nutrients, and enhance tolerance of colonized plants against environmental stresses
(reviewed in (Bamisile et al. 2018; Hu and Bidochka 2019; Vega 2018). Tritrophic
interactions involving EIPF in which the growth or fecundity of herbivorous insects
and plant pathogens that attack endophyte-colonized plants is suppressed could have
important implications for biological control in agroecosystems.
13.2 Role of Fungal Endophytes in Plant Growth Promotion
and Protection
Fungal endophytes in plants are not randomly distributed in plant tissues or in the
environment. Both soil and plant factors exert strong influences (Chaparro et al.
2012, 2014; Hacquard et al. 2015) and opinions are divided on which factors
predominate in the recruitment of endophytes by plants (Berg and Smalla 2009;
Lareen et al. 2016). Soil-borne EIPF are influenced initially in the rhizosphere by
many biotic and abiotic factors, e.g. plant species, plant growth stage, fungal species,
other microbes, soil properties, climate, and geographical characteristics (Glynou
et al. 2016; Lê Van et al. 2017). The factors and interactions in soil that drive
changes in the rhizosphere community are complex, dynamic, and not fully
understood.
Plants can modify soil microbial communities directly, presumably through
differences in root exudates (Chaparro et al. 2014; Hartmann et al. 2009; Oldroyd
2013), or indirectly via their influence on the abiotic environment (Bulgarelli et al.
2013). Qualitatively and quantitatively diverse root exudates play a role in
modulating the microbial composition and assembly in the bulk soil microbiome
(Bruck 2009; Busby et al. 2017; Sasse et al. 2018). Root exudates contain highly
diverse low-molecular weight compounds such as phenolics, metabolites, amino
acids, organic acids and sugars and relatively less diverse high-molecular weight
compounds such as proteins and mucilage (Bais et al. 2006). The same chemical in
root exudates can vary in their function as signals that can attract or deter specific
microbes, thus influencing their interaction with plants (Bais et al. 2006). Fungal
endophytes can modulate the composition of root exudates by altering the level of
phenolics and other metabolites that may contribute to plant growth promotion and
tolerance against stresses (Gargallo-Garriga et al. 2018; Guo et al. 2015). The
composition of root exudates and their interaction with specific microbes is a
signature of chemical communication of the plant and rhizosphere microbiome
(Bais et al. 2006). However, the actual mechanism and the multitude of factors by
which quality and composition of root exudation is controlled are still unclear
(Hu et al. 2018).
The mediation of plant–microbe interactions through root exudates is associated
with significant carbon costs to plants (Uren 2000). Plants release carbon-rich
rhizodeposits that are used as chemical signals that stimulate microbial growth.
For example, the concentration of carbohydrates and organic carbon in the root
exudates of tall fescue was greater in the presence of the endophyte Neotyphodium
coenophialum, compared with endophyte-free plants (Van Hecke et al. 2005). The
13 The Role of Endophytic Insect-Pathogenic Fungi in Biotic Stress Management
381
(reviewed in (Bamisile et al. 2018; Hu and Bidochka 2019; Vega 2018). Tritrophic
interactions involving EIPF in which the growth or fecundity of herbivorous insects
and plant pathogens that attack endophyte-colonized plants is suppressed could have
important implications for biological control in agroecosystems.
13.2 Role of Fungal Endophytes in Plant Growth Promotion
and Protection
Fungal endophytes in plants are not randomly distributed in plant tissues or in the
environment. Both soil and plant factors exert strong influences (Chaparro et al.
2012, 2014; Hacquard et al. 2015) and opinions are divided on which factors
predominate in the recruitment of endophytes by plants (Berg and Smalla 2009;
Lareen et al. 2016). Soil-borne EIPF are influenced initially in the rhizosphere by
many biotic and abiotic factors, e.g. plant species, plant growth stage, fungal species,
other microbes, soil properties, climate, and geographical characteristics (Glynou
et al. 2016; Lê Van et al. 2017). The factors and interactions in soil that drive
changes in the rhizosphere community are complex, dynamic, and not fully
understood.
Plants can modify soil microbial communities directly, presumably through
differences in root exudates (Chaparro et al. 2014; Hartmann et al. 2009; Oldroyd
2013), or indirectly via their influence on the abiotic environment (Bulgarelli et al.
2013). Qualitatively and quantitatively diverse root exudates play a role in
modulating the microbial composition and assembly in the bulk soil microbiome
(Bruck 2009; Busby et al. 2017; Sasse et al. 2018). Root exudates contain highly
diverse low-molecular weight compounds such as phenolics, metabolites, amino
acids, organic acids and sugars and relatively less diverse high-molecular weight
compounds such as proteins and mucilage (Bais et al. 2006). The same chemical in
root exudates can vary in their function as signals that can attract or deter specific
microbes, thus influencing their interaction with plants (Bais et al. 2006). Fungal
endophytes can modulate the composition of root exudates by altering the level of
phenolics and other metabolites that may contribute to plant growth promotion and
tolerance against stresses (Gargallo-Garriga et al. 2018; Guo et al. 2015). The
composition of root exudates and their interaction with specific microbes is a
signature of chemical communication of the plant and rhizosphere microbiome
(Bais et al. 2006). However, the actual mechanism and the multitude of factors by
which quality and composition of root exudation is controlled are still unclear
(Hu et al. 2018).
The mediation of plant–microbe interactions through root exudates is associated
with significant carbon costs to plants (Uren 2000). Plants release carbon-rich
rhizodeposits that are used as chemical signals that stimulate microbial growth.
For example, the concentration of carbohydrates and organic carbon in the root
exudates of tall fescue was greater in the presence of the endophyte Neotyphodium
coenophialum, compared with endophyte-free plants (Van Hecke et al. 2005). The
13 The Role of Endophytic Insect-Pathogenic Fungi in Biotic Stress Management
381