Seedling Root Traits Research Articles

Evaluation of variation in seedling root architectural traits and their potential association with nitrogen fixation and agronomic traits in field pea accessions

AbstractRoot system architecture (RSA) plays a central role in water and nutrient acquisition in plants. Plasticity and genetic variation in RSA can be used as an adaptive strategy to optimize plant performance under variable environments. We quantified phenotypic variation for seedling RSA among 44 diverse pea (Pisum sativum L.) genotypes, including breeding lines and germplasm accessions, grown under controlled conditions for 14 days using two‐dimensional hydroponic root imaging. Root image analysis revealed significant genotypic variability among the lines for all root traits, namely root length (RL), root diameter (RD), root volume, root surface area, number of tips, network width (NW), network depth (ND), and network convex area. Significant positive correlations were observed among the evaluated root traits, ranging from 0.5 to 0.9. Pea lines were ranked based on estimated means for root traits, with lines E20, F1, and F8 showing high rankings, while E4 and F5 received low rankings for most traits. To associate root traits with nitrogen (N) fixation and field agronomic performance, we performed redundancy analysis (RDA). The quantified root traits accounted for significant variation in the agronomic traits (R2 = ∼30%, p < 0.001). RDA showed a positive association between lodging susceptibility and root system NW and between plant height and root system ND. RD was positively associated with grain yield and N fixation. N fixation was positively associated with the number of lateral roots. The findings of this study indicate that variation for seedling root traits in pea could aid selection for N fixation and other important agronomic traits.

Glutaredoxin regulation of primary root growth is associated with early drought stress tolerance in pearl millet.

Seedling root traits impact plant establishment under challenging environments. Pearl millet is one of the most heat and drought tolerant cereal crops that provides a vital food source across the sub-Saharan Sahel region. Pearl millet's early root system features a single fast-growing primary root which we hypothesize is an adaptation to the Sahelian climate. Using crop modeling, we demonstrate that early drought stress is an important constraint in agrosystems in the Sahel where pearl millet was domesticated. Furthermore, we show that increased pearl millet primary root growth is correlated with increased early water stress tolerance in field conditions. Genetics including genome-wide association study and quantitative trait loci (QTL) approaches identify genomic regions controlling this key root trait. Combining gene expression data, re-sequencing and re-annotation of one of these genomic regions identified a glutaredoxin-encoding gene PgGRXC9 as the candidate stress resilience root growth regulator. Functional characterization of its closest Arabidopsis homolog AtROXY19 revealed a novel role for this glutaredoxin (GRX) gene clade in regulating cell elongation. In summary, our study suggests a conserved function for GRX genes in conferring root cell elongation and enhancing resilience of pearl millet to its Sahelian environment.

Glutaredoxin regulation of primary root growth is associated with early drought stress tolerance in pearl millet

Seedling root traits impact plant establishment under challenging environments. Pearl millet is one of the most heat and drought tolerant cereal crops that provides a vital food source across the sub-Saharan Sahel region. Pearl millet’s early root system features a single fast-growing primary root which we hypothesize is an adaptation to the Sahelian climate. Using crop modeling, we demonstrate that early drought stress is an important constraint in agrosystems in the Sahel where pearl millet was domesticated. Furthermore, we show that increased pearl millet primary root growth is correlated with increased early water stress tolerance in field conditions. Genetics including genome-wide association study and quantitative trait loci (QTL) approaches identify genomic regions controlling this key root trait. Combining gene expression data, re-sequencing and re-annotation of one of these genomic regions identified a glutaredoxin-encoding gene PgGRXC9 as the candidate stress resilience root growth regulator. Functional characterization of its closest Arabidopsis homolog AtROXY19 revealed a novel role for this glutaredoxin (GRX) gene clade in regulating cell elongation. In summary, our study suggests a conserved function for GRX genes in conferring root cell elongation and enhancing resilience of pearl millet to its Sahelian environment.

Genetic variation and association between seedling root traits and yield in chickpea (Cicer Arietinum L.)

Genetic variation and association between seedling root traits and yield in chickpea (Cicer Arietinum L.)

