Different clonal responses to cypress canker disease based on transcription of suberin-related genes and bark carbohydrates’ content

Abstract

Suberin metabolism plays a crucial role in the compartmentalization of the necrotic bark tissues in cypress clones resistant to bark canker caused by Seiridium cardinale. In cypress, the main mechanism of resistance to the bark canker caused by the fungal pathogen Seiridium cardinale involves the post-infectional development of a well-structured necrophylactic periderm (NP). The impermeability and effectiveness of NP against pathogens has been associated with cell wall suberization. In canker-resistant and susceptible C. sempervirens clones, the transcript accumulation of four genes involved in suberin biosynthesis (Acyl-CoA thioesterase, stearoyl-ACP-desaturase, Caffeoyl-CoA-3-O-methyltransferase 1 and Peroxidase 21) was studied in inoculated and wounded bark tissues through qPCR assay during a 3 month trial. Quantification of non-structural carbohydrates in the same targeted tissues was also performed by HPLC. In the canker-resistant clone, transcript accumulation of all four examined genes significantly increased after both inoculation or wounding more than in the susceptible clone, and the maximum difference between the two clones was observed after 30 days. The type of clone significantly affected the transcript accumulation of all the four examined genes (main effects ANOVA). The total soluble sugars content detected in the bark tissues was constitutively similar in both clones, and only slight differences in the carbon balance were detected between the two clones 90 days after inoculation or wounding. Histological observations of bark sections stained with Sudan red 90 days after inoculation, showed that in the canker-resistant clone a greater suberin deposition occurred in the NP, which resulted thicker and better structured when compared to the susceptible clone.