Date of this Version
Final Report: JFSP Project Number 2007-1-3-10
A major problem in post-fire restoration of semi-arid shrublands dominated by annual bromes is the presence of carryover seed banks that cannot be controlled using conventional methods. These seeds can provide significant competition for seeded species in the years following treatment. We investigated the feasibility of using a naturally occurring seed pathogen, the ascomycete Pyrenophora semeniperda, as a biocontrol organism for eliminating this carryover seed bank. We carried out the necessary technology development to create and apply field inoculum to cheatgrass- or red brome-infested areas (both burned and unburned) at six sites located in three states across two years of field trials. We found that inoculum application significantly increased the proportion of pathogen-killed Bromus seeds in the seed bank, reduced the density of viable carryover Bromus seeds, and in many cases increased the density of pathogen-killed seeds relative to levels in uninoculated controls. In some treatments, the proportion of field-killed seeds reached 100%, validating the promise of this approach. Even though this pathogen is physiologically capable of infecting the seeds of many grasses and some dicots, we determined that risks to nontarget host seeds can be mitigated. The inoculum usually has a relatively short persistence time in the absence of new host seeds, and the pathogen is readily controlled by fungicides that could potentially be used as seed treatments for desired restoration species. The potential for selection of more virulent P. semeniperda strains for increased biocontrol effectiveness is considerable. In addition, because more virulent strains grow more slowly, they are less likely to persist post-control in competition with faster-growing wild strains. In summary, our study provides proof of concept for use of this pathogen for biocontrol of cheatgrass and red brome, and opens the way for further studies on formulation and delivery technology to bring this promising biocontrol agent closer to market.
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