Review of wheat improvement for waterlogging tolerance in Australia and India: the importance of anaerobiosis and element toxicities associated with different soils

Background and Aims

The lack of knowledge about key traits in field environments is a major constraint to germplasm improvement and crop management because waterlogging-prone environments are highly diverse and complex, and the mechanisms of tolerance to waterlogging include a large range of traits. A model is proposed that waterlogging tolerance is a product of tolerance to anaerobiosis and high microelement concentrations. This is further evaluated with the aim of prioritizing traits required for waterlogging tolerance of wheat in the field.

Methods

Waterlogging tolerance mechanisms of wheat are evaluated in a range of diverse environments through a review of past research in Australia and India; this includes selected soils and plant data, including plant growth under waterlogged and drained conditions in different environments. Measurements focus on changes in redox potential and concentrations of diverse elements in soils and plants during waterlogging.

Key Results

(a) Waterlogging tolerance of wheat in one location often does not relate to another, and (b) element toxicities are often a major constraint in waterlogged environments. Important element toxicities in different soils during waterlogging include Mn, Fe, Na, Al and B. This is the first time that Al and B toxicities have been indicated for wheat in waterlogged soils in India. These results support and extend the well-known interactions of salinity/Na and waterlogging/hypoxia tolerance.

Conclusions

Diverse element toxicities (or deficiencies) that are exacerbated during waterlogging are proposed as a major reason why waterlogging tolerance at one site is often not replicated at another. Recommendations for germplasm improvement for waterlogging tolerance include use of inductively coupled plasma analyses of soils and plants.Key words: Waterlogging, microelements, toxicity, redox potential, wheat, anaerobiosis

‘No grain is ever produced without water, but too much water tends to spoil the grain and inundation is as injurious to growth as dearth of water.’ Narada Smriti XI, 19; circa 3000 bc.‘Waterlogging’ is defined as a condition of the soil where excess water limits gas diffusion; while ‘waterlogging tolerance’ is defined as survival or the maintenance of high growth rates, biomass accumulation or grain yield under waterlogging relative to non waterlogged (usually drained soil) conditions (Setter and Waters, 2003).

     

Root porosity, radial oxygen loss and iron plaque on roots of wetland plants in relation to zinc tolerance and accumulation

Background and aims

Wetland plants have been widely used in constructed wetlands for the clean-up of metal-contaminated waters. This study investigated the relationship between rate of radial oxygen loss (ROL), root porosity, Zn uptake and tolerance, Fe plaque formation in wetland plants.

Methods

A hydroponic experiment and a pot trial with Zn-contaminated soil were conducted to apply different Zn level treatments to various emergent wetland plants.

Results

Significant differences were found between plants in their root porosities, rates of ROL, Zn uptake and Zn tolerance indices in the hydroponic experiment, and concentrations of Fe and Mn on roots and in the rhizosphere in the pot trial. There were significant positive correlations between root porosities, ROL rates, Zn tolerance, Zn, Fe and Mn concentrations on roots and in the rhizosphere. Wetland plants with higher root porosities and ROL tended to have more Fe plaque, higher Zn concentrations on roots and in their rhizospheres, and were more tolerant of Zn toxicity.

Conclusions

Our results suggest that ROL and root porosity play very important roles in Fe plaque formation, Zn uptake and tolerance, and are useful criteria for selecting wetland plants for the phytoremediation of Zn-contaminated waters and soils/sediments.     

Interaction of aluminium and drought stress on root growth and crop yield on acid soils

Background

Aluminium (Al) toxicity and drought stress are two major constraints for crop production in the world, particularly in the tropics. The variation in rainfall distribution and longer dry spells in much of the tropics during the main growing period of crops are becoming increasingly important yield-limiting factors with the global climate change. As a result, crop genotypes that are tolerant of both drought and Al toxicity need to be developed.

Scope

The present review mainly focuses on the interaction of Al and drought on root development, crop growth and yield on acid soils. It summarizes evidence from our own studies and other published/related work, and provides novel insights into the breeding for the adaptation to these combined abiotic stresses. The primary symptom of Al phytotoxicity is the inhibition of root growth. The impeded root system will restrict the roots for exploring the acid subsoil to absorb water and nutrients which is particularly important under condition of low soil moisture in the surface soil under drought. Whereas drought primarily affects shoot growth, effects of phytotoxic Al on shoot growth are mostly secondary effects that are induced by Al affecting root growth and function, while under drought stress root growth may even be promoted. Much progress has recently been made in the understanding of the physiology and molecular biology of the interaction between Al toxicity and drought stress in common bean (Phaseolus vulgaris L.) in hydroponics and in an Al-toxic soil.