Unravelling the Genetic Basis of Moisture Deficit Stress Tolerance in Wheat for Seedling Vigour-Related Traits and Root Traits Using Genome-Wide Association Study.

A key abiotic stress that negatively affects seed germination, plant development, and crop yield is moisture deficit stress. Achieving higher vigour and uniform germination under stress conditions is essential for crop establishment and productivity and to enhance the yield. Hence, revealing wheat's capacity to withstand moisture deficit stress during seed germination and early growth stages is fundamental in improving its overall performance. However, the genetic regulation of moisture deficit stress tolerance during the seed germination phase remains largely unexplored. In this study, a total of 193 wheat genotypes were subjected to simulated moisture deficit stress using PEG-6000 (-0.4 MPa) during the seed germination stage. The induced moisture deficit stress significantly reduced various seedling-vigour-related traits. The genetic regions linked to these traits were found using a genome-wide association study (GWAS). The analysis identified 235 MTAs with a significance -log10(p) value of >4. After applying the Bonferroni correction, the study identified 47 unique single nucleotide polymorphisms (SNPs) that are linked to candidate genes important for the trait of interest. The current study emphasises the effectiveness of genome-wide association studies (GWAS) in identifying promising candidate genes, improving wheat seedling vigour and root traits, and offering essential information for the development of wheat cultivars tolerant to moisture deficit stress.

Soil microbial legacy determines mycorrhizal colonization and root traits of conifer seedlings during subalpine forest succession

Soil microbial legacy determines mycorrhizal colonization and root traits of conifer seedlings during subalpine forest succession

Characterization of a Soybean (Glycine max L. Merr.) Population for Germination and Seedling Root Traits under Water Stress

Dry soil conditions at soybean planting results in poor stand establishment, which often necessitates replanting. We conducted a study to identify soybean genotypes that can maintain germination rates and possess better root morphology under water stress. We tested 41 Plant Introductions (PI) for germination and seedling root traits under controlled environmental conditions at five water potentials: 0.00, −0.27, −0.54, −0.82, and −1.09 MPa (no, low, mild, severe, and extreme water stress, respectively). The same genotypes were tested for emergence and seedling root traits under field conditions in South Carolina (2021 and 2022) and North Carolina (2022). Among the 41 genotypes evaluated, PI 398566 and PI 424605A maintained higher germination percentages (≥63%) under water stress. The same genotypes were ranked among the top 15 genotypes for root traits (total-root and fine-root (diameter between 0.25 and 0.50 mm) length, surface area, and/or volume) under water stress. Furthermore, they had relatively higher emergence percentages under field conditions (≥35% under dry soil conditions). The superior genotypes identified in this study (PI 398566 and PI 424605A) that had better germination and root morphology under water-stress and no-stress conditions and better emergence would be useful for developing varieties with drought tolerance during the emergence phase.

Effects of Liming on the Morphologies and Nutrients of Different Functional Fine Roots of Cunninghamia lanceolata Seedlings

Soil acidification is an important cause of the productivity decline of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook)—one of the most important timber species in China. Although liming is an effective measure for reversing the effects of soil acidification, the effects on the morphologies and nutrients of different functional roots remain ambiguous. Thus, this study aimed to investigate the effects of liming on fine root traits of Chinese fir seedlings between two root function types (absorptive roots (AR) and transport roots (TR)). Chinese fir seedlings with equal performance were planted in each pot with two acidification soils (pH 3.6 and pH 4.3) and three levels of liming (0, 1000, and 4000 kg CaO ha−1). Our data showed that liming had no effect on the root biomass (RB) of AR and TR in mildly acidified soil, but it decreased the RB in severely acidified soil. Specific root length (SRL) of AR and TR were significantly increased by 24% and 27% with a high liming dose in mildly acidified soil, respectively. The specific root areas (SRA) of AR and TR were significantly increased by 10% and 22% with a high liming dose in mildly acidified soil, respectively. Furthermore, root N concentrations were significantly increased by 26% and 30% in AR and TR with a high liming dose in mildly acidified soil, respectively. Root P concentration of AR was significantly increased by 21% with a high liming dose in mildly acidified soil while root Ca concentration was significantly increased with all treatments. A similar trend was also observed in the Ca/Al ratio of roots. Both low and high doses of liming decreased the root Al concentration of AR by 26% and 31% in mildly acidified soil, respectively; however, there was no significant effect on TR in both soils. Our findings indicated that liming could alleviate Al toxicity to fine roots and increase root investment efficiency and absorption capacity. Liming also had coordinate effects on SRL, SRA, Root tissue density (RTD), N, P, Ca and Ca/Al between AR and TR. Our study suggested that to gain a comprehensive understanding of plant growth strategy, researchers in future studies must consider different functional roots rather than just the absorption part. Our results also revealed that the root system became more “acquisitive” due to the remediation of Al toxicity, which may be an important mechanism underlying the increment of the productivity of Chinese fir plantations undergoing liming.

