bluuebunny/crossref_metadata_2025 huggingface dataset:
Epidemiology of Tilletia indica Teliospores in Regulated Wheat Fields in Texas
Authors: Stein J. M. , Maples H. W. , Rush C. M.
Published: May 2007

To examine the epidemiology of Tilletia indica teliospores in naturally infested soils from wheat fields in both Karnal bunt-regulated regions in Texas, soil was grid sampled from fields that were bunted-kernel positive for Karnal bunt in 1997, 2001, both years, or never. Aliquots of soil from each point were pooled, and teliospores were extracted using a size-selective sieving-sucrose centrifugation method. Teliospores were enumerated microscopically, and low quantities (< 8 per 25 g of soil) were identified in 14 of 15 fields sampled from the regulated regions of Texas, including fields that have never tested positive for bunted kernels, indicating a widespread distribution. No teliospores were isolated from the single field examined outside of the regulated regions. The percent clay was significantly, negatively correlated with the baseline teliospore number and the estimated (extrapolated) number of teliospores per sample, indicating a potential impact of soil composition on teliospore survival. The latter factor was also significantly, positively correlated to the number of times a field had tested positive.
Effects of Curing on Green Mold and Stem-End Rot of Citrus Fruit and Its Potential Application Under Florida Packing System
Authors: Zhang Jiuxu , Swingle Patricia P.
Published: May 2007

The potential of citrus fruit curing for the control of green mold caused by Penicillium digitatum, and the impact of this treatment on stem-end rot caused by Lasiodiplodia theobromae were investigated. The optimum temperatures for mycelial growth of P. digitatum and L. theobromae were about 25 and 30°C, respectively. P. digitatum did not grow at 35°C, while L. theobromae did. Injuries of ‘Valencia’ oranges developed less green mold disease at 30 and 35°C than at 25°C or lower. Green mold incidences on ‘Valencia’ oranges treated at 21°C (uncured control), 30 and 35°C for 48 h were 51, 17.4, and 0%, respectively, for inoculated fruit, and 18.8, 11.4, and 0%, respectively, for wounded fruit after 2 weeks of storage at 21°C. However, a significant increase in stem-end rot occurred at 35°C when compared with 21°C (uncured control). In two of three different tests, curing fruit at 35°C for 48 h achieved better green mold control than a shorter curing time of 24 h. Curing ‘Pineapple’ oranges showed a similar or better efficacy for green mold control than imazalil at 500 and 1,000 ppm applied by either dip or packingline drip. The combination of thiabendazole drench (500 ppm) and curing of wounded ‘Valencia’ oranges and inoculated ‘Flame’ grapefruit reduced both green mold and stem-end rot by more than 93%. This study suggests that curing (35°C for 48 h) could be integrated into the current Florida citrus packing system to effectively control postharvest decays.
Field Resistance of Coat Protein Transgenic Papaya to Papaya ringspot virus in Jamaica
Authors: Tennant Paula , Ahmad M. H. , Gonsalves D.
Published: May 2007

Transgenic papayas (Carica papaya) containing translatable coat protein (CPT) or nontranslatable coat protein (CPNT) gene constructs were evaluated over two generations for field resistance to Papaya ringspot virus in a commercial papaya growing area in Jamaica. Reactions of R0 CPT transgenic lines included no symptoms and mild or severe leaf and fruit symptoms. All three reactions were observed in one line and among different lines. Trees of most CPNT lines exhibited severe symptoms of infection, and some also showed mild symptoms. R1 offspring showed reactions previously observed with parental R0 trees; however, reactions not previously observed or a lower incidence of the reaction were also obtained. The transgenic lines appear to possess virus disease resistance that can be manipulated in subsequent generations for the development of a product with acceptable commercial performance.
Effects of Wetness Duration and Grain Development Stages on Sorghum Grain Mold Infection
Authors: Navi S. S. , Bandyopadhyay R. , Reddy R. K. , Thakur R. P. , Yang X. B.
Published: May 2007

Grain mold caused by a complex of fungi is an economically important disease of sorghum worldwide. Little is known about the epidemiology of sorghum grain mold, which is essential for its management. Studies were conducted to quantify the effects of wetness duration on grain mold development under controlled conditions at ICRISAT. Six major sorghum grain mold fungi determined from previous field experiments, Curvularia lunata, Cladosporium oxysporum, Bipolaris australiensis, Fusarium moniliforme, F. pallidoroseum, and Phoma sorghina, were used. Panicles of a pot-grown mold-susceptible sorghum line, IS 10513, were spray inoculated with each fungus at five growth stages: flowering (F), milk (M), soft dough (S), hard dough (H), and physiological maturity (P), and were incubated in dew chambers for 0, 16, 24, 40, 48, and 72 h. Then, the plants were placed on greenhouse benches at 25 ± 1°C to allow grain mold infection to develop. Eight days after treatments, grains from F, M, and S stages were plated onto potato dextrose agar, while those from H and P stages were incubated in blotter paper humid chambers at 28 ± 1°C. Fungal colonization of grains were scored after 7 days. Results indicated a significant (P < 0.01) correlation between wetness duration and grain mold development at different stages of inoculation. Generally, with increasing wetness duration, there was an increase in grain infection by all six fungi. However, infection frequency varied among fungi and grain development stages, indicating that individual fungi might have different windows for maximum infection during the grain development stages.
Evaluation of Soil Fumigants Applied by Drip Irrigation for Liatris Production
Authors: Gerik J. S.
Published: May 2007

