Abiotic stress and control of grain number in cereals

Grain number is the only yield component that is directly associated with increased grain yield in important cereal crops like wheat. Historical yield studies show that increases in grain yield are always accompanied by an increase in grain number. Adverse weather conditions can cause severe fluctuations in grain yield and substantial yield losses in cereal crops. The problem is global and despite its impact on world food production breeding and selection approaches have only met with limited success. A specific period during early reproductive development, the young microspore stage of pollen development, is extremely vulnerable to abiotic stress in self-fertilising cereals (wheat, rice, barley, sorghum). A better understanding of the physiological and molecular processes that lead to stress-induced pollen abortion may provide us with the key to finding solutions for maintaining grain number under abiotic stress conditions. Due to the complexity of the problem, stress-proofing our main cereal crops will be a challenging task and will require joint input from different research disciplines.     

Molecular Improvement of Tropical Maize for Drought Stress Tolerance in Sub-Saharan Africa

The C4 grass Zea mays (maize or corn) is the third most important food crop globally after wheat and rice in terms of production and the second most widespread genetically modified (GM) crop, after soybean. Its demand is predicted to increase by 45% by the year 2020. In sub-Saharan Africa, tropical maize has traditionally been the main staple of the diet, 95% of the maize grown is consumed directly as human food and as an important source of income for the resource—poor rural population. However, its growth, development and production are greatly affected by environmental stresses such as drought and salinization. In this respect, food security in tropical sub-Saharan Africa is increasingly dependent on continuous improvement of tropical maize through conventional breeding involving improved germplasm, greater input of fertilizers, irrigation, and production of two or more crops per year on the same piece of land. Integration of advances in biotechnology, genomic research, and molecular marker applications with conventional plant breeding practices opens tremendous avenues for genetic modifications and fundamental research in tropical maize. The ability to transfer genes into this agronomically important crop might enable improvement of the species with respect to enhanced characteristics, such as enriched nutritional quality, high yield, resistance to herbicides, diseases, viruses, and insects, and tolerance to drought, salt, and flooding. These improvements in tropical maize will ultimately enhance global food production and human health. Molecular approaches to modulate drought stress tolerance are discussed for sub-Saharan Africa, but widely applicable to other tropical genotypes in Central and Latin America. This review highlights abiotic constraints that affect growth, development and production of tropical maize and subsequently focuses on the mechanisms that regulate drought stress tolerance in maize. Biotechnological approaches to manage abiotic stress tolerance in maize will be discussed. The current status of tropical maize transformation using Agrobacterium as a vehicle for DNA transfer is emphasized. This review also addresses the present status of genetically modified organisms (GMOs) regulation in sub-Saharan Africa.     

Closing the global ozone yield gap: Quantification and cobenefits for multistress tolerance

Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean > wheat > maize > rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010–2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the “ozone yield gaps”), adding up to 227 Tg of lost yield. Our modelling shows that the highest ozone‐induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution‐focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap.     

耐非生物胁迫转基因水稻的培育——现在和未来

环境胁迫严重降低了作物产量,日益减少的耕地和膨胀的人口对世界粮食安全造成了威胁。长期以来,改善作物的抗逆性一直是农业生产的主要目标。水稻是重要的粮食作物之一,培育具有抗逆性的水稻品种对全球的粮食生产将产生重要影响。在改善水稻的抗逆性方面,转基因比传统方法更有发展潜力。近年来,已有许多抗逆相关基因转入水稻并获得了一些提高抗逆性的转基因植株,文章重点讨论了耐非生物胁迫转基因水稻的研究进展。     

Improving Salinity Tolerance in Cereals

Cereals are grown in almost every region of the world and are exposed to a variety of environmental stresses that severely affect their growth and grain yield. Of various abiotic stresses, salinity is one of the more significant threats to cereal crops. To ensure food security, there is a need to adopt strategies to overcome this specific threat. Undoubtedly, plant scientists have been exploiting a variety of approaches to achieve enhanced crop productivity on salt affected soils. Of the various biotic approaches, conventional breeding, marker-assisted selection and genetic engineering to develop salt-tolerant lines/cultivars of cereals all seem plausible. Some success stories have been reported for improvement in salt tolerance of wheat and rice, but are scarce for other cereals. A number of barriers to the development of salt-tolerant cultivars/lines have been identified and include a lack of knowledge about the genetics of crops, their physiological and biochemical behavior, wide variation in environmental conditions, and the complex polygenic nature of the salt tolerance character. This review focuses on how improvements have been made in salt tolerance in cereals through different biotic means, such as conventional breeding, marker assisted selection and genetic engineering.     

