Goosefish Lophius americanus fecundity and spawning frequency, with implications for population reproductive potential.

To improve knowledge of goosefish Lophius americanus' reproductive biology, females were collected during 2009-2012 from the Mid-Atlantic Bight shelf region of the U.S. east coast. Batch fecundity increased with total length (LT ), from 229 100 to 2 243 300 mature oocytes per female (LT range: 55·5-112 cm; n = 54). This estimate of fecundity at LT is lower than one derived from a sample collected during 1982-1985. Examination of whole oocyte diameters in different months indicated that L. americanus is a serial spawner, releasing more than one egg veil per spawning season, as suspected or observed for other Lophius species. Seasonality of spawning was evident from whole oocytes and gonad histology, and from larval fish surveys spanning the U.S. north-east shelf, and confirmed a protracted (c. 6 months) spawning period. Peak spawning activity progressed northward from spring to autumn. The population-level implications of these results were explored by estimating population reproductive potential (PRP ), which considered the value of both current and future per capita reproduction using decade-specific age structure and fecundity at length. PRP is now more than 50% lower compared with the historical period (1982-1985), a result of the lower proportions of large females and reduced fecundity across all sizes. Mechanisms that could explain this loss of stock productivity are fishing-induced size-age truncation or regime shifts in egg production caused by changes in energy density of common forage species.

Recurrent selection for wider seedling leaves increases early biomass and leaf area in wheat (Triticum aestivum L.).

The breeding of wheat with greater early vigour has potential to increase water- and nutrient-use efficiency, as well as to improve weed competitiveness to raise crop yields profitably. Given that wheat is inherently conservative in its early growth, a sustained breeding effort was initiated to increase genetically seedling leaf area in developing novel high vigour germplasm. A recurrent selection programme was initiated by intercrossing a genetically diverse set of 28 vigorous wheat lines identified globally. These were intercrossed at random and S1:2 progeny with the largest leaf 1 and 2 widths were intermated to develop new populations for assessment of early growth. This procedure was repeated for up to 60 segregating families per cycle across six cycles over 15 years. Thirty random S1:2 progeny were retained from each cycle and seed-increased together to produce seed for early vigour assessment in multiple sowings. The most vigorous wheat seedlings were identified in later cycles, with some lines producing more than double the leaf area and biomass of elite commercial wheat varieties. Phenotypic selection for greater leaf width was associated with a realized significant (P<0.01) linear increase per seedling of 0.41 mm per cycle (+7.1%) for mean leaf width, and correlated linear increases in total leaf area and biomass of 4.48 cm(2) per cycle (+10.3%) and 10.8 mg per cycle (+5.3%), respectively. Genetic gains in widths of leaves 2 (+8.4%) and 3 (+11.5%) were significantly (P<0.01) greater than for leaf 1 (+5.3%). Selection for greater leaf width was associated with linear increases in coleoptile tiller leaf area, small curvilinear increases in leaf 1 length, and reductions in numbers of leaves and mainstem tillers. Genetic variances were large and heritabilities high for leaf width and total leaf area in each cycle, but reduced linearly in size with selection across cycles. Coupling diverse germplasm with a simple, inexpensive, and repeatable selection process has confirmed the value of recurrent selection in developing uniquely vigorous wheat germplasm for use as parents in commercial breeding.

Soil coring at multiple field environments can directly quantify variation in deep root traits to select wheat genotypes for breeding.

We aim to incorporate deep root traits into future wheat varieties to increase access to stored soil water during grain development, which is twice as valuable for yield as water captured at younger stages. Most root phenotyping efforts have been indirect studies in the laboratory, at young plant stages, or using indirect shoot measures. Here, soil coring to 2 m depth was used across three field environments to directly phenotype deep root traits on grain development (depth, descent rate, density, length, and distribution). Shoot phenotypes at coring included canopy temperature depression, chlorophyll reflectance, and green leaf scoring, with developmental stage, biomass, and yield. Current varieties, and genotypes with breeding histories and plant architectures expected to promote deep roots, were used to maximize identification of variation due to genetics. Variation was observed for deep root traits (e.g. 111.4-178.5cm (60%) for depth; 0.09-0.22cm/°C day (144%) for descent rate) using soil coring in the field environments. There was significant variation for root traits between sites, and variation in the relative performance of genotypes between sites. However, genotypes were identified that performed consistently well or poorly at both sites. Furthermore, high-performing genotypes were statistically superior in root traits than low-performing genotypes or commercial varieties. There was a weak but significant negative correlation between green leaf score (-0.5), CTD (0.45), and rooting depth and a positive correlation for chlorophyll reflectance (0.32). Shoot phenotypes did not predict other root traits. This study suggests that field coring can directly identify variation in deep root traits to speed up selection of genotypes for breeding programmes.

