A worldwide bread wheat core collection arrayed in a 384-well plate

Bread wheat (Triticum aestivum), one of the world’s major crops, is genetically very diverse. In order to select a representative sample of the worldwide wheat diversity, 3,942 accessions originating from 73 countries were analysed with a set of 38 genomic simple sequence repeat (SSR) markers. The number of alleles at each locus ranged from 7 to 45 with an average of 23.9 alleles per locus. The 908 alleles detected were used together with passport data to select increasingly large sub-samples that maximised both the number of observed alleles at SSR loci and the number of geographical origins. A final core of 372 accessions (372CC) was selected with this M strategy. All the different geographical areas and more than 98% of the allelic diversity at the 38 polymorphic loci were represented in this core. The method used to build the core was validated, by using a second set of independent markers [44 expressed sequence tag (EST)-SSR markers] on a larger sample of 744 accessions: 96.74% of the alleles observed at these loci had already been captured in the 372CC. So maximizing the diversity with a first set of markers also maximised the diversity at a second independent set of locus. To relate the genetic structure of wheat germplasm to its geographical origins, the two sets of markers were used to compute a dissimilarity matrix between geographical groups. Current worldwide wheat diversity is clearly divided according to wheat’s European and Asian origins, whereas the diversity within each geographical group might be the result of the combined effects of adaptation of an initial germplasm to different environmental conditions and specific breeding practices. Seeds from each accession of the 372CC were multiplied and are now available to the scientific community. The genomic DNA of the 372CC, which can be entirely contained in a 384-deep-well storage plate, will be a useful tool for future studies of wheat genetic diversity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Association mapping of leaf rust resistance loci in a spring wheat core collection

Key message

We identified 15 potentially novel loci in addition to previously characterized leaf rust resistance genes from 1032 spring wheat accessions. Targeted AM subset panels were instrumental in revealing interesting loci.

Abstract

Leaf rust is a common disease of wheat, consistently reducing yields in many wheat-growing regions of the world. Although fungicides are commonly applied to wheat in the United States (US), genetic resistance can provide less expensive, yet effective control of the disease. Our objectives were to map leaf rust resistance genes in a large core collection of spring wheat accessions selected from the United States Department of Agriculture-Agricultural Research Service National Small Grains Collection (NSGC), determine whether previously characterized race-nonspecific resistance genes could be identified with our panel, and evaluate the use of targeted panels to identify seedling and adult plant resistance (APR) genes. Association mapping (AM) detected five potentially novel leaf rust resistance loci on chromosomes 2BL, 4AS, and 5DL at the seedling stage, and 2DL and 7AS that conditioned both seedling and adult plant resistance. In addition, ten potentially novel race-nonspecific resistance loci conditioned field resistance and lacked seedling resistance. Analyses of targeted subsets of the accessions identified additional loci not associated with resistance in the complete core panel. Using molecular markers, we also confirmed the presence and effectiveness of the race-nonspecific genes Lr34, Lr46, and Lr67 in our panel. Although most of the accessions in this study were susceptible to leaf rust in field and seedling tests, many resistance loci were identified with AM. Through the use of targeted subset panels, more loci were identified than in the larger core panels alone.

     

甘肃省冬小麦生长发育对暖冬现象的响应

运用甘肃省天水、西峰两地1951-2005年的气温资料及天水、西峰农业气象试验站1981-2003年冬小麦物候观测资料,分析探讨了甘肃冬小麦种植区50多年的冬季气温变暖趋势及冬小麦生长发育过程对气候变暖的响应．结果表明：冬季气温升高对冬小麦生长发育产生了较大影响．在最近20多年,冬小麦越冬死亡率下降到2％以下,越冬天数减少了7～8d,整个生育期缩短8～10d,返青一开花期天数延长7d,这有利于冬小麦生产及气候资源的利用-同时,冬季气温升高及降水减少也使冬小麦产量稳定性变差,麦田病、虫危害发生率增加,给冬小麦的安全生产增加了不确定因素．     

Genomic regions associated with the nitrogen limitation response revealed in a global wheat core collection

