Exogenous piperonylic acid and p-coumaric acid differentially influence crown rot caused by Colletotrichum siamense in octoploid strawberries by regulating phenylpropanoid, flavonoid, and lignin metabolism

ABSTRACT Colletotrichum species crown rot causes the accumulation of metabolites involved in phenylpropanoid biosynthesis in octoploid strawberries. Phenylpropanoid biosynthesis is the first step in the flavonoid and lignin biosynthesis pathways and it plays a key role in plant disease resistance. We therefore aimed to determine the influence of exogenous piperonylic acid (PiA) and p-coumaric acid (p-CA) on crown rot in octoploid strawberry. Piperonylic acid restricted mycelial and lesion growth in strawberry crowns, whereas p-CA enhanced crown rot susceptibility by regulating the accumulation of total phenols, flavonoids, and lignin. The total phenol content induced by PiA significantly increased in strawberries infected with Colletotrichum siamense by promoting the activities of phenylalanine ammonia-lyase, but not trans-cinnamate 4-monooxygenase and 4-coumarate-CoA ligase. Lignin contents were relatively stable in strawberries infected with C. siamense, whereas the caffeoyl coenzyme A methyltransferase and cinnamoyl CoA reductase activities associated with lignin biosynthesis were upregulated by PiA. The infection of C. siamense increased flavonoid contents, whereas PiA decreased flavonoid contents. Overall, PiA enhanced C. siamense crown rot resistance via the phenylpropanoid biosynthesis of total phenols and was less associated with the biosynthesis of lignin and flavonoids.