1. 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
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.
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