A mini core subset for capturing diversity and promoting utilization of chickpea genetic resources in crop improvement

A core collection is a chosen subset of large germplasm collection that generally contains about 10% of the total accessions and represents the genetic variability of entire germplasm collection. The purpose of a core collection is to improve the use of genetic resources in crop improvement programs. In many crops the number of accessions contained in the genebank are several thousands, and a core subset consisting of 10% of total accessions would be an unwieldy proposition. In this article we have suggested a two-stage strategy to select a chickpea mini core subset consisting of only about 1% of the entire collection held in trust at ICRISAT’s genebank (16,991 accessions). This mini core subset still represents the diversity of the entire core collection. The first stage involves developing a representative core subset (about 10%) from the entire collection using all the available information on origin, geographical distribution, and characterization and evaluation data of accessions. The second stage involves evaluation of the core subset for various morphological, agronomic, and quality traits, and selecting a further subset of about 10% accessions from the core subset. At both stages standard clustering procedure was used to separate groups of similar accessions. A mini core subset consisting 211 accessions from 1,956 core subset accessions, using data on 22 morphological and agronomic traits, was selected. Newman- Keuls’ test for means, Levene’s test for variances, the chi-square test and Wilcoxon’s rank-sum non-parametric test for frequency distribution analysis for different traits indicated that the variation available in the core collection has been preserved in the mini core subset. The most important phenotypic correlations which may be under the control of coadapted gene complexes, were also preserved in the mini core. This mini core subset, due to its drastically reduced size, will prove to be a point of entry to proper exploitation of chickpea genetic resources. Received: 20 August 2000 / Accepted: 25 September 2000     

Cassava, Manihot esculenta Crantz, genetic resources: origin of the crop, its evolution and relationships with wild relatives

About 98 species of Manihot are known. All of them are native to the New World and are concentrated in four regions in Brazil and Central America. All the Manihot species so far examined have 2n = 36 chromosomes. Interspecific hybrids between cassava and its wild relatives show relatively normal meiosis, and further generations can be obtained. Electrophoresis shows affinity among wild species of different sections, and between some of them and cassava. Both polyploidy and apomixis may have contributed to speciation in this genus. Polyploidy produced genetic variability, while apomixis is responsible for perpetuating new hybrid types adapted to different environments. Cassava may have originated by hybridization between two wild Manihot species, followed by vegetative reproduction of the hybrid.     

5. The use of genetic resources in breeding and breeding research

The dramatic increase in yields of agricultural crops over the last 40 years in developed countries has been attributed equally to improved genetic components and improved agronomic practices. The success of plant breeding is based partly on an increased understanding of the parameters involved, to a great extent on improved and more efficient methods of selection, to greater use of available genetic diversity and also to advances in a number of related disciplines including plant pathology, biochemistry, agronomy and genetics. Successes and problems associated with using various genetic resources in plant breeding are illustrated with examples from some of the world's major crops, including potatoes, barley and cotton.     

1492 and the loss of amazonian crop genetic resources. ii. crop Biogeography at contact

Fifty seven percent of the 138 cultivated plant species present in Amazonia at contact probably originated in the Amazon Basin and another 27% originated in lowland northern South America. The relationship between probable indigenous human population density and resultant agricultural intensification and crop diversity is used to propose the existence of a mosaic of crop genetic resource concentrations in Amazonia at contact, including two centers of diversity, four outlying minor centers, and five regions of diversity. This methodology is extrapolated to present a synthesis of South American crop genetic biogeography at contact.     

