Bacterial extracellular polysaccharides （EPS） show great potential in enhancing plant stress resistance， but their mechanism of action on drought resistance in alfalfa （Medicago sativa） remains unclear. In this study， Alfalfa ‘Juneng 551’ was used as the experimental material， and seed coating technology was employed to investigate the drought resistance effect of Cp2-EPS from Erwinia persicina. Treatments included an uncoated control （CK）， a coating matrix control （T1）， and four Cp2-EPS concentration treatments （0.5， 1.0， 1.5， 2.0 g·L^-1， denoted as T2-T5）. Drought stress was applied after 21 days of seedling growth by maintaining soil relative water content at 40% for 14 days， and related physiological and growth indicators were measured. The results showed that Cp2-EPS coating significantly alleviated the growth inhibition caused by drought in alfalfa， with the 1.0 g·L^-1 （T3） treatment demonstrating the best effect. Compared with CK， the T3 treatment increased root length， shoot length， fresh weight， and dry weight by 17.87%， 17.87%， 74.53%， and 46.34%， respectively. Leaf photochemical quantum yield Y（II）， maximum photochemical efficiency of PSII， and total chlorophyll content were also significantly improved. In summary， Cp2-EPS seed coating can mitigate drought-induced oxidative damage by enhancing photosynthetic performance， and 1.0 g·L^-1 was identified as the optimal concentration. This study provides theoretical and technical references for developing eco-friendly drought-resistant coating agents and sustainable alfalfa production.

Alfalfa  /  Exopolysaccharides  /  Seed coating  /  Drought stress