Enhancing the mineral and vitamin content of wheat and maize through plant breeding

More than half of the world's population suffers micronutrient undernourishment. The main sources of vitamins and minerals (iron, zinc, and vitamin A) for low-income rural and urban populations are staple foods of plant origin that often contain low levels or low bioavailability of these micronutrients. Biofortification aims to develop micronutrient-enhanced crop varieties through conventional plant breeding. HarvestPlus, the CGIAR's biofortification initiative, seeks to breed and disseminate crop varieties with enhanced micronutrient content that can improve the nutrition of the “hard to reach” (by fortification or supplementation programmes) rural and urban poor in targeted countries/regions. In attempting to enhance micronutrient levels in maize and wheat through conventional plant breeding, it is important to identify genetic resources with high levels of the targeted micronutrients, to consider the heritability of the targeted traits, to explore the availability of high throughput screening tools and to gain a better understanding of genotype by environment interactions. Biofortified maize and wheat varieties must have the trait combinations which encourage adoption such as high yield potential, disease resistance, and consumer acceptability. When defining breeding strategies and targeting micronutrient levels, researchers need to consider the desired micronutrient increases, food intake and retention and bioavailability as they relate to food processing, anti-nutritional factors and promoters. Finally, ex ante studies are required to quantify the burden of micronutrient deficiency and the potential of biofortification to achieve a significant improvement in human micronutrient status in the deficient target population in order to determine whether a biofortification program is cost-effective.     

小麦籽粒微量元素含量的研究进展

以禾谷类作物为主食引起的人体摄取必需微量元素(特别是Fe和Zn)不足,已对现代社会和谐发展造成沉重的经济负担和安全隐患。小麦(Triticum aestivumL.)是中国和全球大多数人主要的食物和矿质元素来源。小麦籽粒中Zn、Fe含量普遍较低,已引起国内外学者们的高度关注。本文综述了小麦籽粒微量元素含量器官间、基因型间的差异及其影响因素和相关性状研究进展,介绍了小麦籽粒吸收和富集微量元素的生理与遗传基础,展望了提高小麦籽粒微量元素的研究内容和方向。     

Biofortification strategies to increase grain zinc and iron concentrations in wheat

Micronutrient deficiencies, especially those arising from zinc (Zn) and iron (Fe), pose serious human health problems for more than 2 billion people worldwide. Wheat is a major source of dietary energy and protein for the world's growing population, and its potential to assist in reducing micronutrient-related malnutrition can be enhanced via integration of agronomic fertilization practices and delivery of genetically-manipulated, micronutrient rich wheat varieties. Targeted breeding for these biofortified varieties was initiated by exploiting available genetic diversity for Zn and Fe from wild relatives of cultivated wheat and synthetic hexaploid progenitors. The proof-of-concept results from the performance of competitive biofortified wheat lines showed good adaptation in target environments without compromising essential core agronomic traits. Agronomic biofortification through fertilizer approaches could complement the existing breeding approach; for instance, foliar application of Zn fertilizer can increase grain Zn above the breeding target set by nutritionists. This review synthesizes the progress made in genetic and agronomic biofortification strategies for Zn and Fe enrichment of wheat.     

Management of Soil Micronutrient Deficiencies in the Rice-Wheat Cropping System

Summary

Within the last three decades, the rice-wheat cropping system has triggered, and with time, aggravated soil micronutrient deficiencies in the Indo-Gangetic Plains (IGP). This has largely been due to the shift from an earlier rice and wheat monoculture with low yielding, long duration indigenous varieties, to an intensive rice-wheat rotation cropping system with short duration modern high yielding varieties on the same piece of land. The problems related to micronutrient deficiency in the IGP are more due to the size of its available pools in the soil rather than its total contents and are greatly influenced by crop management, or rather its mismanagement. Deficiency of zinc is widespread in the IGP, but with the extensive use of zinc sulfate, zinc deficiency has reduced in some areas of the region. Meanwhile, the deficiency of Fe, Mn and B has increased in the IGP. Deficiency of Cu and Mo is location specific and can limit rice and wheat yields. The adoption and spread of the rice-wheat system in permeable coarse textured soils, particularly in the western IGP, not only caused iron deficiency in rice but also resulted in the emergence of manganese deficiency in wheat. In highly calcareous and acidic soils, boron is the next limiting micronutrient in crop production after zinc. Bumper rice and wheat harvests in the past decade, the declining use of organic manures in the region and except for the widespread use of zinc sulfate, a general lack of awareness amongst farmers on micronutrient deficiency problems has contributed to micronutrients limiting rice and wheat yields in the IGP. Approaches to alleviating micronutrient deficiencies include matching the crop removals of the micronutrients with its replenishments through their respective external carriers, supplementation through organic sources and mobilization/utilization through cultivation of micronutrient efficient crop cultivars. Identification of efficient micronutrient carriers and finding the optimum rate, mode and time of its application is important in ameliorating the micronutrient deficiencies. This article reviews the extent of micronutrient deficiency and discusses various management options available to reduce micronutrient deficiency induced crop yield reduction for rice and wheat in the Indo-Gangetic Plains.     

