Question 1 What is genetic manipulation?
Question 2 What is plant breeding?
Question 3 What is DNA recombination technology?
Question 4 What are the various steps of genetic improvement?
Question 5 How can hybridisation produce an improved variety of a crop?
Question 6 Define the term acclimatization?
Question 7 What are the objectives of crop improvement?
Question 8 Name the improved variety of wheat and rice?
It means the incorporation of desirable characters in an organism (crop plant) by various methods such as hybridization, mutation, polyploidy and DNA recombinant technology.
In DNA recombinant technology : a gene from one organism can be inserted into the DNA of another organism. The gene that has been isolated for insertion is called donor DNA. The donor DNA is inserted into the host DNA of another organism. The DNA that contains genetic materials from two different organisms is called recombinant DNA. An animal or plant that expresses DNA derived from another species, is called transgenic animal or transgenic plant.
Plant Breeding for High Yielding Crops
The plant breeding means production of new varieties or strains by a programme of artificial selection spanning several generations of the organism concerned.
Various approaches which are used for 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.
1) Introduction: This refers to transportation of crop plants from the place of their cultivation to the place where they were never grown earlier. The process of introducing new plants from their growing place to a new region with a different climate is termed as 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 the other parts of the world.
2) Selection: This process involves selection of the most desirable offspring of a variety of plant for controlled propagation. Selection favours the survival and further propagation of some plants having more desirable characters (related to yield and quality) than others.
There are following two patterns of selection:
(a) Mass selection: Seeds from a number of similar plants having the desired traits are mixed and sown to raise the new offspring. Offsprings with the undesirable traits eliminated and the process is continued with the remaining progeny in the same manner until the desired improvement is achieved.
Grapes, apples, pear, watermelon, radish, onion and maize have been improved by this method
(b) 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 progeny and the process is continued for several generations. The inferior varieties are eliminated in each generation.
3) Hybridisation. The crossing between genetically dissimilar plants to produce a new kind (hybrid) is called hybridisation. 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) characteristies of both parents in one variety.
Selection and hybridisation are often combined in breeding.Repeated mating and selection produces high-yielding maize hybrids.Selection breeding is more successful in wheat, barley, rice and cotton production.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. These varieties are high-yielding and resistant to diseases and pests; they have better quality and early to late maturing time.
Practices of cultivation and yield of crop are directly related to agronomic conditions. These conditions are based on weather, soil quality and water resource availability. Since weather conditions are unpredictable such as drought and flooding situations, therefore, crop varieties have been developed that can be grown in diverse climatic conditions.
Prime objective of crop improvement is to develop superior plants in relation to their use or need of the area.Thus, objectives of crop improvement may differ from crop to crop.
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 varies from crop to crop e.g. baking quality in wheat, protein quality in pulses, oil quality in oil seeds and preserving 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).
For example: MUW 318 is a HYV (high yielding variety) of wheat which is released for cultivation in non-tradional areas as Nilgiri and Palni hills and resistant to all the rusts.
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 system. 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 as light and temperature. Development of photo-insensitive and thermo-insensitive crop varieties will help in crossing the cultivation boundaries.
For e.g: a HYV of wheat, MACS 2469 can tolerate high temperature.
6) Desirable agronomic traits: If we develop those varieties of crops which contain desired agronomic traits then it will help in setting higher production.
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, 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 the crop production under different environmental conditions.
For example: ICPH 8 is a hybrid pigeon pea plant which takes a short duration to mature, escapes diseases, and yields 30 to 40 per cent more than the popular breed. It performs well under drought as well as high-moisture conditions