School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemWheat grain protein content assessment via plant traits retrieved from airborne hyperspectral and satellite remote sensing imagery( 2023-11)Wheat (Triticum spp.) is crucial to food security. The source of a major proportion of humans’ total dietary carbohydrates and protein, it is among the world’s most widely grown crops and receives concomitantly large quantities of nitrogen (N) fertiliser. Wheat grain protein content (GPC; %) is a key to food quality, determining the baking quality of bread, the cooking quality of pasta, and the nutritional value of food products. For these reasons, wheat is classified and growers are typically paid predominantly on the basis of GPC, setting its farm income value. Global population growth encourages a justified focus on increasing yields. However, because grain proteins are diluted by carbohydrate (CHO) additions in the latter part of growing seasons, GPC is in an inverse relationship with yield: Improved yields are attended by the risk of reducing GPC. Moreover, GPC is influenced by interacting genetic and agronomic factors, soil properties and weather conditions that affect crops’ physiological status and stress levels and can therefore exhibit great spatial variability. Of the vast quantities of nitrogen (N) applied to wheat crops, a variable but substantial proportion is lost, inducing environmental damage and financial costs, which should be averted. Accurate GPC prediction could reduce N losses, assist in crop management decisions, and improve farm incomes. Nitrogen is central to proteins and can be strategically supplied to crops in order to achieve GPC benchmarks a precision agriculture (PA) approach. In such scenarios, estimates of GPC potential in advance of harvest could guide fertiliser dosing, improving fertiliser efficiency and potentially reducing costs. In contrast, where strategic fertiliser applications are not favoured, crop management could benefit from prior knowledge through strategic harvesting aimed at maximising payments per unit of grain at receival. However, GPC is a complex variable, influenced by multiple plant traits, themselves affected by soil and moisture conditions and whose effects change through the growing season. While remote sensing (RS) is likely the only practicable method of estimating GPC during seasons, and shows potential, prediction is complex and success has been limited. To make progress, it is necessary to more robustly identify imaging spectroscopy-based physiological traits closely associated with GPC. Traits with known physiological links to GPC, and which can be retrieved from imaging spectroscopy, include leaf area index (LAI) and chlorophyll (Ca+b). Further inspection of these and other RS traits may advance research relevant to PA. The inverse relationship of GPC to CHO assimilation permits the hypothesis that indicators of plant stress can improve GPC estimation. Such stress indicators, including the pigments anthocyanins and carotenoids, can be accurately retrieved along with other biophysical and biochemical quantities from hyperspectral (HS) remote sensing but their relationship to GPC had yet to be tested. Solar-induced fluorescence (SIF), emitted from the photosystems in proportion to instantaneous photosynthetic rate, was also untested as a GPC predictor. Moreover, in addition to the traits themselves, retrieval of plant traits by inversion of radiative transfer models (RTM) also remained untried for GPC estimation. Finally, the crop water stress indicator (CWSI), a proxy for evapotranspiration and hence carbon assimilation, should also show an association with GPC. Because a large majority of GPC studies have been conducted exclusively in the context of experimental plots, it is appropriate to extend research into the commercial cropping domain, populated to date by only two previous studies. This expansion is facilitated by the recent advent of spatially explicit GPC monitoring during crop harvests. While lacking the ultra-high spectral and spatial resolution of airborne HS sensing, satellite RS, in particular the Sentinel-2 (S2) platforms, possess advantages with respect to broadacre PA. These include a focus on reflectance bands adapted to vegetation sensing, appropriate spatial resolution, and frequent return times. This thesis presents results from piloted HS flights and ground campaigns at two dryland field experiments with divergent water supply and wide-ranging N fertiliser treatments, and from HS flights over 17 commercial fields planted to either bread (T. aestivum L.) or durum (T. turgidum subsp. durum (Desf.) Husn.) wheat, across two years in the southern Australian wheat belt. Imagery was acquired with airborne hyperspectral and thermal sensors, with spatial resolutions of approx. 