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Essay on Plant Breeding
Essay Contents:
- Essay on the Definition of Plant Breeding
- Essay on the History of Plant Breeding
- Essay on the Features of Plant Breeding
- Essay on the Field of Plant Breeding
- Essay on the Branches of Plant Breeding
- Essay on the Objectives of Plant Breeding
- Essay on Important Disciplines and Plant Breeding
- Essay on Some Indian Plant Breeders
- Essay on the Significant Achievements of Plant Breeding
- Essay on the Recent Trends Affecting Plant Breeding
- Essay on the Applications of Plant Breeding
- Essay on the Future Prospects of Plant Breeding
Essay # 1. Definition of Plant Breeding:
Plant breeding can be defined as a science as well as an art of improving the genetic make-up of plants in relation to their economic use. Recently plant breeding has been described as a technology of developing superior crop plants for various purposes.
Plant breeding is an applied branch of Botany which deals with the improvement of economically important plants.
Plant breeding is a purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant.
Performance of a crop or animal is mainly due to its genotype and the environment in which it is growing. Environment represents all living and non-living factors surrounding an organism. Genotype is the genetic set up of an organism. Genotype is responsible for performance of an organism. Environment permits the expression of genotype. Variation in skin colour due to shade or by spending more time in sun is due to environmental change. However, normal difference in colour of various organisms is due to their genotypes.
Plant breeding is a long and slow process. It requires technical knowledge, involves many operations, procedures and skill. Plant breeding is both art and a science.
Essay # 2. History of Plant Breeding:
Plant breeding came into existence when man started selecting superior plants for his use. Thus plant breeding originated with human civilization. At that time selection of superior plants was entirely based on human skill and plant breeding was purely an art. The genetic principles were utilized in the development and selection of superior plants after the discovery of sex in plants and Mendel’s laws of inheritance. Since then plant breeding has become a science in addition to an art.
The history of plant breeding is arbitrarily divided into two phases, viz.:
(A) Classical plant breeding, and
(B) Modern plant breeding.
A brief description of these two phases of plant breeding in terms of discoveries made/concepts developed, breeding techniques employed, products developed, and major achievements is presented below:
(A) Classical Plant Breeding [1900-1980]:
Classical plant breeding started after the rediscovery of Mendell’s results in 1900 independently by three scientists [de Vries-Holland, Correns-Germany and Tschermak-Austria], Classical plant breeding used deliberate interbreeding (crossing) of closely or distantly related individuals to produce new crop varieties or lines with desirable properties.
Plants are crossbred to introduce traits/genes from one variety or line into a new genetic background. For example, a mildew-resistant pea may be crossed with a high-yielding but susceptible pea, the goal of the cross being to introduce mildew resistance without losing the high-yield characteristics.
Progeny from the cross would then be crossed with the high-yielding parent to ensure that the progeny were most like the high-yielding parent, (back-crossing). The progeny from that cross would then be tested for yield and mildew resistance and high-yielding resistant plants would be further developed. Plants may also be crossed with themselves to produce inbred varieties for breeding.
(i) Discoveries/Concepts Developed:
Several important concepts of plant breeding were developed by various scientists. The important concepts include principles of Inheritance, progeny selection, individual plant selection, pure line selection, dominance hypothesis, over dominance hypothesis, recurrent selection, backcross, bulk and pedigree methods, single seed descent, Floor hypothesis, multiple factor hypothesis, self-Incompatibility, male sterility, diallel selective mating, bi-parental mating, vertical and horizontal resistance, ideotype breeding, etc.
(ii) Breeding Techniques Used:
Classical breeding relied largely on homologous recombination between chromosomes to generate genetic diversity. The classical plant breeder may also make use of a number of in-vitro techniques such as protoplast fusion, embryo rescue or mutagenesis to generate diversity and produce hybrid plants that would not exist in nature.
In the beginning, mainly plant introduction, mass selection and progeny selection techniques were used. Later inter-varietal hybridization, interspecific hybridization, inter-generic hybridization and mutation breeding techniques were applied, whenever required to meet specific plant breeding objectives.
(iii) Products Developed:
In the beginning, the main products developed included Landraces, mass selected varieties, and exotic varieties. Later on Semi-dwarf varieties in wheat and rice, and hybrids in maize, pearl-millet, sorghum, cotton, pigeon pea, rice, wheat and some vegetable crops were developed.
