Rizobacterização no crescimento de mudas de sibipiruna (Caesalpinia peltophoroides Benth)

Abstract

This work aimed to evaluate the potential of growth-promoting rhizobacteria for seed germination and biomass of the root system and aerial part of seedlings of sibipiruna (Caesalpinia peltophoroides). Isolates pre-selected for eucalyptus were used. Two assays were carried out: A selection assay using rhizobacteria isolates in saline suspension and another with the isolates selected in different formulations (liquid and solid) and saline suspension. The second assay was repeated for confirmation of the results. In the first assay, the following isolates were tested: Ca, FL2, MF2, MF4, RC3, R1, 3918, S1, S2 and CIIB. Thus, samples of vermiculite-based substrate and carbonized rice hull (1:1) were treated with 5 mL of a suspension of each isolate (OD540= 0.2 A)/ tubette of 55 cc capacity corresponding to around 10 ufc/mL. The experimental design was completely randomized (CRD) with five repetitions per treatment, each constituted by 20 seeds. At 40 days, germination percentage and dry mass of the roots and the aerial parts were evaluated. A significant increase was observed in dry matter of the root and aerial part for all the rhizobacteria isolates tested, compared to the control. All the isolates provided significant germination increase, except 3918 and CIB, which did not differ from the control. Among the tested isolates, four were the most promising (FL2, MF4, MF2 and CIIB) and were subsequently tested in two formulations (liquid and solid) and in saline suspension. For each tubette containing 55 cc of substrate, 1 mL of the liquid formulation, 1 g of the solid formulation, and 5 mL of the innoculum were applied in the saline suspension. The experimental design was completely randomized in a factorial scheme (4 x 3) with an additional treatment (control), using the same number of repetitions and seeds of the first assay. The second assay was evaluated at 40 days. No significant difference was found between the liquid, solid formulations and the innoculum in saline suspension, but all differed significantly from the control in height, and root dry matter and aerial part height. The mean gains in dry matter of the aerial part, root dry matter and aerial part height were 57.9%, 51.8% and 17.1%, respectively. This assay was repeated and its evaluation was reduced to 30 days. Differently from assay 2, a significant difference between the liquid/ solid formulations and the saline suspension was observed, with the liquid formulation promoting higher gains in height, dry matter of the aerial part and root system, compared to the innoculum in saline suspension, for the isolates CIIB and MF2. For FL2, the highest gains in dry matter of the root and aerial part were promoted via solid form. The isolate MF4, formulated liquid, did not differ statistically from the MF4 in saline suspension for germination, height and dry matter of the aerial part. When analyzing the mean gain of the isolates superior to the control in the different formulations and saline suspension, it was observed that when the liquid formulation was applied, gains were obtained in germination, height, and dry matter of the root and aerial part of 13.4%, 35.5%, 47.1% and 23.9 %, respectively. For the solid formulation, the gains in germination, height, dry matter of the root and aerial part were 16.3%, 35.0, 46.5, and 19.4 %, respectively, while for the inoculum in saline suspension the gains were 13.8% for germination, 30% for height, 32.3% for root dry matter, and 15.3% for aerial part dry matter. The results obtained show significant gains in seedling production, without any adjustment in nursery management or structure. In addition to this direct gain, it is possible to make a better use of the physical structure of the nurseries by reducing the time needed for seedling formation, reducing the production costs.