Antifungal Activity of Salicylic Acid on Tree Nutshells

Almond and pistachio nutshells were obtained from a local tree-nut farm (Valley Orchard, LLC, Fresno, CA, USA). Four to five tree nutshell particles, depending on their sizes, were aseptically placed onto potato dextrose agar (PDA; BD Life Sciences, Franklin Lakes, NJ, USA) and maintained at 28 °C. The level of fungal contamination was monitored for 72 h.
Then, the level of the antifungal activity of SA against fungi naturally contaminated on the surface of tree nutshells (almond, pistachios) was examined on PDA according to the modified method described previously [26 (link)]. SA (0.8 or 1.6 M) dissolved in 60% ethanol (v/v) was applied to membrane filters (2.5 cm diameter; GE Healthcare, Chicago, IL, USA). SA- or ethanol (control) -saturated filters were positioned onto a PDA Petri plate (100 mm × 15 mm; Corning Inc. Life Sciences, Tewksbury, MA, USA). Two to three tree-nutshell particles, depending on their sizes, were aseptically positioned onto the other half of each PDA. The test plates were incubated at 28 °C to determine the susceptibility of the fungal contaminants to the SA. The control plates contained an ethanol (60%, v/v) filter only. Fungal growth was monitored for 96 h.