Drought tolerance strategies highlighted by two Sorghum bicolor races in a dry-down experiment

Drought stress is the major environmental stress that affects more and more frequently plant growth and productivity due to the current climate change scenario. Unravelling the physiological mechanism underlying the response of plants to water stress and discover traits related to drought tolerance provide new and powerful tools for the selection in breeding programmes. Four genotypes of Sorghum bicolor (L.) Moench were screened in a dry-down experiment using different approaches to discover physiological and molecular indicators of drought tolerance. Different strategies were identified in response to drought among the four genotypes and the two Sorghum race allowing to state the tolerance of durra race compared to the caudatum one and, within the durra race, the drought tolerance of the genotype IS22330. It retained high biomass production and high tolerance index, it had a low threshold of fraction of transpirable soil water and high capacity to recover leaf apparatus after drought stress. Furthermore in this study, the expression levels of four genes highlighted that they could be used as proxy for drought tolerance. Dehdrine (DHN) could be used for screening drought tolerance both in durra and in caudatum races. NADP-Malic Enzyme, Carbonic Anhydrase (CA) and Plasma membrane Intrinsic Protein (PIP2-5), being up-regulated by drought stress only in durra race, have a more limited, though nonetheless useful application. In the tolerant durra genotype IS22330 in particular, the regulation of stomatal openings was strongly related to NADP-Malic Enzyme expression.