Inoculation with Biofilm of Bacillus subtilis Promotes the Growth of Lactuca sativa

In Argentina there are urban areas of intensive cultivation around most of the big cities, where the soils may be unsuitable for some of the horticultural species and the use of chemical fertilizers is common. Bioinoculants based on plant growth promoting rhizobacteria (PGPR) could be an al-ternative for crop improvement, without affecting the environment. These formulations are gen-erally liquid, and their main disadvantage is the low viability of microorganisms. The objectives of this work were to evaluate a different inoculation method, the application of the biofilm pro-duced by Bacillus subtilis as a growth promoter on seeds of three varieties of Lactuca sativa. Biofilm was obtained under static culture conditions, the liquid (planktonic) inoculum was produced at 150 rpm. The major effects were observed with Bacillus subtilis subsp. spizizenii, that showed an-tifungal activity against phytopathogens, synthesize plant growth regulators (IAA, cytokinin and ABA) and solubilize phosphates. The best results were obtained with the Grand Rapid variety inoculated with biofilm, its positive effect was throughout the plant development until the har-vest time, when the bacterium was recovered from the interior of the roots. The biofilm of B. sub-tilis subsp. spizizenii would be an innovative and promising seed inoculant for horticultural spe-cies.