Improvement of crop yield in dry environments: benchmarks, levels of organisation and the role of nitrogen.

Crop yield in dry environments can be improved with complementary approaches including selecting for yield in the target environments, selecting for yield potential, and using indirect, trait- or genomic-based methods. This paper (i) outlines the achievements of direct selection for yield in improving drought adaptation, (ii) discusses the limitations of indirect approaches in the context of levels of organization, and (iii) emphasizes trade-offs and synergies between nitrogen nutrition and drought adaptation. Selection for yield in the water- and nitrogen-scarce environments of Australia improved wheat yield per unit transpiration at a rate of 0.12kg ha(-1) mm(-1) yr(-1); for indirect methods to be justified, they must return superior rates of improvement, achieve the same rate at lower cost or provide other cost-effective benefits, such as expanding the genetic basis for selection. Slow improvement of crop adaptation to water stress using indirect methods is partially related to issues of scale. Traits are thus classified into three broad groups: those that generally scale up from low levels of organization to the crop level (e.g. herbicide resistance), those that do not (e.g. grain yield), and traits that might scale up provided they are considered in a integrated manner with scientifically sound scaling assumptions, appropriate growing conditions, and screening techniques (e.g. stay green). Predicting the scalability of traits may help to set priorities in the investment of research efforts. Primary productivity in arid and semi-arid environments is simultaneously limited by water and nitrogen, but few attempts are made to target adaptation to water and nitrogen stress simultaneously. Case studies in wheat and soybean highlight biological links between improved nitrogen nutrition and drought adaptation.

A rapid, controlled-environment seedling root screen for wheat correlates well with rooting depths at vegetative, but not reproductive, stages at two field sites.

BACKGROUND AND AIMS: Root length and depth determine capture of water and nutrients by plants, and are targets for crop improvement. Here we assess a controlled-environment wheat seedling screen to determine speed, repeatability and relatedness to performance of young and adult plants in the field. METHODS: Recombinant inbred lines (RILs) and diverse genotypes were grown in rolled, moist germination paper in growth cabinets, and primary root number and length were measured when leaf 1 or 2 were fully expanded. For comparison, plants were grown in the field and root systems were harvested at the two-leaf stage with either a shovel or a soil core. From about the four-leaf stage, roots were extracted with a steel coring tube only, placed directly over the plant and pushed to the required depth with a hydraulic ram attached to a tractor. KEY RESULTS: In growth cabinets, repeatability was greatest (r = 0.8, P < 0.01) when the paper was maintained moist and seed weight, pathogens and germination times were controlled. Scanned total root length (slow) was strongly correlated (r = 0.7, P < 0.01) with length of the two longest seminal axile roots measured with a ruler (fast), such that 100-200 genotypes were measured per day. Correlation to field-grown roots at two sites at two leaves was positive and significant within the RILs and cultivars (r = 0.6, P = 0.01), and at one of the two sites at the five-leaf stage within the RILs (r = 0.8, P = 0.05). Measurements made in the field with a shovel or extracted soil cores were fast (5 min per core) and had significant positive correlations to scanner measurements after root washing and cleaning (>2 h per core). Field measurements at two- and five-leaf stages did not correlate with root depth at flowering. CONCLUSIONS: The seedling screen was fast, repeatable and reliable for selecting lines with greater total root length in the young vegetative phase in the field. Lack of significant correlation with reproductive stage root system depth at the field sites used in this study reflected factors not captured in the screen such as time, soil properties, climate variation and plant phenology.

