Efeito da inoculação de bactérias diazotróficas dos gêneros Herbaspirillum e Burkholderia em genótipos de milho

Abstract

The selection of diazotrophic bacteria for application in maize has been the goal of the research in the last the 30 years. First, strains from the Azospirillum genus were used, being the most published literature about the use of A. brasilense. At this moment, the researches disclosed that an amply diverse community of diazotrophic bacteria not only colonizes roots, but also stems and leaves of maize, and new genus and species had been described. The objective of this study was to test the effect of growth promotion of Herbaspirillum and Burkholderia strains, isolated from different places and deposited in the Embrapa diazotrophic bacteria collection at Embrapa Agrobiologia. This selection used 49 strains, being 24 of Herbaspirillum genus and 25 of Burkholderia genus. The selection consisted of a phase where seeds of the hybrid maize SHS 5050 and maize variety BRS Sol da Manhã had been planted in sterile substratum. The inoculated treatments had received 1 mL per seed from a cellular suspension contend 108 - 109 cells and 150 mg of N, being the controls an absolute witness and two witnesses not inoculated, but fertilized with 150 and 300 mg of N, respectively. The used delineation was entirely at random with 4 repetitions. After 40 days the plants had been collected and eva luated dry matter accumulation of the aerial part and root system, root area and length and % nitrogen. All the variables had been evaluated by the Scott-Knott test at 5 % of probability. In the second phase, the same test was done in nonsterile soil. At this moment the best 21 strains were tested. In the third phase, the best strain BR 11417 (ZAE94 Herbaspirillum seropedicae) was evaluated in experiments with maize planted in two periods, normal cycle or safra , and a short cycle or safrinha in 2005/2006. The field experiments were conducted using random blocks with six repetitions. In the safra experiment four genotypes were tested: Sol da Manhã (variety), BRS 106 (variety), BRS 1030 (Hybrid simple), and SHS 5050 (Hybrid triple) in the Embrapa Agrobiologia. At the safrinha , the variety Sol da Manhã was not used. The inoculant containing the selected strain was applied in the absence of N and in the presence of increasing doses of fertilizing N (40 and 80 kg ha-1), besides the same treatments witho ut inoculation. The grain productivity, the number of spikes per plant, and the N level in the grains were evaluated. All the variables in the last phase of selection (field) were evaluated by Scott-Knott test, when the factors inoculation and genotype were tested, and regression test when used the factor fertilization. In addition, the technique of the natural abundance of 15-N was used to quantify the BNF. The results had shown that the application of the inoculant resulted in increment of maize productivity up to 34 %, though it showed to be non-significantly, depending on the maize genotype and the N-mineral dosage. The BNF quantification results had lead to the conclusion that the hybrid SHS 5050, inoculated with the selected strain, presented higher capacity of obtaining contribution to its nitrogen supply from the BFN than the other varieties, inoculated with the same strain in both experiments at different time.