First Report of Downy Mildew on Gynura aurantiaca Caused by Plasmopara halstedii sensu lato in Florida

Gynura aurantiaca is a member of the Senecionaea tribe of the Asteraceae, indigenous to Java. Commonly known as purple velvet plant, this tropical species is well adapted to landscapes in South Florida, but is mostly seen as a potted plant for use in the interiorscape. During February 2013, a local nursery submitted Gynura aurantiaca samples to the Florida Extension Plant Diagnostic Clinic in Homestead, FL, where 30% of 1,000 plants were affected. Downy, white mycelium was observed on the abaxial leaf surface, and the adaxial surface of affected leaves appeared darker in color. Severely affected leaves began to curl as the tissue turned necrotic. The pathogen was identified as Plasmopara halstedii (Farl.) Berl. & De Toni based on the presence of coenocytic mycelium, and right-angled, monopodially branched sporangiophores with sporangia that were hyaline, obvoid to elliptical, and measuring 21 × 29 × 17 to 21 μm (Delanoe 1972). Molecular identification was conducted by extracting pathogen DNA using the QIAGEN Plant DNA kit (QIAGEN, Gaithersburg, MD). PCR of the 5′ terminal domain of the nuclear DNA coding for the large subunit (LSU rDNA) was performed with primers NL1 and LR3 (Kurtzman et al. 1998; Vilgalys and Hester 1990). The PCR product was purified with the QIAquick kit (QIAGEN) according to the manufacturer’s instructions and sequenced bidirectionally. The sequence from our isolate (GenBank Accession No. KR028988) was nearly identical (exhibited 97% nucleotide identity; 98% query coverage; E value = 0.0) to an isolate of P. halstedii (EF553469). A phylogenetic analysis was performed using the obtained sequence data and fifteen Plasmopara sequences from GenBank and a Fusarium solani accession as an outgroup (Maximum Likelihood, Tamura-Nei model). Our isolate grouped with P. halstedii with high bootstrap support (98% bootstrap value, 1,000 replicates) further supporting identification as P. halstedii. Pathogenicity of the sequenced isolate was evaluated in shade-house experiments. Two-month-old Gynura aurantiaca plants were inoculated with a sporangial suspension (1 × 10⁶ sporangia/ml) of P. halstedii that was collected by washing sporangia from the abaxial surface of purple passion leaves using autoclaved distilled water. Inoculum or autoclaved water was sprayed over the foliage until runoff. Six plants were sprayed per treatment and the experiment was repeated twice. Inoculated plants were placed in a shade house (73% shade) when temperatures ranged from 17 to 28°C with 78 to 98% relative humidity. Plants were observed for disease development, and pathogen sporulation occurred within seven days of inoculation. No symptoms developed on the control plants. To our knowledge, this is the first report of Plasmopara halstedii causing downy mildew on Gynura aurantiaca. Gynura aurantiaca is highly valued for its stunning purple foliage and low input production costs, but a disease such as downy mildew has the potential to substantially reduce if not eliminate commercial production.This is the publisher’s final pdf. The published news item is copyrighted by American Phytopathological Society and can be found at: http://apsjournals.apsnet.org/loi/pdi

Self-Catalyzed Vapor-Liquid-Solid Growth of Lead Halide Nanowires and Conversion to Hybrid Perovskites

Lead halide perovskites (LHPs) have shown remarkable promise for use in photovoltaics, photodetectors, light-emitting diodes, and lasers. Although solution-processed polycrystalline films are the most widely studied morphology, LHP nanowires (NWs) grown by vapor-phase processes offer the potential for precise control over crystallinity, phase, composition, and morphology. Here, we report the first demonstration of self-catalyzed vapor-liquid-solid (VLS) growth of lead halide (PbX2; X = Cl, Br, or I) NWs and conversion to LHP. We present a kinetic model of the PbX2 NW growth process in which a liquid Pb catalyst is supersaturated with halogen X through vapor-phase incorporation of both Pb and X, inducing growth of a NW. For PbI2, we show that the NWs are single-crystalline, oriented in the Ÿ¨1Ì…21Ì…0Ÿ© direction, and composed of a stoichiometric PbI2 shaft with a spherical Pb tip. Low-temperature vapor-phase intercalation of methylammonium iodide converts the NWs to methylammonium lead iodide (MAPbI3) perovskite while maintaining the NW morphology. Single-NW experiments comparing measured extinction spectra with optical simulations show that the NWs exhibit a strong optical antenna effect, leading to substantially enhanced scattering efficiencies and to absorption efficiencies that can be more than twice that of thin films of the same thickness. Further development of the self-catalyzed VLS mechanism for lead halide and perovskite NWs should enable the rational design of nanostructures for various optoelectronic technologies, including potentially unique applications such as hot-carrier solar cells

