Genetic Gain In Yield Research Articles

Achievements and Challenges in Improving Temperate Perennial Forage Legumes

The expected move towards more sustainable crop-livestock systems implies wider cultivation of perennial forage legumes. Alfalfa (Medicago sativa subsp. sativa) is the main perennial legume in most temperate regions, especially where farm systems rely largely on forage conservation. White clover (Trifolium repens) and red clover (Trifolium pratense) are dominant in specific regions and farm systems. Although breeding progress for disease and insect resistance has been achieved, these crops have shown lower rates of genetic gain for yield than major grain crops, owing to lower breeding investment, longer selection cycles, impossibility to capitalize on harvest index, outbreeding mating systems associated with severe inbreeding depression, and high interaction of genotypes with cropping conditions and crop utilizations. Increasing yield, persistence, adaptation to stressful conditions (drought; salinity; grazing) and compatibility with companion grasses are major breeding targets. We expect genetic gain for yield and other complex traits to accelerate due to progress in genetic resource utilization, genomics resource development, integration of marker-assisted selection with breeding strategies, and trait engineering. The richness in adaptive genes of landraces and natural populations can be fully exploited through an ecological understanding of plant adaptive responses and improved breeding strategies. Useful genetic variation from secondary and tertiary gene pools of Medicago and Trifolium is being increasingly accessed. Genome sequencing projects in alfalfa and white clover will enrich physical, linkage and trait maps. Genome sequences will underpin fine mapping of useful loci and subsequent allele mining, leveraging the synteny of these crops with M. truncatula. Low-cost genome-wide markers generated through genotyping-by-sequencing will make genomic selection for adaptation and forage yield possible for these crops. Genetic markers will also be used for dissecting quantitative traits and developing toolboxes of functional markers for stress tolerance and other traits. Under current regulatory policies, transgenic approaches are likely to be limited to a few breakthrough traits. The key challenge for future applications of genomics technologies is their seamless integration with breeding system logistics and breeding schemes.

Genetic gain in yield and changes associated with physiological traits in Brazilian wheat during the 20th century

The objective of this study was to characterize physiologically wheat cultivars released in different decades and identify selection criteria for the continued genetic progress in Brazil. Ten cultivars released from 1940 up to 2009 were tested during 2010 and 2011 crop seasons. The following traits were evaluated: grain yield (GY), thousand-kernel weight (TKW), grain number per m−2 (GN), plant height (PH), harvest index (HI), above-ground biomass (BIO), relative Chlorophyll content and leaf gas exchanges. The increase in grain yield was 29kgha−1yr−1 a genetic gain of 0.92%, annually. Grain yield improvement was largely associated with HI (0.94**), number of grainsm−2 (0.93**), BIO (0.88**) and reduced PH (−0.93**). The post-anthesis Chlorophyll content, stomatal conductance and pre/post-anthesis photosynthetic rate were positively correlated with GY. Genetic gains of Brazilian wheat are mainly related to the increases of HI, GN, and BIO. These improvements were achieved by reducing PH and raising gas exchanges and chlorophyll content.

Genetic Improvement of U.S. Soybean in Maturity Groups II, III, and IV

ABSTRACTSoybean improvement via plant breeding has been critical for the success of the crop. The objective of this study was to quantify genetic change in yield and other traits that occurred during the past 80 yr of North American soybean breeding in Maturity Groups (MGs) II, III, and IV. Historic sets of 60 MG II, 59 MG III, and 49 MG IV soybean cultivars, released from 1923 to 2008, were evaluated in field trials conducted in 17 U.S. states and one Canadian province during 2010 to 2011. Averaged over 27 MG II and MG IV and 26 MG III site‐years of data, the estimated rates of yield improvement during the 80 yr were 23 kg ha–1 yr–1 for MGs II and III, and 20 kg ha–1 yr–1 for MG IV cultivars. However, a two‐segment linear regression model provided a better fit to the data and indicated that the average current rate of genetic yield gain across MGs is 29 kg ha–1 yr–1. Modern cultivars yielded more than old cultivars in all environments, but particularly in high‐yielding environments. New cultivars in the historic sets used in this study are shorter in height, mature later, lodge less, and have seeds with less protein and greater oil concentration. Given that on‐farm soybean yields in the United States are also increasing at a rate of 29 kg ha–1 yr–1, it can be inferred that continual release of greater‐yielding cultivars has been a substantive driver of the U.S. on‐farm realized yield increases.