植物遗传资源的评价、保持和利用

阐明了植物遗传资源的重要作用,认为植物遗传资源是人类赖以生存和发展的物质基础,是植物育种丰富的基因资源的重要保证;分析了植物遗传资源评价的重要性,指出对植物遗传资源的正确评价是科学利用的前提;介绍了植物遗传资源的原生境保持和非原生境保持2种重要方法;重点论述了作物的高产基因、抗性基因及抗旱基因与肥高效基因等植物遗传资源的挖掘与利用,为引起人们对植物遗传资源保持重要性的高度认识提供理论参考。     

Genomics-assisted breeding for crop improvement

Genomics research is generating new tools, such as functional molecular markers and informatics, as well as new knowledge about statistics and inheritance phenomena that could increase the efficiency and precision of crop improvement. In particular, the elucidation of the fundamental mechanisms of heterosis and epigenetics, and their manipulation, has great potential. Eventually, knowledge of the relative values of alleles at all loci segregating in a population could allow the breeder to design a genotype in silico and to practice whole genome selection. High costs currently limit the implementation of genomics-assisted crop improvement, particularly for inbreeding and/or minor crops. Nevertheless, marker-assisted breeding and selection will gradually evolve into 'genomics-assisted breeding' for crop improvement.     

Seaweed resources of North America and their utilization

From the coasts of Nova Scotia, Maine, Massachusetts, North Carolina, California and Lower California, seaweeds are harvested that yield agar, algin, carrageenin and iridophycin for industrial use.     

Genetic diversity and conservation and utilization of plant genetic resources

Biodiversity refers to variation within the living world, while genetic diversity represents the heritable variation within and between populations of organisms, and in the context of this paper, among plant species. This pool of genetic variation within an inter-mating population is the basis for selection as well as for plant improvement. Thus, conservation of this plant genetic diversity is essential for present and future human well-being. During recent years, there has been increasing awareness of the importance of adopting a holistic view of biodiversity, including agricultural biodiversity, conservation for sustainable utilization and development. These principles have been enshrined in the Convention on Biological Diversity and the Global Plan of Action of the Food and Agriculture Organization of the United Nations. The emphasis is now to understand the distribution and extent of genetic diversity available to humans in plant species, so that the genetic diversity can be safely conserved and efficiently used. It is generally recognized that plant genetic diversity changes in time and space. The extent and distribution of genetic diversity in a plant species depends on its evolution and breeding system, ecological and geographical factors, past bottlenecks, and often by many human factors. Much of the large amount of diversity of a species may be found within individual populations, or partitioned among a number of different populations.A better understanding of genetic diversity and its distribution is essential for its conservation and use. It will help us in determining what to conserve as well as where to conserve, and will improve our understanding of the taxonomy and origin and evolution of plant species of interest. Knowledge of both these topics is essential for collecting and use of any plant species and its wild relatives. In order to mange conserved germplasm better, there is also a need to understand the genetic diversity that is present in collections. This will help us to rationalize collections and develop and adopt better protocols for regeneration of germplasm seed. Through improved characterization and development of core collections based on genetic diversity information, it will be possible to exploit the available resources in more valuable ways.     

Cassava breeding: opportunities and challenges

Although cassava is a major food crop, its scientific breeding began only recently compared with other crops. Significant progress has been achieved, particularly in Asia where cassava is used mainly for industrial processes and no major biotic constraints affect its productivity. Cassava breeding faces several limitations that need to be addressed. The heterozygous nature of the crop and parental lines used to generate new segregating progenies makes it difficult to identify parents with good breeding values. Breeding so far has been mainly based on a mass phenotypic recurrent selection. There is very little knowledge on the inheritance of traits of agronomic relevance. Several approaches have been taken to overcome the constraints in the current methodologies for the genetic improvement of cassava. Evaluations at early stages of selection allow for estimates of general combining ability effect or breeding values of parental lines. Inbreeding by sequential self-pollination facilitates the identification of useful recessive traits, either already present in the Manihot gene pool or induced by mutagenesis.     

Making the most of 'omics' for crop breeding

Adoption of new breeding technologies is likely to underpin future gains in crop productivity. The rapid advances in 'omics' technologies provide an opportunity to generate new datasets for crop species. Integration of genome and functional omics data with genetic and phenotypic information is leading to the identification of genes and pathways responsible for important agronomic phenotypes. In addition, high-throughput genotyping technologies enable the screening of large germplasm collections to identify novel alleles from diverse sources, thus offering a major expansion in the variation available for breeding. In this review, we discuss these advances, which have opened the door to new techniques for construction and screening of breeding populations, to increase ultimately the efficiency of selection and accelerate the rates of genetic gain.     

