Biotechnology approaches to overcome biotic and abiotic stress constraints in legumes

Summary Biotic and abiotic stresses cause significant yield losses in legumes and can significantly affect their productivity. Biotechnology tools such as marker-assisted breeding, tissue culture, in vitro mutagenesis and genetic transformation can contribute to solve or reduce some of these constraints. However, only limited success has been achieved so far. The emergence of “omic” technologies and the establishment of model legume plants such as Medicago truncatula and Lotus japonicus are promising strategies for understanding the molecular genetic basis of stress resistance, which is an important bottleneck for molecular breeding. Understanding the mechanisms that regulate the expression of stress-related genes is a fundamental issue in plant biology and will be necessary for the genetic improvement of legumes. In this review, we describe the current status of biotechnology approaches in relation to biotic and abiotic stresses in legumes and how these useful tools could be used to improve resistance to important constraints affecting legume crops.     

Integrated “omics” approaches to sustain global productivity of major grain legumes under heat stress

Grain legumes serve as key sources of dietary protein to the global human population. Consequence of high‐temperature (HT) stress is increasingly evident as drastically lost production of different crops including grain legumes worldwide, thus putting the global food security under great threat. In a changing climate scenario, cool season‐adapted grain legumes frequently encounter heat stress (HS) during their reproductive phase, thus witnessing serious yield losses. To combat the emerging challenges of HT stress, an integrated approach demanding collaborative efforts from various disciplines of plant science should be in place. This review summarizes major impacts of HT stress on grain legume, and captures the relevance of crop genetic resources to HS tolerance in these crops. Measurement of physiological traits assumes key place in view of ever‐increasing precision of next‐generation phenotyping assays. We also discuss the significance of genetic inheritance and QTL discovery and evolving “omics” science for developing HS tolerance grain legume crops.     

Screening techniques and sources of resistance to foliar diseases caused by major necrotrophic fungi in grain legumes

Summary Necrotrophic pathogens of the cool season food legumes (pea, lentil, chickpea, faba bean and lupin) cause wide spread disease and severe crop losses throughout the world. Environmental conditions play an important role in the development and spread of these diseases. Form of inoculum, inoculum concentration and physiological plant growth stage all affect the degree of infection and the amount of crop loss. Measures to control these diseases have relied on identification of resistant germplasm and development of resistant varieties through screening in the field and in controlled environments. Procedures for screening and scoring germplasm and breeding lines for resistance have lacked uniformity among the various programs worldwide. However, this review highlights the most consistent screening and scoring procedures that are simple to use and provide reliable results. Sources of resistance to the major necrotrophic fungi are summarized for each of the cool season food legumes. Marker-assisted selection is underway for Ascochyta blight of pea, lentil and chickpea, and Phomopsis blight of lupin. Other measures such as fungicidal control and cultural control are also reviewed. The emerging genomic information on the model legume, Medicago truncatula, which has various degrees of genetic synteny with the cool season food legumes, has promise for identification of closely linked markers for resistance genes and possibly for eventual map-based cloning of resistance genes. Durable resistance to the necrotrophic pathogens is a common goal of cool season food legume breeders.     

Genetic improvement of legumes using somatic cell and molecular techniques

Summary The merits and limitations of somatic cell techniques involving Agrobacterium-mediated transformation, direct gene transfer and protoplast fusion, are discussed in relation to the genetic improvement of forage and grain legumes. Whilst progress with legumes is limited compared to that with plants of other families such as the Solanaceae, the fact that many legumes are readily amenable to tissue culture now permits somatic cell techniques to be targetted to these species. Future development of the subject will necessitate close collaboration between molecular biologists and plant breeders to enable novel plants generated by in vitro technologies to be incorporated into conventional breeding programmes.     

