Root inoculation with Trichoderma harzianum primes metabolic and stress-response pathways underlying growth and...

Trichoderma is a genus of filamentous soil fungi commonly associated with plant roots, where several species act as plant growth-promoting microorganisms and can induce tolerance to biotic and abiotic stress. Here, we evaluated whether root inoculation with Trichoderma harzianum enhances growth and resistance in turnips (Brassica rapa) against grey mold (Botrytis cinerea) and the green peach aphid (Myzus persicae). Plants were root-inoculated with T. harzianum, and vegetative growth, disease lesion development, aphid fecundity, phytohormone accumulation, and transcriptomic responses were assessed using RNA sequencing. Trichoderma inoculation significantly enhanced vegetative growth, reduced the size of grey mold lesions, and decreased aphid fecundity. Transcriptomic analyses revealed enrichment of pathways related to plant hormone signal transduction, glucosinolate biosynthesis, MAPK signaling, and nitrogen metabolism. Genes encoding delta-pyrroline-5-carboxylate synthase (P5CS) isoforms, 4-α-glucanotransferase (DPE2), phosphoglucomutase, and the protein quality-control factor CDC48 were upregulated, whereas transcripts encoding cytosolic glutamine synthetases, FAHD1, and an NRT1/PTR-family transporter were downregulated. These expression patterns indicate a coordinated reprogramming of primary metabolism and defense-associated pathways. Collectively, our results demonstrate that T. harzianum enhances turnip growth and confers resistance to both fungal and insect antagonists through integrated metabolic and stress-response priming, supporting its potential application as a biocontrol and growth-promoting agent.