write steps of plant breeding .
plz stepwise ..
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The four steps are: (1) Creation of genetic variation by various means (2) Selection (3) Evaluation and Release as a variety and (4) Seed multiplication and distribution among farmers.
1. Domestication:
Domestication is the process of growing plants and keeping animals under human care and management. This is the very first step aimed at increasing food production.
2. Germplasm Collection:
a. Germplasm is the sum of all the genes present in a crop, and it includes
(i) All the wild species related to the crop species,
(ii) Cultivated improved varieties,
(iii) Improved varieties that are no more cultivated, and
(iv) Old local or ‘desi’ varieties.
b. Collection of germplasm from different sources is an essential first step in any breeding work.
c. Germplasm is usually stored at a low temperature in the form of seeds.
d. Germplasm collection is done from within the country or from Other countries.
3. Plant Introduction:
a. It is the process of introducing plants or germplasms either from a foreign country or introducing plants or germplasm from one region to other regions of the same country.
b. Plant introduction is followed by acclimatisation, i.e., the adaptation of an individual plant or a population of plants, under the changed climate.
c. Introduction of plants from a foreign country is called intercontinental plant introduction.
For example:
(i) Groundnut has been introduced in India from Brazil,
(ii) Rubber has been introduced from South and Central America to India,
(iii) Mexican wheat varieties have been introduced from Mexico to India.
d. Examples of introduced ornamental plants are innumerable, such as Jacaranda, Bougainvillea, Salvia, Cosmos, Dianthus, Antirrhinum etc.
e. Introduction of plants from one state of a country to another state of the same country is called interstate plant introduction. For example, N.P. wheat varieties were introduced from Delhi to different states of India.
f. Purposes of Plant Introduction
(i) For use in agriculture, forestry and industry.
(ii) For genetical improvement of economical crops.
(iii) For studying the origin, distribution, classification and evolution of the plants.
g. Plant Introduction in India:
Following agencies carry out plant introduction in India:
(i) Plant Introduction Division of IARI, New. Delhi,
(ii) Forest Research Institute, Dehradun.
(iii) Botanical Survey of India.
(iv) Some universities, gardens and agricultural departments also play an important role in introducing plants.
Disadvantages of Plant Introduction:
Along with economically important plants, introduction of harmful crop diseases, insect pests and weeds also occurs sometimes.
Diseases Introduced:
(i) Late blight of potato (Phytophthora infestans)
(ii) Fire blight of apple and pear (Erwinia amylovora)
Insect Pests Introduced:
(i) Potato tuber moth
(ii) Woolly aphis
Weeds Introduced:
(i) Argemone mexicana, Lantana.
All introductions are subjected to quarantine, i.e., they are examined for the presence of insects, weeds and disease-causing organisms, and only those introductions that are free from the above are allowed to enter a country.
4. Hybridization:
Hybridization may be defined as “The mating or crossing of two plants or lines of dissimilar genotype.” The chief objective of hybridization is to create genetic variation. When two genotypically different plants are crossed, the genes from both the parents are brought together in F1generation.
Segregation and recombination produce many new gene combinations in F2 and the later generations, i.e., segregating generations. The degree of variation produced in the segregating generations would, therefore, depend on the number of heterozygous genes in the F1. This will, in turn, depend upon the number of genes for which the two parents differ.
If the two parents are closely related, they are likely to differ for a few genes only. But if they are not related, or are only distantly related, they may differ for several, even a few hundred genes. However, it is most unlikely that the two parents will ever differ for all the genes. Therefore, when it is said that the F1 is 100 percent heterozygous, it has reference only to those genes for which two parents differ. The aim of hybridization may be transfer of one or few qualitative characters, improvement of one or more quantitative characters, or use of the F1as a hybrid variety.
1. Domestication:
Domestication is the process of growing plants and keeping animals under human care and management. This is the very first step aimed at increasing food production.
2. Germplasm Collection:
a. Germplasm is the sum of all the genes present in a crop, and it includes
(i) All the wild species related to the crop species,
(ii) Cultivated improved varieties,
(iii) Improved varieties that are no more cultivated, and
(iv) Old local or ‘desi’ varieties.
b. Collection of germplasm from different sources is an essential first step in any breeding work.
c. Germplasm is usually stored at a low temperature in the form of seeds.
d. Germplasm collection is done from within the country or from Other countries.
3. Plant Introduction:
a. It is the process of introducing plants or germplasms either from a foreign country or introducing plants or germplasm from one region to other regions of the same country.
b. Plant introduction is followed by acclimatisation, i.e., the adaptation of an individual plant or a population of plants, under the changed climate.
c. Introduction of plants from a foreign country is called intercontinental plant introduction.
For example:
(i) Groundnut has been introduced in India from Brazil,
(ii) Rubber has been introduced from South and Central America to India,
(iii) Mexican wheat varieties have been introduced from Mexico to India.
d. Examples of introduced ornamental plants are innumerable, such as Jacaranda, Bougainvillea, Salvia, Cosmos, Dianthus, Antirrhinum etc.
e. Introduction of plants from one state of a country to another state of the same country is called interstate plant introduction. For example, N.P. wheat varieties were introduced from Delhi to different states of India.
f. Purposes of Plant Introduction
(i) For use in agriculture, forestry and industry.
(ii) For genetical improvement of economical crops.
(iii) For studying the origin, distribution, classification and evolution of the plants.
g. Plant Introduction in India:
Following agencies carry out plant introduction in India:
(i) Plant Introduction Division of IARI, New. Delhi,
(ii) Forest Research Institute, Dehradun.
(iii) Botanical Survey of India.
(iv) Some universities, gardens and agricultural departments also play an important role in introducing plants.
Disadvantages of Plant Introduction:
Along with economically important plants, introduction of harmful crop diseases, insect pests and weeds also occurs sometimes.
Diseases Introduced:
(i) Late blight of potato (Phytophthora infestans)
(ii) Fire blight of apple and pear (Erwinia amylovora)
Insect Pests Introduced:
(i) Potato tuber moth
(ii) Woolly aphis
Weeds Introduced:
(i) Argemone mexicana, Lantana.
All introductions are subjected to quarantine, i.e., they are examined for the presence of insects, weeds and disease-causing organisms, and only those introductions that are free from the above are allowed to enter a country.
4. Hybridization:
Hybridization may be defined as “The mating or crossing of two plants or lines of dissimilar genotype.” The chief objective of hybridization is to create genetic variation. When two genotypically different plants are crossed, the genes from both the parents are brought together in F1generation.
Segregation and recombination produce many new gene combinations in F2 and the later generations, i.e., segregating generations. The degree of variation produced in the segregating generations would, therefore, depend on the number of heterozygous genes in the F1. This will, in turn, depend upon the number of genes for which the two parents differ.
If the two parents are closely related, they are likely to differ for a few genes only. But if they are not related, or are only distantly related, they may differ for several, even a few hundred genes. However, it is most unlikely that the two parents will ever differ for all the genes. Therefore, when it is said that the F1 is 100 percent heterozygous, it has reference only to those genes for which two parents differ. The aim of hybridization may be transfer of one or few qualitative characters, improvement of one or more quantitative characters, or use of the F1as a hybrid variety.
suhanianand15:
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