0.3 m and 0.5 m for experimental plots and 1 m / 1.7 m in commercial fields. Leaf clip measurements, leaf and grain samples were collected from plots and through a transect in one field. In commercial fields, ~40,000 records obtained from harvester-mounted protein monitors. CWSI, SIF, vegetation indices and PRO4SAIL RTM inverted parameters were retrieved for each plot and GPC record location. Sentinel-2 (S2) timeseries (TS) were subsequently acquired for > 6,000 ha of commercial dryland wheat fields, inclusive of those included in HS campaigns, also in south-east Australia and through two consecutive years of dissimilar rainfall. In this case, growers provided ~92,000 GPC data points from harvester-mounted protein monitors. For each, Ca+b, leaf dry matter, leaf water content (Cw) and LAI were retrieved from the S2 images by radiative transfer model inversion. A gradient boosted machine learning algorithm was applied to analyse these traits’ importance to GPC and to predict GPC in 30% of samples unseen by the algorithm in training. From HS analyses, the photochemical reflectance index (PRI) related to xanthophyll pigments was consistently associated with GPC at both leaf and canopy scale in the plots and transect. In the commercial crops, a gradient boosted machine learning algorithm (GBM) ranked CWSI as the strongest indicator of GPC under severe water stress, while SIF, PRI and inverted biochemical constituents anthocyanins and carotenoids were consistently important under more moderate growing conditions. Structural parameters inverted from HS were not prominent except under severe drought when CWSI was omitted from models. Statistically significant results were obtained for GPC estimation in unseen samples, with best relationships between predicted and observed GPC of R2 = 0.80 and RMSE = 0.62 in a model built with thermal and physiological traits obtained from the HS and thermal imagery. Trait importance in S2 analyses was consistent with that seen from HS, in that the rankings of physiological, structural and water stress indicators were aligned: severe drought increased the importance of water stress measures relative to other traits, but in milder conditions physiological traits were emphasised. Airborne SIF added substantially to model skill from single-image S2, particularly in moderate conditions. While coefficients of determination varied substantially according to water stress, error metrics invariably sat within a tight range, under 1 % GPC. Overall, these predictive modelling results, obtained at within-field scale and in challenging conditions, place the current study among others in the same research domain, most of which consider either plot or regional scales. The strongest relationships between predicted and observed GPC (R2 = 0.86, RMSE = 0.56 %), in a model built from five S2 images across a season, were better than those from single-date hyperspectral (HS). In severe water stress, LAI was the main predictor of GPC early in the season, but this switched to Cw later. In milder conditions, importance was more evenly distributed both through the years and between traits, and predictive skill was lower. S2 TS had a clear accuracy advantage over single-date S2, and approached that of HS, especially in benign conditions, emphasising its previously unexplored potential for large-scale GPC monitoring. The methods developed are a novel contribution and can be proposed as a useful basis for future research.
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ItemMicrowave and biochar soil treatment alleviates arsenic phytotoxicity in wheat and rice( 2020)Abstract Arsenic (As) is a toxic metalloid, which is carcinogenic i.e. cancerous to humans. Besides the drinking water, accumulation of As in food grains through plant uptake, when cultivated in As contaminated soils, is a potential route of human dietary As exposure. This has inspired research into alleviating grain As accumulation, despite there being already existing strategies with major disadvantages such as low efficiency, high costs, and usage being restricted to smaller-scale operations. Therefore, pre-sowing microwave (MW) soil heating and sawdust biochar were used to investigate if they can reduce As concentration in wheat and rice. Microwave is a form of electromagnetic radiation, which can produce heat in the soil by inducing the rotation of the dipoles of polar molecules (e.g. water). Microwave heating depends on the dielectric properties of the soil. Therefore, a study was conducted to determine the dielectric properties of different types of soils with different moisture content. The results showed that the soil moisture was the major contributor to the dielectric behavior of soil since dielectric properties increase as soil moisture increases. Soil types also had an influence as the dielectric properties of sandy soil were much lower than the other soils such as clay and loam soil. To investigate the effect of MW and biochar on wheat and rice grain As concentration, both the wheat and rice soils were spiked with five As concentrations (As-0, As-20, As-40, As-60, and As-80 mg