The cost of stress: Dry matter partitioning changes with seasonal supply of water and nitrogen to dryland wheat

Spring wheat cv. ‘Gutha’ was grown in continuous wheat (W/W) and narrow-leafed lupin (L. angustifolius L. cv. Yandee)-wheat (L/W) rotation on a yellow earth over mottled clay (Arenic Fragiudult) in a mediterranean climate for two years. The first year had a higher than average rainfall with adequate soil water until anthesis. The second year was very dry (only 232 mm total rainfall) and soil water contents were low throughout the growing season. Nitrogen fertilizer (+N) treatments were included in both years. In the first year an adjacent experiment compared the effects of loosening a pronounced traffic pan which existed on the site (LS)versus unloosened (US). In the first year roots contained more dry matter than tops in the early vegetative stage in all crops and then declined exponentially to a ratio of 0.1 in the US and LS treatments. In the second year however, the decline was both linear and much less, so that root:shoot ratios at harvest were still between 0.4 and 0.8. There was a consistent trend in root:shoot ratios from the most favourable (LS) to least favourable (W/W-N) treatments over the combined two years’ data, and this was also found in grain yield, with a higher yield in year one from the LS than US, and the lowest yield in year two from the W/W-N treatment. The proportion of total biomass recovered from below ground was substantially higher than is commonly reported from studies carried out in temperate, high fertility soils, but probably still under-estimates of the true amount of dry matter in roots because of inadequacies of sampling, washing and storage techniques. Root length densities were much greater in the drier year, especially in the surface 0.1-m, and based on theoretical considerations, much greater than required for extraction of available water. The effect of environmental conditions on the relative size of cereal crop carbon sinks are discussed in relation to these results.     

Nutrient accumulation and translocation in maturing wheat plants grown on waterlogged soil

Wheat plants (Triticum aestivum L., cv. Arina) growing in large pots (perforated at the bottom for controls, intact for flooding) were embedded in the field in spring. Waterlogging was initiated at anthesis and was maintained throughout the maturation period. Grain yield as well as potassium, phosphorus and magnesium contents in the shoot were decreased on flooded soil, while manganese and iron contents increased considerably. Total calcium and zinc contents per shoot remained comparable to those in controls. The reduction of potassium, phosphorus and magnesium contents by waterlogging was greatest in the grains, while manganese and iron accumulated mostly in the vegetative parts and the glumes. Zinc contents were also lowered in the grains during waterlogging due to an inhibited redistribution from the vegetative parts to the grains. Our results indicate that flooding caused not only an accumulation of manganese and iron in the shoot, but also affected the redistribution of macro- and micronutrients to the maturing gains.     

Fate and effects on yield components of extra applications of nitrogen on spring wheat (Triticum aestivum L.) grown in solution culture

Spring wheat (Triticum aestivum L.) was grown with daily additions of nitrate-N. The relative addition rate of nitrate-N was decreased stepwise, and after 125 days of growth, 58 mg N plant^-1 had been introduced. The fate and effect of an extra addition of nitrate (20 mg N plant^-1) at six different times during the ontogeny (37, 54, 66, 79, 94 and 108 days from sowing) on grain yield and grain protein concentration was investigated. The plants absorbed all or most of the extra nitrate at all stages of development evaluated. Dry matter production of both aerial vegetative parts and grains, but not roots, generally increased as a result of the extra nitrate addition. The increase in grain dry matter was mainly an effect of an increased number of grains per plant. Extra nitrate applications had large effects on grain nitrogen content at all stages, but the effect on main shoot and tiller ears varied depending on the time of application. Early applications, i.e. before anthesis, mainly led to increased yield with unchanged protein concentration whereas late applications also led to increased grain protein concentration. The largest effect on grain nitrogen concentration (25–30% increase) was obtained when the extra nitrate was applied late after sowing, i.e. less than four weeks before final harvest. As the extra dose of nitrate was labelled with ¹⁵N, it was possible to follow the movement of the extra nitrogen addition within the plant. Samples were taken at one and five days after ¹⁵N-addition and at final harvest. There were differences in the movement of ¹⁵N depending on when it was introduced. Generally, net movement of the ¹⁵N-labelled N into the grain increased with age at application until 94 days after sowing when a maximum of 90% of the added ¹⁵N ended up in the grain.Abbreviations RN Relative increase in nitrogen content - RA Relative nitrogen addition rate - RG Relative growth rate - N nitrogen     

