Crop selectivity and herbicide safeners: Historical perspectives and development, safener-regulated gene expression, signaling, and new research directions

Herbicide safeners are chemical compounds used to protect monocot crops (typically large-seeded cereals) from herbicide injury. Safeners are chemically diverse and possess the unique ability to selectively protect cereal crops from herbicide injury, which is accomplished by inducing metabolic detoxification reactions (Kraehmer et al. 2014; Riechers et al. 2010; Rosinger et al. 2012). Herbicide safeners are flexible in their application method (e.g., crop seed treatment, preemergence (PRE) with the herbicide, or postemergence (POST) with the herbicide) and are novel crop protection agents in that they only protect cereal crops from herbicide injury (Hatzios 1983, 1991; Parker 1983). Perplexingly, commercial safeners do not confer significant phenotypic effects (i.e., prevention of herbicide injury) in dicot crops or in most weed species (Jablonkai 2013). Most herbicide safeners used today act by stimulating herbicide detoxification mechanisms in cereal crops (Breaux et al. 1989; Cole 1994; Fuerst et al. 1986; Hatzios and Burgos 2004; 124 Riechers et al. 2010), although some examples of “inactive” herbicide antagonists may also be classified as safeners, which will be discussed further below. Chemicals have not been commercialized solely to safen broadleaf crops from herbicides, in spite of ample evidence that safeners induce gene expression in Arabidopsis thaliana (DeRidder et al. 2002, 2006; De Veylder et al. 1997; Hershey and Stoner 1991).