The Role of a Bacterial Siderophore and of Iron in the Germination and Appressorium Formation by Conidia of Colletotrichum acutatum

1 East Malling Research Station, Maidstone, Kent ME19 6BJ, UK 2 Pure and Applied Biology Department, Imperial College, South Kensington, London, UK ABSTRACT SUMMARY: Pseudomonas sp. isolate UV3, when added to conidial suspensions of Colletotrichum acutatum , stimulated germination and appressorium formation on glass slides and on host surfaces. A siderophore (S A ), purified from low-iron culture of the bacteria, stimulated germination and appressorium formation to a significantly greater extent than the bacterial cells alone. The fully chelated siderophore (S A Fe) and free ferric iron were inhibitory in vitro to germination and appressorium formation but inhibited only the latter in vivo . The S A is compared with nutrients at similar concentrations, and the role of the phytoplane microflora and associated siderophores is discussed in relation to fungal infection.