Root Architecture Of Seedlings Research Articles

Genotypic variation and covariation in wheat seedling seminal root architecture and grain yield under field conditions.

Greater embryo size in a large and carefully phenotyped mapping population was genetically associated with a greater number of longer seminal roots to increase grain yield in droughted field environments. Breeding modification of root architecture is challenging in field environments owing to genetic and phenotypic complexity, and poor repeatability with root sampling. Seeds from a large mapping population varying in embryo size were harvested from a common glasshouse and standardised to a common size before assessing in rolled germination paper at 12 and 20 °C for seedling growth. Differences in genotype means were large and heritabilities high (h2 = 0.55-0.93) indicating strong and repeatable genotypic differences for most root traits. Seminal roots 1 to 3 were produced on all seedlings, whereas growth of seminal roots 4, 5 and 6 was associated with differences in embryo size. Increases in seminal root number from 4 to 6 per plant were strongly, genetically correlated with increases in total seminal length (rg = 0.84, < 0.01). Multivariate analysis confirmed initiation and growth of seminal roots 1, 2 and 3, and of roots 4, 5 and 6 behaved as genetically independent (rPg = 0.15ns) cohorts. Tails representing extremes in seedling root length and number were associated with significant differences in grain yield of up to 35% in droughted field environments but were not different in irrigated environments. Increases in grain yield were linked to greater lengths of seminal roots 4, 5 and 6 and were largely independent of plant height or development. This is the first report on the genetic relationship of seedling root architecture and embryo size, and potential in selection of seminal root size for accessing deep-soil moisture in droughted environments.

Phenotyping cowpea for seedling root architecture reveals root phenes important for breeding phosphorus efficient varieties

AbstractCowpea (Vigna unguiculata L. Walp.) is a key climate‐resilient legume for food security, especially in sub‐Saharan Africa. Cowpea yields are limited by edaphic stresses including drought and low phosphorus (P) availability. Identifying genotypes with advantageous root phenotypes can facilitate breeding for improved yield in marginal environments. We evaluated 50 elite genotypes from African and U.S. sources for seedling root architecture and root hair length and density. Significant genotypic variation was detected for all phenes, and high heritability was observed for architectural phenotypes including primary root length (77%), basal root number (72%), and taproot branching density (67%). Moderate heritability was detected for root hair length and density among different root classes (34 to 63%), which were positively associated with each other. Principal component analysis identified three clusters, primarily defined by seed dimension and seedling root architecture. Genotypes were identified with longer root hairs (TVu‐7778, Vita7, and Sanzi) and longer taproots (IT96D‐610, IT98K‐111‐1, and IT97K‐499‐35), as potential parents. Root phenotypes, grain, and fodder yield were assessed on a subset of 20 genotypes under contrasting P availability in the field. Some seedling root phenotypes were significantly related to mature plant dry fodder weight (taproot hair density) and to grain yield (lateral root hair density) under low P. Root hairs are positively related to plant productivity under low P. We suggest selection for longer primary roots, as more basal and lateral root roots may be beneficial for cowpea in drought and low P environments. These findings suggest seedling root phenotypes can support cowpea breeding for suboptimal environments.

Morpho-physiological characterization coupled with expressional accord of exclusion mechanism in wild and cultivated lentil under aluminum stress.

Aluminum stress deteriorates lentil production under acidic soils. Enhanced insight into Al tolerance traits is needed to improve its productivity. Therefore, Al-resistant (L-4602, PAL-8) and Al-sensitive (BM-4, EC-223229) cultivars along with a resistant wild (ILWL-15) were characterized for morpho-physiological traits viz. seedling root architecture (SRA), Al accumulation, and localization via fluorescent and non-fluorescent staining under control and Al-treated conditions. Also, antioxidant activities and organic acid secretion were quantified, and expressions of 10 associated genes were analyzed. Roots of Al-resistant cultivars and wild genotype showed higher root growth, antioxidant enzyme activities, and organic acid secretion than Al-sensitive ones. Among these traits, higher organic acid secretion was influenced by enhanced expression of genes, especially-aluminum sensitive-3 (ALS 3), aluminum-activated malate transporter (ALMT), multidrug and toxic compound extrusion (MATE), citrate synthase (CS), and phospho enol pyruvate carboxylase (PEPC)-which helped in reducing Al and callose accumulation. These genes were located on lentil chromosomes via sequence alignment with lentil draft genome. A strong link between morpho-physiological variation and organic acid secretion was noted which reinforced the prominence of exclusion mechanism. It was complemented by enhanced antioxidant activities at seedling stage which mitigated Al stress effects on SRA. Wild outperformed over cultivars indicating its impregnable evolution which can be exploited to better understand tolerance mechanisms. Al-resistant cultivars had significantly higher seed yield than Al-sensitive and national checks on Al-toxic fields, confirming-tolerance is sustained till reproductive stage in lentil. This study elucidated role of gene families in eliminating Al toxicity that will assist breeders to formulate strategies for developing Al-resistant cultivars.

