High-throughput root phenotyping screens identify genetic loci associated with root architectural traits in Brassica napus under contrasting phosphate availabilities

Abstract

Background and aims: Phosphate (Pi) deficiency in soils is a major limiting factor for crop growth worldwide. Plant growth under low Pi conditions correlates with root architectural traits and it may therefore be possible to select these traits for crop improvement. The aim of this study was to characterize root architectural traits, and to test quantitative trait loci (QTL) associated with these traits, under low Pi (LP) and high Pi (HP) availability in Brassica napus.

Methods: Root architectural traits were characterized in seedlings of a double haploid (DH) mapping population (n = 190) of B. napus ['Tapidor' × 'Ningyou 7' (TNDH)] using high-throughput phenotyping methods. Primary root length (PRL), lateral root length (LRL), lateral root number (LRN), lateral root density (LRD) and biomass traits were measured 12 d post-germination in agar at LP and HP.

Key results: In general, root and biomass traits were highly correlated under LP and HP conditions. 'Ningyou 7' had greater LRL, LRN and LRD than 'Tapidor', at both LP and HP availability, but smaller PRL. A cluster of highly significant QTL for LRN, LRD and biomass traits at LP availability were identified on chromosome A03; QTL for PRL were identified on chromosomes A07 and C06.

Conclusions: High-throughput phenotyping of Brassica can be used to identify root architectural traits which correlate with shoot biomass. It is feasible that these traits could be used in crop improvement strategies. The identification of QTL linked to root traits under LP and HP conditions provides further insights on the genetic basis of plant tolerance to P deficiency, and these QTL warrant further dissection.

Keywords: Brassica napus; Phosphate; QTL; biomass; genetic; heritability; oilseed rape; phosphorus; root.

Fig. 1.

Changes in shoot dry weight (A), root dry weight (B), primary root length (C), lateral root length (D), lateral root number (E) and lateral root density (F) in ‘Tapidor’ and ‘Ningyou 7’ at different external Pi concentrations. Seedlings were grown on trays containing 300 mL 0·8 % (w/v) agar and a modified basal salt mix with 0, 0·006, 0·312, 0·625 or 1·25 mm P for 8 d and images of root systems analysed for root traits. Symbols represent means ± s.e.m. (n = 4).

Fig. 2.

Variation in shoot dry weight (A), root dry weight (B) primary root length (C), lateral root length (D), lateral root number (E) and lateral root density (F) in the ‘Tapidor’ × ‘Ningyou 7’ double haploid (TNDH) mapping population. Seedlings were grown on trays containing 300 mL 0·8 % (w/v) agar and a modified basal salt mix with 0 (LP) or 0·625 (HP) mm P for 12 d. Data are REML-estimated means (n varies between 4 and 16, average 11 observations per line per treatment). Symbols ‘T’ and ‘N’ represent the mapping population parental values for ‘Tapidor’ and ‘Ningyou 7’, respectively. The continuous line represents the 1 : 1 line.