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.