had esterase phenotypes and DNA patterns consistent with M. partityla. Esterase phentoypes were inconsistent with M. incognita and M. arenaria, and DNA patterns were inconsistent with M. incognita, M. javanica, and M. hapla. Specimens at both locations were identified as M. partityla Kleynhans (1). To our knowledge, this is the first report of M. partityla from Georgia and the third report of this nematode outside of South Africa. The first and second report of M. partityla from pecan in the United States occurred in Texas and New Mexico in 1996 and 2001, respectively (3,4). Our inability to culture the M. partityla-GA isolate on tomato substantiates previous experience with this nematode in the United States (3) and is not surprising, since this species has a host range limited to the Juglandaceae. Furthermore, M. partityla may be endemic to North America and not South Africa. It is believed this nematode entered South Africa on pecan seedling roots imported from the United States between 1912 and 1940 (1). The unusually narrow host range may explain why M. partityla has gone unrecognized for so long in the United States compared with the more common Meloidogyne spp. (i.e., M. incognita and M. arenaria) with wider host ranges found in pecan orchards. Determining the distribution of M. partityla within the major pecan-growing regions of Georgia and throughout North America is warranted.

References: (1) K. P. N. Kleynhans. Phytophylactica 18:103, 1986. (2) T. O. Powers and T. S. Harris. J. Nematol. 25:1, 1993. (3) J. L. Starr et al. J. Nematol. 28:565, 1996. (4) S. H. Thomas et al. Plant Dis. 85:1030, 2001.
First Report of a Wilt and Stem Rot of Muskmelon and Watermelon Transplants Incited by Pseudomonas cichorii in Serbia
Authors: Obradovic A. , Arsenijevic M.
Published: May 2007

In 1989, a wilt and stem rot of muskmelon (Cucumis melo L.) was reported on seedlings grown under plastic in northern Serbia (1). In 1998, a similar disease of watermelon (Citrullus vulgaris L.) transplants occurred in central Serbia, resulting in losses estimated at 20% of plants grown in the nursery. Initial symptoms appeared as water-soaked lesions on the stem and lower surfaces of cotyledons and first true leaves. Necrosis started from leaf water-soaked areas and spread over the entire plant. Many stems softened and toppled. Wilting was also associated with the latter stages of the disease. Six representative strains isolated from water-soaked stem lesions on muskmelon in 1989 (three strains) and on watermelon in 1998 (three strains) were characterized. All strains were gram negative, strictly aerobic, motile, rod-shaped, and fluorescent on King's B medium, but negative for levan production, soft rot of potato, and arginine dihydrolase activity. Furthermore, strains were oxidase positive and induced a strong hypersensitive reaction in tobacco leaves. All of these reactions are characteristic of Pseudomonas cichorii (2). All six strains were confirmed to be P. cichorii based on analysis of cell-wall fatty acid profiles using the Microbial Identification System (MIDI, Newark, DE). Similarity indices ranged from 0.87 to 0.97. Pathogenicity of the P. cichorii strains was confirmed by prick inoculation of the hypocotyl of 2-week-old plants of domestic muskmelon cv. Sezam and watermelon cv. Rosa. Six plants of each cultivar were pricked with a dissecting needle dipped into a bacterial suspension (108 CFU/ml) prepared from each of the six strains and placed in a humidity chamber at 26°C for 48 h. Water-soaking occurred on all plants around the inoculation site after 24 h. The upper part of the plants lost turgor and wilted. Eventually, the hypocotyl and leaf veins became water-soaked, and the stem tissue softened, resulting in toppling of plants. The symptoms were identical to those described on muskmelon in 1989 and observed on watermelon in 1998. No symptoms developed on control plants. The bacterium was reisolated from the inoculated plants and shown to be identical to the original strains, confirming that P. cichorii was responsible for the disease of muskmelon and watermelon seedlings in 1989 and 1998, respectively.

References: (1) M. Arsenijevic and V. Stojsin. Contemp. Agric. 9:487, 1989. (2) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470, 1966.