Improving efficiency of breeding for higher crop yield

Summary Exclusive selection for yield raises, the harvest index of self-pollinated crops with little or no gain in total bipmass. In addition to selection for yield, it is suggested that efficient breeding for higher yield requires simultaneous selection for yield's three major, genetically controlled physiological components. The following are needed: (1) a superior rate of biomass accumulation. (2) a superior rate of actual yield accumulation in order to acquire a high harvest index, and (3) a time to harvest maturity that is neither shorter nor longer than the duration of the growing season. That duration is provided by the environment, which is the fourth major determinant of yield. Simultaneous selection is required because genetically established interconnections among the three major physiological components cause: (a) a correlation between the harvest index and days to maturity that is usually negative; (b) a correlation between the harvest index and total biomass that is often negative, and (c) a correlation between biomass and days to maturity that is usually positive. All three physiological components and the correlations among them can be quantified by yield system analysis (YSA) of yield trials. An additive main effects and multiplicative interaction (AMMI) statistical analysis can separate and quantify the genotype × environment interaction (G × E) effect on yield and on each physiological component that is caused by each genotype and by the different environment of each yield trial. The use of yield trials to select parents which have the highest rates of accumulation of both biomass and yield, in addition to selecting for the G × E that is specifically adapted to the site can accelerate advance toward the highest potential yield at each geographical site. Higher yield for many sites will raise average regional yield. Higher yield for multiple regions and continents will raise average yield on a world-wide basis. Genetic and physiological bases for lack of indirect selection for biomass from exclusive selection for yield are explained.     

Yield behavior of bovine cancellous bone

The compressive yield strain was measured for 61 specimens of bovine cancellous bone from three distal femora. There was no significant relationship (p = 0.08, R2 = 0.051) between yield strain and the degree of trabecular orientation. There was a significant positive correlation (p less than 0.00001, R2 = 0.319) between yield strain and structural (apparent) density and significant negative correlation (p less than 0.0025, R2 = 0.145) between yield strain and bone density. Yield strain correlated best with bone solid volume fraction Vv (epsilon y = 0.592 +2- 1.446vv, R2 = 0.337). The quantity, yield strain, is highly dependent on specific definitions of the yield point and the point of zero strain. For this study the yield point was defined by a 0.0003 offset criterion, and the point of zero strain was defined as the point where the tangent at 15 percent of yield crosses zero. The results using these definitions were compared with results using yield strain values determined by other definitions of the yield point and zero strain. The correlations between yield strain and trabecular orientation, structural density and bone density changed very little for differing definitions of yield. The results suggest that yield strain in cancellous bone is isotropic or independent of textural anisotropy, so the yield behaviour may be characterized by a maximum strain yield criterion. The results also suggest that the primary mode of yield in cancellous bone is buckling of the trabeculae.     

The role of chemical and organic fertilizers on yield, yield variability and carbon sequestration— results of a 19-year experiment

Fertilization practice in the North China Plain has been changing since the late 1970s. To evaluate how organic and chemical fertilizers contribute to yield, yield variability and soil carbon sequestration, we analyzed wheat (Triticum aestivum L.) yield data in a long-term fertilization experiment that began in 1989, conducted pot experiments using soils from the long-term fertilization experiment plots, and simulated the soil organic carbon (SOC) dynamics of individual treatments in the long-term experiments. Wheat yield results showed that when organic fertilizer was used as an alternative nutrient source for chemical fertilizers, it was neither directly beneficial to crop yield, nor decreased yield variability when compared to a balanced chemical fertilizer. However, there was a linear relationship between yield trend and SOC change rate (r = 0.951, P?<?0.01). The use of organic fertilizer increased SOC and soil fertility and consequently resulted in a larger yield trend when compared to a balanced chemical fertilizer. Roth-C model simulation and pot experimental results indicated that soils with higher SOC had a higher root/shoot ratio. Therefore, the long-term use of organic fertilizer not only directly increases SOC, but indirectly contributes to carbon sequestration by favoring root development. We found that yield variability was determined by the relative contributions of soil fertility and fertilizer to yield (the contribution of fertilizer to yield is the yield difference between fertilized and unfertilized treatments). The contribution of balanced chemical fertilizer to yield was higher than that of organic fertilizer, resulting in less yield variability in balanced chemical fertilizer treatment. However, if organic fertilizer was used as a complementary nutrient source with chemical fertilizers, it would increase the contribution of fertilizers to yield, thus decreasing yield variability.     

