Genetic Structure of Cochliobolus sativus Populations Sampled from Roots and Leaves of Barley and Wheat in North Dakota

Common root rot (CRR) and spot blotch, caused by Cochliobolus sativus (Ito and Kurib.) Drechsl. ex Dast., are important diseases of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) worldwide. However, the population biology of C. sativus is still poorly understood. In this study, the genetic structure of three C. sativus populations, consisting of isolates sampled respectively from barley leaves (BL), barley roots (BR) and wheat roots (WR) in North Dakota, was analysed with amplified fragment length polymorphism (AFLP) markers. A total of 127 AFLP loci were generated among 208 C. sativus isolates analysed with three primer combinations. Gene diversity (H = 0.277-0.335) were high in all three populations. Genetic variation among C. sativus individuals within population accounted for 74%, whereas 26% of the genetic variation was explained among populations. Genetic differentiation was high (empty set PT = 0.261, corrected G ''(st)= 0.39), whereas gene flow (Nm) ranged from 1.27 to 1.56 among the three populations analysed. The multilocus linkage disequilibrium (LD) ((r) over bard = 0.0760.117) was moderate in C. sativus populations. Cluster analyses indicate that C. sativus populations differentiated according to the hosts (barley and wheat) and tissues (root and leaf) although generalists also exist in North Dakota. Crop breeding may benefit from combining genes for resistance against both specialists and generalists of C. sativus.

Diploid and tetraploid progenitors of wheat are valuable sources of resistance to the root lesion nematode Pratylenchus thornei

The root lesion nematode Pratylenchus thornei is widely distributed in Australian wheat (Triticum aestivum) producing regions and can reduce yield by more than 50%, costing the industry AU$50 M/year. Genetic resistance is the most effective form of management but no commercial cultivars are resistant (R) and the best parental lines are only moderately R. The wild relatives of wheat have evolved in P. thornei-infested soil for millennia and may have superior levels of resistance that can be transferred to commercial wheats. To evaluate this hypothesis, a collection of 251 accessions of wheat and related species was tested for resistance to P. thornei under controlled conditions in glasshouse pot experiments over two consecutive years. Diploid accessions were more R than tetraploid accessions which proved more R than hexaploid accessions. Of the diploid accessions, 11 (52%) Aegilops speltoides (S-[B]-genome), 10 (43%) Triticum monococcum (A (m) -genome) and 5 (24%) Triticum urartu (A (u) -genome) accessions were R. One tetraploid accession (Triticum dicoccoides) was R. This establishes for the first time that P. thornei resistance is located on the A-genome and confirms resistance on the B-genome. Since previous research has shown that the moderate levels of P. thornei resistance in hexaploid wheat are dose-dependent, additive and located on the B and D-genomes, it would seem efficient to target A-genome resistance for introduction to hexaploid lines through direct crossing, using durum wheat as a bridging species and/or through the development of amphiploids. This would allow resistances from each genome to be combined to generate a higher level of resistance than is currently available in hexaploid wheat.

Inheritance of resistance to root-lesion nematodes (Pratylenchus thornei and P. neglectus) in five doubled-haploid populations of wheat

Nematode species Pratylenchus thornei and P. neglectus are the two most important root-lesion nematodes affecting wheat (Triticum aestivum L.) and other grain crops in Australia. For practical plant breeding, it will be valuable to know the mode of inheritance of resistance and whether the same set of genes confer resistance to both species. We evaluated reactions to P. thornei and P. neglectus of glasshouse-inoculated plants of five doubled-haploid populations derived from five resistant synthetic hexpaloid wheat lines, each crossed to the susceptible Australian wheat cultivar Janz. For each cross we determined genetic variance, heritability and minimum number of effective resistance genes for each nematode species. Distributions of nematode numbers for both species were continuous for all doubled-haploid populations. Heritabilities were high and the resistances were controlled by 4-7 genes. There was no genetic correlation between resistance to P. thornei and to P. neglectus in four of the populations and a significant but low correlation in one. Therefore, resistances to P. thornei and to P. neglectus are probably inherited quantitatively and independently in four of these synthetic hexaploid wheat populations, with the possibility of at least one genetic factor contributing to resistance to both species in one of the populations. Parents with the greatest level of resistance will be the best to use as donor parents to adapted cultivars, and selection of resistance to both species in early generations will be optimal to carry resistance through successive cycles of inbreeding to produce resistant cultivars for release.