Soybean Nitrogen Uptake and Utilization in Argentina and United States Cultivars

ABSTRACTCrop production increase needed to satisfy a growing world population depends, at least partially, on increasing current genetic gain in yield. Theory proposes that increased genetic gain can be attained using diverse high‐yielding parents. Physiological traits, compared to molecular or morphological markers, are hypothesized to better estimate parental diversity. A trait‐based hybridization approach will require assessing diversity for physiological traits. Here, we phenotyped several traits using two physiological frameworks to assess diversity in 25 and 65 elite cultivars from Argentina (ARG) and the United States (USA), respectively. First, we identified the highest‐yielding cultivar clusters across two environments in each country. These cultivars had the highest N uptake at both ARG and USA. Therefore, there was no genotypic diversity for total N uptake within each cluster. For other traits, the highest yielding clusters did not show the highest values. There was residual diversity within ARG and USA highest yielding clusters in the temporal pattern of N uptake, N use efficiency, and N harvest index. Stacking these traits in one cultivar could potentially increase yield by 13%. The possibility of such stacking, however, depends on the nature of the phenotypic correlation among traits. We demonstrated that several trade‐off correlations between phenotyped traits, thought to hinder stacking, are actually not biologically based.

Physiological and Phenological Responses of Historical Soybean Cultivar Releases to Earlier Planting

ABSTRACTThe trend toward earlier soybean [Glycine max (L.) Merr.] planting in the midwestern United States has interacted synergistically with genetic yield gain to provide improvement in on‐farm yields. However, the impacts of earlier planting dates and their interaction with genetic gain in physiological and phenological traits remain unclear. The objectives of this study were to determine if a 30‐d difference in planting date affected measured rates of genetic improvement in (i) total dry matter (TDM) production, (ii) harvest index (HI), and (iii) growth‐stage duration in the north‐central United States. Research was conducted at Arlington, WI, Urbana, IL, and Lafayette, IN during 2010 and 2011 using 59 Maturity Group (MG) II cultivars (released 1928–2008) at Wisconsin, and 57 MG III cultivars (released 1923–2007) at Illinois and Indiana, with targeted planting dates of 1 May and 1 June. A mixed‐effect regression analysis was used to model genetic change in TDM, HI, and growth stage duration as impacted by planting date. Breeding efforts have increased TDM(R7), HI, seed‐fill duration (SFD), and reproductive growth duration over time, as vegetative growth duration has been reduced. Early planting provided increased TDM(R7) and longer reproductive growth duration, but had no effect on HI or SFD. A synergistic planting date × year of release interaction existed for TDM(R7) in both maturity groups, but not for HI or SFD, suggesting that the higher yields in newer, early‐planted cultivars resulted from greater TDM production, not improved HI or SFD.

Estimating Soybean Genetic Gain for Yield in the Northern United States—Influence of Cropping History

ABSTRACTMean on‐farm U.S. soybean [Glycine max (L.) Merr.] yield increased at a rate of 23.4 kg ha−1 yr−1 between 1924 and 2010 due to a combination of genetic improvements, agronomic technologies, and climatic changes. To estimate annual rates of genetic yield gain in three northern U.S. soybean maturity groups (MGs) and determine if these estimates are influenced by cropping history, 45 MG II, 40 MG III, and 45 MG IV cultivars released between 1923 and 2008 were evaluated in split‐plot trials conducted in Illinois in 2010 where the main plot prior cropping treatments were either 11 yr of continuous corn (Zea mays L.) or 11 yr of a soybean–corn rotation. The experiment‐wide genetic yield gain estimate was 22.8 kg ha−1 yr−1 and, after covariate adjustment of yields for maturity, the estimate was 19.8 kg ha−1 yr−1. These estimates show that soybean genetic yield potential has been a large contributor to the rate of on‐farm yield improvement. The rate of yield gain estimates were not significantly different (P = 0.38) between the two cropping history treatments on an experiment‐wide basis or at the MG III and MG IV individual locations but were significantly different at the MG II locations, where yield gain for soybean following continuous corn was significantly greater compared with the soybean–corn rotation treatment. Modern cultivars were not observed to be able to close the yield gap between the two cropping history treatments used in this experiment.

