<i>Colletotrichum tofieldiae</i> enhances phosphorus uptake and biomass production and alters the microbial interactions in the rhizosphere of komatsuna (<i>Brassica rapa</i> var. <i>perviridis</i>) grown in phosph

Microbial bioinoculants should play important roles to achieve sustainable phosphorus (P) management in agriculture. <i>Colletotrichum tofieldiae</i> (Ct), a fungal endophyte, is a promising material that supports phosphorus acquisition in <i>Arabidopsis</i> under low phosphorus (P) conditions and promotes maize and tomato growth in a greenhouse. However, its effects on leafy vegetables such as komatsuna, particularly those with a range of P availability in the soil, remain largely unclear. This study evaluated the impact of Ct inoculation on komatsuna growth, P uptake, rhizosphere soil and plant microbiological properties in sterilized and non-sterilized farm soils in Japan. The Ct mycelium was incubated in a mixture of rice bran, wheat bran, and wood chips for two weeks, and then applied to the soils at 0%, 1%, and 5% mass ratios (Ct0, Ct1, Ct5). Ct0 was the sterilized medium applied at a 5% mass ratio. Non-sterilized and sterilized soils received 20 and 80 mg P kg^-1 as low and high P treatments, respectively. Ct significantly increased plant biomass in a manner dependent on the initial inoculation dose in Low P- and High P-amended soils, although Ct-mediated plant growth promotion was more prominent in the low P-supplemented soils. Furthermore, Ct inoculation was found to increase microbial activity such as P solubilization, in rhizosphere soil and/or roots under both P conditions. This study is the first to demonstrate the positive influence of Ct on Brassicaceae growth in not only P-deficient but also P-supplemented soils, confirming its potential to improve plant development under P-deficient and P-supplemented soil conditions.