Use of a Natural Isotopic Signature in Otoliths to Evaluate Scale-Based Age Determination for American Shad

We used delta O-18 signatures in otoliths as a natural tag for hatch year to evaluate the scale-based age determination method used for adult American shad Alosa sapidissima in the York River, Virginia. Juveniles of the 2002 year-class exhibited high delta O-18 values in otolith cores that identified adult members of the cohort as they returned to spawn. Recruitment of the 2002 cohort was monitored for three consecutive years, identifying age-4, age-5, and age-6 individuals of the York River stock. The scale-based age determination method was not suitable for aging age-4, age-5, or age-6 American shad in the York River. On average, 50% of the individuals from the 2002 year-class were aged incorrectly using the scale-based method. These results suggest that the standard age determination method used for American shad is not applicable to the York River stock. Scientists and managers should use caution when applying scale-based age estimates to stock assessments for American shad in the York River and throughout their range, as the applicability of the scale-based method likely varies for each stock. This study highlights a promising new direction for otolith geochemistry to provide cohort-specific markers, and it identifies several factors that should be considered when applying the technique in the future

Bacterial Soft Rot of <i>Oncidium</i> Orchids Caused by a <i>Dickeya</i> sp. (<i>Pectobacterium chrysanthemi</i>) in Florida

Oncidium orchids have been subjected to extensive cultivation in the pot-plant and cut flower industries because of their attractive and numerous flowers. In August 2008, approximately 50 Oncidium ‘Gower Ramsey’ orchids were discovered at a commercial orchid nursery in South Florida with brown, macerated leaves typical of soft rot disease reported in other orchids. Ten plants were selected, and sections were removed from the edge of symptomatic tissue and bacteria were isolated according to the method described by Schaad et al. (3). All isolates were gram negative, anaerobic, degraded pectate, grew at 37°C, produced blue-to-brown pigment on nutrient agar-glycerol-manganese chloride (NGM) medium (1), were sensitive to erythromycin, oxidase negative, and positive for phosphatase and indole production. Further analyses were performed on four of the isolates. MIDI analysis (Sherlock version TSBA 4.10; Microbial Identification, Newark, DE) identified the isolates as Erwinia chrysanthemi (SIM 0.880 to 0.929). Polymerase chain reactions were performed with the 16S primers 27f and 1495r (4) and 1,423 bp of the 16S rDNA gene showed 98 to 99% sequence identity to Pectobacterium chrysanthemi (GenBank Accession No. FM946179). Sequences were deposited in GenBank (Nos. HQ287572–HQ287575). Pathogenicity tests were performed by injecting 10 Oncidium ‘Gower Ramsey’ orchids with 100 μl of a bacterial suspension at 1 × 108 CFU/ml. Ten plants were inoculated with 100 μl of sterile water as controls. Plants were placed in a greenhouse at 26.0°C to 30.0°C and 50 to 83% relative humidity. Soft rot symptoms were observed on all inoculated plants within 24 h while control plants appeared normal. A Dickeya sp. was reisolated and identified according to the method described above. Oncidium orchids are known to be highly susceptible to P. carotovora (= E. carotovora) and soft rot caused by P. carotovora is known to occur frequently on Oncidium orchids (2). Although, an Erwinia sp. has been reported to cause soft rot symptoms on Oncidium aureum, to our knowledge, this is the first report of a Dickeya sp. (= P. chrysanthemi) causing soft rot symptoms on Oncidium orchids grown in large-scale commercial production in the United States. References: (1) Y. A. Lee and C. P. Yu. J. Microbiol. Methods 64:200, 2006. (2) C. H. Liau et al. Transgenic Res. 12:329, 2003. (3) N. W. Schaad et al. Erwinia soft rot group. Page 56 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. N. W. Schaad et al., eds. The American Phytopathological Society, St. Paul, MN, 2001. (4) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991. </jats:p

