bluuebunny/crossref_metadata_2025 huggingface dataset:
Biological Significance of Mefenoxam Resistance in Phytophthora erythroseptica and Its Implications for the Management of Pink Rot of Potato
Authors: Taylor Raymond J. , Pasche Julie S. , Gudmestad Neil C.
Published: May 2007

Tubers from plants treated with in-furrow and foliar applications of mefenoxam were inoculated with eight isolates of Phytophthora erythroseptica having varying levels of sensitivity to the fungicide. Two isolates with effective concentration causing 50% reduction of mycelial growth (EC50) values of 0.02 and 0.04 μg ml-1 were categorized as being mefenoxam sensitive. Isolates with EC50 values >1.0 μg ml-1 were designated as insensitive to mefenoxam and were grouped two each into low intermediate (EC50 = 1.1 and 5.3 μg ml-1), high intermediate (EC50 = 26 and 74 μg ml-1), and resistant (EC50 ≥ 100 μg ml-1). The biological significance of these isolates was examined by quantifying disease control. P. erythroseptica isolates classified in the resistant group infected a significantly greater proportion of untreated tubers than isolates in any other group. Mefenoxam reduced infection frequency of sensitive isolates by as much as 37%. Mefenoxam did not provide disease control of any isolate possessing insensitivity to the fungicide, with the greatest decrease in control observed with the low intermediate group. Aggressiveness indices, representing tuber infection frequency and depth of penetration, were calculated for untreated and mefenoxam-treated tubers. According to these indices, both isolates classified in the resistant group and high intermediate isolate 252–4 were more aggressive than sensitive isolates in the absence of mefenoxam pressure, and significantly so in the presence of mefenoxam. These results suggest that pink rot may become more severe in fields known to contain P. erythroseptica populations with mefenoxam EC50 values >1.0 μg ml-1 if the fungicide is applied. These factors should be considered when developing strategies to manage pink rot and mefenoxam-resistant populations of P. erythroseptica.
A Multiplex PCR Assay to Characterize Potato virus Y Isolates and Identify Strain Mixtures
Authors: Lorenzen James H. , Piche Lisa M. , Gudmestad Neil C. , Meacham Teresa , Shiel Pat
Published: May 2007

Potato virus Y (PVY) has become a serious problem for the seed potato industry, with increased incidence and rejection of seed lots submitted for certification. New PVY strains and strain variants have emerged in recent decades in Europe and North America, including the PVYN strain that causes veinal necrosis in tobacco, and strain variants that represent one or three recombination events between the common strain (PVYO) and PVYN. Several reverse transcription-polymerase chain reaction (RT-PCR) assays have been described that characterize PVY isolates as to strain type, but they are limited in their ability to detect some combinations of mixed strain infections. We report here the development of a single multiplex RT-PCR assay that can assign PVY strain type and detect mixed infections with respect to the major strain types. Validation of this assay was achieved using 119 archived PVY isolates, which had been previously characterized by serology and bioassay and/or previously published RT-PCR assays. Results for single-strain isolates were comparable to previous results in most cases. Interestingly, 16 mixed infections were distinguished that had previously gone undetected. The new multiplex RT-PCR assay will be useful for researchers and seed production specialists interested in determining PVY infection type using a single assay.
Aggressiveness of Typhula ishikariensis Isolates to Cultivars of Bentgrass Species (Agrostis spp.) Under Controlled Environment Conditions
Authors: Chang S. W. , Chang T. H. , Tredway L. , Jung G.
Published: May 2007

Speckled snow mold, caused by Typhula ishikariensis, is one of the most important Typhula snow molds in subarctic zones of the Northern Hemisphere. Nine isolates of three T. ishikariensis varieties (var. ishikariensis, var. canadensis, and var. idahoensis) isolated from infected turfgrasses on golf course fairways throughout Wisconsin were evaluated for their aggressiveness toward nine cultivars of three bentgrass species (three creeping, three colonial, and three velvet cultivars) under controlled environmental conditions. Speckled snow mold severity increased as inoculum concentration of T. ishikariensis was increased. In general, bentgrass susceptibility increased between 9 and 11 weeks after seeding but gradually decreased thereafter, suggesting expression of age-related resistance as plants matured. Significant differences in aggressiveness were detected within and among T. ishikariensis varieties. Significant interactions between T. ishikariensis varieties or isolates and bentgrass species were detected, but there was no interaction between pathogen isolates and bentgrass cultivars. Disease severity evaluations showed significant differences among bentgrass cultivars and species in their response to T. ishikariensis. Since bentgrass species exhibit differential responses to T. ishikariensis varieties, representative isolates of each variety should be employed for screening of bentgrass germplasm for resistance to speckled snow mold.
Resistance to Passion fruit woodiness virus in Transgenic Passionflower Expressing the Virus Coat Protein Gene
Authors: Trevisan F. , Mendes B. M. J. , Maciel S. C. , Vieira M. L. C. , Meletti L. M. M. , Rezende J. A. M.
Published: May 2007

