PLANT DENSITY AND ADD-ON FERTILIZATION EFFECT ON CROP MORPHOMETRICS, CHEMICAL CHARACTERISTICS AND ANTIRADICAL ACTIVITIES OF MENTHA PIPERITA UNDER GREEK ENVIRONMENTAL CONDITIONS Eleni Wogiatzi a ; Nikolaos Gougoulias a ; Alexandros Papachatzis* a ; Dimitrios Kaltsas a ABSTRACT In this work, spatial plant density and fertilization level effect were studied on plant height, dry drogue yield, essential oil production, total phenolics content and antioxidant activity of M. piperita leaf. Plant density increased crop height and expand arithmetically suckers production. Fertilized crops with spatial density of 4 plants /m 2 demonstrated greatest average plant height while crops with plant density of 2 plants/ m 2 maximized their sucker production independently of their fertilization scheme. In terms of dry drogue yield and leaf essential oil content comparison between the two seasonal harvests (early June and September), the first harvest revealed higher delivery quantities for both substance categories than second one. Analytically estimated concentration of total phenolics of the Mentha piperita leaf ranged of from 27.37 to 58.43 mg g -1 and the antiradical activity ranged from 18.01 to 38.73 μmols DPPH • g -1 dry weight. The correlation between total phenolics and antiradical activity appear to be statistically strong (r 2 = 0.9226). Keywords : Mentha piperita; sucker; total phenolics; antiradical activity DPPH • ; essential oil. INTRODUCTION Mentha piperita, family Lamiaceae, is a hybrid derived from a cross between Mentha aquatica and Mentha spicata. It is a perennial plant with erect stems which reaches to 80 cm height and develops numerous suckers. (Marquard R et. al. 2001). Different tissues and organs of Mentha spp. and other related medicinal plants contain provide various chemical and structural composition chemical substances with diverse biological and healing properties. (Pokorny J, et. al. 2001; Wojdylo A, et. al. 2007). In the last years, many studies were focused on evaluation of polyphenols composition and antioxidant activities of M. piperita and of other medicinal plants. (Gougoulias N. 2009; 2012a; 2012b). Polyphenols are well-known as one of the most widely spread secondary metabolites in edible and non-edible plants. (Harborne JB. et. al. 1980; Macheix JJ, et. al. 1990). Concerning their use, they counteract to strong oxidizers which damage protective biomolecules of biological systems related to inflammatory processes (Halliwell B, et. al. 2007) and lipid cellular management. (Halliwell B, et. al. 2007) . a Department of Agronomy Technology, Technological Educational Institute of Thessaly, 41110 Larissa, Greece Correspondence to: Alexandros Papachatzis E-mail: papachad@teilar.gr UNIVERSITATEA DIN CRAIOVA UNIVERSITY OF CRAIOVA Seria:  Biologie  Horticultură  Tehnologia prelucrării produselor agricole  Ingineria mediului Vol. XIX ( LV ) - 2014 647