Interactions between different barley genotypes
and the fungal pathogen Blumeria graminis f.sp. hordei
(Bgh) have a specific impact on the crop physiology.
Within the context of plant resistance phenotyping, it is
relevant to investigate early host–pathogen interactions to
avoid the crop infestation. Analyzing different parameters
of the photosynthesis apparatus gives in-depth information
of the plant’s health status and can be used for a spatial and
temporal assessment of interaction types during plant–
pathogen infestation. In the present study, experiments
were performed with a near-isogenic line of barley cv.
Ingrid WT (susceptible), mlo3 (papilla-based resistance) as
well as a near-isogenic line of cv. Pallas, containing the
Mla1 (hypersensitive response-based resistance) gene.
After inoculation with Bgh isolate K1, the leaves were
measured daily using chlorophyll fluorescence imaging.
Inoculated, susceptible wild-type leaves showed a reduced
effective quantum yield of the photosystem II (UPSII)
already 1 day after inoculation. In accordance with the
quantum yield reduction, the non-photochemical quench-
ing (NPQ) increased, indicating thermal dissipation of
excess energy. The changes of UPSII and NPQ represent
modifications of the leaf metabolism to aid the fungal
nutrition uptake, which is influenced by Bgh. By analyzing
these parameters, it was also possible to indicate resistance
reactions of mlo3 and Mla1 barley genotypes against Bgh.
During papilla formation in mlo3 leaves, UPSII revealed
the lowest values. In contrast, inoculated Mla1 leaves
showed the lowest NPQ. The present study proofs that
chlorophyll fluorescence imaging is a valuable tool for
investigating early plant–pathogen interaction noninva-
sively. Furthermore, this phytopathology study uses
chlorophyll fluorescence imaging, chlorophyll extraction
and microscopic observations to characterize the interac-
tion response of different genotypes to an Bgh infection.