Conclusions

Crops growing on acid soils yield less than their potential because of the poorly developed root system that limits nutrient and water uptake. Breeding for drought resistance must be combined with Al resistance, to assure that drought resistance is expressed adequately in crops grown on soils with acid Al-toxic subsoils.     

Maintaining elevated Fe2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.)

Background and aims

Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes.

Methods

Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe²⁺ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship.

Results

Optimized nutrient solution conditions were 300 mg L^?1 Fe supplied as Fe²⁺ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe²⁺ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P?<?0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress.

Conclusion

This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity.     

Screening rough-seeded lupins (Lupinus pilosus Murr. and Lupinus atlanticus Glads.) for tolerance to calcareous soils

Soil- and solution-based screening methods were used to identify interspecific and intraspecific variation in lupins for tolerance to calcareous soils. Plants were grown for 21 days in a calcareous soil (pH 8.2; 50% CaCO₃; moisture content 90% of field capacity) for soil-based screening and in nutrient solution containing 15 mM KHCO₃ for solution-based screening. Chlorosis as an indicator of tolerance was recorded. Lupinus pilosus Murr. had the most tolerant genotypes and had the greatest range of intraspecific variation. Most genotypes of Lupinus atlanticus Glads. and Lupinus angustifolius L. were moderately intolerant, although two genotypes of L. atlanticus appeared to be tolerant. Lupinus albus L. had moderately tolerant to moderately intolerant genotypes, whilst the single genotypes of Lupinus cosentinii Guss. and Lupinus digitatus Forsk. appeared tolerant. In a field study six genotypes of L. pilosus identified in the soil-based screening as differing in their tolerance to the calcareous soil were grown on comparable calcareous (pH 8.3; topsoil 3% CaCO₃, subsoil 13% CaCO₃) and non-calcareous (pH 7.3) soils within a paddock. Chlorosis and nutrient concentrations in the youngest leaves were measured 53 days after sowing, whilst grain yield was estimated at harvest. Despite the soil containing a much lower CaCO₃ content than used in the screening method, the field study confirmed that moderately intolerant to intolerant genotypes had lower relative grain yields than more tolerant genotypes. Chlorosis rankings of the genotypes were correlated between field and the screening studies. It is suggested that the incorporation of genes conferring tolerance to calcareous soils into high yielding, agronomically suitable genotypes of L. pilosus should be an important objective in a lupin breeding program for calcareous soils.     

Soil aluminium effects on uptake,influx, and transport of nutrients in sorghum genotypes

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop of the world. In South America, it is grown mainly on acid soils, and its production on these soils is limited by deficient levels of available P, Ca, Mg, and micronutrients, and toxic levels of Al and Mn. A greenhouse experiment was undertaken to evaluate the genotypic differences in sorghum for uptake (U), inhibition (IH), influx (IN) into roots, and transport (TR) to shoot for nutrients at three levels of soil Al saturation (2, 41, 64%). Overall shoot nutrient U, IN, and TR showed a significant inverse correlation with soil Al saturation and shoot Al concentration, and a significant positive correlation with shoot and root dry weight. The nutrient uptake parameters differentiated genotypes into most and least efficient categories at various levels of soil Al saturation. The nutrient uptake parameters showed significant differences with respect to soil Al saturation, genotypes, and their interactions. In the current study, Al tolerant genotypes recorded higher IN and TR for P, K, Ca, Mg, Zn, and Fe than Al-sensitive genotypes. Therefore, these U, IN, and TR traits could be used in selection of sorghum plants adaptable to acid soils. Sorghum genotypes used in this study showed intraspecific genetic diversity in U, IN, and TR for essential nutrients. It was concluded that selection of acid soil tolerant genotypes and further breeding of acid (Al) tolerant sorghum cultivars are feasible.IICA/EMBRAPA/World BankIICA/EMBRAPA/World BankIICA/EMBRAPA/World Bank     

