bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Soft Rot Caused by Sclerotinia sclerotiorum on Borage in North Dakota
Authors: Bradley C. A. , del Río L. E. , Chesrown C. D. , Johnson B. L.
Published: May 2007

Borage (Borago officinalis) is an oilseed crop that is being evaluated as an alternative crop in North Dakota. During September 2004, borage plants in a field in Cass County, North Dakota were dying from a watery soft rot. The main stems and lateral branches were affected, and affected plants were usually completely lodged and prostrate. Dead plants had bleached and shredded stems with black sclerotia (9.1 ± 3.0 × 2.6 ± 0.5 mm) inside the pith and on the epidermis. At the time of observation, borage plants were flowering and forming pods and seed. Approximately 60% of the plants were visually affected by the watery soft rot. Sclerotia were collected from diseased plants, soaked in a 0.5% NaOCL solution for 30 s, air dried, and placed in petri dishes containing potato dextrose agar (PDA). A fungus grew from the plated sclerotia that subsequently produced white mycelium and black sclerotia (4.8 ± 1.2 × 2.5 ± 1.0 mm), which is characteristic of Sclerotinia sclerotiorum (Lib.) de Bary (3). To confirm pathogenicity, borage plants were inoculated in the greenhouse with a S. sclerotiorum isolate from field-infected borage. Thirteen borage plants were grown from seed in the greenhouse under natural sunlight at a temperature range of 24 ± 3°C. When plants were at the four-leaf stage (approximately 16 cm high), the second leaf was excised from each plant with the petiole remaining on the plant. The leafless petioles were inoculated using a method previously described (2). Petioles of 10 plants were inoculated with PDA containing mycelium of the S. sclerotiorum borage isolate, while petioles of five plants were inoculated with PDA to serve as a control. Three days after inoculation, plants inoculated with the S. sclerotiorum borage isolate were beginning to wilt and 5 days after inoculation, these plants were completely wilted and prostrate, similar to observations made on field-infected plants. Sclerotia collected from the diseased, inoculated plants were placed on PDA, and S. sclerotiorum was successfully recovered. Control plants inoculated with PDA did not show any disease symptoms. Other plant genera in the Boraginaceae are known hosts of S. sclerotiorum (1); however, to our knowledge, this is the first report of borage as a host.

References: (1) G. J. Boland and R. Hall, Can. J. Plant Pathol. 16:93, 1994. (2) L. E. del Río et al. (Abstr.) Phytopathology 90(suppl.):S176, 2000. (3) D. L. Tourneau, Phytopathology 69:887, 1979.
Field Evaluation of a New Sequential Sampling Technique for Determining Apple Scab “Risk”
Authors: Reardon J. E. , Berkett L. P. , Garcia M. E. , Gotlieb A. , Ashikaga T. , Badger G.
Published: May 2007

Most fungicide sprays applied to apple orchards in the New England states are targeted at the management of apple scab. Researchers have developed action thresholds that aid in decision-making on whether early spring fungicide applications could be eliminated without a significant increase in the incidence of fruit scab at harvest. To facilitate grower adoption of these thresholds, a simplified, sequential sampling technique in autumn to determine the “scab risk” of an orchard for the following spring was proposed in the scientific literature. However, this technique had not been evaluated in the field. In autumn 1999, 2000, and 2001, orchards were evaluated using the new sequential sampling technique to determine scab risk. Risk ratings were compared with those obtained by the original, nonsequential procedure in each orchard. Data also were examined using a simulation sequential sampling computer program to determine whether or not risk ratings would change if different trees or shoots were used. In two of the assessed orchards, “delayed-spray” experiments involving two treatments (a delayed-spray and full-spray treatment) were conducted in 2000 and 2001. Delayed-spray replicates were to receive no fungicide sprays until after the third primary infection period (but before the fourth) or until the pink stage of bud development, whichever came first; full-spray replicates received fungicide sprays starting at the green-tip stage of bud development. The sequential sampling technique provided scab-risk ratings consistent with the original, nonsequential procedure, at potentially significant time savings. Also, following the delayed-spray strategy in low-risk orchards did not result in significant differences in fruit scab at harvest compared with initiating spraying at the green-tip phenological bud stage.
Improving Root Health and Yield of Dry Beans in the Nebraska Panhandle with a New Technique for Reducing Soil Compaction
Authors: Harveson R. M. , Smith J. A. , Stroup W. W.
Published: May 2007

A field study conducted during the 2001 and 2002 growing seasons investigated the integration of fungicide applications and tillage methods for reducing root health problems in dry bean (Phaseolus vulgaris) plants by alleviating soil compaction and its potential exacerbation of root disease. Several cultural practices were combined with applications of the strobilurin fungicide azoxystrobin. Soil compaction was created artificially throughout the entire plot area. Six treatments, consisting of four tillage treatments and two combinations of tillage or applications of azoxystrobin, were tested to alleviate the compaction and enhance root health. Tillage treatments included a compacted control with no additional tillage, formation of beds approximately 10 cm above soil surface, zone tillage with an implement using in-row shanks, and both zone tillage and bedding combined. Fungicide treatments utilized the combination of both zone tillage and bedding with fungicide applications, and a fungicide treatment singly. Effects of compaction on plant vigor and disease development and severity were evaluated 67 and 83 days after planting in 2001 and 2002, respectively, by a visual estimation of plot vigor and by destructively sampling and making root and hypocotyl disease ratings on dry bean plants from nonharvest rows. Soil resistance and moisture were measured in plots 80 and 104 days after planting in 2001 and 2002, respectively, to estimate degree of compaction. In both years, Fusarium root rot, caused by Fusarium solani f. sp. phaseoli, was determined to be the main root disease impacting plant health in studies. All measured variables (root disease index, plant vigor ratings, total seed yield, seed size, and soil resistance) were significantly improved by any treatment that included zone tillage prior to planting. No added advantages were observed for decreasing disease or improving root health and plant performance with the use of azoxystrobin or by planting on raised beds. This is the first study to evaluate zone tillage as a method of reducing plant stress and root disease in dry bean plants.
Effects of Pathogen Density, Soil Moisture, and Soil pH on Biological Control of Clubroot in Chinese Cabbage by Heteroconium chaetospira
Authors: Narisawa K. , Shimura M. , Usuki F. , Fukuhara S. , Hashiba T.
Published: May 2007

