Biostimulant Priming Modulates Photosynthesis and Storability of Salt-Stressed Garlic (Allium sativum L.) in a Cultivar-Dependent Manner

This study evaluated the growth, physiological, chlorophyll fluorescence (JIP-test), and postharvest responses of a shoot-dominant (‘C-P’) and a root-dominant (‘J-L’) garlic material to graded salinity (0, 50, and 200 mM NaCl) in a hydroponic system, with or without seed-clove priming using LEAFENERGY®, a commercial biostimulant mainly composed of naturally derived rare fatty acids. Results showed 50 mM NaCl significantly inhibited shoot growth, while 200 mM nearly arrested growth and induced clove decay. Under moderate salinity, biostimulant priming exhibited cultivar-dependent mitigation. In ‘C-P’, biostimulant priming increased clove soluble sugar content by 1.140 g 100 g−1 FW under 50 mM NaCl and increased dry-weight-based clove water content after cold storage. In ‘J-L’, biostimulant priming increased SPAD values under 50 mM NaCl and reduced the salt-induced increase in clove yellowness index to a level not significantly different from the non-saline control. In conclusion, garlic’s response to salinity is fundamentally dictated by intrinsic resource allocation strategies. Rather than merely promoting growth, biostimulant priming optimizes photosynthetic energy fluxes and reshapes metabolism. This tailored approach effectively preserves the visual marketability of susceptible cultivars while enhancing osmoprotectant accumulation and hydration in vigorous morphotypes, providing a sustainable strategy to safeguard industrial raw materials in salinized controlled cultivation systems.