The aim of this experiment was to determine plant responses to Coccus hesperidum L. infestation on two host plants. Groups of five lemon and five fern plants were colonised by various numbers of mobile C. hesperidum instar nymphs. After 6 months, all scale insect individuals were counted on each plant. According to the insect density, the plants were divided into a five-degree series. In all density classes of host plants tested, the infestation of scale insects decreased the chlorophyll and carotenoid content as well as the value of three indicators of photosynthetic activity. The strongest decrease in the analysed pigments was observed for the smallest abundance of insects (firstclass density) in lemon leaves and in second-class density in fern leaves. The strongest reactions of the chlorophyll fluorescence indicators were observed in density classes III and IV in the fern leaves and density classes IV or V in the lemon leaves. The reactions depended on the specific properties of plants and abundance of insects feeding on them.

The paper deals with the analysis of a ten-year study on the chemical composition of tubers of forty potato cultivars and their physiological indicators. The research was carried out at the experimental station in Parczew, Poland on a podzolic soil with typical granulometric composition of sandy silty clay, using a randomized block design in four replicates. Forty potato cultivars were the subject of this study, including eight very early, seven early, nine medium early, nine medium late and seven late cultivars. The photosynthetic activity of plants was evaluated by measuring chlorophyll a and b determined in raw leaf matter by the spectrophotometric method as well as by measurements of chlorophyll fluorescence induction of potato leaves using a fluorimeter PAM-2000. Measurements of photosynthetic indicators at various stages of potato development revealed that their increase indirectly reflected the prolongation of plant growing period, which might have a direct impact on yield quality. The chemical composition was determined by standard methods used for tubers. The main objective of the study was to determine the chemical composition of potato depending on the values of chlorophyll fluorescence indicators, which will allow prediction of the chemical composition of tubers during the growing season. The obtained results allow us to predict changes in nutrient content in potato tubers based on the indicators such as: chlorophyll a and b content, minimum and maximum fluorescence yield, maximum efficiency of photosystem in dark and mean plant growth rate.

Changes of chlorophyll (Chl) a fluorescence and photosynthetic pigment contents were analysed in galled leaves (visibly damaged and undamaged parts) and intact leaves. The values of minimal fluorescence of the dark-adapted state, maximal quantum yield of PSII photochemistry, effective quantum yield of PSII photochemical conversion, and photochemical quenching coefficient decreased in Ulmus pumila L. leaves galled by Tetraneura ulmi (L.) and in U. glabra Huds. galled by Eriosoma ulmi (L.). Colopha compressa (Koch.) feeding affected these parameters only in damaged parts of U. laevis Pall. galled leaves. The increasing number of T. ulmi galls progressively decreased photosynthetic performance. In gall tissues of all analysed aphid species, the lowest photosynthetic pigment content was found, indicating that the photosynthetic capacity must have been low in galls. Significant reduction of Chl and carotenoid contents were observed in damaged and undamaged portions of galled leaves only in the case of T. ulmi feeding.Additional key words: biotic stress; Eriosomatinae, fluorescence parameters; host plant response. Fm -minimal and maximal fluorescence yield of the dark-adapted state, respectively; F0', Fm' -minimal and maximal fluorescence yield of the light-adapted state, respectively; Fs -steady-state fluorescence yield; Fv -variable fluorescence in the dark-adapted state; Fv/Fm -maximal quantum yield of PSII photochemistry; qN -nonphotochemical quenching coefficient; qP -photochemical quenching coefficient; Y -effective quantum yield of PSII photochemical conversion; ΦPSII -quantum efficiency of PSII electron transport. Acknowledgments: This work was supported by University of Life Sciences in Lublin (Project no. OKE/DS/2 in 2013-2017). Authors thank to three anonymous reviewers for their valuable comments, which helped improve this manuscript.

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Gall-inducing insects may cause multiple physiological changes in host plants, such as the loss of photosynthetic pigments and reduced photosynthetic capacity. However, the direction of these changes is usually insect species-dependent. Therefore, the objective of this research was to characterize the indirect effects of galls induced by asexual generation of Neuroterus numismalis (Fourc.) and N. quercusbaccarum L. on photosynthesis by comparing changes in photosynthetic and photoprotective pigments and chlorophyll a fluorescence in foliar tissue with and without galls in naturally growing pedunculate oak trees (Quercus robur L.). The presence of galls of both Cynipidae species caused a significant decrease of chlorophyll a, b and carotenoids contents. Moreover, photosynthetic parameters (F0, Fm, Fv/Fm, Y, qP, qN) were significantly decreased. These results provide valuable information for diagnosing the oak infections using a non-invasive method, such as chlorophyll a fluorescence and predicting the effect of infections on photosynthetic productivity.