Drought Stress Response in Guar (Cyamopsis tetragonoloba (L.) Taub): Physiological and Molecular Genetic Aspects

Drought has become one of the main factors of crop yield losses worldwide. This negatively affects the plant industry, decreasing crop yields, and it may result in resource deficits in different sectors of the world economy and its national branches. Guar (Cyamopsis tetragonoloba (L.) Taub) represents one of the strategic crops, as its seeds are the source of guar gum, which is critically important in the modern oil industry. Although guar is generally known to be a drought-tolerant plant, it is known that soil dehydration negatively affects plant fitness and crop productivity. As guar genotypes are characterized by high variability in the manifestation of drought tolerance, screening genetic resources for this feature seems to be a promising strategy for accessing drought-resistant varieties. The discovery of drought-tolerant genotypes is mandatory to secure sustainable guar production. In this context, the identification of reliable chemical and molecular markers of drought tolerance (i.e., drought-responsive and/or drought-protective metabolites, proteins and transcripts) will provide the solid basis for marker-driven breeding of new tolerant varieties. Therefore, here we provide a comprehensive overview of the available literature data on guar drought stress response, its physiological and molecular genetic aspects, and considerations on the approaches to improve the quality of this crop.