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Background and aims: Weeds are a major biotic stressor impacting crop production. Improving the competitiveness of wheat (Triticum aestivum L.) could provide a useful tool in integrated weed management. While wheat typically exhibits conservative early growth, early vigour has been increased through long-term recurrent selection for greater early biomass and leaf area. However, the influence of integrating such vigour into breeding lines for improving competitive ability remains to be explored. Methods: In replicated controlled environment experiments, the effect of breeding early shoot vigour on root development and below-ground competitiveness was carefully examined. Physical and chemical characteristics of wheat vigour lines were assessed and compared with commercial cultivars in hydroponics and field soil experiments. Measurements included early root growth, rhizosheath size and growth responses in the presence of annual ryegrass, a major weed in wheat production. Results: The vigorous lines exhibited larger leaf widths, increased cell file number, increased total root length and larger rhizosheaths compared with commercial parents. Numerous secondary metabolites with known allelopathic effects on weeds were detected in the roots and the rhizosphere, and significant allelochemical level differences observed between distilled water and soil water extract-treated plants. Although the vigour lines were significantly more competitive than the commercial cultivars against ryegrass, they produced similar levels of phytotoxic secondary metabolites. Conclusion: Competition below-ground was strongly suppressive of ryegrass for the more vigorous genotypes suggesting that breeding with shoot vigour had pleiotropic effects on key root traits for below-ground wheat competitiveness. [ABSTRACT FROM AUTHOR]

The rhizosheath, the layer of soil tightly attached to the roots, protects plants against abiotic stress and other adverse conditions by providing a bridge from the plant root system to the soil. It reduces the formation of air gaps between the root and soil and facilitates the transportation of water at the root–soil interface. It also serves as a favourable niche for plant-growth-promoting rhizobacteria in the surrounding soil, which facilitate the absorption of soil water and nutrients. This review compares the difference between the rhizosheath and rhizosphere, and summarises the molecular and physiological mechanisms of rhizosheath formation, and identifying the causes of rhizosheath formation/non-formation in plants. We summarise the chemical and physical factors (root hair, soil-related factors, root exudates, and microorganisms) that determine rhizosheath formation, and focus on the important functions of the rhizosheath in plants under abiotic stress, especially in drought stress, phosphorus deficiency, aluminium stress, and salinity stress. Understanding the roles played by the rhizosheath and the mechanisms of its formation provides new perspectives for improving plant stress tolerance in the field, which will mitigate the increasing environmental stress conditions associated with on-going global climate change. [ABSTRACT FROM AUTHOR]

Rhizosheath as a potential adaptive trait can adjust the effects of drought stress by maintaining moisture, and have a positive effect on the uptake of water and nutrients by the plant. The present study was conducted to compare the formation of rhizosheath in different wheat cultivars and its impact on potassium uptake by the plant under drought stress conditions. For this reason, four wheat cultivars, Mihan and Sirvan (irrigated cultivars) and Sadra and Rizhaw (rainfed cultivars) were used. First, the pots were divided into four groups of ten, each group belonging to one cultivar, and in each cultivar, two moisture levels (optimum and stress) were applied. Drought stress started in the pots after plants were established in the soil. After ten weeks, plants were harvested, and separating the rhizosheath of each pot was done. The highest ratio of the rhizosheath dry weight to the root dry weight under stress conditions was observed in Rizhaw (69.22 g/g) and the lowest value was observed in Sadra (60.46 g/g). The highest and lowest value of potassium in the plant under drought stress was obtained in Rizhaw (30.73 mg/pot) and Sirvan (28.73 mg/pot), respectively. The maximum value of available potassium in rhizosheath under drought stress was measured in Mihan (147.45 mg kg-1) and the minimum value in Rizhaw (134.07 mg kg-1). Results showed that the studied cultivars had the same and high ability to form rhizosheath under drought stress conditions. Further studies with different wheat cultivars and other agronomic and horticultural crops are recommended. [ABSTRACT FROM AUTHOR]

A holistic understanding of plant strategies to acquire soil resources is pivotal in achieving sustainable food security. However, we lack knowledge about variety‐specific root and rhizosphere traits for resource acquisition, their plasticity and adaptation to drought. We conducted a greenhouse experiment to phenotype root and rhizosphere traits (mean root diameter [Root D], specific root length [SRL], root tissue density, root nitrogen content, specific rhizosheath mass [SRM], arbuscular mycorrhizal fungi [AMF] colonization) of 16 landraces and 22 modern cultivars of temperate maize (Zea mays L.). Our results demonstrate that landraces and modern cultivars diverge in their root and rhizosphere traits. Although landraces follow a 'do‐it‐yourself' strategy with high SRLs, modern cultivars exhibit an 'outsourcing' strategy with increased mean Root Ds and a tendency towards increased root colonization by AMF. We further identified that SRM indicates an 'outsourcing' strategy. Additionally, landraces were more drought‐responsive compared to modern cultivars based on multitrait response indices. We suggest that breeding leads to distinct resource acquisition strategies between temperate maize varieties. Future breeding efforts should increasingly target root and rhizosphere economics, with SRM serving as a valuable proxy for identifying varieties employing an outsourcing resource acquisition strategy. Summary statement: This study provides novel insights into the diversity of soil resource acquisition strategies within a single plant species. By comparing landraces and modern cultivars of maize and considering plant‐soil‐microbe interactions, we reveal functional differences in root and rhizosphere economics and trait plasticity that shed light on their ecological role and breeding relevance. [ABSTRACT FROM AUTHOR]

Roots play a key role in withstanding wheat abiotic stress. In this work, we phenotyped seedling root morphology of two semi-dwarf bread wheat cultivars, the Chinese cv Lankaodali and the Italian cv Rebelde, under the hypothesis that these two genotypes have contrasting root traits and could be used as donors in breeding programs. Root development was compared in a semi-hydroponic screening, where full-strength (FS) vs. half-strength (HS) complete Hoagland's solution represented high and moderate nutrient availability, and a screening comparing HS solution with tap water corresponding to a condition of nutrient starvation. Genotypes were further compared in soil under full watering (100% of field capacity) vs. drought stress (50% of field capacity). Lankaodali outperformed Rebelde by producing 50% more leaf mass and 70% more root mass in FS solution, 125% more leaf mass and 106% more root mass in HS solution, and 65% more leaf mass and 36% more root mass under nutrient starvation. This cv also showed a positive correlation between leaf mass and root length and mass (between r = 0.82–0.9 and r = 0.83–0.87, respectively, p < 0.05). In the soil screening experiment, Lankaodali produced more biomass than Rebelde regardless of water availability, 48% more leaf mass, 32% more root mass, and 31% more absolute rhizosheath mass (average across water availability treatments). Lankaodali proved to be more responsive than Rebelde to both water and nutrient availability. High values of broad-sense heritability—ranging between 0.80 for root mass and 0.90 for length in a hydroponic screen and 0.85 for rhizosheath size in soil—indicate that these traits could be useful for breeding. [ABSTRACT FROM AUTHOR]