The effects of soil moisture and pH, and pathogen resting spore density, on the effectiveness of the biological control of clubroot by the fungal endophyte Heteroconium chaetospira was evaluated in greenhouse and field experiments. Conditions favoring disease development included low pH (5.5) and high soil moisture content (80%), with significant reductions in the disease being observed at a higher pH (6.3 and 7.2) and lower soil moisture content (40 and 60%). In greenhouse tests, H. chaetospira effectively controlled clubroot (reducing the disease by 90 to 100%) at pathogen resting spore densities of 104 and 105 spores/g of soil at all soil pHs tested (5.5, 6.3, and 7.2). However, when the resting spore density was 106 spores/g of soil, plants were severely diseased, regardless of treatment, and H. chaetospira had no effect on disease. At a soil moisture content of 40%, disease occurrence was low, regardless of pathogen spore density, but disease was significantly lower in H. chaetospira-treated plants at pathogen spore density of 105 spores/g of soil. At 60% soil moisture content, H. chaetospira significantly could affect at pathogen spore densities of 104 and 105 but not 104/g of soil. At 80% soil moisture content, there was no effect of H. chaetospira at pathogen density. In situ, the soil moisture contents were constantly adjusted to relatively low to moderate (pF 2.2 to 2.4 and pF 2.0 to 2.2) and high (pF 1.6 to 1.8). Other environmental conditions, such as resting spore density and soil pH, were maintained at constant levels. Control plants (not treated with H. chaetospira) showed uniformly high disease levels and proportions of diseased plants across all three moisture treatments (disease index = 72 to 80, proportion of diseased plants 85 to 97%). In the field, H. chaetospira-treated plants at low soil moisture (pF 2.2 to 2.4, plot 1) had 68% disease reduction compared with untreated controls and 49% reduction at moderate moisture pF (pF 2.0 to 2.2, plot 2). There was no effect on disease by H. chaetospira at high soil moisture (pF 1.6 to 1.8, plot 3). Based on our results, H. chaetospira is an effective biocontrol agent against clubroot in Chinese cabbage at a low to moderate soil moisture range and a pathogen resting spore density of 105 (or lower resting spores per gram of soil in situ.
Evaluation of Food-Grade Dent Corn Hybrids for Severity of Fusarium Ear Rot and Fumonisin Accumulation in Grain
Authors: Kleinschmidt C. E. , Clements M. J. , Maragos C. M. , Pataky J. K. , White D. G.
Published: May 2007

Fumonisins produced by Fusarium verticillioides (syn = F. moniliforme) and F. proliferatum have been associated with potentially serious toxicoses of animals and humans. Thus, hybrids with low fumonisin accumulation in grain will be valuable for the production of corn-based human food products. We evaluated 68 food-grade dent corn hybrids for severity of Fusarium ear rot and fumonisin accumulation in grain in inoculated trials in Urbana, IL in 2000 and 2001. Our inoculation technique was successful in initiating fumonisin accumulation that allowed discrimination among hybrids. We identified several hybrids that could have acceptable levels (<4 μg/g) of fumonisin accumulation in Illinois in most years. Twenty-six hybrids with low or high fumonisin accumulation in 2000 were reevaluated in noninoculated trials at three locations in Illinois in 2001. Fumonisin concentration in grain at all three locations was relatively low; thus, separation of hybrids was poor. At two locations, those hybrids with the highest fumonisin concentration in grain also had high concentrations following inoculation. However, one hybrid that had relatively low fumonisin concentration following inoculation had unacceptable levels of fumonisin (5 μg/g) in natural conditions. Therefore, hybrids need to be evaluated by inoculation and further evaluated at locations where the environment favors fumonisin accumulation.
Resistance to Leaf Rust, Stripe Rust, and Stem Rust in Aegilops spp. in Israel
Authors: Anikster Y. , Manisterski J. , Long D. L. , Leonard K. J.
Published: May 2007

In all, 1,323 single plant accessions of Aegilops bicornis, A. kotschyi, A. longissima, A. ovata, A. searsii, A. sharonensis, A. speltoides, and A. variabilis collected from 18 regions in Israel and 2 adjacent regions in Lebanon and Egypt were evaluated for leaf rust (Puccinia triticina) and stripe rust (P. striiformis) resistance in field plots and for seedling resistance to leaf rust and stem rust (P. graminis f. sp. tritici) in greenhouse tests. Nearly all accessions of A. speltoides were highly resistant to leaf rust, stripe rust, and stem rust. A. longissima and A. ovata were highly resistant to stripe rust, whereas A. bicornis and A. kotschyi were highly susceptible. A. searsii was highly susceptible to stem rust, but 24 to 51% of accessions of A. bicornis, A. longissima, A. ovata, and A. variabilis were resistant to stem rust. Except for A. ovata and A. speltoides, more than 95% of the Aegilops accessions were susceptible to leaf rust caused by P. recondita alternating on Anchusa spp. Only Aegilops ovata was susceptible to P. recondita from Echium spp. A. bicornis, A. koschyi, and A. searsii were highly susceptible as seedlings to common wheat leaf rust caused by P. triticina. Most accessions of A. variabilis and about half of the accessions of A. longissima had good seedling resistance to P. triticina. Few accessions of A. ovata showed seedling resistance to the P. triticina population in Israel, but 30% were resistant to U.S. isolates. In field tests, A. bicornis showed high susceptibility to common wheat leaf rust, but more than 90% of the accessions of the other Aegilops spp. developed little or no leaf rust on adult plants. The Aegilops spp. in Israel and adjoining countries provide a rich and varied source of rust resistance for wheat breeding.
Weedborne Reservoirs and Seed Transmission of Verticillium dahliae in Lettuce
Authors: Vallad Gary E. , Bhat Ravi G. , Koike Steven T. , Ryder Edward J. , Subbarao Krishna V.
Published: May 2007

