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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

Greenhouse trial 1 to test for the ability of the candidate endophytes to suppress Gibberella Ear Rot (GER) in a modern hybrid. (A, B) GFP-tagged endophyte strain 4G12 visualized inside maize roots, in the (A) absence or (B) presence of propidium iodide that outlines the cell with red color. (C–H) Representative ears from each treatment. (I) Picture of an ear to illustrate the methodology of scoring disease severity: The fungal pathogen was introduced to the tip of the ear, indicated by the asterisk. Therefore, the disease was scored as the ratio of the length of the diseased ear tip portion relative to total ear length, multiplied by 100 to give a percentage. (J, K) Quantification of the effect of different treatments on GER suppression, as: (J) percent ear infection, and (K) average grain yield per plant. For both measurements, n = 20 per treatment (n = 10 for both controls). The whiskers indicate the range of data points. The black asterisk indicates that the treatment means were significantly different from the Fusarium only treatment at p ≤ 0.05. The green asterisk indicates that the treatment means were significantly different from prothioconazole fungicide (Proline) treatment at p ≤ 0.05.
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Figure 7: Greenhouse trial 1 to test for the ability of the candidate endophytes to suppress Gibberella Ear Rot (GER) in a modern hybrid. (A, B) GFP-tagged endophyte strain 4G12 visualized inside maize roots, in the (A) absence or (B) presence of propidium iodide that outlines the cell with red color. (C–H) Representative ears from each treatment. (I) Picture of an ear to illustrate the methodology of scoring disease severity: The fungal pathogen was introduced to the tip of the ear, indicated by the asterisk. Therefore, the disease was scored as the ratio of the length of the diseased ear tip portion relative to total ear length, multiplied by 100 to give a percentage. (J, K) Quantification of the effect of different treatments on GER suppression, as: (J) percent ear infection, and (K) average grain yield per plant. For both measurements, n = 20 per treatment (n = 10 for both controls). The whiskers indicate the range of data points. The black asterisk indicates that the treatment means were significantly different from the Fusarium only treatment at p ≤ 0.05. The green asterisk indicates that the treatment means were significantly different from prothioconazole fungicide (Proline) treatment at p ≤ 0.05.

Mentions: Greenhouse experiments were undertaken to determine if the endophytes could suppress Gibberella ear rot (GER) in planta using a modern maize hybrid, P35F40, which is susceptible to this disease. To confirm that the candidate bacterial strains originally isolated from the two evolutionarily distant maize genotypes (Z. diploperennis and Parviglumis) could colonize the internal tissues of this modern hybrid, thus behaving as endophytes, GFP tagging was conducted. Attempts were made to GFP tag all endophytes, but unfortunately, only strain 4G12 from ancestral Parviglumis, was successfully tagged. GFP-tagged 4G12 was visualized by scanning confocal microscopy and shown to colonize maize roots (Figures 7A,B), confirming its behavior as an endophyte in the modern maize relative. All four endophytes were then tested for their ability to suppress GER under greenhouse conditions in two independent trials (Figures 7, 8). The main entrance routes for F. graminearum in maize are exposed silks where the ascospores can germinate and grow toward the developing ear (Sutton, 1982; Kebebe et al., 2015). Therefore, the disease severity was scored as the length of diseased area, measured from the ear tip where Fusarium spores were introduced, relative to the total length of the ear (Figure 7I). Kernel yields were also quantified:


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)

Greenhouse trial 1 to test for the ability of the candidate endophytes to suppress Gibberella Ear Rot (GER) in a modern hybrid. (A, B) GFP-tagged endophyte strain 4G12 visualized inside maize roots, in the (A) absence or (B) presence of propidium iodide that outlines the cell with red color. (C–H) Representative ears from each treatment. (I) Picture of an ear to illustrate the methodology of scoring disease severity: The fungal pathogen was introduced to the tip of the ear, indicated by the asterisk. Therefore, the disease was scored as the ratio of the length of the diseased ear tip portion relative to total ear length, multiplied by 100 to give a percentage. (J, K) Quantification of the effect of different treatments on GER suppression, as: (J) percent ear infection, and (K) average grain yield per plant. For both measurements, n = 20 per treatment (n = 10 for both controls). The whiskers indicate the range of data points. The black asterisk indicates that the treatment means were significantly different from the Fusarium only treatment at p ≤ 0.05. The green asterisk indicates that the treatment means were significantly different from prothioconazole fungicide (Proline) treatment at p ≤ 0.05.
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Related In: Results  -  Collection

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Figure 7: Greenhouse trial 1 to test for the ability of the candidate endophytes to suppress Gibberella Ear Rot (GER) in a modern hybrid. (A, B) GFP-tagged endophyte strain 4G12 visualized inside maize roots, in the (A) absence or (B) presence of propidium iodide that outlines the cell with red color. (C–H) Representative ears from each treatment. (I) Picture of an ear to illustrate the methodology of scoring disease severity: The fungal pathogen was introduced to the tip of the ear, indicated by the asterisk. Therefore, the disease was scored as the ratio of the length of the diseased ear tip portion relative to total ear length, multiplied by 100 to give a percentage. (J, K) Quantification of the effect of different treatments on GER suppression, as: (J) percent ear infection, and (K) average grain yield per plant. For both measurements, n = 20 per treatment (n = 10 for both controls). The whiskers indicate the range of data points. The black asterisk indicates that the treatment means were significantly different from the Fusarium only treatment at p ≤ 0.05. The green asterisk indicates that the treatment means were significantly different from prothioconazole fungicide (Proline) treatment at p ≤ 0.05.
Mentions: Greenhouse experiments were undertaken to determine if the endophytes could suppress Gibberella ear rot (GER) in planta using a modern maize hybrid, P35F40, which is susceptible to this disease. To confirm that the candidate bacterial strains originally isolated from the two evolutionarily distant maize genotypes (Z. diploperennis and Parviglumis) could colonize the internal tissues of this modern hybrid, thus behaving as endophytes, GFP tagging was conducted. Attempts were made to GFP tag all endophytes, but unfortunately, only strain 4G12 from ancestral Parviglumis, was successfully tagged. GFP-tagged 4G12 was visualized by scanning confocal microscopy and shown to colonize maize roots (Figures 7A,B), confirming its behavior as an endophyte in the modern maize relative. All four endophytes were then tested for their ability to suppress GER under greenhouse conditions in two independent trials (Figures 7, 8). The main entrance routes for F. graminearum in maize are exposed silks where the ascospores can germinate and grow toward the developing ear (Sutton, 1982; Kebebe et al., 2015). Therefore, the disease severity was scored as the length of diseased area, measured from the ear tip where Fusarium spores were introduced, relative to the total length of the ear (Figure 7I). Kernel yields were also quantified:

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