Modern wheat (Triticum aestivum L.) varieties in Western Europe have mainly been bred, and selected in conditions where high levels of nitrogen-rich fertilizer are applied. However, high input crop management has greatly increased the risk of nitrates leaching into groundwater with negative impacts on the environment. To investigate wheat nitrogen tolerance characteristics that could be adapted to low input crop management, we supplied 196 accessions of a wheat core collection of old and modern cultivars with high or moderate amounts of nitrogen fertilizer in an experimental network consisting of three sites and 2 years. The main breeding traits were assessed including grain yield and grain protein content. The response to nitrogen level was estimated for grain yield and grain number per m² using both the difference and the ratio between performance at the two input levels and the slope of joint regression. A large variability was observed for all the traits studied and the response to nitrogen level. Whole genome association mapping was carried out using 899 molecular markers taking into account the five ancestral group structure of the collection. We identified 54 main regions involving almost all chromosomes that influence yield and its components, plant height, heading date and grain protein concentration. Twenty-three regions, including several genes, spread over 16 chromosomes were involved in the response to nitrogen level. These chromosomal regions may be good candidates to be used in breeding programs to improve the performance of wheat varieties at moderate nitrogen input levels.     

A core collection and mini core collection of Oryza sativa L. in China

The extent of and accessibility to genetic variation in a large germplasm collection are of interest to biologists and breeders. Construction of core collections (CC) is a favored approach to efficient exploration and conservation of novel variation in genetic resources. Using 4,310 Chinese accessions of Oryza sativa L. and 36 SSR markers, we investigated the genetic variation in different sized sub-populations, the factors that affect CC size and different sampling strategies in establishing CC. Our results indicated that a mathematical model could reliably simulate the relationship between genetic variation and population size and thus predict the variation in large germplasm collections using randomly sampled populations of 700?C1,500 accessions. We recommend two principles in determining the CC size: (1) compromising between genetic variation and genetic redundancy and (2) retaining the main types of alleles. Based on the most effective scheme selected from 229 sampling schemes, we finally developed a hierarchical CC system, in which different population scales and genetic diversities allow a flexible use of genetic resources. The CC, comprising 1.7% (932) of the accessions in the basic collection, retained more than 85% of both the SSR and phenotypic variations. A mini core collection, comprising 0.3% (189) of the accessions in the basic collection, retained 70.65% of the SSR variation and 76.97% of the phenotypic variation, thus providing a rational framework for intensive surveys of natural variation in complex traits in rice genetic resources and hence utilization of variation in rice breeding.     

Genealogic analysis of the resistance of winter wheat to common bunt

Comparative genealogical analysis of North American (the United States and Canada) and Eastern European (Russia and Ukraine) winter wheat cultivars resistant and susceptible to common bunt has been performed. Analysis of variance applied to North American wheats has demonstrated that resistant and susceptible cultivars significantly differ from each other with respect to the contributions of common ancestors. The contributions of Oro (Bt4 and Bt7), Rio (Bt6), White Odessa (Bt1), and Florence (Bt3) to the resistant cultivars are significantly higher than their contributions to the susceptible ones. This demonstrates that the use of these resistance donors in wheat breeding for several decades has been effective. The contribution of PI-178383 (Bt8, Bt9, and Bt10) is considerably higher in the group of resistant cultivars bred after 1965. The mean contributions of Federation (Bt7) and Nebred (Bt4) are significantly higher in the group of resistant cultivars obtained before 1965; however, the differences in the contributions of these donors between new resistant and susceptible cultivars became nonsignificant. Among the Russian and Ukrainian cultivars, there are differences between groups of resistant and susceptible cultivars from different regions determined by the differences between the regional populations of the pathogen in racial composition. In the northern region, the contributions of the wheat grass (Agropyron glaucum) and the rye cultivar Eliseevskaya are significantly higher in the resistant cultivars; in the southern region, a local cultivar of the Odessa oblast is the prevalent resistant cultivar. In addition, cultivar Yaroslav Emmer is likely to be effective in the northern region; and foreign sources (Oro, Florence, Federation, and Triticum timopheevii), in the southern region. Very few sources of vertical resistance to common bunt are used for winter wheat breeding in Russia and Ukraine. The decrease in genetic diversity in favor of a few identical genes may cause adequate changes in the pathogen population and subsequent proliferation of the pathogen on the genetically identical substrate. A new interpretation of the resistance of line Lutescens 6028 as a source of new genes, Bt12 and Bt13, is suggested. Both genealogical and segregation analyses have shown that the genes determining the resistance of this line may be identical to those described earlier (Bt1, Bt3, Bt4, Bt6, and Bt7); and the high resistance of this line is determined by a combination of these genes.     

