Integrating unconditional and conditional QTLs to dissect the genetic basis of stem mechanical strength in Brassica napus L


Stem mechanical strength (SMS) plays an important role in resisting stem dislodging. However, the genetic regulatory mechanisms underlying SMS in rapeseed remain unclear. In this study, a recombinant inbred line population containing 189 lines was used to investigate four SMS-related traits, namely stem breaking force (SBF), stem diameter (SD), stem weight (SW) and stem breaking strength (SBS). Accordingly, four conditional traits were also generated, namely SBF|SD, SBF|SW, SW|SD and SBS|SW. Quantitative trait locus (QTL) mapping for four unconditional SMS-related traits detected seven major QTLs, four of which were novel loci, with phenotypic contributions ranging from 10.41 to 27.22%. QTL mapping of conditional traits detected five major QTLs (including four novel loci), which explained 11.57 to 38.73% of the phenotypic variation. Comparative analyses between unconditional and conditional QTLs revealed that all 63 QTLs potentially govern biological processes (BPs) or unknown traits (UTs), which then influence SMS-related traits via 12 pathways. SBF was regulated by 13 unconditional QTLs via the QTL-BP-SD-SBF, QTL-BP-UTSD-SW-SBF, QTL-BP-SD-SW-SBF, and QTL-BP-UTSD&SW-SBF pathways, and by six conditional QTLs via the QTL-BP-SBF|SD-SBF and QTL-BP-SBF|SW-SBF pathways. SD was regulated by 18 unconditional QTLs via the QTL-BP-SD pathway, and SW by three regulatory pathways including QTL-BP-SD-SW, QTL-BP-UTSD-SW and QTL-BP-SW|SD-SW pathways. Finally, SBF potentially influences SMS via the SBF-SMS and SBF-SBS-SMS pathways. There were two additional regulatory pathways for SBS, namely QTL-BP-UTSW-SBS and QTL-BP-SBS|SW-SBS. In addition, 12 promising candidate genes were identified through multiple methods. These results contribute to our knowledge about the genetic regulatory mechanisms underlying SMS in Brassica napus.

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Fig. 1
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Fig. 3



Analysis of variance


Biological process


Confidence interval


Inclusive composite interval mapping


ICIM for additive QTL


ICIM for epistatic mapping


Logarithm of odds


Phenotypic variation


Quantitative trait locus


QTL by environment interaction


Stem breaking force


Stem breaking strength


Stem diameter


Stem mechanical strength


Stem weight


Unknown trait


Unknown trait that is highly correlated with SD


Unknown trait that is highly correlated with SW

UTSD and SW :

Unknown trait that is highly correlated with SD and SW


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We thank International Science Editing ( for editing this manuscript.


The work was supported by National Natural Science Foundation of China (31971973); the earmarked fund for China Agriculture Research System (CARS-12); Project Funded by China Postdoctoral Science Foundation (2018M630231); Open Research Fund of Key Laboratory for Biological Sciences and Genetic Improvement of Oil Crops (Ministry of Agriculture and Rural Affairs) (KF2018005); Construction Program of Biology First-class Discipline in Guizhou (GNYL[2017]009); Research Fund for Introducing Talents in Guizhou University (2018036); and Jiangsu Collaborative Innovation Center for Modern Crop Production.

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KY and WZ co-wrote the first draft of the manuscript. JZ and XW designed the project, acquired funding, and finalized the manuscript. KY and FC collected the stem segments of the AH population. KY, CS and MH investigate the phenotypic data of four SMS-related traits. YG, MZ and ET assisted and analyzed the data. All authors have reviewed and approved the final version of the manuscript and therefore are equally responsible for the integrity and accuracy of its content.

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Correspondence to Xiaodong Wang or Jiefu Zhang.

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Yu, K., Zhang, W., Guo, Y. et al. Integrating unconditional and conditional QTLs to dissect the genetic basis of stem mechanical strength in Brassica napus L. Euphytica 217, 34 (2021).

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  • Brassica napus l.
  • Unconditional QTL
  • Conditional QTL
  • Stem mechanical strength
  • Genetic mechanism