Application of in vivo and in vitro mutation techniques for crop improvement

Summary Conventional mutation techniques have often been used to improve yield, quality, disease and pest resistance in crops, or to increase the attractiveness of flowers and ornamental plants. More than 1700 mutant varieties involving 154 plant species have been officially released. In some economically important crops, e.g. barley, durum wheat and cotton, mutant varieties occupy the majority of cultivated areas in many countries. Mutation techniques have become one of the major tools in the breeding of ornamentals such as alstroemeria, begonia, chrysanthemum, carnation, dahlia and streptocarpus. The use of in vitro techniques such as anther culture, shoot organogenesis, somatic embryogenesis and protoplast fusion can overcome some of the limitations in the application of mutation techniques in both seed and vegetatively propagated crops. In vitro culture in combination with induced mutations can speed up breeding programmes, from the generation of variability, through selection, to multiplication of the desired genotypes. The expression of induced mutations in the pure homozygote obtained through microspore, anther or ovary culture, can enhance the rapid recovery of the desired traits. In some vegetatively propagated species, mutations in combination with in vitro culture technique, may be the only method of improving an existing cultivar. Currently, many molecular studies rely on the induction and identification of mutants in model species for construction and subsequent saturation of genetic maps, understanding of developmental genetics and elucidation of biochemical pathways. Once identified and isolated, the genes that encode agronomically-important features can be either introduced directly into crop plants or used as probes to search for similar genes in crop species. It seems most likely that the recent developments based on these technologies will soon provide improved methods for selection of desired mutants.     

观赏植物抗病育种现状

观赏植物种类繁多,在这些植物的育种、销售及栽培过程中,与植物病害相关的各种病原物也被广泛传播。因此,培育抗病品种一直是园艺育种工作者的重要目标性状之一。在粮食作物中,抗病育种方面已经投入了很大的人力物力,新的生物技术不断被用于作物新品种的培育。但对于观赏植物而言,这些新技术应用范围还极为有限。本综述对园艺植物抗病育种现状进行了总结,并对育种前景进行了预测。     

Heterosis in crop mutant crosses and production of high yielding lines using doubled haploid systems

Heterosis appearing in crosses between mutants derived from the same parent variety and crosses of mutants with parent varieties has been observed by many authors for many plant species including such important crops as barley, faba bean, maize, pea, pearl millet, rice, sunflower, sesame, sweet clover, triticale and wheat. Mutant heterosis was reported for crosses of spontaneous mutants, mutants obtained after treatment with various mutagens and recently also for somaclonal variants. The heterotic effects are usually related to an increase in some yield components. There is a lack of correlation between mutation of a particular plant character and appearance of heterotic effect. The yielding performance of a mutant was not correlated with its potential to give yield heterosis in crosses with another mutant, often also a very poor one, or with the parent variety. Poor yielding barley mutants from the collection of semi-dwarf forms of the Department of Genetics, Silesian University gave heterosis in crosses with other mutants or parent varieties for such characters as tillering, grain number and weight per plant. In addition to mutants with deleterious mutations of such characters as chlorophyll synthesis or fasciated stem there were also lines mutated for earliness, semi-dwarfness, low glucoside or high protein and lysine content which gave significant heterosis in crosses. One possible explanation of the phenomenon of mutant heterosis is related to the frequency of mutations induced by chemical and physical mutagens. The appearance and the level of heterotic effect of mutated genes will depend on their interaction with other mutated genes or with genes from the parental genotype. High specific combining ability of mutants giving heterotic effect makes hybrid seed production, based on crosses with defined sources of cytoplasmic or genetic male sterility, unfeasible or even impossible. Doubled haploids provide a unique system to attempt the ‘fixing’ of hybrid performance in homozygous lines and to avoid the step of hybrid seed production. The assumption on the ‘fixability’ of hybrid yield in homozygous lines based on reports that large additive genetic variance is responsible for yield heterosis in wheat or barley was proven also for mutant crosses. This revised version was published online in August 2006 with corrections to the Cover Date.     

