Storage Temperature and Moisture Content Differentially Affect Seed Viability, Biochemical Composition, and Oxidative Status in Lallemantia Seeds

Lallemantia species are oilseed crops grown primarily for their seeds; therefore, maintaining the quality of their seeds is crucial for agricultural productivity. However, declining seed quality constitutes a critical challenge to seed sector stakeholders. Prolonged storage duration, elevated storage temperature, and increased seed moisture content are key factors influencing quality loss. We investigated physiological and biochemical processes associated with seed deterioration in L. iberica and L. royleana seeds stored under different temperatures (15 °C, 35 °C, and 45 °C), moisture contents (5%, 9%, 13%, and 17%), and storage durations (0, 30, 60, and 90 days). Seed viability progressively declined with increasing storage temperature, seed moisture content, and storage duration, reaching 2% in L. iberica and 14% in L. royleana under the most severe storage conditions (45 °C, 17% seed moisture content, and 90 days of storage). Gradual compromise of membrane integrity was associated with increased electrical conductivity (EC), ROS (H2O2 and O2•−), and malondialdehyde (MDA) content. Seed deterioration was also characterized by a compromised antioxidant defense system and degradation of seed storage compounds. We observed negative correlations between EC, pH, H2O2, O2•−, MDA, glucose, and fructose and germination rate, viability, antioxidant system, and seed storage compounds. Lallemantia iberica seeds exhibited higher levels of glucose, fructose, EC, H2O2, O2•−, and MDA, as well as greater susceptibility to adverse storage conditions than those of L. royleana, as evidenced by greater reductions in viability, germination rate, pH, antioxidant system, and seed storage compounds. Among the storage conditions evaluated, seeds stored at 5% seed moisture content and 15 °C for up to 30 days generally maintained higher viability, germination rate, vigor, antioxidant activity, and seed storage compounds, along with lower levels of membrane damage. However, the suitability of storage conditions was species- and duration-specific, as L. royleana maintained 83% viability at 5% moisture content and 35 °C after 90 days. The findings indicate that unfavorable storage conditions induce oxidative stress, membrane damage, weakened antioxidant defenses, and degradation of storage reserves, ultimately reducing seed viability, germination, and vigor.