Plant Passive Immunity: Micromorphological and Biochemical Features of the Maloideae (Rosaceae) External Tissues

The defeat of the fruits of fungal diseases is currently an important issue of plant science and is also
of great economic importance. With the help of microscopic methods the leaves and fruits surface
tissues of plants of four genera of the Maloideae subfamily were screened: Malus Mill., Pyrus L.,
Cydonia Mill., Mespilus L. and attempts were made to explain the dependence of mycosis damage on
micro structural features. The species composition of fungi that cause damage to the Maloideae
leaves and fruits in the Russia southern regions is analyzed. It is established that among pathogens
with different types of parasitism there are common excitants, as well as highly specialized responses
as on Mespilus germanica L. Higher resistance to the complex of fungal diseases, in comparison with
apple and pear, was found in quince and medlar. This stability at the initial stage of the pathological
process is associated with structural features such as micro morphology of the fruits and stomata
cuticle in the abaxial epidermis of leaves. The leaves stomatal openings of medlar are narrow with
raised outgrowths, on the surface of the fruits – the layered structure of the cuticular layer. Quince has
a continuous cuticular cover. In the species least affected by mycoses, a high content of very-longchain
fatty acids in the external tissues was revealed, which may be one of the factors of resistance to
pathogens. In addition, the studied species revealed differences in the content of polyphenols, which
can inhibit the development of pathogens at the stage of their penetration. Thus, during the study,
using the example of the Maloideae subfamily, we identified several factors of passive immunity of
plants. Conventionally, they can be divided into two groups: mechanical and chemical, working at
various stages of pathogen penetration into plant organism.