The seed transmission of Verticillium dahliae was evaluated in lettuce (Lactuca sativa). Seed collected from lettuce plants infected with V. dahliae were plated with or without surface sterilization on Sorenson's modified NP10 medium. Of the seed plated with or without surface sterilization, 90 and 66%, respectively, yielded colonies of V. dahliae. The incidence of Verticillium wilt ranged from 55 to 80% among lettuce plants grown from seed harvested from infected plants. All evaluated isolates of V. dahliae were capable of seed transmission in lettuce. A V. tricorpus isolate failed to cause significant disease in lettuce or to become seedborne. Storage of contaminated seed at seven temperatures ranging from -20 to 15°C for up to 72 weeks did not reduce the incidence of V. dahliae in seed, whereas storage at room temperature (23 ± 2°C) for 20 to 52 weeks reduced the incidence of V. dahliae without affecting seed viability. Of the 11 weed species collected from fields with a known history of Verticillium wilt of lettuce, four yielded V. dahliae. Pathogenicity tests demonstrated that isolates of V. dahliae from Sonchus oleraceus, Capsella bursa-pastoris, and Solanum sarrachoides were as virulent as or more virulent than an isolate of V. dahliae from lettuce. These results demonstrate the potential of seedborne and weedborne inoculum to disseminate V. dahliae.
Co-infection of Beet mosaic virus with Beet Yellowing Viruses Leads to Increased Symptom Expression on Sugar Beet
Authors: Wintermantel William M.
Published: May 2007

Three distinct aphid-transmitted viruses associated with a yellowing disease on sugar beet were examined in single and mixed infections for the effects of virus interactions on plant weight, rate of symptom development, and virus concentration. Sugar beet lines exhibiting different degrees of susceptibility to the virus yellows complex were inoculated with either one, two, or all three viruses. Severe stunting, as measured by fresh plant biomass, was observed with mixed infections with Beet yellows virus (BYV) and Beet mosaic virus (BtMV), compared to single infections of these viruses. In addition, the overall rate of appearance of Beet western yellows virus (BWYV) symptoms increased during co-infection with BtMV. Synergistic effects on stunting severity, as measured by plant biomass, were more pronounced in susceptible beet lines, but similar patterns also were observed in lines exhibiting tolerance to virus yellows. Relative concentrations of viruses were compared among single and mixed infections using dot-blot hybridization with virus specific probes, and quantified by phosphorimage analysis. Titers of all three viruses increased as a result of co-infection compared with single infections.
First Report of Leaf Spot on Japanese Plum Caused by an Alternaria sp. in Korea
Authors: Kim Youngjun , Lee Hyang Burm , Yu Seung Hun
Published: May 2007

Japanese plum (Prunus salicina Lindley) is a deciduous tree in the family Rosaceae. In Korea, this plant is widely distributed in orchards as an important stone fruit as well as in gardens as an ornamental tree because of their abundant white blossoms. Every September to November since 2001, leaf spots were observed on Japanese plum in a garden in Cheongyang, Chungnam District, Korea. Early symptoms consisted of small, brown spots that were 2 to 5 mm in diameter. Later, the leaf lesions became circular or irregular, dark brown, expanded to 15 mm in diameter, and resulted in discoloration with necrosis on twisted leaves that was followed by defoliation. In November, older lesions sometimes appeared blackish brown as sporulation occurred on the lesions. The causal fungus was isolated from diseased leaves and cultured on potato dextrose agar. A culture has been placed in the CABI Herbarium (IMI Accession No. 387139). Conidial dimension averaged 34 × 12 μm. On the basis of morphological characteristics of conidia and conidiophores, the causal fungus was identified as a small-spored species of Alternaria as described by E. G. Simmons (1). Pathogenicity tests were conducted by inoculating slightly wounded and nonwounded leaves with a conidial suspension adjusted to 1 × 106 conidia/ml. Four leaves per each experiment were either wounded or not and inoculated with a spore suspension. The eight leaves were placed in a moist chamber at 25°C. After 6 to 10 days, small brown spots appeared on 87% of the wounded and nonwounded leaves. Control leaves sprayed with distilled water did not develop any symptoms. The causal fungus was consistently reisolated from the leaf spots. Results from pathogenicity tests were similar in a repeated test. It is possible that small-spored Alternaria spp. isolates are host specific (2). Eight Alternaria spp., including A. alternata, A. tenuis, A. tenuissima, and A. citri, have been found to cause black spot on fifteen Prunus spp. in China, Japan, Hong Kong, Libya, Mexico, Australia, and the United States (2). Further studies on the host-specific toxin production, geographical distribution, and host ranges for the species of Alternaria isolated from Japanese plum are in progress. To our knowledge, this is the first report of leaf spot on Japanese plum (P. salicina) caused by a small-spored Alternaria sp. in Korea.

