1 Original Research Article 2 3 THE MALOIDEAE (ROSACEAE) STRUCTURAL AND FUNCTIONAL FEATURES 4 DETERMINING PASSIVE IMMUNITY TO MYCOSIS 5 6 7 With the help of microscopic methods the leaves and fruits surface tissues of plants of four 8 genera of the Maloideae subfamily were screened: Malus Mill., Pyrus L., Cydonia Mill., 9 Mespilus L., as model objects, and attempts were made to explain the dependence of mycosis 10 damage on microstructural features. The species composition of fungi that cause damage to the 11 Maloideae leaves and fruits in the Russia southern regions is analyzed. It is established that 12 among pathogens with different types of parasitism there are common excitants, as well as 13 highly specialized, more represented on Mespilus germanica. Higher resistance to the complex 14 of fungal diseases, in comparison with apple and pear, was found in quince and medlar. This 15 stability at the initial stage of the pathological process is associated with structural features such 16 as micromorphology of the fruits and stomata cuticle in the abaxial leaves epidermis. The leaves 17 stomatal cracks of the medlar are narrow with raised outgrowths, on the surface of the fruit – the 18 layered structure of the cuticular layer. Quince has a powerful continuous cuticular cover. 19 Compared with Malus and Pyrus, Cydonia and Mespilus also have a large (30 % or more) 20 polyphenol content in the pericarp outer layer cells. In addition to the gender-specific differences 21 in the microstructure of the integumentary tissues and the content of polyphenols affecting the 22 resistance to pathogens at the stage of their penetration, general patterns of leaf surface 23 formation, such as hypostomacy, anomocytic stomata, folded microrelief of the cuticular surface, 24 and the presence of single and multicellular trichomes are noted. Epidermal cells from the 4 25 genera examined contained most of the condensed polyphenols compared to the hypodermal 26 cells. 27 Key words: Maloideae; pathogenic fungi; resistance; ultrastructure; polyphenols. 28 29 Introduction 30 Maloideae, or Pomoideae is one of the subfamilies of Rosaceae, which includes the most ancient 31 cultivated representatives of angiosperms, which are widespread in many ecological and 32 geographical zones. It includes such famous fruit plants as pear (Pyrus L.), apple (Malus Mill.), 33 quince (Cydonia Mill.), medlar (Mespilus L.) and others. Their main feature is the fruit, 34 overgrown with a modified hypanthium – prefabricated leaflets or drupaceous modified carpels, 35 called in a broad sense apples (Tsitsin 1962; Kamelin 2006). The large (juicy) part of the fruit is 36 formed due to the succulentization of the tissues of the hippocampus. A typical fruit is typical for 37 apple, pear and quince, and the drupaceous apple is for the medlar germanica (Mespilus 38 germanica). 39 According to practical importance in world production, including in Russia, the apple tree 40 takes the leading place among fruit crops, the second is the pear tree. The enormous consumer 41 value of the fruits of these crops is widely known, which are extensively used in the food, 42 medical, perfume and other industries. Along with vitamin-bearing qualities, the special value of 43 apple and pear fruits is due to good antioxidant properties. Despite the huge number of varieties 44 currently available, there is a need to improve the assortment, since during the long selection 45 process many of the valuable traits that their wild relatives have got were lost. 46 Among the promising cultivated plants is quince common (Cydonia oblonga Mill.). It is 47 quite flexible to the conditions of growth, especially soil, can grow successfully on different 48 types of soils (alluvial, chernozemic, etc.). Also, quince has a high resistance to various stressors, 49 it is light-demanding, heat-resistant, salt-tolerant, fast-growing, durable and fruitful crops. 50 C. oblonga fruits are distinguished by high technological qualities, rich in vitamins, organic 51 acids, microelements, pectin and other substances. Some researchers note that quince to a lesser 1 52 extent than other fruit crops from the subfamily Maloideae is damaged by pests and diseases 53 (Baskakova 2017). Despite the fact that quince is a promising fruit crop in its characteristics, 54 especially for the southern regions of Russia, until now it has not received due attention, and 55 industrial plantations do not exist yet. 56 To the group of promising fruit plants of the fruit (Maloideae) it is possible to include a 57 medlar germanica (Mespilus germanica), which is represented by two ecotypes: xerophilous, 58 confined to open habitats, and mesophilic, forest (Tsitsin 1962; Strasburger 2007). In Russia, it is 59 widespread in the mountain ecosystems of the southern regions, especially in the North Caucasus 60 – from the lower zone to the upper limits of arboreal vegetation (300–2000 m above sea level), 61 as well as in the Crimea and adjacent territories, however, there are no industrial plantations. The 62 value of the medlar is known since ancient times. As a vitamin and medicinal plant, it entered the 63 culture of many countries of the Near and Middle Asia, the Eastern Mediterranean and Western 64 Europe. Many biologically active substances have been found in the vegetative and reproductive 65 organs of M. germanica, in particular, triterpenoids, tannins, phenolic carboxylic acids, 66 flavonoids, catechins, organic acids and their derivatives, aliphatic aldehydes, higher fatty acids, 67 significant amounts of fatty oil in seeds (Stanimirović et al. 1963; Glew et al. 2003). 