Soil and Foliar Applications of Silicon Mitigate Biotic Stress in Cape Gooseberry Plants Caused by Fusarium Vascular Wilt

Vascular wilt caused by Fusarium oxysporum f. sp. physali (Foph) severely limits cape gooseberry (Physalis peruviana L.) production in Andean regions, where management options are restricted and largely dependent on fungicides. Silicon (Si) has been proposed as a sustainable strategy to enhance tolerance to vascular pathogens; however, its role in the cape gooseberry–Foph pathosystem remains unknown. This study evaluated the effects of soil and foliar Si applications on disease development and physiological responses in cape gooseberry plants under greenhouse conditions. Three soil doses and three foliar doses were tested, including inoculated and non-inoculated controls without treatment. Si significantly reduced disease progression, decreasing the area under the disease progress curve (AUDPC) and disease severity index, with efficacy values of up to 69% in inoculated plants, particularly at 8 g kg−1 soil application. Si also reduced vascular browning and mitigated pathogen-induced physiological impairment by maintaining higher stomatal conductance, relative chlorophyll content, maximum quantum efficiency of photosystem II, and plant growth. These findings indicate that Si, especially when soil-applied, enhances physiological tolerance to Foph and represents a promising complementary tool for its integrated management.