Nitrogen dynamics and nitrogen use efficiency of spring cereals under Finnish growing conditions

Nitrogen (N) is one of the main inputs in cereal cultivation and as more than half of the arable land in Finland is used for cereal production, N has contributed substantially to agricultural pollution through fertilizer leaching and runoff. Based on this global phenomenon, the European Community has launched several directives to reduce agricultural emissions to the environment. Trough such measures, and by using economic incentives, it is expected that northern European agricultural practices will, in the future, include reduced N fertilizer application rates. Reduced use of N fertilizer is likely to decrease both production costs and pollution, but could also result in reduced yields and quality if crops experience temporary N deficiency. Therefore, more efficient N use in cereal production, to minimize pollution risks and maximize farmer income, represents a current challenge for agronomic research in the northern growing areas. The main objective of this study was to determine the differences in nitrogen use efficiency (NUE) among spring cereals grown in Finland. Additional aims were to characterize the multiple roles of NUE by analysing the extent of variation in NUE and its component traits among different cultivars, and to understand how other physiological traits, especially radiation use efficiency (RUE) and light interception, affect and interact with the main components of NUE and contribute to differences among cultivars. This study included cultivars of barley (Hordeum vulgare L.), oat (Avena sativa L.) and wheat (Triticum aestivum L.). Field experiments were conducted between 2001 and 2004 at Jokioinen, in Finland. To determine differences in NUE among cultivars and gauge the achievements of plant breeding in NUE, 17-18 cultivars of each of the three cereal species released between 1909 and 2002 were studied. Responses to nitrogen of landraces, old cultivars and modern cultivars of each cereal species were evaluated under two N regimes (0 and 90 kg N ha-1). Results of the study revealed that modern wheat, oat and barley cultivars had similar NUE values under Finnish growing conditions and only results from a wider range of cultivars indicated that wheat cultivars could have lower NUE than the other species. There was a clear relationship between nitrogen uptake efficiency (UPE) and NUE in all species whereas nitrogen utilization efficiency (UTE) had a strong positive relationship with NUE only for oat. UTE was clearly lower in wheat than in other species. Other traits related to N translocation indicated that wheat also had a lower harvest index, nitrogen harvest index and nitrogen remobilisation efficiency and therefore its N translocation efficiency was confirmed to be very low. On the basis of these results there appears to be potential and also a need for improvement in NUE. These results may help understand the underlying physiological differences in NUE and could help to identify alternative production options, such as the different roles that species can play in crop rotations designed to meet the demands of modern agricultural practices.

Genetic Structure of Cochliobolus sativus Populations Sampled from Roots and Leaves of Barley and Wheat in North Dakota

Common root rot (CRR) and spot blotch, caused by Cochliobolus sativus (Ito and Kurib.) Drechsl. ex Dast., are important diseases of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) worldwide. However, the population biology of C. sativus is still poorly understood. In this study, the genetic structure of three C. sativus populations, consisting of isolates sampled respectively from barley leaves (BL), barley roots (BR) and wheat roots (WR) in North Dakota, was analysed with amplified fragment length polymorphism (AFLP) markers. A total of 127 AFLP loci were generated among 208 C. sativus isolates analysed with three primer combinations. Gene diversity (H = 0.277-0.335) were high in all three populations. Genetic variation among C. sativus individuals within population accounted for 74%, whereas 26% of the genetic variation was explained among populations. Genetic differentiation was high (empty set PT = 0.261, corrected G ''(st)= 0.39), whereas gene flow (Nm) ranged from 1.27 to 1.56 among the three populations analysed. The multilocus linkage disequilibrium (LD) ((r) over bard = 0.0760.117) was moderate in C. sativus populations. Cluster analyses indicate that C. sativus populations differentiated according to the hosts (barley and wheat) and tissues (root and leaf) although generalists also exist in North Dakota. Crop breeding may benefit from combining genes for resistance against both specialists and generalists of C. sativus.