The biotechnology of crop legumes

Summary The absence of variety-independent gene transfer methods for major agronomic species has, until now, limited the usefulness of recombinant DNA techniques to crop improvement programs. Until recently, only Solanaceous crops could be used to study fundamental and applied problems in plant sciences. During the past five years rapid advances in cell biology, in combination with the development of novel gene transfer methodology allowed utilization of the tools of plant molecular biology in conventional breeding programs. Cereal and leguminous species were considered to be recalcitrant to genetic manipulation. As a result of the development of direct DNA transfer methodology into organized tissue, we are now in a position to introduce any foreign gene into almost all of the major cereals and legumes. This can be achieved efficiently, often in a variety-independent fashion. The object of this review is to provide a comprehensive account of the state of the art in gene transfer for the cultivated leguminous crops. Important oilseed and feed species primarily in industrialized countries, as well as minor but equally important species for sustaining growth populations in developing countries will be examined. Advantages of the various gene transfer methods that were shown to be useful for specific crops, as well as limitations and problems associated with each crop and gene transfer method will be discussed. Data from field trials of transgenic legumes, where available, will be presented.     

夏播大豆生育期结构和农艺性状的遗传参数研究

试验从339个大豆品种中选取生育期小于100d的103个品种进行生育期结构特性与农艺性状之间的遗传参数分析。结果表明：1）单株荚数与单株粒数、生育前期呈极显著正相关,与R1呈显著正相关;单株粒数与R7呈显著正相关;百粒重与全生育期呈极显著正相关。2）遗传力＞60%的农艺性状分别为结荚高度、株高、主茎节数、R1、百粒重、生育前期、荚长、生育后期、全生育期。3）相对遗传进度的大小依次为主茎分枝数、有效分枝始节、结荚高度、株高、单株粒数。4）遗传变异系数＞25%的为主茎分枝数、有效分枝始节、结荚高度、单株粒数、株高、单株荚数。     

Resistance to insect pests: What do legumes have to offer?

Summary Insect pests are major problems for all crops, worldwide. In this review we will focus on legumes, which are attacked by a range of insect pests including pod/seed feeders, defoliators and sap feeders. We review the history of breeding for resistance to insect pests in legumes, which has had mixed success, and discuss further opportunities in this area. We also review the extraordinary array of direct and indirect mechanisms contributing to insect defence in legumes, the understanding and exploitation of which offer opportunities for both legume and non-legume crops. There is also good potential to improve insect resistance in legume crops through a detailed understanding of the signaling pathways that regulate induced responses to insect feeding, and recent progress in this area, primarily obtained from non-legume systems, is reviewed. The importance legumes play in farming systems, their wide range of novel chemistry and the emergence of model systems suitable for genomic approaches present opportunities for research in this area strongly linked to breeding programs to help develop legume crops with enhanced insect resistance. CSIRO’s right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

转录因子与植物抗逆性研究进展

近年来,转录因子在植物防卫反应和逆境胁迫应答过程中的应用越来越广泛。本文综述了与植物逆境抗性相关的5个转录因子家族: MYB类、bZIP类、WRKY类、AP2/EREBP类和NAC类的调控机制以及它们在植物抗逆基因工程的研究进展。     

Legume breeding for rust resistance: lessons to learn from the model <Emphasis Type="Italic">Medicago truncatula</Emphasis>

Rusts are major biotic constraints of legumes worldwide. Breeding for rust resistance is regarded as the most cost efficient method for rust control. However, in contrast to common bean for which complete monogenic resistance exists and is efficiently used, most of the rust resistance reactions described so far in cool season food legumes are incomplete and of complex inheritance. Incomplete resistance has been described in faba bean, pea, chickpea and lentil and several of their associated QTLs have been mapped. However, the relatively large distance between the QTLs and their associated molecular markers hampers their efficient use for marker assisted selection. Their large genome size drastically hampers the development of genomic resource and limits the saturation of their genetic maps. The use of model plants such as the model legume Medicago truncatula may circumvent this drawback. The important genetic and genomic resources and tools available for this model legume can considerably speed up the discovery and validation of new genes and QTLs in resistance to legume pathogens. Here, the potential of M. truncatula as a model to study rust resistance in legumes, and to transfer rust resistance genes to cool season grain legumes is reviewed.     

