School of Engineering and Science - Jacobs University
School of Engineering and Science - Jacobs University
School of Engineering and Science - Jacobs University
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Introduction<br />
2.1 Biological control <strong>of</strong> plant disease<br />
A promising alternative approach to minimize infectious plant disease is the<br />
application <strong>of</strong> antagonizing organisms with the ability to suppress pathogen<br />
development. This concept is referred to as “biological control” <strong>and</strong> the<br />
operative organism is called biocontrol agent (Wilson, 1997a).<br />
2.1.1 Advantages <strong>and</strong> limitations<br />
The targeted use <strong>of</strong> microbial antagonists <strong>of</strong>fers several benefits. Mass<br />
production <strong>of</strong> the active substance (i.e. fermentation <strong>of</strong> the control organism) is<br />
low-priced compared to chemical synthesis <strong>of</strong> pesticides (Shoda, 2000). Since<br />
biocontrol products can by applied by conventional techniques like spraying or<br />
drenching, their ability to proliferate <strong>and</strong> establish stable populations reduces<br />
application cost to a minimum (Montesinos, 2003). The impact <strong>of</strong> a biocontrol<br />
agent on the on indigenous microbial communities or other organisms in the<br />
ecosystem is less severe as compared to broad-spectrum pesticides (Emmert<br />
& H<strong>and</strong>elsman, 1999). Another significant advantage <strong>of</strong> biological control<br />
results from the flexibility <strong>of</strong> the control agent as living organism. The control<br />
organism can interact with a pathogen in many different ways <strong>and</strong> it is able to<br />
co-evolve with target <strong>and</strong> environment. This minimizes the risk <strong>of</strong> resistance<br />
formation <strong>and</strong> contributes to the potency <strong>of</strong> disease control (Emmert &<br />
H<strong>and</strong>elsman, 1999; H<strong>and</strong>elsman & Stabb, 1996). Biological control systems<br />
can be classified into three major groups: Rhizospherical biocontrol, biological<br />
control in the phyllosphere, <strong>and</strong> post harvest disease control. Post-harvest<br />
disease control <strong>of</strong>fers the unique possibility to keep environmental conditions<br />
constant <strong>and</strong> adjust them in favor <strong>of</strong> the control organism (Janisiewicz &<br />
Korsten, 2002). Disease control in the rhizosphere underlies more variable<br />
conditions, yet root exudates provided by the plant stabilize nutrient supply <strong>and</strong><br />
increase microbial density by orders <strong>of</strong> magnitude. Biocontrol agents have to<br />
cope with high microbial competition, but they can be assisted through direct<br />
support by the host plant (Weller et al., 2002).<br />
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