13.7 Mechanisms of Plant Protection
EIPF employ various strategies to bypass plant host immunity, and the plant
protective effects mediated by EIPF colonization may partially be due to priming
of phytohormone-based defenses (Pieterse et al. 2012), enhanced production of
secondary metabolites (Gibson et al. 2014; Khan et al. 2012; Shrivastava et al.
2015), organic compounds (Bitas et al. 2013), and accumulation of anti-herbivory
fungal metabolites and mycotoxins in plant tissues (Gurulingappa et al. 2010). EIPFmediated plant defense activation or priming effects may be elicited due to endophytic colonization, thus resulting in enhanced plant protection against pests and
pathogens (Pieterse et al. 2012; Raad et al. 2019). Microbe-mediated priming
activates the plant defenses slightly or transiently in the absence of stress. Later,
when a plant perceives a challenging signal, primed plants can activate defense more
quickly, with greater strength and in a more sustained manner compared to
non-primed plants (Martinez-Medina et al. 2016).
Metarhizium spp. can produce secondary metabolites such as destruxins, cytochalasin, and swainsonine (Gibson et al. 2014; Golo et al. 2014; Pedras et al. 2002;
Singh and Kaur 2014). M. robertsii produced multiple destruxins in artificial
medium and endophytically colonized cowpea (Vigna unguiculata) but not in
cucumber (Cucumis sativus) (Golo et al. 2014). Foliar inoculation of seedlings
with M. brunneum resulted in the production of destruxins in potato and melon
leaves (Resquín-Romero et al. 2016). Destruxins were detected in insects that were
fed on M. brunneum-colonized tomato and melon (Garrido-Jurado et al. 2017;
Resquín-Romero et al. 2016). Endophytic M. brunneum in olive produced secondary
metabolites with antagonistic activity against the phytopathogens V. dahliae and
P. megasperma (Lozano-Tovar et al. 2017). Chromatographic analysis showed that
tyrosine betaine was detected from the conidial extract of M. anisopliae (Carollo
et al. 2010).
Beauveria spp. produce various secondary metabolites, including beauvericin,
beauveriolides, bassianolides, oxalic acid, and oosporein (Scharf et al. 2014; Strasser
et al. 2000). Culture filtrates and conidial extracts of B. bassiana produced secondary
metabolites that reduced the survival and fecundity of Aphis gossypii (Gurulingappa
et al. 2010). Oosporein was detected in potato tubers following the application of a
commercial formulation of B. brongniartii to potato fields (Seger et al. 2005).
Secondary metabolites are also produced by other EIPF genera such as
Lecanicillium, Isaria, and Fusarium (Scharf et al. 2014; Zimmermann 2007a,
2007b, 2008). Bassianolides produced by Lecanicillium spp. have antifungal, insecticidal, antibacterial, and anti-tumor properties (Scharf et al. 2014). Mycelial extracts
and culture filtrates of L. lecanii reduced the survival and fecundity of Aphis gossypii
and authors attributed the effects to fungal secondary metabolites (Gurulingappa
et al. 2010). Farinosone was detected in plants that were endophytically colonized by
I. farinosa (Zimmermann 2008).
Plants can also produce secondary metabolites and their concentration and
composition can vary in plant–EIPF interactions through effects on root exudates
(Chaparro et al. 2014; Hartmann et al. 2009; Oldroyd 2013) and by modifying the
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I. Ahmad et al.
EIPF employ various strategies to bypass plant host immunity, and the plant
protective effects mediated by EIPF colonization may partially be due to priming
of phytohormone-based defenses (Pieterse et al. 2012), enhanced production of
secondary metabolites (Gibson et al. 2014; Khan et al. 2012; Shrivastava et al.
2015), organic compounds (Bitas et al. 2013), and accumulation of anti-herbivory
fungal metabolites and mycotoxins in plant tissues (Gurulingappa et al. 2010). EIPFmediated plant defense activation or priming effects may be elicited due to endophytic colonization, thus resulting in enhanced plant protection against pests and
pathogens (Pieterse et al. 2012; Raad et al. 2019). Microbe-mediated priming
activates the plant defenses slightly or transiently in the absence of stress. Later,
when a plant perceives a challenging signal, primed plants can activate defense more
quickly, with greater strength and in a more sustained manner compared to
non-primed plants (Martinez-Medina et al. 2016).
Metarhizium spp. can produce secondary metabolites such as destruxins, cytochalasin, and swainsonine (Gibson et al. 2014; Golo et al. 2014; Pedras et al. 2002;
Singh and Kaur 2014). M. robertsii produced multiple destruxins in artificial
medium and endophytically colonized cowpea (Vigna unguiculata) but not in
cucumber (Cucumis sativus) (Golo et al. 2014). Foliar inoculation of seedlings
with M. brunneum resulted in the production of destruxins in potato and melon
leaves (Resquín-Romero et al. 2016). Destruxins were detected in insects that were
fed on M. brunneum-colonized tomato and melon (Garrido-Jurado et al. 2017;
Resquín-Romero et al. 2016). Endophytic M. brunneum in olive produced secondary
metabolites with antagonistic activity against the phytopathogens V. dahliae and
P. megasperma (Lozano-Tovar et al. 2017). Chromatographic analysis showed that
tyrosine betaine was detected from the conidial extract of M. anisopliae (Carollo
et al. 2010).
Beauveria spp. produce various secondary metabolites, including beauvericin,
beauveriolides, bassianolides, oxalic acid, and oosporein (Scharf et al. 2014; Strasser
et al. 2000). Culture filtrates and conidial extracts of B. bassiana produced secondary
metabolites that reduced the survival and fecundity of Aphis gossypii (Gurulingappa
et al. 2010). Oosporein was detected in potato tubers following the application of a
commercial formulation of B. brongniartii to potato fields (Seger et al. 2005).
Secondary metabolites are also produced by other EIPF genera such as
Lecanicillium, Isaria, and Fusarium (Scharf et al. 2014; Zimmermann 2007a,
2007b, 2008). Bassianolides produced by Lecanicillium spp. have antifungal, insecticidal, antibacterial, and anti-tumor properties (Scharf et al. 2014). Mycelial extracts
and culture filtrates of L. lecanii reduced the survival and fecundity of Aphis gossypii
and authors attributed the effects to fungal secondary metabolites (Gurulingappa
et al. 2010). Farinosone was detected in plants that were endophytically colonized by
I. farinosa (Zimmermann 2008).
Plants can also produce secondary metabolites and their concentration and
composition can vary in plant–EIPF interactions through effects on root exudates
(Chaparro et al. 2014; Hartmann et al. 2009; Oldroyd 2013) and by modifying the
390
I. Ahmad et al.