Abstract
Reducing economic losses and health hazards due to mycotoxins without suffering the side effects of chemical fungicides is a goal of many researchers. The hypothesis of the current study is that naturally occurring phytohormones in the pericarp may be responsible for the protective effect of the pericarp against fungal invasion and toxin production. A spore suspension of Aspergillus parasiticus was used to inoculate yeast extract sucrose (YES) medium as a control; an aqueous extract of the pericarp with or without YES medium (PYES or PS) and YES media containing abscisic, jasmonic and gibberellic acids were used to detect the effect of these phytohormones on fungal growth and toxin production. The growth curve was generated on the basis of dry weights, and the aflatoxin concentration was determined by HPLC at each time interval of the study. The aqueous extract of the pericarp (PS) did not support fungal growth or aflatoxin production. However, PYES showed the highest percentages of inhibition of fungal growth (51%) and aflatoxin production (45%) on days 3 and 9, respectively. The reduction in fungal growth due to the presence of phytohormones was over 70% after 3 days and over 14% on day 12; however, no significant difference was observed between the treatments and the control on days 6 and 9. The growth profile of the control was still in the logarithmic phase on day 12, and the cultures treated with phytohormones reached a plateau on day 9. Phytohormones reduced the aflatoxigenicity of A. parasiticus. The inhibitory activity of the pericarp may be due to the presence of phytohormones.