The Maloideae (Rosaceae) Structural and Functional Features Determining Passive Immunity to Mycosis

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 microstructural 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. 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 micromorphology 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 fruit – the layered structure of the cuticular layer. Quince has a continuous cuticular cover. Compared with Malus and Pyrus, Cydonia and Mespilus also have a large (30 % or more) polyphenol content in the pericarp of outer layer cells. In addition to the general specific differences in the microstructure of the integumentary tissues and the content of polyphenols affecting the resistance to pathogens at the stage of their penetration, general patterns of leaf surface formation, such as hypostomacy, anomocytic stomata, folded microrelief of the cuticular surface, and the presence of single and multicellular trichomes are noted. Epidermal cells from the 4 genera examined contained most of the condensed polyphenols compared to the hypodermal cells.