Advances in mechanisms of drought tolerance in crops, with emphasis on barley

According to Food and Agriculture Organization (FAO), droughts have significant economic, environmental, and social impacts, both direct and indirect. All field crops are affected by drought. Global warming and climate change are expected to exacerbate this phenomenon. Barley (Hordeum vulgare L.) ranks fourth among cereals after wheat (Triticum aestivum L.), maize (Zea mays L.), and rice (Oryza sativa L.). Drought is a significant issue in barley breeding programs. The purpose of this chapter is to review pertinent literature on general drought-tolerance mechanisms in important field crops and provide the latest state-of-the-art information on drought-coping mechanisms in barley, including molecular basis of crop response in moisture-limited environments. We highlight research insights, existing gaps, and future research directions regarding drought tolerance in barley. Known quantitative trait loci (QTL) and genes, such as Dhn and DREB, and their use in marker-assisted selection for drought tolerance are summarized. Traits associated with improved performance (early vigor, plant height, spike waxiness, and thousand-grain weight) under low-moisture stress environments have been identified as useful criteria in breeding for drought-tolerant barley. Low stomatal density cultivars of barley should be developed to combat drought and climate change. Latest innovations in genome-editing technology, such as clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), clustered regularly interspaced short palindromic repeats from Prevotella and Francisella 1 (CRISPR-Cpf1), and multiplexed accurate genome editing with short, trackable, integrated cellular barcodes (MAGESTIC), should be useful for plant breeders in modifying the barley genome, as needed, to develop drought-tolerant cultivars.