Response of millet and sorghum to a varying water supply around the primary and nodal roots.

BACKGROUND AND AIMS: Cereals have two root systems. The primary system originates from the embryo when the seed germinates and can support the plant until it produces grain. The nodal system can emerge from stem nodes throughout the plant's life; its value for yield is unclear and depends on the environment. The aim of this study was to test the role of nodal roots of sorghum and millet in plant growth in response to variation in soil moisture. Sorghum and millet were chosen as both are adapted to dry conditions. METHODS: Sorghum and millet were grown in a split-pot system that allowed the primary and nodal roots to be watered separately. KEY RESULTS: When primary and nodal roots were watered (12 % soil water content; SWC), millet nodal roots were seven times longer than those of sorghum and six times longer than millet plants in dry treatments, mainly from an 8-fold increase in branch root length. When soil was allowed to dry in both compartments, millet nodal roots responded and grew 20 % longer branch roots than in the well-watered control. Sorghum nodal roots were unchanged. When only primary roots received water, nodal roots of both species emerged and elongated into extremely dry soil (0.6-1.5 % SWC), possibly with phloem-delivered water from the primary roots in the moist inner pot. Nodal roots were thick, short, branchless and vertical, indicating a tropism that was more pronounced in millet. Total nodal root length increased in both species when the dry soil was covered with plastic, suggesting that stubble retention or leaf mulching could facilitate nodal roots reaching deeper moist layers in dry climates. Greater nodal root length in millet than in sorghum was associated with increased shoot biomass, water uptake and water use efficiency (shoot mass per water). Millet had a more plastic response than sorghum to moisture around the nodal roots due to (1) faster growth and progression through ontogeny for earlier nodal root branch length and (2) partitioning to nodal root length from primary roots, independent of shoot size. CONCLUSIONS: Nodal and primary roots have distinct responses to soil moisture that depend on species. They can be selected independently in a breeding programme to shape root architecture. A rapid rate of plant development and enhanced responsiveness to local moisture may be traits that favour nodal roots and water use efficiency at no cost to shoot growth.

Traits and selection strategies to improve root systems and water uptake in water-limited wheat crops.

Wheat yields globally will depend increasingly on good management to conserve rainfall and new varieties that use water efficiently for grain production. Here we propose an approach for developing new varieties to make better use of deep stored water. We focus on water-limited wheat production in the summer-dominant rainfall regions of India and Australia, but the approach is generally applicable to other environments and root-based constraints. Use of stored deep water is valuable because it is more predictable than variable in-season rainfall and can be measured prior to sowing. Further, this moisture is converted into grain with twice the efficiently of in-season rainfall since it is taken up later in crop growth during the grain-filling period when the roots reach deeper layers. We propose that wheat varieties with a deeper root system, a redistribution of branch root density from the surface to depth, and with greater radial hydraulic conductivity at depth would have higher yields in rainfed systems where crops rely on deep water for grain fill. Developing selection systems for mature root system traits is challenging as there are limited high-throughput phenotyping methods for roots in the field, and there is a risk that traits selected in the lab on young plants will not translate into mature root system traits in the field. We give an example of a breeding programme that combines laboratory and field phenotyping with proof of concept evaluation of the trait at the beginning of the selection programme. This would greatly enhance confidence in a high-throughput laboratory or field screen, and avoid investment in screens without yield value. This approach requires careful selection of field sites and years that allow expression of deep roots and increased yield. It also requires careful selection and crossing of germplasm to allow comparison of root expression among genotypes that are similar for other traits, especially flowering time and disease and toxicity resistances. Such a programme with field and laboratory evaluation at the outset will speed up delivery of varieties with improved root systems for higher yield.

Quantitative trait loci for carbon isotope discrimination are repeatable across environments and wheat mapping populations.

