Abstract
Since abiotic and biotic factors can compromise the survival of bacteria and their viability, encapsulation of cells in biodegradable gel matrices, a biological macromolecule, is one alternative to have their shelf life extended. Here, it was developed a gel-based formulation of the bioinoculant Azospirillum brasilense strain AbV5 and determined the effect of trehalose and humic acid supplementation in viability and survival of bacteria. For each 2 ml of sodium alginate solution (3%), 1 ml of the inoculum was extruded in a solution containing sodium alginate complexed with calcium chloride, forming calcium alginate beads. Supplements were used in a ratio of 2:2:1. Treatments were peat; alginate; alginate + humic acid; alginate + trehalose 0.1 M; alginate + trehalose 1 M. Morphometric aspects, survival rate and viability were determined in 9 storage periods (3, 5, 7, 14, 21, 30, 45, 60, 90 days). As results, beads were able to sustain the growth of A. brasilense for 90 days. Shelf life quality decreased in all treatments and peat remained the best carrier. Encapsulation, despite promoting the greatest losses in the survival of bacteria in the first days, ensured better cell viability. Trehalose in low concentrations (0.1M) improved cell viability during storage, optimizing plant inoculation.
Highlights
World food production is based on the extensive use of chemical fertilizers, which pollute the environment and are expensive due to their non-renewable sources like fossil fuels, used in their exploitation, transportation and application (Schoebitz, López, & Roldán, 2013)
Eco-friendly and economical alternatives have been increasingly demanded. Among some of these alternatives, plant-growth promoting bacteria (PGPB) are sustainable and low-cost biofertilizers, but need specific formulation when used in agronomical practices (Malusa & Vassilev, 2014)
The encapsulated beads remained with the same morphological appearance throughout the evaluation period, preserving the color and shape until the 90th day (Figures 1A-1D)
Summary
World food production is based on the extensive use of chemical fertilizers, which pollute the environment and are expensive due to their non-renewable sources like fossil fuels, used in their exploitation, transportation and application (Schoebitz, López, & Roldán, 2013). Eco-friendly and economical alternatives have been increasingly demanded. Among some of these alternatives, plant-growth promoting bacteria (PGPB) are sustainable and low-cost biofertilizers, but need specific formulation when used in agronomical practices (Malusa & Vassilev, 2014). Biofertilizers as inoculants must have 3 fundamental characteristics: to promote bacterial growth; to keep the cells viable for a certain period of time and to release a minimum population of bacteria, which will certainly be associated to plants (Yoav Bashan et al, 2014; Shcherbakova et al, 2018). The population of the inoculated bacteria declines progressively over time, preventing the accumulation of a bacterial pool in the rhizosphere sufficient to promote beneficial effects (Yoav Bashan, 1998; Sivakumar, Parthasarthi, & Lakshmipriya, 2014)
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