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.

Effect of Grain Size on The Root System Architecture of Bread Wheat (Triticum aestivum L.)

The aim of this study was to investigate the role of grain size on seedling root architecture. Ten different breadwheat cultivars were selected to examine the effect of grain size on primary root traits under controlled conditions. Seminalroot traits were tested with germination papers at the growth stage 1. Significant differences between seminal root number,total seminal root length, longest root length, and root growth angle were observed among 10 cultivars. The seminal rootnumber per plant was found to be 3.93 in the large, 3.71 in the medium and 3.20 in the small grain groups. Similar rankingsin the seminal root length were observed, while root growth angle did not follow the same trend. The study suggested that thecultivar Atay 85 with superior primary root traits can be an advantage, especially in regions where plants achieve an advantageat a deep soil water level, under water stress at early growth stages.

Unearthing the Plant Growth-Promoting Traits of Bacillus megaterium RmBm31, an Endophytic Bacterium Isolated From Root Nodules of Retama monosperma.

Plants live in association with complex populations of microorganisms, including Plant Growth-Promoting Rhizobacteria (PGPR) that confer to plants an improved growth and enhanced stress tolerance. This large and diverse group includes endophytic bacteria that are able to colonize the internal tissues of plants. In the present study, we have isolated a nonrhizobial species from surface sterilized root nodules of Retama monosperma, a perennial leguminous species growing in poor and high salinity soils. Sequencing of its genome reveals this endophytic bacterium is a Bacillus megaterium strain (RmBm31) that possesses a wide range of genomic features linked to plant growth promotion. Furthermore, we show that RmBm31 is able to increase the biomass and positively modify the root architecture of seedlings of the model plant species Arabidopsis thaliana both in physical contact with its roots and via the production of volatile organic compounds. Lastly, we investigated the molecular mechanisms implicated in RmBm31 plant beneficial effects by carrying out a transcriptional analysis on a comprehensive set of phytohormone-responsive marker genes. Altogether, our results demonstrate that RmBm31 displays plant growth-promoting traits of potential interest for agricultural applications.

Tree Seedling Root Architecture Alteration by Tap Root Pruning1

Abstract Nursery production of strong taprooted woody plants typically includes pruning to interrupt taproot development. To discern the impact this practice could have on seedling root architecture, we quantified changes to root architecture after taproot pruning and restriction separately in Catalpa (Catalpa speciosa) and Kentucky coffee tree (Gymnocladus dioicus). Taproot pruning resulted in a large and significant increase in the number of new, vertically oriented roots from the cut end of the primary root (regenerated taproots) in both species. Catalpa seedlings, which produced many strong laterals on unpruned taproots, showed greater reduction in lateral root number and size after taproot pruning than Kentucky coffee tree (with fewer and smaller natural lateral roots). The two species responded differently to restriction of the single, unpruned taproot by container depth (15, 30, 60 cm). For catalpa, with more shallow laterals naturally, the number of laterals was not significantly changed by restriction of the taproot by air pruning at any container depth, but lateral diameter was reduced by the 15 cm-deep container and biomass was reduced by the 30 cm-deep container, compared to the 60 cm-deep container. For Kentucky coffee tree with fewer natural laterals, restricting the taproot at 15 cm significantly increased the number and diameter of lateral roots compared to the 30 and 60 cm-deep containers, suggesting that restricting the taproot could increase the number of laterals in species that naturally produce fewer. Restricting multiple taproots on root-pruned plants generally did not affect lateral root development for either species, but this may have been due to the low number of lateral roots on those root systems. Index words: root architecture, nursery production, urban soils Species used in this study: Catalpa [Catalpa speciosa (Warder) Warder ex Engelm. ]; Kentucky coffee tree [Gymnocladus dioicus (L.) K. Koch]