References: (1) E. G. Simmons. Mycotaxon 55:79, 1995. (2) K. Inoue and H. Nasu. J. Gen. Plant Pathol. 66:18, 2002.
Sensitivity of Venturia inaequalis Populations to Anilinopyrimidine Fungicides and Their Contribution to Scab Management in New York
Authors: Köller Wolfram , Wilcox W. F. , Parker D. M.
Published: May 2007

Sensitivities of Venturia inaequalis isolates to the anilinopyrimidine fungicides (APs) pyrimethanil and cyprodinil were determined for nine populations by measuring the growth of colonies formed from germinating conidia derived from single scab lesions. At the discriminatory pyrimethanil dose of 0.2 μg ml-1, the mean relative growth range measured for eight V. inaequalis populations (n = 39 to 74) never treated with AP fungicides varied from 18.1 to 48.2, translating into an approximately sixfold difference in mean baseline sensitivities. For the composite of all 469 isolates tested, sensitivities to pyrimethanil and to the sterol demethylation inhibitor (DMI) myclobutanil were significantly correlated. When isolates were organized into subpopulations based on their sensitivities to an individual fungicide, sensitivities to both fungicides declined in parallel through the highly and moderately sensitive spectra of subpopulations, but they diverged for isolates in subpopulations least sensitive to either fungicide. The result suggested that at least one of the multiple genes conferring DMI resistance also lowered the sensitivity to AP fungicides. The relative contribution of AP fungicides to scab management was evaluated at an experimental orchard representative of the Great Lakes region of the United States. Frequencies of DMI-resistant isolates of V. inaequalis had progressed to the stage of practical resistance at the site, and the sensitivity to pyrimethanil was similar to several commercial orchard populations never treated with APs. For management programs at the experimental site involving the AP fungicides cyprodinil and pyrimethanil and conducted from 1996 to 2000, the level of fruit and terminal leaf scab control was inferior to that of nonspecific protectants such as mancozeb or captan. For the control of scab on cluster leaves, the efficacy of AP fungicides equaled the performance of nonspecific protectants. This modest contribution of AP fungicides to scab management might have been caused by a lack of the extended cool temperature conditions that were conducive to AP performance in northern Europe in previous studies, and/or by the reduced sensitivity to AP fungicides in this DMI-resistant V. inaequalis population.
Limited Genetic Diversity in North American Isolates ofPhytophthora erythrosepticaPathogenic to Potato Based on RAPD Analysis
Authors: Peters Rick D. , Clark Rod J. , Coffin Albert D. , Sturz Antony V. , Lambert David H. , Miller Jeff S.
Published: May 2007

Pink rot of potato (Solanum tuberosum), caused by Phytophthora erythroseptica, is found wherever potatoes are grown, and in the last decade, it has reemerged as an economically important disease in Canada and the United States. A selection of isolates of P. erythroseptica from major potato-growing regions in North America, namely Prince Edward Island and New Brunswick, Canada, and Maine and Idaho, U.S.A., was assessed for genetic diversity with randomly chosen decanucleotide primers which were used to amplify regions of DNA to reveal polymorphisms among templates (random amplified polymorphic DNA [RAPD]). The isolates varied in their geographic origin as well as in their sensitivity to mefenoxam, as determined by an in vitro assay. In three separate RAPD screens (I, II, and III) with 23 isolates of P. erythroseptica chosen from a larger collection, 1,410, 369, and 316 robust, scorable bands were amplified, respectively. However, among the bands amplified in screens I, II, and III, only 3, 1, and 3 bands, respectively, were polymorphic. When three primers yielding polymorphisms were used to screen 106 isolates from Prince Edward Island and New Brunswick, or a representative collection of 32 isolates from Prince Edward Island, New Brunswick, Maine, and Idaho, no major variation was discovered. RAPD markers were not correlated with geographic origin or mefenoxam sensitivity of the isolates. From an evolutionary standpoint, the absence of genetic diversity among the isolates of P. erythroseptica we examined may be attributable to the relatively recent introduction of a small founding population of the pathogen in North America.
Seasonal Progression and Agronomic Impact of Tobacco streak virus on Soybean in Wisconsin
Authors: Rabedeaux P. F. , Gaska J. M. , Kurtzweil N. C. , Grau C. R.
Published: May 2007

Pod necrosis and dieback of terminal portions of stems, commonly called bud blight, are observed in soybean fields and associated with Tobacco streak virus (TSV), an understudied virus of soybean. Furthermore, many TSV-infected plants are asymptomatic. The objectives of this study were to characterize the distribution and seasonal progress of TSV-infected plants in both natural and controlled epidemics, and the agronomic impact of TSV on soybean in plots with controlled introduction of inoculum. Incidence of TSV-positive samples ranged from 17 to 56% in a general survey. In the presence of natural sources of inoculum, the incidence of TSV-infected plants ranged from 10 to 95% depending on cultivar and location, and peaked at growth stage R2, but detection dropped dramatically at R5. During 2001, significant yield loss and incidence of mottled seed were associated with TSV, but results were confounded by a high incidence of SMV. In 2002, SMV was controlled by cultivar selection, and a 25% reduction in grain yield was attributable to TSV. The incidence of mottled seed and green stem syndrome were low in the presence of TSV. Reductions in plant density and final plant height contributed to reduced yields. However, no significant differences were found in seed number per plant and 100-seed weight. Data indicate that plant mortality was the main mechanism by which TSV caused yield loss in induced epidemics.
Winter Survival of the Perennial Ryegrass Pathogen Magnaporthe oryzae in North Central Indiana
Authors: Harmon Philip F. , Latin Richard
Published: May 2007