绿肥翻压对土壤微量元素含量及玉米吸收的影响

选取9个春油菜绿肥品种进行田间试验,连续翻压两年后,测定土壤和玉米子粒中的微量元素含量,研究比较不同春油菜绿肥品种翻压对土壤微量元素含量及玉米吸收情况的影响。结果表明,中油肥1804翻压后土壤全量铁、锰和锌含量较春闲田CK处理分别提高了9.31%、5.71%、9.97%,土壤有效态铁、锰、锌含量较春闲田CK处理分别提高37.31%、62.35%、73.99%;中油肥1907翻压后土壤全铜含量较春闲田CK处理显著提高了84.29%;中油肥1901翻压后较春闲田CK处理显著提高了玉米子粒铁、锰、锌的吸收量及玉米产量和品质。不同春油菜绿肥品种翻压后土壤有效态铜含量、玉米子粒铜及锰含量与春闲田CK处理之间差异不显著;土壤有效态微量元素含量与春油菜中微量元素和土壤全量微量元素含量之间存在线性关系,且微量元素与玉米叶片叶绿素、含氮量、产量、可溶性糖、蛋白质呈显著或极显著正相关。华北地区种植并翻压中油肥1804、中油肥1901、中油肥1907能较好地提高土壤微量元素含量、生物有效性及玉米产量和品质。     

Trace element bioavailability as exemplified by iron and zinc

Plant foods can be improved as sources of essential micronutrients either by increasing the concentrations of nutrients in the food, increasing the bioavailability of micronutrients in the food, or both of these. Quantities of minerals in edible portions of crops are influenced by numerous complex, dynamic and interacting factors, including plant genotype, soil properties, environmental conditions and nutrient interactions. Similarly, numerous dietary and host factors interact to affect the bioavailability to animals and people of mineral nutrients in plant foods. Micronutrient bioavailability apparently can be improved by either increasing the quantity of substances within plant foods that enhance the absorption and utilization of micronutrients or by decreasing the quantity of dietary antinutrients that inhibit micronutrient absorption; however, processes that control and regulate the bioavailability of trace elements in plant foods consumed in mixed diets are not fully understood. Use of either stable or radioactive isotopes incorporated intrinsically into edible portions of plant foods during plant growth will likely provide the most reliable estimates of the bioavailability of micronutrients consumed in mixed diets. Increasing the dietary supply of staple plant foods rich in trace elements combined with increased knowledge of micronutrient bioavailability from these foods will meaningfully improve the nutritional health and well being of people.     

Micronutrient bioavailability techniques: Accuracy,problems and limitations

Within the scientific agricultural community it is widely known that the total micronutrient content of soils is not a useful measure of the amount of `available' micronutrients to plants. Thus, soil tests have been developed to determine the amounts of micronutrients in soils available to plants for growth. This same concept applies to plant foods eaten by humans because not all of the micronutrients in plant foods are available (i.e. bioavailable) for absorption and or utilization. Antinutrients and promoter substances within plant foods that can either inhibit or enhance the absorption and/or utilization of micronutrients when eaten. As a result, numerous techniques have been developed to determine the amounts of bioavailable micronutrients present in plant foods when consumed in mixed diets with other dietary constituents that can interact and affect the micronutrient bioavailability. Unfortunately, micronutrient bioavailability to humans fed mixed diets is still a confusing and complex issue for the human nutrition community. Our understanding of the processes that control micronutrient bioavailability from mixed diets containing plant foods is relatively limited and still evolving. It remains the subject of extensive research in many human nutrition laboratories globally. This article reviews some of the numerous methodologies that have arisen to account for the bioavailability of micronutrients in plant foods when eaten by humans.     

