Additive Effects of Silver-coated Cloth in Hydroponic Solution in Protection against Pythium Root Rot of Cucumber and Japanese Hornwort without Residual Silver in Cucumber Fruit

Silver-coated cloth or silver oxide (Ag2O) markedly inhibited root rot diseases of cucumber and Japanese hornwort (Cryptotaenia japonica Hassk.) caused by Pythium spp. Silver oxide (Ag2O) at 30ppb in hydroponic nutrient solution inhibited zoospore motility of Pythium aphanidermatum and Pythium sp. type F. Germination was also inhibited by 10 percent over that of the control which was unexposed to silver oxide. Germination of zoospores was also inhibited completely by 50ppb silver oxide. When the concentration of silver ion eluted from silver-coated cloth into the hydroponic solution was about 40ppb, zoospores of Pythium spp. lost their ability to swim and germinate. After using silver-coated cloth in hydroponic culture of cucumber plants for more than 40 days, the residual amount of silver ion in cucumber fruits was less than the limit of Ag detection by atomic absorption spectrophotometer.