Seedling root architecture and its relationship with seed yield across diverse environments in Phaseolus vulgaris

Seedling root phenotypes may have important impacts on fitness and are more easily measured than mature root phenotypes. We phenotyped the roots of 577 genotypes of common bean (Phaseolus vulgaris), representing the bulk of the genetic diversity for recent cultivars and landraces in this species. Root architectural phenotypes of seedlings germinated for nine days were compared to root architectural phenotypes in the field as well as seed yield across 51 environments with an array of abiotic stresses including drought, nutrient deficiency, and heat, as well as non-stress conditions. We observed repeatability ranging from 0.52–0.57 for measures of root phenotypes in seedlings, significant variation in root phene states between gene pools and races, relationships between seedling and field phenotypes, and varying correlations between seedling root phenes and seed yield under a variety of environmental conditions. Seed yield was significantly related to seedling basal root number in 22% of environments, seedling adventitious root abundance in 35% of environments, and seedling taproot length in 12% of environments. Cluster analysis grouped genotypes by their aggregated seedling root phenotype, and variation in seed yield among these clusters under non-stress, drought, and low fertility conditions was observed. These results highlight the existence and influence of integrated root phenotypes for adaptation to edaphic stress, and suggest root phenes have value as breeding targets under real-world conditions.

Root system size response of bzh semi-dwarf oilseed rape hybrids to different nitrogen levels in the field.

Background and AimsIn oilseed rape (Brassica napus) semi-dwarf hybrid varieties from crosses between bzh dwarf and normal-type lines are of increasing interest. They have improved nitrogen (N) uptake, N-utilization and N-use efficiency compared to normal types. This study aimed to elucidate whether these N-related effects can be explained by the bzh shoot growth-type alone or also by differences in root traits.MethodsRoot system size was measured using root electrical capacitance (EC) in field trials with two N levels in two sets of genotypes segregating for the bzh-locus: (1) 108 doubled haploid (DH) test hybrids in two seasons, 2010–2012, and (2) 16 near-isogenic hybrids in the 2016–17 season. Quantitative trait loci (QTL) for root EC were estimated in DH test hybrids. Seedling root architecture parameters were monitored in vitro.Key Results In vitro root growth showed a higher root: shoot ratio in bzh semi-dwarf hybrids. Root EC in field trials was higher at high N supply than at zero N fertilization. In most trials semi-dwarf hybrids had higher EC than normal-type hybrids, but they reduced root EC in response to N limitation more than normal types. Root EC was more heritable at the end of flowering (h2 = 0.73) than at the beginning of flowering (h2 = 0.36) in near-isogenic hybrids and had a lower heritability in trials of DH test hybrids (h2 = 0.27). A QTL for root EC in the genomic region of the bzh-locus on linkage group A06 was significant at zero N fertilization.ConclusionsRoot EC proved to be a meaningful method in oilseed rape breeding programmes targeting root system size. The greater reduction of semi-dwarf root EC compared to the normal type under low N supply with simultaneous increase in N efficiency implies that in roots it is not a question of ‘the more the merrier’ and that the bzh root system reacts highly economically when N is scarce.

Early root growth and architecture of fast- and slow-growing Norway spruce (Picea abies) families differ-potential for functional adaptation.

The relationship between the growth rate of aboveground parts of trees and fine root development is largely unknown. We investigated the early root development of fast- and slow-growing Norway spruce (Picea abies (L.) H. Karst.) families at a developmental stage when the difference in size is not yet observed. Seedling root architecture data, describing root branching, were collected with the WinRHIZO™ image analysis system, and mixed models were used to determine possible differences between the two growth phenotypes. A new approach was used to investigate the spatial extent of root properties along the whole sample root from the base of 1-year-old seedlings to the most distal part of a root. The root architecture of seedlings representing fast-growing phenotypes showed ~30% higher numbers of root branches and tips, which resulted in larger root extensions and potentially a better ability to acquire nutrients. Seedlings of fast-growing phenotypes oriented and allocated root tips and biomass further away from the base of the seedling than those growing slowly, a possible advantage in nutrient-limited and heterogeneous boreal forest soils. We conclude that a higher long-term growth rate of the aboveground parts in Norway spruce may relate to greater allocation of resources to explorative roots that confers a competitive edge during early growth phases in forest ecosystems.

