Abstract
Major problems for hydroponics are higher operational cost and pollution due to discharge of waste nutrient solution. Besides, water culture has disadvantage for plant pathogenic distribution in the system due to shortage of buffer action in comparison with soil cultivation. To solve these problems, recycling use of nutrient solution by ultrafiltration was studied. Plants used were Lettuce (Lactuca sativa L.) and sporangia of Pythium aphanidermatum, a pathogen. Growth of lettuce was inhibited by inoculation of 2.01×104 sporangia/l or more of sporangia but they recovered viability at 22nd day after inoculation. Inoculation of 1.00×106 sporangia/l represented lethal effect on lettuce. Whether inoculation period of P. aphanidermatum to water culture was at the lst week or month, lettuce deceased. Sporangia of P. aphanidermatum were perfectly removed by untrafiltration. P. aphanidermatum produced pathogenic substance of below 20, 000 MW, which caused lettuce root rod decease. This substance seems unstable under heating condition. Experimental results suggest that ultrafiltration is effective to remove pathogenic microoganisms from nutrient solution but if pathogenic microorganisms produce some harmful substances, another/combined treatment of nutrient solution should be necessary.