Allozyme and morphological variability,outcrossing rate and core collection formation in lentil germplasm

Summary A survey of qualitative genetic variation at 3 morphological trait loci, 17 isozyme loci and a putative isozyme locus (amylase) was made for 105 lentil (Lens culinaris Medikus) germplasm accessions from Chile, Greece and Turkey. New alleles were found for Lap-1, Me-2, Pgm-c, Pgm-p and 6-Pgd-c. The average proportion of polymorphic loci per population was 0.19, with a range of 0 to 0.42 over populations. Germplasm from Chile was equally variable to that from Greece and Turkey on the basis of individual loci and in a multilocus sense, despite its post-Columbus introduction to the New World. Evidence was found from associations between allelic states at different loci of a complex multilocus structure of lentil populations. A single multilocus genotype represented 10.2% of all plants sampled. The rate of outcrossing varied from 2.2% and 2.9% in Turkish and Greek landraces to 6.6% among Chilean populations. Using the survey data, a random sampling strategy for core collection formation was compared with two stratified sampling methods. The advantage of stratified sampling over random sampling was only significant at P=0.28.     

Population structure in a wheat core collection and genomic loci associated with yield under contrasting environments

A set of 96 winter wheat accessions sampled from a variety of geographic origins, including cultivars and breeding lines, were characterized with 46 genome-wide SSR loci for genetic diversity and population structure. The genetic diversity within these accessions was examined using a genetic distance-based and a model-based clustering method. The model-based analysis identified an underlying population structure comprising of four distinct sub-populations which corresponded well with distance-based groupings. Information on the population structure is taken into account in an association mapping study of grain yield from a 3-years field trial incorporating fully irrigated, rainfed and drought stress treatments. A total of 21 marker-grain yield associations (P?<?0.01) were identified with nine SSR markers. Most associations were detected only in one to three environments (treatment/year combination), with an average R ² value around 13?%. However, marker gwm484 (on chromosome 2D) was associated with yield in six environments, including irrigated, rainfed and drought stress treatments, suggesting it could be used to improve grain yield across a range of environments. Variation in grain yield at this locus was associated with earliness, early vigour, kernels per spikelet and harvest index. Microsatellite locus psp3200 (on chromosome 6D) was associated with yield in dry and hot environments, which was related to earliness, early vigour, productive tillering and total biomass per plant. Partial least squares regression, with nine environmental factors, showed that precipitation from tillering to maturity was the main environmental factor causing marker?×?environment associations for grain yield.     

冬小麦抗氧化酶对冬季节律性日变温和非节律性变温的响应

通过对冬季室内和室外分别生长30d的冬小麦在节律性和非节律性融冻变温过程中抗氧化酶活力和渗透调解物含量变化的分析,揭示其在冬小麦适应日融冻胁迫中的作用。结果表明:生育期不同的室内(均温11℃,拔节期)和室外(均温1℃,分蘖静滞期)冬小麦叶片抗氧化酶和脯氨酸对日光强和温度节律变化的响应趋势是一致的,即随日出而增高,中午气温较高时最高,日落而降低;在非节律性变温处理中,室外冬小麦抗氧化酶活力和脯氨酸含量随气温上升至18℃而增高,气温迅速下降到-2.5℃而降低,经历冻-融-冻胁迫冬小麦生长良好。室内冬小麦抗氧化酶活力随气温降低到-6℃,叶片结冻,迅速下降,气温升高到18℃而增加,经历融-冻-融胁迫后植株死亡;室外冬小麦光合速率(Pn)和比室内的低,而抗氧化酶活力高于室内;冬小麦快速提高抗氧化酶活力和脯氨酸含量,抑制氧自由基积累、维护细胞水分平衡,这在适应冬季节律性融冻胁迫中起重要作用;暖冬中冬小麦较高的Pn和较低的抗氧化酶活力可能是引起冬小麦在"倒春寒"中死亡的生理原因。     