Influence of Cooking Conditions on Carotenoid Content and Stability in Porridges Prepared from High-Carotenoid Maize

Maize is a staple food crop in many developing countries, hence becoming an attractive target for biofortification programs toward populations at risk of micronutrient deficiencies. A South African white endosperm maize inbred line was engineered with a carotenogenic mini-pathway to generate high-carotenoid maize, which accumulates β-carotene, lutein and zeaxanthin. As maize porridge is a traditional meal for poor populations in sub-Saharan African countries, high-carotenoid maize was used as raw material to prepare different maize meals. The objective of this work was to assess the impact of popular home-cooking techniques and different cooking parameters (temperature, time and pH) on the final carotenoid content in the cooked product, using a spectrophotometric technique based on the mean absorption of carotenoids at 450 nm. Carotenoid levels were not only preserved, but also enhanced in high-carotenoid maize porridges. The carotenoid content was increased when temperatures ≤95 °C were combined with short cooking times (10–60 min). The most optimum thermal treatment was 75 °C/10 min. When treated under those conditions at pH 5, high-carotenoid maize porridges doubled the initial carotenoid content up to 88 μg/g dry weight. Regarding to cooking techniques, the highest carotenoid content was found when unfermented thin porridges were prepared (51 μg/g dry weight of high-carotenoid maize porridge). We conclude that high-carotenoid maize may contribute to enhance the dietary status of rural populations who depend on maize as a staple food.     

Economics of enhanced micronutrient density in food staples

The combining of benefits for human nutrition and agricultural productivity, resulting from breeding staple food crops which are more efficient in the micronutrient metal uptake from the soil, and which accumulate more micronutrients into their seeds, results in extremely high ex ante estimates of benefit/costs ratios for investments in agricultural research in this area. This finding derives from the confluence of several complementary factors:

• •Rates of micronutrient malnutrition are high in developing countries, as are the consequent costs to human welfare and economic productivity.
• •Because staple foods are eaten in large quantities every day by the malnourished poor, delivery of enriched staple foods (fortified by the plants themselves during growth) can rely on existing consumer behavior.
• •A significant percentage of the soils in which these staple foods are grown are `deficient' in these micronutrient metals, which has kept crop yields low. In general, these soils in fact contain relatively high total amounts of micronutrient metals. However, because of binding to soil constituents, these nutrients have poor soil availability to staple crop varieties that are currently available to farmers.
• •Adoption and spread of nutritionally-improved varieties by farmers can rely on profit incentives, either because of agronomic advantages on trace mineral-deficient soils or incorporation of nutritional improvements in the most productive varieties being released by agricultural research stations.
• •Benefits to relatively small investments in agricultural research may be disseminated widely, potentially accruing to hundreds of millions of people and millions of hectares of cropland.
• •Benefits from breeding advances, derived from initial, fixed costs, typically do not involve high recurring costs, and thus tend to be highly sustainable as long as an effective domestic agricultural research infrastructure is maintained.

     

Germplasm Enhancement and Breeding Strategies for Crop Quality in Japan

Abstract

Rice is the staple food for most Asians. Breeding efforts at the national and international levels have resulted in high-yielding varieties with resistance/tolerance to biotic and abiotic constraints. Consequently Asia has enjoyed rice self-sufficiency in recent years. Now in some countries over-production of rice has occurred, partly because of reduced rice consumption. For instance, in 1962 Japan had a per capita rice consumption of 118.3 kg and then this rapidly declined to about 60kg in 2003. Imbalances between production and consumption in rice and other crops have promoted a paradigm shift of breeding objectives oriented from producers to consumers. Germplasm enhancement (pre-breeding) and breeding strategies now focus on a broad range of crop and food qualities, which are closely associated with industrial and processing properties and human health and nutrition. In particular, physiological functions of chemical compounds involved in crop products are being studied as a part of breeding programs. Diverse plant genetic resources and advances in plant genome research have contributed to successful breeding strategies to improve and manage crop and food quality. Recent progress in germplasm enhancement and breeding strategies for quality improvement of rice, wheat, soybean and sweet potato in Japan is discussed.     

