Shuidong mustard (Brassica juncea var. multiceps) is an important leafy vegetable in South China, yet its production is frequently constrained by seasonal drought stress during autumn sowing. Gamma (γ) radiation can induce genetic variation to potentially improve seed vigor and stress resilience. However, the dose-dependent effects of γ-radiation on seed physiological traits and genome-wide mutations in this crop remain unclear, limiting its effective application in mutation breeding.