Drought is a major threat to food security worldwide. Recently, the root–soil interface has emerged as a major site of hydraulic resistance during water stress. Here, we review the impact of soil drying on whole-plant hydraulics and discuss mechanisms by which plants can adapt by modifying the properties of the rhizosphere either directly or through interactions with the soil microbiome. [ABSTRACT FROM AUTHOR]

Climate change negatively affects crop productivity, threatening the survival of entire populations from many vulnerable hotspot regions of the world with the risk of exacerbating hunger, malnutrition and international inequality. Selecting plant species manifesting abiotic stress-tolerant adaptive traits represents a challenge towards ensuring that crops are more resistant and resilient to environmental perturbations. The rhizosheath, defined as the complex of root hair, exudates and soil that strongly adheres to plant roots, is a promising root adaptive trait in facing conditions of water and nutrient deficits, as well as acidic soil. Several beneficial ecological functions are attributed to the rhizosheath, such as enhancing water and nutrient uptake; protecting from dehydration, heat and acid stresses; and stimulating microbial activities. It has been described in several Angiosperm species, including crops grown in severe habitats. The aim of this review was to collect the relevant literature produced to date regarding rhizosheaths, focusing on (i) the various processes involved in its formation, including both physicochemical and biological ones; (ii) the evolutionary and ecological role of rhizosheaths; and (iii) the most frequently used methodologies for its investigation and characterization. The present work provides a comprehensive overview of this revolutionary root's great agronomic importance in order to address future research aiming to fill the existing knowledge gaps and define a common and shared methodology. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Plant Ecology is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the most prominent changes in the rhizospheric soil structure is associated with the formation of a strongly bound soil layer in the surroundings of the root, which is named rhizosheath. In this study, we investigated how root hair elongation, a ubiquitous root morphological trait, affect the stability of rhizosheath aggregates. Using 13CO2 pulse labeling, we tracked the fate of root-derived 13C inputted into the rhizosheath of two Zea mays L. genotypes with contrasting root hair elongation: a mutant with root hair defective elongation (rth3) and a corresponding wild type (WT). In addition, we also investigated the differences between two 13CO2 labeling approaches (single vs. multiple pulse labeling) in the distribution of 13C in the rhizosheath aggregates. We were able to demonstrate that the rhizosheath aggregate stability and the resulting aggregate size distribution follows the same mechanisms irrespective of the root hair elongation. This result reinforces the assumption that other soil properties are more decisive for the soil structure formation in the rhizosheath in comparison to root hair elongation. The majority of recently deposited root-derived C (57%) was found in the macroaggregates. Increasing the number of pulses (multiple pulse labeling approach) resulted in a higher 13C enrichment of the rhizosheath aggregates fractions in comparison to the application of a single pulse. While both labeling approaches resulted in a similar distribution of 13C in the rhizosheath aggregates, the higher enrichment given by multiple pulse labeling allowed the separation of significant differences between the genotypes in plant C allocation in the rhizosheath. [ABSTRACT FROM AUTHOR]

Abstract Background In hot deserts daily/seasonal fluctuations pose great challenges to the resident organisms. However, these extreme ecosystems host unique microenvironments, such as the rhizosheath–root system of desert speargrasses in which biological activities and interactions are facilitated by milder conditions and reduced fluctuations. Here, we examined the bacterial microbiota associated with this structure and its surrounding sand in the desert speargrass Stipagrostis pungens under the contrasting environmental conditions of summer and winter in the Sahara Desert. Results The belowground rhizosheath–root system has higher nutrient and humidity contents, and cooler temperatures than the surrounding sand. The plant responds to the harsh environmental conditions of the summer by increasing the abundance and diversity of extracellular polymeric substances (EPS) compared to the winter. On the contrary, the bacterial community associated with the rhizosheath–root system and its interactome remain stable and, unlike the bulk sand, are unaffected by the seasonal environmental variations. The rhizosheath–root system bacterial communities are consistently dominated by Actinobacteria and Alphaproteobacteria and form distinct bacteria communities from those of bulk sand in the two seasons. The microbiome-stabilization mediated by the plant host acts to consistently retain beneficial bacteria with multiple plant growth promoting functions, including those capable to produce EPS, which increase the sand water holding capacity ameliorating the rhizosheath micro-environment. Conclusions Our results reveal the capability of plants in desert ecosystems to stabilize their below ground microbial community under seasonal contrasting environmental conditions, minimizing the heterogeneity of the surrounding bulk sand and contributing to the overall holobiont resilience under poly-extreme conditions.

Background and Aims Stomatal regulation allows plants to promptly respond to water stress. However, our understanding of the impact of above and belowground hydraulic traits on stomatal regulation remains incomplete. The objective of this study was to investigate how key plant hydraulic traits impact transpiration of maize during soil drying. We hypothesize that the stomatal response to soil drying is related to a loss in soil hydraulic conductivity at the root–soil interface, which in turn depends on plant hydraulic traits. Methods We investigate the response of 48 contrasting maize (Zea mays) genotypes to soil drying, utilizing a novel phenotyping facility. In this context, we measure the relationship between leaf water potential, soil water potential, soil water content and transpiration, as well as root, rhizosphere and aboveground plant traits. Key Results Genotypes differed in their responsiveness to soil drying. The critical soil water potential at which plants started decreasing transpiration was related to a combination of above and belowground traits: genotypes with a higher maximum transpiration and plant hydraulic conductance as well as a smaller root and rhizosphere system closed stomata at less negative soil water potentials. Conclusions Our results demonstrate the importance of belowground hydraulics for stomatal regulation and hence drought responsiveness during soil drying. Furthermore, this finding supports the hypothesis that stomata start to close when soil hydraulic conductivity drops at the root–soil interface. [ABSTRACT FROM AUTHOR]