The effect of soil moisture on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Commercial narrow-leafed lupins (Lupinus angustifolius L.) grown on calcareous soils commonly display chlorotic symptoms resembling Fe deficiency. The severity of chlorosis increases with concurrent increases in soil moisture content. Our research has indicated that the rough-seeded lupin species, Lupinus pilosus Murr., has a range of adaptation to calcareous soils, from tolerant to intolerant. A pot experiment was conducted comparing a tolerant, a moderately tolerant and a moderately intolerant genotype of L. pilosus. Plants were grown for 35 days in a calcareous soil (50% CaCO₃) at three moisture contents (80%, 100% and 120% of field capacity); the growth was compared with that on a fertile black cracking clay control soil at 70% of field capacity. Visual chlorosis score, chlorophyll meter readings, number of leaves and shoot dry weights were recorded at 14, 21, 28 and 35 days after sowing. Concentrations of chlorophyll, active Fe and nutrients in the youngest fully expanded leaves were also measured. Results showed that increased soil moisture increased the severity of chlorotic symptoms (increased chlorosis score) in all genotypes. The tolerant genotype showed significantly less symptoms than other genotypes at all moisture contents. All genotypes were able to recover from chlorosis symptoms at 80% moisture in the calcareous soil. Chlorosis score negatively correlated with chlorophyll meter readings, chlorophyll concentration and foliar active and total Fe, and Mn concentrations. Visual chlorosis score appeared to be a cost effective, accurate and efficient method enabling classification of the tolerance of genotypes. The chlorotic symptoms were likely to be due to HCO₃ ^- induced nutrient deficiencies or a direct effect of HCO₃ ^- on chlorophyll synthesis. This study indicates that the most probable mechanism of tolerance is related to an ability to prevent uptake of HCO₃ ^- or efficiently sequester it once inside the root which prevents increases in internal pH and transport to the shoots.     

Considerations on the shuttle mechanism of FeEDDHA chelates at the soil-root interface in case of Fe deficiency

Aim

A mechanism of action for the performance of Fe chelates as soil-applied fertilizer has been hypothesized by Lindsay and Schwab (J Plant Nutr 5:821–840, 1982), in which the ligand participates in a cyclic process of delivering Fe at the root surface and mobilizing Fe from the soil. This “shuttle mechanism” seems appealing in view of fertilizer efficiency, but little is known about its performance. The chelate FeEDDHA is a commonly used Fe fertilizer on calcareous soils.

Methods

In this study, the performance of the shuttle mechanism has been examined for FeEDDHA chelates in soil interaction and pot trial experiments.

Results

The specificity of EDDHA ligands for chelating Fe from soils of low Fe availability is limited. Experimental support for a shuttle mechanism in soil-plant systems with FeEDDHA was found: specific metal mobilization only occurred upon FeEDDHA-facilitated Fe uptake. The mobilized metals originated at least in part from the root surface instead of the soil.

Conclusion

The results from this study support the existence of a shuttle mechanism with FeEDDHA in soil application. If the efficiency of the shuttle mechanism is however largely controlled by metal availability in the bulk soil, it is heavily compromised by complexation of competing cations: Al, Mn and particularly Cu.     

Physiological and molecular analysis of aluminum tolerance in selected Kenyan maize lines

Aims

Aluminum (Al) toxicity is an important limitation to maize production in many tropical and sub-tropical acid soil areas. The aim of this study was to survey the variation in Al tolerance in a panel of maize lines adapted for Kenya and look for novel sources of Al tolerance.

Methods

112 Kenyan maize accessions were phenotyped for Al tolerance in solution culture. Several Al tolerance-related parameters including relative net root growth (RNRG), root apex Al accumulation, Al-activated root organic acid exudation, and expression of the maize Al tolerance gene, ZmMATE1, were used to classify Kenyan maize accessions.

Results

Based on RNRG, 42 %, 28 %, and 30 % of the lines were classified as highly tolerant, moderately tolerant and sensitive, respectively. Tolerant accessions accumulated less Al in their root apices compared to sensitive lines. The Kenyan maize line, CON 5, and the Brazilian standard for tolerance, Cateto, exhibited the greatest Al tolerance based on RNRG, but CON 5 had only about 50 % of ZmMATE1 gene expression relative to Cateto. CON 5 also had low root apex Al content and high citrate exudation, suggesting that it may employ a citrate transporter other than ZmMATE1.

