Plant resistance to fungi

There are at least six common forms of resistance exhibited by higher plants towards parasitic fungi and oomycetes: parasite-specific resistance, cultivar resistance, nonhost resistance, organ specific resistance, age-related resistance, and induced resistance. Available evidence suggests that all of these exploit components of the constitutive and inducible defensive factors that every plant possesses. Recent studies have revealed the extraordinary complexity and number of potentially defensive responses trigered in plants by pathogens and other environmental stresses, as well as the large number of fungal and oomycete products that can trigger such responses. In addition, new, and sometimes unexpected, information on which defensive factors are actually involved in specific cases of resistance have-come from the use of transgenic plants. The recent cloning of parasite-specific resistance genes seems to confirm their role in triggering defense responses via a signal transduction cascade. Nevertheless, the most prevalent models to explain disease resistance do not always fit data obtained from specific fungus-plant interactions involving intact plants, suggesting that such models may be too simplistic, or not applicable in certain plant-fungus interactions.