The potential of somatic hybridization in crop breeding

Summary In recent years, the rapid development of somatic cell genetics has made possible the transfer of alien genes over wide taxonomic distances by somatic hybridization. In this review, the potential of somatic hybridization in the breeding of crops within the Brassicaceae, Fabaceae, Poaceae and Solanaceae is discussed. It is evident from these studies that many hybrids, either symmetric or asymmetric, which are fertile have the potential to be used as a bridge between the alien species and the crop. Progeny analysis of some hybrid combinations also reveals intergenomic translocations which may lead to the introgression of the alien genes. Furthermore, fusion techniques enable the resynthesis of allopolyploid crops to increase their genetic variability and to restore ploidy level and heterozygosity after breeding at reduced ploidy level in polyploid crops.     

基层农作物育种的瓶颈与对策

在计划经济时代,作物育种以国家科研单位为主,但随着我国社会主义市场经济体制的建立,特别是<中华人民共和国种子法>和<中华人民共和国植物新品种保护条例>的实施,种业市场全面开放.国营种子公司和日益增多的股份制公司和私营公司,在极力开拓市场、扩大营销的同时,开始涉猎育种,致使从事农作物育种的单位和人员成倍增加.育种单位增多,育出品种自然也多.新育品种参加区域试验,通过审定或备案,特别是在生产上推广应用的难度都大大增加.在品种竞争空前激烈的背景下,长期困扰基层农作物育种存在的一些问题更加凸显出来.正视和突破这些瓶颈因素,就成了基层农作物育种单位实现育种突破,进而在竞争中立于不败之地的关键.     

The potential of high-resolution BAC-FISH in banana breeding

The genetic complexity in the genus Musa has been subject of study in many breeding programs worldwide. Parthenocarpy, female sterility, polyploidy in different cultivars and limited amount of genetic and genomic information make the production of new banana cultivars difficult and time consuming. In addition, it is known that part of the cultivars and related wild species in the genus contain numerous chromosomal rearrangements. In order to produce new cultivars more effectively breeders must better understand the genetic differences of the potential crossing parents for introgression hybridization, but extensive genetic information is lacking. As an alternative to achieve information on genetic collinearity we make use of modern chromosome map technology known as high-resolution fluorescent in situ hybridization (FISH). This article presents the technical aspects and applications of such a technology in Musa species. The technique deals with BAC clone positioning on pachytene chromosomes of Calcutta 4 (Musa acuminata ssp. burmanicoides, A genome group, section Eumusa) and M. velutina (section Rodochlamys). Pollen mother cells digestion with pectolytic enzymes and maceration with acetic acid were optimized for making cell spread preparations appropriate for FISH. As an example of this approach we chose BAC clones that contain markers to known resistance genes and hybridize them for establishing their relative positions on the two species. Technical challenges for adapting existing protocols to the banana cells are presented. We also discuss how this technique can be instrumental for validating collinearity between potential crossing parents and how the method can be helpful in future mapping initiatives, and how this method allows identification of chromosomal rearrangements between related Musa species and cultivars.     

Sexual and somatic hybridization in the genus Lactuca

Summary Various genes for disease resistance identified in wild Lactuca are difficult, even impossible to exploit in lettuce breeding, due to sexual incompatibility between L. sativa and wild Lactuca sp. We adapted two cellular biology techniques to overcome these interspecific barriers: in vitro embryo rescue and protoplast fusion. In vitro rescue of immature embryos was used successfully for sexual hybridization between L. sativa and L. virosa. Vigorous hybrid plants were produced between L. sativa and seven accessions of L. virosa. Protoplast fusion permitted the regeneration of somatic hybrids between L. sativa and either L. tatarica or L. perennis. Hybrids between L. sativa and L. tatarica were backcrossed to L. sativa.     

Secondary somatic embryogenesis and applications in plant breeding

Summary Secondary somatic embryogenesis is the phenomenon whereby new somatic embryos are initiated from somatic embryos. Such cultures have been described in at least 80 Gymnosperm and Angiosperm species. In the initial step (primary somatic embryogenesis) such cultures have to be started from plant explants. In general, primary somatic embryogenesis from vegetative plant explants is, indirect and mostly driven by auxin (AUX) or auxin and cytokinin (AUX/CYT) supplemented media, whereas, from zygotic embryos it is direct and driven, to a larger extent, by CYT or growth regulator free media. Primary somatic embryogenesis from floral plant explants is between these two extremes. Indirect and direct somatic embryogenesis should be seen as two extremes of one continuum: in indirect somatic embryogenesis the embryos develop up to the (pre)-globular stage and in direct somatic embryogenesis to mature stages before they are subjected to secondary embryogenesis. In general, secondary embryogenesis requires no growth regulators in species with CYT driven primary embryogenesis. Whereas, continuous exposure to growth regulators is needed in species with CYT/AUX or AUX driven primary embryogenesis.In most species somatic embryos can be converted into shoots, although the frequencies are mostly low. In general, somatic embryos induced by growth regulator free or CYT supplemented media meet more difficulties in shoot development than embryos induced by AUX supplemented media. Applications of secondary somatic embryogenesis for plant breeding are discussed.     

