Field-grown Winter Wheat Research Articles

Prediction of vernalisation in three Australian Vrn responsive wheats

This study sought to better estimate vernalisation in winter wheats, so that their early development and time of anthesis can be better predicted. For this, an accurate relationship between temperature and the effectiveness of vernalisation is required. Using previously published data, our study found that the relationship between temperature and effectiveness of vernalisation can be suitably described by a quadratic function. In contrast, most previous studies used linear interpolation functions to describe vernalising effectiveness. These consist of a series of linear functions of temperature over adjoining temperature ranges. An advantage of quadratic functions is that they allow effectiveness of vernalisation to be described in terms of underlying physiological processes, and require the estimation of fewer parameters to predict wheat development. Our study found the cardinal temperatures for vernalisation to be –3�C, 6.5�C, and 15.9�C, that is for the lower, optimum, and maximum temperatures respectively. To allow for different upper temperature limits for vernalisation, 2 quadratic temperature-vernalising effectiveness functions were used to predict accumulated daily vernalisation at 3 field sites. These predictions of daily vernalisation were compared with corresponding estimates produced with 3 previously proposed linear interpolation functions. Varying degrees of agreement were found between estimates produced by the 2 types of vernalising effectiveness functions. Equations that have been developed to predict floral initiation in winter wheats have not been previously evaluated in Australian field environments. These equations utilise the same underlying relationship between accumulated daily vernalisation and a measure of floral initiation, often the appearance of double ridges. Two of these equations were used to predict the appearance of double ridges for a field-grown Australian winter wheat, JF87%014. Neither equation could satisfactorily predict the timing of the double ridge development stage for this wheat, whatever vernalising effectiveness function was used to predict vernalisation in the field. Both equations had greatest difficulty in predicting the double ridge stage, in environments where vernalisation most delayed development. This finding suggests that equations currently predicting floral initiation in winter wheats do not utilise an accurate relationship between accumulated vernalisation and floral initiation. An alternative method of predicting anthesis in winter wheats is to predict final leaf number, but this approach has not been reliably applied in environments where vernalising temperatures vary.

Infection of Winter Wheat by a β-Glucuronidase-Transformed Isolate of Cephalosporium gramineum

ABSTRACT Field-grown winter wheat was inoculated with a beta-glucuronidase-transformed isolate of Cephalosporium gramineum in two field seasons to elucidate the mode of infection in resistant and susceptible cultivars. Colonization of viable root epidermis and cortical cells occurred as soon as 15 days postinoculation and the pathogen was found in the vascular tissues by 20 days postinoculation, well before freezing soil temperatures occurred. Penetration occurred directly through the root epidermis and through wounds adjacent to emerging secondary roots. The pathogen also penetrated through root cap cells and colonized meristematic tissues near root tips to gain access to the vascular system. Lower stem base colonization was observed where the pathogen penetrated directly through the epidermis, wounds, or senescent tissues. Appressorium-like structures, which appeared to aid penetration of cell walls, were often found within cells of both roots and stems after initial colonization. The mechanisms of resistance were not apparent, but less colonization occurred in resistant than in susceptible cultivars.

Impacts of ozone on the growth and yield of field-grown winter wheat

Seed of winter wheat ( Triticum aestivum L. cv Riband) was sown on 29 August 1992 in eight field plots. Four plots were exposed to elevated ozone (O 3) concentrations on 16 days between 29 August and 2 October 1992, for 6 h day −1, and on 27 days between 29 March and 24 August 1993, for 7 h day −1. Mean daily O 3 concentrations were ≈30 and 80 nmol mol −1 in ambient and fumigated plots, respectively. Plants were sampled on 5 November (1992), 14 January, 16 February, 1 April, 25 May, 23 June and 24 August (1993). No visible symptoms of O 3 damage or premature senescence were observed at any time over the course of the experiment. Exposure to elevated O 3 decreased the above ground biomass by reducing plant density and individual plant relative growth rate. However, there was no significant influence of the pollutant on the growth of the root relative to the shoot. Assessment of yield characteristics at the final harvest revealed an O 3-induced decrease in the number of grains per ear, as a result of fewer grains per spikelet and an increase in the number of infertile florets per spikelet. No significant effects of the pollutant on the number of ears per plant, spikelets per ear, or 1000 grain weight were found. As a result of the combined effects on the number of grains per ear and the decrease in plant density and growth rate, O 3 exposure reduced grain and straw yields (tonnes ha −1) by 13 and 8%, respectively. However, no significant change in the partitioning of dry matter between the grain and the straw was observed in fumigated plots. The findings are discussed within the context of United Nation Economic Commission for Europe critical level guidelines for the protection of crop yields, in relation to their application to winter-sown crops.

