Plant diseases can be controlled by manipulation of indigenous microbes or by introducing antagonists to reduce the disease-producing pro-pagules (Linderman, 1992). AM fungi and their associated interactions with plants reduce the damage caused by plant pathogens (Harrier and Watson, 2004). These interactions have been documented for many plant species (Tables 1 and 2). With the increasing cost of inorganic fertilizers and the environmental and public health hazards associated with pesticides and pathogens resistant to chemical pesticides, AM fungi may provide a more suitable and environmentally acceptable alternative for sustainable agriculture.
AM fungi are a major component of the rhizosphere of plants and may affect the incidence and severity of root diseases (Linderman, 1992). Comprehensive reviews exploring the possibilities of AM fungi in the bio-control of plant diseases include Schonbeck (1979), Dehne (1982), Bagyaraj (1984), Smith (1988), Caron (1989), Paulitz and Linderman (1991), Linderman (1992, 1994), Siddiqui and Mahmood (1995a), Azcon-Aguilar and Barea (1996), Smith and Read (1997), Mukerji (1999), Siddiqui et al. (1999), Barea et al. (2005). The primary results which can be drawn from the various observations are (1) AM associations reduce the damage caused by plant pathogens, especially those caused by fungi and nematodes; (2) AM symbiosis enhances resistance or tolerance in roots but is not equal in different crops; (3) protection is not effective against all pathogens, and (4) disease protection is modulated by soil and other environmental conditions. Therefore, the interactions between different AM fungi and plant pathogens vary with the host plant and the cultural system. Moreover, the protective effect of AM inoculation may be both systemic and localized. Actions of AM fungi against phyto-pathogens have been categorized into the following three sub-categories:
2.1 Interaction of AM fungi with plant parasitic nematodes
2.2 Interaction of AM fungi with fungal plant pathogens
2.3 Interaction of AM fungi with other plant pathogens.
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