Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
crops produced in container media (Aryantha et al., 2000) and field soils (Downer et al., 2001).
Addition of compost serves two possible purposes significant for the biological control of
Phytophthora cinnamomi: it provides a substrate for the growth of fungal antagonists, and creates
an environment that promotes enzyme activity (Downer et al., 2001). Several potential biocontrol
agents of Phytophthora root and crown rots have been identified from compost amended growing
media, including Pseudomonas spp. (Aryantha et al., 2000); Pantoea spp (formerly Enterobacter
spp) (Krause et al., 2003); Penicillium and Aspergillus spp. (Downer et al., 2001); actinomycetes
(Aryantha et al., 2000) and Trichoderma spp. (Downer et al., 2001).
Pythium is also a destructive, soil-borne parasitic root fungus, which causes damping-off
disease in seedlings and root and crown rot of plants. The suppression of diseases caused by
Pythium spp. has been well documented (Stone et al., 2003). The severity of diseases caused by
the fungus Pythium was reduced by 30-70% when growing media were amended with various
compost products. Adequately mature composts have large microbial populations and high
microbial activity, which have been directly linked to the suppression of Pythium (Ringer et al.,
1997) but this may not hold true for all composts (Craft and Nelson, 1996).
Similarly, Rhizoctonia is a soil-borne pathogenic fungus which causes a range of soil-borne
diseases as well as diseases of aerial parts of plants. Composts have been used with varying
success to suppress Rhizoctonia diseases of several crops (Tuitert et al., 1998).Amendment of
soil or container media with composts reduced diseases caused by the soil-borne pathogenic
fungus Rhizoctonia by up to 70%. Higher levels of microbial biomass and microbial activity have
been reported to suppress Rhizoctonia by increasing competition between compost-inhabiting
microorganisms and Rhizoctonia solani (R. solani) for cellulose or other available nutrients (Diab
et al., 2003). The increase in microbial count (MBC) and microbial number (MBN) indicated growth
of saprophytic microorganisms. The high population density of fluorescent pesudomonads,
actinomycetes and heterotrophic fungi in growing media amended with adequately matured
compost has been found to better suppress Rhizoctonia spp. than the use of less matured
(immature) composts (Diab et al., 2003).
Composts are considered able to induce systemic resistance, which can reduce the
severity of some plant foliage diseases (Stone et al., 2003). However, Krause et al. (2003) reports
that only a small proportion of composts have the ability to suppress foliar diseases. Some
pathogenic Pseudomonas species cause several plant foliar diseases including bacterial speck
and bacterial canker. Compost application has resulted in reduced bacterial speck of Arabidopsis
(mustard family) and tomatoes. In tomatoes, different types of paper mill residue based composts
resulted in the reduction of bacterial speck between 47 to 62% (Vallad et al., 2003).
Similarly pathogenic Xanthomonas spp. causes many plant diseases, including such foliar
diseases as bacterial leaf spot or speck, bacterial blight or angular leaf spot, and stem rot. Two
studies report a reduction in bacterial leaf and fruit spot of vegetables (radish and tomato) caused
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