Effects of Key Environmental Factors on Growth of Alternaria alternata Isolated from Strawberry Jam and Its Production of Alternariol and Alternariol Monomethyl Ether

Alternariol (AOH) and alternariol monomethyl ether (AME) are major mycotoxins produced primarily by Alternaria alternata on cereal grains and fruits. A. alternata is a causative pathogen of strawberry black spot disease. However, little is known about the characteristics of A. alternata, which was isolated from strawberry products. In the present study, we evaluated the influence of temperature, pH, and relative humidity (RH) on the growth of A. alternata OM1 and its production of AOH and AME on different media including strawberry puree agar medium (SPAM) after its isolation from strawberry jam. The fungal strain showed the highest growth rate at 25 °C under pH 6.5 and RH 97%, while the highest amounts of AOH and AME were produced by the strain at 25 °C under pH 4.5 and RH 97%. Additionally, the strain did not produce AOH and AME on SPAM at 25 °C under RH 92% until 7 days. Moreover, RT-qPCR analysis exhibited that relative expression levels of 2 AOH or AME biosynthetic genes (pksI and omtI) in A. alternata OM1 were up-regulated in YES medium, while they were not in MEB medium. Our results demonstrated that the three key environmental parameters had a significant influence on the growth of A. alternata OM1 and its production of AOH and AME. These findings suggest that storage of strawberries below 25 °C under RH 92% could prevent the production of AOH and AME by A. alternata OM1 on them.