Microplastic influences the ménage à trois among the plant, a fungal pathogen, and a plant growth-promoting fungal species

Microplastics (MP) can influence a plethora of fungal species within the rhizosphere. Nevertheless, there are few studies on the direct impacts of MPs on soil fungi and their intricate interplay with plants. Here, we investigated the impact of polyethylene microspheres (PEMS) on the ecological interactions between Fusarium solani, a plant pathogenic fungus, and Trichoderma viride, a fungal plant growth promotor, within the rhizosphere of Solanum lycopersicum (tomato). Spores of F. solani and T. viride were pre-incubated with PEMS at two concentrations, 100 and 1000 mg L-1. Mycelium growth, sporulation, spore germination, and elongation were evaluated. Tomato seeds were exposed to fungal spore suspensions treated with PEMS, and plant development was subsequently assessed after 4 days. The results showed that PEMS significantly enhanced the sporulation (106.0 % and 70.1 %) but compromised the spore germination (up to 27.3 % and 32.2 %) and radial growth (up to -5.2% and -21.7 %) of F. solani and T. viride, respectively. Furthermore, the 100 and 1000 mg L-1 concentrations of PEMS significantly (p<0.05) enhanced the mycelium density of T. viride (9.74 % and 22.30 %, respectively), and impaired the germ-tube elongation of F. solani after 4 h (16.16 % and 11.85 %, respectively) and 8 h (4 % and 17.10 %, respectively). In addition, PEMS amplified the pathogenicity of F. solani and boosted the bio-enhancement effect of T. viride on tomato root growth. Further, PEMS enhanced the bio-fungicidal effect of T. viride toward F. solani (p<0.05). In summary, PEMS had varying effects on F. solani and T. viride, impacting their interactions and influencing their relationship with tomato plants. It intensified the beneficial effects of T. viride and increased the aggressiveness of F. solani. This study highlights concerns regarding the effects of MPs on fungal interactions in the rhizosphere, which are essential for crop soil colonization and resource utilization.