kg-1 soil). In addition to MW, biochar was used to reduce rice grain As accumulation since biochar has been gaining attention for its heavy metal immobilization capacity. After As application, three levels of biochar (BC-0, BC-10, and BC-20 t ha-1 soil) were added only in the rice-growing soil. Then, soils were treated for 0, 3, and 6 minutes (MW-0, MW-3, and MW-6) in an MW chamber to achieve the soil temperature of around room temperature, 60 oC, and 90 oC respectively. The crops were grown in a completely randomized design with four replications in a glasshouse during 2017 (wheat) and 2018 (rice). The results demonstrated that, in both the wheat and rice, MW soil treatments, especially the MW-6, alleviated As phytotoxicity and facilitated less grain total As concentration compared with the MW-0 treatment across all the soil As concentrations. Also, MW treatment significantly reduced the concentration of arsenite [As(III)], the most toxic form of As. Decreased grain As concentration in rice was recorded at BC-10 in lower levels of soil As concentrations (As-20 and As-40) while, a negative impact was observed at BC-20 across all the soil As concentration, compared with BC-0 treatment. Furthermore, rice grain As(III) concentration increased significantly in BC-20 treatment. Thus, MW-6 treatment could be used for the alleviation of grain As concentration in wheat and rice grain, whereas more study is needed for the best biochar application rate. However, understanding the residual effect of MW and biochar is crucial for the sustainability of the treatment. Therefore, the same varieties of wheat and rice were grown in the following year, using the same pots, without the addition of further MW or biochar treatment. The results revealed that, 360 days after MW soil treatments there was still the potential to alleviate grain As concentration in both wheat and rice. A similar result was observed for biochar treatment in the residual year with a positive effect at BC-10 and a negative effect at BC-20 treatment. Furthermore, it is unclear whether MW soil treatment is just a heating effect or if there is some other effect of the electromagnetic wave involved. Therefore, a glasshouse pot study was designed to investigate the effect of MW and conventional electric oven (EO) soil heating on As phytotoxicity alleviation in rice. The soil was spiked with three levels of soil As concentration (As-0, As-40, and As-80 mg kg-1) prior to applying MW and EO heat treatments, to achieve the soil temperature of around 80 - 90 oC. The results showed that, there was no statistically significant difference between MW and EO treatments regarding As phytotoxicity alleviation. However, the positive effect was more in MW treatment than the EO treatment. Significantly less total energy required in the MW to treat the soil than the EO. Besides the As phytotoxicity alleviation, the effect of MW soil heating on soil microorganisms, particularly bacteria, was a topmost concern and investigation was needed to ascertain that MW soil heating does not affect it drastically. Therefore, an experiment was designed to investigate the effect of MW heating (80 - 90 oC) on the soil bacterial community in As contaminated (As-0, As-40, and As-80 mg kg-1 soil) soils. The 16S rRNA bacterial gene copy numbers decreased significantly after MW soil heating but recovered back to its previous number 42 days post treatment. The bacterial diversity also decreased significantly in MW treated soils but did not recover even after 56 days from MW heating. However, there was no noticeable effects of soil As concentration on bacterial community were observed. Furthermore, relative abundance of some beneficial bacteria such as Bacillus and Symbiobacterium were significantly higher in the MW treated soils. Thus, MW soil heating at 80 - 90 oC can potentially be applied for As phytotoxicity alleviation without significantly destroying the ecologically important taxa. Overall, pre-sowing MW soil heating could be applied as a novel technique to alleviate As phytotoxicity in wheat and rice with lower As accumulation in the grain. Thus, application of the MW technology in the As contaminated area like Bangladesh could add another feather in the crown of the As remediation techniques and help to reduce the human health risk through As contaminated food grain. However, further research needed before adopting the MW soil heating technique where different aspects should be explored such as response of MW technology in the field condition, scaling up the MW equipment for field application, cost of MW application in the field at farmers level, long-term effect of MW treatment on soil nutrient dynamics, soil organic matter and soil biota and sustainability of the MW technology in field condition. Also, sawdust biochar could be used in combination with MW soil heating for As phytotoxicity alleviation; however, more study needed to set the appropriate rate of biochar application.