Genetic variation of bioavailable iron and zinc in grain of a maize population

More than one-third of the world's population is afflicted by iron (Fe) and zinc (Zn) deficiencies, since cereal grain as a staple food of the people contains low levels or low bioavailability of Fe and Zn because of phytate. In maize, 80% of grain phosphorus (P) is in the form of phytate, and P could be an indicator of phytate content. The objectives of this study were (1) to estimate genetic variation of Fe and Zn in a maize population including P/Fe and P/Zn molar ratios as quantitative traits; (2) to determine relations among yield, P, Fe, Zn, P/Fe and P/Zn molar ratios; and (3) to define the implications of those on biofortification (breeding) programmes. There were significant genetic variations and workable heritabilities for Fe, Zn, P/Fe and P/Zn estimated in 294 F4 lines of a maize population, but there were no associations among six traits according to both simple correlations and principal component analysis. Weak correlations between P and Fe and between P and Zn indicated feasibility of breeding non low-phytic acid maize genotypes with more appropriate phytate/Fe and phytate/Zn relations. Bioavailability of iron and zinc varied substantially in a maize population justifying utilisation of these unique parameters in biofortification programmes.     

碳氮供给对小麦离体穗培养粒重、微量元素及蛋白质含量的影响

为了解碳氮供给与小麦粒重、Fe、Zn、Mn、Cu等微量元素以及蛋白质含量的关系,在离体穗培养条件下研究了灌浆初期和灌浆中期不同浓度C(蔗糖)、N(硝酸铵)供给对小麦粒重、微量元素(Fe、Zn、Mn、Cu)和蛋白质含量的影响.结果表明,随着培养基糖浓度的增大,粒重和Fe、Mn含量都表现为先升高后降低的趋势,在4%糖浓度时,均达到最高值;籽粒Zn、Cu和蛋白质含量表现为随糖浓度增大而持续降低.随着培养基N浓度的增加,粒重和Fe、Zn、Mn、Cu含量多表现为先升高后降低的趋势,且多在N浓度为0.07%时达到最高值,尤以灌浆中期开始的培养表现明显;籽粒蛋白质含量表现为随N浓度增大而持续增加.由此可见,外源C、N供给对粒重、微量元素和蛋白质含量有明显的调控效应.一定的糖供给可同时提高粒重和Fe、Mn含量,一定的N供给可同时提高粒重及微量元素和蛋白质含量.     

不同基因型小麦的氮吸收特征与农田归还率研究

为以控制农业面源污染为目标的高氮吸收小麦品种的选择与利用提供理论依据,研究了不同基因型小麦品种植株氮素吸收量及其在各部位的分布与归还特征。结果表明,不同基因型小麦品种植株氮吸收量存在不同程度的差异;32个小麦品种中7个品种属于高氮积累类型,平均氮吸收量为228.4kg·hm-2;小麦籽粒产量与植株氮吸收量呈显著正相关;小麦穗部氮吸收量最适于植株总吸氮量的估测,其估算方程为y=0.865x-1.843。秸秆不还田条件下,高吸氮量类型小麦品种收获后植株残体返回到农田的氮量为19.3kg·hm-2,占植株氮吸收量的9.4%;而在秸秆还田条件下,高吸氮量类型小麦品种植株残体返回到农田的氮量为46.1kkg·hm-2,占植株氮吸收量的20.9%。试验说明,高氮吸收小麦可以同时兼顾高产和农业生态环境保护;确定下茬作物的农田施氮量,除了考虑土壤地力和下茬作物养分需求因素外,还应该考虑还田作物含氮量。     