<b>Response to the selection in the 11<sup>th</sup> cycle of reciprocal recurrent selection among full-sib families of maize</b> - doi: 10.4025/actasciagron.v35i4.17489

The continuous gains in cycles of recurrent selection have raised disagreement among researchers. Two hundred and forty-two full-sib families were obtained from CIMMYT and Piranao populations and evaluated in a simple lattice design in two environments to estimate the response to selection in the 11 th cycle of the UENF reciprocal recurrent selection program. No genotype x environment interaction was observed for most of the traits evaluated, indicating that a single recurrent selection program can be conducted for both sites. The population studied exhibited wide genotypic variability and heritability estimates ranged from 33 to 73%, indicating prospects of selection gain for the following cycles. The predicted genetic gain in yield was 12.90%. It is possible to conclude that the populations studied may be promising for the achievement of new selection cycles, which provides a continuous concentration of favorable alleles and the production of hybrids for the North and Northwest regions of the state of Rio de Janeiro.

Genetic Gain in Yield and Yield Related Traits of Groundnut [Arachis hypogea (L.)] in Central Rift Valley of Ethiopia

The progress made to improve groundnut varieties through breeding in Ethiopia has not been yet assessed. Therefore, in this study genetic gain in grain yield and yield related traits of 14 groundnut varieties developed by the Ethiopian Lowland Oil Crops Research Program (now Ethiopian Lowland Oil Crops Research Project) from 1976 to 2009 was assessed. The varieties were evaluated in RCBD design with three replications in the 2010 main cropping season at Melka Werer Agricultural Research Center and Miesso experimental fields. The analysis of variance indicated significant differences among the varieties for all traits except days from sowing to emergence. Positive genetic gains were observed for the yield traits (grain yield and yield components), while negative genetic gains were obtained for the phenological traits (50% flowering and pod filling periods). Grain yield was increased from 1.52 to 2.74 tons ha-1 during the last 33 years and the overall increase in seed yield of the latest variety Fetene over the oldest variety Shulamith was estimated to be 1.142 tons ha-1 or 71.4%. Based on the regression analysis, the estimated average annual rate of increase in grain yield potential was 0.03 tons ha-1 year -1 with an annual relative genetic gain of 1.89%. These results demonstrated the efficiency of the adopted breeding strategies in developing varieties with higher grain yields and earlier maturity. This suggests that groundnut breeders can use similar breeding strategies to exploit the genetic potential of the crop for enhanced production.

Contribution of CIMMYT Wheat Germplasm to Genetic Improvement of Grain Yield in Spring Wheat of Sichuan, Yunnan, Gansu, and Xinjiang Pro-vinces

研究历史品种产量潜力变化规律有助于提高小麦育种水平。2007—2009连续2年度将来自四川、云南、甘肃和新疆的代表性59个品种分别种植在四川成都、云南丽江、甘肃武威和新疆昌吉，在肥水供应充足、控制病虫害和倒伏的条件下分析了产量和相关农艺性状的变化趋势。结果表明，四川、云南、甘肃和新疆品种的产量随育成年份显著增加，年遗传增益分别为0.73%、0.34%、0.58%和1.43%。产量遗传增益四川品种表现与产量构成因子关系不密切；云南品种主要表现为减少穗数和增加穗粒数；甘肃品种主要表现为增加穗粒数；新疆品种主要表现为增加主穗粒重和收获指数，并与成熟期提早及株高降低有一定关系。各地区品种中 Rht-B1b 和 Rht-D1b 矮秆基因均来自CIMMYT种质，其产量潜力的提高主要得益于CIMMYT种质的引进和有效利用，在四川和云南，CIMMYT种质的主要贡献是提高品种的条锈病抗性；而在甘肃和新疆，其被利用的主要特性是矮秆、高产、穗粒数多及广泛适应性。

