Emerging Technologies to Benefit Farmers in Sub-Saharan Africa and South Asia (2009) / Chapter Skim
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3 Plant Improvement and Protection
3 Plant Improvement and Protection
Pages 71-122
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From page 71... ...
The right genes or alleles to overcome the constraints identified in Chapter 2 and enhance desirable traits in a crop are brought together by plant breeding, a complex process that, broadly defined, uses all the tools of modern plant science, including agronomy, field trials, propagation, tissue culture, genomics, molecular biology, biochemistry, and plant physiology. This chapter describes existing and evolving tools for improving and protecting crops.
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From page 72... ...
72 Emerging Technologies to Benefit Farmers Conventional and transgenic approaches to enhance crop performance are complementary and rely on many of the same molecular and informational tools. Box 3-1 contains a list of plant traits of which variants are selected by breeders (sometimes inadvertently)
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From page 73... ...
In particular, two essential features of modern breeding programs should be emphasized. First, successful crop improvement is based on a foundation of knowledge that informs all the intellectual and physical efforts of plant breeders in the laboratory and in the field.
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From page 74... ...
Local and emerging diseases need to be precisely identified for each crop; the involvement of local farmers in the selections and tests could increase the likelihood that the final products will be adopted, and additional local knowledge can be incorporated into the selection processes. The establishment and scale-up of modern plant breeding programs in SSA and SA should have high priority in any organization looking to improve agricultural productivity.
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From page 75... ...
The other is rice, the model plant of the grass species, including maize, wheat, pearl millet, sorghum, and others. Progress in understanding the biology of rice traits will be slower than in that of Arabidopsis, but it will be more directly relevant to cereal crops in the developing world.
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From page 76... ...
That can help in choosing diverse parents for specific traits; in reducing the number of breeding generations by making it possible to select homozygotes more efficiently; in accelerating backcrossing of a trait to an elite parent, especially when the desired trait is recessive; and in selecting desirable progeny while rejecting poorer genotypes without the need for complex assays, such as assays of tolerance to diseases. The use of molecular markers has highlighted the importance of genes from wild relatives for crop improvement (Tanksley and McCouch, 1997; Koornneef et al., 2004)
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From page 77... ...
; this constitutes a nontransgenic method for altering deleterious traits or modifying biochemical pathways. Many approaches to mutant analysis and control of gene expression have been used in Arabidopsis and rice.
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From page 78... ...
In addition, public-sector laboratories responsible for plant breeding in SSA and SA rarely have the means to adopt new technologies rapidly and on a sufficient scale to achieve the high impact that is possible. Using the pace of a multinational plant breeding company as a benchmark, obtaining a research finding and testing it in a model plant might
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From page 79... ...
Creative, world-class research will be needed to move them into practice if they are to be incorporated into plant breeding programs and production agriculture. And the technologies will require education and training for users, from the breeder to the farmer and consumer.
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From page 80... ...
. There is tremendous opportunity to apply 21st century bioinformatics -- which merges techniques from applied mathematics, informatics, statistics, computer science, artificial intelligence, chemistry, and biochemistry -- for effective plant breeding.
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From page 81... ...
However, few breeders recognize the potential importance of that information and are content to focus on "good x good" crosses, ignoring the major benefits that might be hidden in other, less adapted germplasm. Equivalent chromosomal segments evolve independently in different populations but can be brought together in new combinations in breeding programs.
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From page 82... ...
They can also be used by the plant science community, but they will need to be applied on a much greater scale for the relevant germplasm and breeding programs of SSA and SA. Plant breeding depends on assessing large numbers of progeny, and large-scale applications are essential.
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From page 83... ...
; this made clear how much value genome-wide proteomics can bring to genome annotation, including cases in which little or no supplementary information, such as cDNA sequences, is available. Peptide mass spectrometry also permits the identification of single amino acid polymorphisms arising from allelic DNA sequence differences.
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From page 84... ...