Cut-flower growers need alternatives to methyl bromide (MB) for pathogen and weed control. The efficacy of alternative chemicals applied by drip irrigation was tested in a cut-flower production system. In 2002, seven chemical formulations were tested: chloropicrin, iodomethane + chloropicrin, 1,3-dichloropropene + chloropicrin, sodium azide, metham sodium, furfural + allyl isothiocyanate, and furfural + metham sodium. In 2003, an additional treatment, dimethyl disulfide, was added. Most treatments reduced populations of Pythium ultimum and Fusarium oxysporum and increased stem height compared with the nontreated controls. Metham sodium, furfural + metham sodium, sodium azide, and chloropicrin significantly reduced incidence of Liatris stem rot caused by Sclerotinia sclerotiorum. Weed control was not acceptable either year for any treatments. Viable alternatives to MB for cut-flower production will require better treatments for weed control than was achieved in this study.
Natural Occurrence of a Potyvirus on Murraya koenigii in India
Authors: Chandel V. , Hallan V. , Zaidi A. A.
Published: May 2007

Murraya koenigii (L.) Spreng., a small, strong-smelling umbrageous tree with subcampanulate white flowers belonging to the family Rutaceae, is native to India and southeastern Asia (2). It is distributed across the Indian subcontinent excluding the higher elevations of the Himalayas. In India, the leaves are mainly used for culinary purposes. The leaves are commonly known as curry leaves or ‘sweet neem’. The whole plant including bark, root, leaves, fruits, and fruit pulp is used medicinally. This plant was reported to be a host of Citrus tristeza virus (1). In a survey of potyvirus incidence in the northwestern Himalaya foothills of the Kangra and Hamirpur districts in the state of Himachal Pradesh in 2004, M. koenigii plants showing mosaic symptoms on leaves, typical of a virus infection, were frequently observed. Symptomatic leaves were tested for the presence of several viruses using enzyme-linked immunosorbent assay with specific antibodies. Positive results were obtained with potyvirus group specific antibodies (Agdia, Elkhardt, IN) in triplicate analyses of 5 of 15 leaf samples tested. To further identify the infecting virus, RNA from plants was tested using universal potyvirus primer pair P9502 and CPUP (3) and reverse transcription-polymerase chain reaction to amplify a genome fragment encoding portions of the coat protein and the 3′UTR (3). An amplification product of the expected size (~800 bp) was obtained. The product was cloned into the pGem-T easy vector (Promega, Madison, WI), and three clones were sequenced. The sequence (GenBank Accession No. AJ852504) had 92% identity to Chili vein banding mottle virus, a potyvirus infecting pepper reported from Thailand (GenBank Accession No. U72193). To our knowledge, this is the first report of a potyvirus naturally occurring on a Murraya sp.

References: (1) K. Balaram and K. Ramakrishnan. Curr. Sci. 48:453, 1979. (2) J. D. Hooker. Flora British India 1:502, 1875. (3) R. A. A. van der Vlugt et al. Phytopathology. 89:148, 1999.
Outbreak of Powdery Mildew on Common Sage in Argentina
Authors: Madia M. , Gaetán S.
Published: May 2007

Common sage, Salvia officinalis L., is produced primarily in greenhouses for the culinary herb market in Argentina. Since 2003 during autumn and winter, powdery mildew symptoms have been repeatedly observed on potted common sage plants in commercial greenhouses located on the outskirts of Buenos Aires. The average disease incidence during this period was 85 to 90%. Circular, white, powdery patches developed on leaf surfaces and stems. Heavily infected leaves turned brown and died. Hyaline mycelium and nonlobed appressoria were observed. Conidiophores were simple with straight foot cells measuring 53.0 to 80.0 × 10.0 to 12.3 μm. Conidia were aseptate, hyaline, cylindrical to ovoid, measured 33.0 to 40.5 × 15.0 to 18.5 μm, did not contain fibrosine bodies, and were produced in chains. Cleistothecia were not observed. The pathogen was identified as Erysiphe cichoracearum DC (1). Pathogenicity was confirmed by gently pressing leaves displaying abundant sporulation onto the adaxial surface of healthy leaves. After 10 to 12 days, typical signs and symptoms of powdery mildew appeared on all inoculated plants. Pathogenicity tests were conducted in a greenhouse at 20 to 23°C and included 10 sage plants (five inoculated and five noninoculated). The experiment was performed twice, each time with the same result. Control plants did not show any signs or symptoms. E. cichoracearum DC was previously reported in the United States on Salvia sp. (2).To our knowledge, this is the first report of an outbreak of powdery mildew caused by E. cichoracearun on potted common sage plants produced in greenhouses in Argentina.

References: (1) H. J. Boesewinkel. Rev. Mycol. Tome 41:493, 1977. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.
First Report of Bacterial Leaf Spot Caused by Pseudomonas cichorii on Phlox paniculata in Italy
Authors: Garibaldi A. , Bertetti1 D. , Scortichini M. , Gullino M. L.
Published: May 2007

