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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Improved Pathogen Detection and Management of Bulb Diseases

Location: Floral and Nursery Plants Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
The objectives of this research are to develop taxon-specific DNA-based sampling procedures to quantify Fusarium and Rhizoctonia inocula levels in soil and on bulbs; use this information to develop improved disease controls; and develop sections relating to Fusarium and Rhizoctonia diseases for addition to a new WSU “bulb crop” best management website.


1b.Approach (from AD-416):
ARS will acquire the basic molecular knowledge on identification of Rhizoctonia and Fusarium pathogens of bulb crops. This information will be used by the cooperator to jointly develop taxon-specific DNA-based sampling procedures to quantify Fusarium and Rhizoctonia inocula levels in soil and on bulbs. Based on this knowledge, the cooperator will develop improved disease control strategies and develop Fusarium and Rhizoctonia management recommendation for a “bulb crop” best management website.


3.Progress Report:

Ornamental bulbs and flowers are important high-value specialty crops. Maintaining the health of vegetatively-propagated bulbous flower crops is a major challenge for growers. There are a number of fungal diseases, especially those caused by Fusarium and Rhizoctonia, that build up in planting stocks and soil resulting in reduced productivity and increased use of pesticides. Increasing restrictions on the use of pesticides and pesticide resistance in crops also limit grower management options. The overall goals of this project are to develop taxon-specific DNA-based sampling procedures to quantify Fusarium and Rhizoctonia inoculum levels in soil and on bulbs; develop improved disease controls for ornamental flower bulb crops; and develop a “bulb crop” best management web site.

Researchers from Washington State University have used isolates of R. tuliparum to design real time qPCR primers and probes to specifically detect this pathogen. Sensitivity and specificity tests confirmed the validity of this newly developed detection assay, which has been designated “Rtul”. The development of a protocol to quantify Rhizoctonia inocula in soil is complete. The Rtul assay was further tested on artificially infested soil, with a high correlation between CT values and the levels of inoculum in the soil. The Rtul qPCR assay is now being used to detect the quantity of Rhizoctonia inoculum in soil samples collected from one-year-old and two-year-old tulip and iris field trials, all of which are examining the effect of R. tuliparum inoculum levels in the soil on the development of grey bulb rot on these crops. Preliminary analysis of the qPCR data shows that R. tuliparum was detected in nine of the 155 samples taken from the tulip trial and three of the 155 samples taken from the iris trial. We are currently determining the correlation of these positives with the level of inoculum applied the previous year and current year disease development.

The development of primers for use in real-time qPCR to identify specific taxa of F. oxysporum on bulbs continues to be delayed. Five regions of the Fusarium genome that are typically used for detection assays are not usable because there are no nucleotide differences between the Fusarium oxysporum taxa (F. oxysporum f.sp. gladiolii, F. oxysporum f.sp. tulipae, and F. oxysporum f.sp. narcissi). A collaborator at the WSU Puyallup Molecular Bioscience Laboratory is working on identifying regions of the genome of the Fusarium oxysporum taxons that occur on bulbs to identify a region that has nucleotides that will be specific to our target.

A new study was initiated to determine the Botrytis species that are causing disease on peonies in Washington and Alaska. During the 2012-2013 growing season, three field trials at the WSU Puyallup Research center and two off-site trials at a commercial bulb grower’s fields were also established to evaluate the effectiveness of reduced-risk and new biocontrol products for control of Botrytis on tulips, lilies, daffodils and peonies, and leafspot (Mycosphaerella) and Fusarium on iris.

Investigators at Washington State University organized the program for an annual PNW Bulb Grower Conference on January 22, 2013. Approximately 25 growers attended this conference, which included presentations on fertility and nutrient analysis for growing bulb crops, an update on this project, and a summary of surveys conducted in 2011 and 2012 relating to the identification of viruses in small-farm lily and dahlia cut flower crops in western Washington. A Bulb Grower Field Day was held on May 15, 2013 at the WSU Puyallup Research and Extension Center. This event was attended by approximately 25 growers and included information on disease and weed identification and management. In addition, it provided an opportunity for growers to be updated on research being supported by this project. These events were WSDA accredited and provided pesticide recertification credits to all that attended.


Last Modified: 11/27/2014
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