This report investigates population structure and genetic variability of Phytophthora spp. isolated from botanically diverse plants in Florida. Internal transcribed spacer-based molecular phylogenetic analyses indicate that Phytophthora isolates recovered from ornamental plants in Florida represent a genetically diverse population and that a majority of the isolates belong to Phytophthora nicotianae (73.2%), P. palmivora (18.7%), P. tropicalis (4.9%), P. katsurae (2.4%), and P. cinnamomi (0.8%). Mating type analyses revealed that most isolates were heterothallic, consisting of both mating type A1 (25.2%) and mating type A2 (39.0%), and suggesting that they could outcross. Fungicide sensitivity assays determined that several isolates were moderate to completely insensitive to mefenoxam. In addition, several isolates were also moderately insensitive to additional fungicides with different modes of action. However, correlation analyses did not reveal occurrence of fungicide cross-resistance. These studies suggest that a genetically diverse Phytophthora population infects ornamental crops and the occurrence of mefenoxam-insensitive Phytophthora populations raises concerns about disease management in ornamentals. Mitigating fungicide resistance will require prudent management strategies, including tank mixes and rotation of chemicals with different modes of actions.

Early detection of Asian soybean rust (ASR) is essential to help producers minimize the impact of this serious disease. DNA from ASR-infected soybean plants was used to compare conventional and real-time ASR-specific PCR assays at seven laboratories in the United States. Soybean plants were inoculated with four concentrations of rust spores to establish different levels of infection within the plants. Plant tissue was then harvested at 7 time points over the course of 12 days, and DNA was extracted using two commercially available kits. DNA extracted from soybean plants inoculated with different spore concentrations was tested for ASR using conventional or real-time PCR assays. ASR was consistently detected at 6 days following inoculation with both the conventional and real-time PCR assays. This study demonstrates the ability to reliably detect ASR in soybean before the presence of readily visible symptoms. It also demonstrates the reproducibility of the PCR assay across different real-time PCR platforms at multiple laboratories when the assays were performed in multiple diagnostic laboratories. Accepted for publication 5 April 2006. Published 24 May 2006.

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Soybean rust (SBR), caused by the obligate fungus Phakopsora pachyrhizi Syd. & P. Syd., was initially reported on soybean (Glycine max L.) in Louisiana in 2004 and has since been reported on soybean and/or kudzu (Pueraria lobata (Willd.) Ohwi) in 9 states in 2005, 15 states in 2006, and 19 states in 2007 (1). The host range of P. pachyrhizi includes plants that are all in the Fabaceae or legume family. Six plant species in the United States have been reported as hosts of P. pachyrhizi: soybean, kudzu, Florida beggarweed (Desmodium tortuosum (Sw) DC.), dry bean (Phaseolus vulgaris L.), lima bean (P. lunatus L.), and scarlet runner bean (P. coccineus L.) (4). On 17 April 2008, a rust disease was observed on a weedy legume host with red showy flowers that was growing with kudzu in an overgrown vacant lot in the understory of live oak trees (Quercus virginiana Mill.) in Citra, FL. The discovery was made during routine scouting of this Integrated Pest Management Pest Information Platform for Extension and Education (IPM PIPE) mobile sentinel plot (3). The plant was confirmed by University of Florida botanists to be Erythrina herbaceae L., commonly known as coral bean. Coral bean is native to the southeastern United States and also is planted as a perennial ornamental. A sample of leaves exhibiting rust pustules characteristic of P. pachyrhizi uredinia was collected and examined with a microscope. Brown-to-brick red, angular lesions that were 3 to 11 mm in diameter (average 6.75 mm) were observed on the undersides of the leaves of two trifoliates. Within these lesions, there were several uredinia, some exuding hyaline, echinulate urediniospores (20 × 25 μm). The visual diagnosis and the species of the rust fungus were confirmed to be P. pachyrizi by a real-time PCR protocol (2). The diagnosis on this new host was verified by a USDA, APHIS National Mycologist in Beltsville, MD. Coral bean may serve as an additional overwintering host for P. pachyrhizi in the southeast. To our knowledge, this is the first report of soybean rust caused by P. pachyrhizi on E. herbaceae. References: (1) R. S. C. Christiano and H. Scherm, Phytopathology 97:1428, 2007. (2) R. D. Frederick et al. Phytopathology 92:217, 2002. (3) S. A. Isard et al. Online publication. doi:10.1094/PHP-2006-0915-01-RV. Plant Health Progress, 2006. (4) T. L. Slaminko et al. Plant Dis. 92:767, 2008.