Contribution of CIMMYT Wheat Germplasm to Genetic Improvement of Grain Yield in Spring Wheat of Sichuan, Yunnan, Gansu, and Xinjiang Provinces

Information on advances in wheat (Triticum aestivum L.) productivity is essential for genetic improvement on yield potential. Four yield potential trials with totally 59 leading cultivars from Sichuan, Yunnan, Gansu, and Xinjiang, China were conducted using a randomized complete block design with 3 replications under controlled environments in 2 successive cropping seasons from 2007 to 2009. The experimental sites were located in Chengdu in Sichuan, Lijiang in Yunnan, Wuwei in Gansu, and Changji in Xinjiang. Molecular markers were used to detect the presence of dwarfing genes and 1B/1R translocation. The results indicated that the annual genetic gains in yield were 0.73% in Sichuan, 0.34% in Yunnan, 0.58% in Gansu, and 1.43% in Xinjiang. There was no obvious trend of yield component improvement for yield increase in Sichuan; while reduced spikes per square meter and increased kernels per spike were the main factor for yield increase in Yunnan; increased kernels per spike were the main factor for yield increase in Gansu; and increased kernel weight of main spike and harvest index were the main factor for yield increase in Xinjiang, together with the contribution from reduced plant height and earlier maturity. It also indicated that the dwarfing genes Rht-B1b and Rht-D1b were all from International Maize and Wheat Improvement Center (CIMMYT) lines, and the significant progresses of genetic gain in yield in the 4 provinces were mainly due to the direct and indirect use of CIMMYT germplasm. Stripe rust resistance was the main contribution of CIMMYT germplasm in Sichuan and Yunnan; while CIMMYT germplasm contributed to high yield potential with high kernel number per spike, short plant height, and wide adaptability in Xinjiang and Gansu.

Genetic Gain in Yield and Agronomic Characteristics of Cowpea Cultivars Developed in the Sudan Savannas of Nigeria over the Past Three Decades

A field study was conducted to determine the rate of genetic improvement in grain and fodder yields and associated agronomic and physiological changes of determinate and semideterminate cowpea [Vigna unguiculata (L.) Walp.] genotypes developed in the Nigerian Sudan savannas in 1974 to 2004. Results showed that grain yield of determinate cowpea ranged from 796 kg ha−1 for cultivars released in the 1970s to 1485 kg ha−1 for cultivars released in the 2000s with a corresponding genetic gain of 2.93% per year. Mean grain yield of semideterminate cowpea ranged from 638 to 1547 kg ha−1 with relative annual gain of 4.4%, suggesting that more progress was made in breeding semideterminate cowpea cultivars for high grain yield. Fodder yield of determinate cowpea ranged from 1493 kg ha−1 for cultivars released in the 1970s to 2332 kg ha−1 for those released in 2000s, an average 1.74% genetic gain per year. For semideterminate cowpea, fodder yield increased from 1698 kg ha−1 for older cultivars to 2612 kg ha−1 for modern cultivars with relative annual gain of 2.15%. The general gain in fodder yield for both cowpea types indicated that selection for dual‐purpose cowpea cultivars with increased fodder as well as grain yields has been successful. This study also revealed that genetic gains were made in the improvement of yield related traits such as pods per plant, 100‐seed weight, total dry matter, and harvest index (HI) for both plant types. A remarkable progress has been made in increasing the total dry matter over the three decades period. This trait was significantly associated with grain yield (r = 0.60 for determinate cowpea and r = 0.53 for semideterminate cowpea). Other traits that were significantly correlated with grain yield were fodder yield, number of pods per plant, and HI for determinate cowpea and fodder yield, HI, and 100‐seed weight for semideterminate cowpea. The strong relationship between grain and fodder yields showed the success made in selecting for dual‐purpose cowpea cultivars.

