Identificação, quantificação e inoculação de fungos micorrízicos arbusculares no sistema de produção de cana-de-açúcar

Abstract

Brazil is the main sugarcane producer worldwide, with the crop accounting for 15% of the total fertilizers used in the country. In this context, the development and application of arbuscular mycorrhizal fungi (AMF) (Phylum Glomeromycota) inoculants represents a promising alternative for increasing the utilization eficiency of chemical fertilizers, mainly the phosphates In the present work a survey of the AMF community was carried out before planting and after harvesting of the "plant cane" in renewal (rotated or not with Brachiaria ruziziensis) and expansion (previously under pasture) areas. A similar assessment was carried out in sugarcane renovation and expansion areas where two experiments of inoculation with diazotrophic bacterias were being conducted. Under greenhouse conditions, two experiments for selecting AMF strains for sugarcane (Variety SP81-3250) in different soils and substrates were carried out. In renewal areas, after maintained sugarcane monocropping, a rotation cycle with B. ruziziensis between the ratoon removal and the new cane planting doesnot influence the AMF species richness. Prolonged monoculture of sugarcane tends to reduce the AMF diversity after the renewal of the sugarcane plantation, but stills quite high compared to other agricultural systems. In pasture areas converted to sugarcane plantation (expansion) the AMF species richness tends to be higher in the first year after the conversion (plant cane) compared to sugarcane renovation areas. The spore density reached the highest values after the "plant cane" harvesting. The AMF isolates with potentiality to compose a mycorrhizal inoculant for sugarcane areAcaulospora colombiana and Claroideoglomus etunicatum which favoured the development of the pre-sprouted seedlings of sugarcane in soil and substrate. Other isolates that promoted the sugarcane seedlings' development ou nutrition, but still need additional studies are Gigaspora margarita, Scutellospora calospora and Rhizophagus clarus. The expansion area soil (with moderate P content) was the most favorable for the sugarcane growth. The Multiplant substrate promoted the highest growth of the seedlings and favored the AMF colonization. The fertillization recommended for sugarcane seedling production inhibited the plants growth, particularly in the substrate Turfa Fértil. The Sugar Mill substrate stimulated the seedlings growth the least. The rate of dark septate endophytes colonization (DSE) in the sugarcane seedlings of the cultivar SP81-3250 was high, independently of the inoculated AMF isolate. All the AMF isolates tested showed simultaneus colonization with DSE.