Peptide mass spectrometry has the potential to reveal all the relocation dynamics of the proteome and to associate changes with performance traits. Despite the exceptional opportunities for discovery in and practical benefits of peptide mass spectrometry research, there is little grant funding to support it and few people have the training required to do it.
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From page 85... ...
In plant breeding, the phenotype needs to be ascertained for hundreds or thousands of progeny from a large number of crosses for each species to reveal which loci move together in heritable associations. It is also desirable for the strength of the phenotypes to be measured in multiple environments.
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From page 86... ...
Using a systems biology approach to understand plant chemistry and lignin synthesis could help plant breeding programs to improve the nutritional value of forage and would also complement ongoing efforts to enhance the accessibility of cellulosic residues in crops targeted for biofuels. Buckler, 2006)
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From page 87... ...
Such genes are likely to be especially interesting and of special significance in plant breeding. Because the functions of new genes are being discovered rapidly in model plants, it seems important to promote efforts to carry out surveillance of the results with an eye to identifying and testing in crop plants the genes that may have particular relevance for international agriculture.
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From page 88... ...
The ability to capture and transmit the images electronically would allow scientists around the world to conduct plant breeding and development studies much faster and more efficiently. Existing and evolving Tools for Transgenic Crop Improvement Biological limits on the genetic diversity of a crop's germplasm mean that some traits cannot be readily (if at all)
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From page 89... ...
Box 3-6 describes possible opportunities for controlling weeds by engineering other forms of herbicide resistance into crop plants. Transgenes in Metabolic Pathways Although genes for insect and herbicide resistances are the most common transgenes in use today, a growing understanding of metabolic path
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From page 90... ...
Transgenic herbicide resistance would also be useful in sorghum, but because of feral sorghum (shattercane) , it is imperative to develop and use fail-safe mechanisms that prevent gene flow where it is expected that herbicides will be widely used in the future.
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From page 91... ...
A number of recent patents suggest that private enterprises are investigat ing the possibility of producing transgenic plants that degrade mycotoxins. An amino-oxidase active against fumonisins has been isolated and cloned from black yeast, and its activity has been enhanced with mutagenesis (Duvick, 2001)
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From page 92... ...
Thus, breeders are usually obliged to screen hundreds of transgenic plants to find the optimal insertion event because the random locations of insertions result in large variations in expression. It would be desirable to identify the optimal insertion sites and target gene insertion there every time in the process of homologous recombination.
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From page 93... ...
The further development of this technology will bring a new and powerful genetic approach to plant breeding. In addition to inserting genes precisely, it will enable promoters to be exchanged, and this will make it possible to directly alter the expression of genes.
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From page 94... ...
viruses, such as African CMV in SSA and cotton leaf curl in SA -- cause major losses to crops grown by small-scale farmers. Because there seems to be no strong resistance to some of the viruses available in germplasm of conventional breeding programs, the most promising strategies for addressing the pests involve the introduction of transgenes into the host plants.
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From page 95... ...
has suggested using the information to generate RNAi constructs to inactivate one or more of the mycotoxin biosynthesis genes; these could be delivered via viral pathogens of the fungi or by expression in the plant genome. Reducing Apigenin in Fonio and Pearl Millet with RNAi The high consumption of fonio and pearl millet is associated with goiter.
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From page 96... ...
Those approaches facilitate the stacking of new traits at valuable loci in a modular fashion and can integrate new genes at a site in the genome that has already been found to support strong constitutive expression, avoiding disruption of existing genes and adverse agricultural effects. If brought into routine use, the methods will reduce the amount of work needed to stack multiple transgenes or to introgress them between lines in a breeding program and may ease regulatory approval since there is often a requirement in many jurisdictions to provide the DNA sequences flanking the insertion sites, which will be the same whenever site-specific integration is used.
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From page 97... ...
Meiotic Recombination During meiosis in plants, the homologous chromosomes of egg-forming and pollen-forming cells undergo recombination in a process that results in new combinations of genes (alleles)
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From page 98... ...