Winter survival of Magnaporthe oryzae in north central Indiana was investigated in response to reports and observations of sporadic disease incidence. Survival of the fungus in perennial ryegrass residue was assessed. Time course studies were designed to assess the conidia production potential of infested perennial ryegrass residue exposed to ambient and predetermined treatments. Approximately 50,000 conidia per gram dry weight were produced initially on infested residue. In all years of the study, ambient winter conditions in Lafayette, IN, reduced conidia production on residue to fewer than 60 conidia per gram by spring. Unless residue was dried prior to treatment, storage of residue at all temperatures tested reduced conidia production potential. Airborne M. oryzae conidia, over the plot of perennial ryegrass where the winter survival studies were conducted, were estimated from particles collected with a volumetric air sampler. The stand of perennial ryegrass was inoculated with residue infested with M. oryzae in the summer of 2000 and late fall of 2000 and 2001. The stand of ryegrass was not inoculated in the summers of 200l or 2002. Conidia were captured with the air sampler each year in early July, before outbreaks had been observed in north central Indiana, but capture peaked in September when outbreaks most often occur. Cumulative conidia capture followed disease severity in 2000; however, no disease was observed in 2001 or 2002. Results of this study suggest poor survival of M. oryzae, and inadequate populations of viable pathogen limit disease development in north central Indiana. Disease risk assessment in north central Indiana should include an estimate of viable inoculum.
Occurrence of Tospoviruses in Ornamental and Weed Species in Markazi and Tehran Provinces in Iran
Authors: Ghotbi T. , Shahraeen N. , Winter S.
Published: May 2007

Damage to agricultural crops by tospoviruses has occurred sporadically in Iran in the past; however, since 2000, outbreaks of tospoviruses have been recorded every year. The most affected ornamental crops were surveyed in two main cultivation areas in provinces of Markazi (Mahallat) and Tehran in 2000-01 and 2001-02. A few weed species also were collected. In all, 513 samples (with or without any conspicuous virus symptoms) were collected and analyzed by double- and triple-antibody sandwich enzyme-linked immunosorbent assay (ELISA) with polyclonal antibodies to Tomato spotted wilt virus (TSWV), Impatiens necrotic spot virus (INSV), and Tomato Varamin virus (ToVV), a new Tospovirus sp. from Iran. These viruses frequently were detected in samples of many different ornamentals and often in mixed infections, whereas Iris yellow spot virus (IYSV) was detected in only four samples. ToVV also was found in weeds growing in Chrysanthemum fields and in a Cuscuta sp. Applying double-antibody sandwich ELISA, no positive reactions were found with Tomato chlorotic spot virus (TCSV). Of the total of 513 samples tested, 345 samples did not react with any Tospovirus antisera. In Tehran, INSV was identified in 21 samples (10%), IYSV in 4 samples (2%), TSWV in 16 samples (8%), and ToVV in 22 samples (11%). In Markazi province, INSV was identified in 24 samples (8%), IYSV in 1 sample (0.5%), TSWV in 40 samples (13%), and ToVV in 36 samples (12%). ToVV was found to prevail in Tehran province and TSWV in Markazi. Thrips spp. present at the plant sampling sites also were collected and identified.
Diversity and Mealybug Transmissibility of Ampeloviruses in Pineapple
Authors: Sether D. M. , Melzer M. J. , Busto J. , Zee F. , Hu J. S.
Published: May 2007

Mealybug wilt of pineapple (MWP) is one of the most destructive diseases of pineapple (Ananas comosus) worldwide. At least one Ampelovirus species, Pineapple mealybug wilt associated virus-2 (PMWaV-2), and mealybug feeding are involved in the etiology of MWP. A previously undescribed Ampelovirus sharing highest homology with PMWaV-1 and a putative deletion mutant sharing highest homology with PMWaV-2 were detected with reverse transcription-polymerase chain reaction (RT-PCR) assays using degenerate primers. Results were verified with additional sequence information and by immunosorbent electron microscopy. Sequence homology between the virus tentatively designated PMWaV-3, and PMWaV-1 and PMWaV-2, decreases toward the N-terminal across the HSP70 homolog, small hydrophobic protein, and RNA-dependent RNA polymerase open reading frames (ORF). Putative PMWaV-3 could not be detected with four different monoclonal antibodies specific for PMWaV-1 and PMWaV-2. The potential deletion mutant spanning the N-terminal of the HSP70 region was obtained from a pineapple accession from Zaire maintained at the USDA-ARS National Clonal Germplasm Repository in Hawaii. Putative PMWaV-3, like PMWaV-1 and PMWaV-2, is transmissible separately or in combination with other PMWaVs by Dysmicoccus brevipes and D. neobrevipes mealybugs. Plants infected with PMWaV-3 that were continuously exposed to mealybugs did not develop symptoms of MWP in the absence of PMWaV-2. Specific RT-PCR assays were developed for detection of putative PMWaV-3 and the deletion mutant.
Texas Has a New Pathotype of Peronosclerospora sorghi, the Cause of Sorghum Downy Mildew
Authors: Isakeit T. , Jaster J.
Published: May 2007

