For this purpose, rapid, simple and reliable algorithms for pixelwise
image analysis were needed. Bauriegel et al. (2010) used the
class wise cumulation of the pixel distribution of the maximum
quantum yield of electron flow through PSII, i.e. Fv/Fm (starting at
Fv/Fm of 0) at a threshold of 0.3 to efficiently separate healthy
and Fusarium-infected wheat ear tissues. This approach could
indeed be successfully used here on dai 14 to differentiate susceptible
and resistant lettuce cultivars/lines as well as susceptible
batavia lettuce lines and resistant lettuce cultivars/lines and controls.
This was possible despite the fact that there was no symptom
of Bremia visible on any inoculated leaf discs. Obviously, tissue has
been infected by B. lactucae, which pronouncedly inhibitedphotosynthetic efficiency but could not result in sporulation. This
interesting effect certainly needs further investigation.