Screening and selection of rhizospheric bacteria with antagonistic activity against Verticillium dahliae

SAYAGO, P; ALBARRACIN ORIO A; BRÜCHER, E; OTERO, ML; DUCASSE, DA

Workshop; II Latin American PGPR Workshop; 2014

The olive culture has experienced an important expansion in Argentina. The main limiting disease is the Verticillium wilt, caused by the soil borne fungal pathogen Verticillium dahliae Kleb. Since microsclerotia of V. dahliae that develop in the senescing tissues of dead plants may persist in soil for several years, chemical control is nearly impossible. Control of this disease is limited to heat treatment (solarization), or fumigation with broad-spectrum biocides such as methyl bromide that is forbidden nowadays. The screening and identification of beneficial rhizobacteria with antagonistic activity against fungal pathogens has become an environmentally friendly alternative to protect plants. So, we decided to address the biological control as a mean to manage olive Verticillium wilt.For the screening of biocontrol bacteria we sampled soil from olive culture fields situated in La Rioja, Argentina. The Verticillum dahliae strain was isolated from the same region and was characterized as non-defoliant. This pathotype is the most prevalent in our country. Potential antagonistic bacteria were isolated by shaking 1 gram of soil in sterilized saline solution (1%) for 20 min. The soil suspensions were serially diluted and spread on LB plates. The plates were incubated at 28 ± 2º C for 2 days. The antagonistic activity of the bacterial strains against V. dahliae was tested in co-culture essays.We obtained an average of 106 CFU/g of rhizospheric soil. From total bacteria we selected 80 isolates for initial screening of biocontrol activity in co-culture plates. Approximately 19% of the tested bacteria showed a strong antagonistic activity against the fungal pathogen. We found fifteen strains with high percentages of growth inhibition of V. dahliae. The antagonistic capacities ranged from 34.8 to 55.1 %. We observed different levels of mycelial alterations in the fungal colony when growing in co-culture plates.We were able to select biocontrol rhizobacteria with adequate activity against the most limiting pathogen of olive culture worldwide. All the isolates were recovered from soils sampled in a region with high prevalence of V. dahliae.