Studies On Genetic Diversity In Vegetable Crops Of Brassica Campestris By Using AFLP Technique And Differential Display Analysis Of The Development Process Of Heading Chinese Cabbage (Brassica Campestris L.ssp.pekinensis)

This work is part of our research towards the molecular breeding of Chinese cabbage (Brassicacalnpestirs). The work has been done in two steps: the analysis of genetic diversity in vegetablecrops of Brassica campestris using AFLP technique and the mRNA differential display of theheading process of Chinese cabbage.The vegetable crops of Chinese cabbage originated from China, which comprised non-readingChinese cabbage and heading Chinese cabbage. It is the unique species with special tastes amongall kinds of vegetable crops in the world and one of the earliest cultivated vegetables in ChinaIts gennplasm resources are plentiful and have a wide-tange of distribution. Understanding therelationships of different types of Chinese cabbage and their genetic diversity will benefitthe effective collection, documentation and utilization of the gennplasm and further improvethe breeding work.The leafy head of heading Chinese cabbage (Brassica campestrisL. ssp. pekinensis) is typicalan organ of morphological alteration. The vegetative growth of heading Chinese cabbage involvesfour successive stages characterized by definite types of juvenile, rosette, folding and headleaves. From rosette stage to folding stage, morphological and physiological changes occur inthe leaves before the heading process initiates. Studay on the heading process of Chinese cabbagewill help understanding its unique development mechanism and metabolism pathways. It also canserve as the basis for the molecular breeding of Chinese cabbage.In this study, AFLP technique, followed by the detection using the fluorescent and sliverstaining systems, has been used to explore the genetic diversity and taxonomy of 135 accessionsof Brassica campestris collected from different parts of China and forei~ countries. SMcoefficient was chosen to generate similarity coefficient matrix and the dendrogram constructedusing UPGMA method. mRNA differential display analysis was then carried out to see the differencein gene expression at rosette stage and folding stage of the heading Chinese cabbage.The results obtained are:Athe analysis of genetic diversity in vegetable crops of Brassica cawpestiris using AFLPtechnique1 The amplified bands by the two kinds primer combinations E+3/M+2 and E+3/M+3, respectively,were calculated and compared. It was found that the fonner primer combination produced3too many bands, while the later produced a proper number of bands and the AFLPfingerprinting was very clear after the sliver-staining.2It was found that the number of amplified bands, with the 64 pairs of E+3/M+3 primercombinations, was between 16 and 58, the percentage of polymorphic bands was between40%?8%. Four E+3/M+3 primer combinations with the higher number of polymorphic bandswere therefore, selected.3 Clustering results showed that all the accessions were grouped into two separate groups,one included all turnip accessions and another all Chinese cabbage accessions. The headingChinese cabbage and the "taicai" a type of non-heading Chinese cabbage, formed one uniquesubgroup in the group of Chinese cabbage. This suggested that turnip and Chinese cabbagebelong to two different subspecies of Brassica ca'npestris and the heading Chinese cabbageis a special variety within the subspecies.4 That "Taicai" was clustered together with heading Chinese cabbage into one group suggestedthat the "taicai" have a close relationship with the heading Chinese cabbage and may bethe ancestor of the heading Chinese cabbage.6 Clustering results of non-heading Chinese cabbage were complex and showed much deviationfrom those of horticultural taxonomy. This indicates that the difference at the DNA levelis not the same as that at the morphological level in the non-heading Chinese cabbage.The similarity amon...