plant surface microbiology.pdf

with saprobic fungi. Host exclusivity is the exclusive occurrence of a strictly
saprobic fungus on a particular host, while host recurrence is the frequent or
predominant occurrence of a fungus on a particular host.
The basis for host recurrence in saprobic fungi is interesting and several
factors may be responsible.Wong and Hyde (2001) thought that host exclusive
saprobes may be responding to differences in physical structure or nutrient
levels of the potential hosts. There is also the possibility that enzyme production
capabilities may influence whether a certain fungus can decay a certain
host. However, recent studies have shown that most fungi can produce a wide
range of enzymes capable of degrading simple sugars and cellulose (Lumyong
et al. 2002). Fewer fungi can produce enzymes capable of digesting lignins
(Leung and Pointing 2002). This would however, restrict fungi to lignified versus
nonlignified plant tissues and is unlikely to be responsible for host recurrence
(restricting fungi to certain plant species) as a large range of host tissues
incorporate lignins into their tissues.
Wong and Hyde (2001) studied the saprobes on six grass and one sedge
species in Hong Kong and found that certain fungi showed host exclusivity or
specificity. They hypothesized that these fungi may be host-specific endophytes
that later become saprobes. There is much circumstantial evidence
supporting this hypothesis and this has been discussed by Zhou and Hyde
(2001) and Hyde (2001).
8 Conclusions
17 Fungal Endophytes 287
There have now been many studies on the diversity and ecology of endophytes
of grass and nongrass hosts in both tropical and temperate regions
(Viret and Petrini 1994; Bussaban et al. 2001; Photita et al. 2001). The problem
in most of these studies is that two uninformative groups of fungi are generally
isolated; the first major group being typical endophytic genera such as
Colletotrichum, Phomopsis and Phyllosticta while the second are mycelia sterilia.
The first group are rarely recorded as saprobes on the host, although
some may be pathogens. Therefore, the role of these fungi is puzzling and they
may actually have no function. It is possible that the spores have landed on the
plant surface and produced a germ tube which has penetrated the plant
stoma, but then cannot progress further due to plant defense. Future studies
should, therefore concentrate on the role of these common endophytes, rather
than provide uninformative lists with ecological data that have little consequence.
The mycelia sterilia may be a more important group, but until we can find
some way to identify more of them, it is impossible to elucidate their function.
Methods need to be developed to stimulate these fungi to sporulate, or at least
molecular techniques need to be refined in order to make identification simpler.
Future studies should, therefore concentrate on developing these meth-