Assessing the contribution of seedling root traits to phosphorus responsiveness in wheat

Improving uptake efficiency of wheat is important to improving phosphorus (P) recovery and P efficiency. Different root traits have been suggested to be important to P efficiency but their relative importance has seldom been evaluated to identify which traits should be the focus for selection and breeding. This study characterized root traits of 10 varieties of wheat that differed in their responses to fertilizer P in multisite field trials with the aim to understand which traits were contributing to the variation in P efficiency. Seedlings were characterized for seminal and crown root angle, root length, root diameter, root hair length and rhizosheath volume. Experiments were conducted in two soils low in available P, and the effect of P availability on root traits was assessed by using two different rates of P in one experiment. Compared to the varieties that showed a large yield response to P in field trials, varieties with a low P response had narrow seminal roots angles, but wider crown root angles, longer root hairs, larger rhizosheath volume and higher rates of P uptake per unit root length. The importance of these traits to explain the variation in yield and yield response to P among the field trials differed but the root traits most consistently related to yield response were rhizosheath volume and root hair length. Root diameter was associated with grain yield without additional P but was not with response to P. Root angle did not contribute to yield at low P or P response.

QTL mapping of seedling root traits in Synthetic W7984 × Opata M85 bread wheat (Triticum aestivum L.) mapping population

Root system architecture, as a complex trait, has gained attention due to climate change and abiotic stress pressure on crops. The incorporation of root traits in breeding objectives may enable new advances in climate-resilient crops. Here, the genetics of the seedling root system architecture in the Synthetic W7984 × Opata M85 Doubled Haploid mapping population was investigated. Three traits at the seedling stage and mature stage root and shoot biomass traits were mapped for quantitative trait loci (QTL) identification. A total of five different loci on chromosomes 1B, 5A, and 7D with major effects were identified for total root length, primary root length, and seminal root growth angle. Four regions on chromosomes 2A, 5A, and 7D had colocating loci for seedling and mature stage root traits. Chromosome 5A, with a locus affecting most of the seedling root traits, is promising. The correlations between seedling and mature root traits, and newly identified QTL for seedling root traits, maybe promising to unravel the genetic structure of root traits and for the marker-assisted selection.

Genetic analysis of seedling root traits and fine mapping of the QTL <italic>qLRL4</italic> for the longest root length in rice

Genetic analysis of seedling root traits and fine mapping of the QTL <italic>qLRL4</italic> for the longest root length in rice

Genome-Wide Association Mapping of Seedling Biomass and Root Traits Under Different Water Conditions in Wheat

Drought is a major threat to global wheat production. In this study, an association panel containing 200 Chinese wheat germplasms was used for genome-wide association studies (GWASs) of genetic loci associated with eight root and seedling biomass traits under normal water and osmotic stress conditions. The following traits were investigated in wheat seedlings at the four-leaf stage: root length (RL), root number (RN), root fresh weight (RFW), root dry weight (RDW), shoot fresh weight (SFW), shoot dry weight (SDW), total fresh weight (TFW), and total dry weight (TDW). A total of 323 and 286 SNPs were detected under two water environments, respectively. Some of these SNPs were near known loci for root traits. Eleven SNPs on chromosomes 1B, 2B, 4B, and 2D had pleiotropic effects on multiple traits under different water conditions. Further analysis indicated that several genes located inside the 4 Mb LD block on each side of these 11 SNPs were known to be associated with plant growth and development and thus may be candidate genes for these loci. Results from this study increased our understanding of the genetic architecture of root and seedling biomass traits under different water conditions and will facilitate the development of varieties with better drought tolerance.

