Distinguishing Defensive Characteristics in the Phloem of Ash Species Resistant and Susceptible to Emerald Ash Borer

Abstract

We examined the extent to which three Fraxinus cultivars and a wild population that vary in their resistance to Emerald Ash Borer (EAB) could be differentiated on the basis of a suite of constitutive chemical defense traits in phloem extracts. The EAB-resistant Manchurian ash (F. mandshurica, cv. Mancana) was characterized by having a rapid rate of wound browning, a high soluble protein concentration, low trypsin inhibitor activities, and intermediate levels of peroxidase activity and total soluble phenolic concentration. The EAB-susceptible white ash (F. americana, cv. Autumn Purple) was characterized by a slow wound browning rate and low levels of peroxidase activity and total soluble phenolic concentrations. An EAB-susceptible green ash cultivar (F. pennsylvanica, cv. Patmore) and a wild accession were similar to each other on the basis of several chemical defense traits, and were characterized by high activities of peroxidase and trypsin inhibitor, a high total soluble phenolic concentration, and an intermediate rate of wound browning. Lignin concentration and polyphenol oxidase activities did not differentiate resistant and susceptible species. Of 33 phenolic compounds separated by HPLC and meeting a minimum criterion for analysis, nine were unique to Manchurian ash, five were shared among all species, and four were found in North American ashes and not in the Manchurian ash. Principal components analysis revealed clear separations between Manchurian, white, and green ashes on the basis of all phenolics, as well as clear separations on the basis of quantities of phenolics that all species shared. Variation in some of these constitutive chemical defense traits may contribute to variation in resistance to EAB in these species.

Interspecific Comparison of Constitutive Ash Phloem Phenolic Chemistry Reveals Compounds Unique to Manchurian Ash, a Species Resistant to Emerald Ash Borer

“…Phenolic and Lignin Extraction Soluble phenolics were extracted according to Eyles et al (2007) and Cipollini et al (2011). Extracts were stored at −20º C and used in subsequent HPLC analyses within 3 wk following extraction.…”

“…Recently, it was noted that constitutive phenolic compounds, including hydroxycoumarins and phenylethanoid glycosides (calceolariosides A and B), were found in phloem tissue of Manchurian ash but not in green and white ash. These compounds were hypothesized to contribute to the high resistance of Manchurian ash to EAB (Eyles et al, 2007;Cipollini et al, 2011).…”

“…Within the genus Fraxinus, green and white ash are phylogenetically distant from Manchurian ash, and some of the previously documented variation in their phenolic profiles (Eyles et al, 2007;Cipollini et al, 2011) may be the result of evolutionary divergence that is not related to their differences in resistance to EAB. Black and European ash are phylogenetically closely related to the resistant Manchurian ash, with all three species belonging to the section Fraxinus, but both of the former species are highly susceptible to EAB (Wallander, 2008).…”

“…Trees were sampled twice during the growing season to coincide with the phenology of early and late instar EAB. We also quantified interspecific variation in lignin concentrations, a phenolic polymer that can also contribute to insect resistance (Coley, 1986;Wainhouse et al, 1990;Kurokawa et al, 2004;Borg-Karlson et al, 2006), but that showed little variation among a number of Fraxinus species in an earlier study (Cipollini et al, 2011).…”

The Sign and Strength of Plant-Soil Feedback for the Invasive Shrub, Lonicera maackii, Varies in Different Soils

“…This indicates that these two unrelated species modify soils in ways with very similar consequences for subsequent plant growth. It is known that some aspects of their secondary chemistry are similar [18,50]. In fact, Fraxinus is invasive in Hungary where research showed evidence of reduced germination rates and growth of white mustard (Sinapis alba L.) caused by green ash extracts [51].…”