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United States Department of Agriculture

Agricultural Research Service

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Location: Foreign Disease-weed Science Research

2012 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:
This is the final report for this project, which will terminate on 09/14/2012. This project began with the general objective of mass-producing seedlings of Canada thistle systemically diseased with the rust fungus Puccinia punctiformis and transplanting these seedlings into Canada thistle patches to initiate rust epiphytotics. This approach failed because the seedlings died after transplanting. It then became apparent that the paradigm for the disease cycle was wrong and that the cycle of newly infected plants began in the fall of each season. To test this, fall inoculations, in 2008, of rosettes of Canada thistle with ground leaves bearing teliospores of Puccinia punctiformis resulted in systemically diseased shoots the following spring and also systemically diseased shoots in the spring of 2010. By the spring of 2011 there were no Canada thistle plants in the inoculated area. Based on these, and other, 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. 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. By the spring of 2012, thistle density in this field had declined by 54.7percent. In the summer of 2010, a collaborative project on establishing in-field epiphytotics 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. Data on thistle density collected in the spring of 2012 showed that thistle density had declined by an average of 74.6 percent in this field. In the fall of 2011, two other field sites in Keymar, Maryland were repeatedly inoculated with ground diseased leaves bearing teliospores. In the spring of 2012, in both field sites, systemically diseased shoots arose from rosettes, inoculated the previous fall. This was repeated in three field sites in Moscow, Russia with the same results. In each of the nine field sites in three countries, inoculation of Canada thistle rosettes with teliospores in the fall has resulted in the start of epiphytotics of systemic rust disease the following spring. There has been 100 percent success, thus far, in using this approach to establish systemic rust epiphytotics. Data will continue to be collected on initiation of rust epiphytotics from new field sites and on thistle densities following inoculation.

4. Accomplishments

Last Modified: 06/26/2017
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