Agriculture Reference
In-Depth Information
infection of plant surfaces suggests that disruption of this process could be useful in
disease control. Indeed, some fungicides used for control of rice blast have been shown to
interfere with spore adhesion (Inoue
et al
., 1987). In later work, it was shown that adhe-
sion of spores of phytopathogenic fungi on artifi cial and plant surfaces could be inhibited
using zosteric acid (Stanley
et al
., 2002). Zosteric acid (
p
-(sulphoxy) cinnamic acid) is
a naturally occurring compound found in the eelgrass Zostera marina and which inhibits
the attachment of marine bacteria and barnacle larvae (Todd
et al
., 1993). Stanley
et al
.
(2002) showed that zosteric acid not only inhibited attachment of spores of
M
.
grisea
and
Colletotrichum lindemuthianum
, but also inhibited formation of appressoria, leading to a
failure to infect leaves. In fact, on intact plants, zosteric acid reduced lesion development
on rice leaves caused by inoculation with
M. grisea
and delayed lesion development on
bean leaves following inoculation with
C. lindemuthianum
(Stanley
et al
., 2002). These
workers found that zosteric acid was not toxic to the fungi and that the inhibition of spore
adhesion in
M. grisea
was reversible by washing. Although this could lead to transitory
protection under fi eld conditions, Stanley
et al
. (2002) point out that reduced adhesion
could lower inoculum potential, either because non-attached spores could be more eas-
ily detached from leaf surfaces by wind or rain splash, or as in the case of
M. grisea
, the
spores quickly lose viability. This work hints at the considerable potential for the design
of environmentally benign strategies for plant disease control based on agents which
inhibit adhesion (Stanley
et al
., 2002).
12.5
In order to gain access to the nutrient supplies required for their continued growth and
survival, fungal pathogens must breach the outer surfaces of their host plants. Plant
surfaces provide chemical and physical cues that are important factors in the develop-
ment of infection structures of many plant pathogenic fungi. It is no surprise therefore that
disrupting these processes, by coating the leaf with polymer fi lms or applying agents that
interfere with spore adhesion, can reduce infection and provide disease control.
In many parts of the world, farmers and growers have become accustomed to very high
levels of disease control achieved by using fungicides. Similar levels of disease control
are unlikely to be achieved with many novel disease control methods, like polymer or
particle fi lms, or adhesion inhibitors. However, the problems of fungicide resistance,
breakdown in host resistance and increased public concern for the environment, means
that the development of new disease control methods cannot be ignored. Further, there
are many diseases of agricultural and horticultural crops for which no adequate disease
control measures currently exist. New and innovative control measures might be the
answer, but the adoption of such measures will not be easy, since, in some cases, it
will require changes in crop protection practices. For the approaches described in this
chapter, application before the pathogen arrives on the crop is important, since these
approaches will act essentially as protectants. This in turn will require robust systems
of disease forecasting. Some changes, for example alternating use of a novel method
with fungicides in the spray programme, may be easier to integrate into current practice.
However, since information in many of these areas is lacking, there is a clear need for
research on integrating potential novel methods of disease control into crop protection
programmes.
Conclusions
