Validation Of A Quantitative Trait Locus QGWA2 For Plant Weight In Chinese Cabbage(Brassica Rapa L. Ssp. Pekinensis)

Heading-related traits are important factors affecting Chinese cabbage production.In a previous study,a plant weight QTL qGWA2 was positioned on the second chromosome in Chinese cabbage.In this study, Chinese cabbage inbred line ’501’ was used as recurrent parent for integration of qGWA2 into Chinese cabbage inbred line ’601’. Based on the molecular marker-assisted selection technology, four near-isogenic lines (NILs) containing qGWA2 locus were built. One of the four near-isogenic lines were investigated about field traits, combined with phenotypic and genotypic analysis to verify the accuracy of the qGWA2.The experimental results are concluded as following:1.We built four near-isogenic lines with qGWA2 loci,namely D483、D500、 D501 and D508-1, their background recovery rate is higher, up to 96.8%, they contains different fragment size within the target QTL region respectively.2.Near-isogenic lines D483 was identified by phenotypes and genotypes of six polymorphic markers in target QTL qGWA2 region, results show that there was a significant difference (p<0.05) between the target fragment heterozygous genotype groups and recurrent parental genotype groups.In addition, the target fragment with donor parental genotype groups also showed significant difference. The results validated the authenticity of the plant weight traits QTL qGWA2. There was not significant difference between the target fragment heterozygous genotype groups and donor parental genotype groups, So we think that there can be a pair of dominant gene controlling plant weight.3.From F3 to F3BC4 generations, we used two flanking markers cnu_m543a and cnu_m360a closely linked to qGWA2 for foregroud selection. From the beginning of F3 generations, the genetic background of recovery rate increased gradually in background selection, but did not meet expectations; to F3BC4 generations, the average recovery rate was 94.7%, higher than the expected value (93.8%), we selected 2 single plants(C133 and C200) with nice genotype and grow healthy to backcross and obtain F3BC4 generations.4.In the tested 27 F3BC4 individuals, leaving 17 individuals after foregroud seletion, using 12 unrecovered background markers to select background, four individuals D483、 D500、 D501 and D508-1 with higher background recovery rate and different fragment size within the target QTL region to selfing and obtain BC4F2 near-isogenic lines finally.5.Agronomic traits survey found that there was a significant difference (p<0.05) between F3BC2 individuals and recurrent parent’501’in plant weight、 number of outer leaves、 head weight、 head height and head diameter, moreover, there was a significant correlation between gross weight、 head weight、 head height and head diameter.