Developing new and natural sources of plant growth promotors is essential to ensure the safe and sustainable production of vegetables for human consumption. In recent years, the potential of microalgae as plant biostimulants has been investigated. Arthrospira platensis (Spirulina platensis) biomass is a recognized protein source and its enzymatic hydrolysis contains molecules such as polyamines with potential to promote plant growth. Therefore, the aim of the present study was to investigate the biostimulant properties of hydrolyzed biomass of A. platensis. Bioassays were performed to determine auxin-like and cytokinin-like bioactivity of the hydrolysates. In addition, its effect on lettuce seedling growth was investigated and an organic system field trail performed where yield and free polyamine levels in leaves quantified. The hydrolysates had a cytokinin-like effect in the bioassay. Foliar applications promoted the growth of lettuce seedlings with the 4-h reaction hydrolysate (Sph4) being the most effective at promoting growth and increasing the spermine content by 64% in the lettuce leaves. The polyamine concentration was also compared in nonhydrolyzed A. platensis and Sph4. Hydrolysis resulted in a 34% increase in spermine content. It was concluded that Sph4 is a natural plant growth promoter that can be used as a raw material for biostimulants, and spermine could be an active compound and a metabolic indicator of Sph4 bioactivity.

In order to increase the understanding about Arthrospira platensis biomass use to plant growth promotion, the aim of this study was to determine total free amino acid content on lyophilized biomass and the biomass bioactivity on bioassay, as well as, the effects of foliar applications of aqueous suspension of biomass on seedlings growth ascertaining biochemical variables related to the potential bioactivity, and also at field on organically grown red beet yield. The results identified the bioactivity and expressed well the capacity of plant growth promotion related to stimulus on chlorophyll synthesis and on amino acid and protein increments on seedlings leaves. The yield had significant improvement related to hypocotyl growth. The results could be justified by the content of free amino acids on biomass, being them the highest amount of potential bioactive compounds of cyanobacteria. The Arthrospira platensis lyophilized biomass could be considered an efficient biofertilizer-biostimulant source, promoting yield gains by a sustainable way.

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No presente trabalho, objetivou-se avaliar os efeitos da aplicação foliar do extrato da alga Ascophyllum nodosum, do ácido L-glutâmico e do Ca+2, no crescimento e produção de plantas de feijão (Phaseolus vulgaris L.). O experimento foi conduzido em casa de vegetação com os seguintes tratamentos: testemunha; aplicações foliares de soluções contendo 60 g L-1 de ácido L-glutâmico; contendo 60 g L-1 de extrato de alga; contendo 100 g L-1 de Ca+2 na forma de CaCl2; contendo 30 g L-1  de ácido L-glutâmico e 30 g L-1 extrato de alga; contendo 30 g L-1 de ácido L-glutâmico e 100 g L-1 de Ca+2;  contendo 30 g L-1 de extrato de alga e 100 g L-1 de Ca+2; contendo 15 g L-1de ácido L-glutâmico associado a 15 g L-1 de extrato de alga e 100 g L-1 de Ca+2, aos 12, 28 e 42 dias após a emergência das plantas. Para a aplicação foliar, cada solução foi diluída em água na concentração de 3 ml L-1. Ao longo do ciclo foram avaliadas variáveis biométricas e ao final quantificou-se a produção de grãos por planta. Identificou-se o efeito dos tratamentos no crescimento inicial, ao longo do ciclo das plantas e na produção de grãos, caracterizando o efeito bioestimulante da solução contendo 30 g L-1 de extrato de alga e 100 g L-1 de Ca+2, e da solução contendo 15 g L-1de ácido L-glutâmico associado a 15 g L-1 de extrato de alga e 100 g L-1 de Ca+2.

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The identification of natural bioactive sources capable of enhancing yield gains on agriculture is a tool to promote sustainability. In this study, the effect of foliar applications of sugarcane molasses fermented by the bacteria Corynebacterium glutamicum, containing 30% (w/v) of the amino acid L-glutamic acid was tested on organically grown potato for two seasons. Four foliar applications at intervals of ten days were made using solutions with different concentrations of the fermented broth (0.2, 0.4, 0.6, 0.8 mL L-1). Total and commercial potato yield and biochemical alterations on leaves at 50 and 60 days after planting were determined. The applications of the fermented broth promoted yield gains and changes in chlorophylls, carotenoids, nitrate reductase enzyme (EC 1.6.6.1) activity, delaying the senescence and improving the free amino acid and soluble protein content of leaves. It was concluded that the fermented broth was able of improving potato yield by stimulating the nitrate reductase activity.

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