Detection of QTL for phosphorus efficiency at vegetative stage in Brassica napus

Phosphorus (P) deficiency in soils is a major limiting factor for plant growth worldwide. Plants have developed adaptive strategies in response to P deficiency. The objective of this study was to map quantitative trait loci (QTL) for P efficiency using a recombinant inbred (RI) population consisting of 124 lines derived from a cross between Brassica napus P-inefficient cv. B104-2 and P-efficient cv. Eyou Changjia. Six traits (shoot dry weight, root dry weight, root/shoot ratio, P concentration, shoot P uptake and shoot P use efficiency) at vegetative stage were examined under high P (HP, 1 mM) and low P (LP, 5 mu M) conditions during three separate experimental trial periods. Their relative values (i.e., the ratio of a trait value under the LP condition to that under the HP condition) of these six traits were also determined. Eyou Changjia produced more biomass and acquired more P under the LP condition and, thus, had a higher relative dry weight and relative P uptake than B104-2, indicating Eyou Changjia was high P efficiency. A total of 71 QTL were detected on 13 linkage groups, including 28 QTL under the LP condition, 22 QTL under the HP condition and 21 QTL for relative traits. Nineteen and nine QTL were specific for the LP and HP conditions, respectively, suggesting that different mechanisms existed under the two P condition. Twelve of the twenty-one QTL for relative traits co-localized with QTL identified under the two P conditions. In addition, 18 orthologous genes involved in the P metabolic pathway of Arabidopsis were in silico mapped to the QTL confidence intervals identified in B. napus by comparative genomic analysis. These QTL and their corresponding candidate genes should be further investigated to better understand P efficiency in B. napus.