Sainsbury Laboratory, John Innes Centre, Norwich NR4 7UH, UK

Fungi are the most diverse and also the most damaging group of plant pathogens. Within the last few years the application of molecular genetic methods to phytopathogenic fungi has enabled the identification of a variety of genes involved in determining the outcome of encounters between fungi and potential host plants. This overview will be concerned with recent advances in this area. Determinants which have been identified as important include factors involved in the early stages of infection and colonization (hydrophobins, melanin, glycerol accumulation, components of signal transduction pathways, antibiotic-detoxifying enzymes), and fungal products which kill plant cells or which modify plant cell processes (toxins, eficitins, avirulence determinants). More recently the development of the insertional mutagenesis procedure known as restriction enzyme-mediated integration (REMI) has provided a powerful approach for the identification of new pathogenicity factors without any prior knowledge of function.

In parallel with these developments, the completion of the full genomic sequence of yeast and the development of sophisticated techniques for large-scale extensive studies of differential gene expression have stimulated activity in the area of EST sequencing for fungal pathogens. The latter approach is of particular value for those fungi which cannot be grown in culture, and/or which are not amenable to transformation. The application of these different but complementary approaches to fungal pathogens offers great potential for furthering our understanding of the process of fungal pathogenesis, as is already apparent from studies from a number of laboratories working with the rice blast fungus, Magnaporthe grisea.