Improving the Yield and Quality of Tomatoes (Solanum lycopersicum L.) Through Mulching and Beneficial Microbes

The present study was conducted to evaluate the effect of biodegradable mulches and microbial biostimulants (BMs) on processing tomato (Solanum lycopersicum L.) cv. Pietra rossa. A black Mater-Bi®-based film (MB), a black paper film (Np), a light-brown paper film (Sp), and bare soil (BS) were factorially combined with Trichoderma harzianum M10, T. afroharzianum T22, and the metabolite 6-pentyl-α-pyrone (6PP). The mulching practice influenced soil temperatures that were lower under all types of mulching from the end of May up to the first week of June, but, by contrast, they were greater than those of the BS just under MB for the entire next period. Mulching and BM application increased the marketable fruits (by 26% MB vs. BS and by 27% T22 vs. untreated control (CTRL)) and reduced rotten fruits (by 46% Np vs. BS and by 31% T22 vs. CTRL). Lycopene increased under MB and Sp (not Np) vs. BS and with 6PP and T22 (not M10) vs. CTRL, while ascorbic acid was unaffected by mulching and increased only with T22, and total phenols decreased with mulching but were unaffected by BMs. Tomato berry metabolism is treatment-dependent: 6PP consistently separated from the microbial-based treatments (M10 and T22) across all mulching types. Overall, it demonstrated a consistent and distinct impact on a subset of metabolites (i.e., phenolic acids and steroidal glycoalkaloids) across different mulching conditions compared to the microbial treatments, which exhibited a mulch-dependent accumulation.