Long-term comparative study of soil nitrate test,Gilat plant indicator method and wheat nitrogen uptake

A long-term comparison between two routine soil nitrogen tests, soil nitrate versus plant indicator method, was performed on the Negev Desert loessial soil in Israel. The Gilat plant indicator method was found to be a better method to reflect the soil nitrogen availability for wheat under field conditions. It was found that 15 to 38 kg ha^-1 of NO₃-N, measured by nitrate soil test, for each 30 cm soil increment, is not available for plant uptake. This plant unavailable NO₃-N background in the soil cannot be leached by repeated irrigation cycles of 100 mm each, or by heavy rains.     

Molecular characterization of the fate of transgenes in transformed wheat (Triticum aestivum L.)

Molecular analysis of the transgenes bar and gus was carried out over successive generations in six independent transgenic lines of wheat, until the plants attained homozygosity. Data on expression and integration of the transgenes is presented. Five of the lines were found to be stably transformed, duly transferring the transgenes to the next generation. The copy number of the transgenes varied from one to five in the different lines. One line was unstable, first losing expression of and then eliminating both the transgenes in R3 plants. Although the gus gene was detected in all the lines, GUS expression had been lost in R2 plants of all but one line. Rearrangement of transgene sequences was observed, but it had no effect on gene expression. All the stable lines were found to segregate for transgene activity in a Mendelian fashion.     

Influence of soil solution aluminum on root elongation of wheat seedlings

Wheat (Triticum aestivum L.) seedlings were grown for 4 days in an acid soil horizon treated with 10 levels each of Ca(OH)₂, CaSO₄ and CaCl₂. The treatments resulted in a wide range of Al levels and Al speciation in soil solution. Seedling root length in the Ca(OH)₂ treatments was significantly related (p<0.01) to calculated Al³⁺ activity in soil solution. The Al–SO₄ complex in soil solution had a negligible effect on the root growth of Hart wheat, thus confirming the previously reached conclusion concerning the nonphytotoxicity of Al–SO₄. The short-term seedling root growth technique used in this investigation allowed for separation of Al effects on root elongation from those on plant nutrition and should be useful for studying Al toxicity relationships in soil.     

Variation in nitrogen use efficiency among soft red winter wheat genotypes

Summary Nitrogen use efficiency (NUE), defined as grain dry weight or grain nitrogen as a function of N supply, was evaluated in 25 soft red winter wheat genotypes for two years at one location. Significant genotypic variation was observed for NUE, nitrogen harvest index, and grain yield. Genotype x environment interaction for these traits was not significant. Several variables including N uptake efficiency (total plant N as a function of N supply), grain harvest index, and N concentration at maturity were evaluated for their role in determining differences in NUE. Nitrogen uptake efficiency accounted for 54% of the genotypic variation in NUE for yield and 72% of the genotypic variation in NUE for protein. A path coefficient analysis revealed that the direct effect of uptake efficiency on NUE was high relative to indirect effects.The investigation reported in this paper (No. 85-3-122) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director     

The effect of inoculation with Azospirillum brasilense on growth and nitrogen utilization by wheat plants

