Bioprospecção e isolamento de bactérias associadas à cana-de-açúcar (Saccharum officinarum L.) com características para a promoção de crescimento vegetal

Abstract

Given the concern for environmental preservation, by cause of human activities and its profound impacts, research works have led to a shift from conventional said agriculture using agrochemicals and fertilizers to agriculture that pursues ways less harmful to the environment management. The objective was to prospect and also isolate the bacteria with proper characteristics for growth benefits from the rhizosphere sugarcane soil and its subsequent use in production of microbial inoculants. As to reach this purpose, 24 soil samples from sugarcane mills in the state of Alagoas were collected and isolated for qualification and quantification of soluble phosphorus, production of exopolysaccharides (EPS), verification of biofilm formation, production of indole acetic acid (IAA), cytokinins and gibberellins production, rooting induction and sugarcane budding. The used methodology for phosphate solubilization was performed according to the recommendations of the authors referenced in the bibliography. According to the results obtained for phosphate solubilizing growth medium (Nbrip) showed that 17% had high capacity and inorganic phosphate solubilizing growth medium capacity Reached 67%. The others results stayed between low or absence of solubilization. Of the isolates tested, 75 % Were able to grow in medium with low water activity Aw 0919 at 30 °C and the appearance of colonies was Observed five days after inoculation. Results for EPS production at room temperature showed that 4% of the isolates surveyed achieved a hight production, followed by 42% which has achieved average production and the remaining 54% of low production. Analysing biofilm production capacity in TSB medium in absorbance of 540 nm were observed that 4% of the isolates had a higher frequency for biofilm formation, 83% achieved average production and 13% of isolates with low frequency output. Larger quantity for production of IAA in the presence precursor L-tryptophan was observed at the end of 72 hours despite significant differences among the isolates, except for isolate 7 which was considered high 51.62194 μg.mL-1 and isolated 6 to lower production 14.98113 μg.mL-1, all other isolates were classified as high producers. Among the isolates tested 25% were able to synthesize cytokines and 83.33% synthesized gibberellin compared to the control. All isolates, compared in control, increased in size which suggested the action of one or both hormones in question at the same time. The sprouting of inoculated buds compared in control to those without inoculation, the RB72454 variety of sugarcane, in end of the evaluation, in the presence of isolated samples 4, 16, 21 and 24 demonstrated that only 25% of the buds had sprouted and grew roots, not differing significantly from the control. As the result inoculation significantly increased a sprouting rate up to 83.33% of the isolates, and the best results obtained were in samples 7, 12, 19 and 20 (94.5, 100, 95 and 94.5% respectively) in both the number of sprouted buds as for speed emission of shoots and roots.