(iv) Major Achievements:
The significant achievements of classical plant breeding include – (a) development of semi-dwarf varieties of wheat and rice resulting in green revolution, and (b) development of productive hybrids in pearl-millet, sorghum, cotton, pigeon pea, rice, wheat and some vegetable crops.
(B) Modern Plant Breeding [1980 onwards]:
Modern plant breeding started from 1980 onwards with the application of agricultural biotechnology in crop improvement. Modern plant breeding uses techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into plants. Modern facilities in molecular biology have converted classical plant breeding to molecular plant breeding.
A brief description of modern plant breeding in terms of discoveries/concepts developed, products developed, breeding techniques employed and major achievements is presented below:
(i) Discoveries/Concepts Developed:
Several important concepts of plant breeding were recently developed by various scientists. The important concepts include transgenic breeding, molecular plant breeding, terminator technology, traitor technology, organic plant breeding and participatory plant breeding. [Terminator and traitor technologies have not been permitted for use]. Now these concepts are being used widely for development of new crop cultivars to meet specific breeding objectives.
(ii) Breeding Techniques Used:
The important crop improvement techniques which are being used to enhance the speed of the conventional breeding techniques include genetic modification, marker assisted selection, somatic hybridization, plant tissue culture techniques, etc.
(iii) Products Developed:
The important products of the modern plant breeding are transgenic varieties in several crops such as rapeseed and mustard, potato, tobacco, tomato, soybean, sugar beet, Lucerne and hybrids in maize and cotton. Organic varieties are being developed in some vegetable crops.
(iv) Major Achievements:
The significant achievement of modern plant breeding include development of transgenic varieties in many crops as a result of gene revolution [use of agricultural biotechnology]. This has resulted in quantum jump in productivity of various field crops.
Several significant contributions have been made in plant breeding by various workers from time to time.
Essay # 3. Features of Plant Breeding:
The important features of plant breeding are given below:
1. Art refers to human imagination, creativity and skill. Plant breeding is an art because selection of superior plants requires human skill, imagination and experience.
2. Science refers to systematic knowledge of a subject gained through human observations and experiments involving certain principles. Plant breeding is a science because development of superior varieties or hybrids involves genetic principles, sequential steps (hybridization, selection, evaluation, multiplication, release, etc.) and experimentation. It is an applied branch of genetics which is used for improving and changing the genetic makeup of crop plants.
3. Technology refers to development of a useful commercial product/service involving scientific principles and human skill. In plant breeding, the ultimate aim is to develop superior varieties or hybrids for commercial cultivation.
Thus plant breeding is an art, a science and a technology of developing genetically superior plants in terms of their economic utility for the mankind. Since plant breeding deals with genetic improvement of crop plants, it is also known as the science of crop improvement.
4. Plant breeding is considered as the current phase of crop evolution.
Essay # 4. Field of Plant Breeding:
The field of plant breeding can be divided into three important areas, viz.:
1. Plant genetic resources or germplasm,
2. Breeding techniques, and
3. Seed production techniques.
A brief description of each area is presented below:
1. Germplasm:
Germplasm refers to the total variability found in a plant species. Plant genetic resources represent an important area of plant breeding. It deals with collection, conservation, evaluation, documentation and utilization of cultivated and wild relatives of crop plants. Now plant genetic resources is being developed as, a separate discipline in many crop breeding institutes.
2. Breeding Techniques:
This is another important area of plant breeding which deals with various genetic principles and procedures of crop improvement. Various plant breeding methods, their applications, merits and demerits are covered in this area. It consists of general and special breeding methods and mission oriented programmes such as breeding for disease and insect resistance, drought and salinity resistance, improved quality, multiple cropping systems, etc.
(a) General Breeding Methods:
This group includes introduction, selection (pure line selection, mass selection) and hybridization especially inter varietal hybridization.
(b) Special Breeding Methods:
This group deals with mutation breeding, polyploidy breeding, wide crossing and special techniques such as use of tissue culture and genetic engineering in crop improvement.
3. Seed Production Techniques:
The third important area of plant breeding is seed production technology. This is being developed as a separate discipline in many crop breeding institutes. It deals with principles and methods of improved seed production.
Essay # 5. Branches of Plant Breeding:
There are several branches of plant breeding which have been identified on the basis of techniques and experimental material used and plant trait improved.
