Mitigating Salinity Stress in Sugar Beet Seedlings Through Exogenous Application of Putrescine and Salicylic Acid

Salinity stress is a major constraint on the growth and productivity of sugar beet (Beta vulgaris L.). This study evaluated the potential of exogenously applied putrescine (Put) and salicylic acid (SA) to enhance salt stress tolerance. Thirty-day-old seedlings were grown for seven days under control conditions before being subjected to eight treatments for 10 days: (i) Control, (ii) Control + 0.6 mM Put, (iii) Control + 0.6 mM SA, (iv) Control + 0.6 mM Put + 0.6 mM SA, (v) Salinity (150 mM NaCl), (vi) Salinity + 0.6 mM Put, (vii) Salinity + 0.6 mM SA, and (viii) Salinity + 0.6 mM Put + 0.6 mM SA. Put and SA were applied once as a foliar spray at the onset of the treatments. Salt stress significantly reduced plant growth, biomass, chlorophyll content, and photosynthetic efficiency, while increasing reactive oxygen species (particularly H₂O₂) and lipid peroxidation. Foliar applications of Put and SA alleviated these adverse effects, either individually or in combination. Put primarily enhanced plant growth rate, shoot length, plant height, shoot and root biomass, leaf relative water content, respiration activity, and sucrose accumulation. SA improved root length, photosynthetic activity, water-use efficiency, and proline accumulation. When applied together, Put and SA combinedly increased growth rate, shoot length, plant height, shoot biomass, leaf relative water content, stomatal conductance, and the maximum quantum yield of PSII, while more prominently reducing malondialdehyde and H₂O₂ accumulation and enhancing antioxidant enzyme activities. These findings suggest that foliar application of Put and SA enhances salinity tolerance in sugar beet seedlings by improving antioxidant enzyme activities, osmolyte accumulation, and ion homeostasis, thereby mitigating oxidative stress under saline conditions. This outcome could contribute to potential applications in breeding programs and stress management in saline-prone regions.