Effect of secondary metabolites in lemon balm on anthracnose control in strawberry

In strawberry cultivation, anthracnose caused by Colletotrichum gloeosporioides is difficult to control in the major strawberry-producing regions of Japan, and has caused great losses in nurseries and during fruit production. The antifungal functions of herbs of the family Lamiaceae have been exploited in medical and food applications. However, the antifungal effect of Lamiaceae herbs on plant diseases remains unclear. In this study, the antifungal effect of the Lamiaceae herb lemon balm (Melissa officinalis L.) on anthracnose and changes in antioxidative ability in strawberry plants were investigated. Strawberry (Fragaria × ananassa Duch. 'Tochiotome') runner plants were treated twice with a shoot extract (2%) of lemon balm. The plants were then inoculated with 10 mL C. gloeosporioides (10(5) conidia mL(-1)). The incidence and severity of symptoms of anthracnose were alleviated in strawberry plants by the application of a shoot extract of lemon balm. No difference was observed in dry weight of shoots and roots between treatments. On the other hand, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and ascorbic acid content increased in lemon-balm-treated plants. From these findings, lemon balm extract shows an anthracnose-suppressant effect in strawberry plants.