植物矮生性状的分子遗传研究进展

近年来,随着分子生物学和基因组学的飞速发展,对作物高产性状,高产机理及其相关基因的研究愈加深入,应用基因工程技术对作物进行遗传改良已成为提高作物产量的有效途径,培育理想株型已成为作物育种的重要目标。株高是高等作物的重要农艺性状之一,植株过高容易引起倒伏而减产,而矮生植株抗倒能力强,高产,因而矮化育种对培育理想株型十分重要,矮生基因的发掘研究和利用也越来越受到重视。本文综述了目前高等作物矮生性的分子遗传研究进展,特别是对水稻、小麦、玉米、黄瓜、西瓜和番茄等主要作物矮生性状的遗传特点、分子标记、矮生基因的克隆等方面的研究进展做了较为详细的总结和评价,分析了激素对高等植物矮生突变体的调控,提出了高等植物矮生资源的利用和矮化育种中存在的问题,并探讨了高等植物矮生性状分子遗传学研究和分子育种的发展趋势。     

The role of crop-pollinator relationships in breeding for pollinator-friendly legumes: from a breeding perspective

Breeders are encouraged to develop breeding approaches that strive to integrate food production into the healthy functioning of agro-ecosystems. In the case of legumes, this approach should preserve bee fauna by providing suitable floral resources within the crops themselves. In parallel, legume breeding for sustainable agriculture is linked to the development of environmental services. Foraging places and nesting sites for solitary and social bees are some of the ecological services provided for legumes. Crops with floral attractiveness and rewards for insects can be used to enhance pollinator conservation as well as crop yield and yield stability. We analyze how understanding crop-pollinator relationships (CPR) can contribute to the production of high-yielding and pollinator-friendly varieties by examining: (1) The status of knowledge on mating systems and floral traits; (2) The contribution of CPR understanding to plant breeding for both hybrid-seed production and open-pollinated population improvement.     

Participatory plant breeding with maize in Mexico and Honduras

Maize is a staple food crop in many developing countries. However, if seven major maize producing countries are excluded from this group, data indicate that only 34% of the maize area is planted with improved seed despite considerable effort invested in maize breeding. This has led researchers to investigate other options, such as farmer-participatory plant breeding, for delivering the benefits of plant breeding knowledge and technology to farmers in developing countries. This paper describes short-term results from participatory maize breeding studies in Mexico and Honduras. Results from three selection cycles in Mexico suggest that stratified mass selection without pollination control, with selections carried out by researchers in farmers' fields, may be effective at improving yield in farmers' local varieties. In Honduras, mass selection with pollination control, where selections were done by collaborating farmers in their own fields on their own varieties, showed trends (non-significant) towards yield improvement. Farmer selection seemed to offer the greatest yield benefit over experiment station selection on the farm with the lowest yield potential, suggesting that farmer-participatory approaches may be most advantageous in marginal environments where experiment station conditions differ most dramatically from farmers' conditions. These studies highlighted the importance of seed systems knowledge in designing participatory plant breeding programs. For cross-pollinated crops, they also highlighted the need to balance progress from selection and demands on farmers' time and labor in choosing breeding methods. Further work is needed to investigate farmer-participatory breeding approaches that can address post-harvest traits. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genomic resources for breeding crops with enhanced abiotic stress tolerance

To meet the challenges of climate change, exploring natural diversity in the existing plant genetic resource pool as well as creation of new mutants through chemical mutagenesis and molecular biology is needed for developing climate‐resilient elite genotypes. Ever‐increasing area under existing abiotic stresses as well as emerging abiotic stress factors and their combinations have further added to the problems of the current crop improvement programmes. However, with the advancement in modern techniques such as next‐generation sequencing technologies, it is now possible to generate on a whole‐genome scale, genomic resources for crop species at a much faster pace with considerably less efforts and money. The genomic resources thus generated will be useful for various plant breeding applications such as marker‐assisted breeding for gene introgression, mapping QTLs or identifying new or rare alleles associated with a particular trait. In this article, we discuss various aspects of generation of genomic resources and their utilization for developing abiotic stress‐tolerant crops to ensure sustainable agricultural production and food security in the backdrop of rapid climate change.     

Productivity and radiation use efficiency of lettuces grown in the partial shade of photovoltaic panels

Combining photovoltaic panels (PVPs) and crops on the same land unit were recently proposed as an alternative to the conversion of cropland into photovoltaic plants. This could alleviate the increasing competition for land between food and energy production. In such agrivoltaic systems, an upper layer of PVPs partially shades crops at ground level. The aim of this work was to (i) assess the effect on crop yield of two PVPs densities, resulting in two shade levels equal to 50% and 70% of the incoming radiation and (ii) identify morphological and physiological determinants of the plant response to shade. Experiments were conducted on four varieties of lettuces (two crisphead lettuces and two cutting lettuces), during two seasons. In all cases, the relative lettuce yield at harvest was equal or higher than the available relative radiation. Lettuce yield was maintained through an improved Radiation Interception Efficiency (RIE) in the shade, while Radiation Conversion Efficiency (RCE) did not change significantly. Enhanced RIE was explained by (i) an increase in the total leaf area per plant, despite a decrease in the number of leaves and (ii) a different distribution of leaf area among the pool of leaves, the maximal size of leaves increasing in the shade. Our result provides a framework for the selection of adapted varieties according to their morphological traits and physiological responses to PVP shade, in order to optimize agrivoltaic systems.     

