Abstract Description

Commercially, Agaricus bisporus is the most cultivated mushroom due to its substantial yields, desirable texture, and high nutritional value. Its cultivation is hampered by fungal diseases, for example cobweb disease (caused by Cladobotryum dendroides), wet bubble disease (caused by Mycogone perniciosa), dry bubble disease (caused by Lecanicillium fungicola), and green mold disease (caused by Trichoderma aggressivum f. aggressivum). Methods to control mycopathogens include strict hygiene, steam sterilization, and chemical treatments. Repeated use of fungicides (prochloraz-Mn, benomyl etc.) result in resistant strains and some fungicides lost approval (e.g. chlorothalonil, carbendazim) for use, leading to research into alternative control measures for A. bisporus pathogens. Nanosilver (AgNPs) clay (zeolite, montmorillonite, and palygorskite) composites were synthesized by a microwave-assisted surface functionalization technique. The nano-silver composites, namely AgNP-zeolite, AgNP-montmorillonite and AgNP- palygorskite were tested against several A. bisporus fungal pathogens, as well as A. bisporus (in vitro) using PCA containing 1 mg/mL, 5 mg/mL and 10 mg/mL AgNPs. In vivo studies were conducted on mushroom beds (industrial conditions simulated) containing 10 mg/mL AgNP-zeolite in the casing material and A. bisporus mycelial formation and mushroom production monitored. ICP-OES analyses were conducted to determine possible Ag absorption by mushrooms. At 10 mg/mL, AgNP-zeolite and AgNP-montmorillonite inhibited 8 out of 9 pathogens (in vitro), while AgNP-palygorskite only inhibited 1. The AgNPs tested against A. bisporus showed no adverse effects on the mycelial growth (in vitro) at any concentration. The in vivo effect of AgNP-zeolite was tested by adding 10 mg/mL, AgNP-zeolite to the casing material in mushroom beds. While some chemical fungicides can have a negative effect on A. bisporus growth and fruiting, AgNP-zeolite, had no adverse effects with a 3.9% increase in mushroom production. The silver content of all mushrooms (from control and AgNP-Zeolite treated mushroom beds) was below the detection limit (below 0.1 mg/kg) for ICP-OES. This study confirms that AgNP-zeolite and AgNP-montmorillonite composites have effective antifungal properties and can be used as alternative fungicides against mushroom pathogens without affecting A. bisporus growth.