Methodology for Evaluation of Chemical Desiccation Tolerance in Winter Wheat

Postanthesis drought stress is a persistent problem for winter wheat (Triticum aestivum L.) production throughout much of the Great Plains of the USA. Chemical desiccation has been proposed as a method for improving postanthesis drought stress tolerance by identifying genotypes that support grain growth from nonstructural carbohydrates stored in the stems. The objectives of this study were to define cultivar responses to different chemical desiccants and dates of desiccant application and examine grain filling and stem dry weight loss patterns to assess the suitability of chemical desiccation as a screening method for postanthesis drought stress tolerance. In the first year of the study, 10 field-grown winter wheat cultivars were subjected to chemical desiccation with 2% sodium chlorate (NaClO3), 0.15% potassium iodide (KI), and 0.30% KI at 10 and 15 days postanthesis (DPA). Chemical desiccation 10 DPA induced significantly (P≤0.01) greater desiccation injury (for grain yield and its components) than chemical desiccation 15 DPA. Levels of desiccation injury were similar for NaClO3 and 0.30% KI, whereas the 0.15% KI treatment did not induce yield or yield component reduction. The second year of the study included evaluation of stem and grain dry weight changes following chemical desiccation. Chemical desiccation resulted in apparent reduction in grain filling rates and increased stem dry weight losses during grain filling. Cultivars that were more tolerant of chemical desiccation demonstrated increased stem dry weight immediately after anthesis and subsequent increased rates and amounts of stem dry weight loss during grain filling.

Relationship of photosynthetic acclimation to changes of Rubisco activity in field-grown winter wheat and barley during growth in elevated carbon dioxide

The responses of photosynthesis, Rubisco activity, Rubisco protein, leaf carbohydrates and total soluble protein to three carbon dioxide treatments were studied in winter wheat [Triticum aestivum (L.)] and barley [Hordeum vulgare (L.)]. Barley and wheat plants were grown in small field plots during 1995 and 1996 in clear, acrylic chambers (1.2–2.4 m2) and were provided with continuous carbon dioxide fertilization at concentrations of 350, 525 and 700 μmol mol−1. Photosynthetic rates of barley penultimate leaves and wheat flag leaves measured at growth carbon dioxide concentrations decreased with leaf age in all three CO2 treatments during 1995 and 1996. Photosynthetic acclimation to elevated CO2 was observed on seven of eight measurement dates for barley and ten of eleven measurement dates for wheat over both years. Initial Rubisco activity, total soluble protein and Rubisco protein in barley penultimate leaves and wheat flag leaves also decreased with leaf age. Total Rubisco activity was not used because of enzyme degradation. There was a significant CO2 treatment effect on initial Rubisco activity, total soluble protein and Rubisco protein for wheat in 1995 and 1996 and for barley in 1995. Responses of barley penultimate leaf Rubisco activity and leaf protein concentrations to elevated carbon dioxide were nonsignificant in 1996. A significant CO2 treatment effect also was detected when means of Rubisco activity, soluble protein and Rubisco protein for wheat flag leaves were combined over harvests and years. These three flag leaf parameters were not significantly different in the 350 and 525 μmol mol−1 CO2 treatments but were decreased during growth in 700 μmol mol−1 CO2 relative to the other two CO2 treatments. Ratios of photosynthesis at 700 and 350 μmol mol−1 were compared to ratios of Rubisco activity at 700 and 350 μmol mol−1 using wheat flag leaf data from 1995 and 1996. Regression analysis of these data were linear [y = 0.586 + 1.103t x (r2 = 0.432)] and were significant at P ≤ 0.05. This result indicated that photosynthetic acclimation was positively correlated with changes of initial Rubisco activity in wheat flag leaves in response to CO2 enrichment. Effects of elevated CO2 on wheat leaf proteins during 1995 and 1996 and on barley during 1995 were consistent with an acceleration of senescence.

