Eficiência simbiótica da inoculação com bactérias promotoras de crescimento de plantas e fungos micorrízicos arbusculares em mudas de gliricídia

Abstract

Gliricidia sepium, Jacq., Kunth, Walp. is a medium-sized tree belonging to the Leguminosae family, and has great importance for the commercial area, due to its multiple use characteristics. Many leguminous trees, such as gliricidia, are able to form symbiosis with nitrogen-fixing bacteria (NFB) and arbuscular mycorrhizal fungi (AMF), which promote better absorption of nutrients. The BNF is a highly dependent energy process in ATP form. AMF activity therefore benefits this process because these microorganisms promote greater P uptake by plants. Plant growth promoting bacteria (PGPB’s) also can contribute to this process in them they are also able to solubilize phosphates. In this context, the work aimed to evaluate gliricidia’s nodulation and symbiotic efficiency by triple inoculation of PGPB’s - rhizobia - AMF, aiming to optimize BNF process. The experiment was performed in a greenhouse in randomized block design with 11 x 2 (+1) factorial arrangement. The 11 levels corresponded the inoculation of 10 PGPB's jointly inoculated with rhizobia and a rhizobia treatment independently - in presence and absence of AMF -, plus a control (control - no PGPB, AMF or rhizobia). Pots filled with 8 kg of soil (dystrophic Ultisol) were used as experimental unit. In the sowing was done the Rhizobium sp. (BR 8801) inoculation and co-inoculation with AMF + BPCP's. 10 days after sowing (DAS) re-inoculation was performed with Rhizobium sp. During plant growth, a nutrient solution without addition of nitrogen and phosphorus was used. The variables evaluated were: plant height (PH) at 30, 60, 90 and 120 DAS, shoot dry matter (SDM), root (RDM) and nodules (NDM); RDM / SDM ratio; root length (RL), total N accumulated (Nac) in SDM; phosphorus rate in SDM; efficiency of strain (E), phosphorus rate (P), P contents and mycorrhizal colonization (MC). Treatments showed significant effects for all variables. AMF addition in treatments promoted better results for the evaluated variables, observing significant difference (p <0.05) for treatments with co-inoculation of BPCP's and no significant difference (p>0.05) for treatment inoculated with Rhizobium (BR 8801), in presence or absence of AMF. BR 8801+EL-183+AMF treatment promoted the best response for gliricidia