IN-VIVO CHLOROPHYLL FLUORESCENCE IN RUST-INFECTED BEAN-PLANTS

The influence of bean rust on photosynthesis of its host was examined from presporulation to formation of teliospores. With respect to their effect on teliospore production, rust-infected standard and dark-stre ss bean culture variants were compared. The major fluorescence paramet ers diminished during the fungal development on standard-grown plants, which indicates reduced photosynthetic activity. The variable fluores cence (Fv), a measure of photosystem II activity, decreased during pat hogenesis. In the area of green islands there was no higher host vital ity in comparison to the control. With increasing sporulation the elec tron transport within pustules and to a lesser extent in the area of t he green islands decreased to a level below that of the control. Infec ted leaves of both the normal and the stressed plants showed a strong decline in optimal (Fv/Fm) and effective quantum yield (triangle F/Fm' ) during pathogenesis. There was no remarkable difference between the green islands and the control value in these two parameters. As compar ed to normally cultured plants the stress variant showed a reduction o f all parameters at later stages of the fungal development. The format ion of teliospores did not correlate with any of the fluorescence para meters, however, was expressed earlier when the plants were cultured u nder stress conditions. The results are discussed in the context of pl ant senescence and the onset of teliospore production.