Incongruity of interspecific and intergeneric crosses involving Nicotiana and Petunia species that exhibit potential for somatic hybridization

Summary Extensive pollinations were made in attempts to produce selected intergeneric or interspecific hybrids using Nicotiana and Petunia species that exhibit potential for somatic hybridization. Pollination between pairs of species was done by standard and bud-pollination methods. Nicotiana alata or N. tabacum when pollinated reciprocally with selected Petunia species failed to produce hybrids. Likewise, no interspecific hybrids were obtained between Petunia parviflora and 4 Petunia species or P. hybrida. The type of incongruity existing between these species is discussed in relation to the production of hybrids by standard In vitro techniques as compared to somatic hybridization.On leave from the Department of Horticulture, Michigan State University, E. Lansing, Michigan, USA. supported by a European Molecular Biology Organization (EMBO) fellowship and The Fred C. Gloeckner Foundation, N. Y., USA.Supported by the Agricultural Research Council.     

我国农作物育种科研面临的机遇与挑战

分析了我国农作物育种科研发展现状与机遇。对比国际种业育种技术发展现状,针对我国种业研发存在的问题,从政策扶持、科技支撑和知识产权3个方面提出了相关建议及实施路径。     

The potential of kales as a promising vegetable crop

Sixty varieties of kale (Brassica oleracea acephala group) from Galicia (northwestern Spain) were evaluated in two locations along with four commercial kale varieties. Data on 26 agronomic and morphological traits and five nutritional traits (crude fibre, acid detergent fibre, crude protein, calcium and potassium) were recorded. The objectives of this work were (i) to know the potential ability of kale as an horticultural crop, (ii) to assess the characteristics of local varieties of Galician kale in order to select those with the highest yield and a good adaptation to obtain improved varieties. In most traits, significant differences between locations were found, while varieties × location interaction was not significant for most of them. Significant differences were found among varieties and a high intravarietal variability was noticed in some traits. Galician kale germplasm displayed variability in the most important agronomic traits. They are characterized by their long cycles, their susceptibility to Lepidoptera pests, their good yield and adaptation to Galician conditions and their high calcium content. Four local varieties (MBG-BRS0468, MBG-BRS0476, MBG-BRS0477 and MBG-BRS0494) were the most promising for vegetal and fodder use. One of them showed the best early vigor (MBG-BRS0366) and two of them were the most resistant to Lepidoptera pest (MBG-BRS0060 and MBG-BRS0223). Kale varieties showed a high crude fibre content, and also a high acid detergent fibre, crude protein and calcium content. The varieties MBG-BRS0106, MBG-BRS0281, MBG-BRS0335 and MBG-BRS0464 could be candidates for future breeding programs since they had a good agronomic performance and a high calcium content.     

Relationships among symptoms of spotted wilt disease of peanut and their potential impact on crop productivity and resistance breeding

Symptoms of spotted wilt of peanut were evaluated in a field experiment over three years (2010–2012) near Marianna, Florida. Assessment included three visual measures of disease and ImmunoStrip (a form of ELISA) testing of root crowns for the presence of Tomato spotted wilt virus (TSWV), the causal agent of spotted wilt in peanut. Foliar symptoms of spotted wilt on a 1 to 10 scale and on a disease incidence rating (DIR) were highly correlated (r = 0.88; p < 0.001). Foliar symptoms were moderately correlated (0.45 < r < 0.54; p < 0.001) with TSWV infection. However, symptoms on the testa were highly correlated with TSWV infection (r = 0.78; p < 0.001). These results indicate that foliar symptomology is less reliable in assessing TSWV infection than testa symptomology. Regression analysis showed that foliar symptoms underestimated the proportion of plants infected by TSWV. Seed inspection may be a good predictor of plant infection and therefore useful in breeding programmes because it is much less expensive than ELISA. Resistance to TSWV infection is characteristic of some resistant peanut genotypes and a lack of testa symptomology could help to identify those genotypes.     

Intergeneric symmetric and asymmetric somatic hybridization in Festuca and Lolium

Summary Intergeneric symmetric and asymmetric somatic hybrids have been obtained by fusion of metabolically inactivated protoplasts from embryogenic suspension cultures of tall fescue (Festuca arundinacea Schreb.) and unirradiated or 10–500 Gy-irradiated protoplasts from non-morphogenic cell suspensions of Italian ryegrass (Lolium multiflorum Lam.). Genotypically and phenotypically different somatic hybrid Festulolium mature flowering plants were regenerated.Species-specific sequences from F. arundinacea and L. multiflorum being dispersed and evenly-represented in the corresponding genomes were isolated and used for the molecular characterization of the nuclear make-up of the intergeneric, somatic Festulolium plants recovered. The irradiation of Italian ryegrass protoplasts with 250 Gy X-rays prior to fusogenic treatment favoured the unidirectional elimination of most or part of the donor chromosomes. Irradiation of L. multiflorum protoplasts with 500 Gy produced highly asymmetric (over 80% donor genome elimination) nuclear hybrids and clones showing a complete loss of donor chromosomes.The RFLP analysis of the organellar composition in symmetric and asymmetric tall fescue (+) Italian ryegrass regenerants confirmed their somatic hybrid character and revealed a bias towards recipient-type organelles when extensive donor nuclear genome elimination had occurred.Approaches aimed at improving persistence of ryegrasses based on asymmetric somatic hybridization with largely sexually-incompatible grass species (F. rubra and Alopecurus pratensis), and at transferring the cytoplasmic male sterility trait by intra- and inter-specific hybridization in L. multiflorum and L. perenne, have been undertaken.Abbreviations cpDNA chloroplast DNA - CMS cytoplasmic male sterility - 2,4-D 2,4-dichlorophenoxy-acetic acid - IOA iodoacetamide - mtDNA mitochondrial DNA - RFLP restriction fragment length polymorphism     

