School of Engineering and Science - Jacobs University

Introduction
2 Introduction
Like humans and animals, plants are affected by a broad range of pathogenic
microorganisms. Despite expensive pest control measure, infectious plant
diseases significantly interfere with crop production. It is estimated that they
diminish the attainable overall production by approximately 14% while another
6-12% of the actual harvest are lost due to post-harvest diseases (Agrios,
2005). These losses differ between crop varieties and climatic regions, but in
general their percentage is higher in developing countries as compared to the
industrialized world (Oerke et al., 1994). Worldwide, approximately 35 billion
US Dollars are spent on chemicals for plant protection per year (Agrios, 2005).
The high losses (equaling a value of more than 220 billion US Dollar) in spite of
this expenses have various reasons. Increased worldwide trading and traveling
brings about a fast distribution of foreign pathogens to new regions. For
example, the fire blight pathogen E. amylovora was supposed to be indigenous
to North America, but it has been spreading all over Europe by now (Eastgate,
2000). Monocultures grown over large areas favor epidemical spread of
pathogens, while the continued use of pesticides and fungicides to suppress
such outbreaks promotes the occurrence of resistant pathogens (Baker et al.,
1997; McManus et al., 2002). Resistance traits from plant pathogenic bacteria
can be transmitted to human pathogens, so the use of antibiotics in agriculture
is largely restricted (McManus et al., 2002; Teuber, 1999). Many other agrichemicals
have been proven to cause environmental damage, and
consequently have been prohibited. Growing public concern on side effects of
pesticides led to a revision of European commission directive 91/414/CEE
regulating safety requirements and accreditation of plant protection products.
The alteration of this directive in 2002 resulted in the direct withdrawal of 320
substances from the European market while at the same time the legal status
of another 150 products became questionable (European Commission press
release, 2002). As these 470 products equal 60% of all plant protection
products previously available, the need for alternatives becomes most obvious.
2