Trichoderma harzianum M2 Induces Systemic Resistance to Fusarium Crown Rot and Remodels Root Architecture to Promote Phosphorus Uptake in Wheat

Wheat production is severely constrained by Fusarium crown rot (FCR) caused by Fusarium pseudograminearum and low soil nutrient use efficiency, making biocontrol an important strategy for sustainable agriculture. This study characterized a newly isolated Trichoderma harzianum strain, M2, and explored its bioprotective and growth-promoting mechanisms in wheat. Identified via morphological and phylogenetic analyses, strain M2 exhibited 91.24% in vitro inhibition against pathogenic F. pseudograminearum. Its 105 cfu/mL spore suspension remodeled root architecture and increased seedling biomass in hydroponic and pot experiments. Greenhouse and field assays recorded FCR control efficacies of 90.12% and 71.70%, respectively; field application of M2 reduced the disease index from 82% to 28%. RNA-seq and qRT-PCR indicated that M2 confers FCR resistance by triggering induced systemic resistance. Microscopy demonstrated that M2 penetrates root epidermal cells, forms biofilm-like structures and stably colonizes root xylem tissues. Furthermore, M2 enhanced soil phosphorus uptake and phosphorus accumulation in wheat. Collectively, endophytic root colonization and multi-hormone regulatory pathways enable T. harzianum M2 to improve wheat defense and performance, representing a promising agent for eco-friendly wheat production.