Crop transformation and the challenge to increase yield potential

Molecular transformation is commonly offered as a hope to overcome the apparent stagnation in crop yield potential. A basic understanding of the resource limits imposed on crops and the yield hierarchy going from gene expression to harvestable yield leads to a rather negative view that transformations of a few, or even of a complex of genes will result directly in major yield increases. Forty years of biochemical and physiological research illustrate the great difficulty in translating research at the basic level into improvements in crop yield. However, there are a few cases where physiological research has led to improved crop cultivars with increased yield. These successes are instructive in highlighting key elements required to achieve success in developing crop cultivars for increased yield.     

Climatic and technological ceilings for Chinese rice stagnation based on yield gaps and yield trend pattern analysis

Climatic or technological ceilings could cause yield stagnation. Thus, identifying the principal reasons for yield stagnation within the context of the local climate and socio‐economic conditions are essential for informing regional agricultural policies. In this study, we identified the climatic and technological ceilings for seven rice‐production regions in China based on yield gaps and on a yield trend pattern analysis for the period 1980–2010. The results indicate that 54.9% of the counties sampled experienced yield stagnation since the 1980. The potential yield ceilings in northern and eastern China decreased to a greater extent than in other regions due to the accompanying climate effects of increases in temperature and decreases in radiation. This may be associated with yield stagnation and halt occurring in approximately 49.8–57.0% of the sampled counties in these areas. South‐western China exhibited a promising scope for yield improvement, showing the greatest yield gap (30.6%), whereas the yields were stagnant in 58.4% of the sampled counties. This finding suggests that efforts to overcome the technological ceiling must be given priority so that the available exploitable yield gap can be achieved. North‐eastern China, however, represents a noteworthy exception. In the north‐central area of this region, climate change has increased the yield potential ceiling, and this increase has been accompanied by the most rapid increase in actual yield: 1.02 ton ha^?1 per decade. Therefore, north‐eastern China shows a great potential for rice production, which is favoured by the current climate conditions and available technology level. Additional environmentally friendly economic incentives might be considered in this region.     

Potential for Marker-Assisted Simultaneous Improvement of Grain and Biomass Yield in Triticale

Triticale is a promising crop for agricultural biomass production but breeding has until now mainly focused on grain yield. Here, we evaluated the potential of marker-assisted simultaneous improvement of grain yield and biomass yield. To this end, we employed a large triticale doubled haploid population with 647 individuals derived from four families that were phenotyped for grain yield and biomass yield, as well as thousand-kernel weight, tiller density, and plant height in multi-environment field trials. Employing an association mapping approach, we identified quantitative trait loci (QTL) for all the five traits. The phenotypic correlation between grain yield and biomass yield was low, and we detected only one overlapping QTL suggesting different genetic architectures underlying both traits. Our results indicate that a marker-based selection for either grain yield or biomass yield does not adversely affect the other traits. Furthermore, an improvement of the multiplicative yield traits can to some extent also be achieved by selection for QTL identified for the component traits. Taken together, our results suggest that marker-assisted breeding can assist the establishment of dual-purpose triticale cultivars with high grain and biomass yield.     