Advances in Transgenic Rice Biotechnology

Rice is the most amenable crop plant for genetic manipulation amongst monocots due to its small genome size, enriched genetic map, availability of entire genome sequence, and relative ease of transformation. Improvement in agronomic traits of rice is bound to affect a sizeable population since it is a primary source of sustenance. Recent advances like use of ‘clean gene’ technology or matrix attachment regions would help improve rice transformation. Function of several novel genes and their promoters has been analyzed in transgenic rice. Significant progress has been made in introducing traits like herbicide, biotic stress and abiotic stress tolerance. Attempts also have been made to enhance nutritional characteristics of the grain and yield. Identification of genes controlling growth and development can be used to modify plant architecture and heading period. Transgenic rice can serve as a biofactory for the production of molecules of pharmaceutical and industrial utility. The drive to apply transgenic rice for public good as well as commercial gains has fueled research to an all time high. Successful field trials and biosafety of transgenic rice have been reported. This would act as a catalyst for greater acceptance of genetically modified food crops. The lessons learnt from rice can be extended to other cereals thereby opening new opportunities and possibilities.     

Diversifying crops for food and nutrition security – a case of teff

There are more than 50000 known edible plants in the world, yet two‐thirds of global plant‐derived food is provided by only three major cereals – maize (Zea mays), wheat (Triticum aestivum) and rice (Oryza sativa). The dominance of this triad, now considered truly global food commodities, has led to a decline in the number of crop species contributing to global food supplies. Our dependence on only a few crop species limits our capability to deal with challenges posed by the adverse effects of climate change and the consequences of dietary imbalance. Emerging evidence suggests that climate change will cause shifts in crop production and yield loss due to more unpredictable and hostile weather patterns. One solution to this problem is through the wider use of underutilised (also called orphan or minor) crops to diversify agricultural systems and food sources. In addition to being highly nutritious, underutilised crops are resilient in natural and agricultural conditions, making them a suitable surrogate to the major crops. One such crop is teff [Eragrostis tef (Zucc.) Trotter], a warm‐season annual cereal with the tiniest grain in the world. Native to Ethiopia and often the sustenance for local small farmers, teff thrives in both moisture‐stressed and waterlogged soil conditions, making it a dependable staple within and beyond its current centre of origin. Today, teff is deemed a healthy wheat alternative in the West and is sought‐after by health aficionados and those with coeliac disease or gluten sensitivity. The blooming market for healthy food is breathing new life into this underutilised crop, which has received relatively limited attention from mainstream research perhaps due to its ‘orphan crop’ status. This review presents the past, present and future of an ancient grain with a potential beyond its size.     

Enhancing blast disease resistance by overexpression of the calcium‐dependent protein kinase OsCPK4 in rice

Rice is the most important staple food for more than half of the human population, and blast disease is the most serious disease affecting global rice production. In this work, the isoform OsCPK4 of the rice calcium‐dependent protein kinase family is reported as a regulator of rice immunity to blast fungal infection. It shows that overexpression of OsCPK4 gene in rice plants enhances resistance to blast disease by preventing fungal penetration. The constitutive accumulation of OsCPK4 protein prepares rice plants for a rapid and potentiated defence response, including the production of reactive oxygen species, callose deposition and defence gene expression. OsCPK4 overexpression leads also to constitutive increased content of the glycosylated salicylic acid hormone in leaves without compromising rice yield. Given that OsCPK4 overexpression was known to confer also salt and drought tolerance in rice, the results reported in this article demonstrate that OsCPK4 acts as a convergence component that positively modulates both biotic and abiotic signalling pathways. Altogether, our findings indicate that OsCPK4 is a potential molecular target to improve not only abiotic stress tolerance, but also blast disease resistance of rice crops.     

