Enhancing the Storage Longevity of Apples: The Potential of Bacillus subtilis and Streptomyces endus as Preventative Bioagents against Post-Harvest Gray Mold Disease, Caused by Botrytis cinerea

Abstract

Gray mold, caused by <i>Botrytis cinerea</i> Pers. Fr., is one of the most vital plant diseases, causing extensive pre- and post-harvest losses in apple fruits. In the current study, we isolated and identified two potential endophytic bioagents, <i>Bacillus subtilis</i> and <i>Streptomyces endus</i>. Both bioagents exhibited a potent fungistatic effect against <i>B. cinerea</i> under both in vitro and in planta conditions. Moreover, two experiments were carried out; (i) the first experiment was conducted at room temperature after artificial inoculation with <i>B. cinerea</i> to monitor the progression of the infection and the corresponding biochemical responses of the apples. Our in vivo findings showed that the treated <i>B. cinerea</i>-infected apple fruits with the cell-free bacterial filtrate of <i>B. subtilis</i> and <i>S. endus</i> (dipping or wrapping) significantly reduced the rotten area of the treated apple at room temperature. Additionally, <i>B. subtilis</i> and <i>S. endus</i> enhanced the enzymatic (POX and PPO) and non-enzymatic (phenolics and flavonoids) antioxidant defense machinery in treated apples. (ii) The second experiment focused on the preventive effects of both bioagents over a 90-day storage period at 1 °C of healthy apples (no artificial inoculation). The application of both bacterial filtrates prolonged the storage period, reduced the relative weight loss, and maintained high-quality parameters including titratable acidity, firmness, and total soluble solids of apple fruits under cold storage at 1 °C. The Kaplan-Meier analysis of rotten apples over 90 days during cold storage showed that the treated apples lasted longer than the non-treated apples. Moreover, the lifespan of apple fruits dipped in the culture filtrate of <i>B. subtilis</i>, or a fungicide, was increased, with no significant differences, compared with the non-treated apples. The current results showed the possibility of using both bioagents as a safe and eco-friendly alternative to chemical fungicides to control gray mold disease in apples.