Antifungal Properties and Mode of Action of Boric Acid Against Geotrichum candidum From Xiaozhou Mustard Tuber Sour Rot

Sour rot, a prevalent Xiaozhou mustard (Brassica napiformis) tuber disease caused by Geotrichum candidum, results in significant losses during pre- and postharvest periods. Boric acid (BA) is recognised for its safety and environmental compatibility, exhibiting a broad spectrum of antibacterial and antifungal properties. In this study, BA demonstrated significant antifungal efficacy against G. candidum both in vitro and in vivo. The in vitro results demonstrated that 4.0 g/L BA treatment entirely inhibited spore germination and mycelial growth. Meanwhile, 2.0 g/L BA treatment compromised cell and mitochondrial membrane integrity, reduced Na⁺-K⁺ ATPase and Ca²⁺-Mg²⁺ ATPase activities, lowered ATP content and energy charge, decreased total lipid and ergosterol levels and induced intracellular reactive oxygen species accumulation. Moreover, in vivo experiments revealed that immersing postharvest tuber slices in 8.0 g/L BA solution for 10 min inhibited decay completely. Overall, the results indicate that the selected BA concentrations are real alternatives to fungicides for controlling G. candidum in Xiaozhou mustard.