Pseudomonas fluorescens Transportome Is Linked to Strain-Specific Plant Growth Promotion in Aspen Seedlings under Nutrient Stress.

Diverse communities of bacteria colonize plant roots and the rhizosphere. Many of these rhizobacteria are symbionts and provide plant growth promotion (PGP) services, protecting the plant from biotic and abiotic stresses and increasing plant productivity by providing access to nutrients that would otherwise be unavailable to roots. In return, these symbiotic bacteria receive photosynthetically-derived carbon (C), in the form of sugars and organic acids, from plant root exudates. PGP activities have been characterized for a variety of forest tree species and are important in C cycling and sequestration in terrestrial ecosystems. The molecular mechanisms of these PGP activities, however, are less well-known. In a previous analysis of Pseudomonas genomes, we found that the bacterial transportome, the aggregate activity of a bacteria's transmembrane transporters, was most predictive for the ecological niche of Pseudomonads in the rhizosphere. Here, we used Populus tremuloides Michx. (trembling aspen) seedlings inoculated with one of three Pseudomonas fluorescens strains (Pf0-1, SBW25, and WH6) and one Pseudomonas protegens (Pf-5) as a laboratory model to further investigate the relationships between the predicted transportomic capacity of a bacterial strain and its observed PGP effects in laboratory cultures. Conditions of low nitrogen (N) or low phosphorus (P) availability and the corresponding replete media conditions were investigated. We measured phenotypic and biochemical parameters of P. tremuloides seedlings and correlated P. fluorescens strain-specific transportomic capacities with P. tremuloides seedling phenotype to predict the strain and nutrient environment-specific transporter functions that lead to experimentally observed, strain, and media-specific PGP activities and the capacity to protect plants against nutrient stress. These predicted transportomic functions fall in three groups: (i) transport of compounds that modulate aspen seedling root architecture, (ii) transport of compounds that help to mobilize nutrients for aspen roots, and (iii) transporters that enable bacterial acquisition of C sources from seedling root exudates. These predictions point to specific molecular mechanisms of PGP activities that can be directly tested through future, hypothesis-driven biological experiments.

Genome-wide association analysis of seedling root development in maize (Zea mays L.).

BackgroundPlants rely on the root system for anchorage to the ground and the acquisition and absorption of nutrients critical to sustaining productivity. A genome wide association analysis enables one to analyze allelic diversity of complex traits and identify superior alleles. 384 inbred lines from the Ames panel were genotyped with 681,257 single nucleotide polymorphism markers using Genotyping-by-Sequencing technology and 22 seedling root architecture traits were phenotyped.ResultsUtilizing both a general linear model and mixed linear model, a GWAS study was conducted identifying 268 marker trait associations (p ≤ 5.3×10-7). Analysis of significant SNP markers for multiple traits showed that several were located within gene models with some SNP markers localized within regions of previously identified root quantitative trait loci. Gene model GRMZM2G153722 located on chromosome 4 contained nine significant markers. This predicted gene is expressed in roots and shoots.ConclusionThis study identifies putatively associated SNP markers associated with root traits at the seedling stage. Some SNPs were located within or near (<1 kb) gene models. These gene models identify possible candidate genes involved in root development at the seedling stage. These and respective linked or functional markers could be targets for breeders for marker assisted selection of seedling root traits.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1226-9) contains supplementary material, which is available to authorized users.

Studying Shoot and Root Architecture and Growth of Quercus ithaburensis subsp. macrolepis Seedlings; a Key Factor for Successful Restoration of Mediterranean Ecosystems

Quercus ithaburensis subsp. macrolepis is a species of high ecological importance. It forms some of the few deciduous oak forests in the eastern Mediterranean zone, is well adapted to Mediterranean conditions and warm dry periods, develops a deep root system, regenerates easily after fire and is used in many restoration projects. However, information on the nursery production method of Quercus macrolepis seedlings and the growth and architectural development of these produced seedlings is limited. In order to select the best cultivation method to produce high quality seedlings, the objectives of this study were to a) investigate shoot and root architecture of seedlings of Quercus ithaburensis subsp. macrolepis and b) compare the growth rates of the seedlings which were grown as bareroot (i. e. propagated in raised beds) vs. containerized in the nursery. The results of the study showed that both aboveground and belowground morphological characteristics and growth rates of container Quercus ithaburensis subsp. macrolepis seedlings outperformed those of bareroot ones. Shoot height, root collar diameter, shoot and root growth rates, number of first order lateral roots and the tap root of the container seedlings, showed significantly higher values than those of the bareroot seedlings. The high number of first order roots and the long central root of containerized seedlings would facilitate seedlings’ uptake of soil water and nutrients and confirm that they have a better chance of survival in degraded areas. However, the results obtained are not enough to discourage the production of Quercus macrolepis bareroot seedlings. The influence of root pruning, seedbed density and fertilization on the bareroot seedlings quality, deserve future investigation.

