HYBRIDIZATION : TECHNIQUES AND CONSEQUENCES

Hybridization

Hybridization is the mating or crossover of two plants or lines with different genotypes. Pollen grains from one genotype, the male parent, are placed on the stigma of flowers from the other genotype, the female parent, to cross. It’s critical to avoid self-pollination as well as accidental cross-pollination in the female parent’s blooms.

Simultaneously, it must be assured that pollen from the selected male parent reaches the stigma of female flowers in order for fertilisation to be effective. Hybrid or F 1 refers to the seeds as well as the progeny that arise from the hybridization. Segregating generations are F1 offspring formed by selfing or intermating F1 plants, as well as succeeding generations. The term cross is frequently used to refer to the hybridization results, such as F1 and segregating generations.

OBJECTIVES OF HYBRIDIZATION

The main goal of hybridization is to create genetic diversity. The genes from both parents are brought together in F 1 when two genotypically distinct plants are crossed. In F 2 and subsequent generations, i.e. segregating generations, segregation and recombination yield a large number of novel gene combinations.

As a result, the amount of diversity created in successive generations would be determined by the number of heterozygous genes in the F1. This, in turn, is dependent on the amount of genes that vary between the two parents. If the two parents are closely related, just a few genes are likely to vary. However, if they are unrelated or distantly related, they may differ in dozens, if not hundreds, of genes. However, it is unlikely that the two parents’ DNA will ever diverge completely. As a result, when the F 1 is stated to be 100% heterozygous, it solely refers to the genes for which the two parents differ.

The goal of hybridization might be to transmit one or a few qualitative features, improve one or more quantitative characters, or create a hybrid variety from 1. These goals are briefly explored further down.

Combination Breeding : The fundamental goal of combination breeding is to transfer one or more traits from various kinds into a single variety. Oligogenes or polygenes may be in charge of these traits. The new variety’s intensity of the trait is either equivalent to or, more broadly, lower than that of the parent variety from which it was transferred.

In this method, a variety’s yield is increased by fixing flaws in yield-contributing features such as tiller number, grains per spike, and disease resistance test weight. Backcross breeding was created for combination breeding, and the pedigree approach frequently serves the same purpose. The genetic difference between parents is not a key factor in combination breeding. What’s vital is that one of the parents must have the character(s) under transfer in adequate intensity, while the other parent is usually a popular variation.

Transgressive Breeding : Through transgressive segregation, transgressive breeding tries to improve yield or contributing traits. The creation of plants in an F2 generation that are superior to both parents for one or more traits is known as transgressive segregation. Such plants are created by the accumulation of positive or beneficial genes from both parents, which must complement each other and be genetically varied, i.e., extremely distinct.

In this fashion, each parent is predicted to contribute various plus genes, which, when combined through recombination, result in transgressive segregants. As a result, the transgressive segregant, i.e., the new variety, has a higher intensity of character than either of the parents. The pedigree breeding method and its variations, especially the population strategy, are intended to produce transgressive segregants.

Hybrid Varieties : F 1 is more robust and yielding than the parents in most self-pollinated crops. F1 can be utilised directly as a variety anywhere it is financially viable. In such instances, it is critical that both parents generate an exceptional F1.

TYPES OF HYBRIDIZATION

Plants or lines hybridised may be from the same variation, various varieties of the same species, different species of the same genus, or distinct species from other genera. Hybridization may be divided into two categories based on the taxonomic connection between the two parents. : 1. Intervarietal and 2. Distant hybridization

Intervarietal Hybridization : Both parents in a hybridization are from the same species; they might be two strains, varieties, or races of the same spice. Intraspecific hyrbidization is another name for it. Intervarietal hybridization is the most prevalent technique utilised in crop development programmes.

In fact, it is so ubiquitous that it may appear to be the sole kind of crop enhancement hybridization. Crossing two types of wheat, rice, or another crop is an example. Depending on the number of parents involved, intervarietal crosses can be easy or complicated.

Simple Cross : Two parents are crossed to generate the F1 in a basic cross. The F1 is utilised in a backcross programme or selfed to create F2., e.g., A X B –> F1 (A X B)

Complex Cross : To create a hybrid, more than two parents are crossed, and the hybrid is then utilised to generate F2 or used in a backcross. Because this crossover procedure tries to converge, or bring together, genes from numerous parents into a single hybrid, it is also known as convergent cross.

Three Parents (A, B, C)

Hybridization

Agricultural types would accrue more and more favorable genes as crop development progressed. Even unrelated types would become more similar as a result of this. As a result, it’s reasonable to predict that complicated crosses will become increasingly essential in the future. Complex crossings are now a widespread procedure in the breeding of highly enhanced self-pollinated crops like wheat and rice. With the advancement in the degree of development of other self-pollinated crops, complex crosses will become commonplace in the near future.

Distant Hybridization : Crosses between distinct species of the same genus or separate genera are known as distant hybridization. Interspecific hybridization occurs when two species from the same genus cross; however, intergeneric hybridization occurs when two species from different genera cross. The goal of such crosses is usually to transfer one or a few easily acquired traits, such as disease resistance, to a crop species.

Interspecific hybridization has been used to develop new varieties in the past, such as the Clintonoat variety, which was developed from a cross between Avena sativa and Avena byzantina (both hexaploid oat species), and the CO 31 rice variety, which was developed from a cross between Oryza sativa var. indica x Oryza perennis. Almost all modern sugarcane cultivars are the result of intricate crossbreeding between Saccharum officinarum (noble canes), Saccharum barberi (Indian canes), and other Saccharum species, such as S. spontaneum (Kans.).

Crossing Indian Cotton (Gossypium arboreum) with American cultivated Cotton has resulted in greater fibre length; several better varieties have evolved from such crosses. Intergeneric hybridization can also be utilised to create new crop species, like as Triticale, which was created by crossing Triticum sp. with Secale cereale (rye). Genes that aren’t found in cultivated species are frequently found in wild species. Many of the genes for rust resistance in wheat, for example, are obtained from closely related wild species. In the treatment of specific crop species problems, distant hybridization is anticipated to become increasingly essential. In many circumstances, wild species may provide valuable ‘yield genes’ to farmed species as well.

Hybridization pre-requisites Before beginning hybridization, the breeder should have a thorough understanding of the following.

1. Requirements of the tract

2. Local conditions i.e. soil, climate, Agronomic practices and market requirements

3. Existing varieties of crops both local and introduced

4. Facilities like funds, land, labour and equipment

5. Plant material i.e. germ plasm

6. Objectives : Well set objectives and planning

Hybridization procedure or steps involved in hybridization Details of the following steps have to be covered in Practical classes-

1. Choice or selection of parents

2. Evaluation of parents i.e. by selfing and studying the progeny

3. Emasculation

4. Crossing or pollination

5. Bagging & Labelling

6. Harvesting of F1 seed

7. Raising F1 generation From F2 onwards the generations are known as segregating generations and they may be handled either by pedigree method of Bulk method or backcross method for evolving new varieties.

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