There are certain growth-promoting rhizobacteria (PGPRs) that stimulate plant development without being in physical contact with the roots, through the emission of volatile organic compounds (VOCs).
The emission of microbial volatile organic compounds (VOCs) was discovered in 2003 by Ryu et al. More than 365 different volatile substances produced by rhizobacteria have been identified.
Among the genera in which the emission of volatile compounds has been detected are: Azospirillum, Arthrobacter, Azotobacter, Bacillus, Burkholderia, Erwinia, Enterobacter, Klebsiella, Paenibacillus, Pantoea, Pseudomonas, Serratia and Xanthomonas.
The selection of VOC-producing strains is essential, as there is a high strain vs. VOC specificity. VOC profiles may vary depending on genomic content, metabolic capacity, stage of growth, as well as nutrient availability in the medium in which the microorganisms are found.
VOCs fulfil several functions in their plant-microorganism, microorganism-microorganism interaction such as inter-intra species communication or cell-to-cell communication, stimulation of plant growth, activation of the induced systemic resistance (ISR) of the plant, protecting it against possible diseases, as well as inhibition of phytopathogens.
The genus Pseudomonas, is capable of emitting more than 25 different volatile substances, activating genes in Arabidopsis involved in cell wall modification, metabolism, hormone regulation and protein synthesis. It also activates processes such as cell expansion, photosynthetic efficiency and seed formation.
Through studies carried out on Arabidopsis thaliana in co-culture assays on separate plates (see photo), the effect of the VOCs produced by BACNIFOS bacteria on growth promotion and rhizospheric stimulation can be seen. In this assay, the batteries have never been in contact with the plant.
Photo 1. Trial carried out with Arabidopsis thaliana to determine the effect of volatile compounds produced by Pseudomonas sp, bacteria belonging to the BACNIFOS product.
This effect has been reflected in trials carried out on lettuce, where the application of the registered product BACNIFOS in 3 moments of the crop, increases the production by 37.8% in comparison with the control (without the addition of biofertiliser). BACNIFOS represents an increase in profits for the farmer of 3,114 Euros/ha.
Figure 1. Lettuce field trial with the application of BACNIFOS.
**T-student p<0.01. Gross income referring to lettuce prices obtained from the price observatory of the Andalusian Regional Government. http://www.juntadeandalucia.es/agriculturaypesca/observatorio/servlet/FrontController?ec=default
The use of microorganisms as biofertilisation agents plays a fundamental role in sustainable agriculture and increasingly more studies are demonstrating the multiple modes of action they exert on plants.
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