Agriculture Reference
In-Depth Information
Kofoet, 2005). Studies of the effects of
PDFs
on multiple focus epidemics suggest
that disease patterns and epidemic size are strongly influenced by dispersal patterns.
Long range dispersal (shallow
PDFs
) favours more widespread epidemics and
increases the likelihood of disease persistence (Filipe and Maul, 2004). Stochastic
models have been used to study effects of sample quadrat size on measurement of
spatial variability of disease (Xu and Ridout, 2000), effects of sporulation rate,
dispersal distance (Xu and Ridout, 1998) and wind (Xu and Ridout (2001) on
epidemic development. Simulation models are beginning to be used to investigate
real epidemics, such as citrus tristeza virus (Gibson and Austin, 1996), citrus
variegated chlorosis (Martins
et al.,
2000), anthracnose in lupins (Diggle
et al.
,
2002) and downy mildew of radish (Fink and Kofoet, 2005).
Although sophisticated disease simulation models may give insight into factors
affecting epidemic development, they may be too complex for routine disease risk
forecasting. For example, West
et al.
(2003) suggest using a simple exponential
disease decline model to estimate areas of latent infection to guide application of
sprays to disease patches. Shaw (2003) concluded that mathematical representations
of epidemics should be simple and robust as they are often based on limited
information available about the complex, heterogeneous environment of the
agricultural ecosystem.
6.5 CONCLUSIONS
We hope that in this chapter we have shown that inoculum dispersal is of
fundamental importance in the spread of plant disease and that understanding the
processes involved greatly enhances our knowledge of disease epidemic
development. To fully understand the spread of disease epidemics, detailed
knowledge of the patterns of spore dispersal by wind and rain-splash is needed.
This knowledge can be obtained by a judicious combination of experimental
measurements in field and controlled conditions with modelling to improve the
theoretical understanding of the fundamental mechanisms which govern dispersal
processes. The combination of recent advances in molecular diagnostics and fluid
dynamics offer new opportunities for the in-depth study of pathogen dispersal over
complex landscapes and should lead to a better understanding of the role dispersal
plays in agricultural and natural ecosystems. However, we need now to begin to
translate improvements in the understanding of the dispersal phase of epidemics into
recommendations for improving strategies for plant disease control in real
agricultural systems. This could involve changes in agronomic practices resulting
from a better understanding of the effects of crop management on disease spread, or
the development of more accurate disease forecasting schemes as aids to disease
management decision making.
ACKNOWLEDGEMENTS
Rothamsted Research receives grant aided support from the Biotechnology and
Biological Sciences Research Council.
