Weed-induced crop yield loss: a new paradigm and new challenges

A commonly held misconception is that weeds reduce crop yield primarily because of resource competition.Weed presence reduces crop yield regardless of resource availability based on the timing of the critical period for weed control, and resource supplementation, and weed density studies.Weeds alter developmental trajectories of crops early in the growing season that often result in reduced yields.Signals produced by weeds that alter crop growth include light quality alterations, soil-borne chemicals, and/or volatile chemicals.Weed signals elicit a stress response in crops that may suppress growth through repression of the TARGET OF RAPAMYCIN (TOR) signaling system.Identification of weed-inducible genes and promoters will provide tools to investigate mechanisms controlling crop–weed interactions and develop weed-tolerant crops. Direct competition for resources is generally considered the primary mechanism for weed-induced yield loss. A re-evaluation of physiological evidence suggests weeds initially impact crop growth and development through resource-independent interference. We suggest weed perception by crops induce a shift in crop development, before resources become limited, which ultimately reduce crop yield, even if weeds are subsequently removed. We present the mechanisms by which crops perceive and respond to weeds and discuss the technologies used to identify these mechanisms. These data lead to a fundamental paradigm shift in our understanding of how weeds reduce crop yield and suggest new research directions and opportunities to manipulate or engineer crops and cropping systems to reduce weed-induced yield losses.