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United States Department of Agriculture

Agricultural Research Service

Related Topics

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

Location: Biological Integrated Pest Management Unit

2013 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:

Four Long Island greenhouse businesses were sampled for Pythium at Cornell University’s Long Island Horticultural Research and Extension Center. During the spring and summer bedding plant production season, samples were collected weekly from growing crops, pot-filling stations or the ground outside the greenhouses. Eighty Pythium isolates were captured from 657 growing medium and soil samples using potato pieces as baits. These new isolates continued to show the population pattern evident in FY2011-FY2012: the dominant species is Pythium irregulare sensu lato. Future studies thus should focus on this widespread pathogen and its role in compromising root health of greenhouse crops. At Oklahoma State University, Qiagen DNeasy kits were used to extract the DNA from the 80 Long Island greenhouse Pythium isolates collected by Cornell University and to analyze the population structure of collected isolates using ITS sequences. DNA fingerprints of P. cryptoirregulare (one of the cryptic species within P. irregulare sensu lato) isolates, using data from 9 SSR loci, indicate distinct populations at individual greenhouses that have in some cases been exchanged or received from a common source. There is also some indication of hybridization. Studies will continue to differentiate the different cryptic species within P. irregulare.

Soil moisture effects on root disease are not always understood by growers. In a 2012 Cornell University trial conducted with Cornell Cooperative Extension of Suffolk County, garden mums were subjected to low, moderate and high moisture levels by using 1, 2 or 3 trickle irrigation emitters per pot: plants were irrigated for one minute three times per week. Inoculum of Pythium aphanidermatum was added to half of the pots given each irrigation treatment. Excessive irrigation in the presence of Pythium resulted in the poorest roots, but the quality reduction was not significantly greater than that seen with excess irrigation in the absence of the pathogen. The pathogen was recovered from plants given the moderate and high irrigation treatments but not from the plants in the low irrigation treatment. Growers may be able to reduce fungicide root rot treatments in chrysanthemums if irrigation needs can be carefully met and not exceeded.

Effective biocontrol of Pythium root disease is not yet reliably available to growers. Biological control of Pythium root rot on Pinto Classic White geraniums with microbial inoculants was tested at Cornell University. No benefits were seen from incorporation treatments of Streptomyces lydicus (Actino-Iron), Trichoderma harzianum (Root Shield G) or T. harzianum plus T. virens (Root Shield Plus G), and 10 percent v:v vermicompost, but a drench with 100 ml per pot vermicompost tea was beneficial for maximizing growth and protecting against effects of Pythium irregulare inoculation. These promising results will lead to future tests that will evaluate the consistency of the biocontrol effect of vermicompost tea and compare it to drench treatments of other biocontrols.

Chrysanthemum growers need information on which cultivars are resistant to Fusarium wilt. Fifteen red or bronze-flowered cultivars of chrysanthemum were tested at Cornell University for their relative susceptibility to Fusarium wilt caused by F. oxysporum f. sp. chrysanthemi by inoculation at planting in a replicated greenhouse trial in 2012. Symptoms of leaf yellowing and wilting developed in cultivars Ashley Dark Orange and Sly Jenna, and the pathogen was recovered from the roots of these plants as well as from Brunette Barbie and Delightful Victoria Orange. No symptoms were seen in Aideen Red Fire, Aubrey Orange, Dazzling Stacey, Edana Red, Foxy Marjorie Red, Hannah Orange, Harmony Orange Bicolor, Jacqueline Orange Fusion, Raquel Ruby Red, Spicy Cheryl Orange, and Tabitha Scarlet, so these cultivars might perform better for a grower who has had problems with Fusarium wilt in the past.

Results of trials were reported at the Cornell University Long Island Horticultural Research and Extension Center Plant Science Day and in presentations at national conferences such as the Ohio Short Course and the Society of American Florists Pest and Production Management Conference. Methods and results of all experiments are posted online at http://www.longislandhort.cornell.edu/ and this work has also been reported in the trade press.


Last Modified: 4/18/2014
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