Research achievements in plant resistance to insect pests of cool season food legumes

Plant resistance to at least 17 field and storage insect pests of cool season food legumes has been identified. For the most part, this resistance was located in the primary gene pools of grain legumes via conventional laboratory, greenhouse, and field screening methods. The use of analytical techniques (i.e., capillary gas chromatography) to characterize plant chemicals that mediate the host selection behavior of pest insects offers promise as a new, more rapid way to differentiate between insect-resistant and susceptible plant material. Examples of research achievements in mechanisms of resistance and host-plant resistance within the context of integrated control programs are discussed. Accelerating the development and subsequent releases of insect-resistant cultivars to pulse farmers requires more involvement from interdisciplinary teams of plant breeders, entomologists, plant pathologists, plant chemists, molecular biologists, and other scientists.     

Counteracting virulence mechanisms of grain legume pathogens

Summary Grain legumes, in common with all other plants, are subject to biotic constraints of which pathogens form an important group. They are variable in type, number, space and time and, most insidiously, in genetic constitution. Consequently, resistance in the plant to a given pathogen may be quickly nullified by genetic alteration of the pathogen, particularly where this is conferred by a single resistance gene. The products of such resistance genes usually recognise, directly or indirectly, a component of the pathogen, which is encoded by a corresponding avirulence gene. Thus resistance and avirulence genes are specific and complementary and the arrangement is referred to as a gene-for-gene relationship. It follows that alteration of the avirulence gene of the pathogen to give a product that is no longer recognised by the product of the resistance gene of the plant gives rise to a susceptible reaction. A possible solution to this problem is to pyramid several resistance genes, a procedure now facilitated by the techniques of genetic modification. In other interactions genes that reduce susceptibility rather than confer complete resistance have been found and in some cases the loci (quantitative trait loci) responsible have been mapped to specific regions of particular chromosomes. The mechanisms by which these genes limit the virulence of the pathogen are generally unknown. However, by gaining an understanding of the fundamental properties of a pathogen that are necessary for pathogenicity or virulence it may be possible to counteract them. Candidates for such properties are toxins, enzymes and mechanisms that interfere with constitutive or active defence of the plant. Reciprocally, understanding the properties of the plant that confer susceptibility may allow selection of germplasm that lacks such properties. Among the candidates here are germination stimulants of pathogen propagules and signals that promote the formation of infection structures.     

锰元素对不同基因型大豆产量的影响

研究施锰对不同基因型大豆产量影响规律。结果表明,高油大豆垦农18,无论拌种还是叶面喷施,随着锰使用量增加,株荚数、单株粒重有上升趋势,株高、百粒重在锰低用量时上升,高用量时下降;高蛋白大豆东农42,无论拌种还是叶面喷施,随着锰使用量增加,株高、株荚数、百粒重、单株粒重有上升趋势。     

Demand-driven breeding of food legumes for plant-nutrient relations in the tropics and the sub-tropics: serving the farmers; not the crops!

A number of improved cultivars of food legume crops have been developed and released in the tropics and the sub-tropics. Most of these cultivars have been developed through conventional breeding approaches based on the development of crop varieties under optimum soil fertility levels. Nevertheless, it is hardly possible to say that the varietal provisions made by the past approach have been readily accepted, and properly utilized to boost productivity of food legumes grown by resource-poor farmers. The approach itself did not fully appreciate the actual circumstances of the resource-poor farmers where marginal production systems prevail and the poorest farmers could not afford to use cultivars developed under optimum soil fertility level. Therefore, the limitations and strategic implications of past experiences made to develop crop cultivars need to be analyzed in order to formulate better strategies and approaches in the future. The main purpose of this article is to review the efforts made, the technical difficulties associated with the genetic improvement in food legumes as related to plant-nutrient relations, causes of limited breeding success and thereby draw lessons useful to designing future breeding strategies. The scope of nutrient deficiency stress and the approaches to breeding for plant-nutrient relations are discussed and the need for refining the approach and better targeting of the breeding methodologies suggested.     

