Penicillium aculeatum pre-activated with cellulose and different phosphorus sources promotes maize growth, nutrition and mycorrhiza formation, and decreases Microdochium bolleyi root infection.

Microbial plant growth promoters often perform inconsistently under natural soil conditions most likely due to their poor establishment after inoculation. Here, we conducted a growth chamber pot experiment with maize using pre-activated inoculum of the P-solubilizing fungus Penicillium aculeatum to facilitate its establishment in a natural non-sterile agricultural soil. Hence, P. aculeatum was preincubated for one week in soil amended with cellulose as a C source and with different P sources, i.e. sewage sludge ash, Ca3(PO4)2, and no P fertilization as control. Control treatments of C and P sources without P. aculeatum were also included. The pre-activated inocula were mixed into natural agricultural soil (1:40 w/w), maize seeds were sown, and plants were grown for 42 days. Measured variables included shoot and root dry weight, nutrient content, and root colonization by arbuscular mycorrhizal fungi (AMF) and root infection with Microdochium bolleyi. Overall, P. aculeatum inoculation enhanced maize growth, nutrient content and AMF root colonization, while reduced root infection with M. bolleyi, independent of P source used. Both P sources increased maize growth and nutrient content, though sewage sludge ash showed stronger effect than Ca3(PO4)2. None of the P sources affected AMF root colonization, but sewage sludge ash decreased M. bolleyi root infection and increased the population density of P. aculeatum. In conclusion, inoculation with pre-activated P. aculeatum (with cellulose and P sources) enhances maize growth and nutrient uptake, and is associated with increased AMF root colonization and reduced root infection by M. bolleyi.