22
F. M. Romero et al.
perform endophytic interactions and even promote plant growth as evidenced by
Nieva et al. (2019) who demonstrates growth promotion effects by F. solani in the
model legume Lotus japonicus (Nieva et al. 2019).
Root fungal endophytes play an important role in plant growth due to involvement
in nutrient and water acquisition (Lugtenberg et al. 2016). Dark septate endophytes
(DSE) constitute a group of fungal endophytes characterized by their ability to colonize roots without causing damage and having melanin in their hyphae. They have
been defined as multifunctional, taking part in different processes such as nutritional uptake improvement, abiotic stress tolerance, and heavy metal sequestration
(Mandyam and Jumpponen 2005). Besides, they might play important roles as BCAs.
In this trend, there is evidence of DSE fungi controlling V. dahliae in tomato, showing
a reduction of up to 30% in disease symptoms (Andrade-Linares et al. 2011). Another
example is the endophytic fungus Phialocephala fortinii, exhibited75% of inhibition
against F. oxysporum in Asparagus officinalis (Narisawa 2018). Besides, in vitro
antagonism between DSE, ectomycorrhizal fungi, and pathogens such as Pythium
intermedium, Phytophthora citricola, and Heterobasidion annosum has been evaluated (Berthelot et al. 2019). These results could help the development of fungal
consortia to be used as phytostimulant and/or biocontrol products.
Fungi belonging to the Trichoderma genus have been demonstrated to be important biocontrol agents as they manage to induce ISR by activating the JA and SA
signaling pathways (Mukherjee et al. 2012). To date, this organism is the most important bio-fungicide developed and commercialized around the world (Verma et al.
2007), where the use of different Trichoderma spp. strains in disease biocontrol have
been extended to several crops and landscapes. Moreover, colonization of maize
plants by T. atroviride also induces resistance against herbivores such as Spodoptera
frugiperda (Contreras-Cornejo et al. 2018).
In turn, yeast endophytes have been scarcely studied to date. There are evidence
that these organisms survive as endophytes in Z. mays (Nassar et al. 2005) and in
stomata and xylem vessels of Citrus sinensis (Gai et al. 2009), but their potential as
biocontrol agents is yet to be evaluated. Recently, Rhodotorula and Cryptococcus
sp. have been proposed as biocontrol agents against the “witches’ broom disease” of
cacao (Ferraz et al. 2019).
2.3.3 Mechanisms of Biological Control by Fungal
Endophytes
Biological control mediated by fungal endophytes involves the production of
secondary metabolites, such as alkaloids, antibiotics, and/or lytic enzymes (Gao
et al. 2010). Also, as mentioned earlier for bacterial BCAs, volatile compounds
produced by fungal endophytes have been proposed as good biological control agents
(Morath et al. 2012). For example, volatile metabolites produced by the endophyte
F. M. Romero et al.
perform endophytic interactions and even promote plant growth as evidenced by
Nieva et al. (2019) who demonstrates growth promotion effects by F. solani in the
model legume Lotus japonicus (Nieva et al. 2019).
Root fungal endophytes play an important role in plant growth due to involvement
in nutrient and water acquisition (Lugtenberg et al. 2016). Dark septate endophytes
(DSE) constitute a group of fungal endophytes characterized by their ability to colonize roots without causing damage and having melanin in their hyphae. They have
been defined as multifunctional, taking part in different processes such as nutritional uptake improvement, abiotic stress tolerance, and heavy metal sequestration
(Mandyam and Jumpponen 2005). Besides, they might play important roles as BCAs.
In this trend, there is evidence of DSE fungi controlling V. dahliae in tomato, showing
a reduction of up to 30% in disease symptoms (Andrade-Linares et al. 2011). Another
example is the endophytic fungus Phialocephala fortinii, exhibited75% of inhibition
against F. oxysporum in Asparagus officinalis (Narisawa 2018). Besides, in vitro
antagonism between DSE, ectomycorrhizal fungi, and pathogens such as Pythium
intermedium, Phytophthora citricola, and Heterobasidion annosum has been evaluated (Berthelot et al. 2019). These results could help the development of fungal
consortia to be used as phytostimulant and/or biocontrol products.
Fungi belonging to the Trichoderma genus have been demonstrated to be important biocontrol agents as they manage to induce ISR by activating the JA and SA
signaling pathways (Mukherjee et al. 2012). To date, this organism is the most important bio-fungicide developed and commercialized around the world (Verma et al.
2007), where the use of different Trichoderma spp. strains in disease biocontrol have
been extended to several crops and landscapes. Moreover, colonization of maize
plants by T. atroviride also induces resistance against herbivores such as Spodoptera
frugiperda (Contreras-Cornejo et al. 2018).
In turn, yeast endophytes have been scarcely studied to date. There are evidence
that these organisms survive as endophytes in Z. mays (Nassar et al. 2005) and in
stomata and xylem vessels of Citrus sinensis (Gai et al. 2009), but their potential as
biocontrol agents is yet to be evaluated. Recently, Rhodotorula and Cryptococcus
sp. have been proposed as biocontrol agents against the “witches’ broom disease” of
cacao (Ferraz et al. 2019).
2.3.3 Mechanisms of Biological Control by Fungal
Endophytes
Biological control mediated by fungal endophytes involves the production of
secondary metabolites, such as alkaloids, antibiotics, and/or lytic enzymes (Gao
et al. 2010). Also, as mentioned earlier for bacterial BCAs, volatile compounds
produced by fungal endophytes have been proposed as good biological control agents
(Morath et al. 2012). For example, volatile metabolites produced by the endophyte