We report the use of the coat protein (CP) gene from Passion fruit woodiness virus (PWV) to produce resistant transgenic plants of yellow passion fruit. A full-length CP gene from a severe PWV isolate from the state of São Paulo, Brazil (PWV-SP) was cloned into pCAMBIA 2300 binary vector, which was further introduced into Agrobacterium tumefaciens strain EHA 105. Leaf disks were used as explants for transformation assays, e.g., 2,700 and 2,730 disks excised from plants from the Brazilian cultivars IAC-275 and IAC-277, respectively. In vitro selection was performed in kanamycin. After transferring to the elongation medium, 119 and 109 plantlets of IAC-275 and IAC-277, respectively, were recovered. Integration of the PWV CP gene was confirmed in seven of eight plants evaluated by Southern blot analysis, showing different numbers of insertional events for the CP gene. Three transgenic plants (T3, T4, and T7) expressed the expected transcript, but the 32 kDa PWV CP was detected by Western blot in only two plants (T3 and T4). The results of three successive mechanical inoculations against the transgenic plants using three PWV isolates showed that the primary transformant T2 of IAC-277 was immune to all isolates.
Perpetuation of Powdery Mildew Infection and Identification of Erysiphe australiana as the Crape Myrtle Pathogen in Mid-Tennessee
Authors: Shi Ainong , Mmbaga Margaret T.
Published: May 2007

The fungus Erysiphe lagerstroemiae is commonly known as the powdery mildew pathogen in crape myrtle (Lagerstroemiae indica) in the United States, and Erysiphe australiana is the powdery mildew pathogen reported in Japan, China, and Australia. The teleomorph often used to identify powdery mildew fungi rarely develops in crape myrtle, and in our observations, ascocarps never formed. Our study showed that the crape myrtle pathogen overwintered as mycelia on dormant buds. The internal transcribed spacer (ITS) regions of rDNA and the intervening 5.8S rRNA gene were amplified using standard polymerase chain reaction (PCR) protocols and the universal primer pairs ITS1 and ITS4. PCR products were analyzed by electrophoresis in a 1.5% agarose gel and sequenced, and the ITS PCR product was 666 bp from ITS1/ITS4 and 704 bp from ITS1-F/ITS4. BLAST analysis of the sequence of the PCR products showed identical similarity with E. australiana reported in Japan, China, and Australia. Comparison of ITS sequences with information in the GenBank on other powdery mildew fungi showed a closest alignment (93% similarity) to Erysiphe juglandis that infects walnut. Specific primers for E. australiana were developed and evaluated for use as diagnostic tools. Out of 12 specific primer pairs evaluated, four primer pairs and four double primer pairs were highly specific to E. australiana and did not amplify Erysiphe pulchra of dogwood, Erysiphe syringae of common lilac, Erysiphe circinata of maple, or Phyllactinia guttata of oak. The E. australiana-specific primers amplified 16 samples of crape myrtle powdery mildew collected from diverse locations in mid-Tennessee. These results clearly showed that the crape myrtle powdery mildew in mid-Tennessee was caused by E. australiana. Specific primers reported in this article provide a diagnostic tool and may be used to confirm the identity of crape myrtle powdery mildew pathogen in other areas in the United States and wherever the disease occurs.
First Report of Armillaria tabescens Causing Armillaria Root Rot of Pindo Palm in South Carolina
Authors: Schnabel G. , Bryson P. K. , Williamson M. A.
Published: May 2007

A Pindo palm tree (Butia capitata) declined in a commercial landscape setting in Georgetown, SC during June of 2005. In the spring, after looking healthy the previous year, the entire canopy collapsed with leaves attached. The canopy defoliated shortly thereafter. A cross section through primary and secondary roots of the wilting plant revealed necrotic areas with the presence of white mycelial fans. Diseased roots containing mycelial fans were collected and small sections were transferred to benomyl dichloran streptomycin (BDS) selective medium. Fungal cultures grew approximately 1 mm in diameter per day and developed aeriel mycelium first. Later, cultures developed mainly crustose mycelium with some parts being aerial. Ribosomal internal transcribed spacer (ITS) regions 1 and 2 were polymerase chain reaction amplified with universal primers ITS1-F and ITS4 and sequenced (GenBank Accession No. DQ109806). A BLAST search in GenBank of the ITS1-5.8S-ITS2 region identified the pathogen as Armillaria tabescens (Scop.) Emel (synonym Clitocybe tabescens (Fr.) Bres) with 98% sequence homology to A. tabescens single-spore isolate ss23 from South Carolina (Accession No. AY695408). The diploid culture from the roots of the Pindo palm was compatible with haploid tester strains of A. tabescens as indicated by diploidization of the haploid mycelium. The disease has been reported on Pindo palm in Florida (1), but to our knowledge, this is the first report of A. tabescens causing disease on Butia species in South Carolina. Our findings indicate that Pindo palm trees could be at risk for infection and should not be cultivated in soils containing pathogenic Armillaria species.

Reference: (1) S. A. Alfieri, Jr. et al. Index of Plant Diseases in Florida (Revised). Fla. Dep. Agric. Consum. Serv. Div. Plant Ind. Bull. 11:389, 1984.
Occurrence of Botrytis cinerea on Pelargonium spp. in Argentina
Authors: Palmucci H. E. , Wright E. R.
Published: May 2007

Pelargonium spp. are perennial ornamental plants used as potted plants or bedding plants in gardens. During the spring and summer of 2003, symptoms of an unknown disease appeared on florists' geranium (Pelargonium inquinans (L.) L'Herit) and ivy geranium (P. peltatum (L.) L'Herit.) adult plants growing in gardens in the suburbs of Buenos Aires. Flowers showed small, water-soaked spots that expanded and eventually blighted the petals. Brown, circular to irregular, water-soaked spots developed in leaves and advanced into the peduncules. A fungus was isolated from diseased leaf tissue on potato dextrose agar after surface disinfestations in 2% NaOCl for 2 min. Pure cultures formed a whitish, dense mycelial mat and turned gray after 72 h. Conidia were ellipsoid, hyaline, nonseptate, and were formed on botryose heads with an average size of 8.6 × 10.2 μm. Black, round, and irregular sclerotia developed on 7-day-old cultures with an average size of 1.1 × 1.7 mm. Morphological characteristics agree with those described for B. cinerea Pers.:Fr (1). Pathogenicity tests were conducted. Five 3-month-old plants of each host were spray inoculated with a conidial suspension (1 × 106 conidia/ml). Three controls of each host were sprayed with sterile distilled water. Plants were covered with plastic bags for 48 h and incubated at 20 ± 2°C with natural light for 15 days. Lesions similar to those observed in natural infection developed after 4 days. B. cinerea was reisolated from lesions, thus completing Koch's postulates. Controls remained symptomless. To our knowledge, this is the first report of B. cinerea causing a disease on Pelargonium. spp. in Argentina.

