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Our objective was to investigate the physiological basis of grain number per square meter (GN) and yield in two CIMMYT spring wheat (Triticum aestivum L.) lines of large-spike phenotype (LSP), LSP1 and LSP2, and one check cultivar, Bacanora, when grown as single plants in the growth room and at normal sowing densities in high radiation, irrigated field conditions. In the growth room, rachis length, spikelets per spike, and grains per spike were increased by 14 to 39%, 12 to 31% and 8 to 19%, respectively, compared to Bacanora. Increased spikelet number was associated with a longer thermal duration for spikelet primordia production. In the field, averaged over three seasons, 2003-2004 to 2005-2006, spikelets per spike and grains per spike were increased by 4 to 6% and 4 to 5%, respectively, in LSP lines compared to Bacanora (P < 0.05). Overall GN (-23%) and yield (-8%) were decreased in LSP2 compared to Bacanora associated with a lower spike number per square meter (-26%) (P < 0.05). The GN (-9%) and yield (+2%) of LSP1 overall were not different to Bacanora, although LSP1 yielded more in one season, 2004-2005 (+9%) (P < 0.05). LSP1 produced grains about 10% heavier and LSP2, about 20% heavier, than Bacanora, in both growth-room and field experiments. LSP1 showed a positive departure from the overall negative relationship between grains per gram of spike dry matter (at anthesis) and grain weight among the genotypes. LSP1 may represent a source of novel spike morphology for use in breeding programs aimed at boosting grain size at high GN to enhance yield potential.

Spectral indices as a selection tool in plant breeding could improve genetic gains for different important traits. The objectives of this study were to assess the potential of using spectral reflectance indices (SRI) to estimate genetic variation for in-season biomass production, leaf chlorophyll, and canopy temperature (CT) in wheat (Triticum aestivum L.) under irrigated conditions. Three field experiments, GHIST (15 CIMMYT globally adapted historic genotypes), RILsl (25 recombinant inbred lines [RILs]), and RILs2 (36 RILs) were conducted under irrigated conditions at the CIMMYT research station in northwest Mexico in three different years. Five SRI were evaluated to differentiate genotypes for biomass production. In general, genotypic variation for all the indices was significant. Near infrared radiation (NIR)-based indices gave the highest levels of association with biomass production and the higher associations were observed at heading and grainfilling, rather than at booting. Overall, NIR-based indices were more consistent and differentiated biomass more effectively compared to the other indices. Indices based on ratio of reflection spectra correlated with SPAD chlorophyll values, and the association was stronger at the generative growth stages. These SRI also successfully differentiated the SPAD values at the genotypic level. The NIR-based indices showed a strong and significant association with CT at the heading and grainfilling stages. These results demonstrate the potential of using SRI as a breeding tool to select for increased genetic gains in biomass and chlorophyll content, plus for cooler canopies., SIGNIFICANT PROGRESS in grain yield of spring wheat under irrigated conditions has been made through the classical breeding approach (Slafer et al., 1994), even though the genetic basis of yield [...]

The objectives of this study were to assess the potential of using spectral reflectance indices (SRI) as an indirect selection tool to differentiate spring wheat (Triticum aestivum L.) genotypes for grain yield under irrigated conditions. This paper demonstrates only the first step in using the SRI as indirect selection criteria by reporting genetic variation for SRI among genotypes, the effect of phenology and year un SRI and their interaction with genotypes, and the correlations between SRI and grain yield and yield components of wheat. Three field experiments--15 CIMMYT globally adapted genotypes (GHIST), 25 random [F.sub.3]-derived lines (RLs1), and 36 random [F.sub.3]-derived lines (RLs2)--were conducted under irrigated conditions at the CIMMYT research station in northwest Mexico in three different years. Five previously developed SRI (photochemical reflectance index [PRI], water index [WI], red normalized difference vegetation index [RNDVI], green normalized difference vegetation index [GNDVI], simple ratio ISR]) und two newly calculated SRI (normalized water index-1 [NWI-1] and normalized water index-2 [NWI-2]) were evaluated in the experiments. In general, genotypic variation for aH the indices was significant. Near infrared radiation (NIR)-based indices (WI, NWI-1, NWI-2) gave the highest levels of association with grain yield during the 3 yr of the study. A clear trend for higher association between grain yield and the NIR-based indices was observed at heading and grainfilling than at booting. Overall, NIR-based indices were more consistent and differentiated grain yield more effectively compared to the other indices. The results demonstrated the potential of using SRI as a tool in breeding programs for selecting for increased genetic gains for yield., SINCE THE GENETIC BASIS of yield improvement in wheat is not well established (Reynolds et al., 1999), the classical breeding approach for yield improvement still relies on an informed 'numbers [...]

