126
A. Ghasemnezhad et al.
Thus endophytes try to eliminate apoptosis of infected tissue (Alvin et al. 2014).
Induction of plant defense mechanisms by endophyte against pathogens is an attractive phenomenon and acts as control tool used in modern and sustainable farming
methods (Martinez-Klimova et al. 2017).
6.2 What Is Endophyte?
The most important use of the term ‘endophyte’ is for microorganisms whose intrusions are intangible (Kobayashi and Palumbo 2000). Although, their origin dates to
the nineteenth century, its contemporary meaning differs from its original meaning
(Carroll 1986). Today’s applications of this term have not been consistent and none
have been accepted by all researchers. The definition has changed many times
and numerous terms and definitions of endophytic fungi have been proposed by
researchers. Carroll (1986), identified endophytes as cooperative fungi that occupy
the aerial parts of living plant tissues, but do not cause any symptoms. This definition does not include plant pathogenic fungi and mycorrhizal fungi. Endophytes
are closely related to plant pathogens but are of limited pathogenicity and may
have evolved from plant pathogenic fungi. Petrini (1991) proposed a broader definition of endophytes than Carroll’s definition, which includes all living organisms
living in plant organs and can partially occupy host plants without pathogenic effect.
According to this definition, endogenous plant pathogens that live within the host
tissue without symptoms, and have an epiphytic phase in their life cycle, are also
endophytes. Wilson (1995) defined endophytes as fungi or bacteria that invade living
plant tissues throughout or part of their life cycle and induce completely non-obvious,
symptomatic, infection within the plant tissue.
On the other hand, Sikora et al. (2007) noted that, endophytic fungi reside within
the plant tissue and are useful for their host or have no effect on their host. A special
term, ‘endophyte’ is used when we refer to microorganisms present in plants. They
could be considered as bacteria or fungi or actinobacteria, which spend their whole or
part of their life cycle in the inter or intracellular tissues of different plant parts (stems,
petioles, roots, leaves) without causing any apparent diseases to their host plants
(Singh 2019). According to the researchers, endophytic fungi have three classes.
The first category is the pathogenic fungi that are in their non-pathogenic form in
the other host plant, the second group belongs to fungi that are generally pathogenic,
and the third group has mutated and become non-pathogenic fungi for example,
Colletotrichum magna (Backman and Sikora 2008). In general, the definition of the
term endophyte is varied in articles and books that have ever been published. But most
mycologists use the term for fungi that can occupy living and internal host tissues
and do not cause visible disease symptoms (Petrini 1991; Wilson 1995). Endophytes
are microorganisms (mostly fungi and bacteria) that live in the interstitial and intracellular areas of healthy plant tissues at a specific time and can colonize without
harming the host (Bacon et al. 2000; Strobel and Daisy 2003; Khan 2010). The presence of endophytes in plan ts can alter the food cycle and symbiotic composition,
A. Ghasemnezhad et al.
Thus endophytes try to eliminate apoptosis of infected tissue (Alvin et al. 2014).
Induction of plant defense mechanisms by endophyte against pathogens is an attractive phenomenon and acts as control tool used in modern and sustainable farming
methods (Martinez-Klimova et al. 2017).
6.2 What Is Endophyte?
The most important use of the term ‘endophyte’ is for microorganisms whose intrusions are intangible (Kobayashi and Palumbo 2000). Although, their origin dates to
the nineteenth century, its contemporary meaning differs from its original meaning
(Carroll 1986). Today’s applications of this term have not been consistent and none
have been accepted by all researchers. The definition has changed many times
and numerous terms and definitions of endophytic fungi have been proposed by
researchers. Carroll (1986), identified endophytes as cooperative fungi that occupy
the aerial parts of living plant tissues, but do not cause any symptoms. This definition does not include plant pathogenic fungi and mycorrhizal fungi. Endophytes
are closely related to plant pathogens but are of limited pathogenicity and may
have evolved from plant pathogenic fungi. Petrini (1991) proposed a broader definition of endophytes than Carroll’s definition, which includes all living organisms
living in plant organs and can partially occupy host plants without pathogenic effect.
According to this definition, endogenous plant pathogens that live within the host
tissue without symptoms, and have an epiphytic phase in their life cycle, are also
endophytes. Wilson (1995) defined endophytes as fungi or bacteria that invade living
plant tissues throughout or part of their life cycle and induce completely non-obvious,
symptomatic, infection within the plant tissue.
On the other hand, Sikora et al. (2007) noted that, endophytic fungi reside within
the plant tissue and are useful for their host or have no effect on their host. A special
term, ‘endophyte’ is used when we refer to microorganisms present in plants. They
could be considered as bacteria or fungi or actinobacteria, which spend their whole or
part of their life cycle in the inter or intracellular tissues of different plant parts (stems,
petioles, roots, leaves) without causing any apparent diseases to their host plants
(Singh 2019). According to the researchers, endophytic fungi have three classes.
The first category is the pathogenic fungi that are in their non-pathogenic form in
the other host plant, the second group belongs to fungi that are generally pathogenic,
and the third group has mutated and become non-pathogenic fungi for example,
Colletotrichum magna (Backman and Sikora 2008). In general, the definition of the
term endophyte is varied in articles and books that have ever been published. But most
mycologists use the term for fungi that can occupy living and internal host tissues
and do not cause visible disease symptoms (Petrini 1991; Wilson 1995). Endophytes
are microorganisms (mostly fungi and bacteria) that live in the interstitial and intracellular areas of healthy plant tissues at a specific time and can colonize without
harming the host (Bacon et al. 2000; Strobel and Daisy 2003; Khan 2010). The presence of endophytes in plan ts can alter the food cycle and symbiotic composition,