200 years of intense agriculture helped waterhemp weed become a major pest

More than 200 years of modern agricultural expansion and intensification has driven the success of common waterhemp (Amaranthus tuberculatus), one of the most pervasive and damaging herbicide-resistant weed species in North America today. This plant’s expansion resulted from agricultural practices collectively imposing selective pressures on the weed seldom seen in the wild. Through a genomic evaluation of modern and historical samples of the plant, Julia Kreiner and colleagues reveal the human-driven genetic mutations that have made this plant so ubiquitous. These findings could be used to inform future weed management strategies. For more than two centuries, agricultural practices across North America have rapidly intensified, driving extreme environmental changes for many adjacent non-agricultural species, including soil disturbances, water and nutrient addition, and the application of chemical pesticides and herbicides. Some species like common waterhemp – a weed that can compete with important crops like soy and corn – have thrived in the face of these anthropogenic changes. Using genomic data from contemporary waterhemp plants and historical herbarium samples from museums collected between 1828-2011, Kreiner et al. illustrate how the unique environmental consequences of intensive agriculture have rapidly shaped modern waterhemp. According to the findings, genetic changes associated with range expansion, growth, environmental tolerance, and herbicide resistance in this plant became notable in the 1960s and during the agricultural intensification of the “Green Revolution.” “Kreiner et al. show that waterhemp adapted to agricultural intensification through migration and selection of preexisting genetic variation, followed by the rapid evolution of resistance through new mutations,” write Katherine Waselkov and Kenneth Olsen in a related Perspective. “As industrial-scale agriculture becomes more mechanized and technology-driven, new selection pressures will spur the rise of new adaptations and weed species in crop fields."