Serendipita Species Trigger Cultivar-Specific Responses to Fusarium Wilt in Tomato

The endophytic fungi Serendipita indica and S. vermifera have recently gained increasing attention due to their beneficial effects on plant growth and plant health. Little is known about other species, such as S. williamsii and S. herbamans. To test their biocontrol and growth-promoting potential, susceptible and tolerant tomato cultivars (Kremser Perle and Micro-Tom, respectively) were inoculated with S. williamsii, S. herbamans, S. indica, or S. vermifera and challenged with the soilborne pathogen Fusarium oxysporum f. sp. lycopersici (Fol) in greenhouse experiments. Furthermore, in vitro assays on the direct inhibitory effects of Serendipita spp. against Fol were performed. Negative effects of Fol on phenological growth in the susceptible cultivar were alleviated by all four applied Serendipita spp. Apart from these similar effects on biometric parameters, disease incidence was only reduced by S. herbamans and S. vermifera. In the tolerant cultivar, disease parameters remained unaffected although shoot dry mass was negatively affected by S. vermifera. Direct effects of Serendipita spp. against Fol were not evident in the in vitro assays indicating an indirect effect via the host plant. Our results highlight the importance of identifying cultivar-specific effects in pathogen–endophyte–plant interactions to determine the most beneficial combinations.