An assessment of the modulation of the population dynamics of pathogenic Fusarium oxysporum f. sp. lycopersici in the tomato rhizosphere by means of the application of Bacillus subtilis QST 713, Trichoderma sp. TW2 and two composts

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (Fol), results in considerable yield losses for tomato crops throughout the world. In this study, experiments were carried out in situ over two consecutive years to evaluate the efficiency of two biological control agents (BCAs) (Bacillus subtilis QST 713 and Trichoderma sp. TW2), and two composts in controlling the disease. In this context, the quantitative polymerase chain reaction was used along with soil chemical parameters to study the general effects of treatments on the severity of the disease and on the non-target microbial populations residing in the studied rhizosphere and bulk soil. The ecological fitness of the BCAs was also evaluated. Furthermore, as BCAs produce elicitors which may activate plant defense reactions, particular attention was paid to the induction of pathogenesis-related genes (PR) in the roots of tomato plants. The preventative nursery application of all two types of biocontrol agents, that is, Bacillus subtilis QST 713, Trichoderma sp. TW2, and compost, as separate treatments, induced a significant reduction in the disease, compared to the untreated control, and reduced tomato Fusarium wilt by 70%. This result was confirmed by the significant negative correlations between the abundance of biological control agents and the severity of the disease. In general, the BCA and compost treatments did not induce a negative effect on the non-target microbial communities. The transcript levels coding for the studied pathogenesis-related (PR) genes were always higher in the untreated control for all the genes considered in the study. However, the accumulation of transcripts in the tomato roots was different, depending on the treatment. An important level of disease reduction was shown by a decrease in Fol abundance, together with a greater abundance of the inoculated BCAs populations and an accumulation of transcripts encoding PR genes. In short, the results of this study reinforced the concept of the sustainability of treatments based on biological control agents and composts for the management of tomato Fusarium wilt.