Accumulation of phytoalexins in the compatible interaction between Cladosporium fulvum and tomato in relation to colonization

Abstract

The production and distribution of the phytoalexin falcarindiol in tomato foliage infected with leaf mold was examined to determine how the fungus Cladosporium fulvum is able to colonize and sporulate in an apparently antifungal environment. In a compatible interaction (cv. Potentate – C. fulvum race 2.3), by 12 and 15 days after inoculation, solvent-extractable falcarindiol and two other phytoalexins from tomato, compound 2 (probably falcarinol) and compound 3 (unidentified), reached concentrations considerably in excess of ED50 values for inhibition of the fungus. In contrast, intercellular (apoplastic) fluids obtained from similarly infected leaflets contained only traces of falcarindiol. ED50 values for germination and germ-tube growth of C. fulvum increased as the incubation time was extended, suggesting that adaptation or recovery was possible at the concentrations tested. In in vitro experiments, C. fulvum appeared to readily metabolize falcarindiol, as did a Lycopersicon cell suspension culture. Binding of falcarindiol to living and dead fungal and plant cells was also observed. Falcarindiol, injected into tomato leaflets, decreased rapidly and was only recovered in trace amounts by 24 h. The results suggest that falcarindiol and probably the two other phytoalexins do not reach sufficient concentrations in the apoplast of an infected susceptible leaf to have an effect on growth and sporulation of C. fulvum. Key words: leaf mold, Fulvia fulva, falcarindiol, falcarinol.