Abstract
The root of wheat consists of seminal and nodal roots. Comparatively speaking, fewer studies have been carried out on the nodal root system because of its disappearance at the early seedling stage under indoor environments. In this study, 196 accessions from the Huanghuai Wheat Region (HWR) were used to identify the characteristics of seminal and nodal root traits under different growth environments, including indoor hydroponic culture (IHC), outdoor hydroponic culture (OHC), and outdoor pot culture (OPC), for three growing seasons. The results indicated that the variation range of root traits in pot environment was larger than that in hydroponic environment, and canonical coefficients were the greatest between OHC and OPC (0.86) than those in other two groups, namely, IHC vs. OPC (0.48) and IHC vs. OHC (0.46). Most root traits were negatively correlated with spikes per area (SPA), grains per spike (GPS), and grain yield (GY), while all the seminal root traits were positively correlated with thousand-kernel weight (TKW). Genome-wide association study (GWAS) was carried out on root traits by using a wheat 660K SNP array. A total of 35 quantitative trait loci (QTLs)/chromosomal segments associated with root traits were identified under OPC and OHC. In detail, 11 and 24 QTLs were significantly associated with seminal root and nodal root traits, respectively. Moreover, 13 QTLs for number of nodal roots per plant (NRP) containing 14 stable SNPs, were distributed on chromosomes 1B, 2B, 3A, 4B, 5D, 6D, 7A, 7B, and Un. Based on LD and bioinformatics analysis, these QTLs may contain 17 genes closely related to NRP. Among them, TraesCS2B02G552500 and TraesCS7A02G428300 were highly expressed in root tissues. Moreover, the frequencies of favorable alleles of these 14 SNPs were confirmed to be less than 70% in the natural population, suggesting that the utilization of these superior genes in wheat root is still improving.
Highlights
Wheat is one of the most widely cultivated food crops all over the world, with approximately one quarter of the global agricultural area dedicated to wheat cultivation, and it is a main source of food for 30% of the people in the world (Liu et al, 2017)
The mean CVs of the nodal root system were 30.63% (IHC), 26.28% (OHC), and 36.79% (OPC). This result indicated that the variation range of root traits in the pot environment was larger than that in the hydroponic environment and the variation ranges of the nodal roots were larger than that of the seminal roots
Root correlations were low in outdoor hydroponic culture (OHC) vs. indoor hydroponic culture (IHC) and IHC vs. outdoor pot culture (OPC), and all the differences in the nodal root traits among different growth environments were very significant
Summary
Wheat is one of the most widely cultivated food crops all over the world, with approximately one quarter of the global agricultural area dedicated to wheat cultivation, and it is a main source of food for 30% of the people in the world (Liu et al, 2017). In rice, the ability of roots to penetrate strong wax layers under indoor cultivation showed limited association with accessions that present deep root systems in the field (Clark et al, 2002). The density of roots decreases exponentially with depth in the field (Fan et al, 2016), a finding that is inconsistent with many laboratory results (Jin et al, 2015; Gao et al, 2016). These results showed that it was difficult to predict root growth in the field based on laboratory experiments
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