Bactérias diazotróficas endofíticas em cana-de-açúcar : estratégia para uma agricultura sustentável

Abstract

Some Brazilian states, especially the Northeast, has its economy based on the cultivation of sugarcane, which depends on the success of this activity for the subsequent performance of its economy. In this context, priority is performing prospecting work diazotrophs and research to evaluate the potential of biological nitrogen fixation (BNF) in sugarcane under regional condition, applying technologies that enable the sustainable production of this crop. With that aimed to isolate and make characterizations morphophysiological, biochemistry and molecular endophytic bacteria stems and leaves of three varieties of sugarcane (RB1011, RB92579 and RB867515) and to evaluate the response of the cane sugar and the potential of BNF, the efficiency of inoculation of these bacteria as the productivity of stalks and technological qualities of sugarcane in the cycles of plant cane, cane ratoon and cane ressoca as support for sustainable crop production. 56 isolates were endophytic, being 62.5% and 37.5% of the stem of the leaf. We used molecular BOX-PCR technique that allows to differentiate into isolated sections 34 bands, for the formation of five distinct clusters that were selected for biochemical and / or physiological tests. These isolates, 66% were able to solubilize inorganic phosphate; 26% to produce urease, proteases produce 34%; 17% amylase to produce; 68% to produce lipase; 14% to produce chitinase; 17% of producing siderophore; 71% of produce ACC deaminase; 54% to produce N-acyl homoserine lactone (AHL); 51% to produce catalase and 23% showed hydrolytic ability to degrade gelatin; 97% reduced acetylene (ARA) with values between 4.14 and 7.84 nmol C2H4 / hour. To sequence the 16S rRNA ribosomal the presence of seven different genres, 46% identity was observed with the genus Bacillus, 20% to Paenibacillus, 14% Burkholderia, 6% Herbaspirillum, Pseudomonas and Methylobacterium and 3% Brevibacillus . Biochemical and molecular characterization of endophytic isolates stem and leaf of sugarcane revealed a diversity of bacteria colonizing this plant, with biotechnological potential to be used as biofertilizers. Three isolated by the nitrogenase activity and together with the responses of biochemical tests were selected to compose the microbial inoculant that was tested in the field for three years comprising the cycles of sugar cane plant, soca and ressoca the variety of sugarcane RB 92579 . We used the experimental randomized block design in a factorial 10x3, consisting of ten treatments (IPACC9 (Herbaspirillum seropedicae), IPA-CC33 (Pseudomonas sp.), IPA-CF65 (Bacillus Megaterium), IPA-CC9 + IPA-CC33, IPA-CC9 + IPA-CF65, IPA-CC33 + IPA-CF65, IPACC9 + IPA-CC33 + IPA-CF65, mix Embrapa (BR1140 (Azospirillum amazonense) BR11175 (H. seropedicae) BR11192 ( H. rubrisubalbicans) BR11284 (Gluconacetobacter diazotrophicus) and BR11364 (Burkholderia tropica), nitrogen witness (TN) and absolute control (TA)), three crop cycles (plant cane, cane and ratoon cane ressoca) with four replications totaling 40 plots for cultivation were evaluated the following parameters:.plant height, stem diameter, shoot dry weight, total nitrogen leaves +3, fresh stalk yield, sugar yield per hectare (TPH) content solids (° Brix) soluble fiber, total recoverable sugar (ATR) and estimation of the contribution of BNF nutrition of sugarcane by the technique of natural abundance of 15N isotope. Inoculation promoted significant gains compared to TA for the inoculated treatments was up to 57.31%. It found increases in productivity fresh stalk of up to 14 Mg ha-1 compared to TN, but not statistically differing from the other treatments. The similar behavior of the treatments inoculated with TN who received 60 kg ha-1 N, infers in low economic and environmental cost, and gains importance by the need to develop more sustainable agricultural practices to improve the quality of life of the population.