Different Methods

Methods of Crop Improvement
    Different methods used for introduction of variation in the existing gene pool are:-
    1. Introduction/Domestication
    2. Selection
    3. Hybridization
    4. Mutation Breeding
    5. Polyploidy
    6. Genetic Engineering
    1. Introduction
    Primary introduction
    • In this type, the introduced crop/variety is well suited for new environments and released as a commercial variety without any alteration in original genotype. In most of commercial cutflower crops, primary introduction is widely adopted technique for increasing gene pool.
    Secondary Introduction
    • In this, the introduced variety may be subjected to selection, to isolate a superior variety or may be hybridized with a local variety to transfer one or more characters from the local varieties.
    Some plants introduction agencies of India
    1. NBPGR (National Bureau of Plant Genetic Resources, New Delhi)
    2. FRI (Forest Research Institute ,Dehradun)
    3. The Botanical Survey of India
    4. Central Research Institutes for different crops.
    5. NRC Orchids, Gangtok, Sikkim
    2. Selection
    • Selection is one of the oldest method of crop improvement.
    • It refers to the process that favours survival and further propagation of some plants having more desirable characters than others.
    • Selection is more efficient when genetic variation is present in the base population and it utilizes the variation already present in the population.
    • Several outstanding cultivars have been released by selection. Chrysanthemum cvs. ‘Apsara’, ‘Birbal Sahni’, ‘Jayanthi’, ‘Kundan’, have been developed through selection. Similarly cvs. ‘Shubhra’, ‘Dr B.P. Pal’, ‘Partha sarthy’ and ‘Surekha’ in Bougainvillea have been developed. Similarly many new varieties have been released in different floricultural crops.
    • In Bougainvillea varieties, 'Sholay' and 'Usha' are the half sib selection of cv. 'Red Glory' and 'Lady Hope' developed at IIHR, Banglore
    • 'Kamini', 'Poornima', 'Shashank' an 'Violet Cushion' varieties of China Aster are developed from Pedigree selection method
    3. Hybridization
    • It is the mating or crossing of two plants or lines of dissimilar genotype.
    • In plants, crossing is done by placing pollen grains from male parent on the stigma of the flowers of other genotypes is female parent.
    • The seeds and the progeny resulting from the hybridization are called F1 hybrids. The main objective of hybridization is to create genetic variation. When two genetically different plants are crossed the genes from both the parents are brought together in F1.
    Based upon the taxonomic relationship of the two parents involved the hybridization it, may be classified as (1) inter varietal hybridization and (2) distant-hybridization.
    Inter varietal Hybridization
    • The parents involved belongs to the same species, they may be strains, varieties or races of the same species.
    • These crosses may be simple or complex, depending upon the number of parents involved.
    • Gladiolus varieties: Meera (G.P. 1 × Friendship), Nazrana (Black Jack × Friendship), Apsara (Black Jack × Friendship) are some of the examples
    • Intervarietal hybrids of Hibiscus
    1. Basant: IIHR × Rachaiah
    2. Chitralekha: Debby Ann × H. S. 203
    3. Marathi: H. S. (red) × H. S. 123
    4. Nazneen: H. S. 203 × Rashtrapati
    5. Phulhari: H. S. 139 × H. S. 181
    Distant Hybridization
    • Distant hybridization includes cross between different species of the same genus or of different genera.
    • When two species of the same genus are crossed, it is known as inter specific hybridization.
    • Arka Tejas, a carnation cultivar is a interspecific hybrid between Dianthus carophyllus × Dianthus chinensis
    4. Mutations Breeding
    • Mutation is a sudden heritable change in a characteristic of an organism.
    • Mutation may be the result of a change in a gene, a change in chromosomes that involves several genes or a change in a plasma gene.
    • The term mutation was introduced by Hugo de Vries in 1900. Mutation breeding attracted considerable attention during 1950s and 1960s, and several countries took up research projects in mutation breeding.
    • Mutation is the most useful technique of inducing variation among the vegetatively propagated crops, and therefore, holds promise for the development of new varieties in ornamentals which are generally vegetatively propagated.
    • Mutations are of two types:
    1. Spontaneous Mutations
    • The mutations that occur in natural population (without any treatment by man) at a low rate; these are known as spontaneous mutations.
    • The frequency of spontaneous mutations is generally one in 10 lacs, i.e., 10-6.
    • In chrysanthemum varieties like 'Kasturba Gandhi' from 'Mahatama Gandhi', 'Sonar Bangla' from 'Snow Ball', 'White Cloud' from 'Pink Cloud', 'Sharad Shobha' from 'Sharada' were delopped through spontaneous mutations.
    • In Bougainvillea, 'Jawahar Lal Nehru' is a bud sport mutant of cv. 'Lalbaugh' developed at IIHR, Banglore
    2. Induced Mutations:
    • Mutations may be artificially induced by a treatment with certain physical or chemical agents; such mutations are known as induced mutations, and the agents used for producing them are
    termed as mutagens.
    • The utilization of induced mutation for crop improvement is known as mutation breeding. This type of mutation is generally utilized for the development of new varieties in ornamentals.
    • Mutations can be induced by using chemical (colchicine, EMS, MMS etc.) and physical mutagenic (X-rays and gamma rays etc.) agents.
    • In gladiolus cv. 'Shobha' (mutant of 'Wild Rose') developed by 1 kR treatment with gamma rays.
      • 'Pusa Christiana': Mutant of 'Christian Dior', gamma rays induced
      • 'Abhisarika': Mutant of 'Kiss of Fire'
      • 'Madhosh': Mutant of 'Gulzar', EMS (i.e. 0.025% for 8 hours)
      • 'Angara': Mutant of 'Montezumma'
      • 'Sharda': Mutant of 'Queen Elizabeth'
    5. Polyploidy
    • Generally the chromosome number of most of the species is highly stable and referred to as diploid i.e. having 2n number of chromosome.
    • Sometimes a low frequency of irregularities may occur which gives rise to individuals with chromosome numbers different from the normal somatic chromosome number of the species.
    • These changes in basic chromosome number contribute to the evolution of variation in the species.
    • When an individual possess multiple of its own basic chromosome number it is called a polyploidy.
    • Polyploidy has been exploited in ornamentals for induction of vigorous hybrids, double type of flowers, increased yield and for induction of fertility.
    • Aneuploid Hybrid of Bougainvillea: 'Begum Sikander', 'Wajid Ali Shah', 'Chitra' (NBRI, Lucknow).
    • 'Dr. B. P. Pal' (Tetraploid of Shubra), 'Tetra Mrs McClean' (Tetraploid of Mrs McClean).
    • 'Begum Sikander': An aneuploid hybrid of Dr B. P. Pal × Jennifer
    • 'Mary Palmer Special': Triploid seedling of Dr. B. P. Pal × Princess magaret Rose
    • 'Chitra': Tetraploid of Tetra Mrs McClean × Dr. B. P. Pal
    • 'Mohini', a trisomic variety of rose is a cross between Sea Pearl (4n) × Shola (2n)

Last modified: Monday, 6 August 2012, 10:20 AM