Antagonistic activity of PGPR isolated from the avocado (Persea americana) rhizosphere on Phytophthora cinnamomi and Lasiodiplodia theobromae

Abstract

Plant growth-promoting rhizobacteria (PGPR) have proven to be a sustainable alternative for managing plant pathogens. Developing inoculants with these PGPRs requires a rigorous selection of highly effective native bacterial isolates. In the present study, 29 bacterial isolates were obtained from the rhizosphere of ‘Zutano’ avocado (Persea americana Mill.), a rootstock widely used for the commercial cultivar ‘Hass’, from a commercial orchard on the northern coast of Peru. Two antagonistic isolates showing the highest in vitro inhibition capacity were selected to evaluate their efficacy against the pathogens Phytophthora cinnamomi and Lasiodiplodia theobromae, the causal agents of avocado root rot and dieback, respectively. Results demonstrated that Bacillus subtilis exhibited strong in vitro antagonistic activity against P. cinnamomi and L. theobromae, with 44% and 33.33% inhibition, respectively. Additionally, inoculation of B. subtilis in avocado plants infected with P. cinnamomi resulted in an estimated 90% root viability based on a visual disease severity scale, while increasing root dry weight and length by 116.58% and 44.59%, respectively. These results highlight the potential of B. subtilis for the biological control of avocado diseases caused by P. cinnamomi, while Pseudomonas putida showed promising in vitro antagonistic activity.