Different genetic determinants were involved in controlling seed yield and yield-related traits in B. napus under normal and low P conditions. The QTLs detected under reduced P supply may provide useful information for improving the seed yield of B. napus in soils with low P availability in marker-assisted selection.

BackgroundOilseed rape (Brassica napus L.) is one of the most important oil crops. A primary limitation to the cultivation of this crop is the lack of available phosphorus (P) in soils. To elucidate the genetic control of P deficiency tolerance in Brassica napus, quantitative trait locus (QTL) for seed yield and yield related-traits in response to P deficiency were identified using a double haploid mapping population (TN DH) derived from a cross between a P-efficient cultivar, Ningyou 7 and a P-inefficient cultivar, Tapidor.ResultsThree field trials were conducted to determine seed yield (SY), plant height (PH), number of primary branches (BN), height to the first primary branch (FBH), relative first primary branch height (RBH), pod number per plant (PN), seed number per pod (SN) and seed weight of 1,000 seeds (SW) in 188 lines of TN DH population exposed to low P (LP) and optimal P (OP) conditions. P deficiency decreased PH, BN, SN, PN and SY, and increased FBH and RBH with no effect on SW. Three reproducible LP-specific QTL regions were identified on chromosomes A2, A3 and A5 that controlled SN, PN and SW respectively. In addition, six reproducible constitutive regions were also mapped with two each for SY-LP on A2, and FBH-LP on C6 and one each for PH-LP and SW-LP on A3. About 30 markers derived from 19 orthologous genes involved in Arabidopsis P homeostasis were mapped on 24 QTL regions by comparative mapping between Arabidopsis and Brassica napus. Among these genes, GPT1, MGD2 and SIZ1 were associated with two major loci regulating SY-LP and other yield-related traits on A2 between 77.1 and 95.0 cM.ConclusionThe stable QTLs detected under LP conditions and their candidate genes may provide useful information for marker-assisted selection in breeding high-yield B. napus varieties with improved P efficiency.

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High yield is the most important goal in crop breeding, and boron (B) is an essential micronutrient for plants. However, B deficiency, leading to yield decreases, is an agricultural problem worldwide. Brassica napus is one of the most sensitive crops to B deficiency, and considerable genotypic variation exists among different cultivars in response to B deficiency. To dissect the genetic basis of tolerance to B deficiency in B. napus, we carried out QTL analysis for seed yield and yield-related traits under low and normal B conditions using the double haploid population (TNDH) by two-year and the BQDH population by three-year field trials. In total, 80 putative QTLs and 42 epistatic interactions for seed yield, plant height, branch number, pod number, seed number, seed weight and B efficiency coefficient (BEC) were identified under low and normal B conditions, singly explaining 4.15–23.16% and 0.53–14.38% of the phenotypic variation. An additive effect of putative QTLs was a more important controlling factor than the additive-additive effect of epistatic interactions. Four QTL-by-environment interactions and 7 interactions between epistatic interactions and the environment contributed to 1.27–4.95% and 1.17–3.68% of the phenotypic variation, respectively. The chromosome region on A2 of SYLB-A2 for seed yield under low B condition and BEC-A2 for BEC in the two populations was equivalent to the region of a reported major QTL, BE1. The B. napus homologous genes of Bra020592 and Bra020595 mapped to the A2 region and were speculated to be candidate genes for B efficiency. These findings reveal the complex genetic basis of B efficiency in B. napus. They provide a basis for the fine mapping and cloning of the B efficiency genes and for breeding B-efficient cultivars by marker-assisted selection (MAS).

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Brassica napus is an important oilseed and fodder crop grown throughout the world. Although it is widely grown, little is known about the molecular basis of phosphorus (P) homeostasis for this species. In this research, a population of 124 recombinant inbred lines (RILs) (designated as BE-RIL) derived from a cross between P-inefficient cv. 'B104-2' and P-efficient cv. 'Eyou Changjia' was used to construct a genetic map of P homeostasis genes. A set of gene-based markers (GBMs) was developed from functional genes involved in Arabidopsis thaliana P homeostasis. In total, 46 GBMs corresponding to 26 genes, assigned to eight functional categories, were integrated into the BE-RIL map. A total of 243 simple sequence repeat (SSR) markers were developed from 171 bacterial artificial chromosome (BAC) end sequences and/or B. rapa seed BAC sequences. Of these SSR markers, 74 were added to the BE-RIL map. Based on the newly constructed genetic map, comparative genetic analysis between A. thaliana and B. napus was performed.A total of 90 conserved genomic blocks were aligned between A. thaliana pseudochromosomes and the BE-RIL linkage groups. According to physical positions on the Arabidopsis genome, 1223 orthologs of 356 genes involved in Arabidopsis P homeostasis were mapped onto syntenic blocks and insertion segments. This high-density genetic map will be useful for identifying quantitative trait loci (QTL) that control P homeostasis and putative candidate genes for the efficient use of P in B. napus.

A semi‐nested polymerase chain reaction (snPCR) assay was developed for the rapid detection of resistant/susceptible BF haplotypes to Marek’s disease (MD) using the cDNA samples from peripheral blood leucocytes, liver, spleen and heart from Xiayan homozygous chickens: A11, C23, D8 and D12 (resistant to MD), A5 and B21 (susceptible to MD). The snPCR was utilized to span alternative splicing‐out of the sequence encoding the second segment of the cytoplasmic part of the mature BF molecules (exon 7). This alternative exon 7 splice variant was detected in BF*A5 and BF*B21 (susceptible to MD), but not in the MD‐resistant BF*A11, BF*C23, BF*D8 and BF*D12 haplotypes, suggesting a potential role of exon 7 for the detection of resistant/susceptible BF haplotypes to MD.