weight. Photosynthetic pigment levels were lower under LED light compared to control lamps. Phenolic acids and flavonoids were identified in M. communis leaf extracts. Myricetin was the major constituent with highest concentration under red LEDs and highest BA level. Keywords Myrtle · Light quality · Photosynthetic pigments · Secondary metabolites · HPLC Abbreviations LED Light emitting diode B 100% blue LED RB 70% red and 30% blue LED R 100% red LED C Control fluorescent light BA 6-Benzyladenine NAA 1-Naphthaleneacetic acid MS Murashige and Skoog medium HPLC High performance liquid chromatography PPFD Photosynthetic photon flux density Communicated by Sergio J. Ochatt.

Summary Modifications in growing techniques can affect the yield and nutritional quality of various cultivated plants. Among them, the use of biostimulants is environmental friendly method of stimulating crop productivity, stress resistance, and affecting yield or chemical composition of the plants. The aim of the investigation was determining of the effect of biostimulant treatment on yield and its quality of carrot grown for summer harvest. The experiment was carried out in 2009-2011 in the experimental station of the University of Agriculture in Krakow, south Poland. Two experimental factors were taken into consideration: (1) cultivar: Nandrin F1 and Napoli F1 (2) dose of Aminoplant (foliar application): 1.5 and 3.0 dm3∙ha-1 and control (without Aminoplant). Total and marketable yield, root length, its diameter, leaf mass and leaf : root mass ratio were assessed. The dry matter, soluble sugar, carotenoids and nitrate ions contents were analyzed as main determinants of carrot nutritional quality. Aminoplant influenced not only carrot productivity, but mainly chemical composition of the roots. The present results also suggest that carrot reaction to biostimulant treatment was depended on a cultivar more than on environmental conditions in particular growing seasons. The significant effect of Aminoplant in a dose of 1.5 dm3∙ha-1 on the yield of roots and leaf rosette mass of ‘Nandrin F1’ appeared only in the first year of the experiment. Spraying with Aminoplant in a dose of 3.0 dm3∙ha-1 significantly increased the soluble sugars content in carrot roots of both cultivars but only in 2011. Dry matter content was also affected by biostimulant treatment mainly for ‘Napoli F1’, which showed the lowest dry matter content when sprayed with Aminoplant in a dose of 1.5 dm3∙ha-1. In 2010 control plants contained the greater amount of carotenoids, while in next year roots of plants treated with Aminoplant in a dose of 3.0 dm3∙ha-1 had more these compounds. The significant effect of Aminoplant on nitrates content in carrot roots was observed but were not repeatable in the experimental years, so different climatic conditions modified carrot reaction on biostimulant spraying.

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