Soilless cultivation has increased in China. Like vegetables or ornamental plants, tomatoes can be cultivated in soilless culture systems. Fusarium wilt (FW) is an economic tomato disease. The nature and amount of volatile organic compounds in Trichoderma asperellum PT-15 were investigated, and 6-pentyl-α-pyrone (6-PP) was detected. Furthermore, the effect of 6-PP on Fusarium oxysporum HF-26 was evaluated. Results revealed that 25 mg/L 6-PP was the optimal concentration inhibiting F. oxysporum HF-26 and that the content of fusaric acid decreased considerably compared to that of the control. FUB1, FUB4, and FUB10 toxin synthesis and transport genes were downregulated. Additionally, VelA, velB, and LaeA genes were downregulated, reducing F. oxysporum mycelial growth and hyphae formation. 6-PP was added to the soilless culture solution in a greenhouse experiment. The results showed that an antifungal–nutrient solution containing 25 mg/L 6-PP significantly suppressed FW with 70.71% efficacy and a 27.23% disease index (DI), which were higher efficacy and lower DI than that of the control. Furthermore, treatment with an antifungal–nutrient solution containing 6-PP increased the levels of defence enzymes 24 h post-inoculation (hpi) compared with those at other time periods. The relative expression levels of the PR1, NPR1, PR2, and PR5 genes were considerably upregulated at 24 hpi.

Potatoes are among the four most important staple crops worldwide. Verticillium wilt in potatoes caused by Verticillium dahliae is a devastating disease that is difficult to control. To identify potential avenues for disease control, the pathogenicity of 72 V. dahliae isolates was tested here. We also tested the resistance to the most virulent isolate (Vd-36) induced by the attenuated isolate Gibellulopsis nigrescens Vn-1 in potatoes. Induction of Verticillium wilt resistance in potatoes was strongest when using attenuated isolate Vn-1 to inoculate potatoes with a spore suspension concentration of 1 × 106 conidia mL−1, followed by infection with isolate Vd-36 at 5 d intervals. After incubation of potatoes with the attenuated isolate Vn-1 followed by isolate Vd-36, reactive oxygen species (ROS) and hydrogen peroxide (H2O2) were produced and accumulated in potato leaves 12 h post-inoculation. The changes in respective defense enzymes, except phenylalanine ammonia-lyase, were consistent with the changes in ROS and H2O2 levels. Furthermore, the content of salicylic acid (SA) in inoculated plants was higher than that in the control, and biosynthesis-related genes StNPR1, StPR1b, StPR2, StPR5 were activated. However, there was no significant difference in the jasmonic acid and ethylene (JA/ET) content between the treatment and control groups. These results demonstrated that the attenuated isolate Vn-1 enhanced resistance to Verticillium wilt by inducing the SA signalling pathway and weakly activating the JA/ET signalling pathways in potatoes.