Phlox paniculata L. (fall phlox) is a perennial garden species belonging to the Polemoniaceae family. During the spring of 2003 and 2004, leaf spot symptoms were observed on fall phlox plants in some private gardens in the Biella area (northern Italy). Lesions were first observed on leaves at the collar level and later on the entire plant. Lesions started as water-soaked areas, which in few days developed on the upper side of the leaves into irregular, shrunken, reddish brown spots from 1 to 2 mm in diameter. Lesions on the lower surface sometimes had a translucent halo. In many cases, the leaves were completely withered. Disease was particularly severe during the spring and fall and its incidence ranged from 10 to 25%. No fungal structures were observed within the lesions. Small fragments of tissue from affected leaves were macerated in nutrient yeast dextrose broth (NYDA), and dilutions of the resulting suspension were streaked onto NYDA and potato dextrose agar (PDA). Isolations were made from at least 25 leaves. Plates were maintained at 22 ± 1°C for 48 h. No fungi were isolated from the spots on NYDA or PDA. Colonies typical of Pseudomonas species were consistently isolated on NYDA. Isolates were negative for levan, potato soft-rot (pectolytic activity), and arginine dehydrolase while positive for oxidase and hypersensitivity on tobacco leaves. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell protein analysis (1) indicated that the bacterium isolated was similar to Pseudomonas cichorii (Swingle) Stapp NCPPB 943 and 3283 strains. On King's medium B, (2) a typical fluorescent pigment was produced. The pathogen was identified as Pseudomonas cichoriii. Pathogenicity of 10 colonies was tested by growing inoculum in nutrient-broth shake cultures for 48 h, suspending bacterial cultures in water, diluting to 106 CFU/ml, and spraying 10 1-year-old healthy plants of P. paniculata. Ten control plants were sprayed with sterile nutrient broth. Inoculated and control plants were kept covered with plastic bags for 72 h. After 8 days in a growth chamber at 20 ± 1°C, leaf spots identical to those observed in the field developed on leaves of inoculated plants. Control plants remained symptomless. The pathogenicity test was repeated once. Bacteria were reisolated from the spots and identified as P. cichoriii. To our knowledge, this is the first record of bacterial leaf spot of Phlox paniculata in Italy as well as in the world.

References: (1) D. H. Bergey et al. Bergey's Manual of Determinative Bacteriology. Williams and Wilkins, Baltimore, MD, 1994. (2) E. O. King et al. J. Lab. Clin. Med. 44:301, 1954.
Application of Acibenzolar-S-Methyl Enhances Host Resistance in Tomato Against Ralstonia solanacearum
Authors: Pradhanang P. M. , Ji P. , Momol M. T. , Olson S. M. , Mayfield J. L. , Jones J. B.
Published: May 2007

The chemical elicitor acibenzolar-S-methyl (ASM; Actigard 50 WG), which induces systemic acquired resistance (SAR), was investigated to determine the effect on bacterial wilt of tomato caused by Ralstonia solanacearum on moderately resistant cultivars under greenhouse and field conditions. In greenhouse experiments, ASM was applied as foliar spray and/or soil drench (3 μg/ml) before and as foliar spray (30 μg/ml) after transplanting. The chemical elicitor was ineffective in reducing bacterial wilt incidence on susceptible tomato cultivars Equinox and FL 47 when plants were inoculated with R. solanacearum. However, greenhouse studies indicated that ASM significantly enhanced resistance in cultivars with moderate resistance to bacterial wilt such as Neptune and BHN 466. It appeared that ASM-mediated resistance was partially due to prevention of internal spread of R. solanacearum toward upper stem tissues of tomato plants. The effect of ASM on moderately resistant cultivars was consistent in field experiments conducted in 2002 and 2003 in Quincy, FL, where bacterial wilt incidence was significantly reduced in ASM-treated BHN 466 (in 2002), FL 7514 (in 2003), and Neptune (both years) plants. ASM-treated BHN 466 and FL 7514 produced significantly higher tomato yield than the untreated controls. This is the first report of ASM-mediated control of bacterial wilt under field conditions, which suggests that use of this treatment for moderately resistant genotypes may be effective for control of bacterial wilt of tomato.
Detection of a Phytophthora sp. Causing Asparagus Spear and Root Rot in Michigan
Authors: Saude C. , Hausbeck M. K. , Hurtado-Gonzales O. , Lamour K. H.
Published: May 2007

In the spring of 2004, a Phytophthora sp. was isolated from asparagus (Asparagus officinalis) spears, roots, and dormant crowns from several fields in Oceana and Ingham counties in Michigan. Symptomatic spears were often curved, had water-soaked lesions slightly above or below the soil line or were shriveled at the site of infection or both. Infected storage roots had water-soaked lesions but were not soft at the lesion site. Infected crowns had fewer roots than healthy crowns. In the laboratory, plant tissues were rinsed in tap water and blotted dry. Sections from the edge of lesions were placed aseptically onto BARP (25 ppm of benomyl, 100 ppm of ampicillin, 30 ppm of rifampicin, and 100 ppm of pentachloroni-trobenzene) amended unclarified V8 juice agar and incubated at 25°C for up to 7 days. Phytophthora sp. isolates recovered from the infected material produced ovoid, nonpapillate, noncaducous sporangia and amphigy-nous oospores on isolation media. Single-sporangium cultures made for each isolate were stored long term in sterile 2-ml microcentrifuge tubes containing two 7-mm mycelial plugs, two sterile hemp seeds, and 1 ml of sterile distilled water. Sporangia produced on dilute V8 juice agar averaged 45 μm long × 26 μm wide and oospores were 25 to 30 μm in diameter. Chlamydospores were not observed. Five detached ‘Jersey Knight’ spears were inoculated with a 7-mm mycelial plug from the edge of actively growing 5-day-old cultures and incubated at 23 to 25°C for 5 to 7 days in a moist chamber. After 3 days, water-soaked lesions and shriveling and curving of the spears were visible on all inoculated spears. The pathogen was always reisolated from the lesion edge. No symptoms were observed when spears were inoculated with sterile V8 juice agar plugs. DNA was extracted from representative isolates, and the nuclear ribosomal internal transcribed spacer (ITS) region was amplified with ITS6 and ITS4 primers and sequenced. A BLAST search of the NCBI database with the ITS sequence revealed Phytophthora sp. UQ2141, Accession No. AF266795, as the closest match with 99% sequence similarity. These results, coupled with the morphological characteristics of the isolates, indicate that the Phytophthora sp. isolated from asparagus in Michigan is among the constituents of Phytophthora spp. included in the P. megasperma clade 6 (2), whose taxa are currently being reevaluated. Although a Phytophthora sp. has been described previously on asparagus (1,3), this is the first report, to our knowledge, of a Phytophthora sp. on asparagus in Michigan. The occurrence of excessive rainfall in the spring of 2004 is likely responsible for widespread disease and considerable yield losses in production fields.