施加外源物质对盐胁迫下水稻生长发育的影响

水稻是重要的粮食作物之一,属于不耐盐的甜土植物,土壤盐渍化是影响其产量和生长发育的主要因素。消除或缓解盐胁迫是当务之急,目前主要应用传统育种、转基因技术及外源物质缓解盐胁迫。拟从外源物质对盐胁迫下水稻的影响作一综述,旨在为水稻生产及抗性育种提供理论依据和实践方法。     

Genetic Engineering of Energy Crops: A Strategy for Biofuel Production in China Free Access

Biomass utilization is increasingly considered as a practical way for sustainable energy supply and long‐term environment care around the world. In concerns with food security in China, starch or sugar‐based bioethanol and edible‐oil‐derived biodiesel are harshly restricted for large scale production. However, conversion of lignocellulosic residues from food crops is a potential alternative. Because of its recalcitrance, current biomass process is unacceptably expensive, but genetic breeding of energy crops is a promising solution. To meet the need, energy crops are defined with a high yield for both food and biofuel purposes. In this review, main grasses (rice, wheat, maize, sorghum and miscanthus) are evaluated for high biomass production, the principles are discussed on modification of plant cell walls that lead to efficient biomass degradation and conversion, and the related biotechnologies are proposed in terms of energy crop selection.     

Cross-genome map based dissection of a nitrogen use efficiency ortho-metaQTL in bread wheat unravels concerted cereal genome evolution

Monitoring nitrogen use efficiency (NUE) in plants is becoming essential to maintain yield while reducing fertilizer usage. Optimized NUE application in major crops is essential for long-term sustainability of agriculture production. Here, we report the precise identification of 11 major chromosomal regions controlling NUE in wheat that co-localise with key developmental genes such as Ppd (photoperiod sensitivity), Vrn (vernalization requirement), Rht (reduced height) and can be considered as robust markers from a molecular breeding perspective. Physical mapping, sequencing, annotation and candidate gene validation of an NUE metaQTL on wheat chromosome 3B allowed us to propose that a glutamate synthase (GoGAT) gene that is conserved structurally and functionally at orthologous positions in rice, sorghum and maize genomes may contribute to NUE in wheat and other cereals. We propose an evolutionary model for the NUE locus in cereals from a common ancestral region, involving species specific shuffling events such as gene deletion, inversion, transposition and the invasion of repetitive elements.     

Sequence similarity based identification of abiotic stress responsive genes in chickpea

Chickpea (Cicer arietinum L.) is an important food legume crop, particularly for the arid regions including Indian subcontinent. Considering the detrimental effect of drought, temperature and salt stress on crop yield, efforts have been initiated in the direction of developing improved varieties and designing alternate strategies to sustain chickpea production in adverse environmental conditions. Identification of genes that confer abiotic stress tolerance in plants remains a challenge in contemporary plant breeding. The present study focused on the identification of abiotic stress responsive genes in chickpea based on sequence similarity approach exploiting known abiotic stress responsive genes from model crops or other plant species. Ten abiotic stress responsive genes identified in other plants were partially amplified from eight chickpea genotypes and their presence in chickpea was confirmed after sequencing the PCR products. These genes have been functionally validated and reported to play significant role in stress response in model plants like Arabidopsis, rice and other legume crops. Chickpea EST sequences available at NCBI EST database were used for the identification of abiotic stress responsive genes. A total of 8,536 unique coding long sequences were used for identification of chickpea homologues of these abiotic stress responsive genes by sequence similarity search (BLASTN and BLASTX). These genes can be further explored towards achieving the goal of developing superior chickpea varieties providing improved yields under stress conditions using modern molecular breeding approaches.     

Eco-physiological and Biochemical Responses of Rapeseed (Brassica napus L.) to Abiotic Stresses: Consequences and Mitigation Strategies

Rapeseed yield parameters have been altered due to the increased exposure to abiotic stresses. The changing climatic conditions have reduced biomass production and seed yield, which ultimately affect the success of rapeseed crops. The severity and ability of abiotic stresses to act in tandem are a growing concern for agriculture producers across the globe. Rapeseed is one of the most vital cultivars in the world, serving as a major player in edible oil production. Abiotic stress conditions impose various effects on plant metabolism associated with growth stages, soil water storage capacity and plant physiological aspects. Modern agriculture aims to increased plant productivity to ensure global food security for the future. This can be achieved using quality seed, appropriate agricultural practices, measuring pest reduction techniques and understanding crop production challenges. Important tools, including conventional breeding and biotechnological approaches, can be employed to develop abiotic stress tolerance rapeseed. This review highlights the physiological and biochemical responses of rapeseed to abiotic stresses. The review also addresses conventional and modern stress mitigation strategies for the development of climate-smart rapeseed.