Genetic gain in yield and associated changes in phenotype, trait plasticity and competitive ability of South Australian wheat varieties released between 1958 and 2007

To quantify the genetic gain in yield and associated changes in phenotype, we compared 13 South Australian wheat varieties released between 1958 and 2007. Crops were grown in three environments with a range of yield between 4.1 and 6.1 t/ha. Yield increased linearly with year of cultivar release at a rate of 25 ± 3.4 kg/ha per year. Yield improvement was associated with a linear increase in harvest index over the whole period 1958–2007 and increased shoot biomass for varieties released after the early 1980s. A non-linear model with an inflection point at 1982 ± 1.6 emphasised two phases in the time trend of grain size: it decreased between 1957 and 1982 and increased afterwards. The plasticity of grain size increased 2-fold after 1982. Grain number increased until the early 1980s and stabilised afterwards. Grain number was associated with crop growth rate between stem elongation and anthesis, and grain size was associated with crop growth rate per grain. Crop growth rate between stem elongation and anthesis increased after the early 1980s in parallel with increased radiation-use efficiency and independently of changes in capture of radiation. Candidate traits to explain the improvement in radiation-use efficiency include increased stomatal conductance and greener leaves. The concentration of water-soluble carbohydrates in shoots at anthesis increased with year of cultivar release at 0.12 ± 0.018% per year. In two out of three environments, yield response to competition declined with year of cultivar release, which was consistent with the communal plant ideotype.

Genetic Contribution to Advanced Yield for Maize Hybrids Released from 1970 to 2000 in China

Four to five cycles of maize (Zea mays L.) hybrid replacement have occurred in China since the 1970s. Retrospective analyses of genetic yield may provide an understanding of unexploited genetic potential and indicate pathways for future yield improvement. The objective of this study was to assess genetic gains in grain yield, especially those due to increased tolerance to stress in China from the 1970s through the 2000s. Trials were conducted at two locations per year and three densities per location during the 2005–2006 (Exp. 1) and 2007–2008 (Exp. 2) growing seasons. Over a 40‐yr period, the genetic gain in yield averaged 94.7% kg ha−1 per year and 53% of this was attributable to breeding undertaken in China. The newer hybrids showed increased tolerance to compound stress. We estimated that the contribution of stress tolerance to genetic yield gain was equal to 46 or 74% at 60,000 or 75,000 plants ha−1, respectively. Yield improvement has occurred at a slow pace at densities of 60,000 and 75,000 plants ha−1 in China. Further increasing maize grain yield in China will be achieved through higher plant populations, and this will require breeding for greater stress tolerance.

Genetic gain in yield and protein over two cycles of a wheat recurrent selection program

Increasing grain yield and protein are important wheat breeding goals. However, the simultaneous improvement of both traits is complicated by a strong negative correlation and genotype by environment interaction (G×E). A recurrent selection program (RSP) reported here was initiated to produce germplasm, which combined both high yield-potential and increased protein content for the northern wheat-growing region of Australia. Diallel crossing amongst 10 cultivars (6 high yield and 4 high quality cultivars), followed by random mating amongst the F1s were used to produce the founding segregating population. Two years of multi-environment trials were conducted in the GRDC Northern Grain Region (NR) for each of the foundation (RSA0) and first (RSA1) cycles of recurrent selection. Data from the two cycles were analysed to evaluate the genetic gain achieved over the two cycles of selection, based on five potential selection strategies. Selection based on yield or protein or yield-adjusted protein only increased selected trait but reduced the other traits. However, application of selection based on yield and protein or yield and yield-adjusted protein simultaneously increased both yield (4.7%, 6.0% for RSA0 and 4.0%, 4.2% for RSA1 respectively) and protein (2.1%, 1.3% for RSA0 and 1.7%, 1.6% for RSA1 respectively).

