Resumo

Among the different soil microorganisms, the arbuscular mycorrhizal fungi (AMF) are known for interacting directly with plants playing an important role in the balance of plant communities. This study aimed to evaluate the activity of arbuscular mycorrhizal fungi (AMF) in the sugarcane rhizosphere soil naturally infested with Meloidogyne sp., in northeastern Brazil. Composite samples consisting of 10 subsamples from sugarcane rhizosphere soil were collected in the city of Carpina, PE, directly from two experimental sites, one infested with eggs and juveniles of phytonematode Meloidogyne sp. (area A) and the other with absence of Meloidogyne sp. (area B). Glomerospores were extracted from 100 g of soil by wet sieving, followed by centrifugation in water and 50% sucrose and quantified with the aid of a stereomicroscope. Mycorrhizal colonization was evaluated as follows: root samples were washed, cleared with KOH (10%) and stained with Trypan Blue (0.05%). Stained root segments were mounted on slides and observed under a light microscope for the presence/absence of mycorrhizal structures. In each sample the soil was mixed and 10 replicates of 0.25 g were processed to extract easily extractable Bradford reactive soil protein (EE-GRSP) and Bradford reactive soil protein after extensive extraction (TG-GRSP). EE-GRSP was extracted with citrate (20 mm, pH 7.0) at 121 °C for 30 min. TG-GRSP was extracted (50 mM, pH 8.0) at 121 °C. The number of glomerospores was significantly different between A (31.5 glomerospores 100•g^-1 of soil) and B (127 glomerospores 100•g^-1 of soil) areas. The colonization rate of AMF was very high (90%) in both areas. No significant differences were seen in the deposition of glomalin (1.22 to 1.34 and from 1.18 to 1.29 mg•g^-1 aggregates for EE-GRSP and TG-GRSP, respectively) in the two areas evaluated. In general, mycorrhizal activity in the sugarcane rhizosphere was not altered by the presence of Meloidogyne sp.