Inheritance, Association Analysis And QTL Mapping Of Main Head Traits In Cabbage (Brassica Oleracea Var. Capitata L.)

Cabbage(Brassica oleracea var. capitata L.) is cultivated widely in China. Head is the edible part which including trait of head diameter, head height, core length, head weight, head solidity, and rate of core length/head height, they are quantitative traits and vulnerable to environmental impact, and this bring more difficulties for cabbage breeding using traditional breeding methods. Core length is an important trait in cabbage. We have not good method to select, and to get materials which have short core length is difficult. In this study, the genetic effects on six head traits of cabbage were analyzed, then association analysis between markers and traits were subsequently performed, QTL IciMapping3.3 was applied in studying the quantitative trait loci (QTL) controlled six main head traits. The main results of this study are as follows:1. Two diverse advanced homozygous inbred lines of cabbage,96-100 (core lengt≤1/3) and 11-710 (core length≥2/3), were used as the parents to develop population containing P1, P2, F1, B1, B2 and F2 populations. Using mixed major gene plus polygene inheritance model, head diameter, head height, core length, head weight, head solidity and core length/head height of cabbage were investigated. The results showed that, except head solidity was controlled by one gene plus polygenes, the other five head traits were controlled by polygenes.2.Forty polymorphic EST-SSR markers were applied for the genetic structure analysis of a natural population comprised 100 cabbage inbred lines, and association analysis between markers and six head traits of cabbage were subsequently performed using GLM (general linear model) and MLM (mixed linear model) programs of TASSEL3.0 software in this study. Population genetic structure analysis showed that 100 cabbage accessions are composed of 3 subpopulations, and high polymorphism and various degree of linkage disequilibrium were detected among EST-SSR loci. There were 9 alleles of 7 markers associated with head diameter,7 alleles of 6 markers associated with head height,7 alleles of 5 markers associated with core length,4 alleles of 4 markers associated with head weight, 14 alleles of 9 markers associated with head solidity, and 3 alleles of 2 markers associated with core length/head height under GLM program. There were 3 alleles of 3 markers associated with head diameter,7 alleles of 4 markers associated with head height,4 alleles of 3 markers associated with core length,1 allele of 1 marker associated with head weight, 5 alleles of 4 markers associated with head solidity and 2 alleles of 1 marker associated with core length/head height under GLM program. Furthermore,3 alleles of 3 markers associated with head diameter,4 alleles of 3 markers associated with head height,4 alleles of 3 markers associated with core length,1 allele of 1 marker associated with head weight, 3 alleles of 4 markers associated with head solidity and 2 alleles of 1 marker associated with core length/head height were determined under GLM and MLM programs.3. Two diverse advanced homozygous inbred lines of cabbage,11-795 (corelength≥2/3) and 10-344 (core length≤ 1/3), were used as the parents to develop 188 F2 population, and SSR and InDel markers were used to construct a molecular linkage map including 227 markers in nine linkage groups, the molecular linkage map covered 795.25cM. QTL IciMapping3.3 was applied in studying the quantitative trait loci (QTL) controlled six main head traits of cabbage, the LOD value was set to 2.5. Forty-seven QTLs related the six traits were mapped, which variance explained>10%were eight (the ratio was 17.02%) in F2 population. Thirty-four QTLs related the six traits were mapped, which variance explained>10% were twenty (the ratio was 58.82%) in F2:3 population. Seventy-six QTLs related the six traits were mapped in two years and five QTLs were repeated mapped in F2 population and F2:3 population. The results of QTL on six main head traits of cabbage in F2 population and F2:3 population and association analysis between markers and traits show that, there were cross connections in Hs6.1 (Physical position:1975115-4273803bp) which was located the ninth chromosome and BoE691 (Physical position: 37680403-37680630bp) associated with head solidity, and the cross connections BoE974(Physical position:35913297-35913456 bp) maybe exist gene about core length of cabbage.