Construction Of The High-density Genetic Linkage Map And Mapping Of Splitting Resistance, Color And Shape Of The Head In Cabbage

The head of cabbage, as a commodity and edible organ, has rich variety types, morphological diversity and higher nutrition. In recent years, the appearance quality of the head more and more receives takes. It is not only required beautiful head shape, green color, but also the resistant to splitting, storage and transportation. Recently, related research about these traits is still in its infancy. We need to study the genetic regulation, related genes detecting and breeding for head splitting resistance (HSR) varieties urgently.Based on the establishment of HSR evaluation method and screening of germplasm, the cell wall components, related enzyme activity change and the effect of CaCl2and exogenous GA3on mitigating head cracking were uncovered compared with different head splitting resistance materials; DH (double haploid) populations were obtained from F1cross between four high generation inbred lines, which were different form HSR, head color and head shape, using microspore culture. Then the genetic law and QTL detecting were studied with SSR/Indel and high density SNP genetic maps constructing combined with the DH populations. This study lays a theoretical foundation for further research on genetic mechanism, genetic improvement of related characters and related gene cloning, and has important practical value to accelerate the development of cabbage breeding. The summary of key results as follows:1. The HSR evaluation method was established and further be used to screen of74cabbage germplasms for obtaining different HSR materials. The changing characteristics of cell wall components and related enzyme activity during the head growing were not the same in different cultivation season and HSR materials. The content of cellulose and pectin for splitting resistance cabbage is significantly higher while the cellulase and pectinase activity is much lower and changed moderately than those for splitting susceptibility during the whole head developing, especially in the head mature period. Spraying CaCl2and exogenous GA3had no effect for splitting susceptibility cabbage on alleviating crack, but spraying for many times from the early head to mature could reduce the cracking rate and head splitting index for moderate resistance material.2. Two DH (double haploid) populations were obtained from F1cross between four high generation inbred lines, which were different form HSR, head color and head shape, using microspore culture. The genetic models and correlative analysis of HSR, head color, head shape with other important traits using the DH populations combined with major/polygene inheritance method and partial correlative analysis.3. Two SSR/Indel genetic maps were constructed using the above populations. And also, a high density SNP map was constructed by sequencing-based genotyping (GBS) one of the two DH populations with bioinformatics analysis tools. The SNP map includes42901SNP loci (1741bins,24.8SNP/bin) spanning798.8cM with an average of0.46cM maker interval in nine linkage groups.The SNP map is the most saturated reference map currently in B. oleracea vegetables, which not only can be used in fine mapping of important traits, comparative genomics studies, but also assisting the assembly and correction of genome sequence. 4. QTL detecting was performed using the two kinds of maps according to the repeat data of two years. A total of33QTLs distributing all cabbage nine chromosomes were mapped for the five head traits and some QTLs were clustered. Main effect QTL locus for each related traits could be stable detected between different years and different maps, indicated that they were not affected by environmental conditions. Part of repeated results about the minor site were slightly different among years and maps due to the influence of environment. The results from different years and maps complement each other.5. Aiming at the main effect and stabile QTL site of the high density SNP map, a total7candidate genes were screened according to the Brassica oleracea genome data and gene annotation results. Three of the genes participate in the synthesis of cell wall components and Ca2+channel protein, which may closely related to the cabbage HSR; the other four genes participate in the synthesis of chloroplast and chlorophyll or degradation genes, which may be closely related to the head color.