主要麻类作物基因组学与遗传改良:现状与展望

随着测序技术的发展,主要麻类作物(黄麻、红麻、苎麻、亚麻和工业大麻)参考基因组从2011年至2020年陆续完成测序,这标志着麻类作物科学已经进入基因组时代。文章首先详细概述主要麻类作物基因组测序。其次,评述了基于基因组学的麻类作物重要应用价值基因挖掘。基于参考基因组和转录组测序,大量关于纤维发育、响应非生物胁迫的候选基因被挖掘,以促进麻类作物纤维的物种特性和“不与粮食争好地”的逆境农业。同时不同麻类作物特异性状候选基因陆续被报道,如红麻雄性不育、亚麻种子含油量和大麻大麻素相关候选基因等。再次,麻类作物基因组测序完成为基于组学的麻类作物遗传改良提供可能:有助于麻类作物种质资源形成和演化机制研究,系统解析纤维产量、纤维品质、抗病耐逆等农艺性状形成的分子基础;有助于建立高通量基因型-表型数据库,挖掘优异基因资源与创制新种质;有助于创新并集成分子标记辅助选择、基因组选择、转基因等技术,建立高效的快速育种技术体系。宜选育高产高效、抗逆抗病、适宜轻简化机械化、优质专用的多用途麻类作物新品种,以满足麻类作物相关产业的市场需求,适应麻类作物生产方式。尽管已经获得重要基因以及位点的信息,但如何高效率利用已有基因资源对麻类作物进行遗传改良仍需面临一系列挑战,如成熟稳定的遗传转化体系、麻类作物基因编辑体系构建及基因组选择育种等。     

小麦矮秆突变体的鉴定及其突变性状的关联分析

矮秆突变体是小麦育种和株高遗传研究的重要基因资源。通过‘云麦53’成熟种子的EMS (Ethyl methyl sulfonate)诱变及诱变植株连续自交,获得了33个M3代候选突变体。通过诱变亲本与M2和M3代候选植株的株高差异分析,筛选到26个矮秆突变体,其株高变幅为(13.61±0.11)~(44.08±1.73) cm。基于8个矮秆基因的12个特异性标记检测发现, 26个矮秆突变体至少携带2个矮秆基因标记位点。除株高外, 26个矮秆突变体还携带穗长、小穗密度、节间数和平均节间长4个不同突变性状。26个矮秆突变体可聚为5个亚类,第1亚类的小穗数和小花数最少;第2亚类的株高最矮,穗长和平均节间长最短,小穗密度最高;第3亚类突变体的节间数最少。株高与平均节间长和节间数呈极显著相关,偏相关系数分别为0.94、0.58,但与穗长、小穗数、小花数和小穗密度4个性状无相关性。26个矮秆突变体的株高与平均节间长和节间数关联遗传,携带不同的突变基因组合,可用于小麦矮化育种,以及株高、穗长和小穗密度等性状的遗传机制研究。     

Recent developments in genome editing and applications in plant breeding

Increasing genetic variation beyond natural variation is an important aim in plant breeding. In the past 70 years, random mutagenesis by irradiation or by chemicals has created numerous mutants which have been frequently used in breeding. However, their application is hampered by the mutational load due to many background mutations. In the past 10 years, new techniques for site‐directed mutagenesis have been introduced to plant breeding which are commonly referred to as “genome editing.” Among these, the CRISPR/Cas9 system turned out to be the most efficient and easy to apply. DNA is cleaved by a nuclease precisely at a target site where a mutation is likely to be beneficial. The DNA is healed by the cellular repair system either by error‐prone non‐homologous end joining or by homologous recombination, by which small DNA fragments can be inserted at the target site. In this review, we describe the application of targeted mutagenesis to crop plants and the modification of agronomically important traits, which could have direct impacts on plant breeding.     

Genetics,genomics and breeding of groundnut (Arachis hypogaea L.)

