Identification and characterization of improved nitrogen efficiency in interspecific hybridized new-type Brassica napus

Oilseed rape (Brassica napus) is an important oil crop worldwide. The aim of this study was to identify the variation in nitrogen (N) efficiency of new-type B. napus (genome ArArCcCc) genotypes, and to characterize some critical physiological and molecular mechanisms in response to N limitation. Two genotypes with contrasting N efficiency (D4-15 and D1-1) were identified from 150 new-type B. napus lines, and hydroponic and pot experiments were conducted. Root morphology, plant biomass, N uptake parameters and seed yield of D4-15 and D1-1 were investigated. Two traditional B. napus (genome AnAnCnCn) genotypes, QY10 and NY7, were also cultivated. Introgression of exotic genomic components in D4-15 and D1-1 was evaluated with molecular markers. Large genetic variation existed among traits contributing to the N efficiency of new-type B. napus. Under low N levels at the seedling stage, the N-efficient new-type D4-15 showed higher values than the N-inefficient D1-1 line and the traditional B. napus QY10 and NY7 genotypes with respect to several traits, including root and shoot biomass, root morphology, N accumulation, N utilization efficiency (NutE), N uptake efficiency (NupE), activities of nitrate reductase (NR) and glutamine synthetase (GS), and expression levels of N transporter genes and genes that are involved in N assimilation. Higher yield was produced by the N-efficient D4-15 line compared with the N-inefficient D1-1 at maturity. More exotic genome components were introgressed into the genome of D4-15 (64·97 %) compared with D1-1 (32·23 %). The N-efficient new-type B. napus identified in this research had higher N efficiency (and tolerance to low-N stress) than traditional B. napus cultivars, and thus could have important potential for use in breeding N-efficient B. napus cultivars in the field.