Conclusions

We identified a very Al tolerant Kenyan maize line whose Al tolerance may be based in part on a novel tolerance gene. The maize lines identified in this study are useful germplasm for the development of varieties suitable for agriculture on acid soils in Kenya.

     

The reduction in zinc concentration of wheat grain upon increased phosphorus-fertilization and its mitigation by foliar zinc application

Background and aims

Malnutrition resulting from zinc (Zn) and iron (Fe) deficiency has become a global issue. Excessive phosphorus (P) application may aggravate this issue due to the interactions of P and micronutrients in soil crop. Crop grain micronutrients associated with P applications and the increase of grain Zn by Zn fertilization were field-evaluated.

Methods

A field experiment with wheat was conducted to quantify the effect of P applications on grain micronutrient quality during two cropping seasons. The effect of foliar Zn applications on grain Zn quality with varied P applications was tested in 2011.

Results

Phosphorus applications decreased grain Zn concentration by 17–56%, while grain levels of Fe, manganese (Mn) and copper (Cu) either remained the same or increased. Although P applications increased grain yield, they restricted the accumulation of shoot Zn, but enhanced the accumulation of shoot Fe, Cu and especially Mn. In 2011, foliar Zn application restored the grain Zn to levels occurring without P and Zn application, and consequently reduced the grain P/Zn molar ratio by 19–53% than that without Zn application.

Conclusions

Foliar Zn application may be needed to achieve both favorable yield and grain Zn quality of wheat in production areas where soil P is building up.     

Small temporal differences in water uptake among varieties of pearl millet (Pennisetum glaucum (L.) R. Br.) are critical for grain yield under terminal drought

Background and aim

Intuitively, access to water from the soil at key phenological stages is important for adaptation to drought. This study aimed to assess the temporal pattern of water extraction under terminal drought stress.

Methods

Pearl millet genotypes with varying levels of terminal drought tolerance were grown in a lysimetric system with a soil volume and plant spacing similar to field conditions. Water extraction was monitored until maturity under differing water regimes.

Results

The yield did not differ among genotypes under well-watered (WW) conditions, and the water extraction profile of WW plants was similar across all genotypes. In contrast, the yield of sensitive genotypes was 30–100 % lower than that of tolerant lines under water stress (WS). The total volumes of water extracted by tolerant and sensitive genotypes were similar under WS; however, tolerant genotypes extracted less water prior to anthesis, and more water after anthesis. Grain yield was positively related to the amount of water extracted during week three after panicle emergence. Increased water extraction after anthesis benefitted the tillers more than the main culm and was correlated with higher staygreen scores.

Conclusion

Increased water uptake after anthesis, which results from earlier water conservation during pre-anthesis, increases yield under terminal drought in pearl millet.     

Comparison of As sequestration in iron plaque and uptake by different genotypes of rice plants grown in As-contaminated paddy soils

Background and aims

Limited information is available on comparing the iron plaque formation capabilities and their effect on arsenic (As) uptake by different rice plant genotypes grown in As-contaminated soils. This study investigates the effect of iron plaque on As uptake in different rice genotypes grown in As-contaminated soils from the Guandu Plain of northern Taiwan.

Methods

Twenty-eight rice genotypes including 14 japonica and 14 indica genotypes were used in this study. Rice seedlings were grown in As-contaminated soils for 38 days. The iron plaque formed on the rice roots were extracted using dithionite–citrate–bicarbonate. The concentrations of As, Fe, and P in soil solutions, iron plaque, and plants were measured. The speciation of As in the root’s iron plaque was determined by As K-edge X-ray absorption near-edge structure spectroscopy (XANES).

Results

The amounts of iron plaque formation on roots were significantly different among 28 tested rice genotypes, and 75.7–92.8 % of As uptake from soils could be sequestered in iron plaque. However, there were no significant negative correlations between the amounts of Fe or As in the iron plaque and the content of As accumulated in rice plants of tested genotypes. XANES data showed that arsenate was the predominant As species in iron plaque, and there were difference in the distribution of As species among different rice genotypes.

Conclusions

The iron plaque can sequester most of As uptake from soils no matter what rice genotypes used in this study. However, the iron plaque alone did not control the extent of As accumulation in rice plants from As-contaminated soils among 28 tested rice genotypes. Low As uptake genotypes of rice selected from this study can be recommended to be grown in the As-contaminated soils.     

