Identification of quantitative trait loci controlling late bolting in Chinese cabbage (Brassica rapa L.) parental line Nou 6 gou

Abstract

To identify the genes responsible for varietal differences in bolting time in Brassica rapa, we constructed a linkage map of 220 simple sequence repeat (SSR) markers of B. rapa. To construct the map, we used F 2 progeny obtained from a cross between the late-bolting parental line Nou 6 gou (PL6) and the early-bolting parental line Nou 7 gou (A9709). The linkage map covered 875.6 cM and 10 major linkage groups. To investigate the nature of the vernalization response in the B. rapa parental lines, we examined bolting characteristics under two different conditions i.e., greenhouse and open field. Five quantitative trait loci (QTLs) that controlled bolting time were detected by experiments in greenhouse and open field. Interestingly, the QTLs identified in the greenhouse and field experiments did not map to the same loci. Three of five QTLs were colocalized with the orthologs of well-known flowering genes of Arabidopsis, including FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT). The QTLs detected in this study may provide useful information for the selection of bolting traits in Chinese cabbage breeding.

Mapping of quantitative trait loci for the bolting trait in Brassica rapa under vernalizing conditions

“…The other QTLs controlling the bolting trait on linkage group A02 were also reported, and alleles controlling late bolting that were derived from the bolting resistant parent were detected in the above-mentioned research. Most of the QTLs detected that control the bolting trait from previous studies (Lou et al, 2007;Li et al, 2009;Kakizaki et al, 2011) were found on linkage group A10, co-localized with the BrFLC 1 gene. Interestingly, all of the above-mentioned QTLs with BrFLC 1 were only detected under non-vernalized conditions.…”

“…Under natural conditions in autumn, the late bolting parent (P 1 ) used in the present study showed no significant difference compared to their F 1 , which is the opposite result observed when the plants were given low temperature treatment (data not shown). Under different conditions for a given population, QTLs detected with different positions and effects were reported in several studies (Nishiokda et al, 2005;Lou et al, 2007;Li et al, 2009;Zhao et al, 2010;Lou et al, 2011;Kakizaki et al, 2011). In general, the detection of QTLs under different environmental conditions using different phenotypic measurements is an effective method to identify the function of each candidate locus.…”

“…Until now, measuring the bolting trait in Brassica rapa has been a persistent and unresolved problem. Previous studies concerned with QTL mapping of the bolting trait used different measurements, such as the time of appearance of visible flower buds or the floral stalk (Ajisaka et al, 2001;Nishioka et al, 2005;Li et al, 2009), the time of flower stalk appearance or the height of the inflorescence or elongated stem (Li et al, 2009;Kakizaki et al, 2011), the scales of bolting measured at a single timepoint (Zhang et al, 2006;Yang et al, 2007), which depend on materials used in the various studies, growth conditions, and personal perference. Li et al (2009) used three measurements for bolting in the same population, and some of the QTLs detected mapped to a single position.…”

“…As is well known, the Brassica rapa genome contains four FLC homologs, BrFLC 1 , BrFLC 2 , BrFLC 3 (in the A03 linkage group) and BrFLC 5 (in the A03 linkage group). To date, only few QTLs have been associated with BrFLC 5 (Eric Schranz et al, 2002, Kakizaki et al, 2011 and BrFLC 3 (Lou et al, 2011). With the exception of the FLCs, other candidate genes that underlie the flowering-time QTL (Lou et al, 2007;Li et al, 2009;Kakizaki et al, 2011) have also been detected, including CLV1, FLM and LFY, and mapped to the linkage group A06.…”

“…Under three conditions, ten QTLs were identified on A02, A03, A07, A09 and A10 (Lou et al, 2011), using a RIL population with two phenotypic scores, of which, the major QTL, BtoFA10, explaining from 13 to 18% of the phenotypic variation, was mapped at the highermiddle position on linkage group A10. On the basis of two environmental-phenotypic scores in an F 2 population, five QTLs were identified on A02, A03, A07, and A10 ( Kakizaki et al, 2011), and there were no QTLs mapped to the same loci.…”