References: (1) P. A. Ark and J. T. Barrett. Phytopathology 28:754, 1938. (2) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) V. Vujanovic et al. Plant Dis. 87:447, 2003.
Southern Blight of Areca Palm (Chrysalidocarpus lutescens) Caused by Sclerotium rolfsii in California
Authors: Koike S. T.
Published: May 2007

Areca palm (Chrysalidocarpus lutescens) is a popular ornamental palm that can be grown outdoors in mild climates and is commonly used as an indoor ornamental plant. During 2005, commercial palm producers lost significant numbers of areca palm seedlings grown in transplant trays to a crown rot disease. Initial symptoms consisted of a light brown discoloration of stems near the soil line. As disease progressed, the brown discoloration extended up the stem and down into the crown, foliage became gray green, and the entire plant then dried up and died. Extensive, white, cottony mycelium and numerous sclerotia developed externally on the lower stem, crown, attached palm seed, and surrounding peat moss medium. Mycelial growth was so extensive that the fungus often grew from one transplant tray cell, bridged across the plastic cell border, and into an adjacent transplant cell. Tan, spherical sclerotia measured approximately 1 mm in diameter. Isolations from diseased plants resulted in the recovery of the same white fungus that produced sclerotia. On the basis of sclerotia morphology and the presence of clamp connections at hyphal septa, the fungus was identified as Sclerotium rolfsii. Pathogenicity was tested by growing isolates on potato dextrose agar, drying the resulting sclerotia for 48 h, and then depositing 8 to 10 sclerotia at the base of healthy areca palm seedlings. Five isolates were tested using 40 plants per isolate. Non-inoculated controls were also included. All plants were incubated in a greenhouse at 22 to 25°C. After 2 weeks, inoculated plants began to show brown necrosis at the base of the stems; by the third week, plants began to dry up, and mycelium and sclerotia developed on the crowns. S. rolfsii was reisolated from all necrotic crown and stem tissues. Noninoculated controls did not develop any disease symptoms. To my knowledge, this is the first report of southern blight of C. lutescens in California. This disease has been reported on areca palms and other foliage plants in the southern United States and Central and South America (1). Circumstantial evidence (the disease occurred on palm seedlings that were planted in previously unused transplant trays and new peat moss rooting medium) suggests that the pathogen may have been brought in on palm seed. In the nursery, other foliage plants that are susceptible to S. rolfsii were planted in the same rooting medium but were unaffected by southern blight.

Reference: (1) A. R. Chase. Compendium of Ornamental Foliage Plant Diseases. The American Phytopathological Society. St. Paul, MN, 1987.
White Mold of Houndstongue (Cynoglossum officinale) Caused by Sclerotinia sclerotiorum in Canada
Authors: Huang H. C. , Erickson R. S. , Van Hezewijk B. , De Clerck-Floate R.
Published: May 2007

Houndstongue (Cynoglossum officinale L.) is a rangeland weed introduced into Canada from Eurasia, and it can be highly toxic to livestock feeding in pastures (3). During 2004, houndstongue plants near Creston, BC, Canada developed water-soaked lesions with white mycelia and black sclerotia on leaves and crowns. Isolations from diseased leaf tissues and sclerotia on potato dextrose agar (PDA) at 20°C for 5 to 7 days produced fungal colonies with formation of black sclerotia 5 to 10 mm in diameter. A single hyphal tip isolate from houndstongue. Ss-HT-C. was compared with a sunflower isolate of S. sclerotiorum, sun-87 (1), for morphology and pathogenicity. For apothecial production, Ss-HT-C and sun-87 were grown on PDA in petri dishes at 10°C for 10 weeks, and sclerotia produced were harvested, placed on moist vermiculite in petri dishes, and incubated at 20°C under light for 3 weeks. Mature apothecia were excised, stained with acid fuchsin, mounted on slides, and examined for asci and ascospores with a microscope. There were no morphological differences between Ss-HT-C and sun-87, each producing an ascus with eight binucleate, elliptical ascospores, measuring 4 × 10 μm (width × length), supporting the identity of Ss-HT-C as S. sclerotiorum (2,4). For pathogenicity tests of Ss-HT-C and sun-87, mycelial plugs (8 mm in diameter) were removed from the margin of colonies grown on PDA for 5 days at 20°C, and placed on leaves of C. officinale plants that were grown in a greenhouse (20 ± 4°C) to the rosette stage. Inoculated plants were covered with clear plastic bags, kept in the same greenhouse for 3 days, and the diameters of the leaf lesions developed at inoculation sites were measured. The experiment was run twice with 30 plants per isolate and five leaves per plant. Uninoculated plants covered with plastic bags were used as controls. Experiments used a completely randomized design. Results of leaf inoculations showed that Ss-HT-C and sun-87 were pathogenic to hound-stongue. There was no statistical difference between isolates or trials. The frequency of leaves with lesions was 90% for Ss-HT-C and 93% for sun-87. The mean leaf lesion diameters were 32 and 35 mm for Ss-HT-C and sun-87, respectively. Leaves of control plants remained healthy. S. sclerotiorum was reisolated from leaves with lesions, but not from controls. After 14 to 21 days, new sclerotia, 5 to 10 mm in diameter, were formed on leaves of inoculated plants. The plants eventually died. This study confirms that S. sclerotiorum is the causal agent for the disease of hound-stongue in Canada, and to our knowledge, this is the first world record of infection of this weed by S. sclerotiorum.