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ItemUnderstanding and mitigating the impacts of major dietary changes on dairy cows( 2018)Four experiments were conducted to investigate the effects of major dietary changes on ruminal pH, ruminal fluid composition, eating behaviour, feed intake and milk production of dairy cows. The impacts of both diet composition and management strategies were evaluated. The initial experiment investigated the impact of early adaptation when instigating a complete dietary change from one forage to another at calving, as is common practice in Irish dairy farming. Three weeks prior to their expected calving date, 14 spring calving dairy cows were assigned to one of two treatments: pasture silage pre-partum followed by fresh cut perennial ryegrass (PRG) post-partum, or fresh PRG both pre and post-partum. There were no differences in dry matter intake (DMI), body condition score, energy balance or milk yield and composition between the treatments. The results of the initial experiment suggested that early adaptation to avoid a major dietary change at calving did not result in health or production benefits. This was speculated to be due to the similarities of the two diets, creating little challenge for the rumen to adapt. The second experiment focused on a more challenging dietary change, incorporating a large amount of concentrate into a forage-only diet. Thirty-two lactating dairy cows were initially fed 100% lucerne hay cubes, wheat was then gradually substituted in until it comprised 40% of total dry matter (DM) and lucerne hay cubes, the remainder. Wheat was substituted for lucerne cubes via one of four strategies, (1) in six small increments (each 6.7% of total DM) over 6 days; (2) in six small increments (each 6.7% of total DM) over 11 days; (3) in three large increments (each 13.3% of total DM) over 6 days; or (4) in three large increments (each 13.3% of total DM) over 11 days. The 6-day strategies are considered rapid for the dairy industry yet none of the treatments resulted in ruminal fluid pH values that would have compromised ruminal function, nor were there differences in DMI or energy corrected milk (ECM) yields. Furthermore, there were no differences between ruminal fluid volatile fatty acid (VFA), lactate or ammonia concentrations. It is speculated that the properties of the lucerne cubes helped the ruminal contents resist the pronounced declines in pH often seen with the fermentation of large amounts of wheat. These results suggested that changes to rumen function are driven not only by the characteristics of the concentrate being introduced but also by those of the forage. The third experiment aimed to investigate the role of forages in grain adaptation. Twenty-eight lactating dairy cows were fed either PRG hay or lucerne hay and wheat was gradually substituted for forage in three equal increments, over 6 or 11 days, until wheat made up 40% of DM (~ 8 kg DM/cow per day). The results varied significantly with forage type. Cows fed lucerne hay ate more, produced more ECM and had lower ruminal pH values. Furthermore, of the cows fed lucerne hay, those adapted to wheat in the shorter time frame (6 days) exhibited significantly lower mean ruminal pH values. Despite the ruminal pH of these cows declining to levels typically considered low, none of their other measured parameters indicated compromised fermentation or acidosis. Rather, it was these same cows that had the greatest ECM yields, producing an average of 1.5 kg ECM/cow per day more than their 11-day counterparts. The 6-day adaptation strategy allowed for a rapid increase in metabolisable energy, while the hay promoted adequate buffering within the rumen. No difference was seen between adaptation strategies when PRG hay was fed. This was due to the higher metabolisable energy concentration and lower intake of the PRG hay resulting in a less pronounced increase in metabolisable energy intake with the wheat substitution. The greater intakes of cows fed the lucerne hay likely contributed to their greater ECM yields and lower ruminal pH values. However, both forages allowed the rumen contents to resist the large declines in ruminal pH that are typically seen during rapid grain adaptation. The final experiment aimed to further evaluate the role that forage plays in ruminal, behavioural and production responses to the incorporation of large amounts of wheat grain into the diet. Sixteen dairy cows in early lactation were fed a forage only diet of either lucerne hay, PRG hay or one of two cultivars of fresh PRG pasture (cultivar Bealey or Base) for three weeks. The forage-only diet was then supplemented with crushed wheat grain at a rate of 8 kg DM/cow per day, with no adaptation period. Wheat comprised between 32 and 43% of total DMI and was fed over two meals, followed by forage, for one day only. Feeding fresh pasture resulted in lower ruminal pH values, with pH remaining below 6.0 for longer each day. Following supplementation of wheat, cows fed pasture exhibited ruminal fluid pH levels associated with sub-acute ruminal acidosis. Hay created a ruminal environment that was better able to cope with the influx of acid produced as wheat was digested. A combination of increased ruminating time and a decreased rate of fermentation are likely responsible for the higher ruminal fluid pH values. The ruminal environment of cows fed lucerne hay remained most stable throughout the grain challenge, with ruminal fluid spending the least amount of time below pH 6.0. Reducing the introductory time for concentrates into a dairy cow’s diet means an ability to rapidly increase the energy content of a diet, resulting in milk production benefits. However, this thesis highlights the importance of forage choice when determining introduction strategies. Traditional, gradual adaptation strategies must still be employed when feeding highly digestible fresh forages. However, more aggressive adaptation strategies can be implemented when hays are used as the base forage. In situations where high energy grains are substituted for a low energy, high fibre basal forage, rapid introduction can have milk production benefits over gradual strategies.