Genetic and environmental contributions to increased wheat yield in Minas Gerais, Brazil

Producers need wheat cultivars adapted to the predominant climate conditions of the end of the rainy period. Having this in mind, EPAMIG (Agriculture and Livestock Research Institute of Minas Gerais) has been developing a wheat genetic improvement program since 1976, and the estimates of the genetic improvement established by the breeding programs could be useful to quantify their efficiency. This study focused on the quantification of the genetic progress achieved by these improvement programs of dryland wheat in the Brazilian-savanna between 1976 and 2005. The efficiency of these programs was evaluated based on grain yield data of VCU (Value for Cultivation and Use) trials conducted at ten locations in the Minas Gerais State, Brazil. The mean estimated genetic progress for mean grain yield between 1976 and 2005 was 37 kg ha-1 year-1. The genetic yield gain in the study period indicates that the improvement programs of dryland wheat in the Brazilian-savanna are effective. Besides the marked contribution of genetic gain, the environmental and technological improvements were also relevant for the yield, accounting for 47.4% of the total progress in the period. The improvement programs of dryland wheat resulted in a genotype renovation rate of 35% over the years.

Changes in Genetic Diversity of U.S. Flue‐Cured Tobacco Germplasm over Seven Decades of Cultivar Development

Plant breeding methodologies have been applied to flue‐cured tobacco (Nicotiana tabacum L.) for approximately seven decades. As has been observed in several other crops, stringent quality requirements have resulted in use of conservative breeding strategies in the development of new cultivars. The impact of breeding practices on genetic diversity within U.S. flue‐cured tobacco germplasm has not been investigated. In this study, we genotyped 117 tobacco cultivars from eight sequential time periods with 71 microsatellite primer pairs. A total of 294 alleles were scored. Only a fraction (48%) of alleles present in the initial germplasm pool was represented in cultivars released during the 1990s and 2000s. Only 13 and 18 alleles were detected in the 1990s and 2000s, respectively, which were undetected in the initial gene pool. The overall trend was one of gradual reduction in allelic counts at microsatellite loci, indicating a reduction in diversity over time at the gene level. Average genetic similarity was highest among cultivars of the 1990s and 2000s, reflecting a reduction in genetic diversity at the population level. This observed narrowing of the U.S. flue‐cured tobacco germplasm base in combination with low rates of genetic gain for yield in the last 20 years may point to a need for diversification of parental materials used in future breeding crosses. Reported genetic relationships among the group of genotyped cultivars may be valuable for future strategic germplasm choices.

Changes in Yield and Carbon Isotope Discrimination of Italian and Spanish Durum Wheat during the 20th Century

This study evaluates the breeding of durum wheat (Triticum turgidum L. var. durum) during the 20th century with respect to yield and grain carbon isotope discrimination (Δ), and their relationship with plant height, harvest index (HI), days from sowing to anthesis, and days from anthesis to maturity. Twenty‐four cultivars released before 1945 (old), between 1950 and 1985 (intermediate), and between 1988 and 2000 (modern), and previously characterized by whether dwarfing genes were present (semidwarf) or absent (tall), were selected from germplasm obtained in Italy and Spain. Experiments were conducted in six environments with average yields ranging from to 2113 to 4827 kg ha−1. The total absolute genetic gain in yield across countries from before 1945 to 2000 was 20 kg ha−1 yr−1 (51% of increase), which represents a relative genetic gain of 0.61% yr−1. Yield gains led to a loss of stability. The mean increase in Δ13C was 6% (0.014‰ yr−1 or 0.09% yr−1). Early heading and a long grain‐filling period were correlated with high yields in the tall cultivars. Increased plant height and low Δ13C values were associated with high yields for the semidwarf cultivars, while a long grain‐filling period was not advantageous for semidwarf cultivars.

