One of the most pressing Biology Topics of our time is the conservation of endangered species and habitats.
Crop Variety Improvement – Improvement in Food Crops
The art of recognizing valuable traits and incorporating them into future generations is very important in plant breeding. Breeders search for individual plants that exhibit desirable traits. The two most desirable qualities of food plants are high yield and natural resistance to disease. Such traits occasionally arise spontaneously through a process called mutation, but the natural rate of mutation is too slow and unreliable to produce all the plants that breeders would like to see.
Plant breeders select plant varieties with desired characters and cross them. The developed offsprings combine the attributes of both parents. These varieties are multiplied and supplied to farmers.
Need for Higher Crop Yield
1. Higher yield:
The main aim of crop improvement is to improve the productivity of economic produce, e.g., grain, vegetables and fodder. Quality seeds of improved varieties are used for their commercial production.
2. Improved Quality:
Quality considerations of crop products vary from crop to crop, e.g., baking quality in wheat, protein quality in pulses, oil quality in oil seeds, and preserving the quality of fruits and vegetables.
3. Biotic and Abiotic Resistance:
Under different situations, crop suffers due to biotic stresses (such as diseases, insects, and nematodes) and abiotic stresses (such as drought, salinity, water logging, heat, cold, and frost). If we develop crop varieties that are resistant to these stresses, then we can improve significantly crop production. For example, MUW 318 is an HYV (high-yielding variety) of wheat that is released for cultivation in non-traditional areas such as Nilgiri and Palni hills and is resistant to all the rust.
Green Revolution in India
The bumper increase in the yield of food grains (especially the wheat crop) as during the 1970s, is often termed as green revolution. The 1970 Nobel laureate, American scientist Dr.N.E. Borlaug was the person behind triple dwarf Mexican wheat varieties. Their color was changed to Indian liking through gamma irradiation (by M.S.Swaminathan, Father of the Green Revolution in India).
The green revolution has made our country self-sufficient in food, increased the buffer stock of food grains and improved the economic conditions of Indian farmers as well as provided employment avenues to a large number of people.
4. Changes in Maturity Duration:
In some of, the short-duration crops, early maturing varieties can make the crop fit into double and multiple cropping systems. This will also reduce the crop’s cost of production. Uniform maturity will make the harvesting process easy and reduce the loss of produce during harvesting.
5. Photo-Insensitivity and Thermo-Insensitivity:
Most of the plants are sensitive to certain abiotic factors such as light and temperature. Development of photo-insensitive and thermo-insensitive crop varieties will help in crossing the cultivation boundaries, e.g., an HYV of wheat, MACS 2469 can tolerate high temperatures.
6. Desirable Agronomic Traits:
If we develop those varieties of crops which contain desired agronomic traits then it will help in setting higher production. Thus, tallness, high tillering, and profuse branching are desirable characteristics for fodder crops. Whereas, dwarfness is desired in cereals as dwarf varieties provide protection from lodging.
For example, breeding for resistance to red rot has led to sugarcane varieties such as Co 975 and Co 62399 which increase cane production in problem areas. Likewise, new varieties of chicken pea as BG 244 and ICC 34 grow erect, and have many branches and pods from base to tip.
7. Wider Adaptability:
If we develop those varieties of crops which have wider adaptability, then it will help in stabilizing crop production under different environmental conditions. For example, ICPH8 is a hybrid pigeon pea plant that takes a short duration to mature, escapes diseases such as fusarium wilt and sterility mosaic, and yields 30 to 40 percent more than the popular breed. It performs well under drought as well as high-moisture conditions.
Crop Variety Improvement Mechanism
Crop variety improvement is the manipulation of crop plants for increasing their yield, improving quality, suitability to varied conditions, and resistance to biotic and abiotic stresses. Genetic manipulation is the incorporation of new genes for various traits from other genotypes into the crop variety so as to bring about desired changes. It is carried out through hybridization, mutation, breeding, polyploidy, and DNA recombination technology.
Plant breeding means the production of new varieties or straws by a programme of artificial selection spanning several generations of the organism concerned. Plant breeding is a science as well as an art of improving the genetic makeup of plants in relation to their economic use. Various approaches which are used for the genetic improvement of crop plants are referred to as plant breeding methods or techniques.
Genetic improvement of various crop plants has been done by adopting the following three steps: Introduction, Selection, and Hybridization.
This refers to the transportation of crop plants from the place of their cultivation to the place where they were never grown earlier. Thus, the process of introducing new plants from their growing place to a new region with a different climate is termed plant introduction. The adjustment of such plants to their new region is called acclimatization. It is a quick method to bring about improvement with minimum effort and cost. For example, crops such as potato, coffee, tea, tobacco, groundnut, papaya, etc., have been introduced in India from other parts of the world.
