In contrast, in susceptible batavia cultivars downy mildew
developed better in intercostal tissues free of anthocyanins
(Fig. 6). As with visual rating, local variation in Fv/Fm indicated that
only the anthocyanin containing intercostal area retained their
photosynthetic competence. Green tissue lost vitality because of
the highly pronounced Bremia infection (Fig. 6, marked area). In
contrast to susceptible batavia, leaf discs of resistant butterhead
lettuce were physiologicaly active even 14 d after inoculation (c.f.
Fig. 4).