Harboring potential of enzymatic antioxidants in sweet potato [Ipomoea batatas (L.) Lam.] nodal cultures under in vitro NaCl-mediated salinity stress conditions

Salinity stress hinders the production and productivity of sweet potato worldwide. Stringent selection under <i>in vitro</i> salinity conditions would be a nebulous approach to developing stress-tolerant lines. Eight pre-breeding sweet potato genotypes, SP-12, SP-13, SP-23, SP-27, SP-33, SP-42, SP-44, and SP-45, selected from a broad genetic base of 380 germplasms, were evaluated under NaCl-mediated salinity stress conditions using nodal cultures <i>in vitro</i>. Sweet potato nodal cultures were raised in Murashige and Skoog (MS) medium with different levels of salinity (0, 50, and 100 mM). The morphological, physiological, and antioxidative enzyme activities under control conditions and salinity stress were assessed. Shoot and root organogenesis under the NaCl-induced MS medium (100 mM) were consistent in genotype SP-13. The antioxidative enzymes increased significantly [0.1-fold in catalase (CAT) to 2.7-fold in ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)] with increasing salinity stress conditions compared to the control across the genotypes. Genotypes SP-13, SP-12, and SP-42 exhibited a higher stress tolerance index (STI) for antioxidative enzymes (AOEs). Pearson's correlation coefficient (r) matrix revealed a strong integration among the growth parameters and AOEs. Among the antioxidative enzymes, APX (r = 0.74) and dehydroascorbate reductase (DHAR; r = 0.60) showed strong and positive correlations with glutathione reductase (GR). Polyphenol oxidase (PPO) exhibited a strong negative correlation with shoot parameters, including shoot length (r = -0.74) and shoot number (r = -0.71), indicating its association with shoot retardation. Principal component analysis (PCA) and hierarchical clustering indicated that genotype SP-13, followed by genotypes SP-12 and SP-42, is closely related to higher growth performances and better antioxidative enzyme mechanisms. Overall, SP-13, SP-12, and SP-42 performed well, maintaining plantlet growth and AOE properties. The results encourage the rapid screening of the more extensive pre-breeding populations to streamline breeding strategies and develop salinity-tolerant plants.