Diverse and varied crop genetic resources are necessary (though not sufficient) for adequate food production in a rapidly changing world. Since the scientific community first raised public concern several decades ago, modern cultivars have been viewed as the cause of declining diversity in the world's crop genetic resources. This paper tests the hypothesis of increasing genetic uniformity in modern spring bread wheat (Triticum aestivum L.) cultivars from 1965, a year which marks the release of some of the first modern semidwarf cultivars carrying Rht1 and Rht2 genes in the developing world. Results from previously published studies are summarized. Preliminary molecular analyses, and new analyses of cultivar numbers, areas, ages, and genealogies are presented. An estimated 77% of the spring bread wheat area in the developing world today is sown to CIMMYT-related wheats, but this does not imply that they are genetically uniform. The hypothesis of increasing genetic uniformity is tested by assessing changes in the diversity of leading progenitors over three decades, in terms of several dimensions of diversity. Latent dimensions include genetic distance and genealogies. Apparent dimensions include performance with respect to yield potential, maintenance and stability across management (input use), and growing environments. The data are not consistent with the view that the genetic diversity of modern semidwarf wheat grown in the developing world has decreased over time. Moreover, since national programs in developing countries cross CIMMYT lines with their own materials before releasing them, the genetic diversity in their cultivars is at least as great as that present among CIMMYT lines., NEARLY 30 YR HAVE PASSED since in a landmark study, the National Research Council (1972) alerted the scientific community and the public about the dangers of restricting crop improvement to [...]

Population growth, arable land and fresh water limits, and climate change have profound implications for the ability of agriculture to meet this century's demands for food, feed, fiber, and fuel white reducing the environmental impact of their production. Success depends on the acceptance and use of contemporary molecular techniques, as well as the increasing development of farming systems that use saline water and integrate nutrient flows. 10.1126/science.1186834

Abstract: Genetic progress in yield will increase if more traits conferring better agronomic and physiological performance are brought together in the same variety through full exploitation of genotyping and phenotyping techniques in breeding. A set of 288 spring wheat advanced lines was tested in different countries in North Africa, Western and South Asia, as well as in Mexico (total of 12 environments) to: identify high yielding germplasm adapted to the former regions; identify sources of variation for physiological traits; and test the ability of physiological traits to predict yield. A group of high yielding advanced lines has been selected in these environments, but significant genotype by environment interactions were observed and were significantly explained (21% of yield variation) by soil pH and air temperature. Associations between traits were dependent on the environment, specifically TKW was positively associated with yield in almost all environments however in Sudan, negative associations were observed. In contrast cooler CT was consistently associated with yield and the trait showed moderate heritability. Agronomic and physiological variables were able to predict 27% of yield variation across advanced lines (R 2% by ridge regression) using means of all environments and this model became more significant under stress environments (explaining around 34% of yield variation). Results suggested that if drought and heat adaptive traits are brought together in one genotype, yields can be further increased particularly in low yielding environments. [Copyright &y& Elsevier]

Abstract: This paper focuses on the interaction between genotype and environment, a critical aspect of plant breeding, from a physiological perspective. We present a theoretical framework largely based on Bradshaw''s principles of phenotypic plasticity (Adv. Gen. 13: 115) updated to account for recent developments in physiology and genetics. Against this framework we discuss associations between plasticity of yield and plasticity of phenological development. Plasticity was quantified using linear models of phenotype vs environment for 169 wheat lines grown in 6 environments in Mexico, 32 sunflower hybrids grown in at least 15 environments in Argentina and 7 grapevine varieties grown in at least 14 environments in Australia. In wheat, yield ranged from 0.6 to 7.8tha−1 and the range of plasticity was 0.74–1.27 for yield and 0.85–1.17 for time to anthesis. The duration of the post-anthesis period as a fraction of the season was the trait with the largest range of plasticity, i.e. 0.47–1.80. High yield plasticity was an undesirable trait as it was associated with low yield in low-yielding environments. Low yield plasticity and high yield in low-yielding environments were associated with three phenological traits: early anthesis, long duration and low plasticity of post-anthesis development. In sunflower, yield ranged from 0.5 to 4.9tha−1 and the range of plasticity was 0.72–1.29 for yield and 0.72–1.22 for time to anthesis. High yield plasticity was a desirable trait as it was primarily associated with high yield in high-yielding environments. High yield plasticity and high yield in high-yielding environments were associated with two phenological traits: late anthesis and high plasticity of time to anthesis. In grapevine, yield ranged from 1.2 to 18.7tha−1 and the range of plasticity was 0.79–1.29 for yield, 0.86–1.30 for time of budburst, 0.84–1.18 for flowering, and 0.78–1.16 for veraison. High plasticity of yield was a desirable trait as it was primarily associated with high yield in high-yielding environments. High yield plasticity was associated with two phenological traits: plasticity of budburst and plasticity of anthesis. We report for the first time positive associations between plasticities of yield and phenology in crop species. It is concluded that in addition to phenology per se (i.e. mean time to a phenostage), plasticity of phenological development merits consideration as a distinct trait influencing crop adaptation and yield. [Copyright &y& Elsevier]

