Inoculation methods of Azospirillum brasilense in lettuce and arugula in the hydroponic system

Abstract

Lettuce and arugula are the most cultivated leafy vegetables in hydroponic systems in the world, and the little information about Azospirillum brasilense effects in research in this system makes it necessary to verify the best method of inoculation of these bacteria. Therefore, this study aimed to verify the beneficial effects of inoculation methods of A. brasilense on plant growth and nutrition of lettuce and arugula grown in the hydroponic system. The study was conducted in a greenhouse with 30% shading. A randomized block design with five replicates in a 4 × 2 factorial scheme was used. Four A. brasilense inoculation methods (non-inoculated, foliar application, nutrient solution, and nutrient solution + foliar application) and two leafy vegetable species - arugula and lettuce - were evaluated. All inoculation methods improved plant height, shoot fresh and dry mass, root fresh and dry mass, fresh leaf yield, leaf chlorophyll index, accumulation of nitrogen, potassium, calcium, sulfur, phosphorus, iron, manganese, and copper and reduced nitrate accumulation in shoot and root of arugula and lettuce. Inoculation via nutrient solution + foliar application of A. brasilense is the most suitable for hydroponic arugula cultivation because it provides greater fresh leaf yield. All inoculation methods increased leaf yield in hydroponic lettuce. Hydroponic arugula and lettuce plants showed greater accumulation of nutrients and plant growth with less nitrate accumulation in the shoot under inoculation with A. brasilense.

Inoculation with Azospirillum brasilense Strains AbV5 and AbV6 Increases Nutrition, Chlorophyll, and Leaf Yield of Hydroponic Lettuce

“…Therefore, our results described that growth and nutrient accumulation in hydroponic lettuce were improved with inoculation of A. brasilense strains AbV5 and AbV6 at doses between 39 and 50 mL (Figures 1, 3 and 4). The current results were supported by a previous study that verified the use of A. brasilense strains AbV5 and AbV6 increased growth and nutrient acquisition in hydroponic lettuce and arugula [13]. Plants adapt several mechanisms, such as biological nitrogen fixation, phosphate and zinc solubilization, greater root exploration, and induction of resistance to pathogens, when inoculated with A. brasilense.…”

“…The current results showed that the shoot fresh and dry matter of hydroponic lettuce improved with increasing doses of A. brasilense when compared with non-inoculated plants (Figure 1A,C). It may be possible due to higher photosynthetic efficiency, assimilation of carbon, and nutrient acquisition by roots with the inoculation of A. brasilense [13]. It has been reported that inoculation with A. brasilense via nutrient solution at a dose of 10 mL 100 L −1 has increased the number of leaves, fresh and dry mass of shoots, and shoot growth of lettuce and arugula grown in a hydroponic system [13,14].…”

“…It may be possible due to higher photosynthetic efficiency, assimilation of carbon, and nutrient acquisition by roots with the inoculation of A. brasilense [13]. It has been reported that inoculation with A. brasilense via nutrient solution at a dose of 10 mL 100 L −1 has increased the number of leaves, fresh and dry mass of shoots, and shoot growth of lettuce and arugula grown in a hydroponic system [13,14]. The yield and number of leaves of lettuce were increased with the doses of 44 and 20 mL 100 L −1 of the inoculant, respectively, in comparison to non-inoculated plants (Figure 1E,F).…”

“…Inoculation via nutrient solution has not been previously reported in a hydroponic system. A comparative effect of inoculation via foliar and nutrient solution with A. brasilense strains AbV5 and AbV6 in lettuce and arugula showed a similar effect in both cases [13]. Inoculation via nutrient solution with A. brasilense strains AbV5 and AbV6 is a new technique that can increase hydroponic production.…”

“…Inoculation via nutrient solution with A. brasilense strains AbV5 and AbV6 is a new technique that can increase hydroponic production. It has been reported that A. brasilense strains AbV5 and AbV6 via nutrient solution increase the growth of roots and shoots and provide greater accumulation of nutrients in arugula and lettuce plants in a hydroponic system [13]. In addition, inoculation with Pseudomonas fluorescens strain CCTB03, Bacillus subtilis strain CCTB04, and A. brasilense strains AbV5 and AbV6 increased nutrient accumulation in shoots and roots, growth of shoots and roots, and biomass production of shoots and roots of arugula in a hydroponic system [14].…”