*2.1.1 Transmission*

The life history of endophytes in symbiotum with host plant has three modes of reproduction (**Figure 1**). They can either be transmitted (i) vertically from infected plant to offspring via seeds (*Neotyphodium* spp.), (ii) horizontally by sexual spore s from infected individuals (e.g. *Epichloe* spp.) or (iii) mixture of two life cycles [19]. The pure vertical transmission is asexual reproduction of intercellular hyphae of above ground tissues with no symptoms and transmitted vertically via seeds from infected plants to offspring (e.g. *Neotyphodium* spp.). In contrast, the pure horizontal transmission evolves sexual life cycle, relies on the production of contagious

**213**

**Figure 1.**

*Fungal Endophyte-Host Plant Interactions: Role in Sustainable Agriculture*

sexual spores. These spores can only be produced on a fungal structure (stroma) surrounding the grass flag leaf sheath (e.g. some *Epichloe* spp.). Leaves accumulate numerous infections shortly after emergence by means of epiphytic germination of fungal propagules, followed by cuticular penetration or entry through stomata's [20–22] and grow intercellularly within healthy tissues [20, 23]. However, many *Epichloe* spp. use a third mode of reproduction. In this fungi choke some flowering tillers and produce sexual spores leaving majority of tillers uninfected and transmitted asexually via seeds [18]. Endophytes are transmitted vertically (systemic) and horizontally (non-systemic). Vertically transmitted endophytes are mutualistic, whereas those transmitted horizontally depict antagonism to the host [6, 24].

*Asexual and sexual life cycles of* Epichloe festucae *symbiotic with* Festuca *spp. [18].*

In view of escalating pollution and cost due to indiscriminate use of chemical pesticides, diverted researchers interest towards alternative eco-friendly and safe approaches to meet increasing demand of agriculture productivity. Sustainable agriculture requires the use of various strategies to increase or maintain the current rate of food production while minimizing damage to the environment and human health. Symbiotic endophytic fungal associations with crops offer wide range of benefits ranging from the promotion of plant growth to improvements in the tolerance of various biotic and abiotic stresses. Moreover, loss of useful endophytic microbes from crop plants during their domestication and long term cultivation also requires transfer of endophytes from wild relatives of crops to crop species.

Endophytic fungi have gained importance in the area of agriculture because of their ability to confer resistance to various biotic stress conditions like insect

**3. Fungal endophytes for sustainable agriculture**

**4. Fungal endophytes: Biotic stress management**

herbivory, nematicidal attack and by aiding plant growth processes.

*DOI: http://dx.doi.org/10.5772/intechopen.92367*

*Fungal Endophyte-Host Plant Interactions: Role in Sustainable Agriculture DOI: http://dx.doi.org/10.5772/intechopen.92367*

*Sustainable Crop Production*

**2. Fungal endophyte-host plant association**

of infection [7, 8]. Moreover, fungal endophytes have gained significant interest in sustainable agriculture due to their great potential to contribute to secondary compounds with unique structure, including alkaloids, benzopyranones, chinones, flavonoids, phenolic acids, quinones, steroids, terpenoids, tetralones, xanthones, etc. [9–11] produced by the fungi or by the plant due to interaction with the fungi. Among the microorganisms, fungal endophytes are the largest group producing secondary metabolites. Fungal toxins produced by these biotic metabolites contribute to plants tolerance towards various biotic and abiotic stresses. Fungal endophytes are known to produce bioactive compounds toxic to insects, nematodes, produces extracellular enzymes (cellulases, proteinase, lipases, esterases) for degradation of dead soil biomass, solubilize insoluble phosphates and produce plant growth-promoting hormones (auxins, cytokinins, gibberellins). Endophyte infected plants manage plant growth under adverse conditions of drought, salinity, temperature and heavy metal stress through different mechanisms. This chapter outlines various approaches for the use of endophytic fungal inoculants to combat various stresses in agricultural fields, thus increasing global crop productivity.

The association between fungal endophytes and their host plant is due to their unique adaptations which enable the endophytes to harmonize their growth with their host plant [12]. The origin of endophytes is not clear due to complex association between the endophyte and its host plant and the multiplicity of the host's living environment. Exogenous and endogenous are the two hypotheses explaining the origin of endophytes. According to endogenous hypothesis, endophytes are gaged from the mitochondria and chloroplast of the plant, and so it has comparable genetic backgrounds to the host [13], whereas exogenous hypothesis believes that endophytes arrive from outside of the plant and got inserted into the host from root wound, induced channels, or surface [14]. During the long period of coexistence and evolutionary processes, different relationships have been established between endophytic fungi and their host plants ranging from (i) a continuum of mutualism, (ii) antagonism, and (iii) neutralism. As once inside the tissues of a host plant, the endophytic fungi assumed a quiescent (latent) state, either for the whole lifetime of the host plant (neutralism) or for an extended period of time (mutualism or antagonism) until environmental conditions are favorable for endophytic fungi [15]. Endophytes due to its cryptic existence also have its role of decomposers in ecosystem, as they are among the primary colonizers of dead plant

The life history of endophytes in symbiotum with host plant has three modes of reproduction (**Figure 1**). They can either be transmitted (i) vertically from infected plant to offspring via seeds (*Neotyphodium* spp.), (ii) horizontally by sexual spore s from infected individuals (e.g. *Epichloe* spp.) or (iii) mixture of two life cycles [19]. The pure vertical transmission is asexual reproduction of intercellular hyphae of above ground tissues with no symptoms and transmitted vertically via seeds from infected plants to offspring (e.g. *Neotyphodium* spp.). In contrast, the pure horizontal transmission evolves sexual life cycle, relies on the production of contagious

**212**

tissues [16, 17].

*2.1.1 Transmission*

**2.1 Fungal endophytes**

#### **Figure 1.** *Asexual and sexual life cycles of* Epichloe festucae *symbiotic with* Festuca *spp. [18].*

sexual spores. These spores can only be produced on a fungal structure (stroma) surrounding the grass flag leaf sheath (e.g. some *Epichloe* spp.). Leaves accumulate numerous infections shortly after emergence by means of epiphytic germination of fungal propagules, followed by cuticular penetration or entry through stomata's [20–22] and grow intercellularly within healthy tissues [20, 23]. However, many *Epichloe* spp. use a third mode of reproduction. In this fungi choke some flowering tillers and produce sexual spores leaving majority of tillers uninfected and transmitted asexually via seeds [18]. Endophytes are transmitted vertically (systemic) and horizontally (non-systemic). Vertically transmitted endophytes are mutualistic, whereas those transmitted horizontally depict antagonism to the host [6, 24].