QTL marking of duration of the period up to winter wheat heading

Duration of the period up to heading of 107 winter wheat cultivars of different origin has been studied. The most contrast for analyzed character cultivars, as well as F2 Omskaya ozimaya/Numbu Komugi individual plants were investigated with SSR-PCR methods to reveal DNA-markers for QTL of heading temps. Two loci Xgwm512 and Xgwm429 have been revealed to explain 19.3% (part of influence of the first locus--8.9%, of the second 10.4%) differences induration of the period up to heading of the F2 individuals in field conditions.     

Efficient strategies to assess yield stability in winter wheat

Key message

Selecting contrasting environments allows decreasing phenotyping intensity but still maintaining high accuracy to assess yield stability.

Abstract

Improving yield stability of wheat varieties is important to cope with enhanced abiotic stresses caused by climate change. The objective of our study was to (1) develop and implement an improved heritability estimate to examine the required scale of phenotyping for assessing yield stability in wheat, (2) compare yield performance and yield stability of wheat hybrids and inbred lines, (3) investigate the association of agronomic traits with yield stability, and (4) explore the possibility of selecting subsets of environments allowing to portray large proportion of the variation of yield stability. Our study is based on phenotypic data from five series of official winter wheat registration trials in Germany each including 119–132 genotypes evaluated in up to 50 environments. Our findings suggested that phenotyping in at least 40 environments is required to reliably estimate yield stability to guarantee heritability estimates above 0.7. Contrasting the yield stability of hybrids versus lines revealed no significant differences. Absence of stable associations between yield stability and further agronomic traits suggested low potential of indirect selection to improve yield stability. Selecting posteriori contrasting environments based on the genotype-by-environment interaction effects allowed decreasing phenotyping intensity, but still maintaining high accuracy to assess yield stability. The huge potential of the developed strategy to select contrasting and informative environments has to be validated as a next step in an a priori scenario based on genotype-by-location interaction effects.

     

Response of the root system of a winter wheat crop to waterlogging

This study was aimed at analysing and quantifying the response of the root system dynamics of a wheat crop to waterlogging. Two experiments were carried out in parallel: one under controlled conditions with semi-permanent water tables using lysimeters equipped with oxygen measurers, and the other under conditions of artificially drained plots by continually monitoring their hydraulic functioning. The root system was observed frequently using the root mapping method, and this made it possible to measure the growth of the root front, to estimate root densities, and infer growth indices from them. The results showed that the anoxic medium for wheat roots consisted of a water-saturated soil with an oxygen concentration of below a critical threshold estimated to be 0.12 mol m^–3 water. The results also showed that the area which was unfavourable to root growth corresponded to the water table topped with a capillary zone of approximately 6 cm. Once the critical threshold had been reached, it was the water-table duration that explained root behaviour and the first effects were perceptible after approximately 48 h. On the basis of these results, two stress variables were analysed: water-table duration in the root zone (WTD) and proportion of roots in the water table (RPWT). The RPWT variable gave the best results within the two experimental contexts. In the case of the permanent regime, this variable made it possible to consider the root proliferation observations made above the saturated zone. Equations linking the stress variable RPWT to the growth indices are proposed that offer new perspectives to modelling waterlogging effects.     