Analysis of Covariation of Grain Yield and Dry Matter Yield for Breeding Dual Use Hybrid Rye

Winter rye (Secale cereale L.) is becoming increasingly important as substrate for biogas production in Central Europe. Dry matter yield has evolved as a breeding goal comparably important to the traditional grain yield. We analyzed the covariation between both traits and tested other agronomic traits for their correlation to dry matter yield that could be used for prediction of biomass yield. A set of 258 experimental hybrids were tested for dry matter yield harvested at late milk stage and grain yield harvested at full ripening at three to four locations in Germany in 2011 and 2012. We observed a wide range of dry matter yield (10–24 Mg ha^?1) and grain yield (6–15 Mg ha^?1) among testcross progenies. Genetic variances were significantly (P?<?0.01) different from zero for all traits. High entry-mean heritabilities (0.92–0.94) were found for plant height measurements and moderate heritabilities for grain and dry matter yield (0.52 and 0.49, respectively). Relative efficiencies for selection of dry matter yield estimated by second (EC 51–55) and third (EC 73) measurements of plant height were 1.24 and 0.98 respectively, compared to 0.52 for grain yield. Indirect selection for high dry matter yield using late plant height measurements should be successful. Using grain yield for indirect selection was less effective. The observed broad genetic variation for biomass yield in elite hybrid rye gives good prospects for the use as a resource of renewable energy. Plant height is a good predictor of dry matter yield but should be selected together with improved lodging resistance.     

A simple method to evaluate genetic variation in grain zinc concentration by correcting for differences in grain yield

Increasing the grain zinc (Zn) concentration of staple food crops will help alleviate chronic Zn deficiency in many areas of the world. Significant variation in grain Zn concentration is often reported among collections of cereals, but frequently there is a concomitant variation in grain yield. In such cases grain Zn concentration and grain yield are often inversely related. Without considering the influence of the variation in grain yield on Zn concentration, the differences in grain Zn concentration may simply represent a yield dilution effect. Data from a series of field and glasshouse experiments was used to illustrate this effect and to describe an approach that will overcome the yield dilution effect. In experiments with a wide range of bread wheat, synthetic hexaploids and accessions of durum wheat, variation in grain yield among the genotypes accounted for 30–57% of the variation in grain Zn concentration. Variation in kernel weight also occurred, but was poorly correlated with grain Zn concentration. To account for the influence of variation in grain yield on grain Zn concentration grain Zn yield was plotted against grain yield. By defining the 95% confidence belt for the regression genotypes that have inherently low or high grain Zn concentrations at a given yield level can be identified. This method is illustrated using two data sets, one consisting of bread wheat and one comprising a collection of synthetic hexaploids.     

利用分子标记预测杂交水稻产量及其构成因素

利用AFLP、RAPD、SSR技术分析了10个恢复系和5个不育系的931个基因座,利用15个亲本配制了50个杂交组合,在泸州和重庆2个环境下同时种植,考察了产量及其构成因素,从931个基因座中筛选出了与之相关的阳性座位、增效座位、减效座位、非环境型座位,并分析了它们与杂种产量及其构成因素间的关系。结果表明,利用所有座位计算的遗传差异与产量及其构成因素的相关性,绝大多数性状未达显著水平,不能直接用于预测产量及其构成因素。阳性座位在一定程度上可以提高相关系数,因性状不同而存在差异,在多数性状上预测产量及其构成因素还有一定难度;增效座位和减效座位可以大幅度提高相关系数,在不同的环境下也表现一致,可以用来预测产量及其构成因素;非环境型座位计算的相关系数也较高,但低于增效座位和减效座位,说明环境对产量及其构成因素有较大的影响。     

水氮运筹对干旱年型冬小麦旗叶生理性状及产量的交互效应

在大田条件下,探讨了不同灌水和施氮处理对冬小麦叶片生长、生理特性及产量性状的影响。结果表明,干旱年型条件下灌水和氮肥增产效应均显著,但灌水增产潜力更大,灌水两次(拔节和孕穗水),产量较高;灌水3次(拔节、孕穗和灌浆水)增产效果并不明显,氮肥全部底施产量下降,水分胁迫影响肥效发挥,降低产量,但可通过增加施氮量得到弥补,只有水氮合理搭配,才能有效协调各产量构成因素的关系,提高单位面积产量。     

Yield components of potato microtubers: in vitro production and field performance

