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Proper composting is an efficient process for reducing most plant and human
pathogen populations which can be transmitted by compost to farms; its success
depends on different composting parameters as well as complex microbial interac-
tions. First, temperature–time combinations are the most important factors for elim-
inating plant pathogens. Temperatures of 60–65 °C during the thermophilic phase
for several days should eliminate most plant pathogens and 55 °C for 21 days elimi-
nated most of the tested fungal pathogens (Noble and Roberts 2004 ). Moisture con-
tent is another important factor which can influence the elimination level of
pathogens. The occurrence of dry pockets in the composting material is probably
the main cause of pathogen survival. The percentage of moisture content should not
be lower than 40 % (Bollen et al. 1989 ).
Creation of unfavorable conditions for disease development by using good soil
drainage, optimizing plant spacing to reduce relative humidity around plants, and
proper fertilization of the crop are important practices for managing plant diseases.
5.2 Biological Control
Biological control of fungal pathogens is an alternative to using chemical pesti-
cides. It involves using an organism or organisms to lower the inoculum density of
the pathogen and thus reduce crop losses (Bernard et al. 2014 ). Disease suppression
by biocontrol agents results from interactions between the plant, pathogens, and the
microbial community.
Examples of biocontrol organisms that have been widely studied include
Mycorrhizal fungi, Trichoderma spp., Gliocladium spp. and Actinomycetes.
Mycorrhizal fungi increase the capacity of plant roots to absorb nutrients which
increases the ability of plants to withstand the attack of pathogens. Trichoderma spp.
are among the most studied fungi and are commercially marketed as bio- pesticides,
bio-fertilizers and soil amendments (Guzmán-Valle et al. 2014 ; Al-Sadi et al. 2015d).
They can reduce significant diseases caused by Phytophthora spp., Fusarium spp.,
Pythium spp. and others (Punja and Yip 2003 ; Blaya et al. 2013 ). Trichoderma spp.
have a high reproductive capability and vigorous aggregativeness against pathogenic
fungi (Grondona et al. 1997 ). Treating soil with T. harzianum improved the resis-
tance of bean leaves to diseases caused by Botrytis cinerea (Elad et al. 1993 ).
The mechanisms by which antagonistic microorganisms affect fungal pathogens
differ; some attack and kill the mycelium of fungal pathogens while others produce
toxins or metabolites that can affect the growth and reproduction of fungal patho-
gens. Some antagonistic fungi compete for food and space with fungal pathogens
while others induce systemic resistance to the invading pathogens (Agrios 2005 ).
Recent studies have provided evidence that organic materials play an important
role in the suppression of soil-borne diseases (Al-Sadi et al. 2015c). Mechanisms of
disease suppression in composted materials vary according to the biological and
physicochemical characteristics of composts, methods and time of application, as
well as pathogen species, densities and their aggressiveness (Hoitink and Boehm
A.M. Al-Sadi