An integrated control of Pythium root rot of greenhouse tomato.

Pythium root rot caused by Pythium aphanidermatum is one of the most important diseases of greenhouse tomatoes. Hydroponic culture exacerbates the problem. Both nutrient film technique (NFT) and recirculating growing systems pose a challenge in the control of this disease, because the pathogen, especially the zoospores, can spread easily in the recirculating solution to the whole growing system. Fortunately, hydroponically grown plants are easier to manipulate than soil grown plants, proper manipulation of root environments can lead to excellent disease control. This paper reports the development of an effective integrated control measure for pythium root rot of tomato by integrating pH, bioagent, and ultra-violet irradiation in a specific manner. This integrated control consists of three operations: a) before transplanting, the UV system is connected to sterilize the recirculating solution using 100 mJcm-2; b) after transplanting, the nutrient solution is delivered at pH 5.0 regime for five weeks followed by adjusting pH to 5.8 to 6.2 regime for one week; and c) bacterial bioagent, such as Pseudomonas is introduced into the root zone at 100 mL per plant at 10(8) bacteria mL-1 or added to the nutrient solution to arrive at 10(6) bacteria mL-1 in the solution. This report also discusses the advantages and limitations of this measure in the control of pythium root rot.