Phenolic profiles of two Melampyrum species differing in susceptibility to Cronartium rust
Cronartium flaccidum is an important pathogen in boreal forestry where it causes pine stem rust. The hemiparasite Melampyrum sylvaticum serves as a telial host for this heteroecious fungus while the congeneric M. pratense is highly resistant. We hypothesized that the variation in susceptibility is due to differences in the composition of secondary phenolic compounds in host plant tissues. To test this hypothesis, phenolic compounds of leaf extracts taken from both species of Melampyrum were analyzed with HPLC. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used for data processing. PCA indicated difference between the species, with the first two components explaining more than 70 % of the total variance of data that was separated into two distinct groups in a scatter plot. Two clusters, formed by the two species, were also suggested by HCA. Phenolic acids (such as chlorogenic acid), flavanones and apigenin flavonoids dominated the profiles of rust-resistant M. pratense, while kaempferol and luteolin flavonoids occurred in high relative concentrations in rust-susceptible M. sylvaticum. Our results suggest that phenolics may contribute to resistance or susceptibility of Melampyrum to Cronartium rusts as one factor. Future studies on the mode of action of phenolics in this interaction are thus warranted.
KeywordsAlternate hosts Hemiparasites Scots pine blister rust Secondary chemicals
We thank Dr. Michael Hardman for checking the language and Ms. Iryna Semashko for assistance with laboratory analyses.
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