Bactérias halotolerantes associadas a plantas de cana-de-açúcar em solos da Zona da Mata de Pernambuco

Abstract

Brazil is the largest sugarcane producer in the world, with the Pernambuco State presenting a production of nearly 18.4 million tons. However, productivity growth and expansion of this culture has been hampered due to salinity in some soils, especially when subjected to dispose of vinasse, a byproduct of ethanol production. Excess salts cause toxic effects and a lower capacity for water absorption by plants. Like plants, the symbiotic bacteria present variation in salinity tolerance and could be affected in their characteristics of plant growth promotion. This situation can be corrected with the use of bacterial isolates tolerant to salinity. Thus, the objective of this study was to isolate and identify bacterial isolates sugarcane, and salt-tolerant plant growth promoters, which may contribute to the better development of this species, both already producing regions, as in regions of Pernambuco that have saline soils, and until then, there are cultivated with sugarcane. Therefore, root endophytic and rhizosphere were isolated in culture medium supplemented with 0 and 5% NaCl, plant sugarcane, collected in different soils, two under vinasse use and another without vinasse use. After isolation, were evaluated population density and characteristics of plant growth promotion, the tests consisted in checking the potential for biological nitrogen fixation (BNF), production of indole acetic acid (IAA), inorganic phosphate solubilization and production quorum sensing molecule. Furthermore, the diversity cultivable was assessed by means of restriction analysis of amplified ribosomal DNA (ARDRA) with two restriction enzymes. And uncultivable diversity was analyzed using the total DNA of rhizosphere soil and plant tissue (root) using the technique of DGGE of nifH. After the selection of bacterial isolates promoters plant growth, salinity tolerance tests were also performed. As a result, it was possible to isolate 102 bacterial isolates from rhizosphere and endophytic root, sugarcane, with various morphologies. Regarding population density, it was observed that there was no statistical difference between treatments. As for the potential for nitrogen fixation, production of IAA, phosphate solubilization and production of quorum sensing molecule, 72.5; 100; 75.5 and 49% of the isolates were positive, respectively. Both in the ARDRA technique as in DGGE of nifH, the dendrogram showed high genetic variability among isolates and among samples of plant tissue and rhizosphere, respectively. Moreover, it was observed that the salinity directly affects both bacterial growth, as characteristics of plant growth promotion. Therefore, this study contributed to the study of bacteria system/plant/soil, particularly regarding halotolerant bacteria associated with plant sugarcane, selecting isolates that may contribute to the better development of this important crop in different regions Pernambuco State.