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ItemProspects for ammonium sulphate to improve nitrogen and sulphur efficiency in alkaline soils of South Eastern Australia( 2016)Both nitrogen (N) and sulphur (S) are essential nutrients for plants growth. The N is typically provided by urea and S by gypsum fertilizer. The urea-N efficiency is often low due to the potential loss pathways [i.e. ammonia (NH3) volatilization, nitrate (NO3-) leaching intensified by nitrification, and denitrification] in the alkaline soils. This study investigated the effects of fertilization using ammonium sulphate (AS) or urea+AS instead of the most common practice of urea+gypsum on cereal and oil seed production and efficiency of N and S under variable agro-climatic conditions. The study was conducted in two south eastern Australian alkaline soils (i.e. the Vertosols of Nurrabiel and Horsham sites in the Wimmera and the Calcarosols in Nyrraby and Walpeup site in the Mallee region) with wheat and canola crops. The improved efficiency of AS over urea+gypsum was rarely observed in wheat under the Vertosols, however, promising in canola under the Calcarosols. In a 28 day lab incubation study, for example, AS maintained more N in ammonium (NH4+) form and reduced NO3- production with low N loss compared to urea+gypsum in the Walpeup Calcarosol. In glasshouse study of 28-42 days also indicated improved apparent N and S recovery in canola under the Walpeup Calcarosol. In three years (2009-2011) of field observation, the results indicated that biomass, grain yield, N and S recovery varied with soil types, crop types and agro-climatic conditions. The impact of fertilizer type on N and S efficiency was more pronounced with canola in the Calcarosol rather than canola in the Vertosol and wheat in the Calcarosol or Vertosol. For instance, AS increased biomass (39%), grain yield (49%) and N (49%) and S (44%) uptake in canola crops only in the Nyrraby Calcarosol in 2009 compared to urea+gypsum. Moreover, compared to urea+gypsum, the AS or urea+AS increased recovery efficiency of N by 5-8% and S by 17% in canola grown in the Nyrraby and Walpeup Calcarosols. The improvement in N recovery was attributed to the rhizosphere acidification in the Calcarosol as AS reduced soil pH by 0.2-0.5 units compared to urea+gypsum. Moreover, the low S uptake from gypsum compared to AS was caused by the negative interference of calcium (Ca) with N and phosphorus (P) uptake in canola under the Walpeup Calcarosol. Furthermore, an incubation study also showed that AS or urea+AS fertilizer reduced nitrous oxide (N2O 9-11%) emissions compared to urea+gypsum in the Walpeup Calcarosol. However, the advantage of using AS and/ or urea+AS fertilizers over urea+gypsum was variable and limited in wheat and the Vertosols of south eastern Australia. Therefore, AS remained as crop-soil specific in the fertilizer management strategies.