Coca cola® is it! the ubiquitous extractant for micronutrients in soil

Abstract Coca Cola® has been found to be an excellent extractant for micronutrients in soils, particular for manganese (Mn). The main ingredients of Coca Cola®, phosphoric acid, reducing sugar and carbon dioxide are well proven in common extraction recipes. The overall extraction force of Coca Cola® was similar to that of commonly used phosphoric acid methods. Compared to DTP A, Coca Cola® extracted only 27% of iron (Fe), 38 % of copper (Cu), and 86% of zinc (Zn), but 165% of Mn. Correlation coefficients for the relationship between Coca Cola®‐extractable Fe, Zn, and Cu in soils and element concentrations in plants were the same as by means of the DTPA method. For Mn 49% of the variability in Mn concentrations observed in field grown winter wheat plants could be explained by Coca Cola®‐extractable soil Mn, but only 39% when employing DTPA. The critical value for available Mn and Zn on the investigated inceptisols was 17.8 mg/kg Mn and 1.3 mg/kg Zn for Coca Cola® and 9.4 mg/kg Mn and 1.8 mg/kg Zn for DTPA. Tentative critical values for Fe and Cu are 19.3 mg/kg Fe and 0.38 mg/kg Cu for Coca Cola® and 73 mg/kg Fe and 0.96 mg/kg Cu for the DTPA method. Besides the better results in extracting available micronutrient fractions from soils, further advantages of Coca Cola® as an extractant are its ubiquitous availability and readiness for use but also its easy and safe handling and the fact that the procedure has no harmful impacts on environment.

Improved correlation between soil exchangeable K and plant K contents on a tissue water basis

The correlation between the exchangeable K of 184 loess topsoils and K in field grown winter wheat at stem elongation was higher for the tissue water K (r2=0.602) than for the classical K in dry matter (r2=0.278). The tissue water K versus soil K function levelled out at an upper plateau of 207 mmol kg−1. Tissue water K is shown to be a useful indicator to derive critical values of soil K whereas the classical dry matter K is considered to be an inadequate plant K indicator under practical agricultural conditions.

Root decay and turnover of rhizodeposits in field-grown winter wheat and spring barley estimated by 14C pulse-labelling

Root decay and turnover of rhizodeposits in field-grown winter wheat and spring barley were estimated from the difference in 14C distribution between a sampling carried out 3 wk after pulse-labelling and a sampling 15–20 days before crop harvest. Plants were labelled at tillering and at ear emergence on plots under conventional (CONV) and integrated (INT) management. The latter was characterised by reductions in nutrient input, soil tillage and use of biocides. Of the roots formed at the tillering stage, 43% had decayed by the end of crop growth in winter wheat, independent of the management practice. Root decay in spring barley was higher than in wheat, and was higher in CONV (55%) than in INT (49%). Since most of the roots were produced around tillering, these values were used as estimates of accumulated annual root decay. Of the total rhizodeposition of assimilates fixed at tillering 87% was respired by microbes by the end of the growing season with winter wheat, 69% with barley in CONV and 54% with barley in INT. Decay of roots formed at ear emergence and the associated microbial respiration of rhizodeposits was lower than that of roots produced at tillering, but the same crop and management effects were observed. The assumptions underlying the calculations are discussed and the results are compared to data from minirhizotron observations.

