Introduction

There is a basic incompatibility between higher plants and fungi at the species level, an incompatibility which is the norm in interactions between these two types of organism. Plants in general are resistant to most fungal species, even those that are pathogenic on other plants. This type of incompatibility is synonymous with non-host resistance. It is also sometimes termed ‘heterologous incompatibility’ to distinguish it from the specific incompatibility observed in homologous interactions between plants and pathogenic fungal species (Gabriel & Rolfe, 1990). In this chapter I summarise what we know about the recognition and response events which appear to be involved in this basic rejection of fungi by higher plants. The study of ‘higher’ levels of specificity (e.g. the specific incompatibility between races of some biotrophic pathogens and certain cultivars of their hosts) has perhaps attracted more attention, but it can be argued that a better understanding of basic incompatibility would enable more rapid progress to be made in understanding the mechanisms underlying successful infections (basic compatibility) and from thence the higher levels of specific resistance involved in homologous incompatibility.

Defence mechanisms controlling incompatibility

What types of mechanism operate at the level of basic incompatibility to inhibit fungal growth? Although we now seem to know much about the nature of the individual mechanisms that can operate during these interactions, there is certainly much that we do not understand. Plants have a battery of potential defence mechanisms against non-pathogens that differ from species to species, although themes are evident.