Seed priming by application of Microbacterium spp. strains for control of Botrytis cinerea and growth promotion of lettuce plants

The abusive use of chemical pesticides to control plant diseases has caused the loss of soil biodiversity as well as the emergence of resistance by plant pathogens. This effect has forced an urgent search for other environmentally sustainable alternatives that serve to control plant pathogens safely and efficiently. In this sense, the search for new biopesticides is currently a booming field within the field of agro-biotechnology. Volatile compounds produced by plant-associated microorganisms represent a diverse resource to promote plant growth and health. In this work, a collection of 29 strains of the genus Microbacterium from the composting of plant remains was studied. The objective was to determine whether the production of volatile compounds of microbial origin could contribute to the mitigation of symptoms caused by the fungus Botrytis cinerea (gray mold) as well as contribute to the lettuce plant growth in seedbeds. It should be noted that in both the B. cinerea inhibition and seed priming assays, the microorganisms did not come into direct contact with either the pathogen or the seeds. In all cases, incubation was carried out in a closed environment to expose the seeds to the microbial volatiles. Five strains capable of inhibiting the in vitro growth of B. cinerea at levels greater than 30% were pre-selected. Only 3 of these 5 strains, identified as M. aerolatum, M. foliorum and M. profundi showed positive results in the in vitro germination promotion test in lettuce seeds, increasing the radicle weight at levels close to 45%. These strains finally were tested in planta, showing two of them significant palliative effects of B. cinerea and promoting the development of lettuce seedlings both at aerial and root levels.