Endophytic Fungi 32. RELATIONSHIPS AND OCCURRENCE OF ENDOPHYTES
WITHIN THE HOST PLANT TISSUES
Endophytic fungi have been recovered from plants in hot deserts, Arctic
tundra, mangroves, temperate and tropical forests, grasslands and savannas,
and croplands. They are known from mosses and other nonvascular plants,
ferns and other seedless plants, conifers, and flowering plants. Their biological
diversity is enormous, especially in temperate and tropical rainforests. The
fungi are hosted in nearly 300,000 land plant species, with each plant hosting
one or more of these fungi (Arnold, 2008).
A variety of relationships exist between fungal endophytes and their host
plants, ranging from mutualistic or symbiotic to antagonistic or slightly
pathogenic (Arnold, 2007). Results from grass-endophyte systems suggest that
endophytes are herbivore antagonists and enhance plant growth (Clay, 1990).
Correspondingly, mutualistic antagonism towards insects and pathogens has
been claimed also for forest endophytes (Faeth, 2002). Furthermore, a
significant number of fungi exhibit multiple ecological roles, such as the
human pathogen and soil saprotroph Coccidioides posadasii. Similarly, fungi
such as Chaetomium globosum are known as endophytes, saprotrophs, and
pathogens (Arnold and Engelbrecht, 2007). Although it is not yet clear
whether the same genotypes can play each of these roles with equal success,
the ecological lability of these species is remarkable. Understanding the
mechanisms behind that lability represents one among many frontiers in
endophyte biology (Arnold, 2007).
Figure 1. Endophytic fungi hyphae and conidia within a healthy plant tissues
(Photos by Afra Khiralla).