Microorganisms as biological control against pathogenic fungi of agricultural interest

Use of biological control agents, such as plant growth promoting rhizobacteria (PGPR), and Lactic Acid Bacteria (LAB) can be a suitable approach in control of disease in vegetable crops to reduce and limit the widespread use of chemicals. PGPR, such as Pseudomonas and Bacillus strains, are the major root colonizers that can elicit plant defense and compete with pathogens. Lactic Acid Bacteria [LAB] are worldwide known as probiotic microorganisms and one of the most important probiotic feature is their activity against a wide range of harmful bacteria/fungi. Their use as “effective microorganisms” is increasing as active components of soil amendments for sustainable agriculture. This work focuses on the in vitro screening of 32 PGPR and LAB strains isolated from environmental sources against Fusarium spp, Sclerotinia spp. and Rhizoctonia spp which are widely distributed fungi affecting plant, animal and human health. In the agricultural field, they are considered important plant pathogenic fungi, with a record of devastating infections in various economically important crop plants. Fungal inhibition was performed using spot agar test in a triplicate assay with different conditions for LAB and PGPR. All LAB strains (except one) showed an antifungal activity against all Fusarium species tested (inhibition halo between 23.7- 65.3mm); the highest halos were obtained against F. graminearum on which 50% of the strains showed a total growth inhibition of the colony. Among PGPR, preliminary results showed a strong inhibition by some B. subtilis strains against all fungi tested. These results are promising for the formulation of a commercial product that could be used for a wide spectrum of plant crops. In vivo application with the most successful strains is foreseen towards wheat and lettuce to confirm in vitro results.