These branches are defined below:
1. Agricultural Plant Breeding:
It deals with genetic improvement of agriculturally important plants; also known as crop breeding. It includes improvement of various field crops such as cereals, millets, pulses, oilseeds, fibre crops, sugar yielding crops, etc.
2. Horticultural Plant Breeding:
It deals with genetic improvement of various horticultural crops such as vegetables, fruits and ornamental plants.
3. Tree Breeding:
It deals with genetic improvement of forest trees especially timber yielding plants.
4. Medicinal Plant Breeding:
It deals with genetic improvement of various medicinal plants.
5. Stress Breeding:
It deals with development of crop plants resistant to biotic (diseases, insects and parasitic weeds) and abiotic (drought, salinity, alkalinity, acidity, frost, cold, heat, metal toxicity, nutrient deficiency, etc.) stresses; also called resistance breeding.
6. Quality Breeding:
It deals with genetic improvement of crop plants in relation to various quality attributes such as market quality, industrial quality and nutritional quality.
7. Mutation Breeding:
It deals with genetic improvement of crop plants for various economic characters through the use of various physical and chemical mutagens.
8. Polyploidy Breeding:
It deals with genetic improvement of crop plants through manipulation of chromosome number such as development of triploid varieties in banana, grapes, watermelon, etc.
9. Physiological Crop Breeding:
It deals with genetic improvement of crop plants in relation to physiological parameters such as improvement in CO2 fixation efficiency, nutrient uptake capacity, harvest index; and reduction in photo-respiration, transpiration rate, etc. It also includes ideotype breeding.
10. Introgressive Breeding:
In deals with genetic improvement of crop plants by, transferring desirable genes from wild species into the cultivated species.
11. Transgenic Breeding:
It deals with genetic improvement of crop plants for various economic characters, through biotechnology (genetic engineering). It utilizes transgenes bypassing sexual process.
12. Molecular Breeding:
It deals with genetic improvement of crop plants for various economic characters, through indirect selection for linked molecular markers (DNA markers). It utilizes molecular techniques such as RFLP, AFLP, CAPS, RAPD, SSR, etc. for selection of superior plants.
13. Maintenance Breeding:
It deals with principles and methods of pure seed production. It also deals with ways and means of maintaining genetic and physical purity of released and notified varieties and parents of hybrids; also called seed production technology.
14. Plant Genetic Resources:
It deals with collection, conservation, and utilization of crop plants and their wild relatives. Now Plant Genetic Resources is being developed as a separate discipline in many crop breeding institutes.
Essay # 6. Objectives of Plant Breeding:
The prime objective of plant breeding is to develop superior plants over the existing ones in relation to their economic use. The objectives of plant breeding differ from crop to crop. However, there are some objectives which are common in majority of field crops.
A brief account of some important objectives is given below:
1. Higher Yield:
The ultimate aim of plant breeder is to improve the yield of economic produce. It may be grain yield, fodder yield, fibre yield, tuber yield, cane yield or oil yield depending upon the crop species. Improvement in yield can be achieved either by evolving high yielding varieties or hybrids.
2. Improved Quality:
Quality of produce is another important objective in plant breeding. The price of produce is determined by its quality. Again quality differs from crop to crop. It refers to cooking quality in rice, baking quality in wheat, malting quality in barley, fibre length, strength and fineness in cotton, nutritive and keeping quality in fruits and vegetables, protein content in pulses, oil content in oil-seeds and sugar content in sugarcane and sugar beet, etc.
3. Biotic Resistance:
Crop plants are attacked by various diseases and insects, resulting in considerable yield losses. Genetic resistance is the cheapest and the best method of minimizing such losses. Resistant varieties are developed through the use of resistant donor parents available in the gene pool.
4. Abiotic Resistance:
Crop plants also suffer from abiotic factors such as drought, soil salinity, heat, wind, cold and frost. Breeder has to develop resistant varieties for such environmental conditions.
5. Earliness:
Earliness is the most desirable character which has several advantages. It requires less crop management period, less insecticidal sprays, permits double cropping system and reduces overall production cost. Thus earliness is an important objective in plant breeding programmes. Determinate growth habit has close association with earliness.
6. Photo and Thermo-Insensitivity:
Development of varieties insensitive to light and temperature helps in crossing the cultivation boundaries of crop plants. In maize, rice and potato now varieties are available which can be grown during summer as well as winter season. Evolution of photo and thermo-insensitive varieties permits their cultivation in new areas outside the boundaries of cultivation of a crop species.
