Coir has become popular as a potting medium in greenhouse and nursery production. Qualities of coir that make it a good peat substitute include high water holding capacity, excellent drainage, physical resilience, and the fact that it is a renewable resource (Masago et al., 1977; Meerow, 1994; Prasad, 1997). It has been demonstrated that coir can suppress certain soilborne plant pathogens (Candole and Evans, 2004; van der Gaag and Wever, 2005). Combining the disease-suppressive properties of coir with other management strategies such as fungicide application in an integrated pest management program may result in more effective and less costly management of soilborne diseases in greenhouse and nursery production.
Suppressive substrates reduce soilborne diseases by their physical and/or chemical properties such as drainage, pH, and chemical inhibitors (Hoitink and Fahy, 1986; van der Gaag and Wever, 2005) or by supporting beneficial microorganisms that lower disease incidence or severity by mechanisms such as competition, antibiosis, parasitism, or induction of systemic resistance (Han et al., 1998; Hoitink and Boehm, 1999). In addition to coir, soil substitutes such as peat and hardwood bark also have been shown to suppress certain plant diseases (Hoitink and Fahy, 1986). Unautoclaved rockwool recolonized by indigenous microflora was suppressive to Pythium aphanidermatum (Postma et al., 2000).
Horticultural studies suggest that coir may be a suitable organic component in soilless media and is better than most other alternatives, including rock wool (Islam et al., 2002; Meerow, 1994; Meerow, 1995). Trials using tomato (Solanum lycopersicum) as a test crop indicated that coir gave better crop productivity than rockwool (Islam et al., 2002). Population densities of Phytophthora capsici, P. nicotianae, P. aphanidermatum, and P. ultimum were reduced by 76%, 80%, 32%, and 11%, respectively, when tomatoes were grown in coir compared with peat. In the same study, damping-off incidence was reduced by 88%, 90%, and 41% for P. capsici, P. nicotianae, and P. aphanidermatum, respectively (Candole and Evans, 2004). Research has not been done to determine what causes coir to suppress plant pathogens. The objective of this study was to evaluate, in vitro, the ability of coir to suppress soilborne plant pathogens.
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