Reference: (1) M. V. Ellis and J. M. Waller. No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI. Kew, Surrey, UK, 1974.
First Report of Bentgrass Seed Gall Nematode, Anguina agrostis, in Virginia and Minnesota
Authors: Eisenback J. D. , Roane C. W.
Published: May 2007

On August 24, 2003, during a foray for grasses infected with fungi, redtop creeping bentgrass (Agrostis stolonifera L.) was collected on Butt Mountain Lookout near an abandoned fire tower with coordinates 80°37′40.3″ W and 37°22′14.0″N at an altitude of 1,284 m overlooking the New River between the towns of Pembroke and Ripplemead, VA. Seed heads with very elongated glumes, lemmas, and paleas were very common, and the incidence rate was nearly 95% on the basis of symptomatic plants in the immediate area surrounding the tower comprising more than 5 ha of a grassy meadow. Close examination revealed the occurrence of elongated, blackish galls replacing the ovaries and containing Anguina agrostis (Steinbuch, 1799) Filipjev, 1936. Nematode cultures were established and maintained on red top creeping bentgrass (A. stolonifera) in a greenhouse. Identification was based on morphology and measurements of juveniles L = 407 + 22 (376-418) μ, stylet L = 18.5 + 1.7 (17.0-21.3) μ males L = 351 + 17 (339-367) μm; and females L = 455 + 33. Examination of specimens collected previously by C. Roane revealed that another population of Anguina agrostis was also found on August 9, 1990 parasitizing the same host growing along Echo Trail near Big Lake Lodge Rd. in St. Louis County, MN. The infestation at the Virginia site may have been from sowing infested seeds at the disturbed construction site for the fire lookout tower and other buildings. However, the occurrence at the Minnesota site is less likely to be anthropogenic. Voucher specimens from both locations were placed in the Virginia Tech Nematode Collection, and voucher cultures are maintained in the Virginia Tech Nematode Culture Collection.
First Report of Cucumber vein yellowing virus on Cucumber, Melon, and Watermelon in Iran
Authors: Bananej K. , Desbiez C. , Girard M. , Wipf-Scheibel C. , Vahdat I. , Kheyr-Pour A. , Ahoonmanesh A. , Lecoq H.
Published: May 2007

Several viral diseases are responsible for significant economic losses in commercial cucurbit production worldwide. During a survey conducted in July 2002 in cucurbit growing areas in southern Iran, vein-clearing symptoms and leaf chlorosis on older leaves were observed on a cucumber plant near Jiroft (Kerman Province). These symptoms were similar to those caused by Cucumber vein yellowing virus (CVYV, genus Ipomovirus, family Potyviridae), a virus first described in Israel (1) and now widespread in cucurbit crops in the Middle East and Mediterranean Regions (2). The identification of CVYV was established through differential host range reaction and immunosorbent electron microscopy (IEM) experiments. Typical vein-clearing symptoms were observed following mechanical inoculation of cucumber and melon plantlets, but no symptoms were observed in Chenopodium quinoa, C. amaranticolor, Nicotiana tabacum, or Vigna sinensis. Numerous, slightly flexuous, elongated virus particles were observed in infected plant extracts. The particles were decorated by a polyclonal antiserum raised against a Sudanese isolate of CVYV. To confirm CVYV identification, total RNA extracts (TRI-Reagent, Sigma Chemical, St. Louis, MO) were obtained from the original cucumber sample. Reverse transcription-polymerase chain reactions (RT-PCR) were carried out using CVYV-specific primers CVYV-CP-5′: 5′-GCTTCTGGTTCTCAAGTGGA-3′ and CVYV-CP-3′: 5′-GATGCATCAGTTGTCAGATG-3′ designed according to the partial sequence of the coat protein gene of CVYV-Isr (GenBank Accession No. AF233429) (2). A 540-bp fragment corresponding to the central region of CVYV coat protein was obtained from extracts of infected plants but not from healthy plant extracts. Additional watermelon (n = 6) and melon (n = 4) leaf samples collected from plants growing in the same farm were tested for the presence of CVYV using RT-PCR. All samples reacted positively for CVYV. However, a sample of Citrullus colocynthis, a wild relative of watermelon growing nearby, was negative. CVYV was not detected using RT-PCR in 123 additional cucurbit samples collected from the eastern and central regions of Iran during a survey conducted in 2002. To our knowledge, this is the first report of the occurrence of CVYV in Iran. Additional surveys in southern regions where Bemisia tabaci, the vector of CVYV, is abundant are required to better estimate the prevalence of this virus in cucurbit crops in Iran.