Ancient wheats may be a source of traits that are useful for the tolerance of climate change foreseen conditions of raising temperatures and low water availability. Previous research has shown a fine root system and a high mass of rhizosheath per unit root mass in the italian durum wheat (Triticum durum Desf) landrace Saragolle Lucana, and this may be relevant for successfully facing adverse conditions during seedling establishment. We investigated the effect of soil water shortage in Saragolle seedlings on root architecture, rhizosheath formation and biomass allocation. Pot experiments were conducted by comparing two levels of soil available water content (AWC): WW (100% of AWC) and DS (50% of AWC). Phenology was delayed by eight days in DS and above and belowground traits were measured at Zadoks 1.3 for each treatment. Biometric data collected at the same phenological stage show that DS plants did not reach the levels of biomass, surface area and space occupation of WW even after attaining the same developmental stage. Namely, plant dimensions were lower at low soil water availability, with the exception of rhizosheath production: DS yielded a 50% increase in rhizosheath mass and 32% increase in rhizosheath mass per unit root mass. The proportion of plant mass reduction in DS was 29.7% for aboveground parts and 34.7% for roots, while reductions in leaf and root surface areas exceeded 43%. The root/shoot mass and area ratios were not significantly different between treatments, and a higher impact on aboveground than on belowground traits at reduced available water was shown only by a lower ratio of shoot height to root depth in DS than in WW. Increases in rhizosheath in absolute and relative terms, which were observed in our experiment in spite of smaller root systems in the ancient durum wheat variety Saragolle lucana at DS, may provide an interesting trait for plant performance in conditions of low soil water availability both for water-related issue and for other effects on plant nutrition and relations with the rhizosphere. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: In hot deserts daily/seasonal fluctuations pose great challenges to the resident organisms. However, these extreme ecosystems host unique microenvironments, such as the rhizosheath–root system of desert speargrasses in which biological activities and interactions are facilitated by milder conditions and reduced fluctuations. Here, we examined the bacterial microbiota associated with this structure and its surrounding sand in the desert speargrass Stipagrostis pungens under the contrasting environmental conditions of summer and winter in the Sahara Desert. Results: The belowground rhizosheath–root system has higher nutrient and humidity contents, and cooler temperatures than the surrounding sand. The plant responds to the harsh environmental conditions of the summer by increasing the abundance and diversity of extracellular polymeric substances (EPS) compared to the winter. On the contrary, the bacterial community associated with the rhizosheath–root system and its interactome remain stable and, unlike the bulk sand, are unaffected by the seasonal environmental variations. The rhizosheath–root system bacterial communities are consistently dominated by Actinobacteria and Alphaproteobacteria and form distinct bacteria communities from those of bulk sand in the two seasons. The microbiome-stabilization mediated by the plant host acts to consistently retain beneficial bacteria with multiple plant growth promoting functions, including those capable to produce EPS, which increase the sand water holding capacity ameliorating the rhizosheath micro-environment. Conclusions: Our results reveal the capability of plants in desert ecosystems to stabilize their below ground microbial community under seasonal contrasting environmental conditions, minimizing the heterogeneity of the surrounding bulk sand and contributing to the overall holobiont resilience under poly-extreme conditions. [ABSTRACT FROM AUTHOR]

The rhizosheath is a critical interface supporting the exchange of resources between plants and their associated environment of soil. Favorable microenvironment of rhizosphere soil provides the rhizosheath formed and then promotes desert plant survival. However, it remains unclear how rhizosheath benefits the colonization of pioneer plants in alpine desert under changing environment. In this study, we investigated the effect of different soil moisture and sterilization treatments (three moisture levels and unsterilized or sterilized soil) on rhizosheath forming process of Kengyilia hirsuta (K. hirsuta), a sand-inhabiting and drought-resistant pioneer plant of the Tibetan Plateau desert. The results showed that in both unsterilized and sterilized soil, increasing soil moisture first increased and then decreased rhizosheath weight, with the highest value is 25%. During rhizosheath formation, developing rhizosheaths were selectively enriched in the bacterial genera Massilia and Arthrobacter. These suggest the existence of a highly specialized signal recognition system during rhizosheath formation that involves the accumulation of bacteria. These bacterial species exhibited different roles in the process of rhizosheath formation and is an advantageous strategy for K. hirsuta.

The rhizosheath is a critical interface supporting the exchange of resources between plants and their associated environment of soil. Favorable microenvironment of rhizosphere soil provides the rhizosheath formed and then promotes desert plant survival. However, it remains unclear how rhizosheath benefits the colonization of pioneer plants in alpine desert under changing environment. In this study, we investigated the effect of different soil moisture and sterilization treatments (three moisture levels and unsterilized or sterilized soil) on rhizosheath forming process of Kengyilia hirsuta (K. hirsuta), a sand-inhabiting and drought-resistant pioneer plant of the Tibetan Plateau desert. The results showed that in both unsterilized and sterilized soil, increasing soil moisture first increased and then decreased rhizosheath weight, with the highest value is 25%. During rhizosheath formation, developing rhizosheaths were selectively enriched in the bacterial genera Massilia and Arthrobacter. These suggest the existence of a highly specialized signal recognition system during rhizosheath formation that involves the accumulation of bacteria. These bacterial species exhibited different roles in the process of rhizosheath formation and is an advantageous strategy for K. hirsuta. [ABSTRACT FROM AUTHOR]

Ancient wheats may be a source of traits that are useful for the tolerance of climate change foreseen conditions of raising temperatures and low water availability. Previous research has shown a fine root system and a high mass of rhizosheath per unit root mass in the italian durum wheat (Triticum durum Desf) landrace Saragolle Lucana, and this may be relevant for successfully facing adverse conditions during seedling establishment. We investigated the effect of soil water shortage in Saragolle seedlings on root architecture, rhizosheath formation and biomass allocation. Pot experiments were conducted by comparing two levels of soil available water content (AWC): WW (100% of AWC) and DS (50% of AWC). Phenology was delayed by eight days in DS and above and belowground traits were measured at Zadoks 1.3 for each treatment. Biometric data collected at the same phenological stage show that DS plants did not reach the levels of biomass, surface area and space occupation of WW even after attaining the same developmental stage. Namely, plant dimensions were lower at low soil water availability, with the exception of rhizosheath production: DS yielded a 50% increase in rhizosheath mass and 32% increase in rhizosheath mass per unit root mass. The proportion of plant mass reduction in DS was 29.7% for aboveground parts and 34.7% for roots, while reductions in leaf and root surface areas exceeded 43%. The root/shoot mass and area ratios were not significantly different between treatments, and a higher impact on aboveground than on belowground traits at reduced available water was shown only by a lower ratio of shoot height to root depth in DS than in WW. Increases in rhizosheath in absolute and relative terms, which were observed in our experiment in spite of smaller root systems in the ancient durum wheat variety Saragolle lucana at DS, may provide an interesting trait for plant performance in conditions of low soil water availability both for water-related issue and for other effects on plant nutrition and relations with the rhizosphere.

