Integration of Soil Solarization, Trichoderma strain mixture, and Grafting: A Tripartite Root-Zone Strategy for Controlling Tomato Fusarium Wilt

Fusarium wilt (FW), caused by Fusarium oxysporum f. sp. lycopersici (Fol), severely limits tomato production in Saudi Arabia, with few environmentally friendly control options available. To address this challenge, three-week soil solarization (Ss), a soil-applied mixture of Trichoderma asperellum strains (TASMix), and grafting onto the resistant rootstock ‘Maxifort’ (GP), applied alone or in dual and triple combinations, were evaluated as root-zone management practices against FW. The results showed that all treatments significantly reduced FW compared with the untreated control; however, the integrated treatment (GP + TASMix + Ss) provided superior disease control, reducing FW incidence by 37.2 and 68.9% and the disease severity index by 64.2 and 56.82% in greenhouse and field trials, respectively. Quantitative PCR analysis revealed a notable reduction in pathogen abundance in tomato roots and the rhizosphere with this treatment. Moreover, Trichoderma rhizosphere colonization was positively enhanced by Ss treatment. Infection of tomato plants with the pathogen alone results in significant root damage associated with elevated oxidative stress. Concurrently, the combined GP + TASMix + Ss treatment significantly reduced reactive oxygen species (hydrogen peroxide and superoxide), decreased lipid peroxidation, and elevated antioxidant enzyme activities in root tissues. The combined action of GP + TASMix + Ss also led to higher transcript abundances of key defense-related genes involved in jasmonic acid- and salicylic acid-mediated defense responses more efficiently than the other treatments. To our knowledge, this study provides the first evidence of the integrative efficacy of GP + TASMix + Ss for FW management, offering a sustainable alternative to synthetic fungicides in organic farming.