References: (1) S. Cohen and F. E. Nitzany. Phytopathol. Mediterr. 1:44, 1960 (2) H. Lecoq et al. J. Gen. Virol. 81:2289, 2000.
Root Diseases of Wheat and Barley During the Transition from Conventional Tillage to Direct Seeding
Authors: Schroeder K. L. , Paulitz T. C.
Published: May 2007

The use of direct seeding (no-till) in place of tillage can reduce soil erosion and improve water infiltration. However, despite these improvements in soil quality, growers in the Pacific Northwest are reluctant to adopt direct seeding, partially because of fears of increased root diseases caused by Gaeumannomyces graminis var. tritici, Rhizoctonia spp., and Pythium spp. To examine the effect of the transition from conventional tillage to direct seeding, field plots were established at two locations. One site had been managed with direct seeding for 12 years, and the second had been conventionally tilled. Over 4 years, a portion of each plot was tilled or direct seeded, and planted to wheat or barley. Plants in the tilled plots had consistently more crown roots than plants in direct-seeded plots. Rhizoctonia root rot and yield did not differ between tillage types during the first 2 years of the study. However, in the third and fourth years of the transition to direct seeding, a higher incidence of Rhizoctonia root rot, increased hyphal activity of R. solani, and reduced yields were observed in direct-seeded plots. Populations of R. oryzae and Pythium spp., and incidence of take-all were the same for both management practices.
First Report of Downy Mildew Caused by Peronospora parasitica on Iberis sempervirens in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Iberis sempervirens (evergreen candytuft) is a garden species belonging to the Brassicaceae family. During June 2004, a damaging foliar disease was observed in several commercial farms near Albenga (northern Italy) on I. sempervirens plants grown outdoors in containers. More than 30% of the plants were affected. Symptoms appeared on both sides of leaves, buds, flowers, and fruits. Initially, leaves were slightly chlorotic, but within 5 to 7 days a characteristic whitish furry growth developed on the lower and upper leaf surfaces. The efflorescence was particularly evident on the lower surfaces of leaves and consisted of sporangiophores and sporangia. The appearance and severity of the disease increased because of overhead sprinkler irrigation. Microscopic observations revealed dichotomously branched sporangiophores with slender curved tips. Sporangiophores with a length of 115 to 410 μm (average 295 μm) ended with sterigmata bearing single sporangia. Sporangia were ovoid and measured 18 to 28 × 25 to 45 μm (average 22 × 35 μm). The pathogen was identified as Peronospora parasitica on the basis of its morphological characteristics (3). Pathogenicity was confirmed by inoculating leaves of 10 45-day-old healthy plants grown in 14-cm-diameter pots with a sporangial suspension (1 × 103 conidia/ml). Ten noninoculated plants served as controls. Plants were maintained outdoors at 50% light intensity with temperatures ranging between 16 and 25°C (average 18°C) and 85 to 100% relative humidity. The pathogenicity test was carried out twice. After 18 days, typical symptoms of downy mildew developed on the inoculated plants and P. parasitica was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of P. parasitica on evergreen candytuft in Italy. P. parasitica was previously reported on I. sempervirens in the United Kingdom (1) and on I. amara in California (2). Voucher specimens are available at the AGROINNOVA Collection, University of Torino, Italy.

References: (1) S. Francis and G. Waterhouse. Trans. Br. Mycol. Soc. 91:1, 1988. (2) P. R. Muller et al. Index of Plant Diseases in the United States. USDA Handbook No. 165, 1960. (3) D. M. Spencer. The Downy Mildews. Academic Press, New York, 1981.
A Detached Cucumber Fruit Method to Screen for Resistance toPhytophthora capsiciand Effect of Fruit Age on Susceptibility to Infection
Authors: Gevens A. J. , Ando K. , Lamour K. H. , Grumet R. , Hausbeck M. K.
Published: May 2007

Identification and utilization of resistance to Phytophthora capsici could provide the basis for a viable management strategy against cucumber fruit rot, a persistent threat in cucumber (Cucumis sativus) production. Our objectives were to develop a method for testing detached, nonwounded, cucumber fruit for resistance to P. capsici, and to screen cucumber cultivars and plant introductions (collectively referred to as cultigens) for resistance. Four P. capsici isolates (differing in their sensitivity to the fungicide mefenoxam and compatibility type) were compared for their fruit infection capability in 1999 and 2000. No significant differences were found among isolates, and a single isolate was used for all subsequent screens. From 1999 to 2004, 480 cucumber cultigens were grown according to standard practices at Michigan State University research farms in four fields with no history of P. capsici. Commercially mature fruit were harvested, inoculated with P. capsici, and rated for lesion diameter, pathogen sporulation diameter, and density of pathogen sporulation. Although no fruit exhibited complete resistance to P. capsici, some cultigens exhibited limited pathogen sporulation. In the process of screening, it was observed that younger, smaller fruit were comparatively more susceptible than older, larger fruit. Replicated trials with hand-pollinated fruit showed that the transition from susceptible to more resistant appeared to coincide with the transition from the period of rapid fruit elongation to the period of increased fruit diameter. This is the first report using a nonwounded fruit screen to analyze cucumber resistance to P. capsici.
Soybean Stem Colonization by Genotypes A and B of Cadophora gregata Increases with Increasing Population Densities of Heterodera glycines
Authors: Tabor G. M. , Tylka G. L. , Bronson C. R.
Published: May 2007

Growth chamber experiments were conducted to investigate whether parasitism by increasing population densities of Heterodera glycines, the soybean cyst nematode, increases the incidence and severity of stem colonization by the aggressive genotype A and the mild genotype B of Cadophora gregata (Phialophora gregata), causal agents of brown stem rot of soybeans. Soybean genotypes with three combinations of resistance and susceptibility to H. glycines and genotype A of C. gregata were inoculated with each genotype of C. gregata alone or each genotype with two population densities of H. glycines eggs, 1,500 or 10,000 per 100 cm3 of soil. Stems of two H. glycines-susceptible soybeans were more colonized by both aggressive and mild genotypes of C. gregata in the presence of high than in the presence of low H. glycines population density.
Seedling and Slow Rusting Resistance to Stripe Rust in Chinese Common Wheats
Authors: Li Z. F. , Xia X. C. , Zhou X. C. , Niu Y. C. , He Z. H. , Zhang Y. , Li G. Q. , Wan A. M. , Wang D. S. , Chen X. M. , Lu Q. L. , Singh R. P.
Published: May 2007

