Trichoderma enriched compost, BCAs and potassium phosphite control Fusarium wilt of lettuce without affecting soil microbiome at genus level

Fusarium oxysporum f. sp. lactucae (Fol) is the causal agent of Fusarium wilt of lettuce, one of the most troublesome diseases affecting lettuce worldwide. Chemical control strategies are inadequate due to limited fungicide availability and consumer interest in organic vegetable production. Alternative control strategies, such as biological control agents (BCAs), suppressive compost, and resistance inducers, have been intensively studied to test their ability to reduce pathogen attacks. Research has been recently focused on the influence of BCAs on the rhizosphere microbiota, which plays a critical role in soil suppressiveness. In this work, three strategies of integrated pest management (IPM) were tested against Fol attacks in two fields for two consecutive years: (i) a compost enriched with Trichoderma, (ii) a combination of T. gamsii + T. asperellum, Bacillus amyloliquefaciens and potassium posphite and (iii) a combination of T. polysporum + T. atroviride. The rhizosphere microbiota was characterized by high-throughput sequencing of bacterial and eukaryotic rRNA gene markers. Obtained results indicated IPM strategies statistically reduced disease severity, in both fields and years, from 50 % to 70 % compared to untreated controls. An increased crop yield compared to untreated controls was also observed. Predominant phyla were Proteobacteria, Firmicutes and Actinobacteria for bacteria, and Ascomycota for fungi. However, microbiota populations were not affected by any of the treatments, nor were significant differences observed when the soil microbial community was compared to that of untreated controls. Conversely, large differences were observed when comparing the two fields and years, indicating an important microbial buffering effect triggered by the soil.