Evaluation of brassinosteroids and plant growth-promoting bacteria on the growth and yield of Lactuca sativa L. under soilless cultivation conditions

Abstract

Soilless crops have become an important alternative for large-scale vegetable production because of the quality of their products and optimization of resources. Brassinosteroids (Brs) and Plant Growth-Promoting Bacteria (PGPB), has been reported to promote growth and physiological parameters in soil crops, but there are few reports on the application of these compounds in soilless crops. The effects of Brs ((25R)-3_β 5α-dihydroxy-spirostan-6-one) and three strains of PGPB (Bacillus velezensis, Pseudomona sp., and Azospirillum brasilense) on the growth and yield of lettuce under hydroponic conditions were evaluated. Two separate experiments were carried out: one using a substrate in pots under greenhouse conditions and the other using a deep-flow hydroponic system in a growth room with artificial LED lighting. Plant physiological parameters (yield, dry weight, root surface area, and leaf area) and PGPB attributes under in vitro tests (phosphate solubilization and indole-3-acetic acid (IAA) synthesis) were determined using in vitro tests. A completely randomized design was used in all experiments. The results showed that in in vitro tests Azospirillum brasilense and Pseudomonas sp. were the strains that synthesized the highest amounts of IAA (36 mg mL⁻¹ and 34 mg mL⁻¹, respectively). Phosphorus solubilization was significantly higher in the Pseudomonas sp. strain (110.35 µg mL⁻¹). Regarding physiological and quality parameters, the application of Brs (0.5 ppm), Bacillus velezensis, and Azospirillum brasilense (1 × 10⁶ CFU mL⁻¹) caused an increase between 20% and 40% on variables such as plant yield, leaf area, root surface area, and colorimetry of lettuce for substrate or hydroponic conditions, respectively.

Keywords:

• Azospirillum
• Bacillus
• plant hormones
• Pseudomonas
• soilless culture

Acknowledgments

The authors thank the Agricultural Microbiology Research Group of the Institute of Biotechnology.

Disclosure statement

The authors declare no conflicts of interest.

Additional information

Funding

This research was funded by the Universidad Nacional de Colombia, Faculty of Agricultural Sciences, and Institute of Biotechnology. External funding was provided by VeggiesApp, Agricultura Urbana SAS.