Don Cipollini (Advisor), Thomas Rooney (Committee Member), John Stireman (Committee Member)
Master of Science (MS)
Emerald Ash Borer (EAB) is more damaging to North American ashes than Asian ashes. Variation in the resistance of ash species to feeding by larvae of EAB may be related to variation in levels of chemical defenses in the phloem. I compared constitutive and methyl jasmonate (MeJA)-inducible levels of several chemical defenses in the phloem of young Manchurian, Chinese, white, and green ashes. Manchurian ash is known to be highly resistant to attack by EAB in the field, while white and green ashes are both susceptible. The hypotheses of this experiment were that: (1) Manchurian (Fraxinus mandshurica) and Chinese ash (Fraxinus chinensis) trees' phloem or bark contains concentrations of unique secondary compounds and higher level of defense protein activities than white and green ash. (2) MeJA treatment will induce increases in content of protein, Peroxidase (POD), polyphenol oxidase (PPO) content and most of the secondary compounds in all species. Phloem extracts of Manchurian ash showed higher total soluble protein content and significantly faster browning than white and green ash, but lower peroxidase activity and polyphenoloxidase activity. Activities of PPO, POD, phenolic and lignin content, and the rate of browning reactions were not found to exhibit differences between MeJA treated and untreated groups. However, our HPLC results revealed Manchurian ash contained nine unique phenolic compounds: Homovanillic Alcohol, Esculetin, Esculin Related Cmpd, Esculin, Fraxin, Fraxidin hexoside, Pinoresinol dihexoside, Calceolarioside A, Calceolarioside B. We also found obvious increases in specific compounds (of the 20 compounds we reanalyzed in the four ash species) in Green ash, Chinese ash and Manchurian ash in the MeJA treated group. Also, Canonical Discriminant Function Analysis of five common compounds (Tyrosol Hexoside, Mandshurin, Pinoresinol compound, Syringaresinol and Oleuropein) revealed that Manchurian ash was different from the other three ashes, but closer to Green ash and Chinese ash. Green ash and Chinese ash were similar to each other. White ash was very different from all other three ashes. In this study, the highly resistant Manchurian ash was distinguishable from the highly susceptible white ash by having higher total soluble protein content and a significantly faster browning. The susceptible green ash was distinguishable from Manchurian ash by having lower total protein levels and a lower degree of browning. The phloem chemistry of green and Chinese ash was largely similar in this study, indicating that they may be similar in their resistance to EAB, and White ash showed had levels of peroxidase activity, polyphenoloxidase activity, content of phenolic and lower rate of browning reaction than the other three species. From the result of Discriminate Function Analysis, White ash also showed maximal separation from the others. Since White ash is as susceptible as Green ash in North America, White ash may contain different compounds or enzymes than Green that may be attractive to EAB.
Department or Program
Department of Biological Sciences
Year Degree Awarded
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