Age-related Resistance to Plant Pathogens

Plant tissues often show different levels of resistance to pathogens depending on their age. Some of the many types of age-related resistance (ARR) have similarity to known plant defence systems, including preformed defences, race-specific gene-for-gene resistance, systemic acquired resistance and induced systemic resistance. However, the molecular basis for the mature onset of ARR and the nature of the signalling pathways involved are poorly understood. The discovery of a novel form of ARR in the model plant Arabidopsis and the presence in tomato of homologous genes that provide either ARR or seedling resistance to leaf mould are likely to lead to an increased research effort that may address these questions. This review summarises examples of ARR and compares them with more thoroughly characterised forms of disease resistance with a view towards future research.