Wheat productivity is commonly limited by a lack of water essential for growth. Carbon isotope discrimination (Delta), through its negative relationship with transpiration efficiency, has been used in selection of higher wheat yields in breeding for rainfed environments. The potential also exists for selection of increased Delta for improved adaptation to irrigated and high rainfall environments. Selection efficiency of Delta would be enhanced with a better understanding of its genetic control. Three wheat mapping populations (Cranbrook/Halberd, Sunco/Tasman and CD87/Katepwa) containing between 161 and 190 F(1)-derived, doubled-haploid progeny were phenotyped for Delta and agronomic traits in 3-5 well-watered environments. The range for Delta was large among progeny (c. 1.2-2.3 per thousand), contributing to moderate-to-high single environment (h (2) = 0.37-0.91) and line-mean (0.63-0.86) heritabilities. Transgressive segregation was large and genetic control complex with between 9 and 13 Delta quantitative trait loci (QTL) identified in each cross. The Delta QTL effects were commonly small, accounting for a modest 1-10% of the total additive genetic variance, while a number of chromosomal regions appeared in two or more populations (e.g. 1BL, 2BS, 3BS, 4AS, 4BS, 5AS, 7AS and 7BS). Some of the Delta genomic regions were associated with variation in heading date (e.g. 2DS, 4AS and 7AL) and/or plant height (e.g. 1BL, 4BS and 4DS) to confound genotypic associations between Delta and grain yield. As a group, high Delta progeny were significantly (P < 0.10-0.01) taller and flowered earlier but produced more biomass and grain yield in favorable environments. After removing the effect of height and heading date, strong genotypic correlations were observed for Delta and both yield and biomass across populations (r (g) = 0.29-0.57, P < 0.05) as might be expected for the favorable experimental conditions. Thus selection for Delta appears beneficial in increasing grain yield and biomass in favorable environments. However, care must be taken to avoid confounding genotypic differences in Delta with stature and development time when selecting for improved biomass and yield especially in environments experiencing terminal droughts. Polygenic control and small size of individual QTL for Delta may reduce the potential for QTL in marker-assisted selection for improved yield of wheat.

A QTL on chromosome 6A in bread wheat (Triticum aestivum) is associated with longer coleoptiles, greater seedling vigour and final plant height.

Wheat crops with greater early vigour shade the soil surface more rapidly and reduce water loss. Evaporative losses affect water-use efficiency particularly in drier regions where most of the rainfall occurs early in the growing season before canopy closure. Greater seedling leaf area and longer coleoptiles are major determinants of increased vigour and better crop establishment. A previously developed high vigour breeding line 'Vigour 18' was used to establish a large recombinant inbred family and framework map to identify a QTL on chromosome 6A that accounted for up to 8% of the variation for coleoptile length, 14% of seedling leaf width and was associated with increased plant height. The SSR marker NW3106, nearest to the 6A QTL, was also associated with greater leaf width in a breeding population that was also derived from a cross involving the high vigour donor line 'Vigour18'. The association between the NW3106 marker and coleoptile length was validated in a second breeding population which was developed using an unrelated long coleoptile donor line. The 'Vigour18' allele of the QTL on chromosome 6A promoted coleoptile length and leaf width during early plant growth but was also associated with increased plant height at maturity. Markers linked to the QTL are being used to increase the frequency of increased vigour and long coleoptile alleles in early generations of breeding populations.

Molecular mapping of genes for Coleoptile growth in bread wheat (Triticum aestivum L.).

Successful plant establishment is critical to the development of high-yielding crops. Short coleoptiles can reduce seedling emergence particularly when seed is sown deep as occurs when moisture necessary for germination is deep in the subsoil. Detailed molecular maps for a range of wheat doubled-haploid populations (Cranbrook/Halberd, Sunco/Tasman, CD87/Katepwa and Kukri/Janz) were used to identify genomic regions affecting coleoptile characteristics length, cross-sectional area and degree of spiralling across contrasting soil temperatures. Genotypic variation was large and distributions of genotype means were approximately normal with evidence for transgressive segregation. Narrow-sense heritabilities were high for coleoptile length and cross-sectional area indicating a strong genetic basis for differences among progeny. In contrast, heritabilities for coleoptile spiralling were small. Molecular marker analyses identified a number of significant quantitative trait loci (QTL) for coleoptile growth. Many of the coleoptile growth QTL mapped directly to the Rht-B1 or Rht-D1 dwarfing gene loci conferring reduced cell size through insensitivity to endogenous gibberellins. Other QTL for coleoptile growth were identified throughout the genome. Epistatic interactions were small or non-existent, and there was little evidence for any QTL x temperature interaction. Gene effects at significant QTL were approximately one-half to one-quarter the size of effects at the Rht-B1 and Rht-D1 regions. However, selection at these QTL could together alter coleoptile length by up to 50 mm. In addition to Rht-B1b and Rht-D1b, genomic regions on chromosomes 2B, 2D, 4A, 5D and 6B were repeatable across two or more populations suggesting their potential value for use in breeding and marker-aided selection for greater coleoptile length and improved establishment.

