Differential responses of six Casuarina species to NaCl seed priming and salt stress during germination and early seedling growth

Abstract

The degradation of salinized soils is imposing a steady decline in productivity, leading to significant socio-economic and environmental repercussions. As a promising solution for revitalizing depleted soil potential, the cultivation of salt-tolerant plants such as Casuarina emerges as a viable approach. This study delves into this prospect by evaluating six Casuarina species to discern their levels of tolerance to varying concentrations of NaCl, particularly in the initial stages of germination and seedling growth. The imposition of salt stress instigated a reduction in both germination capacity and speed. High variability in salt tolerance was observed between the tested species. Notably, the final germination percentages at 100 mM NaCl unveiled considerable disparities: C. torulosa, C. tenuissima, and C. stricta exhibited percentages of 33%, 19%, and 10%, respectively, while C. cunninghamiana, C. equisetifolia, and C. glauca showcased higher germination rates at 63%, 62%, and 55%, respectively. Furthermore, the increase of the recovery rate with high NaCl concentration confirmed that the salinity caused only an osmotic effect and not a toxic one on the studied species. Additionally, the adoption of seed priming showcased marked enhancements in germination rates across all NaCl concentrations, effectively expediting the germination process. In response to salinity stress, reductions were noted in root length (RL), and shoot length (SL). All germination parameters and the computation of the salt tolerance index (STI) facilitated the classification of the six Casuarina species in a descending order of salinity tolerance: C. cunninghamiana Miq. > C. equisetifolia L. > C. glauca Sieb. > C. torulosa Ait. > C. tenuissima Sieb. > C. stricta Ait.