Breeding progress in morpho-physiological, agronomical and qualitative traits of durum wheat cultivars released in Italy during the 20th century

Fourteen durum wheat ( Triticum durum Desf.) cultivars introduced in Italy between 1900 and 1990 were grown for 2 years (2001 and 2002) at Foggia (Italy) in field trials with three agronomic treatments in order to assess the genetic improvement in agronomic and qualitative parameters. The traits were measured in the field to describe the biomass production and its partitioning to the grain, the phenological behaviours and the photosynthetic properties. Grain protein content, alveograph's W-index, carotenoid pigments content, ash content and the glutenin and gliadin subunit compositions were then measured to assess grain quality. The results showed that differences in agronomic traits among durum wheat cultivars released in Italy in the last century are generally similar to differences observed in hexaploid wheat, with an annual genetic yield gain of 19.9 kg ha −1 year −1. The genetic gain was most clearly associated with a higher kernels number m −2 indicating a larger grain-sink size and a higher number of spikes m −2. The gradual reduction in plant height associated with an increased harvest index has represented the main breeding goal with an effect on the sink capacity and on the biomass partitioning. The progressive incorporation into recent cultivars, of favourable alleles (7 + 8 glutenin subunit composition) coding for superior quality subunits reflects the improvement in pasta making quality of the recent genotypes.

Molecular assessment of genetic diversity in winter barley and its use in breeding

During the last decades extensive progress has been achieved in winter barley breeding with respect to both, yield and resistance to fungal and viral diseases. This progress is mainly due to the efficient use of the genetic diversity present within high yielding adapted cultivars and – with respect to resistance – to the extensive evaluation of genetic resources followed by genetic analyses and introgression of respective genes by sexual recombination. Detailed knowledge on genetic diversity present on the molecular level regarding specific traits as well as on the whole genome level may enhance barley breeding today by facilitating efficient selection of parental lines and marker assisted selection procedures. In the present paper the state of the art with respect to virus diseases, i.e. Barley mild mosaic virus, Barley yellow mosaic virus, and Barley yellow dwarf virus is briefly reviewed and first results on a project aiming on a genome wide estimation of genetic diversity which in combination with data on yield and additional agronomic traits may facilitate the detection of marker trait associations and a more efficient selection of parental genotypes are presented. By field tests of 49 two-rowed and 64 six-rowed winter barley cultivars the genetic gain in yield for the period 1970–2003 was estimated at 54.6 kg ha−1 year−1 (r 2 = 0.567) for the six-rowed cultivars and at 37.5 kg ha−1 year−1 (r 2 = 0.621) for the two-rowed cultivars. Analysis of 30 SSRs revealed a non-homogenous allele distribution between two and six-rowed cultivars and changes of allele frequencies in relation to the time of release. By PCoA a separation between two and six-rowed cultivars was observed but no clear cut differentiation in relation to the time of release. In the two-rowed cultivars an increase in genetic diversity (DI) from older to newly released cultivars was detected.

Physiological Processes Associated with Wheat Yield Progress in the UK

Knowledge of the changes in physiological traits associated with genetic gains in yield potential is essential to improve understanding of yield-limiting factors and to inform future breeding strategies. Our objective was to identify physiological traits associated with genetic gains in grain yield of winter wheat (Triticum aestivum L.) in the UK. The growth and development of eight representative cultivars introduced from 1972 to 1995 (one tall rht-D1b cultivar and seven Rht-D1b, formerly Rht2, semidwarf cultivars) was examined in field experiments at Sutton Bonington in 1996–1997, 1997–1998, and 1998–1999. A linear genetic gain in grain yield of 0.12 Mg ha−1 yr−1 (1.2% yr−1) was positively correlated with both harvest index (HI) and aboveground biomass; a quadratic function fitted to the data showed that progress in HI was most apparent during the earlier phase of the 23-yr period, whereas biomass contributed most since about 1983. There was a linear increase across time of 217 grains m−2 yr−1, but no change in grain weight. Significant genetic changes across time and correlations with grain yield were also found for preanthesis radiation-use efficiency (RUE, 0.012 g MJ−1 yr−1) and water soluble carbohydrate (WSC) content of stems and leaf sheaths at anthesis (4.6 g m−2 yr−1). Our results suggest that recent genetic gains in grain yield have been based on a combination of improved growth rate in the preanthesis period, which has driven increases in number of grains per square meter, and a larger source for grain filling through increases in stem soluble carbohydrate reserves.