Three pathotypes of Peronosclerospora sorghi were known to occur in Texas as of 1980, with pathotype 3 (P3) predominant on sorghum (Sorghum bicolor) grown in the Upper Coast area. Following the use of hybrids resistant to P3, combined with metalaxyl or mefenoxam seed treatment, sorghum downy mildew (SDM) became a minor disease in Texas until the occurrence of a widespread outbreak caused by a P3 strain resistant to metalaxyl and mefenoxam in Wharton County in 2001 (2). During July 2004, <1% of plants in a commercial field in Wharton County planted to two Pioneer Brand P3-resistant hybrids had white stripes on the leaves and leaf shredding typical of systemic SDM. To obtain inoculum for pathogenicity studies, several infected plants were removed from the field and transplanted to pots for growth in a greenhouse. Systemically infected leaves suitable for inoculum production subsequently developed from tillers. Conidia were collected from leaves using a tiered temperature system (1). One-week-old seedlings of 10 sorghum lines used as pathotype differentials for Texas were sprayed until runoff with a conidial suspension (8 × 104 per ml) and incubated for 24 h at 20°C and 100% relative humidity. Seedlings were grown for 6 days in the greenhouse and then incubated overnight at 20°C and 100% relative humidity to promote sporulation of lesions, while systemic symptoms were evaluated after an additional 2 weeks in the greenhouse. There were 10 seeds planted per replicate and four replicates per line. The experiment was repeated once. Sporulation occurred on 54 and 64% of plants, and systemic symptoms on 53 and 82% of plants of P3-resistant line SC155 in two experiments, respectively. There were no local lesions or systemic symptoms on SC155 plants inoculated with several P3 isolates. Lines SC414-12E, QL3-India, 82BDM499, and 85EON495, which are resistant to P3, were also resistant to this isolate (i.e., no local lesions or systemic symptoms). Lines RTx2536, RTx430, CS3541, RTx7078, and SC170-6-17, which are susceptible to P3, were also susceptible to this isolate (54 to 100% incidence of systemic symptoms). An experiment (repeated once) that compared the reaction of this new pathotype on metalaxyl-treated and nontreated seed of a P3-resistant hybrid and a P3-susceptible hybrid, with reactions of metalaxyl-resistant P3 isolate and a metalaxyl-sensitive P3 isolate, showed that this pathotype, in addition to overcoming the genetic resistance, was also fungicide resistant. The pathogenicity of this new pathotype to other commercial P3-resistant hybrids is not yet known. There was no yield loss associated with this outbreak. However, the presence of a new pathotype, in combination with fungicide resistance, could lead to further outbreaks of SDM in the Upper Coast of Texas with the potential for yield loss.

References: (1) J. Craig. Plant Dis. 71:356, 1987. (2) T. Isakeit et al. (Abstr.) Phytopathology 93:S39, 2003.
Brown Ring Patch: A New Disease on Bentgrass Caused by Waitea circinata var. circinata
Authors: Toda Takeshi , Mushika Tomoyuki , Hayakawa Toshihiro , Tanaka Akemi , Tani Toshikazu , Hyakumachi Mitsuro
Published: May 2007

Isolates of an unidentified Rhizoctonia sp. (NP isolates), obtained from creeping bentgrass (Agrostis stolonifera var. palustris) in Japan that exhibited symptoms of a new disease, were compared with isolates of three varieties of Waitea circinata var. oryzae, var. zeae, and var. circinata. NP isolates also were compared with isolates of R. oryzae obtained from creeping bent-grass exhibiting white patch-like symptoms (RW isolates). The color and size of sclerotia, color of mycelia, and pigment deposition of NP isolates was similar to that of RW isolates and W. circinata var. circinata, but distinctly different from W. circinata var. oryzae and W. circinata var. zeae. The optimal temperature for hyphal growth of NP isolates, RW isolates, and W. circinata var. circinata was 28°C, and for W. circinata var. oryzae and W. circinata var. zeae was 30°C. Pathogenicity tests on creeping bentgrass showed that the severity of disease caused by NP isolates, RW isolates, and W. circinata var. circinata was greater than with W. circinata var. oryzae, but lower than with W. circinata var. zeae. No significant differences in symptom expression were apparent among NP isolates, RW isolates, and W. circinata var. circinata. A phylogenic tree, obtained using the results of random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), showed that isolates of W. circinata var. oryzae and W. circinata var. zeae separated into individual clusters, while NP isolates, RW isolates, and W. circinata var. circinata clustered together. The lengths of the rDNA internal transcribed spacer (ITS) region of NP isolates, RW isolates, and W. circinata var. circinata were identical but smaller than those of W. circinata var. oryzae and W. circinata var. zeae. Restriction fragment length polymorphism (RFLP) analysis of the rDNA-ITS region, using three enzymes (HapII, HinfI, and MboI), also showed that NP isolates were the same as RW isolates and W. circinata var. circinata, but different from W. circinata var. oryzae and W. circinata var. zeae. Based on these results, the NP isolates causing a new disease on bentgrass are W. circinata var. circinata, and that RW isolates are also W. circinata var. circinata but not R. oryzae. We propose that the name of the disease on creeping bentgrass caused by W. circinata var. circinata is brown ring patch.
Effect of Planting Date, Cultivar, and Stage of Plant Development on Incidence of Fusarium Wilt of Lettuce in Desert Production Fields
Authors: Matheron Michael E. , McCreight James D. , Tickes Barry R. , Porchas Martin
Published: May 2007

