Tsubasa Tanabe, Department of Environmental Engineering for Symbiosis, Soka University, Hachioji, TOKYO, JAPAN and Shinjiro Sato, Department of Environmental Engineering for Symbiosis, Soka University, Hachioji, Japan
Fertilizer effects of the anaerobic digestion effluents (ADEs) on plant growth have been studied with different types of ADEs and soils. However, only few studies examined a suppression effect of ADE application to soils on soil-borne plant diseases, and many aspects of the effect are unknown. Tomato plants can be infected by and die from a bacterial wilt of tomato (BWT) caused by Ralstonia solanacearum, which can be found around the world and is resistant once infected. Therefore, the objective of this study is to compare the suppression effect of the ADE application with other conventional methods on the BWT. ADEs used were derived from Egeria densa (ED) and a mixture of cow manure and food waste (CF), and sterilized form of each feedstock (EDS and CFS, respectively). The conventional methods include the application of wood vinegar (WV) and hot water (HW). Isolated R. solanacearum was applied except control treatment (CT) to all treatments, and tomato plant was cultivated for 70 days. The ED treatment showed lower disease index of the BWT than the ADE treatments did, but the higher disease index compared with the HW treatment. A study showed an effective suppression effect of ADE on the disease index of the BWT only when ADE application rate was more than 10% (w/w), however in this study, ADE was applied to soil by only 2-4% (w/w). Therefore, it appeared that the amount of ADE applied to soil in this study was not enough to show the suppression effect on the disease index, but delayed pathogenic process of the BWT. The ED treatment decreased the population of R. solanacearum in soil more than other treatments, and increased the population of other gram-negative bacteria, which could prevent R. solanacearum from increasing in soil.