Read this article to learn about Self Pollination and Cross Pollination. After reading this article you will learn about 1. Method of Self Pollination 2. Method of Cross Pollination 3. Mechanism of Self Pollination 4. Mechanism of Cross Pollination.
Methods of Self Pollination:
(i) Mass selection:
Always based on phenotype Individual plants are selected and next generation continued from seeds of selected plants. Rouging or uprooting of undesirable plants and harvesting of remaining plants in mass.
(ii) Pure line selection method:
Concept of pure line was given by – Johnson. Pure line is a progeny of single homozygous, self pollinated crops. Large number of plants are selected from self pollinated crop and tested or evaluated separately & the best progeny (plant) released as pure line varieties. All plants of pure line variety are homozygous due to some genotype.
(iii) Pedigree method:
Individual plants are selected from F2 generation and the subsequent generation & their progeny are tested. During entire operation, a record of all parents’ offspring relationship is kept.
1. Most commonly used method for selection from segregation generations of crosses in self pollinated crops.
2. Useful in selection of new superior recombinant types.
3. Suitable for improving specific traits i.e. plant height, disease resistance, maturity time etc.
(iv) Single seed descent method:
First applied in oat in 1965 by Graphius Single seed descent method continues from F2 to F5/F6 generation in which superior single plants are finally selected, harvested and growing one seed from each plant.
(v) Back cross method:
F1 x one of its parents
1. Used to improve one or two specific defects of a high yielding variety.
2. Commonly used for transfer of disease resistance from one variety to another variety.
(vi) Bulk method:
1st used by Nilson Ehle, 1908
F1 and the subsequent generations are harvested in bulk or mass to rise the next generation. At the end, single plant is selected and tested same as pedigree method.
1. Methods used for handling the segregating generation – Pedigree, Bulk & Single seed descent method.
Methods of Cross Pollination:
(i) Mass selection
(ii) Progeny selection:
1. 1st used by Hopkins in 1908
2. Also known as Ear to row method of selection.
Process:
1. Superior phenotypic selection of 50-100 plants & open pollination in between them and then individual plant seed harvested.
2. Single row of 10-15 plants from each selected plants grown (progeny row). They evaluated for desirable traits and superior progeny are identified.
3. Superior phenotypic plants are selected from superior progeny and allowed to open pollinated.
4. Small progeny row grown (same as in 2) from selected plants and the process repeated.
(iii) Recurrent selection:
Recurrent selection is a method in which desirable scattered favourable genes are selected in different plants in each generation.
(iv) Hybrid varieties:
1st commercially exploited into maize
Hybrid or F1 are the seed as well as the progeny resulting from hybridization (A x B).
Single cross A x B = F1 (Hybrid)
Double cross → (A x B) x (C x D) = Two single cross
Three way cross → (A x B) x C i.e. Ganga Safed-2 variety of maize (OP.)
Double to cross A single cross (A x B) x OP. variety
Top cross → selected variety/line/clone x open pollinated variety
Intraspecific/inter-varietal Hybrid:
A hybrid between genetically deferent genotypes of the same species. Ex. H4, H6, H8, HIO varieties of cotton
Interspecific/intra-generic Hybrid: The F1 progeny (hybrid) between two different species of the same genus. Ex. Varalaxmi (G. hirsutum x G. barbadense) DCH 32, HB 224 varieties of cotton.
(v) Synthetic varieties:
Synthetic variety is produced by crossing in all combinations a number of lines that combine well each other.
Composite variety:
It is produced by mixing the seeds of several phenotypically outstanding lines (varieties) and encouraging open pollination to produce crosses in all combinations among the mixed lines. These varieties are similar in maturity, height, seed size, seed colour etc.
Mechanism of Self Pollination:
(i) Chasmogamy: Flowers open but only after pollination has taken place, ex. rice, moong, oat etc.
(ii) Cleistogamy – Flowers do not open at all ex. wheat, barley etc.
