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Lecture No: 1
Definition, Aim, Objectives and Scope of Plant Breeding
Definition :
Plant breeding can be defined “as an art and science” and technology of improving the
genetic make up of plants in relation to their economic use for the man kind.
or
Plant breeding is the art and science of improving the heredity of plants for the benefit of
mankind.
or
Plant breeding deals with the genetic improvement of crop plants also known as science
of crop improvement.
or
Science of changing and improving the heredity of plants
Aim :
Plant breeding aims to improve the characteristics of plants so that they become more
desirable agronomically and economically. The specific objectives may vary greatly depending
on the crop under consideration.
Objectives of Plant Breeding :
1. Higher yield : The ultimate aim of plant breeding is to improve the yield of “economic
produce on economic part”. 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 quality characters vary from crop to crop. Eg. grain size, colour, milling and baking
quality in wheat. Cooking quality in rice, malting quality in barley, colour and size of
fruits, nutritive and keeping quality in vegetables, protein content in pulses, oil content in
oilseeds, fibre length, strength and fineness in cott on.
3. Abiotic resistance : Crop plants also suffer from abiotic factors such as drought, soil
salinity, extreme temperatures, heat, wind, cold and frost, breeder has to develop
resistant varieties for such environmental conditions.
4. 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.
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5. Change in maturity Duration / Earliness : Earliness is the most desirable character
which has several advantages. It requires less crop management period, less insecticidal
sprays, permits new crop rotations and often extends the crop area. Development of
wheat varieties suitable for late planting has permitted rice-wheat rotation. Thus
breeding for early maturing crop varieties, or varieties suitable for different dates of
planting may be an important objective. Maturity has been reduced from 270 days to 170
days in cotton, from 270 days to 120 days in pigeonpea, from 360 days to 270 days in
sugarcane.
6. Determinate Growth : Development of varieties with determinate growth is desirable
in crops like mung, pigeon pea (Cajanus cajan), cotton (Gossypium sp.), etc.
7. Dormancy : In some crops, seeds germinate even before harvesting in the standing crop
if there are rains at the time of maturity, e.g., greengram, blackgram, Barley and Pea, etc.
A period of dormancy has to be introduced in these crops to check loss due to
germination. In some other cases, however, it may be desirable to remove dormancy.
8. Desirable Agronomic Characteristics : It includes plant height, branching, tillering
capacity, growth habit, erect or trailing habit etc., si often desirable. For example,
dwarfness in cereals is generally associated with lodging resistance and better fertilizer
response. Tallness, high tillering and profuse branching are desirable characters in fodder
crops.
9. Elimination of Toxic Substances : 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 – lentil (Lathyruys sativus) 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. Removal
of such toxic substances would increase the nutritional value of these crops.
10. Non-shattering characteristics: The sha ttering of pods is serious problem in green
gram. Hence resistance to shattering is an important objective in green gram.
11. Synchronous Maturity : It refers to maturity of a crop species at one time. The
character is highly desirable in crops like greengram, cowpea, castor and cotton where
several pickings are required for crop harvest.
12. Photo and Thermo insensitivity: Development of varieties insensitive to light and
temperature helps in crossing the cultivation boundaries of crop plants. Photo and
thermo-insensitive varieties of wheat and rice has permitted their cultivation in new
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areas. Rice is now cultivated in Punjab, while wheat is a major rabi crop in West
Bengal.
13. 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.
14. Varieties for New Seasons : Traditionally maize is a kharif crop. But scientists are now
able to grow maize as rabi and zaid crops. Similarly, mung is grown as a summer crop
in addition to the main kharif crop.
Scope of plant breeding (Future Prospects)
From times immemorial, the plant breeding has been helping the mankind. With
knowledge of classical genetics, number of varieties have been evolved in different crop plants.
Since the population is increasing at an alarming rate, there is need to strengthened the food
production which is serious challenge to those scientists concerned with agriculture. Advances in
molecular biology have sharpened the tools of the breeders, and brighten the prospects of
confidence to serve the humanity. The application of biotechnology to field crop has already led
to the field testing of genetically modified crop plants. Genetically engineered rice, maize,
soybean, cotton, oilseeds rape, sugar beet and alfalfa cultivars are expected to be commercialized
before the close of 20th century. Genes from varied organisms may be expected to boost the
performance of crops especially with regard to their resistance to biotic and abiotic stresses. In
addition, crop plants are likely to be cultivated for recovery of valuable compounds like
pharmaceuticals produced by genes introduced into them through genetic engineering. It may be
pointed out that in Europe hirudin, an anti-thrombin protein is already being produced from
transgenic Brassica napus.
