Use of composts to manage corky root disease in organic tomato production

Corky root disease of tomato caused by Pyrenochaeta lycopersici is an economically important disease in organic tomato production. This study aimed to evaluate the effects of various composts consisting of green manure, garden waste and horse manure against corky root disease through bioassay under greenhouse conditions, where soil naturally infested with P. lycopersici was used as a root substrate. The various composts were mixed at a rate of 20% (v/v) with the infested soil. Disease severity (measured as infected roots) in the unamended soil was compared with that in the soil–compost mixtures. One of the composts made from garden waste significantly reduced the disease, whereas horse manure compost significantly stimulated it. Lower concentrations of NH4-N and total carbon and a higher concentration of Ca in the substrate were correlated with lower level of corky root disease. Addition of green manure or garden waste compost to the infested soil increased total microbial activity or population density of copiotrophic bacteria and actinomycetes, respectively. However, increased microbial activity or microbial population in soil–compost mixtures was not associated with a reduction in corky root disease severity in the present study.