Root-soil contact of field-grown winter wheat

Roots following existing macropores and voids normally have only partial root-soil contact. Roots penetrating the soil matrix (creating new macropores) initially have complete root-soil contact. Partial root-soil contact may decrease the roots effectivity in taking up water and nutrients. If all roots have complete root-soil contact, however, aeration may be problematic unless roots have a high airfilled porosity. For field-grown winter wheat, root-soil contact was quantified from horizontally oriented thin sections at three depths, 15, 25 and 45 cm, respectively. One day prior to sampling, surface-connected pores were stained by infiltrating a methylene blue solution. Roots were observed microscopically using polarized light, and their diameter, roundness (indicating orientation) and degree of soil contact were measured with a Quantimet 970 image analyzer. No relation was found between root-soil contact and root diameter or roundness. At 45 cm depth root-soil contact was less. For two fields, differing in soil organic matter content and current crop management, a different frequency distribution of root-soil contact was found in the plough layer. The percentage of roots with 100% root-soil contact was 65 and 37, that with 0% root-soil contact 5 and 14, respectively. For roots with partial root-soil contact the average degree of contact was about 60% in both cases. Average root-soil contact for the plough layer of the two fields was 84 and 66%, respectively. Roots without direct contact with the soil were growing mostly in surface-connected (blue stained) macropores. There was no difference in blue staining of the macropores with roots with 1–49% root-soil contact and those of the whole sample. Roots with 50–99% root soil contact occurred mostly in relatively small, non-stained pores.

Excised-leaf water status evaluation and associations in field-grown winter wheat

Water status measurements of excised leaves have been proposed as screening criteria for drought resistance in cereal crops. This study was conducted to assess the utility of such measurements in a wheat breeding program, through evaluation of environment and genotype differences in excised-leaf water status and examination of associations with several other traits. Initial water content (IWC) and rate of water loss (RWL) of excised leaves, epicuticular wax content (EW), stomatal frequency (SF), flag leaf area (LA), plant height (HT), heading date (HD), grain yield (GY), and test weight (TW) were measured on 24 winter wheat (Triticum aestivum L.) genotypes grown near Fort Collins, CO, during 1986–1987 and 1987–1988 (F87 and F88, respectively: subirrigated environments) and near Bennett, CO, during 1987–1988 (B88: dryland environment). Differences among genotypes for IWC and RWL were significant for F87 and F88, and nonsignificant for B88. Combined analyses of variance showed significant differences among environments for IWC and RWL. Initial water content was less for B88 than for F87 and F88. Significant genotype × environment (G × E) effects for IWC and RWL suggested that selection for high IWC or low RWL in irrigated environments (F87 and F88) may not provide selections that respond similarly in dryland environments (B88). Correlations for B88 revealed only a small, positive correlation between IWC and GY (r = 0.49*). For F87 and F88, significant correlations were observed between IWC and SF (r = −0.57** and −0.78**), RWL and LA (r = 0.74** and 0.71**), RWL and HT (r = 0.63** and 0.57**), and RWL and HD (r = 0.71** and 0.57**). Neither IWC or RWL were correlated with EW in any environment. Correlations between RWL (subirrigated) and G Y and TW (dryland) suggested that selection for low RWL in irrigated environments could provide some GY or TW advantage in dryland environments, despite observed G × E interaction and lack of RWL differences under the dryland environment. Key words: Cuticular transpiration, Triticum aestivum L., leaf water loss, stomata, drought

The pattern of proteins and of peptide hydrolase activities in shoots of field-grown winter wheat during the cold season

Winter cereals in the field are subject to low temperatures during an early stage of vegetative growth. Metabolic activities are low during this period. The quantities of enzymes involved in nitrogen assimilation, carbon assimilation and photorespiration were analyzed by gel electrophoresis and immunoblotting. The levels of all enzymes studied were well maintained throughout the winter, even during 2 marked low-temperature phases. The activities of various peptide hydrolases were measured in the same samples. The major endopeptidase activity at pH 5.0 remained relatively constant during the winter, while aminopeptidase and carboxypeptidase activities increased during a warmer phase at the beginning of January. The maintenance of important assimilatory enzymes during the period of low metabolic activity may allow a rapid restart of growth in spring.