Molecular mapping of gibberellin-responsive dwarfing genes in bread wheat.

Opportunities exist for replacing reduced height (Rht) genes Rht-B1b and Rht-D1b with alternative dwarfing genes for bread wheat improvement. In this study, the chromosomal locations of several height-reducing genes were determined by screening populations of recombinant inbred lines or doubled haploid lines varying for plant height with microsatellite markers. Linked markers were found for Rht5 (on chromosome 3BS), Rht12 (5AL) and Rht13 (7BS), which accounted for most of the phenotypic variance in height in the respective populations. Large height differences between genotypes (up to 43 cm) indicated linkage to major height-reducing genes. Rht4 was associated with molecular markers on chromosome 2BL, accounting for up to 30% of the variance in height. Confirming previous studies, Rht8 was linked to markers on chromosome 2DS, whereas a population varying for Rht9 revealed a region with a small but significant height effect on chromosome 5AL. The height-reducing effect of these dwarfing genes was repeatable across a range of environments. The molecular markers developed in this study will be useful for marker-assisted selection of alternative height-reducing genes, and to better understand the effects of different Rht genes on wheat growth and agronomic performance.

Breeding for high water-use efficiency.

There is a pressing need to improve the water-use efficiency of rain-fed and irrigated crop production. Breeding crop varieties with higher water-use efficiency is seen as providing part of the solution. Three key processes can be exploited in breeding for high water-use efficiency: (i) moving more of the available water through the crop rather than it being wasted as evaporation from the soil surface or drainage beyond the root zone or being left behind in the root zone at harvest; (ii) acquiring more carbon (biomass) in exchange for the water transpired by the crop, i.e. improving crop transpiration efficiency; (iii) partitioning more of the achieved biomass into the harvested product. The relative importance of any one of these processes will vary depending on how water availability varies during the crop cycle. However, these three processes are not independent. Targeting specific traits to improve one process may have detrimental effects on the other two, but there may also be positive interactions. Progress in breeding for improved water-use efficiency of rain-fed wheat is reviewed to illustrate the nature of some of these interactions and to highlight opportunities that may be exploited in other crops as well as potential pitfalls. For C3 species, measuring carbon isotope discrimination provides a powerful means of improving water-use efficiency of leaf gas exchange, but experience has shown that improvements in leaf-level water-use efficiency may not always translate into higher crop water-use efficiency or yield. In fact, the reverse has frequently been observed. Reasons for this are explored in some detail. Crop simulation modelling can be used to assess the likely impact on water-use efficiency and yield of changing the expression of traits of interest. Results of such simulations indicate that greater progress may be achieved by pyramiding traits so that potential negative effects of individual traits are neutralized. DNA-based selection techniques may assist in such a strategy.

Comparative mapping of wheat chromosome 1AS which contains the tiller inhibition gene (tin) with rice chromosome 5S.

The capacity to tiller is a key factor that determines plant architecture. Using molecular markers, a single major gene reducing tiller number, formally named the tiller inhibition gene ( tin), was mapped to the short arm of chromosome 1A in wheat. We identified a tightly linked microsatellite marker ( Xgwm136) that may be useful in future marker-assisted selection. The tin gene was mapped to the distal deletion bin of chromosome 1AS (FLM value 0.86) and wheat ESTs which were previously mapped to the same deletion bin were used to identify 18 closely related sequences in the syntenic region of rice chromosome 5. For a subset of wheat ESTs that detected flanking markers for tin, we identified closely related sequences within the most distal 300 kb of rice chromosome 5S. The synteny between the distal chromosome ends of wheat 1AS and rice 5S appeared to be disrupted at the hairy glume locus and seed storage protein loci. We compared map position of tin with other reduced tillering mutants characterised in other cereals to identify possible orthologous genes.