Morphological and Physiological Traits Related to the Response and Adaption of Bolboschoenus planiculmis Seedlings Grown Under Salt-Alkaline Stress Conditions.

Soil saline-alkalization is expanding and becoming a serious threat to the initial establishment of plants in inland salt marshes on the Songnen Plain in Northeast China. Bolboschoenus planiculmis is a key wetland plant in this area, and its root tubers provide food for an endangered migratory Siberian crane (Grus leucogeranus). However, the survival of this plant in many wetlands is threatened by increased soil saline-alkalization. The early establishment of B. planiculmis populations under salt and alkaline stress conditions has not been well understood. The aim of this study was to investigate the response and adaption of the seedling emergence and growth of B. planiculmis to salt-alkaline mixed stress. In this study, B. planiculmis root tubers were planted into saline-sodic soils with five pH levels (7.31–7.49, 8.48–8.59, 9.10–9.28, 10.07–10.19, and 10.66–10.73) and five salinity levels (40, 80, 120, 160, and 200 mmol⋅L–1). The emergence and growth metrics, as well as the underlying morphological and physiological traits in response to salt-alkaline stress were explored for 2-week-old seedlings. The seedling emergence, growth, and leaf and root traits showed distinct responses to the pH and salt gradients. Under the lower saline-alkaline condition (pH ≤ 9.10–9.28 and salinity ≤ 80 mmol⋅L–1), the seedling growth was substantially facilitated or not significantly altered. Salinity affected the seedlings more significantly than alkalinity did. In particular, among the salt ions, the Na+ concentration had predominantly negative effects on all the morphological and physiological traits of the seedlings. Seedling emergence was more tolerant to salinity and, based on its observed close relationships with pH and the alkaline ion CO32–, was highly alkalinity-dependent. Moreover, the leaf area and photosynthetic rate, as well as the root surface area and tip number mainly accounted for the response of the seedling biomass to salt-alkaline stress. This is evidence of the adaption of B. planiculmis to saline-alkaline conditions largely due to the responses of its morphological and physiological traits. This study provides a mechanistic process-based understanding of the early seedling establishment of B. planiculmis populations in response to increased soil saline-alkalization in natural wetlands.

Bioinspired Optimization of Germination Nutrients Based on Lactuca sativa Seedling Root Traits as Influenced by Seed Stratification, Fortification and Light Spectrums

Ecophysiological stimulators directly affect root morphology, especially in the embryonic stage. To enhance crop germination, an understanding of the root traits under abiotic inducers is needed. In this study, the combined impacts of white and red-blue light spectrums, cold stratification, and seed fortification involving various concentrations of bioactive chemicals namely simple nutrient addition program solution, gibberellic acid, α-naphthaleneacetic acid with thiamine hydrochloride were evaluated on loose-leaf lettuce (Lactuca sativa var. Altima) seedling root architecture. The growth-promoting effects of these nutrients varied the growth rate and morphology of roots which are immediately shown during the radicle development. Integrated computer vision and computational intelligence were employed for phytomorphological signatures extraction of seedlings that were cultivated in a customized modulable spectrum experimental chamber (MSPEC). Root phenotype model was developed using graph-cut segmentation and region properties, and the ideal germination nutrient concentration was optimized using bioinspired models with firefly algorithm optimal result of 204.1 mg/L for nitrate, 238.15 mg/L for phosphate, and 158.08 mg/L for potassium. It was verified that lettuce seedlings can endure highly concentrated nutrients, however, it is more sensitive to phosphate as this macronutrient significantly promotes root growth with the increased whorl number on white light spectrum exposure with cold stratification.