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ItemTransgene integration patterns in wheat( 2005)Wheat is a major crop worldwide. Continual development of wheat varieties by plant breeders is driven by the increasing demand for high-quality grain for an expanding range of end-uses. Starch quality is a target for improvement, as its end-use suitability depends on its composition and properties. In this thesis, microparticle bombardment was used to introduce an antisense sequence to the starch debranching enzyme, isoamylase into wheat (Triticum aestivum L.) and its diploid wild relative (Aegilops tauschii Cosson). In maize, rice and Arabidopsis, reduced isoamylase activity results in the replacement of amylopectin with a more highly branched polymer known as phytoglycogen. Ae. tauschii is often used in breeding programs as a source of traits for the improvement of bread wheat, but this is the first report of transgenic Ae. tauschii plants. Expression of the bar selectable marker and inheritance in the next generation was demonstrated, although most of the transgenic plants displayed transgene silencing. None of the transgenic bread wheat or Ae. tauschii had altered starch composition. Transgene expression and stability are determined by the structure of the transgenic locus, homologies between transgene and endogenous DNA sequences and the nature of the surrounding genomic DNA. Gene silencing is commonly associated with the presence of multiple intact or truncated transgene copies, which may be arranged as direct or inverted repeats, and the presence of bacterial sequences originating from the transformation vector backbone. This is a common observation amongst transgenic plants obtained via direct DNA delivery methods. The mechanism of transgene integration needs to be understood to enable the development of improved transformation systems and this was addressed as the second objective of this thesis. The structures of the transgenic loci in the wheat and Ae. tauschii were examined to provide possible reasons for transgene silencing and to examine the nature of transgene integration. Characteristics of the transgenic loci structures and the junctions between transgene-transgene and transgene-genomic DNA sequences were consistent with integration by illegitimate recombination involving double-strand break (DSB) repair. The proximity of transgenic loci to retrotransposon sequence may also have contributed to transgene silencing, as retrotransposons are often preferentially inactivated by host defence systems. The results presented in this thesis highlight the problems and limitations of wheat transformation. Improvements to transformation systems are essential to enable the recovery of useful transgenic plants at high frequencies, so that wheat breeders may fully utilise this technology in the development of improved wheat varieties. Agrobacterium-mediated transformation is likely to become the favoured method of transformation as integrated transgenes are more likely to be stably expressed and inherited. Alternative methods for obtaining gene knockouts, such as TILLING, are also discussed, as the adoption of such methods may be essential to allow commercial release of new improved wheat varieties circumventing public concern regarding genetically modified organisms.
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ItemPredicting the grain protein concentration of wheat from non-destructive measurements of the crop at anthesis( 2005)Grain protein concentration is an important specification for wheat, which determines the quality grade and price received by growers. It is difficult to achieve target grain protein concentration in semi-arid southern Australia, because of the low and variable rainfall. Growers may benefit from being able to predict grain protein concentration before harvest, especially where there is a threshold or `window' requirement for a particular grade. Grain outside specifications could be forward sold into other grades while prices were good. Spatial predictions of grain protein concentration would allow the pattern of harvest to be managed to optimise profit. This thesis proposed a method for predicting grain protein concentration from non-destructive measurements of the crop (spikes, spikelets) at or after anthesis. The theoretical propositions underlying the method were then evaluated using data from nitrogen fertiliser experiments, data from the literature, and a simulation exercise. The proposed method was to estimate grain number from spike or spikelet number. Variance in grain number, together with the diminishing returns response of grain number to nitrogen, would then be used. to estimate maximum grain number. Maximum grain number would be linked to a unique `critical' grain protein concentration, from which grain protein concentration at other grain numbers could be estimated. Spike and spikelet number were counted throughout grain-filling in nitrogen fertiliser experiments to determine the importance of time of counting. The time of counting was important for absolute, but not relative spike and spikelet numbers: Spike and spikelet number varied, throughout grain-filling, but interactions with nitrogen treatments were rare. Inclusion of spikelets in counting was based on glume length, which interacted with time of counting. Spike death was frequently observed