Phosphorus (P) deficiency largely restricts plant growth and lead to severe yield losses. Therefore, identification of novel root traits to improve P uptake is needed to circumvent yield losses. White lupin (Lupinus albus) is a legume crop that develops cluster roots and has the high phosphorus use efficiency in low P soils. We aimed to investigate the association between cluster roots (CR) rhizosheath formation and P uptake in white lupin. Rhizosheath formation and P concentration were evaluated under four soil treatments. CR increased up to 2.5-fold of overall plant dry weight under SD–P compared to WW + P (control), partly attributable to variations in CR development. Our data showed that SD–P significantly increase rhizosheath weight in white lupin. Among the root segments, MCR showed improved P accumulation in the root which is associated with increased MCR rhizosheath weight. Additionally, a positive correlation was observed between MCR rhizosheath weight and P uptake. Moreover, high sucrose content was recorded in MCR, which may contribute in CR growth under SD–P. Expression analysis of genes related to sucrose accumulation (LaSUC1, LaSUC5, and LaSUC9) and phosphorus uptake (LaSPX3, LaPHO1, and LaPHT1) exhibited peaked expression in MCR under SD-P. This indicate that root sucrose status may facilitate P uptake under P starvation. Together, the ability to enhance P uptake of white lupin is largely associated with MCR rhizosheath under SD–P. Our results showed that gene expression modulation of CR forming plant species, demonstrating that these novel root structures may play crucial role in P acquisition from the soil. Our findings could be implicated for developing P and water efficient crop via CR development in sustainable agriculture. • Mature CRs of L. albus acquire significantly higher concentration of phosphorus than non-CRs (PR, LR), concomitant with the enhanced MCR rhizosheath formation. • Maximum number of CRs formation are induced under SD-P compared to both WW + P and WW-P conditions in L. albus. • Specific gene expression modulation in YCR and MCR under combined water and P variability treatments indicates their involvement in P uptake, particularly under SD-P condition. [ABSTRACT FROM AUTHOR]

Aims: The interactions between plant roots and the associated microbiota impact soil aggregation, water retention and plant nutrient availability. Thus, selection of plant genotypes that promote microbial species involved in root-adhering soil aggregation and rhizosheath formation could help improve yield sustainably. Here, we tested pearl millet genotypic variation in both root-adhering soil aggregation, microbiological and biochemical characteristics. Methods: A collection of 181 pearl millet inbred lines was phenotyped for their rhizosheath size, and 13 contrasting genotypes were selected and grown under field conditions, and their root-adhering soil (RAS) was sampled. Microbial biomass, pH, mineral N content and six enzymatic activities involved in main nutrients cycles were analyzed, and metabarcoding of 16S rDNA and ITS were performed for bacterial and fungal diversity. Results: Enzymatic activities (chitinase, acid phosphomonoesterase, FDA-hydrolysis and β-glucosidase) were higher in RAS of larger rhizosheath lines than that of smaller rhizosheath one. Bacterial β-diversity showed a separation of the most contrasting lines in the principal coordinate analysis performed with the Bray-Curtis distance matrix. Some bacteria from the Gaiellaceae and Sphingomonadaceae families and the Bradyrhizobium and Mesorhizobium genera were associated with the large rhizosheath phenotype. Concerning the fungal community, we noticed a negative correlation between the specific richness and the rhizosheath size and Trichoderma genus was positively associated to the rhizosheath size. Conclusions: This study demonstrates that in pearl millet, the rhizosheath size is related to soil nutrient dynamics and microbiota diversity. However, it also shows that other factors shape this trait and their relative importance must be determined. [ABSTRACT FROM AUTHOR]

Background and Aims Rhizosheaths are defined as the soil adhering to the root system after it is extracted from the ground. Root hairs and mucilage (root exudates) are key root traits involved in rhizosheath formation, but to better understand the mechanisms involved their relative contributions should be distinguished. Methods The ability of three species [barley (Hordeum vulgare), maize (Zea mays) and Lotus japonicus (Gifu)] to form a rhizosheath in a sandy loam soil was compared with that of their root-hairless mutants [bald root barley (brb), maize root hairless 3 (rth3) and root hairless 1 (Ljrhl1)]. Root hair traits (length and density) of wild-type (WT) barley and maize were compared along with exudate adhesiveness of both barley and maize genotypes. Furthermore, root hair traits and exudate adhesiveness from different root types (axile versus lateral) were compared within the cereal species. Key Results Per unit root length, rhizosheath size diminished in the order of barley > L. japonicus > maize in WT plants. Root hairs significantly increased rhizosheath formation of all species (3.9-, 3.2- and 1.8-fold for barley, L. japonicus and maize, respectively) but there was no consistent genotypic effect on exudate adhesiveness in the cereals. While brb exudates were more and rth3 exudates were less adhesive than their respective WTs, maize rth3 bound more soil than barley brb. Although both maize genotypes produced significantly more adhesive exudate than the barley genotypes, root hair development of WT barley was more extensive than that of WT maize. Thus, the greater density of longer root hairs in WT barley bound more soil than WT maize. Root type did not seem to affect rhizosheath formation, unless these types differed in root length. Conclusions When root hairs were present, greater root hair development better facilitated rhizosheath formation than root exudate adhesiveness. However, when root hairs were absent root exudate adhesiveness was a more dominant trait. [ABSTRACT FROM AUTHOR]