7. Synchronous Maturity:
It refers to maturity of a crop species at one time. This character is highly desirable in crops like green-gram, cowpea, and cotton where several pickings are required for crop harvest.
8. Desirable Agronomic Traits:
It includes plant height, branching, tillering capacity, growth habit, etc. Usefulness of these traits also differs from crop to crop. For example, tallness, high tillering and profuse branching are desirable characters in fodder crops, whereas dwarfness is a desirable character in wheat, rice, sorghum and pearl-millet. Dwarfness confers lodging resistance in these field crops, in addition to better fertilizer response.
9. Removal of Toxic Compounds:
It is essential to develop varieties free from toxic compounds in some crops to make them safe for human consumption. For example, removal of neurotoxin in Khesari, which leads to paralysis of lower limbs, erucic acid from Brassica which is harmful for human health and gossypol from the seed of cotton, is necessary to make them fit for human consumption.
10. Wider Adaptability:
Adaptability refers to suitability of a variety for general cultivation over a wide range of environmental conditions. Adaptability is an important objective in plant breeding because it helps in stabilizing the crop production over regions and seasons.
11. Some other Characters:
In some crops such as green-gram, black-gram and pea, seeds germinate in the standing crop before harvesting if rains are received. A period of dormancy has to be introduced in these crops to check loss due to germination. In arboreum cotton shedding of kapas after boll bursting is a serious problem. Locule retentive varieties have to be developed in this species of cotton. The shattering of pods is serious problem in green-gram. Hence, resistance to shattering is an important objective in green-gram.
Essay # 7. Important Disciplines and Plant Breeding:
Plant breeding involves several disciplines for development of improved cultivars.
The important disciplines which have close relationship with plant breeding and are involved in crop improvement work include:
(1) Cytogenetics and genetics,
(2) Morphology and taxonomy,
(3) Plant physiology,
(4) Plant pathology,
(5) Entomology,
(6) Agronomy and soil science,
(7) Biochemistry,
(8) Agricultural engineering,
(9) Statistics and biometrics,
(10) Computers and
(11) Plant biotechnology (Table 1.1).
Knowledge of all these disciplines is essential for a plant breeder to start a judicious breeding programme.
Relationship of all these disciplines with plant breeding is presented below:
(1) Cytogenetics and Genetics:
Plant breeding is an applied branch of genetics. It involves various genetical principles. Hence, knowledge of cytogenetics and genetics is essential to start a crop improvement programme.
(2) Morphology and Taxonomy:
Resistance to biotic and abiotic factors is generally associated with some morphological characters. Sometimes, resistant genes are found in wild relatives of crop plants. Moreover, development of ideal plant type has some morphological bases. Hence some knowledge of plant morphology and taxonomy is essential to a plant breeder for utilization of morphological variation and transfer of resistant genes from wild sources.
(3) Plant Physiology:
Crop plants suffer from abiotic stresses, viz. drought, salinity, heat and cold. Development of varieties for such situations requires some knowledge of plant physiology. Moreover, sometimes breeder has to develop physiologically efficient genotypes through the exploitation of genetically controlled physiological variation.
For example, there are some physiological parameters, viz.:
(i) High CO2 fixation efficiency,
(ii) High translocation efficiency,
(iii) High nutrients absorption capacity,
(iv) Low transpiration rate,
(v) Low photorespiration,
(vi) High harvest index,
(vii) High sink capacity,
(viii) Photo insensitivity, and
(ix) Thermo insensitivity, which help in promoting crop yield and production.
Utilization of these physiological parameters in plant breeding requires a close cooperation of plant physiologist or some training in plant physiology.
(4) Plant Pathology:
Crop plants are infested by a number of fungal, bacterial and viral diseases. Plant breeder has to evolve resistant varieties for various diseases for which some knowledge of plant pathology is essential. Moreover, close association of plant pathologist is essential for achieving such goals.
(5) Entomology:
Crop plants are also attacked by large number of insect species. In some cases, insects pose serious threat to the cultivation of a plant species. In such situation, genetic resistance is the only answer. For development of insect resistant or tolerant cultivars, a plant breeder needs close cooperation of entomologist or some training in entomology.
(6) Agronomy and Soil Science:
Knowledge of the principles of crop production is essential to raise a good crop. This helps in selection and proper evaluation of breeding material. The material should be evaluated under optimum conditions. Sometimes, the breeder has to evolve crop varieties resistant to salinity or acid sulphate soils. The resistant lines are identified and isolated by screening the available germplasm on saline or acidic soils. Accomplishment of such task requires close cooperation of soil scientist or some training in soil science.
