A very important factor influencing the success of inoculation is
the epidermal and surface (Łaz´niewska et al., 2012) as well as the
total leaf structure of the polluted plant (Lebeda et al., 2008). In the
presented experiment, leaf structure and thickness of leaf discs of
the various resistant and susceptible butterhead and batavia lettuce
plants were subjectively different. This can be assumed to
influence the potential ability of the respective plants to prevent
conidial germination and penetration (Lebeda et al., 2008). It
may also affect the colonization of leaf surfaces by secondary
microorganisms. Very early, it has been shown for Nicotiana tabacum
and N. debneyi that the variation in duvatrienediol contents
of the cuticular waxes may inhibit the germination of Peronospora
hyoscyami conidia (Cruickshank et al., 1977). Consequently,
susceptible lettuces cultivars may be characterized by certain
physiological and morphological/histological drawbacks. This
may facilitate the general decay of inoculated leaf discs even if they
were not successfully infected, i.e. there were no visible symptoms
of sporulation, or contaminated with secondary microorganisms.