Invasive Species As Conduits for Pathogen Spillover Between Natural and Agricultural Systems

Novel crop pathogens have emerged via spillover from wild host plants throughout agricultural history and weeds are well known as pathogen reservoirs. The overarching goal of this project is to elucidate mechanisms of transmission of plant-associated microbes between species and ecosystems and to forecast its consequences for pathogen dynamics and impacts in agriculture in an ongoing epidemic. To address this goal, we focus on the recent emergence of a novel fungal pathogen of industrial hemp (Cannabis sativa), whose cultivation in the US was federally legalized only in 2014. Almost immediately, a little-studied ascomycete fungus Bipolaris gigantea caused massive disease outbreaks on hemp grown for CBD, first in Kentucky and then in 14 other states in the region, with up to 100% crop loss. Prior to emergence on hemp, more than 10 years ago our group documented widespread epidemics of disease caused by the same pathogen on the invasive grass Microstegium vimineum in the same region. B. gigantea populations on Microstegium and other invasive and weedy grasses are therefore ancestral to the epidemic populations on hemp and the source of disease emergence on the crop. This system is ideal to study pathogen spillover between ecosystems Our specific objectives are to: (1) Experimentally test ecological drivers of pathogen transmission between ecosystems; (2) Determine role of pathogen evolution on transmission between ecosystems; and (3) Develop eco-evolutionary models for epidemiological dynamics within and across natural and agricultural landscapes.