This process involves the selection of the most desirable offspring of a variety of plants for controlled propagation. Selection favours the survival and further propagation of some plants having more desirable characteristics (related to yield and quality) than others.
There are following two patterns of selection:
- Mass selection: Seeds from a number of similar plants having the desired traits are mixed and sown to raise new offspring. Offsprings with undesirable traits are eliminated and the process is continued with the remaining progeny in the same manner until the desired improvement is achieved. Grapes, apples, pears, watermelons, radishes, onions, and maize have been improved by this method.
- Pure-line selection: Seeds from a single plant having the desirable trait is sown in separate rows to produce the offspring. Desired plants are again selected from the progeny and the process is continued for several generations. The inferior varieties are eliminated in each generation. Wheat varieties such as Kalyan Sona-227 and PV-18 have been developed by this method.
Selection by human beings is also called artificial selection. The artificial selection operating over long time spans can give rise to varieties strikingly different from starting generation. For example, broccoli, cabbage, cauliflower, and other varieties have been obtained through artificial selection from wild cabbage.
The crossing between genetically dissimilar plants to produce a new kind (hybrid) is called hybridization. Crossing may be between two different varieties (intervarietal cross-breeding), between two different species of the same genus (interspecific cross-breeding), and between different genera (intergeneric cross-breeding). This method incorporates the desired (good) characteristics of both parents in one variety. The most common type of breeding is inter-varietal.
Cross-breeding of two varieties of plants (one high-yielding and the other having resistance to diseases) is carried out to obtain an improved variety of plants that will combine in it both the desired characteristics of the parent crop plants. For example, the new improved variety of crop plants, thus, obtained will give a high yield of food grains and it will be disease resistant too. This process of cross-breeding of different plants to obtain a new improved variety of crops is called hybridisation. The new varieties of crop plants, thus, obtained are called “hybrid varieties” “improved varieties” or “high yielding varieties” (HYV) of crops.
In India, crops are grown in diverse types of soil and different climatic conditions by poor to progressive farmers. Keeping in mind climatic factors, input application, disease, and pest resistance, quality and adaptability, etc., a large number of varieties have been developed in India (Table 1.7). These varieties are high yielding and resistant to diseases and pests; they have better quality and early to late maturing time.
Improved varieties or high-yielding varieties (HYV) of some important crop plants.
|1. Cereals||1. Rice||IR 8, faya, Heera, VL Dhan 221, C ST 7-1, Jawahar, TRC – C 10, IR 36, Pusa Basmati 1, Kasturi, Vikas, PNR – 591 -18, Padma|
|2. Wheat||MIKS 11 KML 7406, HUW 318, MACS 2496, HD 2687, HD 2285, C 306, PBW 154, HW 157, Pusa Lerma, Sharbati Sonora|
|3. Maize||Ganga 5, HIM128, Shakti, Navjot, Vikram|
|2. Pulses||1. Chick pea (gram)||BE 244, ICC 34, K 850, H 208, Pusa 240, Pant 114|
|2. Pigeon pea||ICPH 8, Pusa Ageti, UPAS 120, Pusa 84 Manak, T21|
|3. Urad bean||LB G 17, ADT 3, T9 Pant 430, PS 1, COS|
|4. Moong bean||MLZ 67, C04, PS 16,58, T 44, K851, Aasha|
|3. Oil Seeds||1. Groundnut||MH 2, ICGS 1, M37, GG 11, TMV 12, Kaushal, ICGS 11, ICGS 44|
|2. Mustard||Pusa Bold, Kranti, Pusa Agarni, RLM 514, RH 30|
|3. Soyabean||PK 262, PK 327, Pusa 24, Durga, Gaurav|
|4. Sunflower||BSH 1, MSF H 8, Morden, Arun, Paras|
4. Mutation breeding:
Mutations are sudden inheritable variations. They are produced at random through gamma irradiation and a number of other physical and chemical agents called mutagens. Triple dwarf Mexican varieties of wheat were developed by N.E. Borlaugh (1963) through the incorporation of mutations by selective hybridization. They were, however, red-grained. The same was converted into amber-grained forms (e.g., Pusa Lerma, Sharbati Sonora) through mutation carried out by gamma irradiation.
It is increasing the chromosome number. Polyploids are generally more robust with higher yields, e.g., potato.
6. DNA Recombinant Technology:
This technology refers to the transfer of genes from one organism to another so as to modify the latter. They are called genetically modified organisms (GMOs) or transgenic organisms. Such transgenic food plants are called genetically modified food (GMFs). Bt cotton is a genetically modified crop that carries bacterial genes that protect plants from insects. Bt stands for the bacterium Bacillus thuringiensis whose genes are used by transgenic crops such as cotton, rice, maize, potato, tomato, brinjal, cauliflower, cabbage, etc., to get protection from their insect pests.