Inactivation of Bacterial Wilt in Closed Soilless Cultivation by Photocatalytic Treatment and Silver

Abstract

From the viewpoint of conservation-oriented agriculture, a closed soilless cultivation using an organic substrate is desirable. We found that photocatalytic treatment efficiently decomposed phytotoxic compounds from rice hull, and the growth and yield of tomatoes in a closed system with the treatment were superior to a system without it. To enhance disease control in the system, this study investigated the suppression of bacterial wilt disease in a simulated waste nutrient solution with photocatalytic and silver treatments. The untreated waste nutrient solution had a high total organic carbon (TOC) concentration, and silver in the untreated solution had no antibacterial activity. By contrast, silver in the photocatalytically treated solution showed a high antibacterial effect via the low TOC of the treated solution. A similar trend of disease onset was observed when pathogenic bacteria were inoculated into the solutions used to cultivate tomato seedlings. These results suggest that, even if the concentration of organic species in waste nutrient solution from a closed system is high, lowering the TOC by photocatalytic treatment promotes the suppression of bacterial wilt disease through the antibacterial activity of silver. It is anticipated that combining photocatalytic and silver treatments will help to stabilize crop production in closed soilless cultivation.