References: (1) H. C. Huang and G. C. Kozub. Plant Prot. Bull. 31:333, 1989. (2) L. Kohn, Phytopathology 69:881, 1979. (3) J. A. Pfister et al. J. Range Manag. 45:254, 1992. (4) J. A. L. Wong and H. J. Willetts, J. Gen. Microbiol. 112:29, 1979.
First Report of Alternaria raphani Causing Black Patches on Chinese Radish During Postharvest Storage in Canada
Authors: Su X. J. , Yu H. , Zhou T. , Li X.-Z. , Gong J. , Chu C. L.
Published: May 2007

During November of 2003, Chinese radishes (Raphanus sativus cv. Taibai) harvested in St. Catharines, Ontario and stored in less than 1°C with 98% relative humidity (RH) and 5°C with 96% RH showed symptoms of black and dark brown, irregular patches, with or without decay. The symptoms were closely associated with skin wounds and damaged root hairs. Fungal DNA was extracted from discolored skin samples peeled from a radish, and 18S rRNA genes were amplified with fungal-specific PCR primers (1) EF4f (5′-ggaagggrtgtatttattag-3′) and EF3r (5′-tcctctaaatgaccagtttg-3′). The cloned genes were sequenced using the primer EF4f and compared directly with nonredundant nucleotides in GenBank with BLAST. The results indicated that more than 75% of the fungal microflora on the diseased radish were Alternaria spp. Alternaria sp. was successfully isolated from discolored and decayed radish tissues. Morphological and molecular identification indicated that the isolated Alternaria sp. cultures belong to A. raphani, which was previously reported to cause leaf and pod blight on radish (2). For pathogenicity studies, a spore suspension (1 × 105 conidia/ml) obtained from a 4-week-old A. raphani culture was used to inoculate ‘Taibai’ Chinese radish tissues, including inner tissues and wounded and nonwounded skin. All tests were carried out at room temperature (22 to 24°C). On inner tissue and wounded skin, symptoms of dark brown-to-black patches appeared 2 days after inoculation and progressed with time. No symptoms developed on the noninoculated control or the nonwounded, inoculated treatment. A. raphani was reisolated from symptomatic tissue. Further evidence of pathogenicity was obtained by an additional inoculation and observation of symptoms. The results indicated that A. raphani was the causal agent of the black patches observed on Chinese radish, and to our knowledge, this is the first report that A. raphani could cause a postharvest disease on Chinese radish in storage.

References: (1) J. D. Van Elsas et al. J. Microbiol. Methods 43:133, 2000. (2) M. S. Sangwan et al. J. Mycol. Plant Pathol. 32:125, 2002.
Significance of Preventing Primary Infections by Didymella rabiei and Development of a Model to Estimate the Maturity of Pseudothecia
Authors: Shtienberg D. , Gamliel-Atinsky E. , Retig B. , Brener S. , Dinoor A.
Published: May 2007

The significance of preventing primary infections resulting from the teleomorph stage of Didymella rabiei was tested in field experiments in 1998 and 2000. Control efficacy was greater and yield and its components were higher in plots where the fungicide difenoconazole had been sprayed in time to protect the plants from infections resulting from airborne ascospores than in plots where sprays were not applied on time. Forty empirical models reflecting the influence of temperature and interrupted wetness on initial maturation of D. rabiei pseudothecia were developed and verified by using data recorded in chickpea fields in 1998. Seven of the models then were validated with data recorded in 1999 and 2000. The following model provided the best predictions: starting at the beginning of the rainy season (October to December), the predictor of the model was assigned one severity value unit when there was a rain event (1 day or more) with ≥10 mm of rain and an average daily temperature (during the rainy days) of ≤15°C. According to the model, pseudothecia mature after accumulation of six severity values and ascospores will be discharged during the following rain.
Distribution of Pythium porphyrae, the Causal Agent of Red Rot Disease of Porphyrae spp., in the Ariake Sea, Japan
Authors: Kawamura Y. , Yokoo K. , Tojo M. , Hishiike M.
Published: May 2007

Distribution of Pythium porphyrae, the causal agent of red rot disease of Porphyra spp., in seafloor sediment was investigated in the Ariake Sea, Japan. A total of 170 samples of each 200 ml of sediment was collected from the seafloor at a total of 13 sites across the sea from 1998 to 2002. Each sample was filtered through two layers of nylon mesh with pore sizes of 100 and 15 μm. The residue on 15 μm mesh was assayed by a soil plating technique using a semiselective medium for P. porphyrae and by polymerase chain reaction (PCR) using species-specific primers. P. porphyrae were detected in 6 out of 13 sites and 2 out of 10 sites surveyed by soil plating and PCR, respectively. The representative isolate of P. porphyrae from the sediment was identical to the Porphyra thallus isolate from the same sea based on pathogenicity to the thallus, morphology, and rDNA internal transcribed spacer sequences. Recovery of P. porphyrae propagules in the sediment was up to 60 CFU per 100 ml of the fresh sample and was consistently higher in May than in the other months. The results suggest that P. porphyrae is distributed in the seafloor sediment in a wide area of the Ariake Sea.
Effect of Seeding Rate and Seed Treatment Fungicides on Agronomic Performance, Fusarium Head Blight Symptoms, and DON Accumulation in Two Winter Wheats
Authors: Schaafsma A. W. , Tamburic-Ilincic L.
Published: May 2007

