Drought Resistance Evaluation of Casuarina equisetifolia Half-Sib Families at the Seedling Stage and the Response of Five NAC Genes to Drought Stress

Casuarina equisetifolia (L.) is an indispensable tree species in the construction of the backbone of the shelterbelt system in subtropical coastal regions, as it can resist wind, sand, drought, and salt. Under global warming and water shortage, it is important to clarify the mechanisms through which C. equisetifolia adapts to drought stress and to breed drought-resistant varieties in order to enhance the ecological protection provided by coastal shelterbelts. Here, we aimed to explore the response characteristics of C. equisetifolia to drought stress and investigate the associations of NAC genes with drought resistance. Seedlings of 16 half-sib C. equisetifolia families were subjected to drought treatment. Seedling growth, morphology, physiological and biochemical indices, and drought resistance were comprehensively evaluated. The drought-resistant families designated 4-383, 3-80, 3-265, 3-224, and 1-195 were selected using multiple indices and methods. Correlation and structural equation model analyses revealed that CCG007578 might regulate growth and osmoprotection in C. equisetifolia while CCG028838 and CCG004029 may scavenge reactive oxygen species. The correlation and structural equation model analyses of seedling height growth (& UDelta;H), survival rate (S), malondialdehyde (MDA), superoxide dismutase (SOD), and CCG007578 expression were used to identify drought resistance in C. equisetifolia. The aforementioned drought-resistant families provide basic materials for future research on genes encoding drought-resistance proteins and the molecular breeding of drought-resistant C. equisetifolia.