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United States Department of Agriculture

Agricultural Research Service

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Location: Foreign Disease-weed Science Research

2011 Annual Report

1a. Objectives (from AD-416)
The objectives of this research are to: 1) demonstrate the ability of Canada thistle seedlings, systemically diseased with the rust fungus Puccinia punctiformis, to reduce thistle density and provide sustainable biological control, 2) implement successful biological control of Canada thistle on a relatively large scale, and 3) provide land managers with the techniques to mass produce systemically diseased seedlings, introduce them into thistle patches, and effectively manage the patches to optimize biological control with the rust fungus and expand areas under control.

1b. Approach (from AD-416)
Canada thistle seedlings systemically diseased with the rust fungus, P. punctiformis, will be produced in greenhouses in either Ft. Detrick (for use in Maryland) or at Pennsylvania State University (for use in Pennsylvania). Diseased seedlings will be produced using teliospores of the fungus collected from the state of intended use, and seedlings will be transplanted to healthy patches in April. Either 0, 2, 4, or 6 systemically diseased seedlings will be established per each patch with one inoculum level per patch. At each inoculum level, half the number of the patches will be mowed and the other half left un-mowed. Procedures for producing systemically diseased seedlings will be transferred to stakeholders. We plan on locating and using 96 Canada thistle patches in 12 field sites, with about half of the sites in Maryland and half in Pennsylvania. A minimum of ten healthy thistle patches will be used for each field site. Stakeholders in charge of sites will mow or arrange to mow half of the patches in these sites. Data from each patch will be collected each year in June - July. Dependent variables will be: healthy Canada thistle density, diseased shoot density, and patch diameter. Data collection will be done by student interns under the supervision of a graduate student at Pennsylvania State University.

3. Progress Report
In 2008, fall inoculations of rosettes of Canada thistle, with ground leaves bearing teliospores of Puccinia punctiformis, resulted in systemically diseased shoots the following spring and systemically diseased shoots in the spring of 2010. By the spring of 2011, there were no Canada thistle plants in the inoculated area. In greenhouse tests, inoculation of rosettes with 10 million teliospores per plant produced significantly more systemically diseased shoots than lower inoculum levels. Based on these results, a Canada thistle test plot was established at FDWSRU in the summer of 2009 and individual rosettes were inoculated in September of that year with about 1 gram per rosette of ground leaves bearing teliospores of Puccinia punctiformis. The following spring systemically diseased shoots with P. punctiformis emerged, and 140 systemically diseased shoots emerged in this plot in the following spring of 2011. A subsequent greenhouse test on repeated inoculations of rosettes with 1 million teliospores per rosette each time resulted in a linear and significant increase in proportion of systemically diseased plants with increasing number of inoculations. In the fall of 2010, rosettes of Canada thistle in a farmer’s field in Keymar, Maryland were repeatedly inoculated with suspensions of 1 million teliospores. Repeated inoculations were done on each rosette. In the spring of 2011, systemically diseased shoots emerged in this previously disease-free field. In the summer of 2010, a collaborative project on establishing in-field epidemics of P. punctiformis on Canada thistle was established with the European Biological Control Laboratory and Aristotle University in Thessaloniki, Greece. A set of protocols on collection of diseased leaves bearing teliospores and on repeated inoculations with these leaves was sent to the Greek collaborators who inoculated rosettes in early October of 2010. In the spring of 2011, rosettes receiving multiple inoculations had produced systemically diseased shoots. While searching for the diseased shoots it was noticed that systemically diseased plants had emerged on the windward side of a small hill near the inoculation area. Evidently, teliospore-bearing leaf material from the inoculation area had blown onto this hill which acted like a wind-break and blocked further movement of the leaf material which was deposited on rosettes on the hill. This observation is consistent with what has been observed in Maryland and, in conjunction with results of inoculations with teliospore-bearing leaves, indicates that the form of inoculum responsible for natural epidemics of systemic rust disease is dehiscing and wind-blown leaves bearing high concentrations of teliospores. Now the collaboration on initiating epidemics of P. punctiformis on Canada thistle has been extended to New Zealand, Turkey, and Russia. Canada thistle is a severe weed problem in all of these countries, and the collaborators are enthusiastic about pursuing this international experiment.

4. Accomplishments

Last Modified: 08/18/2017
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