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Biological control of the cucurbit powdery mildew pathogen Podosphaera xanthii by means of the epiphytic fungus Pseudozyma aphidis and parasitism as a mode of action.

Gafni A, Calderon CE, Harris R, Buxdorf K, Dafa-Berger A, Zeilinger-Reichert E, Levy M - Front Plant Sci (2015)

Bottom Line: We identified a unique, biologically active isolate of the epiphytic yeast Pseudozyma aphidis that is capable of inhibiting Botrytis cinerea via a dual mode of action, namely induced resistance and antibiosis.We also show that crude extract of P. aphidis metabolites can inhibit P. xanthii spore germination in planta.Our results suggest that in addition to its antibiosis as mode of action, P. aphidis may also act as an ectoparasite on P. xanthii.

View Article: PubMed Central - PubMed

Affiliation: Plant Pathology and Microbiology, Hebrew University of Jerusalem Jerusalem, Israel.

ABSTRACT
Epiphytic yeasts, which colonize plant surfaces, may possess activity that can be harnessed to help plants defend themselves against various pathogens. Due to their unique characteristics, epiphytic yeasts belonging to the genus Pseudozyma hold great potential for use as biocontrol agents. We identified a unique, biologically active isolate of the epiphytic yeast Pseudozyma aphidis that is capable of inhibiting Botrytis cinerea via a dual mode of action, namely induced resistance and antibiosis. Here, we show that strain L12 of P. aphidis can reduce the severity of powdery mildew caused by Podosphaera xanthii on cucumber plants with an efficacy of 75%. Confocal and scanning electron microscopy analyses demonstrated P. aphidis proliferation on infected tissue and its production of long hyphae that parasitize the powdery mildew hyphae and spores as an ectoparasite. We also show that crude extract of P. aphidis metabolites can inhibit P. xanthii spore germination in planta. Our results suggest that in addition to its antibiosis as mode of action, P. aphidis may also act as an ectoparasite on P. xanthii. These results indicate that P. aphidis strain L12 has the potential to control powdery mildew.

No MeSH data available.


Related in: MedlinePlus

P. aphidis–powdery mildew interactions on cucumber cotyledons. SEM microscopy of cucumber cotyledons treated with P. aphidis and infected with Podosphaera xanthii. (A) Cucumber cotyledons treated with P. aphidis 4 days post-infection with P. xanthii. (B) Closer look at the interaction of P. aphidis and P. xanthii mycelium and spores 1 and 4 days post-infection with P. xanthii. Cucumber cotyledons treated with P. aphidis (PA) or with water (Control) 1 day post-inoculation (C) and 10 days post-inoculation with P. xanthii(D) (sporulation marked with white arrows). (A–C)P. xanthii mycelium and spores are indicated with white arrows and P. aphidis cells and hyphae with dashed arrows; E, extracellular matrix.
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Figure 3: P. aphidis–powdery mildew interactions on cucumber cotyledons. SEM microscopy of cucumber cotyledons treated with P. aphidis and infected with Podosphaera xanthii. (A) Cucumber cotyledons treated with P. aphidis 4 days post-infection with P. xanthii. (B) Closer look at the interaction of P. aphidis and P. xanthii mycelium and spores 1 and 4 days post-infection with P. xanthii. Cucumber cotyledons treated with P. aphidis (PA) or with water (Control) 1 day post-inoculation (C) and 10 days post-inoculation with P. xanthii(D) (sporulation marked with white arrows). (A–C)P. xanthii mycelium and spores are indicated with white arrows and P. aphidis cells and hyphae with dashed arrows; E, extracellular matrix.

Mentions: We demonstrated in vitro that P. aphidis is a dimorphic yeast-like fungus that grows mainly as a yeast in PDB medium but can form hyphae when grown in different media, such as YMPD or MS (Supplementary Figure 4). Using confocal microscopy, we demonstrated the morphological yeast-to-hypha transition (dimorphism) of P. aphidis in planta (Figure 2). P. aphidis was mainly in yeast form on uninfected tissue (Figure 2 Left), whereas on P. xanthii-infected tissue, it was mainly in hyphal form (Figure 2 Right). SEM revealed that the areas infected with powdery mildew were covered with P. aphidis (Figure 3), and that the powdery mildew's hyphae were significantly shorter (by 27%, Supplementary Table 1) when they were associated with P. aphidis at infection initiation 2 dpi (Figure 3C). P. aphidis, on the other hand, formed long hyphae that branched when associated with P. xanthii and attached to the powdery mildew hyphae by coiling around them as seen by SEM analysis (Figures 3A,B). We observed inhibition of growth and sporulation of powdery mildew on the plants that were treated with P. aphidis as compared to control (Figure 3D). We also observed accumulation of extracellular matrix in the area of interaction between P. aphidis and powdery mildew, and that the hyphae of P. aphidis extending from one powdery mildew hypha to another one were thinner (Figures 3A,B and Supplementary Figure 5). Furthermore, P. aphidis behave like an ectoparasite, as demonstrated by confocal and TEM microscopy. We could not detect any GFP fluorescence or P. aphidis cells inside the powdery mildew hyphae using confocal microscopy or TEM, respectively (Figures 4, 5 and Supplementary Movies 1, 2). TEM analysis of powdery mildew cells associated with P. aphidis showed numerous abnormalities: increased vacuolation, deformation of the cell wall and disorganization of the cytoplasm. These abnormalities eventually lead to collapse of the powdery mildew cells (Figure 5). Accumulation of extracellular matrix surrounding P. aphidis was also observed (Figure 5).