(7) Biochemistry:
Various chemical tests are conducted to determine protein, amino acids, oil and fatty acid contents especially in food crops. Moreover, chemical tests are also conducted to determine the presence of toxic compounds in crop like Khesari dal (Lathyrus sativus), brassica and cotton seed. Such task requires close cooperation of a biochemist or some knowledge of biochemistry.
(8) Agricultural Engineering:
Use of machinery in crop harvesting requires development of varieties with adaptation to mechanical harvesting. In wheat, sorghum, berseem and many vegetable crops including tomato and potato, varieties are available which can be harvested with machine. Development of crop varieties suitable for mechanical harvesting needs close cooperation between agricultural engineer and plant breeder.
(9) Statistics and Biometrics:
Plant breeder has to test the performance of various breeding materials in field experiments. Hence, knowledge of experimental designs and statistical methods is essential for a plant breeder. He has to carryout lot of biometrical analysis, viz. correlations, path coefficient, discriminant function, diallel, partial diallel, line x tester analysis, stability analysis, D2 statistics, etc. Hence, he should be well versed with various biometrical techniques.
(10) Computer:
It is difficult to carryout various biometrical analyses with simple calculators. Now computer programmes are available for various biometrical analyses. The calculations which require months together for completion can be finished in few minutes through computers. Moreover, computers are useful in compiling information and plant modeling studies. Thus, some knowledge of computer handling is essential to a plant breeder.
(11) Plant Biotechnology:
Plant biotechnology is a combination of plant tissue culture and genetic engineering. Biotechnology is useful tool for development of transgenic crop plants with herbicide resistance, good quality and resistance to biotic and abiotic stresses. It also makes distant crosses possible through somatic hybridization. Thus, knowledge of plant biotechnology is essential for a plant breeder.
Essay # 8. Some Indian Plant Breeders:
In India remarkable contribution has been made in the field of crop improvement.
The significant contribution of some Indian Plant Breeders is briefly presented below:
1. T.S. Venkatraman:
He was an eminent sugarcane breeder. He transferred thick stem and high sugar contents from tropical noble cane to North Indian Canes. This process is known as noblization of sugarcane. He developed several varieties of sugarcane having high yield and high sugar content. He was Director of Sugarcane Breeding Institute, Coimbatore.
2. B. P. Pal:
He was an eminent breeder known for his contributions to the breeding of superior disease resistant N.P. varieties of wheat. He was the first Director General of ICAR.
3. M.S. Swaminathan:
He is a famous plant breeder responsible for green revolution in India. He developed high yielding varieties of wheat and rice. He was Director General ICAR and later Director General of IRRI, Philippines from 1982-1988.
4. Pushkarnath:
A famous potato breeder who, developed several high yielding varieties of potato. He was director of CPRI, Shimla.
5. N.G.P. Rao:
He is an eminent Sorghum breeder. He developed several high yielding hybrids of grain Sorghum. He was chairman of ASRB and Vice-Chancellor of Marathwada Agricultural University, Parbhani.
6. K. Ramiah:
He was a renowned rice breeder. He developed several high yielding varieties of rice when he was Director of CRRI, Cuttack.
7. Ram Dhan Singh:
He was an inborn plant breeder who developed several superior varieties of wheat in Punjab. His famous variety was C 591.
8. D.S. Athwal:
He is a famous pearl-millet breeder. He worked in PAU, Ludhiana and developed several superior varieties of Pearl-millet (bajra).
9. Bosisen:
He was an eminent maize breeder. He developed several varieties of maize for Hill region of Uttrakhand. He established the Vivekanand Parvatiya Krishi Anusandhan Shala at Almora, Uttrakhand was Director of the same till his death.
10. Dharampal Singh:
He was an eminent oil-seed breeder. He released several varieties of oilseeds (rapeseed and mustard) from Kanpur. He was Vice Chancellor of G.B. Pant University of Agriculture and Technology, Pantnagar.
11. C. T. Patel:
He was a famous cotton breeder who developed world’s first cotton hybrid in 1970 for commercial cultivation in India. He is known as father of hybrid cotton.
