Resistance Mechanism Of Different Ash Species (Fraxinus Spp.) To Emerald Ash Borer (Agrilus Planipennis Fairmaire)

The ash species trees (Oleaceae, Fraxinus L.) are admirable as commercial, protection, and landscape plants for coastal areas in China. Emerald ash borer (EAB) Agrilus planipennis Fairmaire is an important borer pest and damaged the ash tree in China such as Liaoning, Shandong and Tianjin. Since it was discovered in North America, it has killed more than 30 million ash trees in southeastern Michigan alone for decade.By February 2010, EAB infestations were known in thirteen states in the northeastern United States and two provinces in the eastern Canadian. There were limited EAB detection and control methods, and high costs, current objectives have shifted away from eradication to management of the pest. At present, the most promising long-term approach for reducing EAB populations and conserving ash in forested areas of North America is to build mixed forest. The exploration of the resistance mechanism of ash tree is contribute to reveal the reason why the pest outburst, which provide scientific basis of the regional control of EAB.There are selected 8 ash trees which are different degree resistance to EAB. The physical property of barks and organization characteristics of branchs, secondary inclusion and volatile compound in different ash species trees and the resistance to EAB were studied.We explained the preferences differences among different ash species trees, finding the key factors which cause the resistance differences. The main results are as follows:(1) The study found that the harm states were significant difference in EAB to different ash species trees. F. velutina and F. pennsylvanlca were seriously suffered, F. americana and F. excolsior were less than the first two species, however F. mandshurica,F. platypoda,F. rhynchophylla,F. chinensis were the least damaged or no damage.(2) The number of emergence holes of EAB were no significant differences in different directions in the F. velutina. There were significant differences in different height, the emergence holes at the 1 to 2m were much more than others. Further analysis showed that the number of the emergence holes at the 1.5m was the maximum. The normal distribution prediction functions were as follows:(3) The studies on relationship between bark morphology of fraxinus and insect resistance found that the damage of EAB has nothing to do with tree color, but is associated with the stomata size, roughness, the compaction degree and crack size.(4) The relationship between the characteristics and the resistance was studied. The results showed that Vessel areas, lignified cells numbers, lignified cells radius and areas, and sclerotic cell numbers were major factors in sequence from high relations to low relations. Meanwhile, Vessel areas and clerotic cell numbers were negative correlation, while lignified cell radius, lignified cell numbers and lignified cell numbers were positive correlation to the resistance.(5) The relationship between the inclusion of different ash species and the resistance to EAB were studied also. Polyphenol. soluble sugar, reducing sugar and flavone were major factors having intimate relationship with the resistance. The content of polyphenol in F. chinensis, F. rhynchophylla and F. excolsior wrer significantly higher than others, and the content of polyphenol had negative correlations with the resistance. The content of soluble sugar in different trees were not significant difference and had positive correlations with the resistance. The content of reducing sugar in F. chinensis was higher than that in F. rhynchophylla and F. pennsylvanlca, while all the three trees were much more than that in other species left, and the conten of reducing sugar had negative correlations with the resistance. The content of Flavone in the F. chinensis and F. excolsior were more than other ash species trees, and the content of flavone had negative correlations with the resistance.(6) The relationship of volatile compound in different ash species trees and the resistance to EAB were studied. The results showed that the changes of content in various ash species trees were diverse after mechanical damagement. Usually, the trees which had a high level content and kinds of alcohol and hemiterpene were high resistance, and the high content of fatty acid could cause susceptible to the pests. The kinds and contents of each ash species trees in the test were increasing significantly after mechanism damage, and different ash species trees had different releases, the content of esters and ketone were higher than others in the resistant trees, while for the susceptible trees the alcohol was a high quantity, the contents of hemiterpene increased among all trees.