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Biocontrol agents promote growth of potato pathogens, depending on environmental conditions.

Cray JA, Connor MC, Stevenson A, Houghton JD, Rangel DE, Cooke LR, Hallsworth JE - Microb Biotechnol (2016)

Bottom Line: Whilst unprecedented, this finding is consistent with earlier reports that fungi can utilize metabolites derived from bacterial cells.Unless the antimicrobial activities of candidate biocontrol strains are assayed over a full range of field-relevant parameters, biocontrol agents may promote plant pathogen infections and thereby reduce crop yields.These findings indicate that biocontrol activity, therefore, ought to be regarded as a mode-of-behaviour (dependent on prevailing conditions) rather than an inherent property of a bacterial strain.

View Article: PubMed Central - PubMed

Affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, BT9 7BL, Northern Ireland.

No MeSH data available.


Related in: MedlinePlus

Bacillus sp. JC12GB43:Fusarium coeruleum interaction assays carried out on the wounded surface of Desirée (A–C) and Dundrod (D–F) potato tubers. Controls were wounded and inoculated using F. coeruleum only, and the negative control was not inoculated with either the pathogen or biocontrol agent. Treatments 1‐3 (T1‐3) were wounded and inoculated with F. coeruleum in the same way and then, after 24 h, also inoculated with Bacillus sp. JC12GB43 that had been cultured at high water activity (for Treatment 1, on NB at water activity 0.998) or reduced water activity (for Treatment 3, on NB+2 M glycerol at water activity 0.955). For Treatment 2 (T2), tubers were wounded and inoculated with F. coeruleum as described above and then, after 24 h, inoculated with NB+2 M glycerol only (i.e. no biocontrol agent). A suspension of F. coeruleum macroconidia (grown on PDA at 20°C for 17 days) was used for the potato‐pathogen inoculations (5 × 103 ml−1) and a suspension of Bacillus sp. JC12GB43 cells was used for biocontrol‐agent inoculations (1.444 OD600 nm; taken from a late‐exponential phase culture). All tubers (250) were then stored for 100 days at ambient temperature, and without light, prior to assessment. For infected tubers, the mean surface‐area colonized by F. coeruleum (i.e. the area exhibiting dry rot) was quantified (A and D); the number of tubers colonized by F. coeruleum are expressed as a percentage of the total tubers (B and E); and the surface area of tubers colonized by F. coeruleum is also expressed as a total of all (infected plus non‐infected) tubers (C and F). Red bars indicate promotion of the pathogen which may be attributable to the biocontrol agent. Error bars indicate ± standard error.
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mbt212349-fig-0006: Bacillus sp. JC12GB43:Fusarium coeruleum interaction assays carried out on the wounded surface of Desirée (A–C) and Dundrod (D–F) potato tubers. Controls were wounded and inoculated using F. coeruleum only, and the negative control was not inoculated with either the pathogen or biocontrol agent. Treatments 1‐3 (T1‐3) were wounded and inoculated with F. coeruleum in the same way and then, after 24 h, also inoculated with Bacillus sp. JC12GB43 that had been cultured at high water activity (for Treatment 1, on NB at water activity 0.998) or reduced water activity (for Treatment 3, on NB+2 M glycerol at water activity 0.955). For Treatment 2 (T2), tubers were wounded and inoculated with F. coeruleum as described above and then, after 24 h, inoculated with NB+2 M glycerol only (i.e. no biocontrol agent). A suspension of F. coeruleum macroconidia (grown on PDA at 20°C for 17 days) was used for the potato‐pathogen inoculations (5 × 103 ml−1) and a suspension of Bacillus sp. JC12GB43 cells was used for biocontrol‐agent inoculations (1.444 OD600 nm; taken from a late‐exponential phase culture). All tubers (250) were then stored for 100 days at ambient temperature, and without light, prior to assessment. For infected tubers, the mean surface‐area colonized by F. coeruleum (i.e. the area exhibiting dry rot) was quantified (A and D); the number of tubers colonized by F. coeruleum are expressed as a percentage of the total tubers (B and E); and the surface area of tubers colonized by F. coeruleum is also expressed as a total of all (infected plus non‐infected) tubers (C and F). Red bars indicate promotion of the pathogen which may be attributable to the biocontrol agent. Error bars indicate ± standard error.

Mentions: Based on this finding, a parallel series of assays were carried out on potato tubers to characterize Bacillus sp. JC12GB43:F. coeruleum interactions in the context of their in situ ecology (see Experimental procedures). For the high water‐activity inoculum of Bacillus sp. JC12GB43 there was, however, neither any discernible stimulation of F. coeruleum nor prevention of tuber infection (P > 0.05 for mean area of tubers infected, and mean number of tubers infected and total area of tubers infected) (Fig. 6). By contrast, the results of in‐situ assays carried out using low water‐activity inoculum did impact the degree of tuber infection by the pathogen (see below).


