Cheatgrass is one of the most destructive plant invaders in the West with significant economic and ecological impacts on rangelands and agricultural lands. The seed pathogen "black fingers of death" is a promising tool under consideration for biocontrol of cheatgrass. We have now characterized the toxins employed by this pathogen to kill target seeds. We learned that fast-growing pathogen strains are not always most effective for biocontrol, because slow-growing strains produce more cytochalasin B, a powerful toxin that may slow down or stop cheatgrass seed germination.
The seed pathogen "black fingers of death" is being considered as a tool for biocontrol of the invasive winter annual cheatgrass in the context of restoration seeding in the Great Basin. The interaction between this pathogen and its target seeds has been called a "race for survival". Seeds often escape mortality through rapid germination, so our research focused on the hypothesis that fast-growing strains of the pathogen would be most effective for biocontrol.
We learned that slow-growing strains were actually better than fast ones at killing germinating cheatgrass seeds. We then proposed that these slow growers might be spending their energy making energy-costly toxins to stop the seeds in their tracks. We have recently confirmed this idea with the help of colleagues who are experts in secondary products chemistry, who have identified and quantified the toxins produced by our pathogen. Slower-growing strains produced significantly more of the powerful toxin cytochalasin B, a compound that can stop cell division and that probably serves to slow or stop cheatgrass seed germination, providing a longer window for pathogen success. This discovery provides us with a useful selection tool for choosing the best pathogen strains for cheatgrass biocontrol.