12. V. Santhanam:
He is a famous cotton breeder who has developed several high yielding varieties of upland cotton and two varieties of Egyptian cotton. He was the first Project Coordinator of All India Coordinated Cotton Improvement Project and later worked in FAO as cotton consultant.
Essay # 9. Significant Achievements of Plant Breeding:
The significant achievements of plant breeding is to effect genetic improvement in economic plant parts. The economic part of a plant varies from crop to crop. It may be seed, fruit, stem, root, leaf or flower. Moreover, improvement is made for quality, biotic and abiotic resistance, crop duration, etc.
Major achievements of plant breeding include:
(1) Improvement in yield,
(2) Improvement in quality,
(3) Resistance to biotic and abiotic stresses,
(4) Earliness and
(5) Adaptability.
These are briefly discussed below:
(1) Improvement in Yield:
Improvement in yield can be achieved in three ways, viz.:
(i) Through effective control of diseases, insects and weeds,
(ii) Adoption of improved agronomic practices and
(iii) Development of improved cultivars.
There are several examples of improvement in yield through the use of improved cultivars.
The genetic potential for yield can be increased in two ways, viz.:
(i) By increasing the total amount of dry matter production and
(ii) By converting a greater proportion of dry matter into the desired economic produce. The dwarf varieties developed in cereals have higher yield potential because of an improved ratio of grain to total dry matter (harvest index).
The yield potential of wheat, rice, Sorghum and pearl-millet has been doubled throughout the world due to improvement in harvest index. The concept of crop ideotype has also helped in building up of ideal plant types for a given set of environmental conditions. However, the concept of plant type has contributed more in cereals than in other crops.
Higher yields have also resulted due to exploitation of hybrid vigour in many crops. Heterosis has been successfully exploited in maize, Sorghum and pearl-millet. The availability of cytoplasmic male sterility has facilitated the production of hybrid seed in these crops. The tift 23A and Kafir 60 are the important sources of male sterility in pearl-millet and Sorghum respectively.
Efforts were also made for exploitation of hybrid vigour in some self- pollinated crops like, cotton, wheat and rice. India is the pioneer country for the successful exploitation of hybrid vigour in cotton on commercial scale. The first hybrid was released in 1970 from cotton Research Station, Surat of Gujarat Agricultural University by Dr. C.T. Patel.
Since then several cotton hybrids have been released in India. Now Bt. cotton hybrid cover about 96% of total cotton area in India and contribute about 98% to the total cotton production. Hybrid wheat was developed in Japan but much success could not be achieved in this direction. Now China has developed hybrid rice for commercial cultivation.
(2) Improvement in Quality:
Significant achievements have been made in improving the nutritional value of crop products. For example, elimination of the toxic substance erucic acid from the oil of Brassica, entirely through genetic means has greatly enhanced the value of this crop (rape and mustard) as a source of edible oil. Presence of neurotoxin in Khesari dal (Lathyrus sativus) seed has toxic effects on human health, which results in paralysis of lower limbs called lathyrism.
Now varieties of Lathyrus have been developed from IARI which have neurotoxin content below the critical level. In cotton, there is increasing demand for easy care fabrics that are easily washed and need little pressing. Some varieties have been developed in cotton which has easy care properties.
Similarly, varieties with high sugar content in sugarcane and sugar beet, high oil content in oil seed crops and high protein content in pulse crops have been released. In fruit and vegetable crops, varieties with attractive features and good keeping quality have been developed.
(3) Resistance to Biotic and Abiotic Stresses:
Crop plants suffer from both biotic and abiotic stresses. Biotic stress results due to the attack of diseases, insects and parasitic weeds; and abiotic stress is caused due to drought, salinity, cold, heat, etc. The damage from insects and diseases has been substantially reduced in many crops by developing resistant varieties.
For example, in cotton bollworm resistant transgenic Bt. hybrids have been developed. Moreover, protection from diseases has also been provided through the development of multiline cultivars in wheat, barley and oats and synthetic cultivars in maize. Similarly, varieties tolerant to drought and salinity have been developed in many field crops.
Lodging also used to cause considerable yield losses in many field crops like wheat, rice, Sorghum and pearl millet. Now dwarf varieties with stiff straw have been developed in these crops which can very well withstand lodging. The dwarf varieties can be successfully grown under high fertility conditions without the risk of lodging.
