| Boron (B) is an essential microelement for plant growth. Brassica napus needs more B for itsgrowth and it is sensitive to B deficiency. However, significant differences exist in response to Bdeficiency among various cultivars of Brassica napus. Based on the investigation of morphologicdevelopment, B uptake and accumulation in a double haploid population (TN population)derived from a cross between B-efficient parent Ningyou 7 (N) and B-inefficient parentTapidor (T) at seedling stage with solution culture under two B levels, this study was conducted toidentify QTLs (Quantitative trait loci) related to the investigated traits and detect epistaticeffects for each trait throughout the whole genome of Brassica napus L. In addition, theparents' and their population's traits on utilization of phosphorus, calcium, magnesium,iron, copper and zinc were investigated under low and normal boron availability. Themain results were shown as follows.1. Under low B level (0.0025 mg B·L-1), the B-inefficient parent's leaves gotseverely curve after one week from transplanting, but B-efficient parent Ningyou 7 grewnormally. Compared phenotypic differences between two parents on different traits,Ningyou 7 did not show better advantage than Tapidor on a few of absolute traits, such asroot length changed (RL), dry weight, B accumulation etc.; but the advantage wassignificant on B concentration and ratio of phenotypic value under low B level to thatunder normal B level. There were no great differences on phenotypes between the twoparents, but evident differences among lines of the TN population were detected, and thefrequency distribution of the observed traits all obeyed normal distribution.2. By QTL mapping software of WinQTLCart 2.5, a model based on the compositeinterval mapping, 66 QTLs significantly related to 27 traits were identified on 14 linkagegroups(LGs). LOD of the detected single QTL range from 2.37 to 10.67, with a mean of4.22, and the contribution of single QTL in explaining the phenotypic variation in thepopulation ranged from 5.34% to 21.55%, with a mean of 9.40%. Compared the locidistribution, many QTL pairs (or QTL clusters) related to different traits located nearbyor overlapped more or less on each other on the same linkage group(LG), which impliedthat the same locus on a linkage group maybe act as multifunction on B efficiency. Inaddition, QTLmapper 2.0, based on a mixed linear model, was used to detect lociinvolved in digenic interactions and Q×E interactions. A total of 75 pairs of digenicepistatic loci of the 24 traits involved additive×additive interactions and 13 pairs ofdigenic epistatic loci of RL, root weight and shoot weight had a significant interactionwith environments (P＜0.005).3. Traits of parents and their population on utilization of phosphorus (P), calcium(Ca), magnesium (Mg), iron (Fe), copper (Cu) and zinc (Zn) under different boronavailability was observed, and the results showed that B-efficient parent could transportmore Ca and Mg from root to shoot than B-inefficient parent, on trait of element concentration in shoot. But on trait of element accumulation, the ratio of Ca, Mg and Znin root to that in shoot had no significant difference between the two parents or betweenthe two B levels, which implied independence and stability of the distribution of Ca, Mgand Zn in root and shoot of the parents at a certain extent. A larger part of the absorbed Feand Cu remained in root of the parents under both of the two B levels, and the distributionof B, Cu and P in root increased under low B level, comparing with which under normalB level. By the phenotypic investigation of 96 traits related to the uptake andaccumulation of the six elements in the TN population, WinQTLCart 2.5 was used todetect QTLs related to these traits, and a total of 214 QTLs were identified on 18 linkagegroups. A total of 187 pairs of digenic epistatic loci of the traits involvedadditive×additive interactions (P＜0.005). The various pairs of epistatic loci and theirdifferent effect implied that the utilizations of mineral ions for plants were controlled bylarge scale of genetic network. |
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