Fusarium head blight (FHB), caused by Fusarium graminearum, is an important disease of wheat (Triticum aestivum). FHB reduces yield and quality, and the pathogen produces several toxins in the grain, the most important being deoxynivalenol (DON). In North America, the foliar fungicide tebuconazole is used to reduce FHB symptoms and DON accumulation. Because of the narrow window required for its application, uniform flowering of wheat is important. The objective of this study was to investigate the influence of variety, seeding rate, and seed treatment fungicides on the flowering period of winter wheat and their effect on FHB symptoms and DON accumulation. The seed of two winter wheat varieties (Pioneer 25W60 and Pioneer 25R57) was treated with Dividend XL (difeconazole+metalaxyl), Vitaflo 280 (thiram+carbathiin), Raxil (tebuconazole), and Baytan 30 (triadimenol) and planted at 320, 480, and 640 seeds per m2 for each treatment at Ridgetown, ON, Canada in 2000 and 2001. The plots were sprayed with tebuconazole at 50% anthesis and inoculated with F. graminearum 3 days later. Increased seeding rate increased the number of emerged plants, tillers, spikes per m2, and yield. All seed treatments, compared to nontreated controls, increased plant emergence and number of spikes per m2, and all except tebuconazole increased tillering and yield. Increased seeding rate decreased the length of flowering period. As flowering period increased, FHB index and DON level decreased, suggesting that greater infection was linked to more uniform flowering.
First Report of Sclerotinia minor on Sida spinosa in North Carolina
Authors: Hollowell J. E. , Shew B. B.
Published: May 2007

The soilborne fungus Sclerotinia minor Jagger is a major pathogen of peanut (Arachis hypogaea L.) in North Carolina, Virginia, Oklahoma, and Texas. The pathogen attacks several winter annual weed species (1). Economic crops that are hosts to S. minor are seldom grown in rotation with peanut; therefore, its pathogenicity on weed species is of importance in understanding how inoculum densities are maintained between peanut crops. During September 2004, signs of fluffy, white mycelium, small, black sclerotia, and symptoms of bleached leaves and stems were observed on prickly sida (Sida spinosa L.) in a peanut field in Bertie County, NC. Plants of prickly sida with similar signs and symptoms were observed previously in a Chowan County, NC peanut field. Prickly sida is one of several weed species commonly found in peanut fields and rotational crops in agricultural areas of northeastern North Carolina. Cultivation and herbicides usually keep prickly sida under control in the early part of the growing season, but as the summer progresses into early fall, it can become prevalent, as was true in the two fields reported here. Symptomatic tissues were excised into 1- to 2-cm sections, rinsed in tap water, blotted dry, and placed on potato dextrose agar (PDA). The pure cultures with small, black irregular-shaped sclerotia (<2 mm) scattered abundantly over the culture surface were distinctive of S. minor. Pathogenicity was determined by inoculating stems of two symptom-free prickly sida plants with 2-day-old fungal mycelium. Mycelial agar plugs, 4 mm in diameter, were held in place with self-sticking bandaging gauze. Plants were misted, enclosed in plastic bags, and incubated at ambient temperature (24°C) on the laboratory countertop. Fluffy mycelium developed on the stems in 2 days and water-soaked leaves and bleached lesions formed within 6 days after inoculation. Following the incubation period, S. minor was reisolated from the inoculated plants. Two plants treated similarly with plugs of pure PDA remained healthy over the incubation period. The performance of Koch's postulates confirmed that prickly sida is a host of S. minor. To our knowledge, this report of S. minor on prickly sida is also the first report of a plant in the family Malvaceae as a host of S. minor (2).

Reference: (1) J. E. Hollowell et al. Plant Dis. 87:197, 2003. (2) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997.
First Report of Beet pseudo-yellows virus on Cucurbita moschata and C. pepo in Costa Rica
Authors: Hammond R. W. , Hernandez E. , Mora F. , Ramirez P.
Published: May 2007

In early 2004, severe yellowing and chlorosis were observed in field-grown cucurbits in Costa Rica. Symptoms resembled those of the genus Crinivirus (family Closteroviridae), and large populations of whiteflies were observed in the fields and on symptomatic plants. Although the identity of the whiteflies on the curcurbits was not determined, the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) is known to be present in the region from where the samples were obtained. To identify the causal agent of the disease, leaf samples of symptomatic plants were collected from several farms. The leaf samples were dried with silica gel. Total RNA was extracted from leaf tissue of eight representative samples (two from healthy plants and six from symptomatic plants) using TRI Reagent (Molecular Research Inc., Cincinnati, OH). Reverse transcription-polymerase chain reactions (RT-PCR) containing one primer set at a time were performed using the Titan One-Tube RT-PCR kit (Roche Diagnostics Corp., Chicago IL) and primers specific for genes of cucurbit-infecting criniviruses, including the coat protein gene of Cucurbit yellow stunting disorder virus (3) and the minor coat protein gene (CPm) of Beet pseudoyellows virus (BPYV) (4). Primers specific for the heat shock protein (HSP) gene (CYHSPF 5′ GAGCGCCGCACAAGTCATC 3′ and CYHSPR 5′ TACCGCCACCAAAGTCATACATTA 3′) of Cucumber yellows virus (CYV, a strain of BPYV) (1) were designed based on published sequence data. In addition, primers specific for Cucurbit aphid-borne yellows virus (2) and melon yellowing-associated flexivirus (MYVF 5′ GGCTGGCAACATGGAAACTGA 3′ and MYVR 5′ CTGAAAAGGCGATGAACTA TTGTG 3′) were used in RT-PCR reactions. Amplified DNA fragments of 333 and 452 bp were obtained in each of two samples obtained from symptomatic plants and only in separate reactions containing BPYV and CYV primer sets, respectively. Nucleotide sequence analysis of all purified PCR products verified their identity as variants of BPYV, with 97 and 99% sequence identity with reported CPm and HSP sequences, respectively. The two samples from Cucurbita moschata Duch. (ayote or squash) and Cucurbita pepo L.(escalopini or sunburst squash) were taken from a region around Paraiso, Cartago, Costa Rica. To our knowledge, this is the first report of BPYV in Costa Rica. The economic impact on cucurbit production has not yet been determined. Studies are underway to determine the prevalence and genetic variability of BPYV isolates in Costa Rica.