68 The development of the Maloideae of various habitats and the increased adaptability of 69 representatives are based primarily on the development of structural and physiological- 70 biochemical features that also play an important role in resistance to phytopathogenic organisms. 71 For research in this respect, the representatives of the above four genera were taken as model 72 objects. 73 To the anatomical and morphological features of passive immunity, or horizontal 74 stability, include the specificity of the deposition of wax deposits and the thickness of the cuticle 75 of integumentary tissues, the structure of stomata, and a number of other features (Kumakhova 76 and Melikyan 1989). The material on the structure of superficial tissues (epidermis and 77 hypoderma) accumulated by some Maloideae representatives for the vegetative and reproductive 78 organs, as well as for their mycobiota, is fragmentary (Kumakhova 2003; Shkalikov et al. 2005; 79 Pautov et al. 2008). There is insufficient information on the polyfunctionality of the epidermal 80 tissue, the specificity of the microrelief of the leaf epidermis (the formation of cuticular folds, 81 microtens in the stomata and trichomes, peristomatic rings, cork tissue and lentils on the fruits). 82 Their functional significance is not entirely clear to this day. In the literature there are 83 disagreements and assumptions about the mechanism of opening and closing stomata, and also 84 the interaction of the stomata with the surface structures of the leaf (Kumakhova and Melikyan 85 1989, Pautov et al. 2008). The role of the ultrastructure of the cuticle of leaves and fruits in 86 passive immunity for many pathogens also remains controversial, and direct dependence on the 87 type of structure and overall thickness is not revealed. 88 The chemical factors of passive immunity include, first, the content or absence in the 89 plants of substances necessary for the life of the pathogen, and secondly, the presence of 90 substances that oppressively act on it (phytoncides, or phytoantipypsins). The leading role in the 91 formation of the latter belongs to the synthesis and dynamics of various compounds of phenolic 92 nature (from relatively simple phenols to complex polyphenolic composites), toxic to many 93 phytopathogenic fungi (Upadyshev 2008). According to modern concepts of the significance of 94 the features of the structure of the surface and the subcellular structures of plants in protection 95 from phytopathogens, a major role belongs to the synthesis and dynamics of changes in 96 phytohormones (Kumakhova and Skorobogatova 2017). At the same time, the character of 97 distribution of lipophilic components, the specificity of the formation and localization of 98 substances of polyphenolic and terpenoid nature, as well as playing important protective 99 functions against the attack of fungal pathogens in the surface tissues have not been adequately 100 studied. It is shown that the phytoncidal effect of plants on specialized parasites is generally 101 poorly expressed. In most cases, it extends to microorganisms that do not affect this plant. 2 102 Phytoncidal activity is not the same, it varies depending on the grade and age of the plant, as 103 well as on the time of day, the phase of development, weather conditions and other factors. 104 Thus, despite the availability of separate information from biology and disease affection 105 of the most valuable fruit representatives of the Apple Subfamily, no attempts have yet been 106 made to fully study their mechanisms of resistance. 107 In connection with the above, the purpose of this work was to conduct a comprehensive 108 search of micromorphological, anatomical and histochemical, and also ultrastructural and 109 physiological-biochemical features of plants of 4 genera of the Apple Subfamily, and an 110 evaluation of these indicators as markers of passive immunity to phytopathogenic fungi. 111 112 Materials and methods 113 The objects of research (botanical and phytopathological) were the leaves and fruits of 114 plants of different apple varieties (Malus domestica), pears (Pyrus communis) collected from the 115 experimental sites of the North Caucasian Research Institute of Mountain and Foothill 116 Gardening, as well as common quince (Cydonia oblonga Mill.) from planting of private plots, 117 and a wild medlar germanica (Mespilus germanica), which grows in high altitude zones in the 118 North Caucasus. Leaves and fruits for research were selected from the middle part of the crown 119 of model trees.