Phenotyping novel stay-green traits to capture genetic variation in senescence dynamics

Stay-green plants retain green leaves longer after anthesis and can have improved yield, particularly under water limitation. As senescence is a dynamic process, genotypes with different senescence patterns may exhibit similar final normalised difference vegetative index (NDVI). By monitoring NDVI from as early as awn emergence to maturity, we demonstrate that analysing senescence dynamics improves insight into genotypic stay-green variation. A senescence evaluation tool was developed to fit a logistic function to NDVI data and used to analyse data from three environments for a wheat (Triticum aestivum L.) population whose lines contrast for stay-green. Key stay-green traits were estimated including, maximum NDVI, senescence rate and a trait integrating NDVI variation after anthesis, as well as the timing from anthesis to onset, midpoint and conclusion of senescence. The integrative trait and the timing to onset and mid-senescence exhibited high positive correlations with yield and a high heritability in the three studied environments. Senescence rate was correlated with yield in some environments, whereas maximum NDVI was associated with yield in a drought-stressed environment. Where resources preclude frequent measurements, we found that NDVI measurements may be restricted to the period of rapid senescence, but caution is required when dealing with lines of different phenology. In contrast, regular monitoring during the whole period after flowering allows the estimation of senescence dynamics traits that may be reliably compared across genotypes and environments. We anticipate that selection for stay-green traits will enhance genetic progress towards high-yielding, stay-green germplasm.

Post-head-emergence frost in wheat and barley: defining the problem, assessing the damage, and identifying resistance

Radiant frost is a significant production constraint to wheat (Triticum aestivum) and barley (Hordeum vulgare), particularly in regions where spring-habit cereals are grown through winter, maturing in spring. However, damage to winter-habit cereals in reproductive stages is also reported. Crops are particularly susceptible to frost once awns or spikes emerge from the protection of the flag leaf sheath. Post-head-emergence frost (PHEF) is a problem distinct from other cold-mediated production constraints. To date, useful increased PHEF resistance in cereals has not been identified. Given the renewed interest in reproductive frost damage in cereals, it is timely to review the problem. Here we update the extent and impacts of PHEF and document current management options to combat this challenge. We clarify terminology useful for discussing PHEF in relation to chilling and other freezing stresses. We discuss problems characterizing radiant frost, the environmental conditions leading to PHEF damage, and the effects of frost at different growth stages. PHEF resistant cultivars would be highly desirable, to both reduce the incidence of direct frost damage and to allow the timing of crop maturity to be managed to maximize yield potential. A framework of potential adaptation mechanisms is outlined. Clarification of these critical issues will sharpen research focus, improving opportunities to identify genetic sources for improved PHEF resistance.

Post-head-emergence frost in wheat and barley: defining the problem, assessing the damage, and identifying resistance

Radiant frost is a significant production constraint to wheat (Triticum aestivum) and barley (Hordeum vulgare), particularly in regions where spring-habit cereals are grown through winter, maturing in spring. However, damage to winter-habit cereals in reproductive stages is also reported. Crops are particularly susceptible to frost once awns or spikes emerge from the protection of the flag leaf sheath. Post-head-emergence frost (PHEF) is a problem distinct from other cold-mediated production constraints. To date, useful increased PHEF resistance in cereals has not been identified. Given the renewed interest in reproductive frost damage in cereals, it is timely to review the problem. Here we update the extent and impacts of PHEF and document current management options to combat this challenge. We clarify terminology useful for discussing PHEF in relation to chilling and other freezing stresses. We discuss problems characterizing radiant frost, the environmental conditions leading to PHEF damage, and the effects of frost at different growth stages. PHEF resistant cultivars would be highly desirable, to both reduce the incidence of direct frost damage and to allow the timing of crop maturity to be managed to maximize yield potential. A framework of potential adaptation mechanisms is outlined. Clarification of these critical issues will sharpen research focus, improving opportunities to identify genetic sources for improved PHEF resistance.