Effects of soil acidity and water stress on corn and soybean performance under a no-till system

Background and Aims

Field studies have demonstrated that aluminum (Al) toxicity is low in no-till systems during cropping seasons that have adequate and well-distributed rainfall. This study evaluated the performance of corn (Zea mays L.) and soybean (Glycine max L. Merrill) on an acid loamy soil under a long-term no-till system, in response to surface liming and as affected by genotypic tolerance to Al and water stress.

Methods

A field trial examined the effect of surface application of lime (0, 4, 8, and 12 Mg ha^?1) on no-till corn and soybean nutrition and yield. Trials were also carried out in undisturbed soil columns taken from the unlimed and limed plots. Two hybrids/cultivars of corn and soybean, one sensitive and the other moderately sensitive to Al were grown at two soil moisture levels with and without water stress (50 % and 80 % water filled pore space).

Results

Alleviating soil acidity by liming improved nutrition and increased grain yields of corn and soybean. The benefits of liming on root length density, nutrient uptake and shoot biomass production of corn and soybean were more pronounced in Al-sensitive genotypes under water stress.

Conclusions

The results suggest that plants exposed to drought stress under no-till systems are more affected by Al toxicity.     

Aluminum tolerance of wheat does not induce changes in dominant bacterial community composition or abundance in an acidic soil

Aims

Aluminum-tolerant wheat plants often produce more root exudates such as malate and phosphate than aluminum-sensitive ones under aluminum (Al) stress, which provides environmental differences for microorganism growth in their rhizosphere soils. This study investigated whether soil bacterial community composition and abundance can be affected by wheat plants with different Al tolerance.

Methods

Two wheat varieties, Atlas 66 (Al-tolerant) and Scout 66 (Al-sensitive), were grown for 60 days in acidic soils amended with or without CaCO₃. Plant growth, soil pH, exchangeable Al content, bacterial community composition and abundance were investigated.

Results

Atlas 66 showed better growth and lower rhizosphere soil pH than Scout 66 irrespective of CaCO₃ amendment or not, while there was no significant difference in the exchangeable Al content of rhizosphere soil between the two wheat lines. The dominant bacterial community composition and abundance in rhizosphere soils did not differ between Atlas 66 and Scout 66, although the bacterial abundance in rhizosphere soil of both wheat lines was significantly higher than that in bulk soil. Sphingobacteriales, Clostridiales, Burkholderiales and Acidobacteriales were the dominant bacteria phylotypes.

Conclusions

The difference in wheat Al tolerance does not induce the changes in the dominant bacterial community composition or abundance in the rhizosphere soils.     

Genotypes of lucerne (Medicago sativa L.) show differential tolerance to manganese deficiency and toxicity when grown in bauxite residue sand

The physical and chemical characteristics of bauxite residue sand (BRS) affect the availability of a number of nutrients to plants, especially manganese (Mn). Lucerne (Medicago sativa L.) has been chosen as a BRS revegetation species because of its deep-rooting habit and tendency to tolerate moderately alkaline and saline soils, even though it is still prone to Mn deficiency stress. Sixteen commercially available lucerne genotypes were grown in BRS after addition of 5, 50 or 500 g Mn g^–1 BRS in a glasshouse. Manganese deficiency and toxicity symptoms were observed in 5 and 500 g g^–1 treatments, respectively. Symptom expression varied in severity between genotypes. Relative tolerance to Mn deficiency was defined by shoot dry weight at 5 g Mn g^–1 as a percentage of shoot dry weight at 50 g Mn g^–1. Salado, a genotype tolerant to Mn deficiency, and Sirosal, a genotype intolerant to Mn deficiency, were then grown with 0, 10, 20, 50, 100, 200 or 800 g Mn g^–1 BRS and found to have critical shoot Mn concentrations of 17.7 (Salado) and 26.6 g g^–1 (Sirosal). The use of genotypes with high relative Mn deficiency tolerance is recommended to help improve sustainability of BRS revegetation as well as to improve productivity on Mn-fixing agricultural soils.     

Evaluation of salt tolerance at the seedling stage in rice genotypes by growth performance, ion accumulation, proline and chlorophyll content

Aims

The objectives of this study were to evaluate salt tolerance level of rice genotypes using the well-established screening criteria; the salt injury score, survival percentage and ratio between Na⁺ and K⁺, as well as the contents of proline and chlorophyll, and to identify the relationship between salt tolerance and physiological characters.