Background and Aims Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experimentally elucidate some of the impacts that root hairs have on plant performance on a field scale. Methods A field experiment was set up in Scotland for two consecutive years, under contrasting climate conditions and different soil textures (i.e. clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Root hair length, density and rhizosheath weight were measured at several growth stages, as well as shoot biomass, plant water status, shoot phosphorus (P) accumulation and grain yield. Key Results Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions, although significant variations were found between soil textures as the growing season progressed. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance resulting in a less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot P accumulation. Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. Conclusions Selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder's dilemma of trying to simultaneously enhance both productivity and resilience. Therefore, the maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aims: We investigated the effects of water stress under low phosphorus (P) supply on P-acquisition by chickpea, and identified a genotype with faster relative growth and P-acquisition rates. Methods: We grew four genotypes in pots filled with a sand and soil mixture with a low P availability in a glasshouse. Plants were either well-watered or water-stressed, imposed at the reproductive stage. Plants were harvested when water-stressed plants fully closed their stomata. Results: For all four genotypes, water stress reduced shoot and root growth, root mass ratio, and shoot P content, while it increased specific root length (except in ICC 456), water-use efficiency and the amount of rhizosheath carboxylates per gram root dry weight. A faster relative shoot P-acquisition rate in ICC 2884 was associated with a greater specific root length, a smaller mean root diameter and a greater increase in the amount of rhizosheath carboxylates in response to water stress under low P supply. Interestingly, under water stress ICC 2884 also maintained a similar physiological P-use efficiency to that of the well-watered plants. Conclusions: ICC 2884 is recommended as a parental genotype in chickpea breeding programs to develop cultivars for low-P and terminal drought environments. [ABSTRACT FROM AUTHOR]

Background: First discovered on desert plants by Volkens 1887, rhizosheath formation, i.e. soil aggregation at the root surface, is now considered as a very promising adaptive trait to deal with abiotic stress. Indeed, the rhizosheath could help plants better cope with water stress, nitrogen and phosphorus deficiencies, and soil acidity. Scope: We have reviewed studies on the biological factors involved in rhizosheath formation, the methods used to quantify it, and its importance in plant nutrition. Thus, we have collected recent evidence that shows that the rhizosheath is an important trait arising from the morphology and physiology of plant root system, and the cooperation between plant root and its associated microbiota. In particular, the transformation of root exudates by exopolysaccharide-producing bacteria effectively contributes to soil aggregation and thus to increases the volume of the rhizosheath (i.e. root-adhering soil), thereby improving the absorption of minerals and water by plants. The growing interest for this process has led to the genetic mapping of potential plant QTLs controlling this trait in order to provide new tools for the selection of plant varieties with improved tolerance to abiotic stresses. Conclusion: Finally, we discussed some important issues that need to be addressed in order to develop an appropriate selection strategy focused on the rhizosheath, such as the relationship between the genes controlling rhizosheath formation and those controlling other root traits, but also the impact of rhizosheath formation on soil carbon sequestration, a potential strategy for mitigating climate change. [ABSTRACT FROM AUTHOR]

We tested whether selection of ryegrass for reduced root hair length and density would reduce root competition on white clover for phosphate (P). A Rhizosheath Selection Tool was used to select two ryegrass populations with contrasting root hair traits. These were grown at five soil P levels in a glasshouse experiment and rhizosheath trait selection had no effect on growth or shoot P concentrations. The ryegrass populations were also grown with white clover in soils with Olsen P12 or 19 mg L−1. In the Olsen P12 soil, clover grown with the smaller rhizosheath ryegrass had significantly heavier shoots and contained more P than clover grown with the larger rhizosheath ryegrass. In the Olsen P19 soil differences in ryegrass rhizosheath had no effect on clover growth. The results showed that under the experimental conditions, grass-clover competition for soil P could be modified by the rhizosheath traits of ryegrass. [ABSTRACT FROM AUTHOR]

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Plant growth on harsh substrates (habitat specialization) requires specific traits to cope with stressful conditions.We tested whether traits related to nutrient acquisition (root colonization by fungal symbionts, and plant morphological and physiological specializations), and nutrient use (leaf nitrogen (N) and phosphorus (P) concentrations and N‐ and P‐remobilization efficiency), were related to habitat specialization for 27 species of Velloziaceae growing either in soil or on rocks in extremely P‐impoverished campos rupestres habitats. If habitat specialization were to drive trait sorting, then we expect traits to differ between those substrates.Both soil and rock‐dwelling species presented a very low proportion of root length colonized by arbuscular mycorrhizal and dark‐septate fungi. However, rhizosheaths were only observed in soil‐dwelling species, and vellozioid roots, a specialization that allows for mining P and dissolving quartzite rock, were mostly found in rock‐dwelling species. We did not observe differences in nutrient‐use traits between rock‐ and soil‐dwelling species.Root specializations are strongly correlated with microhabitats, and the presence of vellozioid roots seems to mediate bare rock specialization. There is an overall P limitation of plant productivity both on rock and in soil of campos rupestres, which does not drive the sorting of traits related to above‐ground nutrient use and symbiotic P acquisition. Therefore, nutrient impoverishment is indeed a very strong environmental filter in campos rupestres as a whole, but habitat specialization plays an important role in the spatial distribution of Velloziaceae between contrasting substrates. [ABSTRACT FROM AUTHOR]

Aims: Rhizosheath is known as a layer of adhering soil particle to the root surface. Despite several speculations, the positive function of rhizosheath in acquisition of water and nutrients from drying soil has not yet been experimentally proven. The objective of this study was to experimentally show whether an enhanced rhizosheath formation could help plants to better access water from drying soil. Methods: Eight wheat cultivars were grown in a sandy-loam soil. When plants were 35 days old let dry soil to a water content at which evident wilting symptoms appeared on the plant leaves. During this drying cycle, soil water content and transpiration rate of plants were gravimetrically measured by weighing the plant pots. At the end of this drying cycle, the roots were excavated out of the soil and the rhizosheath formation was gravimetrically quantified by weighing the soil attached to the root system. Results: The results showed that plant cultivars with greater rhizosheath formation could sustain higher transpiration rates at dry condition (water content of 0.07 cm3 cm−3) while the plant cultivars with lower rhizosheath formation suffered from drought stress and reached their permanent wilting points at the same water content. Conclusion: The findings of this study gathered evidence that under severe drought condition plant cultivars with an enhanced rhizosheath formation could better survive by sustaining their transpirational and nutritional demands. [ABSTRACT FROM AUTHOR]