Groundnut is an important food and oil crop in the semiarid tropics, contributing to household food consumption and cash income. In Asia and Africa, yields are low attributed to various production constraints. This review paper highlights advances in genetics, genomics and breeding to improve the productivity of groundnut. Genetic studies concerning inheritance, genetic variability and heritability, combining ability and trait correlations have provided a better understanding of the crop's genetics to develop appropriate breeding strategies for target traits. Several improved lines and sources of variability have been identified or developed for various economically important traits through conventional breeding. Significant advances have also been made in groundnut genomics including genome sequencing, marker development and genetic and trait mapping. These advances have led to a better understanding of the groundnut genome, discovery of genes/variants for traits of interest and integration of marker‐assisted breeding for selected traits. The integration of genomic tools into the breeding process accompanied with increased precision of yield trialing and phenotyping will increase the efficiency and enhance the genetic gain for release of improved groundnut varieties.     

棉花叶片突变体的研究进展

为了解并且应用目前的棉花叶片突变体种质资源,本研究综述了6种类型的突变体的起源、遗传研究、基因定位、对农艺与经济性状的影响,以及突变性状可能带来的抗虫性。这6种叶片突变体包括：（1）叶形突变体：鸡脚叶、杯状叶、皱缩叶、波状叶与圆叶;（2）叶色突变体：花叶、红叶、亚红叶与芽黄; （3）自然落叶突变体;（4）叶片蜜腺突变体：无蜜腺;（5）叶片腺体突变体：无腺体;（6）叶片茸毛突变体：毛叶与光叶。得出这些叶片突变性状都是由质量性状控制的,对开展基因组研究是很好的材料,同时可以用作指示性状,另外鸡脚叶、叶片无蜜腺、毛叶和光叶都有形态抗虫性。由于突变性状具有两面性,因此建议育种中如果利用这些性状,要平衡好突变性状的优缺点。     

应用多元统计分析玉米农艺性状

在作物遗传育种研究中,产量及其相关性状多属于数量性状范畴,这类性状由多基因控制,易受环境影响使其遗传极为复杂,并且性状间常存在复杂相关关系.产量及其相关性状间的复杂关系使得育种中对以产量为目标的选择极为困难.多元统计分析是研究客观事物中多个变量之间相互依赖的统计规律性综合分析方法.合理利用多元统计分析可以加深对性状间相互关系的遗传规律及各相关性状对产量影响的主次和依存关系认识,为新品种选育和改良提供理论依据.对35个玉米品种(组合)的20个农艺性状应用GGE双标图、因子分析和聚类分析研究,结果表明,平均日产量、千粒重、穗长与产量呈显著正相关;20个农艺性状可综合为6个公因子;以6个公因子为综合指标对35个品种(组合)聚类结果聚成17个类群,其中G8、G14、G12、G10和G17为综合性状优良品种(组合).     

棉花突变体种子脂肪酸成分变化的诱导

油分在种子中的积累是生物合成的典型范例,其最终产物的多样性和多功能性,使得可通过遗传控制来有目的地提高种子的品质.种子油分含量的自然遗传倾向于低油分方向筛选.而目前,一系列新的育种目标逐渐拓展,以适应生物油脂化工的发展.另外,生物技术的不断创新也为食用及非食用油料作物突变体驯化甚至创造全新作物提供了便利.本研究分析了突变体种子的油分和脂肪含量及脂肪酸的构成,其中第11、7、2、9和5号突变体油分含量较高,这些突变体脂类含量增加了两倍.气相色谱分析表明,第11号突变体脂肪酸含量最高,其次为第7、2、9和5号突变体,在14种脂肪酸中,顺式亚油酸含量在各突变体中均为最高.     

A non-invasive crop ideotype to reduce invasive potential

Summary In plant breeding programs, qualitative and quantitative traits confer market value and, thus, constitute the basis for developing breeding criteria during crop domestication. Some traits such as high male/female fertility are advantageous in the wild and could enable the evolution of cultivated crops into invasive weeds. Other traits, e.g. sterility, are not expected to confer invasiveness. To date there has been very limited involvement in invasion risk assessment by plant breeders. Thus, in this paper we propose that trait-based selection of potential crop species be coupled with species design in the creation of a “non-invasive crop ideotype” as an avenue to reduce invasiveness during domestication. The non-invasive crop ideotype embodies the ideal characteristics for a crop to excel in cultivated environment(s) but minimizes the likelihood it will establish and spread in non-cultivated environments, constituting the underlying foundation for all breeding objectives, choice(s) of breeding methodologies, and propagation techniques for non-invasive crop release. Using ornamental (floriculture) horticultural crops as an example, we identify 10 traits to be used individually or in combination to reduce invasiveness while retaining commercial value: reduced genetic variation in propagules, slowed growth rates, non-flowering, elimination of asexual propagules, lack of pollinator rewards, non-shattering seed, non-fleshy fruits, lack of seed germination, sterility, and programmed death (apotopsis). A non-invasive crop ideotype would constitute the underlying foundation for all breeding objectives, the choice(s) of breeding methodologies, and propagation technique(s). The ideotype should be flexible and should adjust to species- and crop-specific traits to account for the intended use. For example, development of sterile cultivars may have negligible effects in reducing invasiveness if the crops spread vegetatively. A non-invasive crop ideotype may increase the direct participation of plant breeders, who are the professionals directly involved in the collection, development and release of new crops, in reducing the invasive potential of ornamental crops. Future research is required to determine the feasibility of incorporating each trait into various crops, use of classical or molecular techniques for creation of non-invasive crops, trait stability (lack of genotype × environment interaction over years and locations), consumer acceptance, and long-term viability.     