Identification of seedling and slow stripe rust resistance genes is important for gene pyramiding, gene deployment, and developing slow-rusting wheat cultivars to control the disease. A total of 98 Chinese lines were inoculated with 26 pathotypes of Puccinia striiformis f. sp. tritici for postulation of stripe rust resistance genes effective at the seedling stage. A total of 135 wheat lines were planted at two locations to characterize their slow rusting responses to stripe rust in the 2003-2004 and 2004-2005 cropping seasons. Genes Yr2, Yr3a, Yr4a, Yr6, Yr7, Yr9, Yr26, Yr27, and YrSD, either singly or in combinations, were postulated in 72 lines, whereas known resistance genes were not identified in the other 26 accessions. The resistance genes Yr9 and Yr26 were found in 42 and 19 accessions, respectively. Yr3a and Yr4a were detected in two lines, and four lines may contain Yr6. Three lines were postulated to possess YrSD, one carried Yr27, and one may possess Yr7. Thirty-three lines showed slow stripe rusting resistance at two locations in both seasons.
Corn with Symptoms of Reddening: New Host of Stolbur Phytoplasma
Authors: Duduk B. , Bertaccini A.
Published: May 2007

Recurrent epiphytotic outbreaks of a disease of uncertain etiology known as reddening of corn (Zea mays) have occurred in some areas of Serbia during the last 50 years. Affected plants show early and abnormal ripening, dry precociously, and have poor, shriveled grains. Using molecular tools, phytoplasmas were detected in diseased plants and their identity was subsequently deduced as a subgroup 16SrXII-A strain by a variety of supporting assays involving restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction (PCR)-amplified 16S rDNA and tuf gene sequences, selective amplification of phytoplasma DNA using primer pair G35p/m, similarity of 16-23S intergenic spacer region (SR) sequences, and similarity and phylogenetic analysis of 16S rDNA gene sequences. Presence of stolbur phytoplasmas in corn with reddening symptoms is a new finding not only for Serbia: it is the first report of stolbur phytoplasma in this species worldwide.
First Report of Tobacco ringspot virus in Pumpkin (Cucurbita pepo) in Illinois
Authors: Jossey S. , Babadoost M.
Published: May 2007

During a survey of commercial pumpkin and squash fields for viruses, conducted in Illinois in 2005, Tobacco ringspot virus (TRSV) was identified for the first time in symptomatic pumpkin samples collected during August and September from Douglas, Kankakee, Piatt, and Tazewell counties in one of three, one of three, one of one, and one of seven samples tested, respectively. In an earlier study from southern Illinois, the only viruses detected in pumpkins were Cucumber mosaic virus, Papaya ringspot virus, Squash mosaic virus, Watermelon mosaic virus, and Zucchini yellow mosaic virus (2). TRSV has been reported in cucurbits from some states in the United States (1). We detected TRSV in symptomatic leaves exhibiting mild mosaic with leaf yellowing using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) kit (Agdia, Inc., Elkhart, IN). Samples were considered positive if the absorbance readings at 405 nm exceeded 3× the absorbance of the negative control. The presence of TRSV was confirmed by reverse transcription-polymerase chain reactions (RT-PCR). Total RNA was extracted from the symptomatic plants using TRIzol Reagent and reverse transcribed by M-MLV Reverse Transcriptase (Invitrogen, Carlsbad, CA). PCR was conducted using forward primer 5′-CTTGCGGCCCAAATCT ATAA-3′ and reverse primer 5′-ACTTGTGCCCAGGAGAGCTA-3′, which anneal to the conserved region in the coat protein gene. The reaction produced an amplification product of the expected size (348 bp). Hence, utilizing ELISA and RT-PCR tests, the presence of TRSV in pumpkin was determined, to our knowledge, for the first time in Illinois.

References: (1) R. Provvidenti. Tobacco ringspot. Page 42 in: Compendium of Cucurbit Diseases. T. A. Zitter et al., eds. The American Phytopathological Society, St. Paul, MN. 1996. (2) S. A. Walters et al. HortScience 38:65, 2003.
Ergosterol as a Quantifiable Biomass Marker for Diaporthe haseolorum and Cercospora kikuchi
Authors: Xue H. Q. , Upchurch R. G. , Kwanyuen P.
Published: May 2007

The relationship between ergosterol content and biomass was determined for the soybean fungal pathogens Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. sojae, causal agent of Phomopsis seed decay, and Cercospora kikuchii (Matsumoto & Tomoy.), causal agent of leaf blight and purple seed stain. Biomass was manipulated by varying incubation period, and ergosterol was quantified by high-pressure liquid chromatography. Fungal dry mass was linearly correlated with ergosterol content (r2 = 0.90, P < 0.05 for D. phaseolorum, and r2 = 0.95, P < 0.01 for C. kikuchii). In vitro ergosterol content of fungi was 3.16 μg/mg for D. phaseolorum and 2.85 μg/mg for C. kikuchii. Ergosterol content of inoculated seed was qualitatively correlated with observed seed colonization by both pathogens. Soybean variety had a significant effect on fungal colonization by D. phaseolorum and ergosterol content. Results show that ergosterol content can be used to quantify colonization of soybean seed by both pathogens.
Effect of Fungicides and Storage Conditions on Postharvest Development of Citrus Black Spot and Survival of Guignardia citricarpa in Fruit Tissues
Authors: Agostini J. P. , Peres N. A. , Mackenzie S. J. , Adaskaveg J. E. , Timmer L. W.
Published: May 2007

