Abstract
Plant root angle determines the vertical and horizontal distribution of roots in the soil layer, which further influences the acquisition of phosphorus (P) in topsoil. Large genetic variability for the lateral root angle (root angle) was observed in a linkage mapping population (BnaTNDH population) and an association panel of Brassica napus whether at a low P (LP) or at an optimal P (OP). At LP, the average root angle of both populations became smaller. Nine quantitative trait loci (QTLs) at LP and three QTLs at OP for the root angle and five QTLs for the relative root angle (RRA) were identified by the linkage mapping analysis in the BnaTNDH population. Genome-wide association studies (GWASs) revealed 11 single-nucleotide polymorphisms (SNPs) significantly associated with the root angle at LP (LPRA). The interval of a QTL for LPRA on A06 (qLPRA-A06c) overlapped with the confidence region of the leading SNP (Bn-A06-p14439400) significantly associated with LPRA. In addition, a QTL cluster on chromosome C01 associated with the root angle and the primary root length (PRL) in the “pouch and wick” high-throughput phenotyping (HTP) system, the root P concentration in the agar system, and the seed yield in the field was identified in the BnaTNDH population at LP. A total of 87 genes on A06 and 192 genes on C01 were identified within the confidence interval, and 14 genes related to auxin asymmetric redistribution and root developmental process were predicted to be candidate genes. The identification and functional analyses of these genes affecting LPRA are of benefit to the cultivar selection with optimal root system architecture (RSA) under P deficiency in Brassica napus.
Highlights
Oilseed rape (Brassica napus L., 2n = 38, genome AACC) is one of the most important oil crops for vegetable oil, feedstock, and biodiesel worldwide (Angelovicet al., 2013)
A total of 14 QTLs associated with lateral root number (LRN), lateral root density (LRD), and primary root length (PRL) in the agar-based growth system was detected under low P (LP) availability
A smaller lateral root angle was found in the B. napus at LP than at optimal P (OP) in the “pouch and wick” high-throughput phenotyping (HTP) system, indicating that the distribution of P in the growth medium decided root system architecture (RSA)
Summary
Agronomic P-use efficiency, physiological P-use efficiency, and P-utilization efficiency are correlated with root development and architecture traits, especially lateral root number (LRN) and length (LRL). The BnaTNDH population, derived from a P-efficient cultivar, Ningyou and a P-inefficient cultivar, Tapidor, have previously been used to investigate the root morphological traits in both an agarbased growth system (Shi L. et al, 2013) and a “pouch and wick” high-throughput phenotyping (HTP) system (Zhang et al, 2016) under low phosphate (Pi) availability. A total of 14 QTLs associated with LRN, lateral root density (LRD), and primary root length (PRL) in the agar-based growth system was detected under LP availability. In the “pouch and wick” HTP system, a total of 34 QTLs associated with the total root length, the mean LRL, PRL, LRN, and LRD were detected under a suboptimal P supply. The phenotypic variability of the lateral root angle in response to P deficiency and the underlying molecular mechanisms in B. napus are unclear at present
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