Genetic parameters, character association and path analysis for yield components of microtuber production in vitro and their field performance were studied in 37 potato (Solanum tuberosum L.) genotypes. Among the microtuber yield components, average microtuber weight had maximum genotypic (or phenotypic) coefficient of variation, heritability and predicted genetic advance; however, the estimated values of these genetic parameters were maximum for tuber yield among the field yield components. The heritability estimates of field yield components were higher than that of their corresponding in vitro yield components of microtuber production. The highest correlation coefficients between average microtuber weight and microtuber yield suggested that microtuber weight was more important than microtuber number in determining microtuber yield potential in vitro. However, tuber number was found to be more important than tuber weight in determining tuber yield potential under field conditions. Average microtuber weight had maximum direct effect on microtuber yield, whereas tuber number had maximum direct effect on tuber yield under field conditions. The study showed that the relative importance of the components of microtuber production in vitro differed from that of corresponding field yield components. The expression of a genotype for microtuber production in vitro is different from that of tuber production under field situation i.e. the performance of a genotype in vitro is not a measure of its field performance.     

Evaluation of reference lactation length in Chios dairy sheep

Definition and establishment of a fixed reference lactation length could provide useful tools for on-farm comparison of ewes and flock management as well as genetic evaluations for the breeding programme. The objectives of this study were to (i) evaluate different reference lactation lengths for the Chios dairy sheep and (ii) define the most suitable reference length for the breed. A total of 260 042 test-day milk records from 24 474 ewes in 130 flocks collected between 2003 and 2014 were used; 15 different lactation lengths were evaluated ranging from 120 to 260 days, defined at 10-day intervals as reference for the Chios sheep. The evaluation criteria included: (a) heritability and repeatability of milk yield in each reference lactation, (b) genetic correlation of reference lactation milk yield with actual lactation milk yield and yield at first test-day record and (c) correlated response in reference lactation milk yield from selection based on first test-day milk yield. The latter emulates genetic gains achieved for milk yield based on early lactation selection. Heritability and repeatability estimates of reference lactation milk yield and genetic correlation with actual lactation yield favoured long reference lactations (180 to 230 days). On the contrary, correlation with first test-day record milk yield was higher for short lactations (120 to 170 days). Moreover, selection on first test-day record milk yield would lead to a correlated response in reference yield in 220 days equal to 85% of the highest estimate achieved in the maximum reference length of 260 days (190 days when only considering first lactation milk yield). Based on the results of the present study, an overall reference lactation length for the Chios breed of 220 days post-lambing and a first lactation reference length of 190 days post-lambing are recommended.     

The basis for grain yield differences in mungbean cultivars and identifications of yield limiting factors

Summary Eight mungbean cultivars, selected from a cultivar collection on the basis of their grain yield, were grown in a replicated experiment. Morphological and physiological components contributing to grain yield were analysed. The principal yield limiting factor and the desirable yield component of each cultivar have been identified. The rate of dry matter accumulation was low in all cultivars. It is suggested that for a short duration crop like this, selection for rapid rate of dry matter increase would be advantageous. However, it should also be associated with a high partitioning efficiency (Harvest index). The top yielding cultivar had high biological yield and productive racemes.Abbreviations BY biological yield - GY grain yield - HI harvest index - DM dry matter - DW dry weight - LA leaf area - GPP grain protein percent - GW grain weight     

约束选择在小麦育种中的应用研究

对小麦杂种后代进行了约束选择,以无约束选择、单项选择为对照。试验结果表明:约束选择对选择性状的促进和约束性状的控制都有较好的效果。一对正相关的性状被约束者可保持在原平均数稍高水平;负相关的约束者则保持在原平均数略低水平。在对产量的选择中,约束选择的实际效果一般比无约束的为好,其中以约束株高选择产量的效果最佳。最后对约束选择的应用问题作了讨论。     

