Abstract
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.
Highlights
Potato, Solanum tuberosum L., is one of the most important food and crops worldwide, and its production in developing countries increased at the rate of 2.8% annually (CIP 1995)
We aimed to evaluate in vitro and in vivo effectiveness of four bioagents, B. subtilis, P. fluorescence, P. aeruginosa, and Streptomyces spp., against E. carotovora subsp. carotovora (Ecc1 and Ecc2), the causal agent of potato soft rot
The suspension representing each of the two isolates of E. carotovora subsp. carotovora (1 × 105 CFU/cm3) was spread on the surface of the Czabe-dox agar media in petri dishes by a sterilized L-shaped glass rod spreader followed by placing a 7-mm diameter agar disk cut from the margin of a culture grown in a plate on which the biocontrol strain had been grown for 48 h at 28 °C for bacteria and for 7 days for actinomycetes in the center of each plate
Summary
Solanum tuberosum L., is one of the most important food and crops worldwide, and its production in developing countries increased at the rate of 2.8% annually (CIP 1995). Infection by late blight and dry rot pathogens is significant, because of the damage they cause to potato tubers, and because they provide potential avenues of entrance of secondary invasion by Erwinia carotovora subsp. Microorganisms that can grow in potato rhizosphere are ideal to be used as biocontrol agents, since the rhizosphere provides the front line defense for roots and tubers against attack by pathogens (Kabeil et al 2008). Pseudomonas fluorescence, Bacillus subtilis, and E. herbicola showed activity against E. carotovora subsp. Streptomyces is a well-known genus of the order Actinomycetales family. They usually inhabit soil and commonly enhance soil fertility.
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