Induced mutations – A new paradigm in plant breeding

The use of ionizing radiation, such as X-rays, gamma rays and neutrons and chemical mutagens for inducing variation, is well established. Induced mutations have been used to improve major crops such as wheat, rice, barley,cotton, peanuts, and beans, which are seed propagated. Since the establishment of the Joint FAO/IAEA Division of the Nuclear Techniques in Agriculture, more than 1800 cultivars obtained either as direct mutants or derived from their crosses have been released worldwide in 50 countries. In vegetatively propagated plants, many of mutants were derived from irradiating rooted stem cuttings, detached leaves, and dormant plants. According to the FAO/IAEA database, of the 465 mutants released among the vegetatively propagated plants, most are in the floricultural plants and a few in fruit trees. These include chrysanthemum, Alstroemeria, dahlia, bougainvillea, rose, Achimenes,begonia, carnation, Streptocarpus, and azalea. The irradiation of in vitro cultured date palm, apple, potato, sweet potato and pineapple now provides a means to treat large populations which would not have been possible before. Irradiation of micropropagated plants, axillary and adventitious buds, apical meristems, regenerative callus cultures, anthers and microspores, and somatic embryos provides a miniaturized version of trees and seeds in the Petridish instead of the field. During the last decade, the use of radio-actively labeled probes in recombinant DNA research for cloning and mapping plant genes and transgenesis, particularly for RFLP, micro satellite based DNA fingerprinting, has become a routine procedure. Many homeotic mutants that change floral development have been isolated in Arabidopsis, Petunia, Antirrhinum and Lycopersicon. Mutants of Arabidopsis are being used to analyze genes, which determine response to auxins, cytokinins, gibberellin, abscisic acid and ethylene in plant growth, floral development and senescence, fruit formation and ripening. These mutants are facilitating the isolation, identification and cloning of the genes, which would ultimately help in designing crops with improved yield, increased stress tolerance, longer shelf-life and reduced agronomic inputs. The identification and analysis of mutants by using molecular techniques of DNA fingerprinting and mapping with PCR based markers, such as RAPDs, AFLP and STMS, and mutant tagging shall bring a new dimension in gene technology. Already, mutations can be linked to changes in DNA sequences for some plant traits and to establish molecular maps in structural and functional genomics of crop plants. These in turn would lead to a rapid enhancement of crop yields and quality. This revised version was published online in July 2006 with corrections to the Cover Date.     

提高植物抗盐能力的技术措施综述

日益严重的土壤盐渍化抑制作物生长,使栽培作物产量和品质下降。为提高盐胁迫下农作物的产量,研究提高植物抗盐性就有着极为重要的意义。综述了提高植物抗盐性的一些措施,包括培育抗盐作物和品种、利用Ca或微量元素、抗盐剂和植物激素以及增施有机肥、合理灌溉、地膜覆盖等其它措施,以期为植物抗盐栽培提供指导。     

The use of conventional and molecular genetics to produce new diversity in seed oil composition for the use of plant breeders-progress, problems and future prospects

Summary Considerable advances in the manipulation of seed oil yield and quality have been made using conventional breeding methods. Newer methods such as induced mutation and wide crosses have also resulted in significant achievements. These techniques, however, are all limited by the gene pool available in the crop of interest and its near relatives. The prospect of diminishing supplies of non-renewable fossil hydrocarbon reserves and the reality of edible crop surpluses have focused attention on the development of industrial oilseed crops. This will require the production of types of seed fatty acids which are not available in the oilseed crop species that are grown at present.The introduction of novel oil crops via domestication is contrasted with the insertion of alien genes into existing oilseeds to create designer crops. The use of molecular genetics to alter the yield and quality of rapeseed oil is discussed, and strategies for the engineering of seven new designer rapeseed varieties are presented.