The antifungal activity of trans-cinnamic acid and its priming effect in apple in response to Valsa mali

Valsa mali causes Valsa canker, one of the most destructive diseases on apple trees, leading to severe losses for the apple industry in China. Considering the development of fungicide resistance and the harmful effects of chemical residues, it is urgent to identify alternatives to control this disease. Trans-cinnamic acid (t-CA), a compound with good antibacterial, antitumour and anti-inflammatory properties, is widely used in food, medicine and other industries. However, the antifungal activity of t-CA against V. mali and its regulatory role in apple defence against biotic stresses are unclear. Based on a metabolomic assay, we found that Malus yunnaensis (Valsa canker-resistant) twigs infected with V. mali dramatically accumulated t-CA. Exogenous application of t-CA effectively inhibited V. mali growth on potato dextrose agar. The EC50 value of t-CA inhibiting mycelial growth was 200 & mu;g/mL. Malus prunifolia (Valsa canker-susceptible) leaves and twigs pretreated with t-CA had significantly enhanced V. mali resistance. The t-CA application increased salicylic acid but reduced jasmonic acid levels in leaves and twigs. Moreover, the contents of phenolic acids and flavonoids increased in t-CA-treated samples. In addition, t-CA increased the activities of phenylalanine ammonia-lyase, & beta;-1,3-glucanase and chitinase. These results indicate that t-CA plays a significant role in inhibiting V. mali growth and priming apple defence.