Effect of added nitrogen on plant litter decomposition depends on initial soil carbon and nitrogen stoichiometry

Increasing organic carbon inputs to agricultural soils through the use of pastures or crop residues has been suggested as a means of restoring soil organic carbon lost via anthropogenic activities, such as land use change. However, the decomposition and retention of different plant residues in soil, and how these processes are affected by soil properties and nitrogen fertiliser application, is not fully understood. We evaluated the rate and extent of decomposition of 13C-pulse labelled plant material in response to nitrogen addition in four pasture soils of varying physico-chemical characteristics. Microbial respiration of buffel grass (Cenchrus ciliaris L.), wheat (Triticum aestivum L.) and lucerne (Medicago sativa L.) residues was monitored over 365-days. A double exponential model fitted to the data suggested that microbial respiration occurred as an early rapid and a late slow stage. A weighted three-compartment mixing model estimated the decomposition of both soluble and insoluble plant 13C (mg C kg−1 soil). Total plant material decomposition followed the alkyl C: O-alkyl C ratio of plant material, as determined by solid-state 13C nuclear magnetic resonance spectroscopy. Urea-N addition increased the decomposition of insoluble plant 13C in some soils (≤0.1% total nitrogen) but not others (0.3% total nitrogen). Principal components regression analysis indicated that 26% of the variability of plant material decomposition was explained by soil physico-chemical characteristics (P = 0.001), which was primarily described by the C:N ratio. We conclude that plant species with increasing alkyl C: O-alkyl C ratio are better retained as soil organic matter, and that the C:N stoichiometry of soils determines whether N addition leads to increases in soil organic carbon stocks.

High-throughput Phenotyping of Wheat Seminal Root Traits in a Breeding Context

Water availability is a major limiting factor for wheat (Triticum aestivum L.) in rain-fed agricultural systems worldwide. Root architecture has important functional implications for the timing and extent of soil water extraction, yet selection for root traits in wheat breeding programs has been largely limited due to the lack of suitable phenotyping methods. The aim of this research was to develop a low-cost high-throughput phenotyping method to facilitate selection for desirable root traits. We developed a method to assess ‘seminal root angle’ and ‘seminal root number’ in seedlings – two proxy traits associated to root architecture of mature wheat plants (1). The method involves measuring the angle between the first pair of seminal roots and the number of roots of wheat seedlings grown in transparent pots (Figure 1). Images captured at 5 to 10 days after sowing are analyzed to calculate seminal root angle and number. Performing this technique under “speed breeding” conditions (plants grown at a density of 600 plants / m2, under controlled temperature and constant light) allows the selection based on the desired root traits of up to 5 consecutive generations within 12 months. Alternatively, when focusing only on germplasm screening, up to 52 successive phenotypic assays can be conducted within 12 months. This approach has been shown to be highly reproducible, it requires little resource (time, space, and labour) and can be used to rapidly enrich breeding populations with desirable alleles for narrow root angle and a high number of seminal roots to indirectly target the selection of deeper root system with higher branching at depth. Such root characteristics are highly desirable in wheat to cope with the climate model projections, especially in summer rainfall dominant regions including some Australian, Indian, South American and African cropping regions, where winter crops mainly rely on deep stored water.

Genomic regions influencing seminal root traits in barley

Water availability is a major limiting factor for crop production, making drought adaptation and its many component traits a desirable attribute of plant cultivars. Previous studies in cereal crops indicate that root traits expressed at early plant developmental stages, such as seminal root angle and root number, are associated with water extraction at different depths. Here, we conducted the first study to map seminal root traits in barley (Hordeum vulgare L.). Using a recently developed high-throughput phenotyping method, a panel of 30 barley genotypes and a doubled-haploid (DH) population (ND24260 × 'Flagship') comprising 330 lines genotyped with diversity array technology (DArT) markers were evaluated for seminal root angle (deviation from vertical) and root number under controlled environmental conditions. A high degree of phenotypic variation was observed in the panel of 30 genotypes: 13.5 to 82.2 and 3.6 to 6.9° for root angle and root number, respectively. A similar range was observed in the DH population: 16.4 to 70.5 and 3.6 to 6.5° for root angle and number, respectively. Seven quantitative trait loci (QTL) for seminal root traits (root angle, two QTL; root number, five QTL) were detected in the DH population. A major QTL influencing both root angle and root number (RAQ2/RNQ4) was positioned on chromosome 5HL. Across-species analysis identified 10 common genes underlying root trait QTL in barley, wheat (Triticum aestivum L.), and sorghum [Sorghum bicolor (L.) Moench]. Here, we provide insight into seminal root phenotypes and provide a first look at the genetics controlling these traits in barley.