Cropping effect and variety adaptability of winter-seeded spring wheat in Inner Mongolia Plain irrigation area

<p indent=0mm>Growing spring wheat in Inner Mongolia is challenging because of the short growing period, dry-hot winds, and heat-forced maturity. There are also problems with growing winter wheat varieties, such as frost damage, spring droughts, or “late spring cold”. These factors have restricted efforts to increase yields. In order to cope with these challenges, this study adopted a “winter-seeded spring wheat” planting model for growing wheat in Inner Mongolia and investigated wheat varieties with different vernalization requirements through two consecutive field trials. The effects of different varieties on seed germination and seedling emergence, growth, leaf physiological, root traits, and yield formation were analyzed. The results indicated that the spring varieties and some winter varieties of the tested wheat varieties were overwintered as seed and passed the vernalization stage, and matured normally in the following year. Under winter sowing conditions, the spring field germination rate of the tested wheat varieties was lower than that of spring sowing wheat, but the root system developed, and the adaptability to low temperature and drought was stronger. Three wheat varieties suitable for winter-sowing in the Inner Mongolia plain irrigation area were screened out by systematic clustering, including the spring variety Yongliang 4, winter cultivar Ningdong 11 and semi-winter cultivar Henong 7106. Their common characteristics were higher overwintering emergence rate, stronger stress resistance, relatively well-developed root system and higher yield performance, among which, Yongliang 4 could reach the same level as spring-seeded.

Mapping Quantitative Trait Loci for Soybean Seedling Shoot and Root Architecture Traits in an Inter-Specific Genetic Population.

Wild soybean species (Glycine soja Siebold & Zucc.) comprise a unique resource to widen the genetic base of cultivated soybean [Glycine max (L.) Merr.] for various agronomic traits. An inter-specific mapping population derived from a cross of cultivar Williams 82 and PI 483460B, a wild soybean accession, was utilized for genetic characterization of root architecture traits. The objectives of this study were to identify and characterize quantitative trait loci (QTL) for seedling shoot and root architecture traits, as well as to determine additive/epistatic interaction effects of identified QTLs. A total of 16,469 single nucleotide polymorphisms (SNPs) developed for the Illumina beadchip genotyping platform were used to construct a high resolution genetic linkage map. Among the 11 putative QTLs identified, two significant QTLs on chromosome 7 were determined to be associated with total root length (RL) and root surface area (RSA) with favorable alleles from the wild soybean parent. These seedling root traits, RL (BARC_020495_04641 ~ BARC_023101_03769) and RSA (SNP02285 ~ SNP18129_Magellan), could be potential targets for introgression into cultivated soybean background to improve both tap and lateral roots. The RL QTL region harbors four candidate genes with higher expression in root tissues: Phosphofructokinase (Glyma.07g126400), Snf7 protein (Glyma.07g127300), unknown functional gene (Glyma.07g127900), and Leucine Rich-Repeat protein (Glyma.07g127100). The novel alleles inherited from the wild soybean accession could be used as molecular markers to improve root system architecture and productivity in elite soybean lines.

Use of Inoculator Bacteria to Promote Tuber melanosporum Root Colonization and Growth on Quercus faginea Saplings

Research Highlights: Mycorrhizal helper bacteria (MHB) promote mycorrhization processes and are commonly found in the mycorrhizosphere of fungi, such as the edible hypogeous fungus Tuber melanosporum Vittad. Background and Objectives: The effectiveness of MHB in promoting the mycorrhization process and the root development of Portuguese oak (Quercus faginea Lam.) seedlings destined for truffle plantations has not been determined. The main aim of this study was to shed light on the effect of bacterial inoculation on fungal root tip colonization and seedling root traits. Material and methods: We performed a co-inoculation trial using three bacteria naturally present in the T. melanosporum niche (i.e., Pseudomonas fluorescens, Pseudomonas putida, and Bacillus amyloliquefaciens) and two different bacterial inoculation times (one month and nine months after fungal inoculation) under glasshouse conditions. Results: Only P. fluorescens had a significant mycorrhizal promoter effect, increasing the truffle inoculation rates of root tips by more than 10% compared with seedlings that received non-bacterial inoculation treatments. Simultaneously, the co-inoculation of P. fluorescens with T. melanosporum improved seedling root growth parameters compared with those of seedlings that received non-bacterial inoculation treatments. The different bacterial inoculation times and applications of uninoculated bacterial growth media did not affect the root traits analyzed or the root mycorrhization rates. Conclusions: These results suggest that P. fluorescens bacteria have a potential commercial application as a treatment for truffle-inoculated seedlings to improve both seedling quality and mycorrhizal colonization under nursery conditions.

