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United States Department of Agriculture

Agricultural Research Service

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Research Project: Tracking and Managing Diseases of Floriculture Crops Caused by Oomycetes and Fungi

Location: Biological Integrated Pest Management Unit

2011 Annual Report


1a.Objectives (from AD-416)
Both oomycetes and fungi can be serious pathogens of floriculture crops, causing diseases that destroy the aesthetic quality and marketability of these economically important plants. Since each production business grows numerous plant species, there are many different plant-pathogen combinations that can result in harmful diseases. Introductions of new cultivars, shifts in weather patterns, changes in cultural practices, or even changes in control efforts against other greenhouse pests can suddenly favor pathogen development and lead to explosive disease outbreaks. New disease-causing agents, including familiar but genetically different pathogens, frequently are encountered on floriculture crops due to the introductions from exotic locations. The global movement of seeds, cuttings, and plants allows global spread of pathogens, despite our best quarantine and other regulatory efforts. This project will focus on some of the more common diseases affecting floriculture crops as well as some of the newer and more unusual diseases.

We intend to develop information to help growers reduce crop losses caused by various plant pathogenic fungi and oomycetes as well as key insect pests, including important vectors of plant pathogens. New methods and tools will be developed and effective integrated management practices will be identified. The objectives are to.
1)reduce crop losses caused by Pythium and Phytophthora species,.
2)better understand the threat of Fusarium wilt in floriculture crops.
3)develop more effective management strategies for fungi that commonly cause root rots, especially Thielaviopsis basicola and Rhizoctonia solani,.
4)develop effective management programs for rust diseases on roses and chrysanthemums, and.
5)improve the integration of root rot disease management practices with biologically-based IPM programs being developed for insect pests. The latest scientific methods will be employed in order to improve the success of IPM programs for floriculture crop production.


1b.Approach (from AD-416)
Project objectives will be addressed by testing disease management strategies—including sanitation methods and cultural practices as well as biopesticides and chemical fungicides—in greenhouse and field trials at Cornell University’s Long Island Horticultural Research and Extension Center. Research plots will be replicated and the data will be statistically analyzed. We also will collaborate closely with researchers at Oklahoma State University to improve our greenhouse sampling techniques for oomycete pathogens and to learn how to use molecular tools effectively to pinpoint the source of pathogen outbreaks within production pathways. This work will involve sampling from cooperating greenhouse operations and identifying isolates by morphological and molecular-based methods in the laboratory. Conducted in cooperation with USDA-ARS researchers at Ithaca, NY, laboratory assays and small-scale greenhouse tests will elucidate the nature of Bradysia fungus gnat/Pythium associations and the role of fungus gnats in root rot disease outbreaks and also assess compatibilities among fungicides used for control of root rot diseases and beneficial fungi (mycoinsecticides) used against insect pests.


3.Progress Report

Objective 1. Reduce crop losses caused by Pythium & Phytophthora. Root rotting Pythium species were profiled in greenhouses at Long Island businesses. Samples of potting media were collected during 2–9 visits/business during the spring season; a potato-bait method collected 224 Pythium isolates from 672 total samples. According to microscopic identification, these were predominately P. irregulare, but molecular analysis of 145 isolates identified many as P. cryptoirregulare, a species identifiable only by molecular means. To improve identification, collaborators at OSU designed & evaluated new DNA-based primers for P. aphanidermatum, P. irregulare, P. cryptoirregulare, & P. sylvaticum. Primers for P. aphanidermatum, P. deliense, & P. sylvaticum are highly specific; however, primers for P. irregulare & P. cryptoirregulare are being redesigned because both give positive results for isolates that are neither P. irregulare nor P. cryptoirregulare, but belong to a cluster of morphologically similar species currently being described. Objective 2. Better understand the threat of Fusarium wilt in floriculture. In a study of Fusarium susceptibility in chrysanthemum, 1 of 36 yellow cultivars (12 from each of 3 major propagators) was found to be highly susceptible to F. oxysporum f. sp. chrysanthemi in greenhouse trial. The pathogen was also recovered from many cultivars that weren't showing obvious symptoms 10 weeks after inoculation. Objective 3. Develop more effective management strategies for common root rot fungi. In a study of effects of cultural factors on black root rot (Thielaviopsis basicola), disease severity was compared for calibrachoa Cabaret Cherry Rose Improved grown in a Cornell peat-lite medium at two lime levels (5 and 15 lbs per cubic yard), or in MetroMix 360 or ProMix BX. Calibrachoas were grown in the different media with and without inoculation with the pathogen. Symptom development was suppressed & plant vigor was high in MetroMix 360 relative to the other treatments. Results were reported at an open house at the Long Island Horticultural Research & Extension Center and in presentation at the OFA Short Course. Objective 5. Improve integration of root rot disease-insect IPM management practices. Cornell and USDA researchers further elucidated the role of Bradysia fungus gnats in the transmission of oomycete and fungal plant pathogens. Findings support our previous conclusions that these insects are not important vectors of Pythium root rot pathogens. Two manuscripts were submitted to research journals:.
1)reporting that the Pythium-vectoring capacity of fungus gnat larvae was markedly lower in plug cells with a peat-based potting medium than in Petri dish assays & highly dependent upon species & strain of the Pythium pathogen and.
2)showing that both larval and adult fungus gnats are strongly attracted to plants infected with a broad range of microbes (revealing that a fungus gnat-diseased plant association is not necessarily indicative of a vectored-disease problem). Project activities have been monitored by the ADODR via telephone conversations, e-mail communications, and meetings at Cornell University.


Last Modified: 12/24/2014
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