Wheat cultivars often show highly significant genotype by environment interaction (G×E) for yield, even when comparing different years within a relatively stable location. This study attempts to explain some of the physiological bases of G×E in two experiments: (i) historic yield potential trials (HYPTs) of bread wheat (BW) (Triticum aestivum L.), durum (T. durum Desf.) and triticale (TCL) (X Triticosecale Wittmack) cultivars grown under agronomically optimal conditions; (ii) an elite spring wheat yield trial (ESWYT) of 30 BW genotypes cultivated at 27 international locations. For the HYPT, the main objectives were to determine the environmental variables during different phenological stages associated with: (i) G×E among the three crop species, (ii) G×E within each species, and (iii) underlying physiological causes of G×E. For ESWYT, meteorological data were not available and so mean site values of certain crop parameters were used as proxy environmental data to determine whether conditions either pre- or post-anthesis were more influential in determining G×E. Partial least squares analysis (PLS) and factorial regression (FR) models were used to identify the environmental factors best explaining G×E independent of the main effects. Of the three crops, durums were shown to be the most sensitive to conditions pre-anthesis, requiring higher radiation and cooler average temperatures (Txs) in order to set high grain number. TCL, despite having the highest average yield and biomass, performed relatively poor when conditions from spike growth stage onwards were sunny and warm. BW appeared to be the most robust of the three species. Considering yield, biomass, and yield components, it was apparent that the spike primordia growth stage was generally the most sensitive to environmental factors causing G×E. Results for the ESWYT suggested that conditions post-anthesis were more influential on G×E than conditions pre-anthesis. Implications for how such analysis may assist with both conventional and molecular approaches to breeding are discussed. [Copyright &y& Elsevier]

Abstract The 7DL.7Ag translocation from Lophopyrum elongatum that carries Lr19 , a leaf rust resistance gene, was found to be associated with a significant increase in grain yield under irrigated, disease-free conditions, but a generally lower yield under moisture stress conditions. These studies, however, involved a limited number of genetic recipients and environments, and the effect of the translocation on physiological traits was not considered. We examined the translocation effect in six different recipient genotypes and under five environmental conditions, including drought and heat stress. The increase in grain yield under irrigated conditions was associated with a higher rate of biomass production in the 7DL.7Ag lines and may be attributed to higher sink strength. Effect of the translocation on physiological traits was noted only under heat stress and was not associated with difference in yield. Under moisture stress conditions, 7DL.7Ag lines yielded less than their corresponding recipients, possibly because of a longer growing cycle. It is concluded that the effect of the 7DL.7Ag translocation may very much depend on the phenological adaptation of the recipient genotype and the translocation may be useful for enhancing yield, mainly under favourable conditions. [ABSTRACT FROM AUTHOR]