分子标记及其在作物遗传育种研究中的应用

本文介绍了分子标记的概念和主要类型，以及RFLP、FAPD、SSR和AFLP等4种常用分子标记的基本原理与特点，讨论分子标记在锻造物遗传育种研究中的主要应用。     

Somatic hybridization as a tool for tomato breeding

Protoplast fusion can be used to produce somatic hybrids of species that cannot be obtained by sexual hybridization. The possibility to introgress genes from Solanum species into the cultivated tomato species Lycopersicon esculentum, and to obtain novel cytoplasm-nucleus combinations (cybrids) was considered as an important strategy to extend the genetic variation available for tomato breeding. Somatic hybrids between L. esculentum and other Lycopersicon species, as well as between L. esculentum and Solanum or Nicotiana species, have been produced. Specific mutants, genotypes with antibiotic resistances, and metabolic inhibition by iodoacetate or iodoacetamide and irradiation were used for the selection of hybrids. In addition, the improvement of protoplast culture techniques and the use of the favourable tissue culture traits derived from species such as L. peruvianum, which have been introduced into tomato by classical breeding, allowed the efficient recovery of somatic hybrids. However, the occurrence of somatic incongruity in fusion combinations of L. esculentum and Solanum and even more in L. esculentum and Nicotiana, did not allow the production of true cybrids and/or fertile hybrids, indicating the importance of both cytoplasm-nucleus and nucleus-nucleus interactions in somatic incongruity. Another problem with fusions between distantly related species is the strongly reduced fertility of the hybrids and the very limited homoeologous recombination between chromosomes of the parental species. Partial genome transfer from donor to recipient through microprotoplast (+) protoplast fusion, and the production of monosomic or disomic chromosome addition lines, light overcome some of these problems. In symmetric somatic hybrids between L. esculentum and S. tuberosum the occurrence of limited somatic and meiotic recombination was demonstrated. Fertile progeny plants could be obtained, though at a low frequency, when embryo rescue was performed on a large scale after backcrossing hexaploid somatic tomato (+) potato hybrids with a tetraploid potato genotype. The potential value of genomic in situ hybridization (GISH) and RFLPs for the analysis of the genome/chromosome composition of the hybrids has been demonstrated for intergeneric somatic hybrids between Lycopersicon and Solanum.Abbreviations cpDNA chloroplast DNA - mtDNA mitochondrial DNA     

农作物种子育繁推法律法规的完善

从农作物种子育繁推现状,浅析目前我国种子法律法规制定、实施过程中出现的不足,并提出解决相关问题的建议。     

加强作物育种攻关促进农业结构调整

国务院发布的<农业科技发展纲要>中指出,"十五"期间,农业科技工作要围绕调整农业和农村经济结构,提高农业效益,改善生态环境和提高国际竞争力,重点组织实施"十大科技行动".实施作物良种科技行为,促进种植业结构调整是十大行动之一.该<纲要>的发布,给育种工作者提出了今后一段时期育种工作的研究方向、目标和要求.     

Review of research on use of radiation-induced mutations in crop breeding in Japan

In Japan, the research on radiation-induced mutation has been conducted as one of the promising methods of plant breeding. Although in the beginning the principal methods used are X-rays and ³²P, we now have various kinds of radiation facilities available for mutation breeding. The fundamental aspects of mutation breeding are investigated at several universities and institutes, and the practical breeding work is carried out by the general organization for crop breeding.Among the characters that have been observed as mutated in rice, chlorophyll deficiency, heading time, culm length and grain-weight are most easily obtained. Some of the induced mutants showed the same or higher productivity as compared to the mother variety. Up to date there are many experiments on the procedural problems associated with radiation-induced mutations in crop breeding. The results of these experiments are reviewed in this paper.     

四川农作物商业育种现状与发展建议

对当前四川农作物商业化育种创新存在的种子企业小散弱、创新能力不强、融资难融资贵、基础设施条件差的现状进行了阐述;对制约四川农作物商业化育种创新主要原因进行了分析,在此基础上提出了加大育繁推一体化领军龙头企业的培育、加大对商业化育种创新的政策扶持力度、构建科企联合育种新机制、培育夯实商业化育种创新主体的建设性建议。