Legume genetic resources: management, diversity assessment, and utilization in crop improvement

Grain legumes contribute significantly to total world food production. Legumes are the primary source of dietary proteins in many developing countries, where protein hunger and malnutrition are widespread. Grain legumes germplasm constitute ~15% of the 7.4 M accessions preserved globally. Nearly, 78% of the CGIAR??s, 0.217 M accessions, have been characterized, compared to 34% of national genebank collections. Interestingly, limited data on grain quality are available as the primary focus has been on morpho-agronomic traits. Clearly, more resources should be targeted on biochemical evaluation to identify nutritionally rich and genetically diverse germplasm. The formation of core and mini core collections has provided crop breeders with a systematic yet manageable entry point into global germplasm resources. These subsets have been reported for most legumes and have proved useful in identifying new sources of variation. They may however not eliminate the need to evaluate entire collections, particularly for very rare traits. Molecular characterization and association mapping will further aid to insights into the structure of legume diversity and facilitate greater use of collections. The use of high resolution elevational climate models has greatly improved our capacity to characterize plant habitats and species?? adaptive responses to stresses. Evidence suggests that there has been increased use of wild relatives as well as new resources resulting from mutagenesis to enhance the genetic base of legume cultigens.     

Rj (rj) genes involved in nitrogen-fixing root nodule formation in soybean

It has long been known that formation of symbiotic root nodules in soybean (Glycine max (L.) Merr.) is controlled by several host genes referred to as Rj (rj) genes, but molecular cloning of these genes has been hampered by soybean’s complicated genome structure and large genome size. Progress in molecular identification of legume genes involved in root nodule symbiosis have been mostly achieved by using two model legumes, Lotus japonicus and Medicago truncatula, that have relatively simple and small genomes and are capable of molecular transfection. However, recent development of resources for soybean molecular genetic research, such as genome sequencing, large EST databases, and high-density linkage maps, have enabled us to isolate several Rj genes. This progress has been achieved in connection with systematic utilization of the information obtained from molecular genetics of the model legumes. In this review, we summarize the current status of knowledge of host-controlled nodulation in soybean based on information from recent studies on Rj genes, and discuss the future research prospects.     

基于文献计量学的根瘤固氮对豆科植物影响研究可视化分析

本研究旨在为豆科植物根瘤固氮领域的研究提供数据参考。检索中国知网(CNKI)和Web of Science核心集(WOS),从建库到2020年初根瘤固氮对豆科植物影响的相关文献,应用文献计量学方法和CiteSpace 5.5.R2软件对其发表时间、期刊、研究机构、国家、研究主题与关键词进行分析和可视化展示。共检索中英文文献4886篇,包括中文文献3015篇和英文文献1871篇。发文量总体呈增长趋势,美国、中国和巴西发文量居于前三位,法国农业科学研究院发文数量最多。涉及期刊940种,以微生物学、土壤和农业类期刊为主,其中《大豆科学》和《PLANT AND SOIL》发文量较多;根瘤固氮对豆科植物抗逆性影响和根瘤菌基因与遗传多样性是当前研究的主要方向。目前豆科植物根瘤固氮研究仍受到国内外学者的重视,已形成相对稳定的研究群体。根瘤固氮发生及调控机制、根瘤菌基因与遗传多样性的研究是当前的研究热点和未来可能的发展方向。     