小麦肉桂酰辅酶A还原酶（CCR）基因的分离和功能分析

作为植物界广泛存在的一类酚类聚合物，木质素是陆生植物正常生长发育过程中非常重要的生物大分子，而且与人类的生活息息相关。利用分子生物学手段和基因工程方法，从小麦中分离木质素生物合成途径的关键酶-肉桂酰辅酶A还原酶基因（CCR），研究肉桂酰辅酶A还原酶基因在木质素代谢途径中的调控规律，从其催化的限速步骤入手，来调控木质素的合成，有效的改变木质素的组成、含量和结构，是改善木质素在植物生长发育中的作用乃至开发木质素资源的关键所在。本文就小麦肉桂酰辅酶A还原酶基因的分离、表达特征及其在木质素合成途径中的作用开展了研究工作。 首先用RACE方法从小麦中克隆了CCR的两个cDNA的部分序列，序列分析表明它们编码的蛋白具有CCR的典型特点，GC含量高于均60%，两者在核酸水平和蛋白水平的同源性为76%和 69%，证明在小麦中至少存在着两个CCR基因。通过 RT-PCR和Northern 杂交确定W-cr6和W-cr19在小麦的发育中具有不同的表达特征，W-cr6主要在茎中表达，而W-cr19的表达集中在根中。以W-cr6为探针，从cDNA文库中筛选到一个全长1317bp的cDNA，命名为TaCCR1。TaCCR1包括开放阅读框 (ORF) 1047bp、5′端侧翼 72bp和3′端侧翼198bp的非翻译序列。TaCCR1能够编码由349个氨基酸组成的蛋白质，预期的分子量为37.4kD。同源性比较显示TaCCR1基因在核酸水平和蛋白质水平与其他物种的CCR基因的同源性高于60%。 为了分析CCR在木质素合成中的作用，用TaCCR1构建了用于转化烟草的正义和反义表达载体pStCCR和pAtCCR、用于转化小麦的正义和反义表达载体pBSC1和pBAC1。通过农杆菌介导得到了30株反义转基因烟草和12株正义转基因烟草。由于外源基因的抑制作用，转基因烟草在形态、木质素组成和含量、木质部显微结构上都程度不同的发生了变化。正义和反义的转基因株系呈现出株型矮化、木质素含量下降、木质部导管细胞壁受到破坏等现象。同时利用花粉管通道法转化小麦种子5000多粒，部分处理经过初步的PCR和 Southern分子鉴定获得了1株转基因株系，需要对其遗传、生理和形态特征做进一步的研究。 本文还对木质素对小麦茎杆的机械强度的影响做了初步的探讨，得到的结果是小麦茎杆的木质素含量、维管束的数量、茎杆有效的横界面积与其最大弯曲应力存在着正相关，而维管束的结构、密度对茎杆的最大弯曲应力没有明显的影响，从而为通过CCR基因来改善小麦茎杆的抗倒特性建立了生理学基础。

