Ecological and biochemical aspects in algal infectious diseases

Infectious diseases in algae are caused by a wide variety of organisms, fro m virus to other algae. In recent years, important advances in understandin g some of these diseases from ecological, cellular and biochemical view poi nts have been done. In an ecological context, epidemiological studies are v ery limited and restricted to red algal hosts. Those studies show that infe ctions appear to affect large segments of host populations, and the express ion of some diseases is clearly aggregated, with consistent patterns of sea sonal fluctuation. This, together with host specificity trials and transpla nt experiments, strongly suggests a genetic base as determinant of host sus ceptibility and disease expression. In a biochemical context, the highly specific association established betwe en the sporophytic phase of the red algal host Chondrus crispus and its gre en algal endophytic pathogen Acrochaete operculata provides an excellent mo del to investigate the biochemical basis of recognition and signal transduc tion which determines host susceptibility, specificity and pathogenicity. O ur results emphasize the role of oligosaccharide signals in modulating resi stance against pathogens in marine algae. These results are discussed in th e light of recent reports of an oligoalginate-induced oxidative burst in th e brown algal kelp Laminaria digitata and of oligoagarose-induced responses in the association between Gracilaria conferta and a pathogenic marine bac terium.