change in the composition of root exudates may be due to the presence of
endophytes or may be a strategy by plants to attract endophytes to cope with nutrient
deficiency stress. Physico-chemical properties of soils can directly select for specific
microbes by creating conditions that benefit them and influence the availability of
plant root exudates affecting microbial recruitment by the plant. For example, soil
pH and nutrient availability (e.g., C, N, P) can affect the abundance of both pest and
beneficial soil biota in crops (Dumbrell et al. 2010; Garbeva et al. 2004).
13.3 EIPF and Their Role in Plant Growth Promotion
EIPF can live as saprophytes on soil organic matter, as plant symbionts, and as
pathogens of insects (Moonjely et al. 2016; Vega 2018). The relationship between
EIPF and plants appears to be facultative as they can survive and reproduce solely on
insect hosts. Many genera are classified as EIPF but among them the most wellstudied are fungi in the genera Beauveria and Metarhizium (Bamisile et al. 2018;
Vega 2018; Zhang et al. 2018).
EIPF in the genus Metarhizium occur primarily in soil, have a broad arthropod
host range, and are well-adapted to agricultural systems (Meyling and Eilenberg
2007; Steinwender et al. 2011; Tiago et al. 2014). Metarhizium spp. can infect more
than 200 arthropod host species from 17 families of Insecta and Acari (Roberts and
St. Leger 2004; Zimmermann 2007b). In agricultural soils, the prevalence of
Metarhizium spp. can reach 10
6 colony forming units (CFU) g
À1 soil and are
among the most abundant soil-borne entomopathogenic fungi (Lomer et al. 2001).
Even though the insect host range at the generic level is very broad, at the species
level, Metarhizium contains both specialist and generalist insect pathogens (Gao
et al. 2011). Some level of plant specificity of Metarhizium spp. has been observed in
nature. For example, at two experimental locations in Ontario, Canada, the association of M. brunneum, M. robertsii, and M. guizhouense with different plant species
(shrubs, grasses, trees, and wildflowers) was recorded (Wyrebek et al. 2011). When
co-occurring, M. robertsii was found associated with grass roots, whereas
M. guizhouense and M. brunneum were exclusively associated with the rhizosphere
of wildflowers. M. guizhouense was found associated with the rhizosphere of trees,
whereas M. brunneum was associated with the rhizosphere of trees and shrubs
(Wyrebek et al. 2011). Fisher et al. (2011) reported varying degree of association
and diversity of four Metarhizium spp. with the rhizosphere of blueberry (Vaccinium
corymbosum), grapevines (Vitis vinifera), strawberry (Fragaria ananassa), and
Christmas tree spp. (Picea engelmannii, Abies procera, and Pseudotsuga menziesii
(Pinales: Pinaceae) in the USA. Strawberry and Christmas trees had greater species
richness and were colonized by M. robertsii, M. brunneum, M. guizhouense, and
M. flavoviride. Blueberry and grape vines had lower species richness and diversity.
Blueberry was colonized only by M. brunneum and M. guizhouense, whereas grapes
were colonized by M. robertsii, M. brunneum, and M. guizhouense (Fisher et al.
2011). In another study in Japan, there was fungal diversity in the rhizosphere soil
but there was no evidence of specificity of M. robertsii, M. lepidiotae, M. pemphigi,
382
I. Ahmad et al.
endophytes or may be a strategy by plants to attract endophytes to cope with nutrient
deficiency stress. Physico-chemical properties of soils can directly select for specific
microbes by creating conditions that benefit them and influence the availability of
plant root exudates affecting microbial recruitment by the plant. For example, soil
pH and nutrient availability (e.g., C, N, P) can affect the abundance of both pest and
beneficial soil biota in crops (Dumbrell et al. 2010; Garbeva et al. 2004).
13.3 EIPF and Their Role in Plant Growth Promotion
EIPF can live as saprophytes on soil organic matter, as plant symbionts, and as
pathogens of insects (Moonjely et al. 2016; Vega 2018). The relationship between
EIPF and plants appears to be facultative as they can survive and reproduce solely on
insect hosts. Many genera are classified as EIPF but among them the most wellstudied are fungi in the genera Beauveria and Metarhizium (Bamisile et al. 2018;
Vega 2018; Zhang et al. 2018).
EIPF in the genus Metarhizium occur primarily in soil, have a broad arthropod
host range, and are well-adapted to agricultural systems (Meyling and Eilenberg
2007; Steinwender et al. 2011; Tiago et al. 2014). Metarhizium spp. can infect more
than 200 arthropod host species from 17 families of Insecta and Acari (Roberts and
St. Leger 2004; Zimmermann 2007b). In agricultural soils, the prevalence of
Metarhizium spp. can reach 10
6 colony forming units (CFU) g
À1 soil and are
among the most abundant soil-borne entomopathogenic fungi (Lomer et al. 2001).
Even though the insect host range at the generic level is very broad, at the species
level, Metarhizium contains both specialist and generalist insect pathogens (Gao
et al. 2011). Some level of plant specificity of Metarhizium spp. has been observed in
nature. For example, at two experimental locations in Ontario, Canada, the association of M. brunneum, M. robertsii, and M. guizhouense with different plant species
(shrubs, grasses, trees, and wildflowers) was recorded (Wyrebek et al. 2011). When
co-occurring, M. robertsii was found associated with grass roots, whereas
M. guizhouense and M. brunneum were exclusively associated with the rhizosphere
of wildflowers. M. guizhouense was found associated with the rhizosphere of trees,
whereas M. brunneum was associated with the rhizosphere of trees and shrubs
(Wyrebek et al. 2011). Fisher et al. (2011) reported varying degree of association
and diversity of four Metarhizium spp. with the rhizosphere of blueberry (Vaccinium
corymbosum), grapevines (Vitis vinifera), strawberry (Fragaria ananassa), and
Christmas tree spp. (Picea engelmannii, Abies procera, and Pseudotsuga menziesii
(Pinales: Pinaceae) in the USA. Strawberry and Christmas trees had greater species
richness and were colonized by M. robertsii, M. brunneum, M. guizhouense, and
M. flavoviride. Blueberry and grape vines had lower species richness and diversity.
Blueberry was colonized only by M. brunneum and M. guizhouense, whereas grapes
were colonized by M. robertsii, M. brunneum, and M. guizhouense (Fisher et al.
2011). In another study in Japan, there was fungal diversity in the rhizosphere soil
but there was no evidence of specificity of M. robertsii, M. lepidiotae, M. pemphigi,
382
I. Ahmad et al.