elisabetta.loffredo@uniba.it http://www.dibca.uniba.it/ BENEFITS FROM COMPOST USE IN THE PREPARATION OF PLANT GROWING SUBSTRATES: INHIBITION OF THE PHYTOPATHOGEN FUSARIUM OXYSPORUM AND PLANT GROWTH STIMULATION Elisabetta Loffredo, Andreina Traversa, C. Eliana Gattullo and Nicola Senesi Dipartimento di Biologia e Chimica Agro-forestale e Ambientale, University of Bari Aldo Moro, Bari, Italy elisabetta.loffredo@uniba.it http://www.dibca.uniba.it/ INTRODUCTION Compost utilization in the preparation of plant growing substrates represents a recent sustainable technology which achieves environmental and agricultural benefits in comparison with the use of conventional matrices, such as peat. In the last years, a number of investigations have demonstrated the effectiveness of composts and their humic fractions in suppressing soil-borne plant pathogens, and their application to soil has been proposed as an environmentally safe alternative to pesticides. OBJECTIVES To test the effects of two concentrations of humic acids (HA) isolated from a green compost (C) and mixtures of C with peat (P) at various rates on the growth in vitro of Fusarium oxysporum f. sp. callistephi (Foc); To test the effects of the bulk substrates on the growth and health of the ornamental plant China aster (Callistephus chinensis L. Nees) repeatedly infected with Foc. MATERIALS AND METHODS Substrates and Humic acids (HAs): a green compost (C), a peat (P), and mixtures at 20, 40 and 60% (v/v) of C with P (C20+P, C40+P and C60+P). The HAs were isolated from these substrates using conventional procedures. Fungal growth: The HAs were tested at concentrations of 50 and 300 mg L-1 on the growth of Foc on PDA (potato dextrose agar) under controlled conditions. Plant growth: China aster seedlings were grown for 14 weeks in a Phytotron growth chamber into plastic pots containing the above substrates. During the experimental time, the fungus Foc was inoculated three times in the substrate. Pathogenicity was monitored observing the apparent symptoms of plant suffering, such as root injuries and rot, and measuring plant biometric parameters, such as height, number of leaves and the length of the main leaf vein after 10, 12 and 14 weeks from transplanting. Statistical analysis: All experiments were replicated 6 times and all data obtained were statistically analysed by ANOVA and the LSD test. RESULTS Fig. 1 Fig. 2 Fungal growth (FIG. 1): Any HA sample at both concentrations significantly inhibited the mycelial growth of Foc during the 13 days of experiments, with an almost total fungal suppression by HA at the highest dose from the mixture at 40% of C with P after 18 h from inoculation. Plant growth (FIG. 2): The mixtures at 40% and 60% of C resulted highly effective in the protection of China aster from Foc producing a relevant increase of the number of leaves per plant, plant height, and the average length of the main leaf vein, with respect to P alone, whereas C alone resulted lethal for plants even before the first fungal inoculation. CONCLUSIONS In in vitro experiments, humic acids isolated from a green compost and mixtures of the compost with peat at various rates exhibited a significant suppressiveness against F. oxysporum f. sp. callistephi. In in vivo experiments, the partial and moderate replacement of the conventional substrate peat with compost in potted-plant systems resulted in benefits for the health and vigour of the ornamental plant China aster. Thus, this study adds new scientific evidence for the suitable and valuable use of compost in the preparation of potting mixtures for ornamental plants. REFERENCES Pascual, J. A., Garcia, C., Hernandez, T., Lerma, S., Lynch, J.M. (2002): Effectiveness of municipal waste compost and its humic fraction in suppressing Pythium ultimum. Microbial Ecology 44, 59-68. Litterick, A.M., Harrier, L., Wallace, P., Watson, C.A. and Wood, M. (2004) The role of uncomposted materials, composts, manures, and compost extracts in reducing pest and disease incidence and severity in sustainable temperate agricultural and horticultural crop production - A review. Crit. Rev. Plant Sci., 23, 453-479. Loffredo, E., Berloco, M., Casulli, F., Senesi, N. (2007). In vitro assessment of the inhibition of humic substances on the growth of two strains of Fusarium oxysporum. Biology and Fertility of Soils 43, 759-769. Loffredo, E., Berloco, M. and Senesi N. (2008) The role of humic fractions from soil and compost in controlling the growth in vitro of phytopathogenic and antagonistic soil-borne fungi. Ecotox. Environ. Safe., 69, 350-357. Loffredo, E. and Senesi, N. (2009) In vitro and in vivo assessment of the potential of compost and its humic acid fraction to protect ornamental plants from soil-borne pathogenic fungi. Sci Hortic., 122, 432–439.