The optimization of crop response to climatic stress through modulation of plant stress response mechanisms. Opportunities for biostimulants and plant hormones to meet climate challenges

This review discusses the use of agronomic management practices to enhance crop stress resilience to climate stress through the modulation of natural plant growth regulatory pathways. The use of biostimulants or plant hormones to improve crop resilience is subject to strict regulatory oversight if changes in the regulation of plant growth are implied. Climate change is a major threat to crop potential and is characterized by both long-term shifts in temperature and precipitation patterns as well as increased occurrence of extreme weather events, posing an immediate threat to agriculture. Breeding and exogenous inputs have been used to enhance cropping system resilience, although these management practices are either too slow or constrained by cost and availability, to address rapidly emerging climate challenges. Exogenous biostimulants, microbials and plant hormones have shown great promise as novel mechanisms to optimize natural plant resilience, resulting in immediate but non-permanent improvements in plant responses to climate-induced stresses, representing a powerful but underexplored approach to enhance crop productivity under climate stress. The use of these exogenous inputs is, however, constrained by outdated and scientifically unsound regulations that consider any such modification as pesticidal in nature. The failure to modernize regulatory frameworks for the use of biostimulants in agriculture will constrain the development of safe effective tools and deprive growers of means to respond to climate change. Here, we discuss the scientific rationale for eliminating the regulatory barriers governing biostimulants or products that modulate plant regulatory networks and propose a framework for enabling legislation to strengthen cropping system resilience.