Genetic mapping and localization of a major QTL for seedling resistance to downy mildew in Chinese cabbage (Brassica rapa ssp. pekinensis) |
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Authors: | Shuancang Yu Fenglan Zhang Renbo Yu Yanmin Zou Jiani Qi Xiuyun Zhao Yangjun Yu Deshuang Zhang Li Li |
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Institution: | (1) Beijing Academy of Agriculture and Forestry Science (BAAFS), Beijing Vegetable Research Center (BVRC), Beijing, 100097, China |
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Abstract: | Downy mildew caused by the fungus Peronospora parisitica is a serious threat to members of the Brassicaceae family. Annually, a substantial loss of yield is caused by the widespread
presence of this disease in warm and humid climates. The aim of this study was to localize the genetic factors affecting downy
mildew resistance in Chinese cabbage (Brassica rapa ssp. pekinensis). To achieve this goal, we improved a preexisting genetic map of a doubled-haploid population derived from a cross between
two diverse Chinese cabbage lines, 91-112 and T12-19, via microspore culture. Microsatellite simple sequence repeat (SSR)
markers, isozyme markers, sequence-related amplified polymorphism markers, sequence-characterized amplified region markers
and sequence-tagged-site markers were integrated into the previously published map to construct a composite Chinese cabbage
map. In this way, the identities of linkage groups corresponding to the Brassica A genome reference map were established. The new map contains 519 markers and covers a total length of 1,070 cM, with an
average distance between markers of 2.06 cM. All markers were designated as A1–A10 through alignment and orientation using
55 markers anchored to previously published B. rapa or B. napus reference maps. Of the 89 SSR markers mapped, 15 were newly developed from express sequence tags in Genbank. The phenotypic
assay indicated that a single major gene controls seedling resistance to downy mildew, and that a major QTL was detected on
linkage group A8 by both interval and MQM mapping methods. The RAPD marker K14-1030 and isozyme marker PGM flanked this major
QTL in a region spanning 2.9 cM, and the SSR marker Ol12G04 was linked to this QTL by a distance of 4.36 cM. This study identified
a potential chromosomal segment and tightly linked markers for use in marker-assisted selection to improve downy mildew resistance
in Chinese cabbage. |
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Keywords: | Brassica rapa ssp pekinensis Seedling resistance to downy mildew Doubled haploid (DH) Genetic mapping QTL (quantitative trait loci) |
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