| Summary: | Potato (<i>Solanum tuberosum</i> L.) tubers are a highly important food crop in many countries due to their nutritional value and health-promoting properties. Postharvest disease caused by <i>Phytophthora infestans</i> leads to the significant decay of stored potatoes. The main objective of this study was to evaluate the effects of the endophytic bacteria, <i>Bacillus subtilis</i> (strain 10–4), or its combination with salicylic acid (SA), on some resistance and quality traits of stored <i>Ph. infestans</i>-infected potato tubers. The experiments were conducted using hydroponically grown potato mini-tubers, infected prior to storage with <i>Ph. infestans</i>, and then coated with <i>B. subtilis</i>, alone and in combination with SA, which were then stored for six months. The results revealed that infection with <i>Ph. infestans</i> significantly increased tuber late blight incidence (up to 90–100%) and oxidative and osmotic damage (i.e., malondialdehyde and proline) in tubers. These phenomena were accompanied by a decrease in starch, reducing sugars (RS), and total dry matter (TDM) contents and an increase in amylase (AMY) activity. Moreover, total glycoalkaloids (GA) (α-solanine, α-chaconine) notably increased in infected tubers, exceeding (by 1.6 times) permissible safe levels (200 mg/kg FW). Treatments with <i>B. subtilis</i> or its combination with SA decreased <i>Ph. infestans</i>-activated tuber late blight incidence (by 30–40%) and reduced oxidative and osmotic damages (i.e., malondialdehyde and proline) and AMY activity in stored, infected tubers. Additionally, these treatments decreased pathogen-activated GA accumulation and increased ascorbic acid in stored tubers. Thus, the results indicated that endophytic bacteria <i>B. subtilis</i>, individually, and especially in combination with SA, have the potential to increase potato postharvest resistance to late blight and improve tuber quality in long-term storage.
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