Eruca vesicaria leaf extracts and intercropping mitigate the Kiwifruit Vine Decline Syndrome and modulate the rhizosphere pathobiome

Background: Kiwifruit Vine Decline Syndrome (KVDS) is the most significant soil-borne disorder affecting Actinidia spp., impacting both yield and economics, often forcing farmers to switch crops once the diseases occur. The Oomycota phylum is a key component of the root rhizosphere pathobiome. Aside from proper irrigation—preventing KVDS-favourable conditions—there are no effective management strategies. Yet, the lack of soil treatments and concerns over fumigants drive the search for sustainable alternatives. Methods: In this study, leaf extracts from rocket (Eruca vesicaria subsp. sativa) were tested for their potential to control KVDS. The isothiocyanates, key components of rockets, are known to counteract soil-borne pathogens. The extracts were applied in different concentrations to kiwifruit plants (Actinidia chinensis var. deliciosa ‘Hayward’) grown in pots with KVDS-promoting soil. Additionally, kiwifruit plants were intercropped with rocket (‘Astra’, ~ 20 plants per pot) to evaluate whether intercropping could also help control KVDS. Results: The highest dose of rocket leaf extract and intercropping reduced KVDS symptoms by 70–80% compared to untreated plants (p < 0.05). To further investigate the mode of action of rocket extracts and intercropping, their effects on the rhizosphere Oomycota pathobiome were analysed using a metabarcoding approach. To achieve this aim, an in-house reads reference dataset was created and implemented due to the lack of public reference databases. Data were processed via QIIME2, identifying six out of twelve oomycetes at species level. Treatments altered the pathocommunity, reducing several pathogens—most notably Phytopythium vexans (p < 0.05). Concurrently, Globisporangium intermedium increased in treatments with the highest extract dose and intercropping, correlating with symptom reduction (r2: -0.86). Discussion: Our results suggest G. intermedium being less pathogenic than P. vexans yet competes for the same root niche. In fact, P. vexans highly correlated with symptoms display (r2: 0.97). Lastly, P. asiatica was also identified, another oomycete strongly associated with the dysbiosis. These findings suggest that rocket-based treatments could be a promising strategy for KVDS management, potentially applicable in field conditions.