Wheat cultivars often show highly significant genotype by environment interaction (G×E) for yield, even when comparing different years within a relatively stable location. This study attempts to explain some of the physiological bases of G×E in two experiments: (i) historic yield potential trials (HYPTs) of bread wheat (Triticum aestivum L.), durum (T. durum Desf.) and triticale (X Triticosecale Wittmack) cultivars grown under agronomically optimal conditions; (ii) an elite spring wheat yield trial (ESWYT) of 30 bread wheat genotypes cultivated at 27 international locations. For the HYPT, the main objectives were to determine the environmental variables during different phenological stages associated with: (i) G×E among the three crop species, (ii) G×E within each species, and (iii) underlying physiological causes of G×E. For ESWYT, meteorological data were not available and so mean site values of certain crop parameters were used as proxy environmental data to determine whether conditions either pre- or post-anthesis were more influential in determining G×E. Partial least-squares analysis and factorial regression models were used to identify the environmental factors best explaining G×E independent of the main effects. Of the three crops, durums were shown to be the most sensitive to conditions pre-anthesis, requiring higher radiation and cooler average temperatures in order to set high grain number. Triticale, despite having the highest average yield and biomass, performed relatively poor when conditions from spike growth stage onwards were sunny and warm. Bread wheat appeared to be the most robust of the three species. Considering yield, biomass, and yield components, it was apparent that the spike primordia growth stage was generally the most sensitive to environmental factors causing G×E. Results for the ESWYT suggested that conditions post-anthesis were more influential on G×E than conditions pre-anthesis. Implications for how such analysis may assist with both conventional and molecular approaches to breeding are discussed. [Copyright &y& Elsevier]

Discusses the potential application of selection technologies in breeding of wheat to improve the probability of identifying higher-yielding genotypes. Trends in yield potential from 1966 to the present, and future demand; Physiological basis of genetic improvement in yield; Genetic basis of yield improvement.

This study examines genotype×organ–temperature depression (TD) interactions and whether differences in plant morphology influence organ-TD and its correlation with canopy temperature depression (CTD) and grain yield. Field experiments were conducted with 13 spring wheat genotypes planted on three dates in the 2000–2001 winter cropping cycle in NW Mexico. Surface temperatures of flag leaves, peduncles, spikes and canopy were measured with a hand-held infrared thermometer. Morphological and yield components were also measured. Results indicated that there is genetic variability for organ-TD. CTD showed strong positive correlations with organ-TD and grain yield. Organ-TD and CTD were positively correlated with leaf area index, and CTD was probably little affected by leaf rolling. Spike temperature was generally higher than leaf temperature, but lower than ambient air temperature. The interactions between grain yield and spike-TD and CTD were not significant. Results of this study indicate that CTD does not mask confounding interactions between organ temperatures and thus can be used reliably to measure TD during grain filling under heat stress conditions. [Copyright &y& Elsevier]

A model of the lodging process has been successfully adapted for use on spring wheat grown in North-West Mexico (NWM). The lodging model was used to estimate the lodging-associated traits required to enable spring wheat grown in NWM with a typical yield of 6 t ha −1 and plant height of 0.7 m to achieve a lodging return period of 25 years. Target traits included a root plate spread of 51 mm and stem strength of the bottom internode of 268 N mm. These target traits increased to 54.5 mm and 325 N mm, respectively, for a crop yielding 10 t ha −1 . Analysis of multiple genotypes across three growing seasons enabled relationships between both stem strength and root plate spread with structural dry matter to be quantified. A NWM lodging resistant ideotype yielding 6 t ha −1 would require 3.93 t ha −1 of structural stem biomass and 1.10 t ha −1 of root biomass in the top 10 cm of soil, which would result in a harvest index (HI) of 0.46 after accounting for chaff and leaf biomass. A crop yielding 10 t ha −1 would achieve a HI of 0.54 for 0.7 m tall plants or 0.41 for more typical 1.0 m tall plants. This study indicates that for plant breeders to achieve both high yields and lodging-proofness they must either breed for greater total biomass or develop high yielding germplasm from shorter crops. [ABSTRACT FROM AUTHOR]

Lodging-related traits were evaluated on the CIMMYT Core spring wheat Germplasm Panel (CIMCOG) in the Yaqui Valley of North-West Mexico during three seasons (2010–2013). Genetic variation was significant for all the lodging-related traits in the cross-year analysis, however, significant G × E interaction due to rank changes or changes in the absolute differences between cultivars were identified. The inconsistences on cultivar performances across seasons particularly reduced the heritability of key characters related to root lodging resistance (anchorage strength). Target characters related to stem lodging resistance (stem strength) showed good heritability values equal or above 0.70. Positive correlations between stem strength and stem diameter and between root plate spread and root strength were found. Selecting for greater stem diameter and wall width, greater root plate spread and shorter plant height could enable breeders to increase lodging resistance by increasing stem strength, root strength and decreasing plant leverage, respectively. Achieving a lodging-proof crop will depend on finding a wider root plate spread and implementing new management strategies. Genetic linkages between lodging traits will not constrain the combination of the key lodging-trait dimensions to achieve a lodging-proof ideotype. However, strong association between stem strength and stem wall width will increase the total biomass cost needed for lodging resistance. [ABSTRACT FROM AUTHOR]