不同质地土壤的水热状况及其对冬小麦产量形成的影响

对豫东平原３种质地土壤的水热状况和冬小麦籽粒生长特征进行了研究．结果表明,冬小麦籽粒生长阶段,粘壤土５ｃｍ处的日平均温度最低,为１８．３℃,砂壤土最高,为１９．５℃,中壤居中,为１９．１℃．３种土壤的含水量大小顺序为粘壤＞中壤＞砂壤,粘壤土上小麦籽粒灌浆时间最长,千粒重最高,分别为３８ｄ和４５．５ｇ,砂壤土小麦籽粒灌浆时间最短,千粒重最低,分别为３３ｄ和４２．４ｇ,中壤土小麦２项指标居中,分别为３６ｄ和４３．１ｇ．高产栽培条件下,粘壤土冬小麦产量最高,为８２５３ｋｇ·ｈｍ－２,中壤次之,为７９８０ｋｇ·ｈｍ－２,砂壤最低,为７６１７ｋｇ·ｈｍ－２     

Characteristics of resistance to the grain aphid Sitobion avenue in winter wheat

Five stocks of winter wheat were resistant to S. avenae in glasshouse screening tests, where resistance was more evident in older than younger plants but different types of resistance were not separated. Antibiosis was measured from the growth and reproduction of caged individual aphids and antixenosis from the settling of adult aphids on detached leaf portions. Cvs Bounty, Rapier and Virtue were resistant due to antibiosis, whilst cv. Kador and line A4501-4E showed antixenosis. These and other differences indicated that these five wheat stocks probably include at least four distinct sources of resistance to S. avenae. The existence of different types of resistance could account for variability in the results of screening tests.     

Photosynthesis and yield responses of ozone-polluted winter wheat to drought

Winter wheat (Triticum aestivum L. cv. Jingdong 8) was exposed to short-term high ozone treatment after anthesis and then was either well irrigated with soil water content (SWC) of 80–85 % (O₃+W) or drought treated (SWC 35–40 %, O₃+D). Short-term ozone exposure significantly decreased irradiance-saturated net photosynthetic rate (P _N) of winter wheat. Under good SWC, P _N of the O₃-treated plant was similar to that of control on 2 d after O₃-exposure (6 DAA), but decreased significantly after 13 DAA, indicating that O₃ exposure accelerated leaf senescence. Meanwhile, green flag leaf area was reduced faster than that of control. As a result, grain yield of O₃+W was significantly decreased. P _N of O₃+D was further notably decreased and green flag leaf area was reduced more than that in O₃+W. Consequently, substantial yield loss of O₃+D was observed compared to that of O₃+W. Although P _N was significantly positively correlated with stomatal conductance, it also had notable positive correlation with the maximum photochemical efficiency in the dark adapted leaves (F_v/F_m), electron transport rate (ETR), photochemical quenching (q_P), as well as content of chlorophyll, suggesting that the depression of P _N was mainly caused by non-stomatal limitation. Hence optimal soil water condition should be considered in order to reduce the yield loss caused by O₃ pollution.     

Components of partial resistance to Septoria nodorum in winter wheat

Components of partial resistance to Septoria nodorum were investigated in 10 cultivars of winter wheat having similar field resistances. The components measured were infection frequency, latent period, size, shape and rate of growth of lesions, spore production and its rate of increase. Latent period was found to be lognormally distributed. Some of the components of resistance were found to be significantly different between cultivars. Cluster analysis also showed that cultivars could be distinguished on the basis of their components of resistance. Principal components analysis indicated that resistance could be broken down into four underlying factors, three of which could be readily interpreted. The measurements of the components of resistance were combined in a model, the r-index, based on Van der Plank's r. The amount of variation between cultivars cast some doubt on the predictive value of the index but all the cultivar values were well within the range bounded by two ‘synthetic’ cultivars made up of combinations of either the most resistant or the most susceptible components. It is considered that the r-index has potential in screening for field resistance. The possibility of incorporating the most resistant-type components into one cultivar is discussed. The use of cultivar mixtures containing cultivars having similar field resistances is also discussed in the light of the variability found in this study.     

