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Biological control of apple blue mold with Pseudomonas fluorescens
Hassan-Reza Etebarian1, Peter L Sholberg, Kenneth C Eastwell
1Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, Canada.
Abstract:
Pseudomonas fluorescens isolate 1100-6 was evaluated as a potential biological control agent for apple blue mold caused by Penicillium expansum or Penicillium solitum. Both the wild-type isolate 1100-6 and a genetically modified derivative labeled with the gene encoding the green fluorescent protein (GFP) were compared. The P. fluorescens isolates with or without GFP equally reduced the growth of Penicillium spp. and produced large zones of inhibition in dual culture plate assays. Cell-free metabolites produced by the bacterial antagonists reduced the colony area of Penicillium isolates by 17.3% to 78.5%. The effect of iron chelate on the antagonistic potential of P. fluorescens was also studied. The use of iron chelate did not have a major effect on the antagonistic activity of P. fluorescens. With or without GFP, P. fluorescens significantly reduced the severity and incidence of apple decay by 2 P. expansum isolates after 11 d at 20 degrees C and by P. expansum and P. solitum after 25 d at 5 degrees C when the biocontrol agents were applied in wounds 24 or 48 h before challenging with Penicillium spp. Populations of P. fluorescens labeled with the GFP were determined 1, 9, 14, and 20 d after inoculation at 5 degrees C. The log CFU/mL per wound increased from 6.95 at the time of inoculation to 9.12 CFU/mL (P < 0.05) 25 d after inoculation at 5 degrees C. The GFP strain did not appear to penetrate deeply into wounds based on digital photographs taken with an inverted fluorescence microscope. These results indicate that P. fluorescens isolate 1100-6 could be an important new biological control for apple blue mold.
Insights
Pseudomonas fluorescens isolate 1100-6 effectively controls apple blue mold caused by Penicillium species. This biological control agent, even when modified with green fluorescent protein (GFP), significantly reduces fruit decay and exhibits strong antagonistic activity.
Area of Science:
- Agricultural Science
- Microbiology
- Plant Pathology
Background:
- Apple blue mold, caused by Penicillium expansum and Penicillium solitum, is a significant post-harvest disease.
- Biological control using beneficial microorganisms offers a sustainable alternative to synthetic fungicides.
Purpose of the Study:
- To evaluate Pseudomonas fluorescens isolate 1100-6 as a biological control agent against apple blue mold.
- To compare the efficacy of wild-type and genetically modified (GFP-labeled) P. fluorescens.
Main Methods:
- Dual culture plate assays to assess inhibition zones.
- Application of cell-free metabolites to quantify reduction in Penicillium colony area.
- In vivo testing on apples to determine reduction in decay severity and incidence.
- Monitoring of P. fluorescens populations using green fluorescent protein (GFP) labeling.
Main Results:
- P. fluorescens isolate 1100-6, with or without GFP, significantly inhibited Penicillium spp. growth and reduced apple decay.
- Cell-free metabolites reduced Penicillium colony area by up to 78.5%.
- Iron chelate had no major impact on the antagonistic activity of P. fluorescens.
- P. fluorescens populations increased in apple wounds over time, with limited deep penetration observed.
Conclusions:
- P. fluorescens isolate 1100-6 demonstrates significant potential as a biological control agent for apple blue mold.
- The use of GFP labeling is a viable tool for tracking biocontrol agent populations.
- Further research may optimize application strategies for enhanced efficacy.
