The effect of fungal metabolites on leaves as detected by chlorophyll fluorescence

The effect is reported here of cytochalasin E isolated from the fungus Rose llinia necatrix on photosynthesis in young leaves of Malus domestica (apple ). Cytochalasin E was administered via the petiole to excised leaves. The chlo rophyll fluorescence emission spectrum and time resolved fluorescence decay were measured up to the point where visible leaf damage was observed. Within 2 h, the ratio of fluorescence emission at 730 nm decreased with res pect to the peak at 690 nm. Over 6 h a small blue shift in the 690 nm emiss ion band to 685 nm was seen. The time resolved fluorescence decay showed ch anges over a similar timescale after administration of cytochalasin E. The control decay could be fitted by two components, tau (1), 112 ps, tau (2), 402 ps, but after 6 h treatment with cytochalasin E the decay required a fu rther component tau (3), 4.25 ns for a good fit. Cytochalasin E has a direct effect on photosynthesis, possibly as a result of impairment of light harvesting. This might partially account for the pat hogenicity of the root infecting R. necatrix. Fluorescence techniques may t herefore provide an early detection system for the fungus, a necessary prer equisite for development of a control strategy.