Fluorescence Imaging Of The Infection Pattern Of Apple And Pear Seedlings With Erwinia Amylovora

Abstract

Analysis of changes in chlorophyll fluorescence patterns due to infection of apple and pear leaves with Erwinia amylovora was performed by the chl-FIS and the PEA. The chl-FIS measured three different parameters: maximal (M) and steady state (S) fluorescence and the maximum quantum efficiency of PSII (φPSII). M showed a transient increase in M9 apple leaves upon inoculation with both the WT and the GFP E. amylovora. No change in S and φPSII was detected in the GFP E. amylovora inoculated tissues, whereas inoculation with WT E. amylovora resulted in a transient increase in S and an increase in φPSII. The parameters obtained by the PEA (area, Vj, Vi, φP0, Sm and N) showed a similar result. Inoculation of M9 apple leaves with GFP E. amylovora resulted in a change of three parameters. Inoculation with the WT bacteria resulted in changes of all six parameters. This difference in reaction of apple leaves might be explained by the difference in virulence of the two bacterial strains. The WT bacteria are more virulent than the GFP bacteria. The GFP-FIS enabled us to follow the migration of the GFP marked bacteria inside the leaf. In M9 apple leaves the bacteria were seen to migrate along the midrib inside the leaf and much slower from the cut into the mesophyll and side veins, even when no symptoms were visible.