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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

2012 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; and develop a “bulb crop” best management web site.

Researchers from Washington State University have conducted pathogenicity trials to identify specific taxa of F. oxysporum isolates obtained from daffodil, iris, and tulip bulbs. These tests identified 5 isolates of F. oxysporum f.sp. gladiolii from iris, 2 isolates of F. oxysporum f.sp. tulipae from tulips, and 3 isolates of F. oxysporum f.sp. narcissi from daffodils. These isolates will be used to develop primers for use in real-time qPCR to identify specific taxa of F. oxysporum on bulbs. Several isolates of Rhizoctonia spp. were analyzed by DNA sequencing of the ITS region to verify species. A phylogenetic tree was produced and showed that isolates of R. tuliparum were significantly different from various R. solani anastamosis groups. R. oryzae. R. tuliparum isolates were used to design real time qPCR primers and probes to specifically detect this pathogen. Tests are currently underway to confirm the effectiveness of the new primer and probe set in detecting R. tuliparum in artificially infested soil and bulbs. Data were also collected from field and container plots to examine the effect of inoculum levels in the soil on the development of Rhizoctonia gray bulb rot on tulips and iris. Data analysis showed that there was a highly significant correlation between the inoculum level and the number of emerged and/or healthy iris and tulips plants. The highest inoculum levels resulted in a three-fold reduction in the number of tulips that emerged and reduced the number of healthy iris plants by one half. Field trials were also conducted to evaluate the effectiveness of new reduced-risk fungicides in controlling fire (Botrytis) on tulips and leafspot (Mycosphaerella) on iris.

Investigators at Washington State University organized an Annual PNW Bulb Grower Conference held on January 24, 2012 that was attended by approximately 20 growers. The program included presentations on approaches being used to manage pests and diseases on bulb crops in England, an update on this project, and a summary of surveys relating to the identification of viruses in small-farm lily and dahlia cut flower crops in western Washington. They also hosted a Bulb Grower Field Day on May 16, 2012 at the WSU Mount Vernon Research and Extension Center. This event was attended by approximately 25 growers and included information on disease and weed identification and provided an opportunity for growers to be updated on research being supported by this project.


Last Modified: 4/16/2014
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