355 Anthocyanin Concentration of Croton (Codiaeum variegatum) Leaves as Affected by Cotton Gin Trash Compost M. Papafotiou 1 , B. Avajianneli 1 , C. Michos 1 , I. Chatzipavlidis 2 and V. Liakoura 3 1 Department of Crop Science, Laboratory of Floriculture and Landscape Architecture, Agricultural University of Athens, Athens, Greece 2 Department of Agricultural Biotechnology, Laboratory of Agricultural Microbiology, Agricultural University of Athens, Athens, Greece 3 Department of Agricultural Biotechnology, Laboratory of Plant Physiology and Morphology, Agricultural University of Athens, Athens, Greece Keywords: colour, growth medium, substrate, foliage potted plant, ornamentals Abstract Research was carried out in order to evaluate compost from cotton gin trash as a peat substitute in Codiaeum variegatum (L.) production. Rooted cuttings were grown for eight months in media containing cotton gin trash compost (CGC), peat and perlite in 1:3:4, 1:1:2 and 3:1:4 ratios, respectively, and their growth was compared to a control medium of 1 peat : 1 perlite (by volume). At the end of the experiment, the plant height, leaf number, leaf length, leaf width, and the dry weight of the roots were measured. Even when 75% of peat in the control medium was replaced by CGC, foliage and root growth was not affected negatively, while root dry weight was increased in the medium with 25% peat replacement. There was however an effect of CGC on the colour of plant foliage. The anthocyanin concentration in basal, middle and apical leaves was measured, at the end of the experiment, and it was found that the gradual increase of CGC level in the growth medium caused a gradual increase of the anthocyanin concentration in the leaves. This effect is discussed in relation to chemical properties of the media. The gradual increase of CGC level caused a gradual increase of N, P and K concentrations in the medium. Also, media with CGC had high electrical conductivity at the beginning of the culture period, related to CGC level, which it was reduced to values similar to that in the control medium after 50 days of culture. The Na concentration in the media ranged similarly to electrical conductivity. The pH of media with high CGC level was increased during the whole culture period. INTRODUCTION Most potted ornamental plants are grown in soilless media, which usually consist of a mixture of peat with inorganic materials like perlite and vermiculite. In recent years the use of peat in horticulture is under discussion as being a non-renewable resource that should be preserved (Scott and Bragg, 1993). A parallel environmental issue is the disposal of agricultural wastes. Composts from agricultural wastes have the potential to replace a significant proportion of peat in the growth medium of potted ornamentals (Burger et al., 1997; Papafotiou et al., 2001a, b, 2004; Wang and Blessington, 1990). In various experiments on plants which bear red colour leaves, intense red colour was observed in growth media that contained compost (personal observations). So, the present study was conducted in order to investigate the effect of cotton gin trash compost (CGC) on plant growth and leaf colour of Croton (Codiaeum variegatum L.). MATERIALS AND METHODS Rooted cuttings of Codiaeum variegatum cv. Norma (50 days old) were potted on 15 July in 14 cm (1300 ml) black plastic pots, in the following potting media (ratios by volume): 0 CGC: 1 peat: 1 perlite (0% CGC, control), 1 CGC: 3 peat: 4 perlite (12.5% CGC concentration, 25% peat replacement by CGC), 1 CGC: 1 peat: 2 perlite (25% CGC concentration, 50% peat replacement by CGC) and 3 CGC: 1 peat: 4 perlite (37.5% CGC concentration, 75% peat replacement by CGC). A sphagnum peat moss was used with a Proc. IS on Growing Media Ed.: J.-C. Michel Acta Hort. 779, ISHS 2008