Shorter and stiffer straw enables the plant to carry a heavy crop and withstand the battering of strong winds and heavy rains. Norin 10 in wheat and Dee-Geo-Woo-Gen in rice are the important sources of dwarfing genes. In Castor bean, plant height has been reduced from 10 meters to 1.5 meters. In cereals like wheat and rice, reduced stem height leads to increased development of ear resulting in improved harvest index and higher yields.
(4) Earliness:
Earliness is a desirable character which has several advantages. Early varieties permit multiple cropping systems, escape from late season pests, and reduce cost on pesticidal sprays and management of crop.
Maturity duration has been reduced in many crops. For example, maturity has been reduced from 270 days to 170 days in cotton, from 270 days to 120 days in pigeon-pea, from 360 days to 270 days in sugarcane and from 270 days to 180 days in castor bean.
Development of early maturing varieties in these crops has significantly contributed to increased production, because early varieties can fit well in the multiple cropping systems resulting in increase of overall production.
(5) Adaptability:
The crop production has significantly increased after 1965 in many crops. This has resulted mainly due to high yield potential and stable performance of newly developed cultivars in various crops. Development of the concept of stability analysis has helped in evaluation of crop varieties in terms of their adaptability.
Stability refers to suitability of a variety for general cultivation over a wide range of environmental conditions. Adaptability is assessed through multi location or multi season testing. Varieties with wide adaptability have been developed in wheat, rice Sorghum, maize, pearl-millet and many other crops.
The adaptation of crops for mechanical harvesting is also important. In cereals like wheat and rice, varieties of uniform height and maturity has been developed which facilitate mechanical harvesting. In USA, cotton varieties which can be mechanically picked have been released for commercial cultivation.
Essay # 10. Recent Trends Affecting Plant Breeding:
Gepts and Hancock (2006) have reviewed the major themes discussed during a symposium hosted 10-11 March, 2005 by the Plant Breeding and Genetics Group at Michigan State University, USA.
These themes included defining plant breeding, describing plant breeding education and employment, designing a contemporary education in plant breeding, supporting plant breeding education programmes, addressing the critical needs of breeding specialty and subsistence crops and promoting awareness of plant breeding.
According to this review, plant breeding is affected by increasing globalization in two major ways, namely, an increasing commercialization of agricultural products with its additional export opportunities and increased competition from other regions with lower production cost.
Furthermore, new trade rules and award of subsidies can rapidly change the competitive climate among countries leading to change in value of individual commodities at the international level and thus increasing or decreasing the importance of plant breeding programmes over a short period of time.
The rules and regulations on access to biodiversity have come into play. Biodiversity laws and treaties and rules on protection of plant varieties allow institutions and companies to have ownership of germplasm and cultivars. This is needed to have required investment in R&D programmes so that innovative cultivars keep on coming through public and private sector seed companies.
However, the full impact of this change on plant breeding innovation, germplasm accessibility and germplasm exchange remains to be seen. Public research and even private research establishments have shifted their focus from applied field experiments to genomics and molecular biology.
However, it must be kept in mind that improved cultivars are still bred through conventional breeding approaches, although trait integration, a component of plant breeding, is a different story where molecular breeding has rightfully occupied centre stage.
Pursuing genetic engineering as an alternative rather than as a complement to plant breeding has large consequences on choices about R&D investment, education and employment. In many developing countries, plant breeders are replaced by biotechnologists. This change in focus, will not lead to increase in productivity unless a critical mass of conventional plant breeders remains in place to translate technologies into new cultivars.
A successful plant breeder needs knowledge on principles and practices of plant breeding, Mendelian/transmission genetics, applied statistics and experimental design, quantitative genetics and selection theory, production principles and practices for agronomic, horticultural and tree crops, pest science (plant pathology, entomology and weed science), applied genomics, including marker assisted selection, and plant reproductive biology.
Additional areas of lesser importance are biotechnology (tissue culture, transformation), evolutionary and population genetics, crop physiology and plant biochemistry, and cytogenetics. A modern day plant breeder must also have exposure to business management, human resources, priority setting, budget, intellectual property rights and leadership and teamwork.
Private sector can play a significant role in plant breeding curriculum through participation in thesis and curriculum committee, guest lectures, seminars, Q&A sessions, internship with private seed company breeders, endowment of professorships or breeding programmes, provision of scholarships, provision of grants for research, study or conferences.
Novel collaborations could be forged between universities and plant breeding research institutes, such as the centres of the Consultative Group on International Agricultural Research (CGIAR). The universities could provide basic education in plant breeding and research institutes could provide practical and field breeding experience.
