Abstract
Chinese cabbage (Brassica rapa L. var. pekinensis) is an important vegetable in Asia. Most Japanese commercial cultivars of Chinese cabbage use an F1 hybrid seed production system because of the high yielding cultivars produced. An efficient method for predicting hybrid performance in the parental generations is desired, and genetic distance between parental lines might be a good indicator of the level of hybrid vigor in a cross. Information concerning the genetic relationships among parental candidate inbred lines is useful for variety protection. The number of DNA markers available that can be used to assess the purity of inbred lines is limited in B. rapa. The aim of this study is to use DNA markers to assess the genetic distance between inbred lines to examine early developmental and yield heterosis so as to develop methods for selecting the best parental lines for the production of hybrids. We screened highly polymorphic SSR and CAPS markers to assess the genetic uniformity of inbred lines and characterize their genetic relationship. We examined the early size and yield heterosis in 32 F1 hybrids of Chinese cabbage. There was a moderate correlation in mid-parent heterosis between leaf size at 21days after sowing and harvested biomass but not in best-parent heterosis. In contrast there was no correlation between genetic distance and mid-parent or best-parent heterosis, indicating that genetic distance does not predict the heterosis phenotype.
Highlights
Brassica rapa L. comprises commercially important vegetable crops consumed worldwide such as leafy vegetables including Chinese cabbage, pak choi, and komatsuna, root vegetables including turnip, and oilseed
To find simple sequence repeats (SSRs) makers that can efficiently detect polymorphisms among Chinese cabbage genotypes, we screened SSR markers using an F2 population derived from an F1 hybrid cultivar
We examined the cotyledon area at 6 days after sowing (DAS) and leaf area at 14 DAS when grown on MS medium in a growth chamber of 12 F1 hybrids to confirm that both heterotic and nonheterotic hybrids are included in this sample
Summary
Brassica rapa L. comprises commercially important vegetable crops consumed worldwide such as leafy vegetables including Chinese cabbage (var. pekinensis), pak choi (var. chinensis), and komatsuna (var. perviridis), root vegetables including turnip (var. rapa), and oilseed (var. oleifera). Brassica rapa L. comprises commercially important vegetable crops consumed worldwide such as leafy vegetables including Chinese cabbage As the genome sequence of Chinese cabbage (Chiifu-401-42). ⁎ Corresponding author at: Graduate School of Agricultural Science, Kobe University, Rokkodai, Nada-ku, Kobe 657-8501, Japan. In Japan, most commercial cultivars of Chinese cabbage are F1 hybrids because of their agronomic benefits such as high yield, stress tolerance, disease resistance, and uniform phenotype. When breeding F1 hybrid cultivars, breeders developed elite pure lines (inbred lines) as parents for hybrid production. About five to seven generations of selfing and selection based on traits concerned with the breeding objective are required for developing inbred lines as parental candidates. The level of heterosis of crosses of all possible combinations of the inbred lines is used to identify suitable parents for
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