Main conclusion: Rhizosheath comprises soil that adheres firmly to roots. In this study, two ecotypes of switchgrass with different rhizosheath sizes after drought stress were analyzed which showed metabolic differences under drought conditions. The rhizosheath comprises soil that adheres firmly to roots by a combination of root hairs and mucilage and may aid in root growth under soil drying. The aim of this work is to reveal the potential metabolites involved in rhizosheath formation under drought stress conditions. Panicum virgatum L. (switchgrass), which belongs to the Poaceae family, is an important biofuel and fodder crop in drought areas. Five switchgrass ecotypes (cv. Alamo, cv. Blackwake, cv. Summer, cv. Cave-in-Rock and cv. Kanlow) have a broad range of rhizosheath weight under drought conditions. For two selected ecotypes with contrast rhizosheath weight (cv. Alamo and cv. Kanlow), root hair length and density, lateral root number, root morphological parameters were measured, and real-time qRT-PCR was performed. Gas chromatography mass spectrophotometry (GC–MS) was used to determine the primary metabolites in the shoots and roots of selected ecotypes under drought stress conditions. The change trends of root hair length and density, lateral root number and related gene expression were consistent with rhizosheath weight in Alamo and Kanlow under drought and watered conditions. For root morphological parameters, Alamo grew deeper than Kanlow, while Kanlow exhibited higher values for other parameters. In this study, the levels of amino acids, sugars and organic acids were significantly changed in response to drought stress in two switchgrass ecotypes. Several metabolites including amino acids (arginine, isoleucine, methionine and cysteine) and sugars (kestose, raffinose, fructose, fucose, sorbose and xylose) in the large soil-sheathed roots of Alamo and Kanlow were significantly increased compared to small or no soil-sheathed roots of Alamo and Kanlow. Difference in rhizosheath size is reflected in the plant internal metabolites under drought stress conditions. Additionally, our results highlight the importance of using metabolite profiling and provide a better understanding of rhizosheath formation at the cellular level. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms that underlie the generation of beta‐diversity remains a challenge in ecology. Underground plant adaptations to environmental gradients have received relatively little attention.We studied plant nutrient‐acquisition strategies and nutrient‐use efficiency at three stages of pedogenesis in infertile soils from campos rupestres and on less infertile soil from cerrado sensu stricto in Brazil. All soils support very high plant diversity with high species turnover between soil types at small spatial scales (metres). We expected that differences in nutrient‐acquisition and ‐use strategies would be associated with this high species turnover. With severely decreasing phosphorus (P) availability, we expected the effectiveness of arbuscular mycorrhizal (AM) symbioses for plant P acquisition to decrease, and reliance on nonmycorrhizal strategies (NM) to increase, while maintaining efficient nutrient use.Concentrations of total soil P and nitrogen (N) were greater in soils in cerrado than in those from campos rupestres, and the more weathered soils from campos rupestres were severely P and N impoverished. The proportion of the root length colonized by AM fungi was 71% in the soils from the cerrado and <1% in the most P‐impoverished soil type from campos rupestres. Conversely, the proportion of species with nonmycorrhizal P‐acquisition strategies such as rhizosheaths was greater in the most P‐impoverished soils. Leaf [P] and [N] were very low and decreased with decreasing soil [P] and [N]. Leaf N:P ratios suggest P limitation of plant productivity in the campos rupestres but N‐P colimitation in the cerrado. Photosynthetic rates decreased with increasing P impoverishment, but photosynthetic P‐use efficiency was very high and photosynthetic N‐use efficiency moderately high on all soils. Most species had very high P‐remobilization efficiency during leaf senescence (>70%), but only moderate N‐remobilization efficiency (~50%).Synthesis. We observed very high P‐use efficiency and moderately high N‐use efficiency in campos rupestres and cerrado species, consistent with plant productivity being more strongly limited by P than by N. Our findings demonstrate that different soil characteristics (nutrient availability and soil texture) select for species differing in nutrient‐acquisition and ‐use strategies (especially below‐ground traits) which is likely key for the very high species turnover at a very small scale between soil types (i.e., beta‐diversity) in campos rupestres and cerrado. [ABSTRACT FROM AUTHOR]

• The mechanisms controlling the genesis of rhizosheaths are not well understood, despite their importance in controlling the flux of nutrients and water from soil to root. • Here, we examine the development of rhizosheaths from drought-tolerant and droughtsensitive chickpea varieties; focusing on the three-dimensional characterization of the pore volume (> 16 lm voxel spatial resolution) obtained from X-ray microtomography, along with the characterization of mucilage and root hairs, and water sorption. • We observe that drought-tolerant plants generate a larger diameter root, and a greater and more porous mass of rhizosheath, which also has a significantly increased water sorptivity, as compared with bulk soil. • Using lattice Boltzmann simulations of soil permeability, we find that the root activity of both cultivars creates an anisotropic structure in the rhizosphere, in that its ability to conduct water in the radial direction is significantly higher than in the axial direction, especially in the drought-tolerant cultivar. We suggest that significant differences in rhizosheath architectures are sourced not only by changes in structure of the volumes, but also from root mucilage, and further suggest that breeding for rhizosheath architectures and function may be a potential future avenue for better designing crops in a changing environment. [ABSTRACT FROM AUTHOR]

Aims: Low-molecular-weight organic anions (carboxylates) influence rhizosphere processes and may enhance plant phosphorus acquisition. We examined the root exudate profile of a range of pasture and grain legumes and focused on the little-investigated carboxylate, citramalate.Methods: Twelve species of pasture legumes and herbs, including four Lotus spp. and two crop legumes, Cicer arietinum and Lupinus albus, were grown in a glasshouse for six weeks. The composition and amounts of carboxylates were measured in rhizosheath soil as well as in root exudates from roots washed free of their rhizosheath.Results: Citrate and malate were found in the rhizosheath of all species. However, citramalate was present in the rhizosheath of only Lotus species (10-82% of total exuded carboxylates). Cicer arietinum had the largest amount of carboxylates in its rhizosheath and fastest rate of carboxylate exudation into the trap solution.Conclusions: Citrate and malate were found in the rhizosheath of all species in this study, but citramalate was only found in the root exudates and rhizosheath of Lotus spp. Further investigation into the role of citramalate in Lotus spp. is merited. [ABSTRACT FROM AUTHOR]