吐鲁番洋海墓地植物遗存与古洋海人及环境之间的关系

古民族植物学（Paleoethnobotany）在我国尚属一个比较年轻的学科，其主要研究对象是先民们所栽培或利用过的植物遗存（Plant remains），目的在于揭示古代人们对食物的选择，栽培植物的起源，早期农业的出现以及居址周围的自然与生态环境。吐鲁番地区降水稀少。干燥的环境，使得考古遗址中的植物遗存得以完好的保存。本论文首次对吐鲁番洋海墓地（2500 B. P. ）的包括木材、果实、种子、茎杆、叶片等在内的植物遗存进行了系统的研究，依此分析了当时的植被及环境，并对与当时的土著居民密切相关的植物类群进行了详细研究。 研究表明，吐鲁番洋海墓地植物群包括木材、禾本科粮食作物、杂草及其它植物共18 种。其中我们详细研究了14 种，隶属于7 科14 属，它们分别为禾本科黍属中的黍（Panicum miliaceum），大麦属中的青稞（Hordeum vulgare var. nudum），小麦属中的普通小麦（Triticum aestivum），芦苇属的芦苇（Phragmites australis），虎尾草属的虎尾草（Chloris virgata），小獐毛属的小獐毛（Aeluropus pungens var. pungens），稗属的稗子（Echinochloa crusgali），大麻科大麻属中的大麻（Cannabis sativa），紫草科紫草属中的小花紫草（Lithospermum officinale）， 豆科槐属中的苦豆子（Sophora alopecuroides var. alopecuroides），茄科枸杞属中的黑果枸杞（Lycium ruthenicum），松科云杉属中的云杉属未定种（Picea sp.）， 杨柳科杨属的胡杨（Popules euphratica）及柳属未定种（Salix sp.）。研究表明，这些植物遗存渗透到古洋海人生活的方方面面。其中，粮食作物为可能以黍为主，以普通小麦及青稞为辅;用以作装饰的为小花紫草的小坚果;可能与其原始宗教及医药相关的为大麻;与建筑相关的植物有芦苇、黑果枸杞、云杉（Picea sp.）、胡杨及柳（Salix sp.）等;与当地居民意义不大的杂草有稗子、苦豆子、小獐毛、虎尾草等。其中，大麻及小花紫草遗存的出土意味着当时的土著居民对当地的植物已经有了很高的认识水平;黍、青稞及普通小麦的出土意味着他们可能与东西方文化均有接触，为东西方文明的交融起了桥梁作用;所出土的部份植物如小獐毛、小花紫草、柳、苦豆子，尤其是稗子、芦苇及香蒲属植物等都属于喜湿植物。这说明，在当时的洋海墓地周边环境与今天相似，亦为一块植被丰富的绿洲，其中可能有大面积的湿地。

小麦幼苗阶段体内同化产物的运输和分配

用14C示踪法研究了冬小麦（Triticum aestivum L.）在整个冬前分蘖期内各个叶龄期主茎各叶位叶片同化产物的运输方向和供应范围，同时测定了主茎各叶位叶片净同化量对主茎叶片总同化量的贡献及其同化产物的运转率，对于各个分蘖出现后不同叶龄期接受主茎输出同化产物的量进行了定量的估计。得到以下主要结果： 1、整个冬前分蘖期，主茎一般维持有4-5片叶行使光合功能。其中顶部两片叶对植株同化产物的贡献最大。这两片叶的净同化量占主茎叶片总同化量的60%以上。主茎各叶位叶片在24小时内对标记同化产物的运转率在60%-85%之间。随着叶位下降，由于叶片衰老，不仅净同化量下降，而且叶片的同化物运转率也下降。整个分蘖期内，主茎叶片同化物的总运转率逐渐提高。 2、主茎叶片输出的同化物除主要供应主茎本身的顶端生长部位外，有相当大的一部分（约50%）供应给各分蘖，而不输入已经展开的主茎叶片。主茎顶部的两片主要功能叶主要供应主茎本身的顶端生长部位，0叶对主茎本身顶端生长部位的供应量始终保持在50%以上。随着叶位下降，对主茎本身的供应减少，而对分蘖的供应大大增加。 3、在向各分蘖的供应中，主茎顶部的三片主要功能叶集中供应正在出现（即正在长-1叶）的主茎一级分蘖和只有一片展开叶的主茎一级分蘖，对其它一级分蘖的供应，随蘖位降低，供应减少。其它主茎叶片都是主要供应本叶腋所包的上一节位的主茎一级分蘖，其次是本节位和上二节位的一级分蘖。每一主茎叶片的供应范围可分别达上、下两个节间距离。 4、各一级分蘖从主茎接受同化产物的量具有相同的变化规律。既分蘖在伸出叶鞘前和伸出后的早期（具有两片展开叶前）生长，从主茎接受相当大的部分同化物（约占主茎叶片总输出量的10-20%）;当分蘖具有两片展开叶时，从主茎接受同化物的量明显减少（占主茎叶片总输出量的10%）;当分蘖具有三片展开叶时，从主茎接受同化物已很少（5%以下）。作者认为，可以把具有两片展开叶的分蘖视为开始营养独立的分蘖。 5、主茎运向二级分蘖的同化物很少（5%以下）。主茎基部的一至两片叶对根系供应较多。但与地上部相比，主茎运往根系的同化物也比较少（10%以下）。 6、一级分蘖叶片的同化产物主要供应一级分蘖本身的生长部位和它所带的二级分蘖;一级分蘖叶片对二级分蘖的供应方式与主茎对一级分蘖的供应方式相同。一级分蘖的同化产物运向主茎和其它蘖群及分蘖很少。

