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

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

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

CatingRHermistonAgricResExtenCenterFirstReportDowny.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

CatingRHermistonAgricResExtenCenterFirstReportDownySup.2.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

Migratory behavior of American shad in the York River, Virginia, with implications for estimating in-river exploitation from tag recovery data

Tagging of American shad Alosa sapidissima may alter their migratory behavior, causing some tagged individuals to cease or delay the spawning run. In a tag recovery study designed to assess fishery impacts, this altered behavior would reduce the number of tagged fish available to the target fishery and would bias estimates of exploitation and fishing mortality rates. To investigate this possibility, we fitted 29 prespawning adults with acoustic tags and released the fish into the middle reaches of the York River, Virginia. Movements of individuals were remotely monitored at three hydrophone stations: (1) 7 river kilometers (rkm) downriver of the release site; (2) on the Mattaponi River, 48 rkm upriver of the release location; and (3) on the Pamunkey River, 56 rkm upriver of the release location. Almost half of the fish were apparently affected by capture, handling, and tagging, as they either abandoned their migration or delayed their upstream movements. The movements of some fish appeared to be unaffected by capture; these fish were not detected at the downriver station and were detected on the spawning grounds 2-5 d after release. Eighteen fish remained on the spawning grounds for 17-51 d (average = 34.4 d) and were last detected at the downriver location, presumably during their seaward migration. Of the 26 tagged fish that migrated to either tributary after release, 15 originally selected spawning grounds on the Mattaponi River and I I selected the Pamunkey River. One fish occupied both tributaries for several weeks each, suggesting possible spawning at both locations. We conclude that tagging protocols designed to measure the impacts of fishing on American shad should include telemetry to assess altered migratory behavio