From lab to field: Open tools facilitating the translation of maize root traits

Abstract Variation of root traits is associated with soil resource acquisition under abiotic stresses. However, plant breeding programs targeting beneficial root traits are hampered by lacking appropriate phenotyping tools. The availability of high-throughput root phenotyping technologies for seedlings as well as for mature plants grown in the field enabled us to investigate trait translation from the lab to the field. Here we used the established phenotyping techniques Rhizoslides, Shovelomics, and the image-based root phenotyping software, Digital Imaging of Root Traits (DIRT) to phenotype root traits of thirty seedlings and mature maize donor lines from the Drought Tolerance Maize for Africa (DTMA) project. The experiments were carried out in a controlled-environment and a field trial under well-watered and drought conditions. We found significant correlation between seedlings seminal and crown root number in the field (r = 0.68). Primary root branching of seedlings was negatively correlated with crown root branching of field-grown plants (r=-0.54). Our study showed indirect translation of traits between primary root length (r = 0.29) and primary root branching (r = 0.20) with plant performance in the field under drought. Our results suggest that root traits of maize seedlings are predictive for mature maize root traits and plant performance in the field. Our findings suggest that using open tools for high-throughput root phenotyping to screen in maize seedling could be beneficial for breeding programs and paves a cost-efficient way for plant improvement and breeding programs in developing countries.

Heterotic loci analysis for root traits of maize seedlings using an SSSL test population under different nitrogen conditions

Exploitation of heterosis is an efficient strategy to increase crop production, improve quality, and enhance resistance to biotic and abiotic stresses. However, heterosis shows significant genetic × environment effects. Nitrogen is an important nutrient that affects crop development and grain yield. Hybrid maize performs significantly and differently depending on the nitrogen conditions, but the genetic basis of maize heterosis under different nitrogen conditions is unclear. In this study, a test population comprising a set of single segment substitution lines (SSSLs) was used to identify heterotic loci (HL) for root-related traits of maize seedlings under two nitrogen conditions. We identified 80 HL for the root system and related traits in maize seedlings, consisting of 16, 18, 10, 11, 11, and 14 HL associated with root length (RL), root surface area (RSA), root average diameter (RAD), shoot dry weight (SDW), root dry weight (RDW), and plant height (PH), respectively. Among them, 13% of the HL were detected under both nitrogen conditions simultaneously, including the HLs hRL1b, hRL7, hRL9, hRSA7a, hRSA9a, hRAD1a, hSDW6, hSDW7a, hSDW7b, and hPH6a, but most of the HLs (87%) were not detected under both nitrogen conditions. The results indicated that, in maize, heterosis also exists in the interaction between genotype and nitrogen level.

Variation Analysis of Root System Development in Wheat Seedlings Using Root Phenotyping System

Root system architecture is a vital part of the plant that has been shown to vary between species and within species based on response to genotypic and/or environmental influences. The root traits of wheat seedlings are critical for their establishment in soil and evidently linked to plant height and seed yield. However, plant breeders have not efficiently developed the role of RSA in wheat selection due to the difficulty of studying root traits. We set up a root phenotyping platform to characterize RSA in 34 wheat accessions. The phenotyping pipeline consists of the germination paper-based moisture replacement system, image capture units, and root-image processing software. The 34 accessions from two different wheat ploidy levels (hexaploids and tetraploids), were characterized in ten replicates. A total of 19 root traits were quantified from the root architecture generated. This pipeline allowed for rapid screening of 340 wheat seedlings within 10 days. At least one line from each ploidy (6× and 4×) showed significant differences (p &lt; 0.05) in measured traits, except for mean seminal count. Our result also showed a strong correlation (0.8) between total root length, maximum depth and convex hull area. This phenotyping pipeline has the advantage and capacity to increase screening potential at early stages of plant development, leading to the characterization of wheat seedling traits that can be further examined using QTL analysis in populations generated from the examined accessions.