Unravelling the genetic bases of non-target-site-based resistance (NTSR) to herbicides: a major challenge for weed science in the forthcoming decade.

Non-target-site-based resistance (NTSR) can confer unpredictable cross-resistance to herbicides. However, the genetic determinants of NTSR remain poorly known. The current, urgent challenge for weed scientists is thus to elucidate the bases of NTSR so that detection tools are developed, the evolution of NTSR is understood, the efficacy of the shrinking herbicide portfolio is maintained and integrated weed management strategies, including fully effective herbicide applications, are designed and implemented. In this paper, the importance of NTSR in resistance to herbicides is underlined. The most likely way in which NTSR evolves-by accumulation of different mechanisms within individual plants-is described. The NTSR mechanisms, which can interfere with herbicide penetration, translocation and accumulation at the target site, and/or protect the plant against the consequences of herbicide action, are then reviewed. NTSR is a part of the plant stress response. As such, NTSR is a dynamic process unrolling over time that involves 'protectors' directly interfering with herbicide action, and also regulators controlling 'protector' expression. NTSR is thus a quantitative trait. On this basis, a three-step procedure is proposed, based on the use of the 'omics' (genomics, transcriptomics, proteomics or metabolomics), to unravel the genetic bases of NTSR.