Tailor-made green composts with suppressive properties against tracheofusariosis of wild rocket (Diplotaxis tenuifolia): useful option for sustainable circular horticulture

Intensive cultivation systems of wild rocket (Diplotaxis tenuifolia) are threatened by the outbreak of tracheofusariosis caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. raphani. The disease is difficult to eradicate by curative methods due to the endophytic progression of the pathogen. Suppressive composts can help to prevent this adversity by providing organic matter carrying chemical and biological components that can directly and/or indirectly interfere with the plant-pathogen system. In this study, a collection of seven promising composts from different selected green feedstocks were investigated for their suppressive properties towards wild rocket Fusarium wilting. In planta assays identified two composts, obtained from olive tree pruning+plant and tomato residues, and from olive waste+straw+wool residues, with the highest levels of suppressiveness, influenced by both application dose and plant development stage. These active composts showed overlapping 13C-NMR profiles as in vivo suppressiveness, being positively correlated with the organic aliphatic alkyl, OAryl and carboxyl C fractions and subsequently with the hydrophobic index and alkyl ratio, and negatively with the lignin ratio. On the contrary, although biotic compost components showed antifungal effects, biological properties did not correlate with in planta wilting suppression. Consistently, reflectance spectroscopy in the Vis-NIR-SWIR highlighted the clustering of samples depending on their feedstock and chemical composition. The results allow the hypothesis of a plant-mediated suppression mechanism. The composting of crop residues improves the circularity of horticulture and makes it possible to produce, from selected matrices, tailored compost towards the sustainable cultivation of wild rocket.