Abstract
To understand the genetic regulation of the domestication trait leafy-head formation of Chinese cabbages, we exploit the diversity within Brassica rapa. To improve our understanding of the relationship between variation in rosette-leaves and leafy heads, we phenotyped a diversity set of 152 Chinese cabbages. This showed correlation between rosette-leaf traits and both head traits and heading capacity. Interestingly, the leaf number of the mature head is not correlated to heading degree nor head shape. We then chose a non-heading pak choi genotype to cross to a Chinese cabbage to generate populations segregating for the leafy head traits. Both a large F2 (485 plants) and a smaller Doubled Haploid (88 lines) mapping population were generated. A high density DH-88 genetic map using the Brassica SNP array and an F2 map with a subset of these SNPs and InDel markers was used for quantitative trait locus (QTL) analysis. Thirty-one quantitative trait loci (QTLs) were identified for phenotypes of rosette-leaves in time and both heading degree and several heading traits. On chromosome A06 in both DH-88 and F2-485 QTLs for rosette leaf length and petiole length at different developmental days and an F2 QTL for head height co-located. Variation in head height, width and weight all correlate with variation in heading degree with co-locating QTLs, respectively, on chromosome A03, A05, and A08 in F2-485. The correlation between rosette-leaf and heading traits provides not only insight in the leaf requirements to form a head, but also can be used for selection by Chinese cabbage breeders.
Highlights
Brassica rapa is an economical important species that includes many morphotypes that are cultivated as vegetable, oil and fodder crops (Prakash and Hinata, 1980; Gómez-Campo, 1999; Hanelt, 2001)
core length (CL) and heading degree (HDe) clustered into one group and LVL, leaf area length (LL), petiole length (PL), HtO, HI, head length (HH) formed another group, with significant correlation among these traits
Identification of quantitative trait locus (QTL) and the underlying causal genes can both shed light on the mutations and pathways that were selected for during domestication, but will generate tools for breeders to select for optimal size and shape of Chinese cabbages
Summary
Brassica rapa is an economical important species that includes many morphotypes that are cultivated as vegetable, oil and fodder crops (Prakash and Hinata, 1980; Gómez-Campo, 1999; Hanelt, 2001). At the end of the rosette stage, the folding leaves (FL) are large and round with short petioles, but curve more inward and thereby form a mold for further head development. Details of leaf development are rarely described and the correlation between variation of leaves in rosette/folding stage with timing of head formation and head shape is still unclear. Several genomic studies are conducted that describe gene expression profiles during Chinese cabbage development (Wang et al, 2012, 2013; Gau et al, 2017) When these are combined with phenotyping of both the complete plant and the anatomy of leaves and meristems, our understanding of leafy head formation will increase
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