Evaluation of five strategies for obtaining a core subset from a large genetic resource collection of durum wheat

The use of plant genetic resources contained in a large collection may be enhanced by specifying subsamples, called core samples. Five strategies for selecting a core sample from a collection of 3000 durum wheat accessions were applied and evaluated using four qualitative and eight quantitative spike characters. Each of the following strategies generated about 500 accessions for the core sample: random, random-systematic according to chronology of entry of the accessions into the collection, stratified by countryof-origin, stratified by log frequency by country-of-origin, and stratified by canonical variables. The first three strategies produced samples representative of the whole collection, but the remaining two produced the desired effect of increasing frequencies from less-represented countries-of-origin for several characters. The stratified canonical sample increased phenotypic variances. The quality of core samples is dependent upon good passport and evaluation data to partition the collection. The multivariate approach is extremely useful, but requires considerable data from the whole collection. Ecogeographic origin may be used in the absence of evaluation data on several characters to select useful core samples.     

Development of a Brazilian maize core collection

The aim of this study was to evaluate methods for developing a Brazilian maize core collection. For an initial survey of the active collection, passport information, as well as characterization and evaluation of accessions, were taken into consideration, these then being divided according to geographic region and kernel-type. Multiple sampling methods were evaluated. The strategy of constant sampling generated extensive alterations in extract accession frequency. The multivariate strategy with dispersion graphs and principal components associated with the Tocher method was considered efficient for identifying the most divergent genotypes. The multivariate strategy generated greater alterations in the variance of traits. The average number of traits revealed few modifications with the various sampling strategies used. Therefore, the active collection could be considered as possessing a satisfactory amount of information for most of its accessions. Moreover, the multivariate strategy generated modifications in the variance of the traits, independent of sampling intensity.     

Effect of seed depth on slug damage to winter wheat

In a field experiment drilled at two depths on three dates in autumn 1988, with or without methiocarb pellets broadcast on the soil surface immediately after drilling, 26% of seeds of winter wheat sown at c. 20 mm depth were killed by slugs compared with only 9% of seeds sown at c. 40 mm. The protection from slug damage provided by this additional 20 mm of depth was comparable with that provided by methiocarb pellets. The effects of seed depth and pellet application did not interact and were consistent on all drilling dates. Thus, fewest seeds and seedlings were killed where methiocarb pellets were broadcast on a seed-bed with seeds sown at 40 mm depth. Intermediate damage was recorded where seeds were sown at 40 mm depth without pellets, or where pellets were broadcast on seeds sown at 20 mm depth. Most seeds and seedlings were killed where seeds were sown at 20 mm depth without pellets. Sublethal damage to seedlings was not affected by sowing depth but was reduced where pellets were broadcast immediately after sowing.     

春灌模式对晚播冬小麦水分利用及产量形成的影响

为了明确华北严重缺水区晚播冬小麦耗水规律及高产高效灌溉制度,在大田条件下设置不灌水(W0)、1水(W1,拔节水)、2水(W2,拔节水+开花水)、3水(W3,起身水+孕穗水+开花水)和4水(W4,起身水+孕穗水+开花水+灌浆水)等五种春季灌溉模式,研究了不同灌溉模式下晚播冬小麦水分利用特征及产量形成特点.结果表明,在晚播且免浇冬水条件下,春季每增加750m3/hm2的灌溉水量则减少土壤水消耗量约440 m3/hm2,增加小麦总耗水量约230m3/hm2;从播种到拔节,小麦阶段耗水强度低,此生育阶段控制灌溉可显著降低总耗水量;春季第一水推迟至拔节期可提高土壤水消耗量占总耗水量比例至50%,土壤水利用率增加;开花前仅灌一次拔节水可基本满足拔节-开花期耗水需要,其群体库容量与开花前灌起身水+孕穗水模式无显著差异,且由于相对降低了开花期群体叶面积,显著增加了群体粒叶比; 晚播密植条件下,单位面积穗数是群体库容形成的主要贡献因素,在保证大库容建成条件下,灌浆期灌水会降低开花前贮藏物质向籽粒再转运比例,而后期控水可显著提高开花前贮藏物质再转运比例和对库容填充的贡献率,且较高的群体库源比增强了库对源的反馈促进作用,使花后单位叶面积的物质生产能力提高,这可补偿后期水分亏缺对叶片光合生产的不利影响.连续两年试验结果显示,晚播密植条件下,春季灌拔节水和开花水可以实现高产与水分高效利用的统一.