Identification Of QTL For Boron Efficiency In Brassica Napus And Development Of The Near Isogenic Line For Three QTL Clusters

Boron (B) is an essentical element for the growth and development of plants, which has the important physiological functions in plants. However, B deficiency in soils is a major agricultural problem worldwide, becoming a main limiting factor for the production of many crops. Oilseed rape (Brassica napus L.) is one main oil crop in the world, which is a high B demand species and is extremely sensitive to B deficiency. Significant genotypic vatiation was existed among the different B. napus cultivars in response to B deficiency. In this study, quantitative trait locus (QTL) for B-efficiency traits in B. napus was analyzed using the QW DH population derived from a cross between B-efficienct parent Qingyou10and B-inefficient parent Westar10, and near-isgenic lines (NILs) for major effect QTLs for B efficiency were also developped. The main results are as follows:1. QTL analysis for B-efficiency traits in B. napusThe QW DH genetic map was constructed using420simple sequence repeat (SSR) and153amplified fragment length polymorphism (AFLP) markers. The total length of this map was1923.15cM with an average marker density of0.30marker/cM and an average interval of3.35cM between adjacent markers. Phenotypes of QW DH population and their partental lines were investigated under normal B (25μM B) and low B (0.25μM B) levels by three independent solution culture trials. A total of eight traits were selected as the B-efficiency traits, including increment of primary root length (IPRL), shoot dry weight (SDW), root dry weight (RDW), shoot B concentration (SBC), root B concentration (RBC), shoot B accumulation (SBA), root B accumulation (RBA) and B efficiency coefficient (BEC). The QTLs for these eight traits were analyzed using the QW DH genetic map. A total of71QTLs were obstained, including30under normal B level,35under low B level and6for BEC, which explained single the phenotypic variation ranged from4.58%to48.34%. The QTLs distributed on eighteen linkage groups in QW DH genetic map. Moreover, the QTL clusters were observed on A3, A4, A5and C4linkage groups. QTL-cluster-A3a located in the interval of58.8-82.5cM on A3, including the QTLs for IPRL, SDW, RDW, SBA, RBA at low B level and BEC whose phenotypic varation ranged from14.80%-48.34%, was deemed as the major QTL for B efficiency of B. napus.2. Construction of high density genetic map and QTL mapping for B-efficiency traitsBased on the Brassica60K SNP BeadChip Array, a total of11,754single nucleotide polymorphism (SNP) markers were obstained in the QW DH population, classified into the1,346bins. The high density genetic map was constructed using these SNP-bins and the primary markers in the QW DH genetic map. The final high density genetic map contained1,398markers, covered2139.34cM, with an average marker density of0.65marker/cM and an average distance between adjacent markers of1.53cM. Linear relationship was observed between two genetic maps based on the commom marker. The QTL for B-efficiency traits was reanalyzed using the high density genetic map. In total,75QTLs were detected for associated with B efficiency. Of them,30QTLs were detected under normal B level,41QTLs were detected under low B level and4QTLs for BEC, respectively. Each QTL accounted for7.26%-31.56%of phenotypic variation. Among these QTLs,34were common detected across QW DH and high density genetic maps. Moreover, the QTL clusters on A3, A4and C4were also observed in high density genetic map, which located on the same chromosome regions with those observed in QW DH genetic map.3. Construction near isogenic lines of three QTL clusters for B efficiency in B. napusBased on the QTL results in QW DH population, QTL-cluster-A3a, QTL-cluster-A4and QTL-cluster-A5were selected as the target QTLs for construction the NIL. Backcross populations were constructed using B-inefficienct parent Westar10as recurrent parent. Every progenies were screened by the phenotypc investigation response to B deficiency and foreground and bachgroud analysis for high progenies, finlly, six BC4F1lines derived from a cross between BC3F1contained the different target QTLs and Westar10were used for investigation the phenotypic varation response to B deficiency. BC4F1.3, including three target QTLs simultaneously, showed the most widely variations among six lines. Substitution mapping revealed that the major QTL, QTL-cluster-A3a, was mapped in the interval between CNU384-BnGMS436.4. QTL analysis for mineral concentraions in shoot of B. napusThe mineral concentrations in shoot of QW DH population were investigated under normal B and low B levels. Compared with normal B, the concentrations of K and Mn were increased by B deficiency, however, the concentrations of P, Fe and Zn were decreased. The concentrations of Ca, Mg and Cu were not affected by B deficiency. Significant positive or negative relationships were observed among most of mineral concentrations. QTL for mineral concentrations was analyzed using QW DH genetic map. A total of28and27QTLs for macro-element concentrations and micro-element concentrations were detected, resceptively, explaining10.44%-30.97%of phenotypic variation. The co-locations of QTLs for different mineral concentrations were observed in QW DH genetic map.