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Bacterial endophytes from wild maize suppress Fusarium graminearum in modern maize and inhibit mycotoxin accumulation.

Mousa WK, Shearer CR, Limay-Rios V, Zhou T, Raizada MN - Front Plant Sci (2015)

Bottom Line: The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels.Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture.We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Agriculture, University of Guelph Guelph, ON, Canada ; Department of Pharmacognosy, Mansoura University Mansoura, Egypt.

ABSTRACT
Wild maize (teosinte) has been reported to be less susceptible to pests than their modern maize (corn) relatives. Endophytes, defined as microbes that inhabit plants without causing disease, are known for their ability to antagonize plant pests and pathogens. We hypothesized that the wild relatives of modern maize may host endophytes that combat pathogens. Fusarium graminearum is the fungus that causes Gibberella Ear Rot (GER) in modern maize and produces the mycotoxin, deoxynivalenol (DON). In this study, 215 bacterial endophytes, previously isolated from diverse maize genotypes including wild teosintes, traditional landraces and modern varieties, were tested for their ability to antagonize F. graminearum in vitro. Candidate endophytes were then tested for their ability to suppress GER in modern maize in independent greenhouse trials. The results revealed that three candidate endophytes derived from wild teosintes were most potent in suppressing F. graminearum in vitro and GER in a modern maize hybrid. These wild teosinte endophytes could suppress a broad spectrum of fungal pathogens of modern crops in vitro. The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels. A fourth, less robust anti-fungal strain was isolated from a modern maize hybrid. Three of the anti-fungal endophytes were predicted to be Paenibacillus polymyxa, along with one strain of Citrobacter. Microscopy studies suggested a fungicidal mode of action by all four strains. Molecular and biochemical studies showed that the P. polymyxa strains produced the previously characterized anti-Fusarium compound, fusaricidin. Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture. We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

No MeSH data available.


Related in: MedlinePlus

Origin of endophytes used in this study and results of the in vitro anti-Fusarium screen. (A) A map showing the origin of maize genotypes previously used to isolate the endophytic library. (B) Examples of endophytes from the library isolated from different Zea genotypes as indicated. (C) Example of an endophyte culture showing suppression of F. graminearum hyphae (white) using the dual culture method. (D) Quantification of the inhibitory effect of the endophytes or fungicide controls, amphotericin B and nystatin (at concentrations of 5 and 10 μg/ml, respectively), on the growth of F. graminearum in vitro. For these experiments, n = 3. The error bars indicate the standard error of the mean. The black asterisk indicates that the treatment means are significantly different from the fungicide Nystatin at p ≤ 0.05. The green asterisk indicates that the treatment means are significantly different from the fungicide Amphotericin at p ≤ 0.05.
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Figure 1: Origin of endophytes used in this study and results of the in vitro anti-Fusarium screen. (A) A map showing the origin of maize genotypes previously used to isolate the endophytic library. (B) Examples of endophytes from the library isolated from different Zea genotypes as indicated. (C) Example of an endophyte culture showing suppression of F. graminearum hyphae (white) using the dual culture method. (D) Quantification of the inhibitory effect of the endophytes or fungicide controls, amphotericin B and nystatin (at concentrations of 5 and 10 μg/ml, respectively), on the growth of F. graminearum in vitro. For these experiments, n = 3. The error bars indicate the standard error of the mean. The black asterisk indicates that the treatment means are significantly different from the fungicide Nystatin at p ≤ 0.05. The green asterisk indicates that the treatment means are significantly different from the fungicide Amphotericin at p ≤ 0.05.

Mentions: The dual culture method was used to screen 215 bacterial endophytes, previously isolated from diverse maize genotypes (Figures 1A,B), for their ability to suppress the growth of F. graminearum. Zones of inhibition of F. graminearum were measured after 24–48 h of co-incubation (Figures 1C,D). The results revealed that four bacterial endophytes could consistently inhibit the growth of F. graminearum (strains 1D6, 3H9, 4G12, and 4G4). Strain 1D6 resulted in the greatest growth inhibition, while 3H9 caused the least growth inhibition to F. graminearum (Figure 1D). Three of these endophytes were isolated from wild maize genotypes (teosintes): strain 1D6 from Z. diploperennis and strains 4G12 and 4G4 from Parviglumis, the direct ancestor of modern maize (Figures 1A,2A). The remaining candidate endophyte (strain 3H9) was isolated from a modern commercial variety (Z. mays ssp. mays, Pioneer 3751 hybrid).


