24-Epibrassinolide Improves Potato (Solanum tuberosum L.) Tolerance to Alkaline Salt Stress by Regulating Antioxidant Defence and Photosynthetic Properties

Alkaline salt stress, as a more diverse stress, severely affects the growth and development of potato (Solanum tuberosum L.) and leads to yield reduction. Brassinosteroids have been shown to regulate plant growth and play an essential role under environmental stress. However, the physiological responses by which brassinosteroids confer alkaline salt stress tolerance in potato remain unclear. We used potato 'Atlantic' as experimental material. The effects of 0.01, 0.1, 1 and 10 mu mol<middle dot>L-1 of 24-epibrassinolide (EBR) on the physiological and photosynthetic characteristics of potato under alkaline salt stress (300 mmol<middle dot>L-1 NaHCO3) were studied. The results showed that exogenous EBR increased the antioxidant enzyme activities, increased the content of osmoregulatory substances and decreased the production of peroxidation products in potato leaves under alkaline salt stress. EBR treatment improved the photosynthetic characteristics by accumulating more photosynthetic pigments. This was manifested by an increase in net photosynthetic rate, transpiration rate and stomatal conductance, and a decrease in intercellular carbon dioxide concentration. In addition, exogenous EBR increased the maximal quantum yield of photosystem II photochemistry and the effective PSII quantum yield of potato PSII under alkaline salt stress and ultimately increased yield. Potato tuber yield was significantly increased by 27.31% and 29.17% in T4 treatment compared to T1 in 2022 and 2023, respectively. Cluster and correlation analyses further demonstrated the beneficial effects of exogenous EBR on physiology, photosynthetic characteristics and potato yield under alkaline salt stress. In conclusion, exogenous EBR can enhance the tolerance of potato to alkaline salt stress by improving the antioxidant system and photosynthesis.