Potencial de Trichoderma spp na solubilização de fosfato e promoção de crescimento vegetal

Abstract

Phosphorus is an essential element for plant growth and development; however, its limited availability, rapid immobilization, and leaching in the soil pose environmental and economic challenges. Plant growth-promoting fungi have the ability to solubilize phosphate complexed with other elements, produce phytohormones, and protect plants from phytopathogen attacks. These fungi can also synthesize enzymes, such as phosphatase and phytase, which aid in the mineralization of immobilized phosphate in organic molecules, making it more available to plants. Based on these aspects, the objective of this study was to optimize phosphate solubilization and evaluate plant growth-promoting characteristics in new Trichoderma isolates. Fungal growth was conducted in Pikovskaya medium with 0.5% phosphate fertilizers for 7 days at 28°C. After incubation, the inocula were filtered, and the supernatant was used for pH measurement and soluble phosphorus quantification. After selecting phosphate-solubilizing fungi, the following parameters were evaluated: solubilization time, phosphate sources, production of indole-3-acetic acid (IAA), siderophores, organic acids, and phosphatase and phytase enzymes. Finally, a greenhouse experiment was conducted to assess the plant growth-promoting effects of Trichoderma sp. G41 on corn (Zea mays ADV9339) seeds. Among the 22 fungi tested, Trichoderma sp. G41 proved to be the most promising, exhibiting phosphate solubilization of Ca3(PO4)2 (696.55 µg P mL-1), AlPO4 (421.98 µg P mL-1), and FePO4 (9.91 µg P mL-1) after 10 days of incubation. It also solubilized different commercial phosphate fertilizers, including thermophosphate tal qual (12.88 µg P mL-1), granulated thermophosphate (8.31 µg P mL-1), MV27 (169.66 µg P mL-1), and superphosphate (483.19 µg P mL-1). The fungus produced acid phosphatase (4.37 U mL-1) and phytase (1.51 U mL-1) enzymes, siderophores (74%), IAA (42.197 µg mL-1), organic acids, and exhibited growth tolerance in the presence of curbix (insecticide) and atrazine (herbicide). Trichoderma sp. G41 also maintained its phosphate-solubilizing capacity under stress conditions. In the presence of NaCl 150 mM, it reached 949.27 µg P mL-1, while at NaCl 300 mM, it solubilized 936.20 µg P mL-1. Under droght stress, it achieved 452.15 µg P mL-1 at -0.5 MPa and 498.27 µg P mL-1 at -1 MPa after 10 days of growth.In a greenhouse experiment with corn, treatments that received half the phosphate fertilizer dose and were inoculated with Trichoderma sp. G41 showed a 47% increase in root fresh matter and a 38% increase in shoot biomass. Inoculated plants exhibited higher chlorophyll, carotenoid, amino acid, and reducing sugar levels. Additionally, soil acid phosphatase and phytase activity increased in the presence of G41 under both fertilizer doses. Fluorescein diacetate hydrolysis indicated higher microbial activity in rhizospheric soil inoculated with the fungus. Based on these findings, Trichoderma sp. G41 demonstrated great potential as a phosphate-solubilizing agent, promoting corn growth and reducing the need for phosphate fertilizers. Thus, it stands out as a sustainable alternative for improving soil quality and enhancing agricultural efficiency.