Effects Of Grafting Onto Artemisia Annua On The Aphid Resistance In Chrysanthemum

In this study,Artemisia annua L.with high aphid resistance was selected as the rootstock,and chrysanthemum cultivars‘hangbaiju',‘jinsiju'and‘huangju'were used as scions.Firstly,the orientation of aphid and the classification of aphid resistance were carried out on grafted seedlings and cuttings.Then the effects of anatomical structure,volatile substances,defense enzymes activity and metabolites on aphid resistance of grafted seedlings and cuttings were compared and analyzed.The physiological mechanism of effect the aphid resistance of grafted seedlings were explored.The main findings were as follows:1.Research on the tropism of aphisThe tropism of Macrosiphoniella sanbourni Gillette changed significantly between grafted seedlings and corresponding cuttings.The Selection rate of aphis to the grafted seedlings of‘hangbaiju',‘jinsiju'and‘huangju'were 0.19±0.07?0.35±0.03 and 0.25±0.07,respectively,which were significantly lower than the corresponding cuttings(0.81±0.07^**?0.65±0.03^**and 0.75±0.07^**).2.Classification of aphid resistance of tested materialsSecond-instar aphids by hunger treatment were inoculated into the top tender leaves of the tested plants.Each material inoculated ten aphids and repeated ten times.The number of aphids on the plants was counted every day after inoculation,and statistics were continuously recorded for 10 days.The reproduction ratio method was applied to identify the aphid resistance.The results showed that there were significant differences in the resistance grades of grafted seedlings and corresponding cuttings.The aphid resistance levels of‘huangju',‘jinsiju'and‘hangbaiju'grafted seedlings are high?2.4±1.3?,medium?5.4±0.4?and medium?4.3±0.4?,respectively,while the corresponding cuttings are medium?4.4±2.7^*?,low?9.9±1.7^*?and non-resistant(11.0±0.7^**).3.Analysis of leaf anatomical structure of tested materialsAfter grafting treatment,the anatomical structure of the grafted seedlings was significantly different from the corresponding cuttings.In grafted seedlings,the thickness of both the palisade tissue and the lower epidermis,and the thickness ratio of palisade to sponge all increased in varying degrees,while the leaf thickness and the sponge tissue thickness did not change significantly.4.Study on volatile substances in leaves of tested materialsVolatile substances in leaves of‘huangju',‘jinsiju'and‘hangbaiju'grafted seedlings and cuttings were determined by headspace-solid phase microextraction?HSSPME?and gas chromatography-mass spectrometry?GC/MS?before inoculation.The results showed that the varieties and relative contents of volatile substances in the three varieties were significantly different,and the specific components of volatile substances in the leaves of grafted seedlings and corresponding cuttings were significantly different.5.Study on the change of defense enzyme activity of tested materialsAfter inoculated aphids,the activities of defensive enzymes?POD,SOD,PPO,PAL?of all the tested materials showed the double-peak or three-peak type.Compared with the corresponding cuttings,the defense enzyme activity of the grafted chrysanthemum seedlings increased rapidly and greatly,and the activity was still high in a long time after inoculation.6.Study on the changes of metabolites in tested materialsAfter inoculated aphids,the contents of soluble protein and flavonoid in grafted seedlings and cuttings were both increased,while the contents of soluble protein and flavonoids in the grafted seedlings changed more rapidly and significantly than the corresponding cuttings.The soluble sugar content showed a downward trend after inoculated aphids,while the grafted seedlings reacted more rapidly with higher decrease amplitude.