Undesirable effects
Plant breeding has several useful applications in the improvement of crop plants.
However, it has five main undesirable effects on crop plants.
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.
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3. Danger of Uniformity : Most of the improved varieties have some common parents in
the pedigree which may cause danger of uniformity.
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.
5. Increased susceptibility to minor diseases and pests : Due to emphasis on breeding for
resistance to major diseases and insect pests often resulted in an increased susceptibility
to minor diseases and pests. These have gained importance and, in some cases, produced
severe epidemics. The epidemic caused by Botrytis cinerea (grey mold) in chickpea
during 1980-82 in Punjab and Haryana. The severe infection by Karnal bunt (Tilletia sp.)
on some wheat varieties, infestation of mealy bugs in Bt cotton.
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History and development of plant breeding
- About 10,000 years ago when man is believed to have started agriculture.
- Plant breeding began when man first choose certain plants for cultivation.
- The process of bringing a wild species under human management is referred to as
domestication
- Domestication may be the most basic method of plant breeding
- All other breeding method become applicable to a plant species only after it has been
successfully domesticated.
- Domestication continuous today and is likely to continue for some time in future
- Ex : In case of timber trees medicinal plants, microbes
- During the long period of historic cultivation natural selection has definitely acted on the
domesticated species.
- Movement of man from one place to another brought about the movement of his
cultivated plant species
- 700 BC - Babylonians and Assyrians pollinated date palm artificially
- 17th century - several varieties of heading lettuce were developed in France
- 1717 - Thomas Fair Child - produced the first artificial hybrid, popularly known as
Fair Child’s mule, by using carnation with sweet William
- 1727 - The first plant breeding company was established in France by the vilmorins.
- 1760-1766 - Joseph koelreuter, a German, made extensive crosses in tobacco.
- 1759-1835 – Knight was perhaps the first man to use artificial hybridization to develop
several new fruit varieties.
- Le couteur and Shireff used individual plant selections and progeny test to develop some
useful cereal varieties
- 1873 - the work of Patrick Shireff was first published.
- He concluded that only the variation heritable nature responded to selections, and that
there variation arose through ‘natural sports’ (= mutation) and by ‘natural hybridization’
(= recombination during meiosis in the hybrids so produced).
- 1856 - Vilmorin developed the progeny test and used this method successfully in the
improvement of sugar beets.
- 1900 - Nilson-Ehle, his associates developed the individual plant selection method in
Sweden.
- 1903 - Johannsen proposed the pureline theory that provided the genetic basis for
individual plant selection.
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- The science of genetics began with the rediscovery of Gregor Johan Mendel’s paper in
1900 by Hugo de veris, Tshermark and Correns which was originally published in 1866.
- The modern plant breeding methods ha ve their bases in the genetic and cytogenetic
principles.
- Numerous workers who determined the various modes of inheritance have contributed to
the development and understanding of plant breeding.
- The discovery of chromosomes as carriers of genes has led to the development of
specialized plant breeding methods for chromosome engineering.
- The totipotency of plant somatic and gametic cells allows regeneration of complete plants
from single cells. This, coupled with the development of recombinant DNA technology,
has enabled the transfer of desirable genes from any organism into plants. Crop varieties
developed in this manner are already in cultivation in several countries.
History of plant breeding in India
- 1871 – The Government of India created the Department of Agriculture
- 1905 – The Imperial Agricultural Research Institute was establish in Pusa, Bihar
- 1934 – The buildings of the institute damaged in earthquake
- 1936 – Shifted to New Delhi
- 1946 – Name was changed Indian Agricultural Research Institute
- 1901-05 – Agricultural Colleges were established at Kanpur, Pune, Sabour, Llyalpur,
Coimbatore
- 1929 – Imperial council of Agricultural Research was established
- 1946 – Name was change to Indian Council Agricultural Research
- 1921 – Indian Central Cotton Committee was established – Notable researches on
breeding and cultivation of cotton. Eg : 70 improved varieties of cotton
- 1956 – Project for intensification of regional research on cotton, oilseeds and millets
(PIRRCOM) was initiated to intensify research on these crops – located at 17 different
centres through out the country
- 1957 – All India Coordinated maize improvement project was started with objective of
exploiting heterosis
- 1961 - The first hybrid maize varieties released by the project
- ICAR initiated coordinated projects for improvement of the other crops
- 1960 – First Agricultural University established at Pantnagar, Nainital, U.P.