References: (1) S. Hartono et al. J. Gen. Virol. 84:1007, 2003. (2) M. Juarez et al. Plant Dis. 88:907, 2004. (3) L. Rubio et al. J. Gen. Virol. 82:929, 2001. (4) I. E. Tzanetakis et al. Plant Dis. 87:1398, 2003.
Effect of Fungicide Treatments and Sanitation Practices on Brown Rot Blossom Blight Incidence, Phytotoxicity, and Yield for Organic Sour Cherry Production
Authors: Holb I. J. , Schnabel G.
Published: May 2007

Demand for organically grown fruit, including sour cherry, is rising in Europe and the United States, but the limited tools for disease management have not been thoroughly investigated. In this study, management of brown rot blossom blight, caused by Monilinia laxa, was examined for organic sour cherry production in Hungary. Combinations of sanitation practices and fungicide treatments, including copper hydroxide, lime sulfur, and micronized and nonmicronized wettable sulfur, were investigated in 2 years and two cultivars. The effect of fungicide treatments on yield and phytotoxicity on spur-leaf clusters was also determined. Among fungicide treatments suitable for organic production, copper hydroxide and lime sulfur alone or in combination with micronized wettable sulfur were most effective for blossom blight control when applied twice (at closed blossom and full bloom) or three times (at closed blossom, full bloom, and petal fall) during bloom. Both treatments were not as effective as the conventional standard and caused more damage on spur-leaf clusters during wet weather conditions, but significantly increased crop yield compared with the untreated control or wettable sulfur treatments. Micronized and nonmicronized sulfur applied up to three times during bloom were equally effective, did not impact yield, were not phytotoxic, and reduced blossom blight compared with the untreated control. Sanitation (the removal of blighted twigs and mummified fruit) reduced blossom blight in both cultivars compared with nonsanitized plots when disease pressure was high. The need for an integrated approach to effectively manage blossom blight in organic sour cherry production is discussed. This is the first in-depth characterization of cultural and chemical brown rot blossom blight control options for organic sour cherry production.
First Report of Sclerotinia Stem Rot and Watery Soft Rot Caused by Sclerotinia sclerotiorum on Sand Rocket (Diplotaxis tenuifolia) in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Several species of Diplotaxis (D. tenuifolia, D. erucoides, and D. muralis), known as wild or sand rocket, are widely cultivated in Italy. Rocket is used in Mediterranean cuisine as salad, a component of packaged salad products, and as a garnish for food. In winter 2003, a severe disease was observed on D. tenuifolia grown in unheated glasshouses on commercial farms near Albenga in northern Italy. Initial symptoms included stem necrosis at the soil level and darkening of leaves. As stem necrosis progressed, infected plants wilted and died. Wilt, characterized by the presence of soft and watery tissues, occurred within a few days on young plants. The disease was extremely severe in the presence of high relative humidity and mild temperature (15°C). Necrotic tissues became covered with white mycelium that produced dark sclerotia. Diseased stem tissue was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm streptomycin sulfate. Sclerotinia sclerotiorum (1) was consistently recovered from infected stem pieces. Sclerotia observed on infected plants measured 1.23 to 3.00 × 1.40 to 5.38 mm (average 2.10 × 2.85 mm). Sclerotia produced on PDA measured 1.00 to 4.28 × 1.00 to 6.01 mm (average 2.38 × 3.23 mm). Pathogenicity of three isolates obtained from infected plants was confirmed by inoculating 30-day-old plants of D. tenuifolia grown in 18-cm-diameter pots in a glasshouse. Inoculum, 2 g per pot of wheat kernels infested with mycelium and sclerotia of each isolate, was placed on the soil surface around the base of each plant. Three replicates of five pots each were used per isolate. Noninoculated plants served as controls. The inoculation trial was repeated once. All plants were kept at temperatures ranging between 10 and 26°C (average 15°C) with an average relative humidity of 80% and were watered as needed. Inoculated plants developed symptoms of leaf yellowing within 12 days, soon followed by the appearance of white mycelium and sclerotia, and eventually wilted. Control plants remained symptomless. S. sclerotiorum was reisolated from inoculated plants. To our knowledge, this is the first report of infection of D. tenuifolia by S. sclerotiorum in Italy as well as worldwide. The disease currently has been observed in the Liguria Region but not yet in other areas where sand rocket is cultivated. The economic importance of this disease for the crop can be considered medium at the moment, but is expected to increase in the future.

