Mapping of QTLs for Bolting Time in Brassica rapa (syn. campestris) under Different Environmental Conditions

Abstract

The bolting time of varieties used as leafy vegetables or turnips within the Brassica rapa (syn. campestris) species is important, because it affects the yield and quality of the harvested products. In Brassica rapa, the transition from the vegetative to reproductive phase is influenced by environmental factors, such as daylength and low temperature. In order to analyze the genetic basis of bolting time, an AFLP linkage map was constructed using doubled haploid (DH) lines derived from the F 1 hybrid between A9408 and Homei P09. QTL analysis of bolting time was performed based on the evaluation under two field conditions and three artificial conditions differing in day-length and/or temperature. Out of a total of ten QTLs detected, two QTLs showed a low temperature sensitivity. The most effective QTL, BT1, was found to be the main locus controlling the vernalization response and the allele of Homei P09 was highly responsive to low temperature compared with that of the late parent A9408. These results could be useful for marker-assisted selection and isolation of the genes responsible for bolting time in Brassica rapa.

Development of Microsatellite Markers by ISSR-suppression-PCR Method in Brassica rapa

“…Especially, in East Asia, many varieties of B. rapa are used as agronomically important vegetables. For B. rapa, several molecular linkage maps have been constructed (Song et al 1991, Chyi et al 1992, Ajisaka et al 2001, Nishioka et al 2005) and mapping of loci controlling traits of interest has been reported (Teutonico and Osborn 1995, Kole et al 1996, Ignatov et al 2000.…”

“…To integrate the isolated microsatellite markers into the genetic linkage map of B. rapa (Nishioka et al 2005), 200 doubled haploid (DH) lines derived from A9408 × Homei P09 were used.…”

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

“…In the present study, two phenotypic assessments, bolting index (BI) and flowering time (FT), served as bolting trait measurements and were used for QTL detection. Flowering time has been more frequently used for QTL mapping because of the relative ease of the measurement (Nishioka et al, 2005). QTL mapping of the flowering time trait in Brassica rapa has been previously reported in several populations (Teutonico and Osborn, 1995;Osborn et al, 1997;Lou et al, 2007;Li et al, 2009;Zhao et al, 2010;Lou et al, 2011).…”

“…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.…”

“…Some QTLs detected for the bolting trait in previous studies (Ajisaka et al, 2001;Nishioka et al, 2005;Zhang et al, 2006;Yang et al, 2007) cannot be compared to others, because the linkage groups cannot be aligned to the reference linkage groups. Of these, only a small number of the QTL mapped to the same loci, which indicates that the bolting trait appears to be affected by the environment.…”