Novel fungitoxicity assays for inhibition of germination-associated adhesion of Botrytis cinerea and Puccinia recondita spores.

Botrytis cinerea and Puccinia recondita spores adhere strongly to polystyrene microtiter plates coincident with germination. We developed assays for inhibition of spore adhesion in 96-well microtiter plates by using sulforhodamine B staining to quantify the adherent spores. In both organisms, fungicides that inhibited germination strongly inhibited spore adhesion, with 50% effective concentrations (EC(50)s) comparable to those for inhibition of germination. In contrast, fungicides that acted after germination in B. cinerea inhibited spore adhesion to microtiter plates only at concentrations much higher than their EC(50)s for inhibition of mycelial growth. Similarly, in P. recondita the ergosterol biosynthesis inhibitors myclobutanil and fenbuconazole acted after germination and did not inhibit spore adhesion. The assays provide a rapid, high-throughput alternative to traditional spore germination assays and may be applicable to other fungi.