Zijian Zhang, Guansen Cao, Lihua Yang, Yaqing Sun, Guolong Li, Ningning Li
Soil salinity restricts sugar beet growth and productivity, creating a need for effective agronomic approaches to improve plant performance under salt-affected conditions. However, the comparative responses of sugar beet to different foliar-applied exogenous substances under controlled NaCl stress and field saline-alkali conditions remain insufficiently understood. In this study, sugar beet (Beta vulgaris L.) cultivar 'HI0479' was used to evaluate the effects of different concentrations of PAA@Mn3O4 nanoparticles (PMO), methyl jasmonate (MeJA), and γ-aminobutyric acid (GABA). A pot experiment was first conducted under controlled NaCl stress to identify concentrations for subsequent field evaluation, followed by a one-season field experiment under non-saline-alkali and saline-alkali soil conditions. Based on the overall responses of growth and physiological traits, 100 mg L-1 PMO, 100 mg L-1 MeJA, and 1000 mg L-1 GABA were selected for field evaluation. Under the imposed NaCl treatment, these foliar treatments improved growth and physiological performance and were associated with changes in photosynthetic characteristics, antioxidant enzyme activities, MDA content, osmolyte accumulation, and selected growth-related hormone levels. Under saline-alkali field conditions, PMO, MeJA, and GABA increased storage-root yield by 13.59%, 12.69%, and 12.37%, respectively, compared with the control. Although estimated storage-root sugar concentration decreased, the corresponding estimated sugar yields increased by 10.77%, 9.79%, and 7.41%, respectively. These results show that the three foliar treatments produced favorable growth- and yield-related responses under the experimental conditions evaluated while also revealing a trade-off between storage-root yield and estimated storage-root sugar concentration. The findings provide a basis for further agronomic evaluation of foliar PMO, MeJA, and GABA in sugar beet grown under salt-affected conditions.