The term endophyte was coined by De Barry and is applied to all microorganisms present within the plant tissues, which are either bacteria or fungi. They live within plants for most of their life cycles without causing any visible disease (Petrini, 1991; Bacon and White, 2016). Endophytism is thus, a unique cost-benefit plant-microbe whose association is defined by a habitat that is impermanent, symptomless and observed totally within the host plant tissues (Kusari and Spiteller, 2012). All reviews have shown that vascular plants are host for endophytic organisms (Selim et al., 2012). The plant may provide fundamental compounds for the completion of the lifecycle of the endophytes (Strobel, 2002). Ascomycetes, Basidiomycetes and Deutromycetes fungi are stated as endophytic fungi (Ruby and Raghunath, 2011). Endophytic fungi are non-host specific and they have a wide spectrum of host range. Endophytes are the potential source of raw organic metabolites (Bhardwaj and Agrawal, 2014). Some major therapeutics from endophytic metabolites could be used in pharmaceutical, agriculture, and industry.
Many endophytes have the potencial to synthesize a diverse range of bioactive substances that may externally or internally be used as therapeutic agents against diseases (Kusari et al., 2012; Jalgaonwala and Mahajan, 2011). Understanding the ecology of microbes and plant biology becomes important (Nair and Padmavathy, 2014). Environmental conditions like soil, temperature, and humidity etc. might also be expected to affect the nature and the population of endophytes (Santamaria and Bayman, 2005). Plants growing in the tropical rainforest where the competition for light and nutrient is intense, are most likely to host the highest number of bioactive endophytes (Griffiths and Siddiqi, 1961). Endophytes from tropical regions produce considerably more bioactive compounds than those temperate parts of the world (Bills et al., 2002). Advancement of endophyte resources could give us a mixture of benefits, such as new and potential metabolites that cannot be synthesized by synthetic reactions (Cragg and Newman, 2013). Endophytes and pathogens together, they have virulence factors that are counteracted by plant defense mechanisms. If the plant defense mechanisms neutralize the fungal virulence, the fungus will be destroyed. The plant-pathogen interaction would lead to plant infection.