Azospirillium brasilense is a rhizosphere bacteria that has been reported to improve yield when inoculated on wheat plants. However, the mechanisms through which this effect is induced is still unclear. In the present work, we have studied the effects of inoculating a highly efficient A. brasilense strain on wheat plant grown in 5 kg pots with soil in a greenhouse, under three N regimes (0, 3 or 16 mM NO₃ ^–, 50 ml/pot once or twice-a -week), and in disinfected or non-disinfected soil. At the booting stage, the inoculated roots in both soils showed a similar colonization by Azospirillum sp. that was not affected by N addition. The plants grown in the disinfected soil showed a higher biomass, N content and N concentration than those in the non-disinfected soil, and in both soils the inoculation stimulated plant growth, N accumulation, and N and NO₃ ^– concentration in the tissues.At maturity, the inoculated plants showed a higher biomass, grain yield and N content than the uninoculated ones in both soils, and a higher grain protein concentration than the uninoculated. It is concluded that in the present experiments, A. brasilenseincreased plant growth by stimulating nitrogen uptake by the roots.     

Seedling root response of some Kenyan bread wheat cultivars grown in acid nutrient culture solution containing aluminum

The objective of this study was to determine whether a series of Kenyan bread wheat cultivars differed in tolerance to aluminum toxicity. Fourteen Kenyan wheat cultivars representing current and former widely grown cultivars of diverse pedigree origin, and two control cultivars, Maringa (Al-tolerant) and Siete Cerros (Al-susceptible), were tested in solution cultures with 0 (control), 148, 593, and 2370 M Al at pH 4.6. Highly significant (p0.01) differences in seedling growth were observed among cultivars for root mass, root length and root tolerance index (RTI). Significant (p0.05) cultivar × treatment interactions were observed for root mass and RTI. All characters were negatively affected by increased Al concentration, with root length and root mass being affected the most. RTI is a commonly used index which measures the relative performance of individual cultivars with and without aluminum stress. High levels of tolerance to Al were identified in the Kenyan cultivars by evaluating RTI with this simple nutrient solution technique. Romany and Kenya Nyumbu had RTI values approaching those of the Al tolerant Brazilian cultivar Maringa, a spring wheat standard that has been used for high Al tolerance.     

Accelerated production of transgenic wheat (Triticum aestivum L.) plants

We have developed a method for the accelerated production of fertile transgenic wheat (Triticum aestivum L.) that yields rooted plants ready for transfer to soil in 8–9 weeks (56–66 days) after the initiation of cultures. This was made possible by improvements in the procedures used for culture, bombardment, and selection. Cultured immature embryos were given a 4–6 h pre-and 16 h post-bombardment osmotic treatment. The most consistent and satisfactory results were obtained with 30 g of gold particles/bombardment. No clear correlation was found between the frequencies of transient expression and stable transformation. The highest rates of regeneration and transformation were obtained when callus formation after bombardment was limited to two weeks in the dark, with or without selection, followed by selection during regeneration under light. Selection with bialaphos, and not phosphinothricin, yielded more vigorously growing transformed plantlets. The elongation of dark green plantlets in the presence of 4–5 mg/l bialaphos was found to be reliable for identifying transformed plants. Eighty independent transgenic wheat lines were produced in this study. Under optimum conditions, 32 transformed wheat plants were obtained from 2100 immature embryos in 56–66 days, making it possible to obtain R3 homozygous plants in less than a year.     

Fertilizer nitrogen budgets of 15N-labelled sugarbeet (Beta vulgaris) tops and Na 15NO3 dressings split-applied to winter wheat (Triticum aestivum) in microplots on a loam soil

The fate of N from sugarbeet (Beta vulgaris L.) tops returned to the soil (50 T ha^-1) in autumn 1986 before sowing winter wheat (Triticum aestivum L.), and from NaNO₃ split-applied in 3 equal dressings (at tillering, stem elongation and flag leaf stages) was studied using isotopically labelled ¹⁵N in open stainless-steel cylinders pressed into the soil.At harvest, the percentage utilization (PU) of N from sugarbeet was very low (6.66%) and negatively influenced by fertilizer N (5.59%), while that of fertilizer N was rather high (69.64%) and unchanged by addition of tops. Residual N in soil represented 25.9% of the amount applied in tops and ranged from 33% for the tillering application to 21% for the flag leaf application. N losses (mainly denitrification) from sugar beet tops amounted to 67% and were very low for mineral fertilizer (less than 5%).     