1. The importance of genetic resources in plant breeding

Modern agricultural technology and the introduction of new high-yielding varieties are largely eliminating the wide range of crop genetic diversity that has evolved during the five to ten thousand years since food plants were first domesticated. Related wild species are also on the decline because of new land use policies. These gene pools (or what is left of them) are generally spoken of as genetic resources, and are vitally needed in the creation of new crop varieties by plant breeders. Wild species and land races often furnish genes conferring resistance to diseases and pests and adaptation to environmental stresses which cannot be found in the modern crop varieties.
The study of genetic diversity of crops, its storage in gene banks or in natural reserves, its evaluation and enhancement, are briefly described. The genetic resources work of the Food and Agriculture Organisation of the United Nations (FAO) and other international agencies such as the International Board for Plant Genetic Resources (IBPGR) is outlined.     

Improving efficiency of breeding for higher crop yield

Summary Exclusive selection for yield raises, the harvest index of self-pollinated crops with little or no gain in total bipmass. In addition to selection for yield, it is suggested that efficient breeding for higher yield requires simultaneous selection for yield's three major, genetically controlled physiological components. The following are needed: (1) a superior rate of biomass accumulation. (2) a superior rate of actual yield accumulation in order to acquire a high harvest index, and (3) a time to harvest maturity that is neither shorter nor longer than the duration of the growing season. That duration is provided by the environment, which is the fourth major determinant of yield. Simultaneous selection is required because genetically established interconnections among the three major physiological components cause: (a) a correlation between the harvest index and days to maturity that is usually negative; (b) a correlation between the harvest index and total biomass that is often negative, and (c) a correlation between biomass and days to maturity that is usually positive. All three physiological components and the correlations among them can be quantified by yield system analysis (YSA) of yield trials. An additive main effects and multiplicative interaction (AMMI) statistical analysis can separate and quantify the genotype × environment interaction (G × E) effect on yield and on each physiological component that is caused by each genotype and by the different environment of each yield trial. The use of yield trials to select parents which have the highest rates of accumulation of both biomass and yield, in addition to selecting for the G × E that is specifically adapted to the site can accelerate advance toward the highest potential yield at each geographical site. Higher yield for many sites will raise average regional yield. Higher yield for multiple regions and continents will raise average yield on a world-wide basis. Genetic and physiological bases for lack of indirect selection for biomass from exclusive selection for yield are explained.     

Macroalgae (seaweeds): industrial resources and their utilization

Summary Seaweeds are distributed widely in all oceans of the world, but exploited in limited areas. These plants have been used for food and as soil conditioners for centuries, with industrial application of extractives a relatively recent innovation generally limited to the more developed areas of the world. There are relatively few species of industrial importance, and these occur in both the red (Rhodophyta) and brown (Phaeophyta) algal divisions.The principal value of phycocolloids is in their gelling and stabilizing properties. Species of red algae may elaborate agar or carrageenan. Both are complex polysaccharides with innumerable structural possibilities, hence physical properties, and phycocolloids from various species can have specific applications. Carrageenans are employed mostly in the food industry, and agars in both the food and pharmaceutical sectors of the economy. Alginates, another family of complex polysaccharides, are obtained from various species of brown algae and are the third major algal gum of commerce. Alginates are used in the food and pharmaceutical industries and have other industrial applications.Issued as NRCC No. 23603.     

