Analysis Of Genetic Diversity And Mechanism Of Resistance To Aphid In The Germplasm Resources Of Ethiopian Mustard

The genetic background of Brassica vegetable varieties is becoming more and more limited now,and such result in the higher homogeny among the new varieties of Brassica vegetables.In order to solve this problem,some excellent germplasm need to be urgently identified and utilized in breeding practice.Ethiopia mustard(B.carinata L.)is the member of the family of Brassica vegetables,which has deep roots with higher drought resistance,thick leaf wax with better temperature resistance,disease and insect resistance and lodging-resistance characteristics.It has important value for genetic improvement of Brassica crops.At present,it is lack of good genetic resources of drought resistance,high temperature resistance and pest resistance for breeding practice of Brassica vegetables.However,some good agronomic traits,such as higher resistnce,were found in Ethiopia mustard and black mustard plants.In this study,75 genetic resources of Ethiopia mustard which contain good quality and multi-resistant genes had been introduced.By analyse and evaluation of large-scale genetic diversity using field-morphology and SSR molecular markers,we hope to establish long-term and stable Ethiopia mustard genetic resource bank for breeding of Brassica crops.Subsquently,the identification system of aphid ratio method and electrical penetration graph(EPG)have been utilized to evaluate the accessions of Ethiopia mustard and locate aphid resistance factors in these accessions.Finally,we analyse the resistance mechanism of aphid by the traditional mode of ―insect resistant three mechanisms(antixenosis,tolerance and antibiosis)‖ preliminarily.The surface morphology and longitudinal anatomical structure of the leaves have been observed in Ethiopia mustard plant by scanning electron microscopy and semi-thin section techniques.The component and content of glucosinolate in leaves of Ethiopia mustard were measured by liquid chromatography-mass spectrometry.The deposition of callose was observed in vascular bundle by using frozen section.We explored differences between the aphid-sucking condition on different materials which was induced by callose deposition.Results of this study are summarized as follows:(1)To analyse the genetic diversity of 75 Ethiopia mustards by morphological markers and SSR molecular markers.The 29 morphological markers and 48 pairs of polymorphic SSR markers have been used to analyze the genetic relationship within the 75 Ethiopia mustard accessions.Morphological markers divide 75 materials into 4 major subgroups and 9 small classes,while the tested accessions were subdivided into 7 subgroups by using Structure software with the results of SSR markers.There was a certain relationship between the classification of clusters and the geographical origin of accessions.(2)To establish the identification method and grading standard of Ethiopia material for aphid resistance,we successfully obtained 3 highly sensitive materials and 5 medium materials.In this study,we carried out the comprehensive evaluation of 75 accessions of Ethiopia mustard through indoor aphid resistance identification system and aphid ratio method.we obtained three high susceptible accessions(BC01、BC25 and BC60)and three moderate resistant accessions(BC13、BC47 and BC51)depend.on the evaluation result of aphid numbers at 21 d after inoculation aphid(AIA).There were 16 accessions which reached the average aphid number of more than 600,accounting for 21.3% while the average aphid number below 300 were only 6 accessions.These results indicate that B.carinata are susceptible for Myzus persicae during the seedling period.(3)The surface tissue,structure of the leaf and xylem maybe related to the aphid resistant factor by the technique of electronic penetration graph(EPG).In order to explore the mechanism of aphid resistance,we use three high susceptible accessions(BC01,BC25 and BC60)and three moderate resistant accessions(BC13,BC47 and BC51)to locate the aphid resistance factor through EPG parameter position in the tissue site.The number of probes,duration of total NP(No Probe),duration of total probe and duration of total E were not significant.Time of first E,duration of 1st probe and duration of total G were significant.It is concluded that the related leaf surface tissue,leaf structure and xylem are related to aphid resistance.(4)The morphology and density of hairy bodies and stomatal density were not correlated with aphid resistance,but the stomatal size is likely related to aphid resistance.The electronical microscope and semithin sectioning have been employed to compare the susceptiptible and resistant accessions leaf structure.It was found that medium resistant materials have thinner leaf thickness,high ratio of palisade/spongy tissue and thicker longitudinal anatomy.(5)Ethiopia mustard contains 7 common components of glucosinolate,and the content of indole and aliphatic glucosinolates is correlate wih the aphid resistance.In this study,7 common glucosinolates,???? have been detected by LC-MS,and this result consistant with the previous studies.Result showed the average content of glucosinolate is 5.87±0.10 μmol/g,which is about 39.60 % less than in Chinese kale.The ratio of the indole and aliphatic glucosinolates is correlate wih the aphid resistance.(6)The amount of callose deposition on the resistant accessions increased faster than on the susceptible accessions during the sucking of M.persicae.The frozen section and callose staining techniques had been utilized to compare their callose deposition between the susceptible and resistant accessions on six samples of different time periods with aphids.It was found that the content of callose deposition of resistant materials went faster in 12～24 h.The susceptible accessions have a rapid growth trend in 24～72 h phase.Resistant accessions and susceptible accessions showed callose deposition in the parenchyma epidermal tissue,phloem and xylem.