Phenylpropanoid metabolism may dominate the black spot resistance of Chinese olive (Canarium album)

The black spot of Chinese olive (Canarium album) seriously reduces the appearance quality and economic value of this fruit. In this study, we identified a black spot resistant variety called ‘Shuanghuxiang’ (CS) and a susceptible variety called ‘Yunzhi’ (CY), and investigated the underlying resistance mechanisms. Paraffin sectioning analysis indicated greater susceptibility of CY fruit epidermis to breakage post black spot infection compared to CS, with SEM analysis showing lower pathogen presence on CS fruits. These results revealed that the variation in black spot resistance could be attributed to differences in fruit epidermis structure and antimicrobial properties. Through conjoint transcriptomic and metabolomic analyses, we observed enrichment of genes (particularly CaPAL1 and Ca4CL1) and metabolites (particularly trans-cinnamate, ferulic acid and sinapate) related to phenylpropanoid metabolism in CS. These results indicated that the phenylpropanoid metabolism may play a crucial role in black spot resistance. This study provides theoretical basis and valuable material for the breeding of resistant varieties of Chinese olive.