The tomato late blight pandemic of 2009 made late blight into a household term in much of the eastern United States. Many home gardeners and many organic producers lost most if not all of their tomato crop, and their experiences were reported in the mainstream press. Some CSAs (Community Supported Agriculture) could not provide tomatoes to their members. In response, many questions emerged: How did it happen? What was unusual about this event compared to previous late blight epidemics? What is the current situation in 2012 and what can be done? It's easiest to answer these questions, and to understand the recent epidemics of late blight, if one knows a bit of the history of the disease and the biology of the causal agent, Phytophthora infestans.
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.
Plum pox, also known as Sharka, is one of the more significant viral diseases of stone fruit trees such as plum, peach, and apricot. It was first reported in Europe in the early 1900s and more recently in Chile in 1992, the United States (Pennsylvania) in 1999, Canada (Ontario and Nova Scotia) in 2000, China in 2001, and Argentina in 2004. Plum pox virus (PPV) was recently detected in two plum (Prunus domestica) trees in an orchard in Niagara County, NY, located within 5 miles from a Canadian plum pox eradication zone. Typical symptoms of chlorotic rings and spots were observed on some of the leaves from these trees. No symptoms were reported prior to the survey collection in July 2006. Survey samples were screened for the presence of PPV by ELISA using the Agdia PPV (Agdia, Elkhart, IN) specific kit that recognizes all strains but C of PPV. Approximately 5% of the survey samples were additionally analyzed by a validated immunocapture reverse transcription (IC-RT)-PCR TaqMan assay in a Cepheid SmartCycler (Cepheid, Sunnyvale, CA). Both replicates of the two New York plum trees produced a positive ELISA reaction in two consecutive tests. The ELISA-positive samples also produced positive results when subjected to the real-time IC-RT-PCR test. The PPV-positive trees were sampled again and an additional 53 samples were collected from trees in the surrounding area. Suspect trees again tested positive, while all the trees in the surrounding area tested negative. The methods used for confirmation included two ELISA tests (Durviz [Valencia, Spain] DAS indirect monoclonal ELISA and Agdia DAS polyclonal ELISA). Confirmatory real-time IC-RT-PCR was performed using universal 3′ nontranslated region (NTR) primers (2,3) in a SYBR Green assay format and a coat protein (CP) primers/probe TaqMan assay (3,4). Further, the New York PPV isolate was identified as PPV D group using a subgroup specific conventional IC-RT-PCR (1). A 1.4-kb sequence fragment from the 3′ end of the New York PPV was sequenced (GenBank Accession No. DG 883816). Comparison of the sequence with the database confirmed this isolate as subgroup D and exhibited a high degree of identity with other PPV D accessions (PPV D Teycheney [Accession No. X16415]; Penn4 [Accession No. DQ465243] Cnd 123-1 [Accession No. AY9553267]; and Cnd 3 [Accession No. AY953262]). To our knowledge, this is the first report of PPV in New York. References: (1) T. Candresse et al. Phytopathology. 88:198, 1998. (2) L. Levy et al. J. Virol. Methods. 49:295, 1994. (3) V. Mavrodieva and L. Levy. Acta Hortic. 657:141, 2004. (4) T. Wetzel et al. J.Virol. Methods 33:355, 1991.
The National Plant Diagnostic Network (NPDN), comprising diagnostic professionals from more than 70 pathology, entomology, and nematology laboratories, safeguards U.S. plant systems through accurate diagnosis and effective communications with clients, partners, and stakeholders. As a USDA-NIFA extension program built on the land-grant university system, the network has dual responsibilities to extension clientele such as farmers and the green industry, as well as state and federal regulatory agencies. Following strategic planning in 2019, the network emerged with a concise plan and strong committees of network participants to enhance and sustain service to NPDN clientele and partners, even through significant disruptions like the 2020 coronavirus pandemic. The commitment to building diagnostic capacity and expertise across the country allows these plant clinics to assist during a response to detections of high-consequence plant pathogens by clearing healthy plants for commerce while identifying potential positives for regulators to quarantine and/or eradicate, similar to the test and trace efforts for human diseases such as COVID-19. In this review, we describe the network’s recent activities to protect U.S. plant agriculture and natural ecosystems and its plans to improve and expand capacity for national plant biosecurity.
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