and occurred in proportion to post-anthesis growth, at 0.187(±0.018) spikes/g. The rate with respect to grain yield was similar, at 0.190(±0.038) spikes/g. An analysis of mass/number relationships between grain, spike and spikelet number, and crop and spike biomass at anthesis, showed that grain number was better related to spike biomass, and that spike and particularly spikelet number, were better related to crop biomass. Spikelet number changed at .a rate of between 6.6 and 9.3 spikelets/g biomass across 'a range of experiments; spike number changed at a rate between 0.14 and 0.62 spikes/g. The interrelationships showed grain number should be related to spikelets/spike, and proportion of crop biomass in the spike. The relationships, however, only existed in some experiments and were not universal. An alternative suggested by the analysis was use of spike number as a direct proxy for grain number (ie. assuming constant grains per spike). Spike number was tested as a proxy for grain number initially by analysing the components of variance of grain number across nitrogen, rotation and plant density experiments. Spike number was the main component of variance in grain number (59.8- 71.0% of log(variance)) in nitrogen experiments, with no significant covariance between spike number and grains per spike. Grains per spike and covariance were much greater components of variance in plant density experiments, and grains per spike and spike number were equal sources of variance in rotation experiments, with small positive covariance. Spike number would be an unbiased, but not perfect proxy for grain number when nitrogen was the main factor varying, but not for factors related to rotation or plant density. Spike number and crop biomass at anthesis were compared as estimators of grain number in nitrogen experiments, in an analysis of the nature of the responses to nitrogen fertiliser. Grain number as an estimator of grain yield was included in the analysis to understand the likely effect of using grain number rather than yield as a predictor of grain protein concentration. Crop biomass at anthesis, spike number and grain number all reached maxima at similar nitrogen fertiliser rates, but crop biomass at anthesis was a more precise estimator for the maximum rate required for grain number (RMSE of nitrogen for maximum, 2.4 kg N/ha vs. 26.4 kg N/ha). Grain number had a maximum consistently higher (+32.6±8.0 kg N/ha) than the maximum for yield. Once nitrogen fertiliser rates were corrected for the different maxima, grain number and yield had identical relative response rates to nitrogen. The response rates of crop biomass at anthesis and spike number were both related to the response rate of grain number by a power relationship with exponent 0.6. The lack of methods for anticipating phase differences caused by late nitrogen application and pre-anthesis water deficit will prevent exploitation of these relationships in all environments. The estimation of maximum spike number from its variance was simulated across the width of an air-seeder, using consistent variations in nitrogen fertiliser rate between tynes to drive variance in spike number. Nitrogen fertiliser was normally distributed. It was possible to extrapolate the variance/spike number relationship to estimate the maximum only where the slope of the relationship was negative. Slopes close to zero caused errors. of fitting, where the `signal' from the relationship was indistinguishable from the `noise' in estimating variance. This coincided with low (below 0.8) relative spike numbers and led to over-estimation of low relative spike numbers. Low spike number because of sub- or supra-optimal nitrogen could be distinguished by the second derivative of the fitted function, which was positive for supra-optimal nitrogen. There was no unique `critical' grain protein concentration (for maximum yield or grain number) in southeastern Australia, but there was a consistent relationship between `critical' grain protein concentration and grain weight. The relationship in terms of grain nitrogen content was a linear function of grain weight. The parameters also varied with genotype, and signed relative grain number, calculated as GRS=1-G/GMax for supraoptimal nitrogen, and GRS=G/GMax-1 for sub-optimal nitrogen, where G is grain number. The best estimation of grain nitrogen across genotypes was: Grain N (mg N/grain) = 0.317 + 1.00 x GRS + (0.0115 -0.0181 x GRS) x W, where W is grain weight in mg/grain. The root mean squared error of grain protein concentration estimated from this function was 0.91%. Grain weight would need to be estimated to estimate grain protein concentration. Errors due to grain weight had more effect at higher GRS, and at lower grain weight. The conclusion was that grain protein concentration may be predicted using crop biomass or spike number as a proxy for grain number. Predictions would be best in the absence of pre-anthesis water deficit or nitrogen applied after Zadoks 32. The predictions would be best for relative grain number greater than 0.8 at sub-optimal nitrogen, and for any relative grain number at supra-optimal nitrogen. A confidence interval could still be provided for grain protein concentration at lower relative grain numbers with sub-optimal nitrogen. Predictions would be most accurate if grain weight was reliably above 35 mg/grain.