Citrus black spot (CBS) is caused by Guignardia citricarpa, which incites lesions on citrus fruit and can induce fruit drop. Quiescent infections occur during the spring and summer, and symptoms appear at fruit maturity or after harvest. Thus, fruit from citrus areas affected by CBS represent a risk for introduction of this pathogen into new areas. The effects of preventive field fungicide programs, postharvest fungicide drenches, packinghouse fungicide applications, and storage temperatures on postharvest symptom development and viability of G. citricarpa in lesions were evaluated in five experiments on Murcott tangor, Valencia oranges, and lemons. Preventive field treatments and fruit storage at 8°C consistently reduced postharvest CBS development, whereas a postharvest fungicide drench or packinghouse treatment with fungicides had no effect on postharvest symptom development. In a separate experiment, postharvest appearance of symptoms was related to the percentage of fruit with symptoms at harvest. The preventive field fungicide program also consistently reduced the percentage of isolation of G. citricarpa from affected fruit, whereas storage temperature and packinghouse fungicide treatment gave variable results. The viability of the fungus declined with storage time of fruit after harvest, but G. citricarpa could still be readily isolated regardless of treatment. In another experiment, the viability of the fungus in detached fruit or peel was minimally affected by temperature or moisture during storage. The frequency of successful isolation declined with time, but G. citricarpa was still recovered frequently from symptomatic tissue at later times. The most effective means to reduce postharvest development of symptoms is through preventive application of fungicides during the fruit growing season and storage of harvested fruit at cold temperatures. None of the measures evaluated substantially reduced viability of G. citricarpa, and the pathogen would likely be introduced on symptomatic fruit from citrus areas with CBS.
First Report of Arceuthobium hondurense and Sruthanthus deppeanus in Nicaragua
Authors: Mathiasen R. , Sediles A. , Sesnie S.
Published: May 2007

The Honduran dwarf mistletoe, Arceuthobium hondurense Hawksw. & Wiens (Viscaceae), is one of the rarest dwarf mistletoes known in Central America (1,2). It is only known from four general areas in Honduras, but has also been reported from three locations in southern Mexico (2,3). At one time, A. hondurense was thought to be in danger of extinction (1). During March 2006, we found three new populations of this rare dwarf mistletoe in the Cordillera Dipilto in northern Nicaragua (Department Nueva Segovia). One population was approximately 11 km northeast of San Fernando (13°44′55″N, 86°19′07″W; elevation 1,130 m), the second population was approximately 9 km north of Mozonte (13°44′09″N, 86°24′54″W; elevation 1,415 m), and the third population was approximately 6 km southwest of Depilto (13°42′51″N, 86°32′22″W; elevation 1,340 m). Honduran dwarf mistletoe was parasitizing Pinus tecunumanii Equiluz & J.P. Perry at each of these locations, and at the Mozonte population, it was also infecting P. oocarpa Schiede ex Schlecht. Only a few pines were infected at each of these localities and no pine mortality associated with dwarf mistletoe infection was observed. However, even lightly infected trees had large witches' brooms and some trees were severely broomed. These populations are 50 to 65 km southeast of the nearest population of Honduran dwarf mistletoe in Honduras and they represent the southern most populations of Arceuthobium spp. in the New World (1). The mistletoe, Struthanthus deppeanus (Cham. & Schlecht.) Bl. (Loranthaceae), also parasitizes pines in Central America and southern Mexico (3). We observed this mistletoe parasitizing P. tecunumanii at the San Fernando location described above, on P. oocarpa approximately 7 km north of Mozonte (13°43′57″N, 86°24′49″W; elevation 1,490 m), and on P. oocarpa approximately 3 km southwest of Dipilto (13°43′40″N, 86°31′56″W; elevation 1,170 m). Again, only a few pines were infected at each of these locations, and we did not observe pine mortality associated with infection by S. deppeanus. S. deppeanus does not cause the formation of witches' brooms on infected pines, but the mistletoe plants are often greater than 1 m long so they are easily observed. This mistletoe was most common southwest of Depilto. To our knowledge, this is the first report of A. hondurense and S. deppeanus in Nicaragua. Specimens of A. hondurense and S. deppeanus from Nicaragua have been deposited at the Deaver Herbarium, Northern Arizona University, Flagstaff (Accession Nos. 81561–81567).

References: (1) F. Hawksworth and D. Wiens. Dwarf mistletoes: Biology, pathology, and systematics. USDA For. Serv. Agric. Handb. 709, 1996; (2) R. Mathiasen and J. Melgar, Plant Disease 90:685, 2006; (3) R. Mathiasen et al. Madrono 50:115, 2003.
Downy Mildew of Rudbeckia fulgida cv. Goldsturm by Plasmopara halstedii in Virginia
Authors: Hong C. X.
Published: May 2007