Flavell (2004) has elaborated on conventional plant breeding and its integration with plant biotechnology in perspective. He puts historical perspectives and states that plant breeding has been practiced in primitive forms in the early civilization where settlements were made possible by the purposeful growing of specific selected plants, i.e. agriculture for food, feed and fibre.
These selected plants (lanraces) formed the basis of agriculture for thousands of years. Most of the plants used directly to produce agricultural products today have been selected and bred specifically for the purpose from their wild relatives.
Today’s most advanced plant breeding involves the improvement of plants by selection of the most favourable combinations of the alleles in the species via knowledge based procedures and in some cases via addition of new genes designed in the laboratory to confer specific properties.
The whole process involves integration of genetics, mathematics with statistics, chemistry, pathology, cytology, molecular biology and computational biology, together with considerable automation, data handling and analytical systems.
According to him, it is molecular biology, automation and data handling that have changed drastically over the past several years. These technical advances have been extraordinary and have set the stage for developments that offer opportunities unparalleled in the history of man’s exploitation of plants.
There are many outcomes that illustrate the success of plant breeding globally. For example, cultivated maize and wheat are essentially man made crops. Their ancestral wild forms are considerably inferior for food production. Today’s tomatoes and potatoes have been bred from small toxic wild forms.
The Green Revolution in wheat and rice has been possible because of the recognition and incorporation of novel dwarfing mutant alleles into cultivars in 1950s and 1960s. In any plant breeding programme, the product development depends on the knowledge of the consumers and farmers to be served and the environments, in which, the plant has to be grown and biological and genetic features of the species. Yield is near universal breeding objective.
To optimize yield, one has to select for resistance/tolerance to pests and diseases and abiotic stresses. The genetic features of a species determine whether true breeding homozygous cultivars or F1 hybrids need to be bred. In case of development of true breeding cultivars, the breeding strategy involves creation of new combination of genes, selection of preferred phenotypes followed by production of homozygous lines.
Homozygosity could also be created through double haploidy in certain crops. For out-breeding or cross-pollinated species, the ultimate cultivar can be an improved population of genotypes (mass selected populations, composites, synthetics) or single or double cross hybrids, etc. Plant breeding and plant performance are based on all the genes in a plant. Thus, they have a very complex basis.
This complexity has been modelled by quantitative geneticists, but now the complexity is being redefined in physical and functional details by genomics. Genomics is the term given to the generation and study of large quantities of data comprising chromosomal DNA sequences, genes, the time and place of expression of the genes, gene-phenotype associations, genetic and physical maps and details of the genetic variation.
Essay # 11. Applications of Plant Breeding:
Plant breeding has several useful applications in the improvement of crop plants.
However, it has four main undesirable effects on crop plants, viz.:
(1) Reduction in genetic diversity
(2) Narrowing of genetic base,
(3) Danger of uniformity, and
(4) Undesirable combinations.
These are discussed below:
(1) Reduction in Diversity:
Modern improved varieties are more uniform than land races. Thus plant breeding leads to reduction in diversity. The uniform varieties are more prone to the new races of pathogen than land races which have high genetic diversity.
(2) Narrow Genetic Base:
Uniform varieties have narrow genetic base. Such varieties generally have poor adaptability. On the other hand diverse genotypes like land races or primitive cultivars have wide adaptability.
(3) Danger of Uniformity:
Most of the improved varieties have some common parents in the pedigree which may cause danger of uniformity. However, danger of uniformity can be avoided through development of multiline varieties in self-pollinated crops and synthetic and composite varieties in cross pollinated species.
(4) Undesirable Combinations:
Sometimes, plant breeding leads to undesirable combinations. The examples of man-made crops having undesirable combination of characters are Raphanobrassica and Pomato.
Essay # 12. Future Prospects of Plant Breeding:
Plant breeding has played and shall continue to play an important role in the improvement of crop plants. Now new plant breeding approaches, viz. somatic hybridization and genetic engineering are available. In future, biotechnology which includes tissue culture and genetic engineering will supplement the conventional plant breeding methods for genetic improvement of crop plants.
Moreover, crop improvement is the current phase of crop evolution. And evolution is a continuous process. Plant breeding has played key role in increasing the yield levels of cereals, millets and many other crops. There is ample scope for genetic improvement of pulses and oilseed crops, and development of crop varieties with resistance to biotic and abiotic factors.
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