Genetic basis of yield as viewed from a crop physiologist's perspective

The final yield of a crop is the product of growth during the growing season and a number of developmental processes occurring throughout the life cycle of a crop, with most genes influencing the final outcome to a degree. However, recent advances in molecular biology have developed the potential to identify and map many genes or QTLs related to various important traits, including yield, plant adaptation and tolerance to stresses. Significant G×E interactions for yield have been identified, as have interactions associated with QTLs for yield. However, there is little evidence available to confirm that a QTL for yield from a parental line in one mapping population may improve yield when transferred into an adapted, high‐yielding line of another population. In order to narrow the apparent gap between the genotype and the phenotype with regard to yield, it is important to identify key traits related to yield and then attempt to identify and locate the genes controlling them. The partitioning of the developmental time to anthesis into different phases: from sowing to the onset of stem elongation and from then to anthesis, as a relatively simple physiological attribute putatively related to yield, is discussed. If the relationship holds in a wider range of conditions and the genetic factors responsible are located then the genetic basis of yield should be identified. There has also been significant progress in crop simulation modelling. Using knowledge of crop physiology and empirical relationships these models can simulate the performance of crops, including the G×E interactions. Such models require information regarding the genetic basis of yield, which are included in the form of genetic coefficients. Essentially models are constructed as decision‐making tools for management but may be of use in detecting prospective traits for selection within a breeding programme. Problems associated with this approach are discussed. This review discusses the need to use crop physiology approaches to analyse components of yield in order to reliably identify the genetic basis of yield.     

Yield of tomato and maize in response to foliar and root applications of triacontanol

Triacontanol applied to tomato plants as a foliar spray caused a significant increase in total yield and yield per plant. When triacontantol was added to the growth medium, only a temporary increase in yield and number of fruits was observed. The yield of maize was unaffected by triacontanol, either applied to the leaves or to the growth substrate. These results support an earlier observation that a reduction in photorespiration is involved in the regulatory function of triacontanol, since only the yield of tomato, a C₃ plant, was increased. The application method was an important factor in it's effectiveness.     

Genetic dissection of grain yield in bread wheat. I. QTL analysis

Grain yield forms one of the key economic drivers behind a successful wheat (Triticum aestivum L.) cropping enterprise and is consequently a major target for wheat breeding programmes. However, due to its complex nature, little is known regarding the genetic control of grain yield. A doubled-haploid population, comprising 182 individuals, produced from a cross between two cultivars ‘Trident’ and ‘Molineux’, was used to construct a linkage map based largely on microsatellite molecular makers. ‘Trident’ represents a lineage of wheat varieties from southern Australia that has achieved consistently high relative grain yield across a range of environments. In comparison, ‘Molineux’ would be rated as a variety with low to moderate grain yield. The doubled-haploid population was grown from 2002 to 2005 in replicated field experiments at a range of environments across the southern Australian wheat belt. In total, grain yield data were recorded for the population at 18 site-year combinations. Grain yield components were also measured at three of these environments. Many loci previously found to be involved in the control of plant height, rust resistance and ear-emergence were found to influence grain yield and grain yield components in this population. An additional nine QTL, apparently unrelated to these traits, were also associated with grain yield. A QTL associated with grain yield on chromosome 1B, with no significant relationship with plant height, ear-emergence or rust resistance, was detected (LOD ≥2) at eight of the 18 environments. The mean yield, across 18 environments, of individuals carrying the ‘Molineux’ allele at the 1B locus was 4.8% higher than the mean grain yield of those lines carrying the ‘Trident’ allele at this locus. Another QTL identified on chromosome 4D was also associated with overall gain yield at six of the 18 environments. Of the nine grain yield QTL not shown to be associated with plant height, phenology or rust resistance, two were located near QTL associated with grain yield components. A third QTL, associated with grain yield components at each of the environments used for testing, was located on chromosome 7D. However, this QTL was not associated with grain yield at any of the environments. The implications of these findings on marker-assisted selection for grain yield are discussed.     