     

Is Yield Increase Sufficient to Achieve Food Security in China?

Increasing demand for food, driven by unprecedented population growth and increasing consumption, will keep challenging food security in China. Although cereal yields have substantially improved during the last three decades, whether it will keep thriving to meet the increasing demand is not known yet. Thus, an integrated analysis on the trends of crop yield and cultivated area is essential to better understand current state of food security in China, especially on county scale. So far, yield stagnation has extensively dominated the main cereal-growing areas across China. Rice yield is facing the most severe stagnation that 53.9% counties tracked in the study have stagnated significantly, followed by maize (42.4%) and wheat (41.9%). As another important element for production sustainability, but often neglected is the planted area patterns. It has been further demonstrated that the loss in productive arable land for rice and wheat have dramatically increased the pressure on achieving food security. Not only a great deal of the planted areas have stagnated since 1980, but also collapsed. 48.4% and 54.4% of rice- and wheat-growing counties have lost their cropland areas to varying degrees. Besides, 27.6% and 35.8% of them have retrograded below the level of the 1980s. The combined influence (both loss in yield and area) has determined the crop sustainable production in China to be pessimistic for rice and wheat, and consequently no surprise to find that more than half of counties rank a lower level of production sustainability. Therefore, given the potential yield increase in wheat and maize, as well as substantial area loss of rice and wheat, the possible targeted adaptation measures for both yield and cropping area is required at county scale. Moreover, policies on food trade, alongside advocation of low calorie diets, reducing food loss and waste can help to enhance food security.     

Water stress resilient cereal crops: Lessons from wild relatives

Cereal crops are significant contributors to global diets. As climate change disrupts weather patterns and wreaks havoc on crops, the need for generating stress-resilient, high-yielding varieties is more urgent than ever. One extremely promising avenue in this regard is to exploit the tremendous genetic diversity expressed by the wild ancestors of current day crop species. These crop wild relatives thrive in a range of environments and accordingly often harbor an array of traits that allow them to do so. The identification and introgression of these traits into our staple cereal crops can lessen yield losses in stressful environments. In the last decades, a surge in extreme drought and flooding events have severely impacted cereal crop production. Climate models predict a persistence of this trend, thus reinforcing the need for research on water stress resilience. Here we review: (i) how water stress (drought and flooding) impacts crop performance; and (ii) how identification of tolerance traits and mechanisms from wild relatives of the main cereal crops, that is, rice, maize, wheat, and barley, can lead to improved survival and sustained yields in these crops under water stress conditions.     

Global food insecurity. treatment of major food crops with elevated carbon dioxide or ozone under large-scale fully open-air conditions suggests recent models may have overestimated future yields

Predictions of yield for the globe's major grain and legume arable crops suggest that, with a moderate temperature increase, production may increase in the temperate zone, but decline in the tropics. In total, global food supply may show little change. This security comes from inclusion of the direct effect of rising carbon dioxide (CO2) concentration, [CO2], which significantly stimulates yield by decreasing photorespiration in C3 crops and transpiration in all crops. Evidence for a large response to [CO2] is largely based on studies made within chambers at small scales, which would be considered unacceptable for standard agronomic trials of new cultivars or agrochemicals. Yet, predictions of the globe's future food security are based on such inadequate information. Free-Air Concentration Enrichment (FACE) technology now allows investigation of the effects of rising [CO2] and ozone on field crops under fully open-air conditions at an agronomic scale. Experiments with rice, wheat, maize and soybean show smaller increases in yield than anticipated from studies in chambers. Experiments with increased ozone show large yield losses (20%), which are not accounted for in projections of global food security. These findings suggest that current projections of global food security are overoptimistic. The fertilization effect of CO2 is less than that used in many models, while rising ozone will cause large yield losses in the Northern Hemisphere. Unfortunately, FACE studies have been limited in geographical extent and interactive effects of CO2, ozone and temperature have yet to be studied. Without more extensive study of the effects of these changes at an agronomic scale in the open air, our ever-more sophisticated models will continue to have feet of clay.     