植物游离小孢子及其培养所获得的组织在遗传转化中的应用

植物游离小孢子及其培养所获得的组织是植物基因工程中优良的受体,它们具有单倍性和较高胚胎发生能力的特性。因此,以它们为受体构建遗传转化体系可以快速获得纯合的转基因植株。通过综述植物游离小孢子及其培养所获得的胚状体、愈伤组织作为转化受体在根癌农杆菌介导法、基因枪轰击法、激光微孔穿刺法、显微注射法、电激法、PEG介导法等转化技术中的应用研究进展,对目前游离小孢子作为转化受体存在的问题及发展前景进行了探讨。     

Integrated gene resource management of underutilized legumes in India

The Indian gene centre possesses a rich legume biodiversity––1,152 species comprising cultivated, underutilized edible and forage legumes. Majority of the underutilized food legumes are widely distributed as wild species in various agro-ecological regions of peninsular India. Indian legume species (62%) contribute to the food and health security of ethnic communities. A total of 66,546 accessions of legume gene resources including underutilized species are conserved in the National Gene Bank. Collection, characterization and conservation efforts regarding the diversity of these beans are described. The importance of genetic variation in legumes and their wild relatives as a source of desirable resistance to pests and diseases in a changing climate scenario is discussed. Information on legumes used in Indian and modern systems of medicine and ethno-botany as well as the scope for bio-prospecting are presented. Advanced biotechnological applications in legume research for sustainable utilization of these resources are highlighted. An integrated gene resource management strategy to combat malnutrition, identify gene resources for legume improvement and enhance their value as traditional food and medicine is described.     

Heritability of frost-seeded red clover establishment

In the colder parts of the United States (north of 32° N latitude and east of 92° W longitude), in late winter after disappearance of snow cover, red clover (Trifolium pratense) is often broadcast seeded into forage legume-depleted grass pastures to increase pasture forage quality. This method of establishment is referred to as frost seeding. However, in an estimated 30–40% of frost seeded pastures in Wisconsin, USA the legumes fail to establish. In this study 40 red clover halfsib families from one breeding population and ten check populations were evaluated for spring frost-seeded establishment in three environments. Seedling establishment counts and plant heights were measured 3 months after frost-seeded planting. One of the three environments experienced a stand establishment failure. Narrow sense heritability estimates on a halfsib family basis for stand counts and heights were 0.07 and 0.63, respectively. Seedling counts were greatly affected by environment with micro-environmental effects contributing to low heritability. Additive by environment genetic variance was large, again leading to low seedling count heritabilities. These results, based on one population, suggest that it may be difficult to select for increased frost-seeded seedling establishment and that many test environments are needed to achieve genetic gains for this trait. In comparison, seedling height was very heritable with relatively small additive by environment genetic variances. The genetic correlation between seedling count and height using frost-seeded establishment was r _A = 0.42.     

DTA-6对两种食用豆生理代谢及产量的影响

为探究2-N,N-二乙氨基乙基己酸酯（diethyl aminoethyl hexanoate,DTA-6）对食用豆叶片的生理代谢及产量的调控效应,选用芸豆（英国红）和小豆（龙垦2号）为试验材料,采用大田完全随机试验方法,于芸豆和小豆的初花期叶面喷施DTA-6,以喷施清水为对照（CK）,测定各生育时期叶片光合参数、碳代谢产物、干物质、产量及产量构成因素。结果表明：DTA-6提高了2种食用豆各生育期的SPAD值、盛花期和鼓粒期的净光合速率（P_n）、蒸腾速率（T_r）、气孔导度（G_s）和胞间CO₂浓度（C_i）,显著增加了叶片蔗糖和可溶性糖的含量,促进了叶片淀粉的积累;与CK相比,DTA-6提高了2种食用豆的地上部单株干物质积累量,并且显著提高了芸豆和小豆鼓粒期荚分配率;DTA-6可有效调控2种食用豆的单株荚数、单株粒数和百粒重,从而提高产量,DTA-6处理的芸豆和小豆产量分别较CK增加13.30%和12.91%,增产显著。