利用重组自交系进行陆地棉产量及产量构成因子性状的QTL定位

以高产陆地棉栽培品种中棉所12和8891的杂交组合湘杂棉2号为材料,采用单粒传法构建了含有180个家系的重组自交系(RILs)群体。本研究的目的是分析产量及其构成因子的相互关系并进行相应的QTL定位。重组自交系群体、两亲本和F1于2002年、2003年分别种植于南京农业大学江浦实验农场和江苏省灌云棉花基地。收获每行中间五株的籽棉并考察产量及产量构成因子性状。调查的产量及产量构成因子性状包括单株籽棉产量、单株皮棉产量、单株铃数、铃重、衣分、衣指和籽指。筛选了4,106对SSR引物和384个AFLP引物组合,分别得到127和18个多态位点;此外,2个RAPD引物、1个SRAP引物组合以及来自亲本8891的显性黄花药基因P1也被用来作为标记检测群体基因型。最终共获得149个多态位点,其中132个位点分布于26个染色体/连锁群,覆盖865.20cM,约占棉花基因组的18.57%,标记间平均距离6.55cM。利用此遗传图谱结合重组自交系群体3个环境下的产量及产量构成因子性状,应用QTLCartographer2.0的复合区间作图法进行单位点QTL定位。对各环境资料的分离分析共定位出34个QTL,而利用三环境平均值的联合分析定位出15个QTL。本研究定位的QTL可为棉花产量育种提供信息,其中衣分QTLqLP-A10-1在联合分析及分离分析下的两个环境都能检测到,可能对标记辅助选择有实际应用价值。通径分析结果表明,各产量构成因子中,铃数对皮棉产量贡献最大,这与产量构成因素性状在F1的杂种优势表现一致;因此,在棉花育种上,可优先考虑单株铃数并结合其它产量构成因素进行品种选育和杂交组合选配。     

基于地表水与地下水分割校正的漓江流域水供给服务时空格局研究

喀斯特区域水循环过程与其他地区存在显著区别,其水供给服务也具有独特的空间分布特征。然而,目前针对喀斯特地区产水量的时空变化研究较少考虑喀斯特生态系统的特殊性,导致产水量的空间模拟结果存在一定偏差。根据喀斯特地貌形态和地下水补径排泄特征提出了一种产水量分割方法,并基于水量平衡原理建立了地表水与地下水分割校正概念模型。选取喀斯特山区典型区域漓江流域为研究区,通过上述方法校正了InVEST模型产水量模拟结果,从栅格、地貌分区和子流域3个尺度分析了漓江流域2000—2020年产水量校正前与校正后时空分布格局。研究结果表明：(1)漓江流域2000—2020年InVEST模型产水量呈现先减后增再减的趋势,水供给服务空间分布格局为北高南低。产水深度在岩溶区和非岩溶区几乎没有差异,但在岩溶区内部差异明显：裸露型岩溶区产水深度高于覆盖型和埋藏型,峰林平原产水深度高于峰丛洼地。子流域分区平均产水深度排序为漓江上游区>漓江中游区>恭城河区>荔浦河区>漓江下游区。(2)利用地表与地下水分割校正后,水供给服务空间分布格局为四周高于中部,西北部高于东南部。非岩溶区产水深度明显高于岩溶区,埋...     

Effect of greenbugs (Homoptera: Aphididae) on yield loss of winter wheat

The effect of greenbug, Schizaphis graminum (Rondani), feeding on the yield of four winter wheat cultivars commonly grown in Oklahoma was studied. Cultivars tested were 'Karl', a recent derivative 'Karl-92', and '2163', all greenbug-susceptible cultivars; and 'TAM-110', a cultivar with resistance to biotype E greenbugs. The objectives were to determine the effect of different greenbug densities during fall and spring on yield of winter wheat, and to develop mathematical models to quantify the effect of greenbugs on yield loss. The intensity of greenbug infestations achieved in plots by artificial infestation varied among years and growing seasons within a year, but was generally sufficient to cause a reduction in yield. Among yield components, the number of heads per square meter and the number of seeds per head were frequently negatively correlated with the accumulated number of greenbug-days per tiller. Seed weight was rarely affected by greenbug infestation. A regression model estimated yield loss for greenbug-susceptible cultivars at 0.51 kg/ha loss of yield per greenbug-day in years with near normal precipitation, and a loss of 1.17 kg/ha under severe drought conditions. The susceptible winter wheat cultivars exhibited similar yield loss in relation to the intensity of greenbug infestation, as indicated by a common slope parameter in the regression model. Results suggest that the model is robust for predicting yield loss for susceptible cultivars.