Characterization of haplotypes and single nucleotide polymorphisms associated with Gn1a for high grain number formation in rice plant

Rice serves as one of the essential staple food for half of the global human population. However, due to rapid human population growth, there is an increase in food demand across the globe. Thus, to lessen the gap between food demand and supply, there is an urgent requirement for grain yield enhancement in various important cereals crops, including rice. In the present study, the authors attempted to characterize haplotypes and single nucleotide polymorphisms associated with Gn1a for high grain number formation in rice plants. Result obtained reveals that high grain number gene sequences are under balancing selection and four high grain number specific missense SNPs decreases the stability of Gn1a. Earlier studies have also suggested that decreases Gn1a expression causes cytokinin accretion in inflorescence meristems, which in turn led to increase in grain yield. Hence, these four SNPs may be utilized for increasing grain yield in rice plants.     

Identification and characterization of wheat long non-protein coding RNAs responsive to powdery mildew infection and heat stress by using microarray analysis and SBS sequencing

Background  

Biotic and abiotic stresses, such as powdery mildew infection and high temperature, are important limiting factors for yield and grain quality in wheat production. Emerging evidences suggest that long non-protein coding RNAs (npcRNAs) are developmentally regulated and play roles in development and stress responses of plants. However, identification of long npcRNAs is limited to a few plant species, such as Arabidopsis, rice and maize, no systematic identification of long npcRNAs and their responses to abiotic and biotic stresses is reported in wheat.     

Genetic transformation of wheat: progress during the 1990s into the Millennium

Wheat transformation technology has progressed rapidly during the past decade. Initially, procedures developed for protoplast isolation and culture, electroporation- and polyethylene glycol (PEG)-induced DNA transfer enabled foreign genes to be introduced into wheat cells. The development of biolistic (microprojectile) bombardment procedures led to a more efficient approach for direct gene transfer. More recently, Agrobacterium-mediated gene delivery procedures, initially developed for the transformation of rice, have also been used to generate transgenic wheat plants. This review summarises the considerable progress in wheat transformation achieved during the last decade. An increase in food production is essential in order to sustain the increasing world population. This could be achieved by the development of higher yielding varieties with improved nutritional quality and tolerance to biotic and abiotic stresses. Although conventional breeding will continue to play a major role in increasing crop yield, laboratory-based techniques, such as genetic transformation to introduce novel genes into crop plants, will be essential in complementing existing breeding technologies. A decade ago, cereals were considered recalcitrant to transformation. Since then, a significant research effort has been focused on cereals because of their agronomic status, leading to improved genetic transformation procedures (Bommineni and Jauhar 1997). Initially, the genetic transformation of cereals relied on the introduction of DNA into protoplasts and the subsequent production of callus from which fertile plants were regenerated. More recently, major advances have been accomplished in the regeneration of fertile plants from a range of source tissues, providing an essential foundation for the generation of transgenic plants. This review summarises procedures, vectors and target tissues used for transformation, high-lights the limitations of current approaches and discusses future trends. The citation of references is limited, where possible, to the most relevant or recent reports.     

China's success in increasing per capita food production

China has to feed 20% of the global population with only about 5% of the planet's water resources and 7% of its arable land. With such limited natural conditions, however, China's grain production has increased from about 200 kg per capita in 1949 to about 400 kg in the early 1990s. Hunger as a social problem has largely disappeared after being prevalent in China for several thousand years with the rise and decline of dynasties. This achievement has been accompanied by a 2.5-fold increase in the population and a 4.5-fold increase in total grain production. Although total cropped land has increased slightly in some areas, land used for cropping has decreased from 0.18 hectare per capita in the 1950s to less than 0.1 hectare per capita today. Apparently, yield increase or improved land productivity is the major contributor to the increase of food production per capita. What are the major reasons for the unprecedented achievement in China's food production? Political decisions, good or bad, on land distribution and ownership changes, have caused unusual fluctuation in grain production. Technical progress, however, has maintained a long-term increasing trend. The semi-dwarf cultivars of rice and wheat, the use of heterosis in rice and maize, and the alleviation of salinized soil stress in the major grain-producing areas have all played significant roles in increasing China's food production capability.