Abstract
Useful applications are anticipated for organic materials such as anaerobically digested slurry (ADS). In this study, the effects of ADS on soil-borne diseases were evaluated in soil culture and hydroponics using a pumice medium. The addition of ADS (10% w/w) to soil decreased the disease index of bacterial wilt in tomato caused by Ralstonia solanacearum from 3.3 to 0.2 (dead=4, healthy=0). The population of R. solanacearum in soil decreased more rapidly after an ADS application. The soil microbial activity measured by the dehydrogenase activity was enhanced by the application of ADS. The disease index of lettuce root rot caused by Fusarium oxysporum f. sp. lactucae was also reduced from 2.7 to 1.4 when ADS was applied to the infested soil at 20% (w/w). The addition of ADS had no inhibitory effects on the growth of tomato or lettuce; in fact, it resulted in increased growth. In a hydroponic culture using a pumice medium, an ADS application suppressed both the bacterial wilt of tomato and the damping-off of lettuce and spinach caused by Pythium ultimum and Rhizoctonia solani. It also delayed outbreaks of lettuce root rot. When an agar medium was added with filter-sterilized ADS, ammonia, and acetic acid, the growth of R. solanacearum and E oxysporum f. sp. lactucae was suppressed, suggesting that the chemical components in ADS have a direct suppressive effect on the soil-borne pathogens. These results indicated that ADS may function as an agent that reduces soil-borne diseases as well as an organic fertilizer.