Modelling potassium uptake by wheat (Triticum aestivum) crops

Spring wheat was grown in the field under deficient and sufficient levels of soil K and with high and low supplies of fertiliser nitrogen. Measurements were made of K uptake, soil nutrient supply parameters, root growth and, in solution culture, root influx parameters. Mechanistic models predicted uptake reasonably well under K-deficient conditions, but over-predicted uptake, by as much as 4 times, under K-sufficient conditions. The over-prediction was apparently due to poor characterisation of plant demand.     

Interaction of salinity and enhanced ammonium and potassium nutrition in wheat

Wheat (Triticum aestivum L.) was grown to maturity in a pot experiment in a calcareous silty sand soil. N was applied at two levels as granulated N-P fertilizers, amended or not with nitrification inhibitors (1% and 5% DCD, 1% N-serve). Potassium as KCl was given at three levels of application. P was applied at a uniform rate. Two levels of salinity were obtained by using the soil as such (EC= 0.3 mmho/cm) and by adding NaCl to the same soil (EC=2.4 mmho/cm). 1% DCD and 1% N-serve treatments gave significantly higher wheat grain yields and N-uptake than the other ones. Nitrate content of leachates indicated a prevalent nitrate nutrition in the treatment without nitrification inhibitors. The 5% DCD treatment showed a yield depression. In the lower N level treatments, a significant yield increase, generated by 1% DCD and N-serve was found in the salinized soil as compared to the non-saline soil. Soil salinity reduced N-uptake when nitrification inhibitors were not present. In treatments having the inhibitors, N-uptake was equal or greater in the salinized than in the non saline soil. An enhanced ammonium nutrition increased the P uptake.     

The control of boron accumulation by two genotypes of wheat

The mechanism of boron (B) uptake in wheat was studied using two genotypes with known differences in their ability to accumulate B. Influx and efflux of B was measured in the roots of intact 21 d old plants.Roots grown in 15 M B, when transferred to solutions containing 1mM B showed a rapid increase in B content for up to 60 min, after which no further increase was evident up to 4 h. No genotypic difference in B influx was apparent over these time periods. Roots grown in 1mM B for 7 d and then rinsed in B-free solutions quickly lost most of B that they contained within 1 hour; little further efflux was observed over the following three hours. As with the influx, no genotypic difference in B flux was evident.It is suggested that the lack of genotypic difference in the short-term B fluxes could be due to a masking effect of extracellular B bound in the cell walls of the roots.Department of Botany, University of Adelaide     

Identification of C-banded chromosomes in meiosis of common wheat,Triticum aestivum L.

Summary The C-banding pattern of nine meiotic chromosomes of common wheat (Triticum aestivum L.) as described. In F₁s of crosses between monosomics of Chinese Spring and two Spanish wheat cultivars, univalent chromosomes were used to aid the recognition and analysis of the C-banding pattern for the individual chromosomes. The identification of one chromosome involved in one translocation in Chinese Spring x Pané 247 has been made through heterochromatin bands observed in the chromosomes involved in multivalents.     

Mapping QTLs for nitrogen uptake in relation to the early growth of wheat (Triticum aestivum L.)

The objective of this study was to map QTLs for N uptake (NUP) in wheat, and to investigate factors influencing NUP. Two independent field trials with low N (LN) and high N (HN) treatments were conducted in the growing seasons of 2002–2003 (trial 1) and 2003–2004 (trial 2) to measure NUP per plant (N accumulated in the aerial part at maturity stage) of a doubled haploid (DH) population consisting of 120 DH lines derived from winter wheat varieties Hanxuan 10 and Lumai 14. A hydroponic culture with all nutrients supplied sufficiently was conducted to investigate shoot dry weight (SDW), root dry weight (RDW), tiller number (TN) and NUP (total plant N uptake) per plant of this mapping population at seedling stage. SDW, RDW, TN and NUP investigated in the hydroponic culture were significantly and positively correlated with each other, and with NUP under both LN and HN conditions in the field trials. Nine and eight QTLs for NUP were detected under LN and HN conditions in the field trials, respectively. Four to five QTLs for SDW, RDW, TN and NUP were detected in the hydroponic culture. One SDW QTL, three RDW QTLs, two TN QTLs detected in the hydroponic culture were linked with QTLs for NUP under LN or HN condition in the field trials. The positive correlation and genetic linkage for the traits between the field trials and the hydroponic culture demonstrated that greater seedling vigor of root and shoot is an important factor influencing N uptake in wheat. Diaoguo An and Junying Su: These authors contributed equally to this work. Section Editor: H.J. Kronzucker     