小麦穗、小穗及子粒差异的生理原因

本文研究了冬小麦(Triticum aestivum L)在生长发育过程中，穗、小穗及子粒等产量构成因素不均衡性的生理原因。主要是从碳氮营养角度及维管系统分布等方面对造成主茎德及分蘖穗，穗中不同部位小穗、不同粒位子粒分化发育差异的生理原因进行了探讨，得到了下主要结果。 1、主茎及一蘖、二蘖的穗下节间及穗下第二节间横切面的各性状有明显的差异。穗下节间及穗下第二节间的直径，基本组织面积、中央维管束总面积及韧皮部总面积均以主茎为最大，一蘖次之，二蘖再次之。维管束数目以主茎为最多，一蘖、二蘖顺次减少。 2、从返青到拔节期。主茎叶鞘及叶片中可浴性糖含量最高，一蘖次之，二蘖再次之。尤为叶鞘中可溶性糖含量明显高于一蘖和二蘖。拔节期后，主茎叶鞘中可溶性含量较低，分蘖中含量较高。在此时期内，主茎叶鞘及叶片中可溶性氨基酸含量较低，而分蘖中氨基酸含量较高。 3、在小花两极分化期，即从药隔形成期至抽穗期，穗不同位小穗中可溶性糖及可浴性氨基酸含量不同，基本小穗中氨基酸含量最高，但可浴性糖含量最低。上部小穗中可浴性糖含量最高，但氨基酸含量最低。中都小穗中，碳氮含量较为平衡。 4。在子粒形成期，中部小穗各子粒中可溶性糖及氨基酸含量不同。第一粒位子粒中可溶性糖含量最高，二、三、四子粒顺次减少。尤其是第四子粒中可溶性糖含量极低。第二及第四子粒中氨基酸含量较高，第一及第三子粒中氨基酸含量较低。 5、在子粒形成期，不同部位小穗同一粒位子粒中可溶性糖及氨基酸含量不同，顶部小穗子粒中可溶性糖含量最高，中部小穗子粒次之，基部小穗子粒再次之。各子粒中氨基酸含量无明显差别，子粒形成初期，中部小穗子粒中氨基酸含量较高。 6、在子粒灌浆期，初期中部结实三粒的小穗第一子粒中可溶性糖含量最高，第二子粒次子，第三子粒最少。以后各子粒中可溶性糖含量无明显差别。灌浆始期，第一子粒的干重最重。第二粒次之，第三粒最轻。从灌浆中期开始，第二粒干重逐渐赶上并超过第一粒，最终子粒干重表现为II＞I＞Ⅲ。 7、在子粒灌浆初期，不同穗位小穗同一粒位子粒中可溶性糖含量有明显差别。中部小穗子粒中可溶性糖含量最高，上部小穗子粒次之，下部小穗子粒含量最低。以后各子粒中可溶性糖含量无明显差别。在整个灌浆过程中，中部小穗子粒的干重始终保持最高，上部及下部小穗子粒干重明显地低于中部小穗子粒干重。 8、穗内部维管束分布是不均衡的，中部小穗的小穗轴中维管数目多，面积大。而顶部及基部小穗的小穗轴中维管束数量较少，面积也较小。在同一小穗中，通向小花的维管束随着花位的升高，数量越来越少，面积越来越小。但通向一、二花的维管束数量及面积较为接近，差别不明显，通向三花、四花的维管束数目明显减少，面积明显减小。通入第一、二花的维管束是独立的，均直接来自小穗轴，第三花以上的小花和二花构成串联关系。 本文最后对小麦体内碳氮营养、维管束的分布和小麦主茎、分蘖及穗内部发育不均衡的关系进行了讨论。