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ItemA molecular genetic study of seed dormancy in aegilops tauschii and expression of sprouting resistance in common hexploid wheat( 2004)The wild wheat relative Aegilops tauschii, has been identified as a useful source of preharvest sprouting (PHS) resistance for hexaploid bread wheat. Seed dormancy, a major contributor to PHS resistance, was shown to be partly expressed in hexaploid wheat derived from direct hybridisation between Triticum aestivum and Ae. tauschii. The enhanced seed dormancy possessed by the Ae. tauschii derived direct-cross wheat lines was manifested by embryo and seedcoat related mechanisms. The embryo related mechanism could not confer full expression of dormancy without the presence of seedcoat related factors, suggesting that the two mechanisms may be independently inherited. The presence of seedcoat related dormancy however, was not associated with the red seedcoat phenotype, which has traditionally been associated with PHS resistance in wheat. Red pigmentation of the seedcoat is likely to be "involved in the extreme dormancy possessed by Ae. tauschii but does not preclude partial expression within a white seedcoat background. The ability of Ae. tauschii derived wheat lines to enhance seed dormancy may have potential economic benefit to breeding for PHS resistance in white wheat varieties. Presently, white wheat varieties grown in the sprouting susceptible regions of Australia possess inadequate protection, costing the industry up to $100M annually. Inheritance of seed dormancy in Ae. tauschii was found to be controlled by one or two major genes which were influenced by minor genes and/or environmental factors. These results are consistent with the findings of several previous reports. Inheritance was shown to be dominant at the F3 grain generation, consistent with the generally dominant nature of dormancy possessed by red seeded genotypes. However, preliminary assessment of individual F2 seeds indicated recessive control of dormancy. Because genes possessed by the maternal tissues of the seedcoat do not segregate until the F3 seed generation, the F2 recessive model may be indicative of separate genetic control for the embryo related dormancy mechanism(s). Based on the above inheritance information, a bulked segregant analysis approach was initially undertaken for the development of linked molecular markers for seed dormancy. One microsatellite marker on chromosome 1D produced polymorphism between resistant and susceptible DNA bulks. A mapping approach was subsequently undertaken, revealing two significant QTL mapping to chromosome 1D. The putative QTL for seed dormancy will relate to the embryo component of dormancy, as the trait data employed related to the F2 seed generation, which was segregating for embryo related genes. The D genome of hexaploid wheat presently possesses the fewest QTL for PHS resistance of the three contributing genomes. Within the D genome, chromosome 1D was poorly represented in the literature. As such, 4e. tauschii represents a potential to bolster numbers of QTL for sprouting resistance in hexaploid wheat. Given the homology between the D genomes of Ae. tauschii and T aestivum, the microsatellite markers identified, flanking the putative QTL, will likely be transferable to hexaploid bread wheat. Seed dormancy is strongly influenced by conditions during growth. As such, unambiguous selection through use of molecular markers will expedite the introgression of this economically important trait into elite wheat cultivars.
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ItemA study of factors influencing in vitro stability of nitrate reductase from wheat leaves( 1979)This review and the following chapters are concerned predominantly with the processes occurring in higher and lower plants which regulate the amount of NR present in vitro as controlled by degradation, and the level of activity of the existing enzyme. Those factors regulating the synthesis of NR will not be discussed in any detail but only mentioned where they also affect other mechanisms regulating NR. Nitrate reductase is unstable both in vivo and in vitro (101,193, 252). In vitro instability occurs since the isolation of enzymes and other cell components from plant tissue involves disruption of the plant cell. This results in mixing of substances which in situ were rigidly compartmentalized and is likely to result in the isolation of an enzyme which is modified from its native form. Factors present in plant cells which make plant proteins particularly unstable in vitro have been reviewed by Stahrran (216) and Pirie (157). They include vacuole acids, carbohydrates, hydrolytic and oxidative enzymes and phenolic components and their derivatives. In vivo variation in activity occurs in response to a number of other factors, including tissue age (103,129,166,243,264) and environment (15,72,82,1.03,129,261). Tissue age has been shown to influence the activity or stability of NR extracted from a number of species including corn (194,195,264), wheat (221), oats (194,195), tobacco (195) and barley (48). Nitrate reductase has been demonstrated in nearly all plant parts (16) and its ubiquitous presence suggested in higher plants (16,184). Nevertheless, due to the number of factors involved, detection of activity would only occur given suitable physiological and environmental conditions together with use of the correct extraction and assay procedure. Determining if the level of activity derived is an accurate estimate of the in situ activity is even more difficult. This has been attempted by correlating NR activity and grain or plant nitrogen (28, 36) . In vivo instability is indicated by the decline in NR activity with the onset of darkness, depletion of nitrate supply, and water or heat stress (11,82,121,168,235). Under appropriate conditions these factors could also affect the enzyme in vitro.
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