| Both chrysanthemum and pyrethrum are perennial herbaceous flowers and belong to the Compositae family. Chrysanthemum is one of the top ten Chinese traditional flowers and four famous cut flowers in the world, which widely used and had a big market. But during the growth and development, chrysanthemum have often been invaded by insects, particularly aphids, which secreted honeydew can also cause disease, affecting the ornamental value of chrysanthemum even death. Pyrethrum is an ancient and insecticidal plant. The insecticidal compounds, known as pyrethrins, are mainly extracted from the pyrethrum flower head, and can kill aphids and other insects efficiently. Therefore, pyrethrins have become one of internationally recognized, safe, economically viable and pollution-free insecticides.In this study, the anti-aphid of chrysanthemum cultivars was investigated in the indoor test and in the field. The trichome types, cell ultrastructure, densities and distribution of chrysanthemum cultivars and pyrethrum were also observed, and then the inclusions of trichomes were extracted and analyzed by gas mass spectrometry to identify the chemical composition. The objectives of the present study were to determine the relationships among the trichome density, inclusions and anti-aphid, and to evaluate the trichome functions. The main results were as follows:(1) In the field investigation, we found plenty of insects on twenty nine chrysanthemum cultivars, and they belonged to five categories, namely aphids, white grubs, leafhoppers, chrysanthemum leaf mine and stinkbug class. The damages caused by aphids were the most serious. According to the evaluation criteria of average aphid population density on inflorescence, the chrysanthemum cultivars were divided into six grades, and they were high sense, moderate sense, sense, moderate resistance, resistance and high resistance, respectively.(2) The indoor insect experiments were conducted with eight chrysanthemum cultivars which were selected from the twenty nine cultivars. They were three high sense cultivars’Sanhua Xiandong’,’Ziyan Xinzhuang’and’1581’; a sense cultivar ’Quanxiang Mengzhiju’, a moderate sense cultivar’Quanxiang Chongtian’, two moderate resistant cultivars’Jinsidie’and’Ruizhugong’, a resistant cultivar’Jinluan Baodian’. When stems were used as the materials, the number of survival aphids on cultivars was used as an evaluation criterion of anti-aphid. The results showed that’1581’ was a high sense chrysanthemum cultivar, and sense cultivars ’Quanxiang Chongtian’ had lower resistance to aphids than’1581’.’Quanxiang Mengzhiju’ belonged to moderate sense cultivar; Moderate resistance cultivars ’Jinsidie’ and ’Sanhua Xiandong’ had closer insect-resistant ability with insignificant difference.’Jinluan Baodian’ and ’Ziyan Xinzhuang’were the most resistant in all investigated chrysanthemum cultivars. When ray florets were used as the materials, the survival rate of adult aphids was used as an evaluation criterion of anti-aphid. The results showed that ’Quanxiang Chongtian’ was highly susceptible to aphids.’Jinluan Baodian’ was sense cultivar. ’Ruizhugong’ was moderate sense cultivar. Moderate resistance cultivars’1581’,’Sanhua Xiandong’ and ’Jinsidie’ had insignificant difference in insect resistance.’Quanxiang Mengzhiju’ had the strongest resistance to aphids in all the tested cultivars. The results of these indoor experiments did not get the consistent results, and they are needed a further study.(3) The trichomes of chrysanthemum and pyrethrum were observed in the study, and three types of trichomes, peltate glandular trichomes, T-type hairs and fractured tube hairs were found. T-type hairs mainly distributed in stems and leaves, but T-type hairs had slightly differences between two species. The T-type hair densities of pyrethrum were higher than chrysanthemum, especially on the back of leaves. In contrast, the glandular trichomes were few or not observed on chrysanthemum ovary of tested cultivars, but pyrethrum ovary is the most concentrated distribution parts of the glandular trichomes. The glandular trichome densities of chrysanthemum from high to low were corolla of disc floret, abaxial surface of leaf, adaxial surface of leaf, abaxial surface of ray floret, stem, adaxial surface of ray floret. However, the glandular trichome densities of pyrethrum from high to low were the ovary, corolla of disc floret, both sides of leaf, abaxial surface of ray floret. In addition, the glandular trichomes had different developmental stages, such as generation, growth, secreting, wilting. Some fractured tube hairs were observed on the leafstalk and nervure of chrysanthemum. Compared the results of (2) and (3), we found that there were not significant correlation among trichome densities on flowers, anti-aphid of indoor test and observation in the field.(4) The glandular trichomes on the stalks of pyrethrum genotype ’No.39’ and the chrysanthemum cultivars’Ruizhugong’and’1581’were isolated by alternating liquid nitrogen and spiral shock meter, then chloroform was used to extract the inclusions, and finally analyzed by gas mass spectrometry. The results indicated that seven basic substances identified in the glandular trichomes of chrysanthemum, they were 1-Octen-3-ol、Eucalyptol、Bicyclo[3.1.1] hept-2-en-6-one,2,7,7-trimethyl-、Naphthalene、E-β-Farnesene、7,10-Octadecadienoic acid, methylester [s-(E,E)]-、Octadecanoic acid. For pyrethrum, there were eight basic substances identified in the glandular trichomes, they were 2H-pyran-3-ol,6-ethenyltetrahydro-2,2,6-trimethyl-, n-Tridec-1-ene,Decane,2,3,5,8-tetramethyl-,(Z)-β-Farnesene,1,6-Cyclodecadiene,1-meth yl-5-methylene-8-(1-methylethyl)-, [s-(E, E)]-, Phenol,2,4-bis (1,1-dimethylethyl)-n-Hexadecanoic acid,6-Hydroxy-l-oxogermacr-4,10 (15),11 (13)-trien-12,8-olide. It can be concluded that the trichomes on both of pyrethrum and chrysanthemum contained the E-β-Farnesene, and the differences of anti-aphid between the two species were possibly attributed to the differences in inclusions. Further qualitative and quantitative studies were needed to determine these inclusions. |
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