Fusarium wilt of lettuce, first recognized in Japan in 1955, has since been discovered in the United States (California in 1990, Arizona in 2001), Iran (1995), Taiwan (1998), and Italy (2001). In Arizona, the causal agent, Fusarium oxysporum f. sp. lactucae, has been recovered from lettuce plants in 27 different lettuce fields during the 2001 to 2003 production seasons. Studies were initiated to examine the impact of planting date, cultivar, and stage of plant development on the incidence of disease in the field. In 2002 and 2003, tested lettuce cultivars were sown in at least one of the following planting windows; early-season (September), mid-season (October), and late-season (December). Within each planting window, significant differences in disease incidence among lettuce cultivars were noted at plant maturity. The mean incidence of Fusarium wilt on cultivars sown in September, October, and December was 92.3, 15.1, and 2.0%, respectively, in 2002 and 74.2, 5.1, and 0.7%, respectively, in 2003. The mean soil temperatures at the10-cm depth during the September, October, and December plantings for both years were 26, 14, and 14°C, respectively. Initial symptoms of Fusarium wilt were apparent as early as 14 days after seeding, with increasing incidence of disease noted as the crop developed and reached maturity. Among all lettuce cultivars planted in September, only one and two cultivars of romaine in 2002 and 2003, respectively, reached maturity with ≤5% incidence of Fusarium wilt, whereas the lowest incidence of disease among crisphead, green leaf, red leaf, or butterhead cultivars was 73.7, 27.0, 20.2, and 65.7%, respectively, in 2002 and 62.1, 29.0, 100, and 100%, respectively, in 2003. For October plantings, all romaine cultivars had ≤5% incidence of Fusarium wilt at maturity, whereas disease incidence among tested cultivars of crisphead lettuce in 2002 and 2003 ranged from 0.8 to 66.8% and 0.3 to 43.3%, respectively. When planted in December, 82 and 88% of tested cultivars, including all romaine entries, reached maturity with ≤1% incidence of Fusarium wilt. Selection of appropriate lettuce cultivars and planting times should allow successful production of lettuce in the southwestern Arizona production region with minimal or no incidence of disease in fields infested with F. oxysporum f. sp. lactucae. On the other hand, successful production of lettuce in infested fields when temperatures favor disease development will not be possible until lettuce cultivars are developed that possess high tolerance or resistance to the pathogen.
Crop Damage Estimates for Crown Rot of Wheat and Barley in the Pacific Northwest
Authors: Smiley Richard W. , Gourlie Jennifer A. , Easley Sandra A. , Patterson Lisa-Marie , Whittaker Ruth G.
Published: May 2007

Crown rot of wheat and barley in the Pacific Northwest is caused by a complex of Fusarium pseudograminearum, F. culmorum, F. avenaceum, Bipolaris sorokiniana, and Microdochium nivale. Yield-loss estimates were made by evaluating yield components on tillers collected from commercial fields and sorted by disease severity classes, and by comparing yields for field plots inoculated with F. pseudograminearum with yields in naturally infested soil. Increasing crown rot severity caused an increase in grain protein content and reduction in grain yield, kernels per head, kernel weight, test weight, tiller height, and straw weight. Crown rot reduced winter wheat yield as much as 1,550 kg/ha (35%, $219/ha) in commercial fields, with a 13-field mean of 9.5% ($51/ha). Inoculation reduced yields as much as 2,630 kg/ha (61%, $372/ha) over that caused by the native pathogen flora. Rain-induced crusting of the soil surface greatly amplified preemergence damping-off caused by F. pseudograminearum. Crown rot caused the greatest losses during seasons of lowest precipitation but also damaged crops under wet conditions. Aboveground symptoms were not always apparent under conditions of moderate infection and yield constraint. Damage from crown rot in the Pacific Northwest is more widespread and damaging than previously recognized.
Disease Development on Lisianthus Following Aerial Transmission of Fusarium avenaceum by Adult Shore Flies, Fungus Gnats, and Moth Flies
Authors: El-Hamalawi Z. A. , Stanghellini M. E.
Published: May 2007

Fusarium crown and stem rot of lisianthus (Eustoma grandiflorum), caused by Fusarium avenaceum, is a destructive disease in California. The pathogen produces large masses of orangecolored macroconidia on stem lesions that extend up to 35 cm in length from the soil surface. Populations of macroconidia (97% viability) range from 1.1 × 108 to 1.9 × 108 per cm of infected stem tissue. An aboveground life stage for a soilborne pathogen could serve as a source for acquisition and aerial dissemination by adult shore flies, fungus gnats, and moth flies. Our results provide evidence that these three insects are attracted to and readily acquire (either externally and/or internally) macroconidia of F. avenaceum produced on naturally infected lisianthus stems and then disseminate acquired macroconidia to healthy plants, which subsequently died, or to an abiotic substrate (Komada's medium, KM). The high percentage of transmission, as evidenced by both the number of KM plates colonized by the pathogen (up to 68.5% within 18 h) and the number of plants infected (75% within 4 days), reflects the efficiency of these insects as vectors.
Management of Xanthomonas Leaf Blight of Onion with a Plant Activator, Biological Control Agents, and Copper Bactericides
Authors: Gent David H. , Schwartz Howard F.
Published: May 2007

Xanthomonas leaf blight (Xanthomonas axonopodis pv. allii) is a yield-limiting disease of onion (Allium cepa) in the western United States. Frequent applications of copper-based bactericides amended with an ethylenebisdithiocarbamate fungicide (e.g., maneb or mancozeb, class B2 carcinogens) provide some disease suppression, but strategies to reduce conventional bactericide use are needed to minimize grower costs, environmental impact, and public exposure to class B2 pesticides. Applications of acibenzolar-S-methyl reduced in planta and epiphytic populations of X. axonopodis pv. allii as effectively as applications of copper hydroxide-mancozeb in growth chamber studies. Under field conditions, four weekly applications of acibenzolar-S-methyl reduced severity of Xanthomonas leaf blight as or more effectively than 9 to 12 weekly applications of copper hydroxide or copper hydroxide-mancozeb. Acibenzolar-S-methyl applications did not increase bulb yield or grade compared with copper bactericide treatments. However, bulb yield was reduced 22 to 27% when 10 weekly applications of acibenzolar-S-methyl were made in the absence of disease. Application of a commercial formulation of both Pantoea agglomerans strain C9-1 and Pseudomonas fluorescens strain A506 reduced severity of Xanthomonas leaf blight in field experiments. Weekly copper hydroxide applications starting 1 to 2 weeks before bulb initiation were as effective as weekly applications started 3 to 4 weeks before bulb initiation, irrespective of the maneb rate used. Integration of acibenzolar-S-methyl and biological control agents with copper hydroxide in a carefully timed spray program may eliminate the use of the class B2 carcinogens maneb and mancozeb on onion without compromising efficacy for management of Xanthomonas leaf blight.
Influence of pH and NaHCO3 on Effectiveness of Imazalil to Inhibit Germination of Penicillium digitatum and to Control Postharvest Green Mold on Citrus Fruit
Authors: Smilanick J. L. , Mansour M. F. , Margosan D. A. , Gabler F. Mlikota , Goodwine W. R.
Published: May 2007

