Studies On Aphid Resistance And Mechanisms In Chrysanthemum And It's Related Species At Seedling Stage

Chrysanthemum is one of ten traditional famous flowers in China and four most important cut flowers in the world, it was planted throughout China. Chrysanthemum plays an important position on production and gardens. However, the yield and quality of chrysanthemum is severely affected by pests in the process of production. Aphid is an important pest of chrysanthemum and usually hurts wand, back of leaf and bud, inhibits the plant growth and development, resulting in dwarf plant, leaf rolling and dead. It is a cause of sooty mould, and its indirect action as a vector of viruse. Thus, the improvement of the resistance to aphid infestation has become a priority in chrysanthemum breeding programmes. The related species of Chrysanthemum with many elite genes which cultivate Chrysanthemum lacks are the valuable resources of genetic improvement. However, there were no reports on aphid resistance identification and related mechanisms in related species of Chrysanthemum yet. The purposes of this study were to explore the method of the identification of aphid-resistance in related species of Chrysanthemum, discover good-quality germplasm for aphid-resistance breeding of chrysanthemum and study the mechanisms of aphid resistance. The main results were followed:1. In order to discover aphid-resistant germplasm from Chrysanthemum and its closely related genera, aphid resistance ability of eleven species from Chrysanthemum and Artemisia L. were evaluated at seedling stage under the field and lab conditions. The results showed that the aphid-resistance reduced with average damage index of aphid (I*) value increased under field condition. A. vulgaris'Variegate', A. scoparia and A. annua with the 0.00 I* value were aphid immunity; A. japonica with the I* value of 0.13 was high resistant; the I* value of aphid resistant of the C. crassum was 0.25; C. dichrum with the I*value 0.37 was moderately resistant; C. yoshinaganthum and C. japonicum with the I* value of 0.51-0.75 were aphid sensitive; C. boreale, C. zawadskii and C. nankingense with the I* value> 0.75 were highly sensitive. Under lab condition, aphid resistance varied among species. Eleven species can be divided into five different grades in terms of aphid resistance according to the multiplication rate (MR). For example, the A. vulgaris'Variegate', A. japonica, A. scoparia and A. annua with a MR of 0.00 belonged to the highest resistance species; C. crassum with a MR of 5.86 belonged to moderate resistance species; C. dichrum, C. yoshinaganthum and C. japonicum with a MR of 7～10 are low resistant species; C. boreale, C. zawadskii and C. nankingense with a MR> 10, were non-resistant species. The aphid resistance under field condition is overall consistent with that under lab condition. The aphid resistance of eight species such as A. vulgaris'Variegate'and A. scoparia were consistent with either under field or lab conditions. However, A. japonica was high resistant under field condition while the highest resistant one under lab condition; C. crassum was resistant under field condition but was moderate resistant one under lab condition; and C. dichrum was of moderate resistance under field condition but low resistance under lab condition. Aphid resistant species of A. vulgaris'Variegate', A. scoparia, A. japonica, A. annua and C. crassum are promising germplasms for aphid resistance improvement of cultivated chrysanthemum.2. This paper studied the leaf structure, related enzyme activity and gene expression after aphid inoculation in the two related species of chrysanthemum A. vulgaris'Variegata' (high resistant) and C. nankingense (susceptible). Leaf structures in two materials were compared by paraffin section method and observed under a microscope, determining the variation on POD, PPO, PAL activity and the POD, PPO, PAL expression level by Real-time qPCR during the aphid inducement. The results showed that the two materials vary markedly in their resistance. A. vulgaris'Variegata', the high resistant, produced the thicker palisade tissue, the higher thickness ratio of palisade to sponge, the thinner sponge tissue, thickness and less sponge tissue layers in the leaf; the gene POD, PPO, PAL expressions and the enzymes activities were enhanced by aphid herbivory in the two materials; in the high resistant (A. vulgaris'Variegata'), the activity and gene expression of POD, PPO, PAL rapidly increased following aphid inducement, and their level remained higher in the late period after inoculation than in C. nankingense (susceptible); while the change of enzyme activity followed the related gene expression in A. vulgaris'Variegata'or C. nankingense. These results suggested that leaf structure and these defense gene expressions contribute to aphid resistance of these materials, which can be used as an indicator of aphid resistance evaluation at seedling stage.3. The purpose of this work was to investigate whether SA was involved in the defense response to the aphid Macrosiphoniella sanbourni between the high resistance material Artemisia vulgaris'Variegata'and the susceptible material Chrysanthemum nankingense. The effect of SA was measured by physiological indicators (chlorophyll, soluble sugars and soluble protein), reactive oxygen species (ROS) and malondialdehyde (MDA), flavonoids and related genes expression(PAL, CHS, CHI, F3H, F3'H, DFR). Among these indicators, chlorophyll, soluble sugars contents were reduced, while soluble protein, H2O2 and O2-, MDA, flavonoids content and related genes expression(PAL, CHS, CHI, F3H, F3'H, DFR) were enhanced by aphid and pre-SA aphid treatments; the high resistant material Artemisia vulgaris'Variegata'showed more rapid and earlier responses than the susceptible material Chrysanthemum nankingense by pre-SA treatment and aphid inoculation, respectively suggesting both SA and resistant level of plant material play an important role in aphid resistance of chrysanthemum.