Effect of Phloem Interruption on Senescence and Protein Remobilization in the Flag Leaf of Field-grown Wheat

Summary The phloem represents a link between senescing leaves (sources) and maturing (major sinks) in plants characterised by monocarpic senescence such as cereals. The redistribution of nutrients and assimilates might be involved in the control of senescence on a whole plant level. Field-grown winter wheat was steam-girdled at the base of the flag leaf lamina or below the ear in order to interrupt the phloem at these positions and to identify effects on flag leaf senescence. A phloem interruption below the ear delayed senescence of the flag leaf lamina as judged by chlorophyll contents and activities of assimilatory enzymes (phosphoribulokinase, glutamine synthetase). The rate of net photosynthesis was lowered in these leaves during the first week after the treatment, recovered and remained afterwards higher than in those of untreated control plants. Steam-girdling at the base of the leaf initiated its rapid senescence. The rate of photosynthesis declined rapidly after this treatment and was completely lost within one week, while dark respiration was initially slightly stimulated and decreased later than photosynthesis. The good correlations between enzyme activity measurements and immunoblot analyses indicate that not only the activities, but also the quantities of assimilatory enzymes were reduced. The interruption of source/sink relations affected flag leaf senescence, but the effects strongly depended on the position of the treatment. Leaf constituents were rapidly degraded after steam-girdling at the leaf base, although the export of breakdown products became impossible.

Cytokinins and abscisic acid in hardening winter wheat

During overwintering in a northern climate, winter wheat goes through a hardening process, followed by dehardening in late winter – early spring. This sequence of events may be partially controlled by changes in endogenous hormone levels. Crowns and leaf tissue from field grown winter wheat (Triticum aestivum L. cv. Norstar) seeded at the beginning of September were collected and freeze-dried at monthly intervals during the winters of 1985–1986 and 1986–1987. Material was also sampled and freeze-dried from seedlings grown in a growth chamber under hardening conditions (21 °C for 2 weeks plus 3 °C for 6 weeks) or nonhardening conditions (3 weeks at 21 °C). The tissues were analysed for cytokinins and abscisic acid. Cytokinin levels, measured with the soybean hypocotyl section assay, declined from October onwards and then rose to a peak in late winter (January and February, winter 1986–1987; February and March, winter 1985–1986), subsequently declining again. Abscisic acid, quantitated as the methyl ester by gas chromatography with an electron capture detector, increased in level from October to December, then decreased to a relatively low level between January and March. Hardened seedlings from the growth chamber contained significantly higher abscisic acid levels and significantly lower cytokinin levels than did the nonhardened seedlings. Key words: abscisic acid, cytokinins, hardening, Triticum aestivum, winter wheat.

Micronutrient inflow rates and mobilisation into soil solution in the root zone of winter wheat (Triticum aestivum L.)

Concentrations of Cu, Mn and Zn in root-zone soil solutions were determined for a field-grown winter wheat crop, and their inflow rates were calculated. This latter parameter was highest in mid-July. Depletion rates of the root-zone soil solution were calculated for Cu, Mn and Zn. Although calculated depletion rates indicated adequate early season levels of micronutrients, these reserves were depleted more rapidly than could be explained by plant uptake. The size of the soil solution reservoir of micronutrients appears to depend on the balance between mobilisation and immobilisation which in turn depends on the flux of biologically produced chelating ligands.

The Redistribution of Assimilate in Field-grown Winter Wheat

Les experiences relatees ont pour objet l'evolution et l'etude dynamique du stockage et de la remobilisation des assimilats au niveau des tiges de ble d'hiver cultive au champ. Cette etude, utilisant le 14 CO 2 comme traceur est effectuee a differents stages de developpement de la plante

Vorkommen diazotropher Bakterien in der Endorhizosphäre und Rhizoplane von Winterweizen auf einem Sandstandort mit gemäßigtem Klima

Summary Diazotrophic bacteria were isolated from the endorhizosphere and rhizoplane of field-grown winter wheat at two stages of plant growth (ZADOKS 23 and 59). On the rhizoplane their numbers were 400 times higher than in the endorhizosphere and the rhizoplane contains 66% diazotrophic bacteria of the bacterial population and the endorhizosphere 47%. Besides bacterial types are known as nitrogen fixers like Azospirillum, Pseudomonas, Klebsiella and Enterobacter there have been isolated nitrogen fixing strains of the genera Serratia, Acinetobacter and Lactobacillus. Most of the isolates showed a very low nitrogen-fixing activity — between 0.05 and 5 nmol C2H4 · tube−1.

