Differential effects of foliar and seed priming glycine betaine application on quinoa physiology under varying salinity level

Rising soil salinity hinders global crop yields by damaging plants, threatening food security. This study assessed glycine betaine (GB) application methods (foliar, seed priming) and salinity levels (0, 60, 120, 180 mM NaCl) on quinoa over two seasons. For ionic homeostasis, seed priming improved K⁺/Na+ ratio by 10–15 % at low salinity, while foliar was 12–18 % more effective at high salinity. Seed priming remained 10–15 % superior for roots. Foliar enhanced osmolytes by 12–16 % at low salinity, but seed priming had 16–20 % stronger effects at high salinity. Under low salinity, seed priming provided 8–12 % better protection for chlorophyll and photosynthetic efficiency. At high salinity, foliar GB was 10–15 % best for chlorophyll, seed priming 12–16 % more effective for photosynthetic rate, and foliar GB had an 8–10 % edge for Fv/Fm. GB reduced MDA by 8–12 % at low salinity, 12–16 % with seed priming at medium salinity in 2023, and 16–20 % with foliar in 2024. At high salinity, seed priming decreased MDA by 20–25 % in 2023, while foliar showed a 24–28 % reduction. GB moderately enhanced antioxidants by 8–12 % under mild stress, but seed priming and foliar differed 16–20 % in effectiveness under severe stress. For nutrients, seed priming had a 12–16 % advantage for nitrogen at medium salinity in 2023, while foliar excelled with a 16–20 % increase under high stress in 2024. Seed priming was 16–20 % better for phosphorus at high salinity in 2023, but foliar had 20–25 % superior results in 2024. These findings highlight complex plant responses to GB-salinity interactions, with optimal methods varying by trait, stress level, and environmental conditions.