Breeding Opportunities for Increasing the Efficiency of Water Use and Crop Yield in Temperate Cereals.

Genetic advances in grain yield under rainfed conditions have been achieved by empirical breeding methods. Progress is slowed, however, by large genotype x season and genotype x location interactions arising from unpredictable rainfall, which is a feature of dry environments. A good understanding of factors limiting and/or regulating yield now provides us with an opportunity to identify and then select for physiological and morphological traits that increase the efficiency of water use and yield under rainfed conditions. The incorporation of these traits into breeders' populations should broaden their genetic base. It also may lead to faster selection methods and selection for the traits may result in correlated gains in yield. Here, we undertake a review of factors that limit yield in rainfed environments and discuss genetic opportunities and genetic progress in overcoming them. The examples given are for wheat (Triticum aestivum L.), but the principles apply to all cereal crops grown in dry environments.

Improving Intrinsic Water-Use Efficiency and Crop Yield.

Greater yield per unit rainfall is one of the most important challenges in dryland agriculture. Improving intrinsic water-use efficiency (W(T)), the ratio of CO(2) assimilation rate to transpiration rate at the stomata, may be one means of achieving this goal. Carbon isotope discrimination (Delta(13)C) is recognized as a reliable surrogate for W(T) and there have now been numerous studies which have examined the relationship between crop yield and W(T) (measured as Delta(13)C). These studies have shown the relationship between yield and W(T) to be highly variable. The impact on crop yield of genotypic variation in W(T) will depend on three factors: (i) the impact of variation in W(T) on crop growth rate, (ii) the impact of variation in W(T) on the rate of crop water use, and (iii) how growth and water use interact over the crop's duration to produce grain yield. The relative importance of these three factors will differ depending on the crop species being grown and the nature of the cropping environment. Here we consider these interactions using (i) the results of field trials with bread wheat (Triticum aestivum L.), durum wheat (T. turgidum L.), and barley (Hordeum vulgare L.) that have examined the association between yield and Delta(13)C and (ii) computer simulations with the SIMTAG wheat crop growth model. We present details of progress in breeding to improve W(T) and yield of wheat for Australian environments where crop growth is strongly dependent on subsoil moisture stored from out-of-season rains and assess other opportunities to improve crop yield using W(T).

Selectable traits to increase crop photosynthesis and yield of grain crops.

The grain yield of cereals has almost doubled this century as a result of genetic manipulation by plant breeding. Surprisingly, there has been no change in the rate of photosynthesis per unit leaf area to accompany these increases. However, total photosynthesis has increased as a result of an increase in leaf area, daily duration of photosynthesis or leaf area duration. There remain substantial opportunities to continue to improve total photosynthesis and crop yield genetically using conventional breeding practices. Selectable traits are discussed here in the context of increasing total above-ground biomass under favourable conditions. Opportunities exist to alter crop duration and the timing of crop development to match it better to radiation, temperature and vapour pressure during crop growth, and to increase the rate of development of early leaf area to achieve rapid canopy closure. The importance of these traits will depend on the environment in which the crop is grown. Increases in crop photosynthesis through breeding are also likely to come via indirect means. Selection for a high and sustained stomatal conductance during the period of stem elongation is one way. Increasing assimilate allocation to the reproductive primordia so as to establish a large potential sink should also indirectly increase total crop photosynthesis. Evidence in the major grain crops suggests that by anthesis the capacity for photosynthesis is high and that photosynthesis is not limiting during grain filling. To use this surplus capacity it is suggested that carbon and nitrogen partitioning to the reproductive meristem be increased so as to establish a high potential grain number and the potential for a large grain size. It is then expected that additional photosynthesis will follow, either by a longer daily duration of photosynthesis or by an extended leaf area duration.