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Self-incompatibility in Brassica rapa L. is a major impediment to experimental studies on the genetic control of quantitative traits such as seed glucosinolate (GSL) content. In this paper, we report quantitative trait loci (QTL) mapping of total seed GSL content using a recombinant inbred line (RIL) population derived from two self-compatible high- and low-GSL B. rapa grown under different environmental conditions. Furthermore, quantitative genetic analysis using the parents and their F₁, F₂, B₁ (F₁ backcrossed to high-parent P₁), B₂ (F₁ backcrossed to low-parent P₂), and self-pollinated progenies of B₁ generation populations are also reported. Quantitative genetic analysis showed that additive genetic variance was consistently significant under different environments, while the dominance effect was significant under one growth condition. However, a simple additive-dominance model was inadequate to explain the segregation variation among the generation means. Nonallelic interaction effects were important in the genetic control of GSL content in early generations where the levels of heterozygosity remained high. QTL mapping detected three loci at the linkage groups A2, A7, and A9 involved in the control of this trait. These QTL individually explained 5 to 22% of total phenotypic variation. The QTL on A9 was detected in all environments and explained 22%, the greatest amount of phenotypic variation. No additive × additive gene interaction was detected based on QTL analysis, and this also largely agreed with quantitative genetic analysis. Similarly, the number of loci detected based on QTL mapping also agree with the results obtained from quantitative genetic analysis. |
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