Identification of phenolic compounds and active antifungal ingredients of walnut in response to anthracnose (Colletotrichum gloeosporioides)

Abstract

Phenolic compounds play important roles in pharmacology, nutrition and inhibition of pathogens. However, there are few studies on the identification of phenolic compounds related to walnut anthracnose resistance. In this study, we examined the walnut cultivars ‘Amigo’ and ‘HuoTe’, which are resistant and susceptible to anthracnose (Colletotrichum gloeosporioides), respectively. After inoculation with C. gloeosporioides, the overlapping differentially expressed genes of ‘Amigo’ and ‘HuoTe’ were mainly enriched in the phenolic compound biosynthesis pathway, and the genes related to chorismate and phenylalanine upstream metabolism pathways were induced. The phenolic compounds in the husks of ‘Amigo’ and ‘HuoTe’ were mainly phenylpropanoids-phenolic acids, benzoic acid derivatives-phenolic acids, procyanidins and flavonols. Further analysis revealed that 11 phenolic compounds were putatively related to the response to C. gloeosporioides. Subsequently, we conducted sensitivity tests with these potential active ingredients and found that 4-coumaric acid and p-hydroxybenzoic acid inhibited C. gloeosporioides growth and can be used as effective antifungal agents. The minimum inhibitory concentrations (MICs) of 4-coumaric acid and p-hydroxybenzoic acid were 1 g L−1 and 2 g L−1, respectively. The mixed antifungal agents composed of 4-coumaric acid and p-hydroxybenzoic acid had an obvious inhibitory effect on C. gloeosporioides in walnut fruit with an MIC ratio of 1:2. These results reveal the induced phenolic compounds of walnut husk and their active ingredients in response to anthracnose and provide a basis for further research on regulating and controlling anthracnose disease.