Mushroom waste biomass alters the yield, total phenolic content, antioxidant activity and essential oil composition of Tagetes patula L.

Champignon stalks are organic waste material widely underrated as a source of nutrients and substances with bio-stimulatory properties. French marigold (Tagetes patula L., Asteraceae) is an important crop plant that can be used in variety of different industries. This study assessed the usefulness of waste mushroom biomass - WMB (obtained in the production of champignon Agaricus bisporus), in the pot cultivation of two T. patula cultivars ('Mikrus' and 'Petit Yellow'). It examined growth, plant biomass, photosynthetic pigments content, leaves and petals color and their antioxidant potential as well as the essential oil content and composition of plants grown in 100 % peat (control) and peat supplemented with WMB (5 % by volume). Postharvest physicochemical properties and nutrient status of the media were also investigated. The addition of WMB enriched the medium in nitrogen, potassium and sulfur (by 14-28 %, 106-160 % and 33-100 %, respectively), and reduced its C:N ratio without affecting its electrical conductivity and pH. The plants growing in peat supplemented with WMB had greater fresh weight (by 32-54 %) and number of flowers (by 35-46 %), higher total chlorophyll content in the leaves (by 73-117 %) and more intense color of leaves and petals than those growing in peat alone. Moreover, the leaves and petals had greater content of total polyphenols and higher antioxidant activity (determined by DPPH, ABTS and FRAP). The results of gas chromatography-mass spectrometry (GC-MS) analysis of essential oils revealed that the oils of leaves contained higher amounts of spathulenol (2.3-2.9 %), isopropyl myristate (2.6-13.3 %) and palmitic acid (20.7 %-22.7 %). Whereas, the oils of the petals showed higher concentration of caryophyllene (1.5-4.6 %), myristic acid (11.0-19.1 %) and 2,2':5'2 ''-terthiophene (7.7-12.8 %). Interestingly, dodecanoic acid (2.7-3.8 %) was found only in the oils obtained from T. patula petals. Moreover, the slightly higher content of this compound was found in the plants growing in peat supplemented with WMB (3.8 % and 2.9 % for 'Mikrus' and 'Petite Yellow' cultivars, respectively). In conclusion, the present study suggests a new, environmental-friendly strategy to increase plant productivity and bioactive compounds content by using champignon stalks as a medium supplement.