| Pakchoi is a subspecies of Brassica rapa L. ssp. chinensis, and is an important vegetable and widely cultivated in Asia. Its molecular marker-based linkage map construction and QTL mapping will provide an available reference to genomic structural study and genetic breeding in Pakchoi. In this study a DH population of Pakchoi was obtained through isolated microspore culture, and then used for molecular genetic linkage map construction, and QTL analysis for major morphological traits and plant color on the map. The main results of the present study were as follows:In order to establish a highly effective system of microspore culture in Pakchoi, we investigated the effect of culture conditions on embryo genesis, embryonic development and plant regeneration. And the methods of ploidy identifieation for microspore-derived plantswere studied. There was a significant variation in the response of the eighteen cultivars to microspore culture.’YS07’(24.00embryos/bud) was the highest responsive accessions studied, while’YS12’was the non-responsive microspore culture genotype. Heat shock treatment at33℃for24h was more beneficial for microspore embryogenesis. The NLN medium supplemented with0.1mg/L6-BA and0.05mg/L NAA showed the best response on microspore embryogenesis. The frequency of embryogenesis on Pachkoi was improved by shaking during isolated microspore culturing. Agar concentration at10g/L was proved to be the most effective for plantlet regenerationand the frequency of other tissues (callus, browing, vitrification) were delined. The best medium was MS+3%sucrose+1.0%agar+0.1g·L-l activated charcoal. Ventilate well sealed film was beneficial to form plantplet.’1/2MS+NAA0.1mg-L"1+3%sucrose+0.8%agar’and’MS+NAA0.1mg·L-1+3%sucrose+0.8%agar’are suitable mediums for rooting.Totally1070regenerated plants were investigated, in which18.22%were identified as haploids,24.95%were polyploids,3.83%was identified as ploidy mixed. The average spontaneous doubling frequency of the different genotypes of Brassica rapa was59.81%.A molecular marker based genetic linkage map of Pakchoi was constructed by using the intervarietal mapping population containing182DH lines from’YS06’. There were143molecular markers on the linkage map, comprising78SSR markers and114SRAP markers. The total length of the map was995.3cM including10linkage groups and the average interval distance of the linkage map was7cM. Based on the SSR markers provided anchors to previously published map for genome A of Brassica, we associated the linkage groups to the10chromosomes. A total of30.07%distorted markers were distributed in the map and clustered on some region of the linkage group.DH poulation and constructed linkage map were employed to map QTL for13morphological traits using composite interval mapping method. Thirty-three putative QTL were identified on5linkage groups, including2QTL for plant height,1QTL for plant dismeter,1QTL for head diameter,1QTL for waist diameter,7QTL for petiole length,2QTL for leaf width,4QTL for leaf length,2QTL for petiole width,2QTL for petiole thickness,3QTL for leaf number,3QTL for plant weight,3QTL for petiole weight, and2QTL for leaf weight. The QTL of associated traits often located on the same loci or near region of a linkage group. It was consistent with the high coefficients between phenotypic traits.DH poulation and constructed linkage map were employed to map QTL related to leaf color and petiole color. Tristimulus colorimeter and ocula measurement were used to measure the traits related to leaf color and petiole color. A total of28QTL were detected on7linkage groups, including5QTL for CLL*,3QTL for CLa*,6QTL for CLb*,2QTL for CLO,4QTL for CPL*,3QTL for CPa*,3QTL for CPb*, and2QTL for CPO. The QTL of associated traits often located on the same loci or near region of a linkage group. These mapped QTL could be used to develop a marker assisted selection program for leaf color and petiole color in Brassica rapa crops. |
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