The effect of gall mites on the condition of Tilia cordata assimilation apparatus

The aim of this research was to study the effects of gall mites on the condition of linden leaves (Tilia cordata Mill.). The research presents the results of the study of two species of gall mites, Eriophyes tiliae and E. leiosoma, which are widely distributed within the range of the linden. We collected material in the village of Osinovka, Kilmez district, Kirov region in August 2016-2017 and in Kirov city in August 2017 (See Fig. 1). The studied territories belong to the subzone of the southern taiga. We selected plant species with distinct characteristics which had attained their generative age state, and also leaves from the bottom of the crown on different sides. To determine the degree of plant damage by gall, we collected leaves (10 leaves from 10 trees) at each site. To define the morphological parameters in the areas with the highest degree of damage by gall mites, 50 damaged and 50 undamaged leaves were randomly selected. The length and the width of the leaf were measured. Leaves for determining linden photosynthetic pigments were selected in the morning (10:00-12:00). Leaf samples (150-200 mg) were fixed with 100% boiling acetone. The content of green and yellow pigments in Tillia cordata leaves in the acetone extract was determined by spectrophotometer SPEKOL 1300 (Analytik Jena, Germany) at wavelengths 662 and 644 nm for chlorophyll a and b, respectively. Determination of carotenoids was carried out at 470 nm. Two species of gall mites inhabit the studied sites of linden: Eriophyes tiliae Pagenstacher and E. leiosoma Nalepa. E. tiliae forms typical highly elongated galls on the upper side of the leaf. E. leiosoma damage shows yellowish-white felts on the underside of the leaf. We established that the studied species of mites react differently to environmental conditions and differ in their habitat distribution. E. tiliae mite occupies a wider range of habitats than E. leiosoma. We noted that both species of mites do not occur on the same leaf of the same tree. In the vicinity of the village of Osinovka, we collected material in the Loban river floodplain and in a birch forest (See Fig. 2). On the territory of the village, no gall mites were found on the linden. E. leiosoma mite was only encountered in the forest biotope. We observed infestation of linden leaves by E. tiliae mites both in the floodplain area and in the birch forest. E. tiliae mites severely damaged linden leaves in the river floodplain. In urban areas, linden damage by E. tiliae mites was higher in parks than along streets, whereas E. leiosoma was mainly found in street plantations and not in parks (See Fig. 3). We revealed that in all investigated areas, leaf damage causes a statistically significant (p <0.05) reduction in the length and width of leaves (See Fig. 4 and 5). The identified morphological changes in leaves indicate the negative impact of gall mites on the condition of the assimilative organs, which can lead to the inhibition of plant growth and development. To assess the state of plants, we used physiological and biochemical characteristics of the assimilating organs that determine the growth and reproductive processes. Data analysis of the content of plastid pigments in T. cordata leaves with gall showed that the degree of change in the pigment fund depends on the type of gall mites. E. leiosoma caused a significant decrease in chlorophylls (See Fig. 6 and 7). E. tiliae did not cause changes in the content and ratio of chlorophylls, but induced the accumulation of carotenoids in leaves (See Table). The level of yellow pigments in leaves with galls was significantly higher (16%), compared to undamaged leaves. Of the green pigments, chlorophyll b was more sensitive to leaf damage by gall mites. Carotenoids, in comparison with chlorophylls, were characterized by a greater resistance to leaf infestation by mites. Thus, the identified changes in Tillia cordata assimilation apparatus demonstrate the dangers of gall mites for Tillia cordata plantations in cities and emphasize the necessity to improve the monitoring of these phyllophages and measures to combat them. The paper contains 7 Figures, 1 Table and 20 References.

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