Aims: The rhizosheath is defined as the weight of soil adhering strongly to roots on excavation, and current interest in this trait as a potential tolerance mechanism to abiotic stress has prompted us to explore the extent of its occurrence throughout the angiosperm phylogeny. Methods: Here we describe a robust, novel method which was used to screen species for the presence/absence and strength of a rhizosheath. We correlate the latter with root hair length to provide insight into some of the factors affecting its formation. We go on to compare experimental data with previous observations in the literature. Results: Results of a glasshouse screen demonstrate that rhizosheaths exist in species from many angiosperm orders, and the frequency of their occurrence and their strength and size are related. No correlation between root hair length and rhizosheath size was found, except when root hairs were extremely short, but the presence of root hairs was required for rhizosheath formation. Conclusions: The rhizosheath is present in species from many angiosperm orders. Potential to enhance the trait is likely to exist in a range of crop species and could help contribute to future agricultural sustainability. [ABSTRACT FROM AUTHOR]

The article discusses the novel results presented by L. K. Brown and colleagues in their study "The Rhizosheath--A Potential Threat for Future Sustainability Occurs Throughout the Angiosperms." Topics covered include distinction between rhizosheath and rhizosphere, formation of rhizosheath in angiosperms, and the relationship between rhizosheath formation and root hair length.

Root exudation contributes to soil carbon allocation and also to microbial C and energy supply, which subsequently impacts soil aggregation around roots. Biologically-driven soil structural formation is an important driver of soil fertility. Plant genetic determinants of exudation and more generally of factors promoting rhizosphere soil aggregation are largely unknown. Here, we characterized rhizosphere aggregation in a panel of 86 pearl millet inbred lines using a ratio of root-adhering soil dry mass per root tissue dry mass (RAS/RT). This ratio showed significant variations between lines, with a roughly 2-fold amplitude between lowest and highest average values. For 9 lines with contrasting aggregation properties, we then compared the bacterial diversity and composition in root-adhering soil. Bacterial a-diversity metrics increased with the "RAS/RT ratio." Regarding taxonomic composition, the Rhizobiales were stimulated in lines showing high aggregation level whereas Bacillales were more abundant in lines with low ratio. 184 strains of cultivable exopolysaccharides-producing bacteria have been isolated from the rhizosphere of some lines, including members from Rhizobiales and Bacillales. However, at this stage, we could not find a correlation between abundance of EPS-producing species in bacterial communities and the ratio RAS/RT. These results illustrated the impact of cereals genetic trait variation on soil physical properties and microbial diversity. This opens the possibility of considering plant breeding to help management of soil carbon content and physical characteristics through carbon rhizodeposition in soil. [ABSTRACT FROM AUTHOR]

* Background and Aims Long root hairs enable the efficient uptake of poorly mobile nutrients such as phosphorus. Mapping the chromosomal locations of genes that control root hair length can help exploit the natural variation within crops to develop improved cultivars. Genetic stocks of the wheat cultivar 'Chinese Spring' were used to map genes that control root hair length. * Methods Aneuploid stocks of 'Chinese Spring' were screened using a rapid method based on rhizosheath size and then selected lines were assayed for root hair length to identify chromosomes harbouring genes controlling root hair length. A series of lines with various fractional deletions of candidate chromosomes were then screened to map the root hair loci more accurately. A line with a deletion in chromosome 5A was analysed with a 90 000 single nucleotide polymorphism (SNP) array. The phosphorus acquisition efficiency (PAE) of one deletion line was compared with that of euploid 'Chinese Spring' by growing the seedlings in pots at low and luxury phosphorus supplies. * Key Results Chromosomes 1A, 1D and 5A were found to harbour genes controlling root hair length. The 90 000 SNP array identified two candidate genes controlling root hair length located on chromosome 5A. The line with a deletion in chromosome 5A had root hairs that were approx. 20 % shorter than euploid 'Chinese Spring', but this was insufficient to reduce its PAE. * Conclusions A rapid screen for rhizosheath size enabled chromosomal regions controlling root hair length to be mapped in the wheat cultivar 'Chinese Spring' and subsequent analysis with an SNP array identified candidate genes controlling root hair length. The difference in root hair length between euploid 'Chinese Spring' and a deletion line identified in the rapid screen was still apparent, albeit attenuated, when the seedlings were grown on a fully fertilized soil. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is one of the essential nutrients for plants, and is indispensable for plant growth and development. P deficiency severely limits crop yield, and regular fertilizer applications are required to obtain high yields and to prevent soil degradation. To access P from the soil, plants have evolved high- and low-affinity Pi transporters and the ability to induce root architectural changes to forage P. Also, adjustments of numerous cellular processes are triggered by the P starvation response, a tightly regulated process in plants. With the increasing demand for food as a result of a growing population, the demand for P fertilizer is steadily increasing. Given the high costs of fertilizers and in light of the fact that phosphate rock, the source of P fertilizer, is a finite natural resource, there is a need to enhance P fertilizer use efficiency in agricultural systems and to develop plants with enhanced Pi uptake and internal P-use efficiency ( PUE). In this review we will provide an overview of continuing relevant research and highlight different approaches towards developing crops with enhanced PUE. In this context, we will summarize our current understanding of root responses to low phosphorus conditions and will emphasize the importance of combining PUE with tolerance of other stresses, such as aluminum toxicity. Of the many genes associated with Pi deficiency, this review will focus on those that hold promise or are already at an advanced stage of testing ( Os PSTOL1, AVP1, PHO1 and Os PHT1;6). Finally, an update is provided on the progress made exploring alternative technologies, such as phosphite fertilizer. [ABSTRACT FROM AUTHOR]