A severe foliage disease was observed on black-eyed Susan (Rudbeckia fulgida cv. Goldsturm) at a commercial nursery in Virginia Beach, VA in early June of 2005 and 2006. In both years, disease symptoms began after plants were transferred from 1-liter (1quart) to 4-liter (1-gallon) containers. Several hundred ‘Goldsturm’ plants were grown at this nursery but none was marketable because of this disease. Typical symptoms were dark, blotchy necrotic areas on the upper leaf surface. Fuzzy, grayish white zoosporangiophores and zoosporangia were commonly produced on the underside of affected leaves. These disease signs also were observed on both sides of new leaves in severely affected plants. Zoosporangiophores were monopodially branched at right angles with acutely tapering termini. Zoosporangia were ovoid to elliptical, hyaline, and measured 19 to 28 × 17 to 21 μm. On the basis of these morphological characters and host specificity, the organism was identified as Plasmopara halstedii (Farl.) Berl. & De Toni in Sacc. Inoculum at 1.4 × 104 zoosporangia/ml was prepared by washing diseased leaves with deionized reverse osmosis water and applied with a hand sprayer onto the foliage of test plants until runoff. Control plants were treated with deionized reverse osmosis water only. Inoculated and control plants were placed in plastic bags to keep moist for 48 h at 20°C. The inoculated plants developed the same symptoms with fresh crops of the zoosporangiophores and zoosporangia of P. halstedii on the underside of leaves, while the control plants remained healthy 14 days after treatment. The source of the primary inoculum is not known. Interestingly, none of 12 other Rudbeckia spp. and cultivars (R. hirta cvs. Autumn Colors, Becky, Cherokee Sunset, Indian Summer, Irish Eye, Prarie Sun, and Sonora, R. laciniata, R. maxima, R. missouriensis, R. occidentalis cv. Green Wizard, and R. speciosa cv. Viette's Little) grown at the same nursery adjacent to those severely diseased ‘Goldsturm’ plants was affected. Although downy mildew was reported on rudbeckias in north Florida previously (1), to my knowledge, this is the first report from Virginia. This pathogen attacks a number of plants in the genera of Centaurea, Coreopsis, Erigeron, Helianthus, and Verbena in addition to Rudbeckia spp. (2). Thus, it could significantly impact the ornamental plant nursery industry.

References: (1) H. Dankers et al. Plant Health Progress. Online publication. doi:10.1094/PHP-2004-0119-01-HN, 2004. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.
Molecular Monitoring of Wild-Type and Genetically EngineeredColletotrichum coccodesBiocontrol Strains In Planta
Authors: Dauch A. L. , Ahn B. , Watson A. K. , Seguin P. , Jabaji-Hare S. H.
Published: May 2007

Two strains of Colletotrichum coccodes, the wild type (DAOM 183088) and T-20a, engineered with the necrosis- and ethylene-inducing peptide (NEP1) gene for hypervirulence on velvetleaf (Abutilon theophrasti, Medik.), were monitored in planta for the first 2 weeks after infection. Real-time quantitative polymerase chain reaction (QPCR) was used to assess the extent of colonization of both strains on velvetleaf using SYBR Green chemistry. Quantification of both strains was successful as soon as the conidia were sprayed on the leaves and up to 14 days after infection. The increase in fungal DNA amounts corroborated with the appearance of necrotic lesions on velvetleaf leaves infected with the wild-type strain. The wild-type C. coccodes was more efficient at infecting velvetleaf than the transgenic T-20a strain. In addition, detection of host DNA allowed us to quantitatively monitor the decrease in plant DNA amounts in response to wild-type strain infection. Expression of the NEP1 transgene by conventional retro-transcription (RT)-PCR was absent from T-20a growing on either V8 agar or in planta, suggesting that the gene may be silenced. The application of QPCR to monitor fungal growth was proven to detect the target organisms in planta prior to the appearance of symptoms.
First Report of Bacterial Blight of Romanesco Cauliflower (Brassica oleracea var. botrytis) Caused by Pseudomonas syringae pv. alisalensis in California
Authors: Koike S. T. , Kammeijer K. , Bull C. T. , O'Brien D.
Published: May 2007

In 2005, a new disease was detected on commercial, organically grown romanesco (green) cauliflower (Brassica oleracea var. botrytis) grown in San Benito County, California. Initial symptoms consisted of small (1 to 2 mm in diameter), angular, water-soaked flecks. These flecks developed into tan-to-gray, angular lesions measuring as much as 5 mm in diameter. Lesions were usually surrounded by chlorotic borders. Coalescing lesions caused the leaf to turn papery in texture and have a blighted appearance. A blue-green fluorescing pseudomonad was consistently isolated from lesions on King's medium B. Strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction in tobacco (Nicotiana tabacum cv. Samsun). These data indicated that the bacteria belonged to Lelliot's LOPAT group 1 (2). This was confirmed with data from fatty acid methyl ester analysis (MIS-TSBA version 4.10, MIDI, Inc., Newark, DE), which showed that the strains were highly similar (similarity = 0.921 or greater) to Pseudomonas syringae. Amplification of repetitive bacterial sequences (rep-PCR) using the BOXA1R primer and the polymerase chain reaction resulted in identical banding patterns for the romanesco strains and the P. syringae pv. alisalensis pathotype strain. Pathogenicity was demonstrated by growing inoculum of six strains in nutrient broth shake cultures for 48 h (24°C), adjusting the bacterial suspension to 106 CFU/ml, and spraying the resulting suspension onto green cauliflower (cv. Romanesco Precoce). Plants were enclosed in plastic bags for 24 h and then incubated in a greenhouse (24 to 26°C). Control plants were misted with sterile water and treated the same way. After 5 days, foliar symptoms identical to symptoms seen in the field developed on all inoculated plants, and reisolated strains were characterized and found to be identical to P. syringae pv. alisalensis by the tests described above. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. To our knowledge, this is the first report of commercially grown romanesco green cauliflower as a host of P. syringae pv. alisalensis. The infested field had approximately 30% of the plants affected, with perhaps 10% sustaining some crop loss. This bacterial pathogen has previously been reported on commercial plantings of arugula (Eruca sativa), broccoli (Brassica oleracea var. botrytis), and broccoli raab (Brassica rapa var. rapa) and under experimental (greenhouse) conditions causes disease on additional hosts, including members of the Poaceae (1).

