Enhancing Sorghum Growth: Influence of Arbuscular Mycorrhizal Fungi and Sorgoleone

The low availability of phosphorus (P) in soil is one of the main constraints on crop production. Plants have developed several strategies to increase P use efficiency, including modifications in root morphology, the exudation of different compounds, and associations with microorganisms such as arbuscular mycorrhizal fungi (AMF). This study aimed to investigate the effect of sorgoleone compound on AMF colonization and its subsequent impact on P uptake, rhizosphere microbiota, and sorghum growth. The experiment was conducted in a greenhouse using the sorghum genotype P9401, known for low sorgoleone production. Three doses of purified sorgoleone (20 μM, 40 μM, and 80 μM) were added to low-P soil and plants were harvested after 45 days. Treatments included inoculation with the arbuscular mycorrhizal fungi Rhizophagus clarus and a negative control without inoculum. The addition of 40 and 80 μM of sorgoleone did not significantly increase mycorrhization. However, treatment with 20 μM sorgoleone combined with R. clarus inoculation significantly increased total sorghum biomass by 1.6-fold (p ≤ 0.05) compared to the non-inoculated treatment. AMF inoculation influenced only AMF colonization and the fungal microbiota, without affecting the bacterial community, whereas sorgoleone showed no effect on either. The activities of acid and alkaline phosphatases in the rhizospheric soil did not differ significantly among the treatments. Furthermore, the sorghum genes CYP71AM1, associated with sorgoleone biosynthesis, and Sb02g009880, Sb06g002560, Sb06g002540, and Sb03g029970 (related to phosphate transport induced by mycorrhiza) were significantly upregulated (p ≤ 0.05) in fine roots under these conditions. The 20 μM concentration of sorgoleone can enhance AMF colonization in sorghum and promote plant growth under low-P conditions, without significantly altering the microbiota.