North Sinai deserts were surveyed for the predominant plant cover and for the culturable bacteria nesting their roots and shoots. Among 43 plant species reported, 13 are perennial (e.g. Fagonia spp., Pancratium spp.) and 30 annuals (e.g. Bromus spp., Erodium spp.). Eleven species possessed rhizo-sheath, e.g. Cyperus capitatus, Panicum turgidum and Trisetaria koelerioides. Microbiological analyses demonstrated: the great diversity and richness of associated culturable bacteria, in particular nitrogen-fixing bacteria (diazotrophs); the majority of bacterial residents were of true and/or putative diazotrophic nature; the bacterial populations followed an increasing density gradient towards the root surfaces; sizeable populations were able to reside inside the root (endorhizosphere) and shoot (endophyllosphere) tissues. Three hundred bacterial isolates were secured from studied spheres. The majority of nitrogen-fixing bacilli isolates belonged to Bacillus megaterium, Bacillus pumilus, Bacillus polymexa, Bacillus macerans, Bacillus circulans and Bacillus licheniformis. The family Enterobacteriaceae represented by Enterobacter agglomerans, Enterobacter sackazakii, Enterobacter cloacae, Serratia adorifera, Serratia liquefaciens and Klebsiella oxytoca. The non-Enterobacteriaceae population was rich in Pantoae spp., Agrobacterium rdiobacter, Pseudomonas vesicularis, Pseudomonas putida, Stenotrophomonas maltophilia, Ochrobactrum anthropi, Sphingomonas paucimobilis and Chrysemonas luteola. Gluconacetobacter diazotrophicus were reported inside root and shoot tissues of a number of tested plants. The dense bacterial populations reported speak well to the very possible significant role played by the endophytic bacterial populations in the survival, in respect of nutrition and health, of existing plants. Such groups of diazotrophs are good candidates, as bio-preparates, to support the growth of future field crops grown in deserts of north Sinai and irrigated by the water of El-Salam canal.

Rhizosheaths comprise soil bound to roots, and in wheat (Triticum aestivum L.) rhizosheath size correlates with root hair length. The aims of this study were to determine the effect that a large rhizosheath has on the phosphorus (P) acquisition by wheat and to investigate the genetic control of rhizosheath size in wheat grown on acid soil. Near-isogenic wheat lines differing in rhizosheath size were evaluated on two acid soils. The soils were fertilized with mineral nutrients and included treatments with either low or high P. The same soils were treated with CaCO3 to raise the pH and detoxify Al3+. Genotypic differences in rhizosheath size were apparent only when soil pH was low and Al3+ was present. On acid soils, a large rhizosheath increased shoot biomass compared with a small rhizosheath regardless of P supply. At low P supply, increased shoot biomass could be attributed to a greater uptake of soil P, but at high P supply the increased biomass was due to some other factor. Generation means analysis indicated that rhizosheath size on acid soil was controlled by multiple, additive loci. Subsequently, a quantitative trait loci (QTL) analysis of an F6 population of recombinant inbred lines identified five major loci contributing to the phenotype together accounting for over 60% of the total genetic variance. One locus on chromosome 1D accounted for 34% of the genotypic variation. Genetic control of rhizosheath size appears to be relatively simple and markers based on the QTL provide valuable tools for marker assisted breeding. [ABSTRACT FROM AUTHOR]

Rhizosheaths comprise soil that adheres to plant roots and, in some species, are indicative of root hair length. In this study, the genetics of rhizosheath size in wheat was investigated by screening the progeny of multiparent advanced generation intercrosses (MAGIC). Two MAGIC populations were screened for rhizosheath size using a high throughput method. One MAGIC population was developed from intercrosses between four parents (4-way) and the other from intercrosses between eight parents (8-way). Transgressive segregation for rhizosheath size was observed in both the 4-way and 8-way MAGIC populations. A quantitative trait loci (QTL) analysis of the 4-way population identified six major loci located on chromosomes 2B, 4D, 5A, 5B, 6A, and 7A together accounting for 42% of the variation in rhizosheath size. Rhizosheath size was strongly correlated with root hair length and was robust across different soil types in the absence of chemical constraints. Rhizosheath size in the MAGIC populations was a reliable surrogate for root hair length and, therefore, the QTL identified probably control root hair elongation. Members of the basic helixloop- helix family of transcription factors have previously been identified to regulate root hair length in Arabidopsis and rice. Since several wheat members of the basic helix-loop-helix family of genes are located within or near the QTL, these genes are candidates for controlling the long root hair trait. The QTL for rhizosheath size identified in this study provides the opportunity to implement marker-assisted selection to increase root hair length for improved phosphate acquisition in wheat. [ABSTRACT FROM AUTHOR]

Background and Aim Aluminium (Al3+) inhibits root growth of sensitive plant species and is a key factor that limits durum wheat (Triticum turgidum) production on acid soils. The aim of this study was to enhance the Al3+ tolerance of an elite durum cultivar by introgression of a chromosomal fragment from hexaploid wheat (Triticum aestivum) that possesses an Al3+ tolerance gene. Methods A 4D(4B) substitution line of durum wheat ‘Langdon’ was backcrossed to ‘Jandaroi’, a current semi-dwarf Australian durum. In the second backcross, using ‘Jandaroi’ as the recurrent parent, a seedling was identified where TaALMT1 on chromosome 4D was recombined with the Rht-B1b locus on chromosome 4B to yield an Al3+-tolerant seedling with a semi-dwarf habit. This seedling was used in a third backcross to generate homozygous sister lines with contrasting Al3+ tolerances. The backcrossed lines were characterized and compared with selected cultivars of hexaploid wheat for their Al3+ and Na+ tolerances in hydroponic culture as well as in short-term experiments to assess their growth on acid soil. Key Results Analysis of sister lines derived from the third backcross showed that the 4D chromosomal fragment substantially enhanced Al3+ tolerance. The ability to exclude Na+ from leaves was also enhanced, indicating that the chromosomal fragment possessed the Kna1 salt tolerance locus. Although Al3+ tolerance of seminal roots was enhanced in acid soil, the development of fine roots was not as robust as found in Al3+-tolerant lines of hexaploid wheat. Analysis of plant characteristics in the absence of Al3+ toxicity showed that the introgressed fragment did not affect total grain yield but reduced the weight of individual grains. Conclusions The results show that it is possible to increase substantially the Al3+ tolerance of an elite durum wheat cultivar by introgression of a 4D chromosomal fragment. Further improvements are possible, such as introducing additional genes to enhance the Al3+ tolerance of fine roots and by eliminating the locus on the chromosomal fragment responsible for smaller grain weights. [ABSTRACT FROM PUBLISHER]