Question

If a breeder wants to evolve a disease resistant strain what steps will be taken first?

Answer 1

Answer:

Plant Breeding: Steps and Methods of Plant Breeding for Disease Resistance!

Green Revolution:

Traditional farming can only yield limited food for humans and animals. Better management can increase yield but only to a limited extent.

But plant breeding as a technology increased yield to a very large extent. In India, “Green Revolution” was responsible for our country to not only meet our requirements in food production but also helped us to export it.

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Monkambu Sambasivan Swaminathan (M.S. Swaminathan) initi­ated collaboration with Dr. Borlaug which reached the highest point into the “Green Revo­lution” through introduction of Mexican varieties of wheat in India. Green Revolution de­pended mainly on plant breeding techniques for high yielding and disease resistant varieties in wheat, rice, maize, etc.

1. What is Plant Breeding?

Plant breeding is the genetic improvement of the crop in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant. Conventional plant breeding is in practice from 9,000-11,000 years ago. Most of our major food crops are derived from the domesticated varieties.

But now due to advancements in genetics, molecular biology and tissue culture, plant breeding is being carried out by using molecular genetics tools. Classical plant breeding includes hybridization (crossing) of pure lines, artificial selection to produce plants with desirable characters of higher yield, nutrition and resistance to diseases.

When the breeders wish to incorporate desired characters (traits) into the crop plants, they should increase yield and improve the quality. Increased tolerance to salinity, extreme temperatures, drought, resistance to viruses, fungi, bacteria and increased tolerance to insect pests should also be the desired traits in these crop plants.

Various Steps Required For Developing New Varieties:

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The various steps required for developing new varieties are as follows:

(i) Collection of Germplasm:

Germplasm is the sum total of all the alleles of the genes present in a crop and its related species. The germplasm of any crop species consists of the following types of materials:

(i) cultivated improved varieties,

(ii) improved varieties that are no more in cultivation,

(iii) old local or ‘desi’ varieties, (iv) pure lines produced by plant breeders, and (v) wild species related to the crop species.

The entire collection (of plants/seeds) having all the diverse alleles for all genes in a given crop is called germplasm collection. A good germplasm collection is essential for a success­ful breeding programme.

(ii) Evaluation and Selection of Parents:

The germplasm is evaluated to identify plants with desirable combination of characters. Selection of parents is picking up seeds of only those plants for multiplication which have the desired traits. For example, grain length in rice is variable— longer grains, intermediate grains and shorter grains. If we select the seeds of the longest grains and sow them to grow the next generation, the selected population of rice plants will have on average, longer grains than the original population.

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(iii) Cross-Hybridization among Selected Parents:

Hybridisation is the most com­mon method of creating genetic variation. Hybridisation is crossing of two or more types of plants for bringing their traits together in the progeny. It brings about useful genetic/ heritable variations of two or more lines together. Line is a group of individuals related to descent and have similar genotype. The individuals or lines used in hybridisation are called parents. Hybridisation takes a lot of time.

As stated earlier a wheat variety HUW 468 took 12 years to develop. Hybridisation may involve a single cross (two plants) or multiple cross (more than two plants). Wheat variety C-306 was developed through multiple cross between C-591 (Reagent 1974 x Ch2-3) and hybrid of P-19 x C-281. Hybridisation may further be:

(i) intravarietal,

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(ii) intervarietal (= intraspecific) or

(iii) interspecific and

(iv) intergeneric. Intervarietal hybridisation is the process of crossing individuals of different lines or varieties of the same species to produce hybrid, e.g., different varieties of wheat are mated. Interspecific hybridisation is the process of crossing individuals of two different species to produce a hybrid. Examples of interspecific hybridisation are the development of rice variety ADT-37 from a cross between Oryza japonica and O. indices and all the sugarcane varieties being cultivated today. In intergeneric hybridisation, the cross is between two different genera.