Nitrogen assimilation in field-grown winter wheat: Direct measurements of nitrate reduction in roots using15N

Nitrate fertiliser labelled with15N was applied to a field grown crop of winter wheat. Uptake and assimilation of fertiliser nitrate was studied by monitoring the appearance of labelled nitrate and labelled amino acids in the xylem sap. Shortly after applying15N-nitrate to the soil about 30 per cent of recently absorbed15N was in the reduced form, indicating that roots of cereal crops can make a substantial contribution in reducing nitrate. Seasonal changes in crop growth andin vivo NRA are also described.

Effect of Water Stress on the Chloroplast Antioxidant System

The effect of water stress on glutathione reductase and catalase activities was evaluated in leaf blades of field-grown winter wheat (Triticum aestivum L.). Wheat was sown at two seeding rates under both irrigated and dryland conditions. Flag leaves from dryland plants sown at 60 kilograms/hectare showed no change in either glutathione reductase or catalase activities per unit leaf area, while leaves from the basal portion of the canopy exhibited a 273% increase in glutathione reductase activity and a 60% increase in catalase activity. Glutathione reductase activity in dryland plants sown at 120 kilograms/hectare increased 25% in flag leaves and 225% in basal leaves. No change in catalase activity was observed in either flag or basal leaves from these same plants. The increase in glutathione reductase activity in response to water stress was observed when activity was expressed on either a per unit leaf area, protein, or chlorophyll basis. No change in catalase activity was detected when enzyme activity was expressed on a protein basis.

A laboratory investigation of a physical rnechanisim for the extended infrared absorption (‘red shift‘) in wheat

Laboratory spectral measurements, on the components of both greenhouse and field grown winter wheat, were performed to identify the component and its appropriate response which gave rise to the extended infrared absorption or 'red shift' reported by Collins. Results of this study indicated that inherent intraplant adaxial (upper) leaf reflectances were of sufficient variability to suggest that an admixture of mechanisms may have utility on identifying the booting and head emergence stages in the life cycle of wheat. The physical mechanism for the shift was found to be relatively independent of the inherent variability in leaf spectra, and to be dependent upon the difference in the mode of deposition of cuticle upon the abaxial (lower) surface relative to that of the adaxial (upper) surface, the position of the flag leaf, and thus the surface exposed to the incident light during heading and after emergence of the head.

Leaf appearance and extension in field-grown winter wheat plants: the importance of soil temperature during vegetative growth

SUMMARYMainstem leaf appearance and leaf extension were monitored at 7-day intervals throughout the vegetative development of field-grown winter wheat plants, during two growing seasons 1977–9. Using hourly air and soil temperature records, it was found that the rate of leaf appearance was controlled by soil temperature, with the best linear relationships being obtained using accumulated soil temperature above a base temperature of 0 °C at 1 and 5 cm depth. Leaf appearance could be predicted equally well using 09.00 G.M.T. screen air temperatures although deviations from each linear relationship were found during very cold periods when slow leaf extension rates delayed leaf appearance.Leaf extension was also found to be linearly related to temperature, with the best fit being obtained using accumulated soil temperature above 2·5 °C at 5 cm depth, suggesting a threshold of 2·5 °C for leaf extension. The response to temperature (extension per unit of accumulated temperature) was the same for all the leaves of a given plant, or sowing date; however, the fact that the rate of leaf extension increased progressively with sowing date suggests that plant response to temperature may be determined at crop emergence (possibly mediated by rate of change of day length). Leaf extension rates could be predicted satisfactorily using 09.00 G.M.T. soil temperatures (5 or 10 cm) but less so using screen air temperatures.The prediction of plant leaf areas or crop leaf area indices using such relationships between temperature and leaf growth was found to be hampered by rapid and irregular rates of leaf senescence.