As discussed earlier, it may be possible to insert into a chromosome sequences that preferentially undergo recombination at specific locations that is catalyzed by specific nucleases and in this way direct meiotic recombination events to some positions and away from others. Artificial Chromosomes Crop improvement involves combining the best alleles for key genes in a single variety.
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From page 99... ...
As the availability of valuable genes for crop improvement increases, it will be necessary to address questions of where and how to insert multiple genes for long-term utility. Given the potential power of this technology, a large number of projects using artificial chromosomes could be envisioned.
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From page 100... ...
With additional research, it might be possible to design transgenes and insert them into crop plants to change the mode of plant seed production from sexual fertilization to apomixis. Whether it is possible to find genes that provide such a switch and to deploy them while maintaining high seed yields is an open question.
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From page 101... ...
As the history of insect control teaches, resistance to almost all interventions evolves eventually. Thus, although the effectiveness and specificity of Bt toxins in transgenic plants are extremely important for the future (Federici, 2007; Uneke, 2007)
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From page 102... ...
Current Bottlenecks in crop improvement Transformation and Regeneration The ability to introduce new genes into plants depends on many factors, especially the frequency with which transformed cells can be induced to divide, form embryos, and then form plantlets. The genetics of the host
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From page 103... ...
The required genetic systems might come from bats, which perceive radio waves in their echolocation systems. plant are influential; many elite cultivars are among the most difficult to grow in tissue culture and to induce to form new embryos.
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From page 104... ...
Because the plant science community has made a major investment in the use of trans
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From page 105... ...
Finally, as discussed in the next section, technologies are emerging to eliminate gene flow and the problem of outcrossing with other plants. Control of Gene Flow from Transgenic Plants Fail-safe mechanisms are needed to contain gene flow and mitigate the effects of a transgene's escape to wild and weedy relatives of the crop (Valverde, 2005)
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From page 106... ...
The long history of plant breeding as the focus of plant protection efforts in Africa (Hahn et al., 1989) has meant relatively weak support for biocontrol initiatives.
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From page 107... ...
In terms of yield, they offer benefits comparable with those of long-term breeding programs for maize and cassava. The use of biocontrol agents can help to preserve the biodiversity of crop varieties inasmuch as the agents can be used with all varieties whereas conventional or transgenic breeding of varieties with insect-resistance traits usually involves a small number of varieties.
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From page 108... ...
are promising candidates to exploit as biocontrol agents against the pod borer in western Africa, where it has few natural enemies. Biocontrol with pesticides based on natural pathogens is one method
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From page 109... ...
. Viruses also have the potential to be used as biocontrol agents for biting insects.
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From page 110... ...
Biological Control of Weeds Insects are not the only organisms for which there are applications of biocontrol. For example, fungi have been isolated that control Striga in limited inundative biocontrol trials.
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From page 111... ...
2007. Biological control of bruchids in festing cowpea by the introduction of Dinarmus basalis (Rondani)
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From page 112... ...
2002. Milestones in chloroplast genetic engineering: an environmentally friendly era in biotechnology.
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From page 113... ...
Pp. 97-119 in Genomics Assisted Crop Improvement, Vol.
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From page 114... ...
Pp. 347-358 in Hymenoptera: Evolution, Biodiversity, and Biological Control.
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From page 115... ...
1984. Genetic control of meiosis in rice, Oryza sativa L
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From page 116... ...
2004. First report of cassava mosaic disease and cassava mosaic geminiviruses in Gabon.
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From page 117... ...
1997. Genome mapping, molecular markers and marker-assisted selection in crop plants.
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From page 118... ...
2005. Genetic manipulation of natural enemies: Can we im prove biological control by manipulating the parasitoid and/or the plant?
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From page 119... ...
2003. Biological control, a non-obvious component of integrated pest management for cowpea.
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From page 120... ...
2005. Implications and containment of gene flow from herbicide-resistant rice (Oryza sativa)
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From page 121... ...
1997. Efficacy of Exserohilum monoceras for the control of Echinocloa species in rice (Oryza sativa)
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