CatingRHermistonAgricResExtenCenterFirstReportDownySup.1.pdf

Gynura aurantiaca is a member of the Senecionaea tribe of the Asteraceae, indigenous to Java. Commonly known as purple velvet plant, this tropical species is well adapted to landscapes in South Florida, but is mostly seen as a potted plant for use in the interiorscape. During February 2013, a local nursery submitted Gynura aurantiaca samples to the Florida Extension Plant Diagnostic Clinic in Homestead, FL, where 30% of 1,000 plants were affected. Downy, white mycelium was observed on the abaxial leaf surface, and the adaxial surface of affected leaves appeared darker in color. Severely affected leaves began to curl as the tissue turned necrotic. The pathogen was identified as Plasmopara halstedii (Farl.) Berl. & De Toni based on the presence of coenocytic mycelium, and right-angled, monopodially branched sporangiophores with sporangia that were hyaline, obvoid to elliptical, and measuring 21 × 29 × 17 to 21 μm (Delanoe 1972). Molecular identification was conducted by extracting pathogen DNA using the QIAGEN Plant DNA kit (QIAGEN, Gaithersburg, MD). PCR of the 5′ terminal domain of the nuclear DNA coding for the large subunit (LSU rDNA) was performed with primers NL1 and LR3 (Kurtzman et al. 1998; Vilgalys and Hester 1990). The PCR product was purified with the QIAquick kit (QIAGEN) according to the manufacturer’s instructions and sequenced bidirectionally. The sequence from our isolate (GenBank Accession No. KR028988) was nearly identical (exhibited 97% nucleotide identity; 98% query coverage; E value = 0.0) to an isolate of P. halstedii (EF553469). A phylogenetic analysis was performed using the obtained sequence data and fifteen Plasmopara sequences from GenBank and a Fusarium solani accession as an outgroup (Maximum Likelihood, Tamura-Nei model). Our isolate grouped with P. halstedii with high bootstrap support (98% bootstrap value, 1,000 replicates) further supporting identification as P. halstedii. Pathogenicity of the sequenced isolate was evaluated in shade-house experiments. Two-month-old Gynura aurantiaca plants were inoculated with a sporangial suspension (1 × 10⁶ sporangia/ml) of P. halstedii that was collected by washing sporangia from the abaxial surface of purple passion leaves using autoclaved distilled water. Inoculum or autoclaved water was sprayed over the foliage until runoff. Six plants were sprayed per treatment and the experiment was repeated twice. Inoculated plants were placed in a shade house (73% shade) when temperatures ranged from 17 to 28°C with 78 to 98% relative humidity. Plants were observed for disease development, and pathogen sporulation occurred within seven days of inoculation. No symptoms developed on the control plants. To our knowledge, this is the first report of Plasmopara halstedii causing downy mildew on Gynura aurantiaca. Gynura aurantiaca is highly valued for its stunning purple foliage and low input production costs, but a disease such as downy mildew has the potential to substantially reduce if not eliminate commercial production

First Report of <i>Sclerotium rolfsii</i> on <i>Ascocentrum</i> and <i>Ascocenda</i> Orchids in Florida

Southern blight caused by Sclerotium rolfsii is known to occur on several economically important orchid hosts, including Vanda species and hybrids (1–3). In the summer and fall of 2008, an outbreak of southern blight on Vanda orchids was seen in several commercial nurseries and landscapes throughout South Florida. More than a dozen orchids were affected at one of the locations, and symptoms of S. rolfsii were observed on Ascocentrum and Ascocenda orchids, which are also common in the trade and demand a resale value ranging from $20 to$150 for specimens in bloom. Affected Ascocentrum and Ascocenda orchids were found severely wilted at the apex, while around the base of the plants, tan, soft, water-soaked lesions were present. As the lesions progressed, leaves around the base of the plants began to fall off, leaving the stems bare. After 2 days, white, flabellate mycelium was seen progressing up the stem and numerous, tan-to-brown sclerotia were present. Leaves and portions of the stems were plated on acidified potato dextrose agar (APDA) and grown at 25°C. White, flabellate mycelium and tan sclerotia approximately 2 mm in diameter were produced in culture and microscopic examination revealed the presence of clamp connections. The fungus was identified as S. rolfsii and a voucher specimen was deposited with the ATCC. A PCR was performed on the ITS1, 5.8S rDNA, and ITS2 and the sequence was deposited in GenBank (Accession No. GQ358518). Pathogenicity of an isolate was tested by placing 6-mm plugs taken from APDA plates directly against the stem of five different Ascocentrum and Ascocenda orchids. Five Ascocentrum and Ascocenda orchids were inoculated with 6-mm plugs of plain APDA and five were untreated controls. Plants were housed under 50% shade, 60 to 95% humidity, and temperatures ranging from 75 to 88°F. Within 7 days, all inoculated plants developed symptoms that were identical to those observed on original plants and S. rolfsii was consistently reisolated from symptomatic tissue. Ascocentrum and Ascocenda were previously reported under miscellaneous orchid species and hybrids as hosts for S. rolfsii (1). However, this report was highly ambiguous and the most current edition does not report the host fungus combination (2). To our knowledge, this is the first report of S. rolfsii affecting Ascocentrum and Ascocenda orchids. References: (1) S. A. Alfieri, Jr., et al. Diseases and Disorders of Plants in Florida. Bull. No. 11. Division of Plant Industry, Gainesville, FL, 1984. (2) S. A. Alfieri, Jr., et al. Diseases and Disorders of Plants in Florida. Bull. No. 14. Division of Plant Industry, Gainesville, FL, 1994. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. </jats:p