Bacterial endophytes from wild maize suppress Fusarium graminearum in modern maize and inhibit mycotoxin accumulation.

Mousa WK, Shearer CR, Limay-Rios V, Zhou T, Raizada MN - Front Plant Sci (2015)

Origin of endophytes used in this study and results of the in vitro anti-Fusarium screen. (A) A map showing the origin of maize genotypes previously used to isolate the endophytic library. (B) Examples of endophytes from the library isolated from different Zea genotypes as indicated. (C) Example of an endophyte culture showing suppression of F. graminearum hyphae (white) using the dual culture method. (D) Quantification of the inhibitory effect of the endophytes or fungicide controls, amphotericin B and nystatin (at concentrations of 5 and 10 μg/ml, respectively), on the growth of F. graminearum in vitro. For these experiments, n = 3. The error bars indicate the standard error of the mean. The black asterisk indicates that the treatment means are significantly different from the fungicide Nystatin at p ≤ 0.05. The green asterisk indicates that the treatment means are significantly different from the fungicide Amphotericin at p ≤ 0.05.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4593954&req=5

Figure 1: Origin of endophytes used in this study and results of the in vitro anti-Fusarium screen. (A) A map showing the origin of maize genotypes previously used to isolate the endophytic library. (B) Examples of endophytes from the library isolated from different Zea genotypes as indicated. (C) Example of an endophyte culture showing suppression of F. graminearum hyphae (white) using the dual culture method. (D) Quantification of the inhibitory effect of the endophytes or fungicide controls, amphotericin B and nystatin (at concentrations of 5 and 10 μg/ml, respectively), on the growth of F. graminearum in vitro. For these experiments, n = 3. The error bars indicate the standard error of the mean. The black asterisk indicates that the treatment means are significantly different from the fungicide Nystatin at p ≤ 0.05. The green asterisk indicates that the treatment means are significantly different from the fungicide Amphotericin at p ≤ 0.05.
Mentions: The dual culture method was used to screen 215 bacterial endophytes, previously isolated from diverse maize genotypes (Figures 1A,B), for their ability to suppress the growth of F. graminearum. Zones of inhibition of F. graminearum were measured after 24–48 h of co-incubation (Figures 1C,D). The results revealed that four bacterial endophytes could consistently inhibit the growth of F. graminearum (strains 1D6, 3H9, 4G12, and 4G4). Strain 1D6 resulted in the greatest growth inhibition, while 3H9 caused the least growth inhibition to F. graminearum (Figure 1D). Three of these endophytes were isolated from wild maize genotypes (teosintes): strain 1D6 from Z. diploperennis and strains 4G12 and 4G4 from Parviglumis, the direct ancestor of modern maize (Figures 1A,2A). The remaining candidate endophyte (strain 3H9) was isolated from a modern commercial variety (Z. mays ssp. mays, Pioneer 3751 hybrid).

Bottom Line: The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels.Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture.We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Agriculture, University of Guelph Guelph, ON, Canada ; Department of Pharmacognosy, Mansoura University Mansoura, Egypt.

ABSTRACT
Wild maize (teosinte) has been reported to be less susceptible to pests than their modern maize (corn) relatives. Endophytes, defined as microbes that inhabit plants without causing disease, are known for their ability to antagonize plant pests and pathogens. We hypothesized that the wild relatives of modern maize may host endophytes that combat pathogens. Fusarium graminearum is the fungus that causes Gibberella Ear Rot (GER) in modern maize and produces the mycotoxin, deoxynivalenol (DON). In this study, 215 bacterial endophytes, previously isolated from diverse maize genotypes including wild teosintes, traditional landraces and modern varieties, were tested for their ability to antagonize F. graminearum in vitro. Candidate endophytes were then tested for their ability to suppress GER in modern maize in independent greenhouse trials. The results revealed that three candidate endophytes derived from wild teosintes were most potent in suppressing F. graminearum in vitro and GER in a modern maize hybrid. These wild teosinte endophytes could suppress a broad spectrum of fungal pathogens of modern crops in vitro. The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels. A fourth, less robust anti-fungal strain was isolated from a modern maize hybrid. Three of the anti-fungal endophytes were predicted to be Paenibacillus polymyxa, along with one strain of Citrobacter. Microscopy studies suggested a fungicidal mode of action by all four strains. Molecular and biochemical studies showed that the P. polymyxa strains produced the previously characterized anti-Fusarium compound, fusaricidin. Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture. We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

No MeSH data available.


Related in: MedlinePlus