陕西玉米育种现状、问题与对策

分析了陕西玉米育种的现状和存在的问题。种质创新能力不足、育种技术、育种方法、抗逆性育种重视不够是目前品种的现实产量潜力不大、品种适应性和抗逆性不强的主要原因。提出了组织协同攻关、调整育种目标、提高适应性,加强种质扩增、改良和创新,强化和改进育种选择方式,重视基础理论研究、推进新技术应用,密切玉米育种和栽培的合作等对策。玉米育种思路以增强玉米品种适应农业资源(水分、土壤等)的约束和玉米高产优质为目标,以本土化的种质为基础,构建杂种优势群为核心,强化逆境人工选择、采用密植育种策略,探索"高配合力(杂种优势)＋株型(结构、生理)＋广适(生态)"的玉米生理生态育种技术。     

Causes for soil sickness affecting early plant growth in aerobic rice

In aerobic rice, adapted varieties are grown in non-flooded and non-saturated soil. In the Philippines, occasional poor crop growth and yield failures have been reported. To investigate the underlying causes, we conducted 3 pot experiments using the aerobic rice variety Apo and so-called “sick soil” from a field where aerobic rice failed in four successive dry seasons. The (experimental) aerobic rice crop replaced the farmer's practice of wet-season lowland rice and dry season sweet potato cropping. We hypothesized that abiotic factors, especially the inter-relationship between high soil pH and impaired micronutrient uptake, restrict plant growth, and that ammonium sulfate has an ameliorating effect. Experiment 1 used “sick soil” collected from around yellowing and dying plants in a field experiment with aerobic rice yield failure, and “healthy soil” collected from around well-growing plants in the same field. We used three N fertilizer treatments (ammonium sulfate, urea, no application) and two soil water conditions (well drained and water-logged). In experiment 2, the treatments were a combination of sick and healthy soil, N fertilizer, soil acidification, and foliar application of Fe. Experiment 3 compared the irrigation water used at the experimental field site with reverse-osmosis water. Irrigation with water from the field site increased soil pH, impaired plant growth, and induced chlorosis. The application of ammonium sulfate reduced soil pH to values below 6 and increased plant micronutrient (Fe, Mn and Zn) contents and plant growth. In early vegetative plant growth, the high soil pH appeared to be the key determinant of “sick soil”, while root knot nematodes were most likely secondary causes for poor plant growth.     

Variation in grain quality of pearl millet from Sahelian West Africa

Agricultural intensification through the application of mineral fertilizers, the recycling of crop residues and animal manures and through plant breeding are the only means to increase food supply in the poverty ridden West African Sahel, where pearl millet (Pennisetum glaucum (L.) R. Br.) is the dominant staple. Research on the effects of soil amendments on the quality of millet straw and grain is scarce, comparative studies of possible quality differences in traditional landraces versus improved varieties and hybrids are lacking. This paper reports results from 22 landrace populations, 22 improved varieties, six inbred×variety hybrids (IVHs, fertile inbred×open-pollinated varieties) and four topcross hybrids (TCHs, male-sterile line×open-pollinated varieties), whose grains were analyzed for protein concentration and amino acid composition, macro- and micronutrients (total and phytate P, K, Ca, Mg, Zn, Cu), metabolizable energy (ME), fat and β-carotene. At similar yield levels, landraces showed a 2.9 and 3.5% higher protein concentration compared with improved varieties and hybrids without a detrimental effect on protein quality as determined by the relative amount of lysine and threonine. Landrace populations also had the highest fat concentrations and the largest micronutrient densities. However, in-vitro digestibility and ME were (79.8% and 12.2 MJ kg⁻¹ respectively) larger for both groups of hybrids. The concentration of β-carotene was (0.13 μmol kg⁻¹) highest in the improved varieties, but appeared overall too low to significantly contribute to vitamin A nutrition in local diets. While the results of this genotype screening need to be verified in replicated multi-location trial studies, they underline the potential of including landraces in breeding programs to concurrently improve grain yield and grain quality in this area of the world.     

