Commercial Food Grade Cinnamon Products Inhibit Mycelia Growth of Four Fungi In Vitro

Fungal contamination in tissue culture applications can lead to the loss of valuable plant material, and current in-vitro fungicides can be costly. This experiment evaluates the fungicidal efficacy of food grade preparations of Cinnamomum spp. against four common plant parasitic fungi. Ground cinnamon and cinnamon oil purchased from a local supermarket  were added to potato dextrose agar (PDA) with pH adjusted to 5.6 at nine concentrations (0 g/L, 0.52 g/L, 1.04 g/L, 2.09 g/L, 3.13 g/L, 4.18 g/L, 5.23 g/L, 10.46 g/L, 20.92 g/L and 0 mL/L, 1 mL/L, 2 mL/L, 4 mL/L, 6 mL/L, 8m L/L, 10 mL/L, 20 mL/L, 40m L/L, respectively). Agar was poured into quadraplex 150 x 10mm petri dishes. Fourteen-day-old cultures of Rhizoctonia spp., Phytophthora spp., Colletotrichum spp., and Fusarium spp. were used to inoculate media by placing a four-millimeter plug of each species in one of the four quadrants. Cultures were placed in dark at 22 °C and observations were made after three and seven days. There were significant differences in growth rate of cultures placed on ground cinnamon treatments after three days. Overall, the higher concentrations of ground cinnamon (5.23 g/L–20.92 g/L) had inhibited mycelia growth, while no significant difference was observed between the control and lower concentrations. The three highest concentrations of ground cinnamon, beginning with 5.23 g/L, showed a linear decrease of mycelia growth with no apparent mycelia growth observed on the highest concentration (20.92g/L), after three days. The seventh day after inoculation, mycelia growth on control and lower concentrations of ground cinnamon filled their respective quadrant while higher concentrations of ground cinnamon (10.46 g/L and 20.92 g/L) continued to have inhibited mycelia growth. Cinnamon oil treatments showed slight decreases in growth of Rhizoctonia spp., Fusarium spp., and Colletotrichum spp., at higher concentrations (20m L/L–40m L/L) after three and seven days; however, no apparent decreases of Phytophthora spp. growth were observed with any rate of cinnamon oil in this experiment. These results indicate that ground cinnamon may be an effective, low-cost fungicidal amendment to tissue culture media.