Assessment of suitability and suppressiveness of on-farm green compost as a substitute of peat in the production of lavender plants
2017
Chilosi, Gabriele | Aleandri, Maria Pia | Bruni, Natalia | Tomassini, Alessia | Torresi, Veronica | Muganu, Massimo | Paolocci, Marco | Vettraino, Annamaria | Vannini, Andrea
Suppression of root rot diseases of ornamental plants is a potential benefit of formulating soilless container media with compost. A green compost (green nursery compost, GNC), obtained by a circular-economy approach from residues of pruning of woody plants and grass clippings during the nursery activities was analysed for its suppressiveness of root rot diseases using lavender. To this end, a bioassay was develop by formulating potting mixes containing GNC with two rates of peat substitution (25% and 50%) and infested with the root rot pathogens Sclerotinia sclerotiorum, Rhizoctonia solani and Phytophthora nicotianae . Contrasting results were obtained by using both substrates with a significant reduction of root rot by S. sclerotiorum , no effect on the containment of that by P. nicotianae , and an increase of symptoms caused by R. solani . The specific suppressiveness observed may be attributed to the colonisation of compost by specific groups of antagonistic microorganisms. This hypothesis was investigated by the analysis of culturable fungal community, which resulted in the isolation of Trichoderma harzianum and T. atroviride as preponderant fungal species. Trichoderma representative isolates exerted in vitro antagonistic activities against the target pathogens with varying efficiencies indicating the employment of multiple complementary mechanisms, which may have contributed to the observed specific suppressiveness. Both substrates containing GNC resulted suitable for nursery cultivation of lavender, showing a growth performance similar to that obtained with peat-based substrate. Present results indicate that on-farm compost is a suitable component of mixed-peat substrates capable to support plant growth and provide specific disease suppression.
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