Biocontrol agents promote growth of potato pathogens, depending on environmental conditions.

Cray JA, Connor MC, Stevenson A, Houghton JD, Rangel DE, Cooke LR, Hallsworth JE - Microb Biotechnol (2016)

Bacillus sp. JC12GB43:Fusarium coeruleum interaction assays carried out on the wounded surface of Desirée (A–C) and Dundrod (D–F) potato tubers. Controls were wounded and inoculated using F. coeruleum only, and the negative control was not inoculated with either the pathogen or biocontrol agent. Treatments 1‐3 (T1‐3) were wounded and inoculated with F. coeruleum in the same way and then, after 24 h, also inoculated with Bacillus sp. JC12GB43 that had been cultured at high water activity (for Treatment 1, on NB at water activity 0.998) or reduced water activity (for Treatment 3, on NB+2 M glycerol at water activity 0.955). For Treatment 2 (T2), tubers were wounded and inoculated with F. coeruleum as described above and then, after 24 h, inoculated with NB+2 M glycerol only (i.e. no biocontrol agent). A suspension of F. coeruleum macroconidia (grown on PDA at 20°C for 17 days) was used for the potato‐pathogen inoculations (5 × 103 ml−1) and a suspension of Bacillus sp. JC12GB43 cells was used for biocontrol‐agent inoculations (1.444 OD600 nm; taken from a late‐exponential phase culture). All tubers (250) were then stored for 100 days at ambient temperature, and without light, prior to assessment. For infected tubers, the mean surface‐area colonized by F. coeruleum (i.e. the area exhibiting dry rot) was quantified (A and D); the number of tubers colonized by F. coeruleum are expressed as a percentage of the total tubers (B and E); and the surface area of tubers colonized by F. coeruleum is also expressed as a total of all (infected plus non‐infected) tubers (C and F). Red bars indicate promotion of the pathogen which may be attributable to the biocontrol agent. Error bars indicate ± standard error.
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mbt212349-fig-0006: Bacillus sp. JC12GB43:Fusarium coeruleum interaction assays carried out on the wounded surface of Desirée (A–C) and Dundrod (D–F) potato tubers. Controls were wounded and inoculated using F. coeruleum only, and the negative control was not inoculated with either the pathogen or biocontrol agent. Treatments 1‐3 (T1‐3) were wounded and inoculated with F. coeruleum in the same way and then, after 24 h, also inoculated with Bacillus sp. JC12GB43 that had been cultured at high water activity (for Treatment 1, on NB at water activity 0.998) or reduced water activity (for Treatment 3, on NB+2 M glycerol at water activity 0.955). For Treatment 2 (T2), tubers were wounded and inoculated with F. coeruleum as described above and then, after 24 h, inoculated with NB+2 M glycerol only (i.e. no biocontrol agent). A suspension of F. coeruleum macroconidia (grown on PDA at 20°C for 17 days) was used for the potato‐pathogen inoculations (5 × 103 ml−1) and a suspension of Bacillus sp. JC12GB43 cells was used for biocontrol‐agent inoculations (1.444 OD600 nm; taken from a late‐exponential phase culture). All tubers (250) were then stored for 100 days at ambient temperature, and without light, prior to assessment. For infected tubers, the mean surface‐area colonized by F. coeruleum (i.e. the area exhibiting dry rot) was quantified (A and D); the number of tubers colonized by F. coeruleum are expressed as a percentage of the total tubers (B and E); and the surface area of tubers colonized by F. coeruleum is also expressed as a total of all (infected plus non‐infected) tubers (C and F). Red bars indicate promotion of the pathogen which may be attributable to the biocontrol agent. Error bars indicate ± standard error.
Mentions: Based on this finding, a parallel series of assays were carried out on potato tubers to characterize Bacillus sp. JC12GB43:F. coeruleum interactions in the context of their in situ ecology (see Experimental procedures). For the high water‐activity inoculum of Bacillus sp. JC12GB43 there was, however, neither any discernible stimulation of F. coeruleum nor prevention of tuber infection (P > 0.05 for mean area of tubers infected, and mean number of tubers infected and total area of tubers infected) (Fig. 6). By contrast, the results of in‐situ assays carried out using low water‐activity inoculum did impact the degree of tuber infection by the pathogen (see below).

Bottom Line: Whilst unprecedented, this finding is consistent with earlier reports that fungi can utilize metabolites derived from bacterial cells.Unless the antimicrobial activities of candidate biocontrol strains are assayed over a full range of field-relevant parameters, biocontrol agents may promote plant pathogen infections and thereby reduce crop yields.These findings indicate that biocontrol activity, therefore, ought to be regarded as a mode-of-behaviour (dependent on prevailing conditions) rather than an inherent property of a bacterial strain.

View Article: PubMed Central - PubMed

Affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, BT9 7BL, Northern Ireland.

No MeSH data available.


Related in: MedlinePlus