Binucleate Rhizoctonia (Ceratorhiza spp.) as non-mycorrhizal endophytes alter Pinus sylvestris L. seedling root architecture and affect growth of rooted cuttings

The main aim of this study was to assess critically the effects of binucleate Rhizoctonia (BnR) inoculation on Scots pine (Pinus sylvestris L.) seedling and hypocotyl root architecture and early plant growth in tree seedling nursery soil, Sphagnum peat and forest humus. The BnR isolates (251, 266, 268, 269) stimulated early seedling growth in the nitrogen-limited nursery soil 86 days postinoculation (p.i.). These seedlings exhibited significantly higher root length and reduced root width, although percentage root infection levels were <6%. At a harvest 240 days p.i., no significant plant and root growth differences were identified, although short root numbers were significantly increased. BnR infection detected in roots was characterized by the presence of intercellular fungal hyphae and subtending intracellular monilioid fungal cells located in outer cortical cells of long roots. Similar endophytic infection morphology was detected in adventitious roots generated in prerooted hypocotyl cuttings [Kaparakis, G. & Sen, R. (2006). Scandinavian Journal of Forest Research, 21] exposed to all BnR isolates in nursery peat and forest humus, although isolate-specific cutting growth was detected. In conclusion, these BnR isolates, known to be genetically related to orchid mycorrhizal Ceratorhiza spp., are non-pathogenic and have the capacity to stimulate significantly early Scots pine root development in nursery soils and forest humus.

Development of Douglas-fir seedling root architecture in response to localized nutrient supply

Three months following sowing, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were transplanted into pots with controlled-release fertilizer (CRF) applied at rates of 0, 8, 16, and 24 g/2200 cm3 soil as a single uniform layer beneath the root system. Seedlings were destructively harvested periodically, and roots were divided into vertical segments above (S1), within (S2), and below (S3) the fertilizer layer. Two months following transplant, the number of active root tips was positively correlated with CRF rate in S1 and negatively correlated with rate in S2 and S3. At 6 months, root penetration into S3 was severely restricted at 16 and 24 g. This was attributed to detrimental changes in soil osmotic potential in S2. Fertilizer improved seedling growth at 8 g after 6 months compared with controls but was inhibitory at 24 g. Photochemical quantum yield was higher in all CRF treatments compared with controls 3 months following transplant, which corresponded with rapid initial CRF nutrient release. Despite improvements in nutrient release technology with CRF, high application rates may result in excessive concentrations of fertilizer nutrients in media, which can restrict root penetration and negatively affect seedling growth. Conservative application rates and improvements in CRF technology will help reduce the potential for adverse effects on seedling development.

Seedling root anatomy and morphology: an examination of ecological differentiation with rainfall using phylogenetically independent contrasts.

We examined patterns of seedling root architecture, morphology and anatomy in Australian perennial plants chosen as phylogenetically independent contrasts (PICs) for rainfall in the areas they inhabit. Our objective was to assess whether there are consistent evolutionary patterns in structure of seedling root systems in species from different rainfall environments when examined across multiple evolutionary lineages. Seedlings were grown to a standardised developmental stage under controlled conditions. We found that seedling root systems of species restricted to low rainfall environments are characterised by greater proportional allocation to main root axis and have proportionally smaller main root axis diameter and areas of stele and xylem. Species of low rainfall environments also had higher specific root length (SRL) of the main axis, but lower SRL when the entire root system was considered. Seedling root system elongation rates were higher in species of high rainfall relative to those of low rainfall environments, paralleling expected differences in relative growth rate. The higher root system elongation rates in species of high rainfall environments were associated with greater numbers of growing tips in the root system, but not with differences in elongation rates of individual tips, relative to species of low rainfall environments.