Identifying superior drought-tolerant Bermudagrass accessions and their defensive responses to mild and severe drought conditions

The natural variation of drought tolerance among eight Iranian bermudagrass ( Cynodon dactylon L.) accessions was evaluated and compared with a commonly used variety by measuring various morphological, growth, physiological and molecular responses during mild and severe drought stress conditions. A combined multivariable analysis using principal component analysis, hierarchical clustering analysis, as well as drought-tolerance ranking measurement showed that the accessions were clustered into three groups in terms of drought tolerance. This method evaluated three accessions (Maragh, Abyaneh, and Badrood) as superior drought-tolerant, three (Karshahi, Josheghan, and Kashan) as relatively drought-tolerant, and three (Ardeha, SWI-7, and Khonb) as drought-sanative genotypes. Drought-tolerant accessions generally showed improved growth and relative water content (RWC), minor electrolyte leakage (EL) and lipid peroxidation (MDA), higher content of pigments (Chlorophyll and carotenoid) and dark green color index (DGCI), more significant up-regulation of two stress-related genes ( ECERIFERUM1 and Delta 1-pyrroline-5-carboxylate synthetase), as well as higher accumulation of proline content compared to sensitive accessions under drought stress. On the other hand, drought-sensitive accessions typically had more activity of antioxidant enzymes (catalase and ascorbate peroxidase), and higher amounts of soluble sugars (glucose, mannose, and rhamnose), compared to tolerant accessions under drought stress. In conclusion, different defensive strategies may be recruited by tolerant or sensitive bermudagrass genotypes during encountering to drought stress.