et al. 2012 ). Recent studies have shown that endophytes are not host-specific
(Cohen 2006 ). A single species of endophytes can invade a wide range of hosts
while several studies have suggested that same fungus isolated from different parts
of the same host shows diverse abilities to utilize different substances (Carroll and
Petrini 1983 ), thus host endophyte relationship may vary from host to host and
endophyte in general.
9.3 The Plant-Endophyte Interaction
The relationship between the endophyte and its host may range from mutualistic
symbiosis to phytopathogenesis. Sometimes the endophyte remains latent, with
symptomless nature, inside the host plant until the environmental conditions are
favorable for the fungus or the ontogenetic state of the host changes to the
advantage of the fungus (Rodriguez and Redman 2008 ; Sieber 2007 ). Therefore,
with time, endophytic fungi can also be aggressive saprophytes or opportunistic
pathogens as well (Strobel and Daisy 2003 ; Tan and Zou 2001 ; Rodriguez and
Redman 2008 ).
The mutualistic relationship between the fungal endophytes and the host plants
are somewhat complex, but results infitness benefits for both partners. The plants
provide endophytes with nutrients, protection from desiccation, spatial structure,
and transmission via seed dissemination to the next generation of host (Guo et al.
2008 ). The plant may also provide important chemical compounds that are essential
for the endophytes’growth and self-defense (Metz et al. 2000 ; Strobel 2002 ). On
the other hand, endophytes contribute significant benefits to their host plants by
producing a plethora of bioactive substances required to adapt to abiotic and biotic
stress factors (Guo et al. 2008 ). Resistance to abiotic stress is enhanced by
increasing tolerance to drought or water stress, high temperature, low pH, high
salinity and presence of heavy metals (Jalgaonwala et al. 2011 ). In a study done in
Lassen Volcanic and Yellowstone national park, it has been shown that an endo-
phyticCurvulariaspecies isolated from a grass species collected from geothermal
soils gives thermotolerance to the host, probably as a result of production of cell
wall melanin that may disperse heat along fungal hyphae (Gunatilaka 2006 ).
A study conducted with an endophyticPenicillium minioluteumspecies and soy-
bean has shown that endophytic association has significantly ameliorated the
negative effects of salinity stress damage and increased the growth and metabolism
of the soybean (Khan et al. 2011 ).
Plants encounter biotic stress due to bacterial and fungal pathogens, and attack of
insects, nematodes, and mammalian herbivore (Rodriguez et al. 2009 ). The
bioactive secondary metabolites produced by the endophytes living in these plants
are known to induce resistance to biotic stress factors (Gunatilaka 2006 ). Previous
researches have reported that in many cases tolerance to biotic stress has been
correlated with fungal natural products (Tan and Zou 2001 ; Zhang et al. 2006 ; Aly
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