Introduction to Fungi, Third Edition

GLOMERELLACEAE
389
infection process stalls. Infection is continued on
the ripened fruits after a period of storage.
This infection strategy enables the pathogen to
avoid the high levels of phytoalexins in unripe
fruits (Latunde-Dada, 2001). Resumption of development
is triggered by the strong increase in
ethylene levels associated with fruit ripening
(Flaishman & Kolattukudy, 1994).
Endophytic colonization
Several anthracnose pathogens including
C. musae, C. coccodes and strains of C. gloeosporioides
develop a prolonged latent phase inside their
host plant (Rodriguez & Redman, 1997).
Colonization during the endophytic phase may
begin by infection through stomata rather than
direct penetration of the epidermis, and intercellular
colonization of host tissue. During
senescence of the host plant, the host’s
immune system degenerates and active colonization
may ensue, resulting in the development of
sporulating anthracnose-type lesions. Freeman
and Rodriguez (1993) and Redman et al. (1999a)
have shown that the deletion of a single gene
can convert an aggressive pathogen (C. magna)
to a permanently symptomless endophyte.
This finding emphasizes the possibility that
‘endophytic mutualism is only a gene away
from pathogenicity’ (Latunde-Dada, 2001), and
also indicates one mechanism by which endophytes
may evolve in nature. A further fundamental
point of interest is that colonization by
such symptomless endophytes renders the host
plant resistant against infection by pathogenic
strains of the same species, and also other fungal
pathogens (Redman et al., 1999b).