In vitro, spores of Penicillium digitatum germinated without inhibition between pH 4 and 7, but were inhibited at higher pH. Estimated concentrations of imazalil (IMZ) in potato-dextrose broth-Tris that caused 50% reduction in the germination of spores (ED50) of an IMZ-sensitive isolate M6R at pH 4, 5, 6, and 7 were 0.16, 0.11, 0.015, and 0.006 μg/ml, respectively. ED50 IMZ concentrations of an IMZ-resistant isolate D201 at pH 4, 5, 6, and 7 were 5.9, 1.4, 0.26, and 0.07 μg/ml, respectively. The natural pH within 2-mm-deep wounds on lemon was 5.6 to 5.1 and decreased with fruit age. IMZ effectiveness to control green mold and its residues increased with pH. The pH in wounds on lemon fruit 24 h after immersion in 1, 2, or 3% NaHCO3 increased from pH 5.3 to 6.0, 6.3, and 6.7, respectively. NaHCO3 dramatically improved IMZ performance. Green mold incidence among lemon fruit inoculated with M6R and treated 24 h later with IMZ at 10 μg/ml, 1% NaHCO3, or their combination was 92, 55, and 22%, respectively. Green mold among lemon fruit inoculated with D201 and treated 24 h later with water, IMZ at 500 μg/ml, 3% NaHCO3, or their combination was 96.3, 63.0, 44.4, and 6.5%, respectively. NaHCO3 did not influence IMZ fruit residue levels.
Epidemiology and Chemical Control of Soybean Rust in Southern Africa
Authors: Levy C.
Published: May 2007

Phakopsora pachyrhizi was discovered on soybeans in Uganda in 1996. This was the initial confirmation of the pathogen on soybeans in Africa, although there had been earlier unsubstantiated listings on other legumes. Thereafter, it was wind-dispersed southward to Rwanda, Zimbabwe, and Zambia in February 1998, where it severely damaged commercial plantings. It also devastated small-scale fields in eastern Nigeria at about this time. Rust continued its southward movement to southern Mozambique in early 2000, and into eastern South Africa in March 2001. By early 2003, substantial losses were being reported from western Cameroon. Scientists in Zimbabwe and South Africa have coordinated their research to combat the pathogen and have developed a strategy based on the effective, economical use of fungicides and the development of resistant germ plasm. The chemical and spraying recommendations resulting from field studies are discussed in relation to their practicalities, and a preliminary analysis of the meteorological data recorded will show the fundamental factors that influence the development of an epidemic.
First Report of Perithecia of Phaeoacremonium viticola on Grapevine (Vitis vinifera) and Ash Tree (Fraxinus latifolia) in California
Authors: Eskalen A. , Rooney-Latham S. , Gubler W. D.
Published: May 2007

Esca and Petri diseases on grapevine are caused by Phaeomoniella chlamydospora and species of Phaeoacremonium including P. aleophilum, P. viticola, P. angustius, P. parasiticum, P. inflatipes, P. rubrigenum, and P. mortoniae. The teleomorphs of P. aleophilum and P. mortoniae have been recently confirmed as Togninia minima(Tul. & C. Tul.) Berl. (2,3), and T. fraxinopennsylvanica (Hinds) Hausner, Eyjólfsdóttir & J. Reid, respectively (1,2,3). Teleomorphs of other Phaeoacremonium spp. have not been identified, although molecular data suggests that Phaeaoacremonium spp. are linked to the genus Togninia. Naturally infected vineyards with symptoms of esca disease were surveyed during the summer and fall of 2004. Samples were collected from declining ash trees surrounding the vineyards, as well as from symptomatic grapevine trunks, cordons, and spurs. Samples were processed as previously described (1). Sterile isolations were also made from symptomatic vascular tissue of the samples and cultured on potato dextrose agar (PDA)-tet medium. Perithecia were found on the surfaces of old pruning wounds and in the cracks of cordons and trunks on Vitis vinifera cvs. Thompson Seedless, Riesling, and Cabernet Sauvignon. Perithecia were observed on grapevines in vineyards in six of nine counties, viz. Yolo, Mendocino, El Dorado, Tulare, Madera, and Sonoma. Perithecia were also observed in dead vascular tissue of declining ash tree branches (Fraxinus latifolia) located in the vicinity of vineyards in Sonoma and Yolo counties. Perithecia were black, globose to subglobose, ranging from 160 to 215 μm in diameter, and were both embedded in and superficial on the wood tissue. Neck lengths ranged from 55 to 340 μm. The asci were hyaline, clavate, and ranged in size from 12.5 to 19.5 × 3.2 to 4.5 μm. Ascospores were hyaline, ellipsoid to allantoid, and ranged in size from 3.1 to 4.1 × 1.8 to 2.1 μm. Morphologically these perithecia resemble those of Togninia spp. When plated onto PDA-tet medium, ascospores formed colonies of P. viticola after 10 days of incubation at room temperature. Additionally, P. viticola was isolated from vascular tissue of the collected plant specimens. To our knowledge, this is the first time that P. viticola has been linked to a sexual state.

References: (1) A. Eskalen et al. Plant Dis. 89:528, 2005. (2) L. Mostert et al. Mycologia 95:646, 2003. (3) S. Rooney-Latham. Plant Dis. 89:177, 2005.