Biological control of the cucurbit powdery mildew pathogen Podosphaera xanthii by means of the epiphytic fungus Pseudozyma aphidis and parasitism as a mode of action.

Gafni A, Calderon CE, Harris R, Buxdorf K, Dafa-Berger A, Zeilinger-Reichert E, Levy M - Front Plant Sci (2015)

P. aphidis–powdery mildew interactions on cucumber cotyledons. SEM microscopy of cucumber cotyledons treated with P. aphidis and infected with Podosphaera xanthii. (A) Cucumber cotyledons treated with P. aphidis 4 days post-infection with P. xanthii. (B) Closer look at the interaction of P. aphidis and P. xanthii mycelium and spores 1 and 4 days post-infection with P. xanthii. Cucumber cotyledons treated with P. aphidis (PA) or with water (Control) 1 day post-inoculation (C) and 10 days post-inoculation with P. xanthii(D) (sporulation marked with white arrows). (A–C)P. xanthii mycelium and spores are indicated with white arrows and P. aphidis cells and hyphae with dashed arrows; E, extracellular matrix.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 3: P. aphidis–powdery mildew interactions on cucumber cotyledons. SEM microscopy of cucumber cotyledons treated with P. aphidis and infected with Podosphaera xanthii. (A) Cucumber cotyledons treated with P. aphidis 4 days post-infection with P. xanthii. (B) Closer look at the interaction of P. aphidis and P. xanthii mycelium and spores 1 and 4 days post-infection with P. xanthii. Cucumber cotyledons treated with P. aphidis (PA) or with water (Control) 1 day post-inoculation (C) and 10 days post-inoculation with P. xanthii(D) (sporulation marked with white arrows). (A–C)P. xanthii mycelium and spores are indicated with white arrows and P. aphidis cells and hyphae with dashed arrows; E, extracellular matrix.
Mentions: We demonstrated in vitro that P. aphidis is a dimorphic yeast-like fungus that grows mainly as a yeast in PDB medium but can form hyphae when grown in different media, such as YMPD or MS (Supplementary Figure 4). Using confocal microscopy, we demonstrated the morphological yeast-to-hypha transition (dimorphism) of P. aphidis in planta (Figure 2). P. aphidis was mainly in yeast form on uninfected tissue (Figure 2 Left), whereas on P. xanthii-infected tissue, it was mainly in hyphal form (Figure 2 Right). SEM revealed that the areas infected with powdery mildew were covered with P. aphidis (Figure 3), and that the powdery mildew's hyphae were significantly shorter (by 27%, Supplementary Table 1) when they were associated with P. aphidis at infection initiation 2 dpi (Figure 3C). P. aphidis, on the other hand, formed long hyphae that branched when associated with P. xanthii and attached to the powdery mildew hyphae by coiling around them as seen by SEM analysis (Figures 3A,B). We observed inhibition of growth and sporulation of powdery mildew on the plants that were treated with P. aphidis as compared to control (Figure 3D). We also observed accumulation of extracellular matrix in the area of interaction between P. aphidis and powdery mildew, and that the hyphae of P. aphidis extending from one powdery mildew hypha to another one were thinner (Figures 3A,B and Supplementary Figure 5). Furthermore, P. aphidis behave like an ectoparasite, as demonstrated by confocal and TEM microscopy. We could not detect any GFP fluorescence or P. aphidis cells inside the powdery mildew hyphae using confocal microscopy or TEM, respectively (Figures 4, 5 and Supplementary Movies 1, 2). TEM analysis of powdery mildew cells associated with P. aphidis showed numerous abnormalities: increased vacuolation, deformation of the cell wall and disorganization of the cytoplasm. These abnormalities eventually lead to collapse of the powdery mildew cells (Figure 5). Accumulation of extracellular matrix surrounding P. aphidis was also observed (Figure 5).

Bottom Line: We identified a unique, biologically active isolate of the epiphytic yeast Pseudozyma aphidis that is capable of inhibiting Botrytis cinerea via a dual mode of action, namely induced resistance and antibiosis.We also show that crude extract of P. aphidis metabolites can inhibit P. xanthii spore germination in planta.Our results suggest that in addition to its antibiosis as mode of action, P. aphidis may also act as an ectoparasite on P. xanthii.

View Article: PubMed Central - PubMed

Affiliation: Plant Pathology and Microbiology, Hebrew University of Jerusalem Jerusalem, Israel.

ABSTRACT
Epiphytic yeasts, which colonize plant surfaces, may possess activity that can be harnessed to help plants defend themselves against various pathogens. Due to their unique characteristics, epiphytic yeasts belonging to the genus Pseudozyma hold great potential for use as biocontrol agents. We identified a unique, biologically active isolate of the epiphytic yeast Pseudozyma aphidis that is capable of inhibiting Botrytis cinerea via a dual mode of action, namely induced resistance and antibiosis. Here, we show that strain L12 of P. aphidis can reduce the severity of powdery mildew caused by Podosphaera xanthii on cucumber plants with an efficacy of 75%. Confocal and scanning electron microscopy analyses demonstrated P. aphidis proliferation on infected tissue and its production of long hyphae that parasitize the powdery mildew hyphae and spores as an ectoparasite. We also show that crude extract of P. aphidis metabolites can inhibit P. xanthii spore germination in planta. Our results suggest that in addition to its antibiosis as mode of action, P. aphidis may also act as an ectoparasite on P. xanthii. These results indicate that P. aphidis strain L12 has the potential to control powdery mildew.

No MeSH data available.


Related in: MedlinePlus