Empirical models to approximate calcium and magnesium ameliorative effects and genetic differences in aluminium tolerance in wheat

The activities of inorganic, monomeric aluminium (Al) species in the root environment are important in the toxicity of Al to plant roots, which may be ameliorated by increased activities of basic cations. Additionally, it has been suggested that electro-chemical processes in walls of root cells play a role in Al tolerance. Empirical models were proposed to accomodate genetic and calcium (Ca) and magnesium (Mg) ameliorative effects on Al toxicity. The models were tested using data from a solution culture study (with ionic strength 1.6 to 8.6 mM) in which wheat (Triticum aestivum L.) cvv. Warigal (Al-sensitive) and Waalt (Al-tolerant) were grown for 28 d at 0, 10 and 20 M Al, in factorial combination with 200, 400, 800 and 1600 M Ca and 100, 200, 400 and 800 M Mg. There was a poor relationship between relative total dry mass (TDM) (calculated as a percentage of the average TDM of each cultivar in the absence of added Al) and the activity of Al³⁺ or the sum of the activities of the monomeric Al species in solution. A model based on the ratios of activities of cations in solution, taking valency into consideration, was more successful, accounting for ca 85% of the observed variation in relative TDM. There were no systematic variations between observed values and those estimated by the model.     

The contribution of different regions of the seminal roots of wheat to uptake of nitrate from soil

A technique was developed to determine the physiological activity of defined sections of seminal roots of wheat grown in sand. Wheat plants were grown for 2 weeks in narrow columns of N-deficient sand to which all other nutrients had been added. The columns were split longitudinally and ¹⁵N-labelled nitrate, in an agar medium, supplied to 2 cm sections of root. Shoots and roots were analysed after 24 h to determine the uptake of ¹⁵N. Three sections were examined on either the secondary or tertiary seminal root: 1 cm from the seed (basal segment), 35 cm from the seed (middle segment) and 4 cm from the root apex (apical segment). Total uptake was greatest from the basal and middle segments, declining by 50% from the apical segment. However, uptake per unit root length, including exposed sections of lateral roots, was not significantly different along the root.     

Nitrogen uptake in relation to water availability in wheat

Nitrogen uptake and distribution in wheat (Triticum aestivum L.) are dependent on environmental conditions and in particular on the water regime. Under Mediterranean conditions, where high water stress at the end of the crop cycle is frequent, nitrogen uptake can be reduced, affecting yield and quality of the grain. To disclose these relations a field experiment was carried out in Central Portugal. Wheat was grown on a clay soil (Vertisol) at three water treatments: rainfed (WO), with 80 mm of irrigation (W1) and with 50 mm and 70 mm irrigations (W2). All treatments received 50 kg ha^–1 of N prior to sowing and were top-dressed with 140 kg ha^–1 of N, splitted in two applications, Kjeldahl N was determined in green leaves (GL), yellow leaves (YL), stems (ST), chaff (CH) and grain (GR). N uptake after anthesis was 40% of the total in W2, but was not noticeable in the other two treatments. N concentrations in the total above-ground plant dry matter, and in both YL and ST were not very different according to treatment, but water availability increased grain-N concentration. It seems, therefore, that grain protein concentration and N uptake can be substantially increased by late irrigations.