South Asia, which is already home to more than one-fifth of the world's population and rapidly growing, will require wheat yields to rise annually by 2.0–2.5% to meet demand and maintain food security. To address these challenges, a wheat phenotyping network was established in the region in 2009 to support national breeding programs by applying practical phenotyping techniques to increase selection success using a cooperative multi-location testing network. A number of trials have been grown to introduce new genetic diversity for stress adaptive traits, to establish their genetic bases, and to test a new generation of lines developed using physiological approaches. The 17th Semi-Arid Wheat Yield Trial (SAWYT), consisting of a group of 50 elite spring bread wheat advanced lines, bred in Mexico using both conventional (CON) and physiological trait (PT) approaches, was grown for two seasons 2009/10 and 2010/11. Data showed that PT lines gave superior yields overall, associated with higher grain weight, and with cooler vegetative and grain-filling canopy temperatures (CT); the CT trait is considered indicative of increased gas exchange, a likely consequence in these environments of superior vascular capacity including deeper rooting to access subsoil water. Local check genotypes, which were generally well adapted to the stressed environments tended to be 3–5 days earlier to heading than CIMMYT cultivars. Results demonstrate the potential to integrate physiological breeding approaches into genetic improvement for the region, particularly as future wheat production will take place under increasing water scarcity. [ABSTRACT FROM AUTHOR]

Highlights: [•] The inheritance of tolerance to high temperature stress was investigated using QTL analysis on a doubled haploid population. [•] Seven stable QTL were identified for HSI of traits, mapping to chromosomes 1D, 6B, 2D and 7A. [•] Three QTLs related to HSI of grain filling duration, two to thousand grain weights and one each to grain yield and canopy temperature. [•] The QTL analysis for the direct traits GY, TGW, GFD and CT led to detection of 22 QTLs spread over to 17 chromosomal regions. [•] A QTL for TGW on chromosome 6B under normal sown co-located with HSI (TGW) QTL QHTgw.bhu-6BL. [Copyright &y& Elsevier]

• Screening lodging traits for lodging resistance is key for wheat improvement. • Screening seven plants per plot is enough to find genetic variation for lodging traits. • Four key lodging traits can be measured to estimate lodging performance in wheat. Lodging is a complex phenomenon affecting wheat production worldwide and is a consequence of the interaction of wheat plants with abiotic (wind, rain, etc.) and biotic (e. g. plant disease, etc.) factors. Wheat breeders rely heavily on incidences of natural lodging to select lines with resistance; however, the intermittent nature of lodging events means this approach is unreliable. A model of the lodging process has been published to estimate the lodging susceptibility of plants that uses information from 15 stem and root characteristics of field grown plants that influence lodging. This approach estimates lodging susceptibility in the absence of natural lodging. However, the main shortcoming of this methodology for plant breeders is the amount of time required to measure these traits (100–150 min per plot). This study investigated two strategies to optimise the methods of estimating lodging risk in the absence of natural lodging: i) determining the minimum number of plants that must be measured per experimental plot (sample size) to identify genetic differences and ii) minimizing the number of traits required to assess lodging susceptibility increasing the feasibility to apply the methodology in a breeding context. Spring wheat grown under North West Mexico environmental conditions was established during four crop seasons (2010−11, 2011−12, 2012−13 and 2013−14) for this study. Results indicated an optimum sample size of seven plants per plot as the minimum required to identify genetic differences between cultivars with good statistical power and precision (assuming each treatment plot was replicated 3 times). Cultivar ranking and absolute values for trait dimensions were maintained when compared with larger sample sizes. A reduced number of traits can be used to estimate cultivar lodging susceptibility performances and key traits include: plant height, ear number per plant, ear area, natural frequency, breaking strength, length, diameter and wall width of one basal internode, structural rooting depth and root plate spread. Targeting these key traits, this study established that on a daily basis, 10 (47 min per plot) plots can be assessed by measuring seven plants per plot per person. Moreover, if the screening focuses only on the key traits for leverage/stem/root dimensions, then the daily plot assessment capacity would increase to 25. [ABSTRACT FROM AUTHOR]