Biological control of potato soft rot caused by Erwinia carotovora subsp. carotovora

Four bioagents, Bacillus subtilis, Pseudomonas fluorescence, P. aeruginosa, and Streptomyces spp., were used in vitro and in vivo against two pathogenic isolates of Erwinia carotovora subsp. carotovora (Ecc1 and Ecc2), the causal agent of potato soft rot. In vitro Streptomyces spp. showed the strongest effect against Ecc1 and Ecc2 and gave the highest values of the inhibition zones, being 37 and 40 mm, respectively followed by P. fluorescence, B. subtilis, and P. aeruginosa, where the inhibition zones reached, respectively, 32, 28, and 24 mm against Ecc1 and 35, 29, and 26 mm against Ecc2. Also, these results confirmed those of the in vivo experiment (in pots) since Streptomyces spp. bioagent exhibited the lowest number of infected tubers followed by P. fluorescence, B. subtilis, and P. aeruginosa, respectively, against the two isolates Ecc1 and Ecc2. Also, disease severity of soft rot caused by each of the two isolates, Ecc1 and Ecc2, was decreased by using bioagents, and the lowest disease severity values were obtained by using Streptomyces spp., P. fluorescence, B. subtilis, and P. aeruginosa, respectively.