Nutrient resources for crop production in the tropics

For the foreseeable future a majority of the population, and almost all the mal- and under-nourished, will continue to be found in the tropics and subtropics. Food security in these parts of the world will have to be met largely from local resources. The productivity of the land is to a large extent determined by the fertlity of the soil, which in turn is mostly determined by its organic matter content and stored nutrients. Soil organic matter is readily lost when organic matter inputs are reduced upon cultivation and more so upon intensification. The concomitant loss of topsoil and possible exposure of subsoil acidity may cause further soil degradation.<br>Plant nutrients to replenish what is yearly taken from the soil to meet the demands for food and fibre amount to 230 million tonnes (Mt). Current fertilizer consumption stands at about 130 Mt of N, P₂O₅,and K₂O, supplemented by an estimated 90 Mt of N from biological nitrogen fixation worldwide. Although 80 per cent of the population lives in the developing world, only half the world''s fertilizer is consumed there. Yet, as much as 50% of the increase in agricultural productivity in the developing world is due to the adoption of fertilizers. World population growth will cause a doubling in these nutrients requirements for the developing world by 2020, which, in the likely case of inadequate production, will need to be met from soil reserves. Because expansion of the cultivable land area is reaching its limits, the reliance on nutrient inputs and their efficient use is bound to grow.<br>With current urban expansion, nutrients in harvested products are increasingly lost from the rural environment as a whole. Estimates of soil nutrient depletion rates for sub-Saharan Africa (SSA) are alarmingly high. The situation may be more favourable in Latin America and Asia where fertilizer inputs are tenfold those of SSA. Closing the nutrient cycle at a community level in rural areas may be tedious; on an inter-regional level it is associated with considerable costs of collection, detoxification and transportation to the farms. Yet, at the rate at which some of the non-renewable resources such as phosphorus and potassium are being exploited, recycling of these nutrients will soon be required. <br>     

Protoplast fusion for crop improvement and breeding in China

Protoplast fusion offers an opportunity for circumventing barriers to sexual reproduction and allows for gene transfer of nuclear and cytoplasmic genomes to enrich the gene pool of cultivated species. Moreover, protoplast fusion effectively generates novel germplasm for elite breeding of conventional crosses and promotes crop improvement in existing cultivars. Over the past few decades, protoplast fusion in China has considerably progressed not only for food crops but also for economic plants. In this review, we present and discuss the development of somatic hybrids in wheat, rapeseed, citrus, and cotton, some of which are already in use or have potential for future commercial use in China. For example, an elite salt- and drought-resistant line, Shangrong No. 3, has already been registered as a commercial wheat cultivar. Some other hybrids have been found to have disease resistance as well as modified fatty acids, high oil and protein contents, novel cytoplasmic male sterility, and numerous other desirable agronomic characteristics that are useful for further breeding.     

In situ conservation of crop genetic resources through maintenance of traditional farming systems

A strategy is suggested for in situ conservation of crop genetic resources whereby conservation efforts are linked to rural development projects in Third World countries. We describe development projects that emphasize preservation of traditional farming systems and succeed in sustaining production by relying on the maintenance of biological and genetic diversity in these systems. Basing agricultural development efforts on indigenous knowledge, technology, and social organization can provide important guidelines for the design of cropping systems that allow lowincome farmers to produce subsistence and cash crops without dependence on external inputs and seed supplies. By incorporating landraces and wild relatives of crops into these cropping systems, major achievements in the conservation of crop genetic resources can be obtained.     

Cassava, Manihot esculenta Crantz genetic resources: VI. Anatomy of a diversity center

Central Brasil is one of the four centers of diversity of Manihot species. Of 26 wild Manihot species reported to occur in this region, 20 were collected from two limited areas, each less than 100 km in diameter. These two areas are Goiás Velho and Corumbá de Goiás. Considering the Harlan concept of geographic patterns of variation of cultivated crops, it is assumed that the two areas are microcenters of cassava diversity. Topographic, soil and ethnological data of these species were collected and compared.     

广西的红树林资源及其开发利用

广西的红树林植物种类计有10科14属14种,现有红树林面积5654hm~2。红树林是广西的优势海洋资源之一,其动植物资源潜力大,生态景观旅游价值高,同时,是良好的生态养殖场所。受沿海经济发展和人口增加等因素的影响,红树林资源的破坏日益严重,如何合理利用红树林资源是一个必须认真研究的课题。