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The aim of this work was study the use of an experimental product containing chitosan and chelated cooper (Cu) as a sustainable tool for the protection of tomato plants, to understand which are the mechanisms involved in resistance promotion and what could be the anatomical changes on tomato leaves related to those defense responses. The experiment was conducted in a greenhouse with tomato plants grown in pots and subjected to weekly foliar sprays of a suspension containing chitosan associated with Cu-EDTA (ChiCu). The increase in the phenolic compound concentrations and phenylalanine ammonia-lyase (PAL) enzyme activities were detected 24 hours after. In addition, an increase was observed in the activity of chitinase and β-1,3-glucanase, enzymes related to defense responses. Also, an increase was found in the thickness of the outer periclinal wall on the adaxial epidermal surface in leaves submitted to 4 ml L-1 ChiCu. The proportion of the epiderm to the leaf blade was also higher. Although the pathogenicity-related enzymes were activated as well as phenolic compounds were increased, these changes did not affected the biometric and biochemical parameters related to the primary metabolism and essential for the maintenance of productive potential of tomato plants. The increase in the outer periclinal wall as a result of ChiCu sprays could have contributed to the resistance against diseases since it is the first barrier to the infection of a wide of pathogens.

The search for new natural sources for plant growth promotion and yield gains can contribute to ensuring safe and sustainable vegetable production. The potential of microalgae as a plant biostimulant source has been investigated in recent years, while the use of humic substances is well established; however the study of the combination of both is novel, and is the aim of this work. A step-by-step approach was adopted, conducting three experiments using the microalgae Scenedesmus subspicatus combined with humic acid: i) rooting bioassays in a growth chamber to identify bioactivity of microalgae, humic acid and their mixtures using Vigna radiata as a model plant. ii) immersion treatments of two onion cultivar seedlings at transplantation which were then grown in pots in a greenhouse, iii) immersion treatments of two onion cultivar (open-pollinated and hybrid) seedlings at transplantation which were then grown at field in organic system. Growth and biochemical variables, yield and nutrient content of onion leaves and bulbs were evaluated. The bioactivity of microalgae biomass, of humic acid and their mixtures were identified on bioassays, and synergy was found. The immersion of onion seedlings in microalgae plus humic acid solutions showed growth promoting effects at the early stages, improved bulb caliber and yield of the hybrid cultivar, and incremented sugars and proteins content in bulbs. The yield gain was not related to nutrients uptake stimuli.