Effect of Chitosan–Caffeic Acid Conjugate and Bacillus subtilis Bacteria on the Protective Reactions in PVY-Infected Plants under Soil Water Deficit

The effect of chitosan–caffeic acid (Ch–CA) conjugate separately and in combination with a mixture of Bacillus subtilis 47 on the plant defense against PVY under optimal hydration and water deficit in soil was evaluated. The treatments of Ch–CA and Ch–CA+B. subtilis 47 on healthy potato plants under optimal soil moisture conditions demonstrated the accumulation of proline and phenolic compounds, as well as the activation of PPO, which collectively led to an increase in the nonspecific plant defenses. The application of Ch–CA resulted in a reduction of PVY infection in potato plants grown under both optimal and soil moisture-deficient conditions and led to an increase in the potato mini-tuber’s mass. The combination of B. subtilis 47 and Ch–CA proved effective in reducing the infection level exclusively under conditions of soil water deficit. It has been demonstrated that the primary factor influencing the development of resistance in potato plants to PVY under moisture-limiting conditions is associated with an elevated peroxidase activity and alterations in antioxidant activity within plant tissues.