Reference: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 75, 1949.
First Report of the Aecial State of Melampsora larici-populina on Larix spp. in North America
Authors: Grondin J. , Bourassa M. , Hamelin R. C.
Published: May 2007

Melampsora larici-populina Kleb. was reported for the first time in eastern North America during 2002, on Populus spp., its telial host (1). M. larici-populina, a heteroecious rust, alternates between species of Populus and Larix. Since M. larici-populina was observed again in 2003, we investigated the possibility that its basidiospores may infect larch (Larix spp.) resulting in spermogonia and aecia. Identification of Melampsora species from aeciospore morphology is difficult but urediniospores are distinctive. This is important since the native M. medusae also alternates between Populus and Larix spp. During the spring of 2004, aecia were observed on needles of exotic (Larix decidua Mill. and L. leptolepis (Siebold and Zucc.) Gordon) and indigenous (L. laricina (K. Koch)) larch in an arboretum in Lotbinière (Quebec, Canada) where M. larici-populina has previously been found. Larch needles with yellow blister-like fructifications were collected in May 2004 and fixed on top of petri plates to allow aeciospore release onto leaves of Jackii poplar (Populus balsamifera L. × P. deltoides Marsh.). After approximately 10 days, uredinia appeared on the abaxial surface of the poplar leaves. Some of the many needles collected yielded uredinia cultures on Jackii poplars. The majority of these cultures were identified as being M. larici-populina; one was M. medusae. M. larici-populina urediniospores were 32 to 48 μm long and possessed a characteristic apical bald spot. DNA was extracted from aecia and uredinia, and the internal transcribed spacer (ITS) of the ribosomal RNA gene was amplified in real-time polymerase chain reaction (PCR) by specific primers for M. medusae or M. larici-populina created from sequences (GenBank Accession Nos. AY429656 and AY429657). The 120 base pairs target fragments amplified only with the M. larici-populina specific primers with the 14 samples that were identified as M. larici-populina by morphological characteristics of the urediniospores. No PCR amplification was obtained with M. medusae primers. These results were not unexpected since larch has been previously reported as an aecial host of M. larici-populina elsewhere (2). The ability of M. larici-populina to overwinter and complete its life cycle has important consequences since it proves that it is established and can go through sexual reproduction. A complete life cycle in eastern North America may allow M. larici-populina to generate pathogenic variation that will challenge poplar breeders in this region.

References: (1) L. Innes et al. Plant Dis. 88:85, 2004. (2) G. Newcombe et al. Plant Dis. 78:1218, 1994.
Natural Occurrence of Viruses in Lycopersicon spp. in Ecuador
Authors: Soler S. , López C. , Nuez F.
Published: May 2007

The Andean region is home of important genetic diversity for the genus Lycopersicon. A survey of three asymptomatic populations of L. hirsutum, 17 of L. parviflorum, 188 of L. pimpinellifolium, and four cultivated populations of L. esculentum was made in nine departments of Ecuador. Samples were analyzed serologically for Tomato spotted wilt virus (TSWV), Tomato mosaic virus (ToMV), Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), Potato virus Y (PVY), Potato virus X (PVX), Groundnut ringspot virus (GRSV), Tomato chlorosis spot virus (TCSV), and Pepino mosaic virus (PepMV). Samples positive as determined using double-antibody sandwich enzyme-linked immunosorbent assay (absorbance values three times higher than negative controls) were analyzed using reverse transcription-polymerase chain reaction (RT-PCR) with virus-specific primers. L pimpinellifolium was the only species of the four found to be infected with viruses. In the department of Manabí, ToMV was detected in 15 of 16 plants from one population, but only a single plant was infected with PepMV. In this department, PepMV was also detected in a single-plant population that corresponded to a volunteer plant found in the wild and TSWV was detected in another plant. In Esmeraldas and Guayas, two single-plant populations were found infected with PepMV and CMV, respectively. TMV, PVY, PVX, GRSV, and TCSV were not detected in this survey. Specific primers were selected for ToMV (To1/To2, genome coordinates 3498-3518/4902-4922, AJ417701), PepMV (Pe1/Pe2 genome coordinates 5030-5050/5913-5935, AJ606359), CMV (Cm1/Cm2 genome coordinates 541-561/1756-1779, D00356), and TSWV (Ts1/Ts2 genome coordinates 4078-4101/4738-4769, AF208498). Amplicons of the expected size were obtained using RT-PCR and then cloned and sequenced. DNA fragments of ToMV, PepMV, and TSWV showed identities greater than 99% with respective sequences in the GenBank database. The highest identity of the CMV DNA fragment was 92% with an isolate from Indonesia (AB042292). The occurrence of viruses such as CMV, ToMV, and TSWV in coastal Ecuador was not surprising. However, infected plants were not found among the samples collected in the departments of Azuay, Carchí, El Oro, Imbabura, Loja, and Pichincha in eastern Ecuador. L. chilense, L. chmielewskii, L. parviflorum, and L. peruvianum were previously reported as natural hosts of PepMV in central and southern Peru (2), and the virus was also detected in L. esculentum in Chile (1). Our results show that PepMV now occurs in wild L. pimpinellifolium populations along the Pacific coast of the South American continent and that it must have efficient means of transmission, although no specific vectors have as yet been identified for this virus. To our knowledge, this is the first report of PepMV in Ecuador and L. pimpinellifolium as a natural host of PepMV.

References: (1) M. Muñoz et al. Fitopatología 37:67, 2002. (2) S. Soler et al. J. Phytopathol. 150:49, 2002.