Principles of Plant Genetics and Breeding. George Acquaah
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breeders need to understand the reproductive biology of their plants as well as their taxonomic attributes. They need to know if their plants to be hybridized are cross‐compatible, as well as know in fine detail about flowering habits, in order to design the most effective crossing program.
Plant physiologyPhysiological processes underlie the various phenotypes we observe in plants. Genetic manipulation alters plant physiological performance, which in turn impacts the plant performance in terms of the desired economic product. Plant breeders manipulate plants for optimal physiological efficiency so that dry matter is effectively partitioned in favor of the economic yield. Plants respond to environmental factors, biotic (e.g. pathogens) and abiotic (e.g. temperature, moisture). These factors are sources of physiological stress when they occur at unfavorable levels. Plant breeders need to understand these stress relationships in order to develop cultivars that can resist them for enhanced productivity.
AgronomyPlant breeders conduct their work in both controlled (greenhouse) and field environments. An understanding of agronomy (the art and science of producing crops and managing soils) will help the breeder to provide the appropriate cultural conditions for optimal plant growth and development for successful hybridization and selection in the field. An improved cultivar is only as good as its cultural environment. Without the proper nurturing, the genetic potential of an improved cultivar would not be realized. Sometimes, breeders need to modify the plant growing environment to identify individuals to advance in a breeding program to achieve an objective (e.g. withholding water in breeding for drought resistance).
Pathology and entomologyDisease resistance breeding is a major plant breeding objective. Plant breeders need to understand the biology of the insect pest or pathogen against which resistance is being sought. The kind of cultivar to breed, the methods to use in breeding and evaluation all depend on the kind of pest or pathogen (e.g. its races or variability, pattern of spread, life cycle, and most suitable environment).
StatisticsPlant breeders need to understand the principles of research design and analysis. This knowledge is essential for effectively designing field and laboratory studies (e.g. for heritability, inheritance of a trait, combining ability), and evaluating genotypes for cultivar release at the end of the breeding program. Familiarity with computers is important for record keeping and data manipulation. Statistics is indispensable to plant breeding programs. This is because the breeder often encounters situations in which predictions about outcomes, comparison of results, estimation of response to a treatment, and many more, need to be made. Genes are not expressed in a vacuum but in an environment with which they interact. Such interactions may cause certain outcomes to deviate from the expected. Statistics is needed to analyze the variance within a population to separate real genetic effects from environmental effects. Application of statistics in plant breeding can be as simple as finding the mean of a set of data, to complex estimates of variance and multivariate analysis.
BiochemistryIn this era of biotechnology, plant breeders need to be familiar with the molecular basis of heredity. They need to be familiar with the procedures of plant genetic manipulation at the molecular level, including the development and use of molecular markers and gene transfer techniques.
Table 1.2 An operational classification of technologies of plant breeding.
| Classical/traditional tools; e.g. | Common use of the technology/tool |
| Emasculation | Making a completer flower female; preparation for crossing |
| Hybridization | Crossing unidentical plants to transfer genes or achieve recombination |
| Wide crossing | Crossing of distantly related plants |
| Selection | The primary tool for discriminating among variability |
| Chromosome counting | Determination of ploidy characteristics |
| Chromosome doubling | Manipulating ploidy for fertility |
| Male sterility | To eliminate need for emasculation in hybridization |
| Triploidy | To achieve seedlessness |
| Linkage analysis | For determining association between genes |
| Statistical tools | For evaluation of germplasm |
| Relatively advanced tools | |
| Mutagenesis | To induce mutations to create new variability |
| Tissue culture | For manipulating plants at the cellular or tissue level |
| Haploidy | Used for creating extremely homozygous diploid |
| Isozyme markers | To facilitate the selection process |
| In situ hybridization | Detect successful interspecific crossing |
| More sophisticated tools | |
| DNA markers | |
| RFLP | More effective than protein markers (isozymes) |
| RAPD | PCR‐based molecular marker |
| Advanced technology | |
| Molecular markers | SSR, SNPs, ISSR, DART, etc. |
| Marker‐assisted selection | Facilitate the selection process |
| DNA sequencing, NGS | Ultimate physical map of an organism |
| Plant genomic analysis‐ | Studying the totality of the genes of an organism |
| Bioinformatics | Computer‐based technology for prediction of biological function from DNA sequence data |
| Microarray analysis | To understand gene expression and for sequence identification |
| Primer design | For molecular analysis of plant genome |
| Plant transformation | For recombinant DNA work |
| OMICS technologies | For studying various aspects of the entire genome |
| Genome editing | For more efficient manipulation of the genome |
| Genome mapping | For more efficient gene discovery |
Whereas the training of a modern plant breeder includes these courses and practical experiences in these and other disciplines, it is obvious that one cannot be an expert in all of them. Modern plant breeding is more of a team than