Mapping soil micronutrients

Soils vary widely in their micronutrient content and in their ability to supply micronutrients in quantities sufficient for optimal crop growth. Soils deficient in their ability to supply micronutrients to crops are alarmingly widespread across the globe, and this problem is aggravated by the fact that many modern cultivars of major crops are highly sensitive to low micronutrient levels. Original geologic substrate and subsequent geochemical and pedogenic regimes determine total levels of micronutrients in soils. Total levels are rarely indicative of plant availability, however, because availability depends on soil pH, organic matter content, adsorptive surfaces, and other physical, chemical, and biological conditions in the rhizosphere. Micronutrient availability to plants can be measured in direct uptake experiments, or estimated with techniques that correlate quantities of micronutrients extracted chemically from soils to plant uptake and response to micronutrient fertilization. Rational management of micronutrient fertility and toxicity requires an understanding of how total and plant-available soil micronutrients vary across the land. A variety of approaches have been used to survey and map the geographic distribution of soil micronutrient content and availability at scales ranging from global to sites within single production fields. Soil micronutrient maps covering large areas improve our understanding of the nature and extent of micronutrient problems, and aid in determining their relationships with climate, soil properties, and soil genetic characteristics determined at similar scales, for example, Soil Taxonomy to the order, sub-order, or great group levels. Intermediate scale maps can be useful in delineating specific areas where deficiencies or toxicities are likely for agriculture, and in determining localized soil characteristics that may be associated with such problems. Highly detailed maps of soil micronutrient content and availability in individual fields are being developed for site-specific precision agriculture. Soil micronutrient maps have fostered discovery of relationships between soil micronutrient content and availability and some human and livestock health problems such as goiter, Keshan and Kaschin–Beck diseases, and cancer. Advances including the global positioning system (GPS), geographic information systems (GIS), inductively coupled plasma (ICP) spectrometry, geostatistics, and precision agriculture facilitate soil micronutrient mapping and provide quantitative support for decision and policy making to improve agricultural approaches to balanced micronutrient nutrition.     

糯玉米育种概况及育种方法探讨

介绍了国内外糯玉米育种概况和常用的糯玉米育种方法,并对糯玉米育种方法进行了探讨。美国糯玉米育种和生产与糯玉米作为工业原料紧密联系在一起,品种大多属专用化深加工型;当前我国糯玉米主要用作鲜食,糯质资源丰富,但生产上应用的糯玉米品种血缘较为狭窄,符合鲜食要求的品种尚不多。探索鲜食糯玉米育种新方法,育成适口性佳、产量高、抗逆性强的鲜食糯玉米品种,是现今我国鲜食糯玉米育种的重要研究方向。     

Insights from in vitro exploration of factors influencing iron,zinc and provitamin A carotenoid bioaccessibility and intestinal absorption from cereals

Developments in genetics, agronomics and processing has positioned staple cereals as important sources of iron, zinc and provitamin A (pVA) carotenoids for nutritionally vulnerable populations. Significant effort has been placed on understanding the bioavailability of these micronutrients from cereal foods, including the exploration of underlying mechanisms by which their bioavailability can be modified. While micronutrient bioavailability is preferably assessed in clinical trials, relevant in vitro digestion and intestinal cell culture models have been applied to study effects of genetic, agronomic, post-harvest and food processing on micronutrient bioavailability. This review (1) critically assesses the application of in vitro models in the exploration of mechanisms associated with iron, zinc and provitamin A carotenoid bioaccessibility and intestinal absorption from cereal foods, and (2) identifies remaining gaps in order to frame future strategies to improve the nutritional impact of cereal foods.     

Reducing the incidence of allergy and intolerance to cereals

This paper reviews studies on allergy, intolerance and sensitivity to cereals, especially to wheat, barley, rye, maize, rice and oats with regard to reducing their incidences. Prevalence of allergy to cereals is generally low; prevalence of other cereal-related diseases are highest for wheat and lowest for oats. Compared to the other cereals, wheat (and its components wheat starch and vital gluten) are most abundantly applied in a broad range of food products world-wide, which justifies the major focus of this review on wheat. Current knowledge on diagnosis of the cereal-related diseases and on detection and characterization of the relevant proteins is discussed in the context of the development of prevention strategies. Aiming at their design and implementation, such strategies require building of knowledge frameworks at the primary, secondary and tertiary prevention levels. In this regard, selection and breeding of low-allergenic/low-intoleragenic crop varieties, application of processing and technological approaches, and the introduction of alternative safe cereal crops is discussed. Sustainable reduction of immune-related diseases in general (including cereal allergies and intolerances) is discussed with regard to eating habits and lifestyle factors, human genetic and physiological characteristics, and the role of the intestinal micro-flora.