Agriculture Reference
In-Depth Information
CHAPTER 16
ENVIRONMENTAL BIOPHYSICS APPLIED TO THE
DISPERSAL OF FUNGAL SPORES BY RAIN-SPLASH
L. HUBER, L. MADDEN AND B.D.L. FITT
16.1 INTRODUCTION
In the past two decades, there has been considerable work on spore dispersal by
rain-splash and review articles have been published (Fitt and McCartney, 1986; Fitt
et al.
, 1989; Madden, 1992) which discuss spore dispersal from a biological point of
view. Topics covered included the characteristics of splash-dispersed fungi,
mechanisms of splash dispersal and methods for studying them, the dispersal of
specific pathogen spores by different types of rain under controlled conditions or in
field situations and recent spatial distribution and modelling studies.
By contrast, this chapter aims to provide a physical/meteorological perspective
on inoculum dispersal by rain-splash and to summarise articles published since
the review of Madden (1992). It considers information from plant pathology,
epidemiology, agricultural meteorology and soil science that is relevant to
understanding splash dispersal and suggests further investigation and application of
splash dispersal from the physical/meteorological point of view. It reviews 1. the
splash process as a biophysical process; 2. the dispersal of splash droplets or
inoculum in relation to physical characteristics of incident drops; 3. the influence of
target characteristics on splash efficiency and dispersal; 4. the relevant properties of
rainfall above, inside and below the crop canopy in relation to splash dispersal; 5.
meteorological instrumentation in relation to rainfall and methodology to quantify
splash potential of rain. Dispersal by rain is also discussed in Chapter 6.
16.2 REMOVAL OF SPORES BY SPLASH OF SINGLE INCIDENT DROPS
Beside studies describing spatial patterns of splash-dispersed fungal spores (Fitt
et al.
, 1989; Jenkinson and Parry, 1994; Hörberg, 2002), attempts have been made to
quantify the number of spores (or rarely bacteria, Butterworth and McCartney,
1991) removed in splash droplets, by establishing relationships between incident
drop properties and subsequent numbers of spores removed for given target
characteristics (e.g. leaf structure and lesion pattern). Although seed dispersal by
rain-splash has been known for more than 100 years, it has received little attention
(Nakanishi, 2002). Occasionally, efforts based on classical or newly-developed
techniques (Saint-Jean
et al
., 2005) have been made to understand the mechanisms
of incorporation of spores into the population of splash droplets in relation to their
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