Methods

One hundred and six rice genotypes were grown in hydroponic solutions subjected to salt stress and evaluated for salt tolerance ability and the physiological parameters. Multivariate cluster analysis was performed based on salinity tolerance scores (ST scores; score 1 being the most tolerant, score 9 the most sensitive), survival percentage and Na⁺/K⁺ ratio.

Results

ST scores based on salt injury symptoms were negatively correlated with survival percentage and chlorophyll concentration in the stressed seedlings but positively correlated with Na⁺/K⁺ ratio and proline content. Rice genotypes were classified into five salt tolerance groups: tolerant (T), moderately tolerant (MT), moderately sensitive (MS), sensitive (S) and highly sensitive (HS). The means of ST scores were significantly different among the five tolerance groups indicating that the ST score was the most reliable index for identifying salt tolerance. The means of Na⁺/K⁺ ratio and proline content in stressed seedlings were distinctively different between the extreme T and HS groups, but the means among the intermediate groups (MT, MS and S) were not significantly different. Chlorophyll content, on the other hand, was not related to the levels of salt tolerance.

Conclusions

In addition to the commonly used Na⁺/K⁺ ratio, proline content is suggested to be another useful criterion to differentiate salt-tolerant from salt-sensitive rice. This study also identified several Thai improved and local cultivars with the level of salt tolerance and physiological characters comparable to Pokkali, the standard salt-tolerant donor and may be utilized as alternative sources of salt tolerance alleles.     

Genetic analysis of the effect of zinc deficiency on Arabidopsis growth and mineral concentrations

Aims

Zinc deficiency is a common micronutrient deficiency in plants growing in many different regions of the world and is associated with disturbances in uptake and accumulation of mineral nutrients. Despite many published data on physiological factors affecting ion accumulation in Zn deficient plants, there is very little information about the genetic factors underlying this. We aim to identify genetic loci involved in mineral accumulation and plant performance under Zn deficiency.

Methods

Genetic loci were identified using the genetically segregating Ler × Cvi recombinant inbred line (RIL) population grown under Zn deficient conditions. Lines were analysed for the concentrations of Zn, Fe, Mn, K, Ca, Mg, P, Cu, S and Al in shoot dry matter. The same was done for the same lines grown under Zn sufficient conditions.

Results

We found considerable heritable variation for most mineral concentrations. In general, there was a positive correlation between mineral concentrations. For Zn only condition-dependent QTLs were identified, while for most other mineral concentrations both condition-dependent and -independent QTLs were identified. Several QTLs co-localize, including co-localization to loci controlling shoot biomass and to mineral concentration loci found previously in this and other RIL populations.

Conclusions

There are different genetic loci controlling Zn accumulation under deficient and sufficient Zn supply. Only for few minerals, their accumulation is controlled by Zn-supply-specific loci.     

Does radial oxygen loss and iron plaque formation on roots alter Cd and Pb uptake and distribution in rice plant tissues?

Background and Aims

Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant.

Methods

A rhizobag experiment was employed to investigate the correlations among radial oxygen loss (ROL), Fe plaque formation and uptake and distribution of Cd and Pb in 25 rice cultivars.

Results

Large differences between the cultivars were found in rates of ROL (1.55 to 6.88 mmol O₂ kg^?1 root d.w. h^?1), Fe plaque formation (Fe: 6,117–48,167 mg kg^?1; Mn: 127–1,089 mg kg^?1), heavy metals in shoot (Cd: 0.13–0.35 mg kg^?1; Pb: 4.8–8.1 mg kg^?1) and root tissues (Cd: 1.1–3.5 mg kg^?1; Pb: 45–199 mg kg^?1), and in Fe plaque (Cd: 0.54–2.6 mg kg^?1; Pb: 102–708 mg kg^?1). Rates of ROL were positively correlated with Fe plaque formation and metal deposition on root surfaces, but negatively correlated with metal transfer factors of root/plaque and distributions in shoot and root tissues.

Conclusions

ROL-induced Fe plaque promotes metal deposition on to root surfaces, leading to a limitation of Cd and Pb transfer and distribution in rice plant tissues.