SYMBIOTIC AGRICULTURE: PLANT GROWTH PROMOTIO AND BIOCONTROL ACTIVITY OF BENEFICIAL MICROORGANISMS.

Symbiotic microbial inoculation is emerging as a potential technology for sustainable agriculture. Towards a sustainable agricultural vision, crops need to be equipped with disease resistance to various biotic and abiotic stresses, together with better nutritional value. To fulfil the above desired crop properties, one possibility is to use soil microorganisms (bacteria, fungi, algae, etc.) in order to enhance microbial biodiversity. Among these potential soil microorganisms, bacteria known as plant growth promoting rhizobacteria (PGPR) are the most promising. In the present study three Streptomyces sp. strains SB14, SA51 and SL81, two Pseudomonas sp. strains PT65 & PN53 and one Agrobacterium sp. strain AR39 were evaluated in vitro for different plant growth promoting and biocontrol activities. Our aim is to identify possible antagonists able to inhibit different plant bacterial pathogens like Xanthomonas vesicatoria, Clavibacter michiganensis subsp. michiganensis, Clavibacter michiganensis subsp. sepedonicus, Acidovorax citrulli and Ralstonia solanacearum. All the strains were screened for biocontrol activity on three different media ISP – 2 (International streptomyces project), PDA (Potato Dextrose Agar) and HPDA (Half Strength PDA) and AIA (average inhibition area) was calculated. Among the isolates, each strain showed different ability to inhibit the pathogens: Streptomyces sp. strain SA51 was found to be most active. The most prospective strains were further evaluated in the field, as possible biocontrol agents for the tomato spot disease (X. vesicatoria), singularly and as a consortium. Results will improve our understanding on the use of such microbial biocontrol agents and will implement innovative biocontrol strategies to bacterial diseases