References: (1) N. A. Cintas et al. Plant Dis. 86:992, 2002. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.
First Report of Phomopsis amygdali Causing Fruit Rot on Peaches in Greece
Authors: Michailides T. J. , Thomidis T.
Published: May 2007

In the summer of 2005, the fungus Phomopsis amygdali (Del.) Tuset & Portilla was frequently isolated from decayed peaches (Prunus persica cv. Andross) grown in the province of Imathia, Greece. Fruit infected by P. amygdali developed gray-to-brown decay lesions with white mycelium forming on the surface of lesions. Identification of the pathogen was based on morphological characteristics. Dark-pigmented pycnidia (flask-shaped, conidia-bearing fruiting bodies) were produced over the surface of potato dextrose agar. The pycnidia exuded conidia in white tendrils 7 days later. Koch's postulates were completed in the laboratory by inoculating mature and immature cv. Andross peach fruits with an isolate of P. amygdali isolated from decayed cv. Andross peaches. Thirty peach fruit were surface sterilized by dipping them into 0.1% chlorine solution and allowing them to dry in a laminar flow hood. The peach fruit were wounded with a 2-mm diameter glass rod and a 40-μl drop of 5 × 105 conidia of P. amygdali per milliliter suspension was applied to the wound. Thirty control fruits were similarly wounded and inoculated with a 40-μl drop of sterile water. All inoculated and noninoculated fruit were incubated at 24 to 26°C for 7 days. Koch's postulates were satisfied when the same fungus was reisolated from 100% of inoculated mature and immature fruit that developed symptoms similar to diseased fruit collected from orchards. Although P. amygdali has been previously reported as a causal agent of canker disease (2) and fruit rots of peaches (1) in other countries, to our knowledge, this is the first report of the occurrence of P. amygdali causing a fruit rot of peaches in Greece.

References: (1) Y. Ko and S. Sun. Plant Pathol. Bull. 12:212, 2003. (2) E. I. Zehr, Constriction canker. Page 31 in: Compendium of Stone Fruit Diseases. J. M. Ogawa et al., eds. The American Phytopathological Society, St. Paul, MN, 1995.
Spatial Pattern of Trees Affected by Black Spot in Citrus Groves in Brazil
Authors: Spósito M. B. , Amorim L. , Ribeiro P. J. , Bassanezi R. B. , Krainski E. T.
Published: May 2007

Citrus black spot (CBS), caused by Guignardia citricarpa, is the most important fungal disease of orange trees in Brazil. The spatial pattern of CBS-symptomatic trees was evaluated using the binomial dispersion index (D), Ripley's K function (K), and a Monte Carlo test for minimum mean distance (d) to understand the distribution of the pathogen. Disease was monitored in 7,790 citrus trees from four commercial groves. In one grove, disease incidence was assessed from 1999 to 2001 and, in the others, disease assessments were conducted only in 2002. Infected trees were aggregated based on the three statistical analyses used (D, K, and d) regardless of the CBS incidence. The binomial index of dispersion (D) indicated aggregation of CBS-affected trees for all groves and for various quadrat sizes (2 by 2, 3 by 3, 4 by 4… up to 10 by 10). According to Ripley's K function, the dependence among symptomatic trees comprised two to three neighboring trees. Disease dispersion occurred at distances below 24.7 m according to the test for d. This suggests that the dispersion of inoculum is highly important over short distances. As a consequence, the required sample size to achieve a level of accuracy of C = 20% increases exponentially with the decrease in incidence of CBS below 15% infected plants.
Number of Experiments Needed to Determine Wheat Disease Phenotypes for Four Wheat Diseases
Authors: Bockus William W. , Su Zhaohui , Garrett Karen A. , Gill Bikram S. , Stack James P. , Fritz Allan K. , Roozeboom Kraig L. , Martin T. Joe
Published: May 2007

Disease phenotypes for winter wheat cultivars were determined in numerous inoculated greenhouse and field experiments over many years. For four diseases, Fusarium head blight, tan spot, Septoria leaf blotch, and Stagonospora leaf blotch, at least 20 cultivars each had been evaluated in a minimum of five experiments. Reference cultivars of known disease reaction were included in each experiment, which allowed transformation of the percent disease severity data to a 1-to-9 scale for comparisons between experiments. Variations in scale values obtained for individual cultivars among the different experiments were used to calculate standard deviations for disease phenotype data. Standard deviations were used to calculate the number of experiment repetitions needed within each disease to achieve different levels of accuracy (margins of error). A margin of error of ±1.5 for the 1-to-9 scale was chosen as the best level of accuracy. Rounding values within this range would put the estimated disease phenotype within ±1 unit of the actual phenotype. To achieve a margin of error of ±1.5 for Fusarium head blight, tan spot, Septoria leaf blotch, and Stagonospora leaf blotch would require a mean that was calculated from a minimum of five, five, seven, and eight experiments, respectively. Personnel who report disease phenotype data to wheat producers or breeders should be aware of the number of experiments upon which they are basing their reports and adjust any disclaimers accordingly. Similarly, wheat breeders should be aware of the inherent variability in phenotyping these four wheat diseases and make appropriate adjustments to their selection protocols. With a minimum of five experimental repetitions, disease phenotype values obtained from inoculated greenhouse and field experiments had very high correlations (r = 0.81 to 0.92, P < 0.0001) with published Kansas State University Research and Extension ratings obtained from commercial fields.