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Plant Breeding is art and science of improving the heredity of plants for benefit of mankind. In Evolutionary concept, plant breeding is merely a continuation of the natural evolution of the crop species, changing its course of direction in the benefit of greater use to mankind.
This also be defined as science of selection -Plant breeding is essentially an election made by man of the best plants within a variable population as a potential cultivar. In other words plant breeding is a ‘selection’ made possible by the existence of variability. Selections become the earliest form of plant breeding.
History of plant breeding
Plant breeding started with sedimentary agriculture and domestication of the first agriculture plants, the cereals were chosen by the early man. They learned to look for superior plants to harvest. The domestication was hastened by early practice of harvesting mutant plants with special traits. This forms the ancient type of plant breeding. Before Mendal’s discovery there was some plant breeding include selection and hybridization experiments. But the plant breeding was only hastened after discovery of Mendal’s law on pea, thus lead a new science “Genetics”. Modern plant breeding is applied genetics but its scientific basis is broader and uses conceptual and technical tools, molecular biology, cytology, systemetics, physiology, pathology, entomology, chemistry, and statistics (biometrics) and has also developed own technology.
Plant Breeding efforts may be divided into different historical landmarks-
1. Prehistoric plant breeding- domestication of crops
This includes domestication of crops by ancient people. Domestication is also continued so far.
2. Pre-mendel Plant Breeding
Economic botany and great Columbian exchange-
There were some experiments before Mendel on hybridization and selection. Some seed companies were also established based on success on selection. Another part discovery of North America by Columbus in 1492 triggered unprecedented transfer of plant resources, first from old world to the new world, or the New World to the old. This increased variability in total genetic resources.
3. Mendelian genetics and the green revolution
Mendel's experiment stimulated research by many plant scientists dedicated in improving crop production (plant breeders) through plant breeding. The most famous contribution of Mendelian genetics was hybridization. There was remarkable improvement in three economically important crops that made the food deficit world into a food surplus world. This is called the green revolution. The first, development of hybrid maize, the second development of high yielding and input responsive “semi-dwarf wheat” (CIMMYT breeder N.E. Borlaug received Nobel prize for peace in 1970), the third is high yielding “short sutured rice” cultivars. Similarly the remarkable improvements were done in other crops like sorghum and alfalfa.
4. Molecular genetics and bio-revolution
Totipotency shown by plants gave rise to tissue culture techniques such as somatic hybridization, doubled haploid production, clonal propagation, and in-vitro selection. Intensive research in molecular genetics has led to development of recombinant DNA technology (popularly called Genetic Engineering). Advancement in Biotechnological techniques has opened many possibilities for breeding crops. Thus mendelian genetics allowed plant breeders to perform some genetic transformation in few crops, molecular genetics provides key not only the manipulation of the internal structure but also their “crafting” according to plan.
Physiological and Molecular Wheat Breeding
Plant breeding has traditionally applied a trial-and-error approach in which large numbers of crosses are made from many sources of parental germplasm. Progenies are evaluated for characters of direct economic interest (e.g., grain yield and grain quality) in target environments. Good performing parental germplasm, crosses, and progenies are selected for further use or testing. In many programs “breakthroughs” in improvement are made simply by finding superior sources of parental germplasm among the numerous sources tested. This conceptually simple approach has been highly successful in many crop species and numerous breeding programs. The approach has often succeeded in the absence of in-depth knowledge about the physiological basis for superior performance. In some crops such knowledge has been obtained by doing retrospective analyses of prior genetic gains. Breeders have not applied this knowledge to a significant extent as a guide to further improvements, but instead have taken any avenue of improvement that happens to arise from direct selection for yield and economic performance. However with increased population, there is need to increase yield further and breeding require more scientific approaches to handle the problem.
Genetic basis of physiological traits
During the past two decades, molecular tools have aided tremendously in the identification, mapping, and isolation of genes in a wide range of crop species. The vast knowledge generated through the application of molecular markers has enabled scientists to analyze the plant genome and have better insight as to how genes and pathways controlling important biochemical and physiological parameters are regulated. Three areas of biotechnology have had significant impact: the application of molecular markers, tissue culture, and incorporation of genes via plant transformation. Molecular markers have enabled the identification of genes or genomic regions associated with the expression of qualitative and quantitative traits and made manipulating genomic regions feasible through marker assisted selection. Molecular marker applications have also helped us understand the physiological parameters controlling plant responses to biotic and abiotic stress or, more generally, those involved in plant development.
Molecular Wheat Breeding
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Molecular wheat breeding is application of biotechnological tools in wheat improvement such as gene transfor (genetic engineering) and marker assisted selection. Such changes aims to alter the physiological pathways through change in genetic structures. There are many successful examples of such kind.
References on application
PHYSIOLOGICAL TRAITS FOR IMPROVING WHEAT YIELD UNDER A WIDE RANGE OF CONDITIONS pdf file
Physiological approaches to wheat breeding FAO site
Physiological traits for abiotic stress tolerance breeding
Physiological Traits to Improve the Yield of Rainfed Wheat: Can Molecular Genetics Help?CIMMYT site link
Evaluating Potential Genetic Gains in Wheat Associated with Stress-Adaptive Trait Expression in Elite Genetic Resources under Drought and Heat Stress crop science
Physiological traits for biotic stress tolerance breeding
M. J. Foulkes, N. D. Paveley, A. Worland, S. J. Welham, J. Thomas, J. W. Snape. Major Genetic Changes in Wheat with Potential to Affect Disease Tolerance. Phytopathology, July, Volume 96, Number 7, Pages 680-688 (doi: 10.1094/PHYTO-96-0680)click link
Rosyara, U.R., K. Pant, E. Duveiller and R.C. Sharma. 2007. Variation in chlorophyll content, anatomical traits and agronomic performance of wheat genotypes differing in spot blotch resistance under natural epiphytotic conditions. Australasian Plant Pathology 36 : 245–251.
Rosyara, U.R., R.C. Sharma, and E. Duveiller. 2006. Variation of canopy temperature depression and chlorophyll content in spring wheat genotypes and association with foliar blight resistance. J. Plant Breed. Gr. 1 : 45-52.
Rosyara, U.R., R.C. Sharma, S.M. Shrestha, and E. Duveiller. 2005. Canopy temperature depression and its association with helminthosporium leaf blight resistance in spring wheat. Journal of Institute of Agriculture and Animal Science 26: 25-28.
Rosyara, U.R., R.C. Sharma, S.M. Shrestha, and E. Duveiller. 2006. Yield and yield components response to defoliation of spring wheat genotypes with different level of resistance to Helminthosporium leaf blight. Journal of Institute of Agriculture and Animal Science 27. 42-48.
Rosyara, U. R. 2002. Physio-morphological traits associated with Helminthosporium leaf blight resistance in spring wheat. Masters’ Thesis. Tribhuvan University, Institute of Agriculture and Animal Science, Rampur, Chitwan, Nepal. supported by CIMMYT International. Available at CIMMYT library
Useful Books
Hayward, M. D., N. O. Bosemark, and I. Romangosa. 1993. Plant Breeding: Principle and Prospects. Chapman and Hall, London.
Wood, D. R., K. M. Rawal, and M. N. Wood (eds). 1983. Crop Breeding. American Society of Agronomy, Crop Science Society of America, Madison, Wisconsin.
Allard, R. W. 1960. Principles of Plant Breeding. John Wily and Sons Inc. New York.
Simmonds, N. W. 1979. Principles of Crop Improvement. Longman Group Limited, London.
Singh, B. D. 2000. Plant Breeding. Sixth ED. Kalyani Publishers, New Delhi.
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