For investigators engaged in the study of toxins generally, and
host-specific toxins in particular, it is a rare treat to attend a
meeting in which toxins involved in plant pathogenesis are emphasized. A
gathering of this type provides opportunity to consider the discovery of
new toxins, their chemical structures, genes encoding enzymes that
control their biosyntheses, their sites of action and physiological
effects on plants, and their roles (if any) in pathological processes.
Having acknowledged the inspiration fostered by a 'toxin meeting',
however, it is important to point out that the program of this symposium
was generously sprinkled with 'nontoxin' talks. These contributions
generated cross-disciplinary discussion and promoted new ways of
thinking about relationships among factors required for plant disease
development. The point can be illustrated by considering just one
example. We have in the past often regarded diseases mediated by
host-specific toxins and diseases involving 'gene-for-gene'
relationships as representing two different classes of fungal/plant
interaction. This is largely because the key molecular recognition event
in so-called 'toxin' diseases leads to compatibility, whereas the
corresponding event in 'gene-for-gene' diseases leads to
incompatibility. Yet the race specific elicitors produced by the
'gene-for-gene' fungi Cladosporium fulvum (De Wit, Adv. Bot. Res.
21:147- 185, 1995) and Rhynchosporium secalis (Rohe et a1., EMBO J.