Disease suppression in the circular economy using spent mushroom compost

Mushroom (Agaricus bisporus) has gained increased attention as an alternative protein source to meat and for its beneficial nutritional and medicinal properties. However, after the harvest of edible products, mushroom cultivation generates huge amounts of used compost, known as spent mushroom compost (SMC). In Europe, more than three million tons of SMC are produced every year. Thus, the management of SMC has become an important environmental issue. Sustainable solutions are also required to replace peat as a growth medium, synthetic fertilisers and chemical plant protection products in primary food production. In this context, SMC could be utilized as a growth medium, bio-fertiliser, bioremediation material and tool to control plant diseases. This study investigates whether SMC in either a solid or water phase can suppress root diseases in horticultural production systems. The suppressive potential of SMC in a solid phase was evaluated toward the root pathogen Phytophthora cactorum (PC) in tunnel-grown strawberry plants. SMC was mixed with peat and evaluated with or without the presence of PC. The suppressive effect of SMC toward the root pathogen Pythium aphanidermatum (PA) was evaluated in dill using a SMC water extract and plants cultivated in a substrate naturally infected with PA or healthy substrate artificially infected with PA. The results indicated that disease symptoms of dill roots were less severe in peat: SMC proportions of 50%: 50% compared to 70%:30%. Moreover, disease symptoms were lowest in the naturally infected substrate treated with SMC water extract. Treatment with the SMC extract also reduced disease symptoms in the healthy substrate artificially infected with PA.