Sentinel plots for monitoring Asian soybean rust (ASR) caused by Phakopsora pachyrhizi Syd. were initiated in 2005 at Isabela (EEI), Adjuntas (EEA), and Juana Diaz (EEJD) experiment stations. Until 2009, no signs or symptoms of ASR were observed in soybean (Glycine max [L.] Merr.) or common bean (Phaseolus vulgaris L.). These sites were found to be negative for the occurrence of ASR based on PCR with specific primers Ppa1 and Ppa2 (2). However, P. meibomiae, the cause of American soybean rust (AmSR) endemic to this region, was found in Adjuntas naturally infecting numerous wild and cultivated legumes, particularly Lablab purpureus (3). Symptoms of AmSR in L. purpureus appeared as reddish-brown spots on the underside of the leaves with three to four uredia per lesion. On February 12, 2011, leaf samples of soybean in beginning pod-fill (R5) and beginning-maturity (R8) growth stages were collected in a winter nursery at EEI and found to have small brown specks with chlorotic haloes on the underside of the leaves and leaf sections from symptomatic areas indicated an abundance of uredinia. Under the light microscope, urediniospores observed at 40× were morphologically similar to Phakopsora spp. Total DNA was extracted from leaf discs using the Qiagen DNeasy Plant Mini Kit following the methods of Frederick et al. (2). Detection of ASR pathogen was achieved via PCR amplification with Ppa1 and Ppa2 primers that are specific for P. pachyrhizi Syd. After sequencing the amplicon, BLAST analysis of the internal transcribed spacer (ITS) region of the ribosomal RNA genes indicated 100% identity with known P. pachyrhizi sequences in GenBank. The sequence of isolate P. pachyrhizi EEI-2011 was submitted to GenBank as JX994293. No amplification was observed after PCR with species-specific primers Pme1 and Pme2 specific for P. meibomiae (Arthur) Arthur. L. purpureus collected from EEA and Utuado only appears to be infected by P. meibomiae and no mixed infections with P. pachyrhizi were apparent, based on the PCR test. Leaf samples from EEI were sent to the UF Plant Diagnostic Center in Gainesville, FL, where quantitative PCR with primers Ppa1 and Ppa2 confirmed the presence of P. pachyrhizi; while P. meibomiae was not detected with primers Pme1 and Pme2. Pathogenicity tests were conducted on the soybean cv. Williams with isolate EEI-2011. Fifteen-day-old soybean plants were inoculated by attaching an infected and sporulating 1 cm2 piece of soybean leaf from EEI-2011 with an average of 4.5 × 105 urediniospores per cm2 (1). Inoculated plants were placed in a growth chamber at 20°C night and 28°C day temperatures, 80% humidity, and a 12-h light photoperiod. Small reddish brown spots with chlorotic haloes developed 4 to 6 days after inoculation and tan lesions appeared 10 to 15 days later. Mature tan lesions developed in 2 weeks with an average of 2.4 uredinia/lesion. Urediniospores were observed with light microscope and these were morphologically similar to those spores observed in the original diseased samples. Another PCR test confirmed P. pachyrhizi after amplification with the species-specific primers. The pathogenicity test was repeated twice with the same cultivar. To our knowledge, this is the first report of ASR in Puerto Rico and this finding will have implications as another overwintering site for Asian soybean rust in the Caribbean region. References: (1) C. Estévez de Jensen et al. J. Agric. Univ. P.R. 93:125, 2009. (2) R. D. Frederick et al. Phytopathology 92:217, 2002. (3) B. Vega and C. Estévez de Jensen. J. Agric. Univ. P.R. 94:211, 2010.