Mechanism of Cross Pollination:
(i) Dicliny – flowers are either staminate (male) or pistilate (female)
(ii) Dichogamy – male and female flowers of a hermaphrodite flowers matures at different time.
Types:
1. Protogyny →Gynus = female, female matures before male i.e. Bajra;
2. Protondry →Andrus = male, male matures first i.e. Maize
(iii) Geitonogamy: Pollen from a flower of one plant falls on the stigmas of other flowers of the same plant, ex. Maize
(iv) Monocius: Male (staminate) and female (pistilate) flowers occur on the same plant ex. Maize, castor, coconut, colorcasts etc.
(v) Diocius: Male and female flowers occur on different plants ex. Papaya, datepalm etc.
(vi) 1st Inter-generic hybrid: Raphino brassica (Radish x Cabbage) – developed by Karpencheko, 1927
(vii) For hybrid variety release, we use:
1. Rice-GMS&CGMS line
2. Pigeonpea – GMS line
3. Maize (DCH)-CGMS line
4. Chilly-GMS line
(viii) Koelreuter carried out hybridization experiments in tobacco in between 1760-1766.
(ix) The first artificial plant hybrid was produced by the crossing between carnation and sweet William by Thomas Fairchild.
(x) Heterosis: Superiority of F1, hybrids over both of its parents.
When the heterosis is estimated over the mid parent, i.e. mean or average value of two parents
(xi) Crossing over:
Exchange of chromatin between non-sister chromatids of homologous chromosomes. It releases genetic variability by forming new gene combinations.
(xii) Inbreeding Depression (ID):
Loss or decrease in vigour and fitness as a result of inbreeding. Degree of inbreeding depression is:
1. High I.D. – Alfalfa, Carrot etc.
2. Moderate I.D. – Maize, Sorghum, Bajra etc.
3. Low I.D. – Onion, Cucurbits, Sunflower etc.
4. No LD.-Self pollinated species.
(xiii) Mutation:
1. Sudden heritable change in any characteristics of an organism.
2. Mullar first used X-rays as mutagen.
3. Natural mutation is of low frequency 10 -6
4. Muton is the unit in which mutation occurs.
Mutagens are the chemicals or physical agents which greatly enhance the frequency of mutation.
Some commonly used mutagens are:
(a) Physical mutagens: X-rays, Gama rays, Alfa particles, Bita particles etc.
(b) Chemical mutagens: Ethyl methane sulphonate. Methyl methane sulphonate, Nitrous acid, 5 Bromo Uracil etc.
(xiv) Male Sterility:
A condition in which either pollen is absent or non functional in flowering plants.
Types of Male Sterility:
1. Genetic Male Sterility (GMS)-Pollen sterility, caused by nuclear genes.
2. Cytoplasmic Male Sterility (CMS) – Pollen sterility, caused by cytoplasmic genes.
3. Cytoplasmic Genetic Male Sterility (CGMS) – Caused by cytoplasmic & nuclear genes.
4. Chemically induced Male Sterility- induced by various chemical called Male Gametocytes.
5. Transgenic Male Sterility (TMS) – Induced by the technique of genetic engineering.
(xv) Transgenic plants:
Plants in which specific foreign(s), isolated from diverse biological systems, viz. fungi, bacteria, virus, plants or animals has/have been transferred genetic engineering and stable integrated into their genomes, and the transferred genes are able to perform their specific functions.
(xvi) Norin 10 and Tom Thumb are the source of reduced height (rht) genes used in wheat breeding.
(xvii) Triticale is a man made cereal, usually hexaploid species and has the genomic constitution AABBRR.
The cultivated banana is auto triploid.
(xviii) De-tasseling: Removal of the entire tassel (male inflorescence of maize) from the plant before pollen to initiate cross hybridization.
(xix) Drosophila melanogaster (organism) is regarded as the “Queen of Genetics”.
(xx) Agrobaderium is called as natural genetic engineer.
(xxi) Brassica triangle: ‘U’s triangle given by U. Nagaheru (1935).