PLANT BREEDING

PLANT BREEDING:

  • Plant breeding as a technology has helped increase yields to a large extent.
  • Green revolution was not only responsible to meet the national requirement of food, but also helped us even to export it.
  • Green revolution is due to plant breeding techniques which developed high yielding variety of wheat, rice, maize etc.

What is plant breeding?

  • Plant breeding is the purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant.
  • Classical plant breeding involved crossing or hybridization of pure lines followed by artificial selection to produce plants with desirable traits of higher yield, nutrition and resistance to diseases.

Trait for which plant breeding done:

  • Trait or characters that the breeders have tried to incorporated into the plants are as follows:
    • Increased crop yield
    • Improve quality
    • Increased tolerance to environmental stresses (salinity, extreme temperature, and drought).
    • Resistant to pathogens ( viruses, fungi, and bacteria)
    • Increase tolerance to insect pest.

Steps in plant breeding techniques:

  • Collection of variability:
    • Genetic variability is the root of any breeding programme.
    • Pre-existing genetic variability is available from wild relatives of crop.
    • Collection and preservation of all the different wild varieties, species and relatives of the cultivated species.
    • Evaluation for their characteristics.
    • The entire collection (of plants /seeds) having all the diverse alleles for all genes in a given crop is calledgermplasm collection.

 

  • Evaluation and selection of parents:
    • The germplasm is evaluated so as to identify plants with desirable combination of characters.
    • The selected plants are multiplied and used in hybridization.
    • Pure line is created wherever desirable and possible.

 

  • Cross hybridization among the selected parents:
    • Cross hybridization of two selected parent by emasculation and bagging, to produce hybrid of combined character of both parents.
    • For example high protein quality of one parent may need to be combined with disease resistance from another patent.
    • Usually one in few hundred to a thousand crosses offsprings shows desirable combinations.

 

  • Selection and testing of superior recombinants:
    • Selection is done from the progeny of hybrids produced by cross hybridization.
    • It requires careful scientific observations and evaluation of progeny.
    • Hybrid plants that are superior to both of the parents are selected.
    • These hybrids are self-pollinated for several generations till they reach a state of uniformity (homozygosity).

 

  • Testing, release and commercialization of new cultivars:
    • Selected pure lines are evaluated for their yield and other agronomic traits of quality, disease resistance etc.
    • This evaluation is done in the research fields and recording their performance under ideal fertilizer, irrigation
    • Testing is done in the farmers ‘fields’ at least for three generation.
    • The material is compared with best available local crop cultivar.

Product: Wheat and Rice:-

  • Production of wheat and rice increased in many folds due to semi-dwarf variety during the period of 1960-2000.
  • Nobel laureate Norman E.Borlaug, at international centre for wheat and Maize improvement in Mexico, developed semi-dwarf variety of wheat.
  • In 1963 several varieties such Sonalika and Kalyan Sona high yielding variety was introduced in India.
  • Semi-dwarf rice was derived from IR-8(developed at International Rice Research Institute (IRRI) Philippines) and Taichung Native –I (from Taiwan).
  • Jayaand Ratna, semi dwarf rice variety developed in India.

Product: sugarcane:

  • Saccharum barberi of north India with poor sugar content and yield crossed with Saccharum officinarum with thick stems and higher sugar content to produce sugar cane of high yield, thick stems, and high sugar.

Plant breeding for Disease Resistance:

  • A wide range of fungal, bacterial and viral pathogens, affects the yield of cultivated crop species, they lessens the yield upto 20-30 % sometime total.
  • Development of cultivars resistant to diseases is essential.
  • This also reduce he dependence on he fungicide or insecticide.

 

  • Pathogen causing different diseases in plants:
    • Fungi: brown rust of wheat, red rot of sugarcane, late blight of potato.
    • Bacteria: black rot of crucifer,
    • Virus: tobacco mosaic, turnip mosaic etc.

Method of breeding for disease resistant:

  • Screening of germplasm for resistance sources.
  • Hybridization of selected parent.
  • Selection and evaluation of hybrids
  • Testing and release of new varieties.

 

Mutation breeding:

  • Genetic variability is created by induced mutation. (By application of mutagen, chemical or physical).
  • Screening and selection of the parent with desirable character used as a parental plant for breeding programme.
  • In mung bean, resistance to yellow mosaic virus and powdery mildew were induced by mutation.
  • Natural wild varieties of plant with disease resistant genes are available but low yield.
  • These wild varieties are hybridized with high yield varieties to make them disease resistant and also high yielding variety.
  • Resistance to yellow mosaic virus in bhindi (Abelmoschus esculentus) was transferred from a wild species and resulted a new variety of A.esculentus called Parbhani kranti.

Plant breeding for Developing Resistant to insect pest:

  • Another major cause of large scale destruction of crop plants is the insect and pest infestation.
  • Insect resistance in host crop is due to morphological, biochemical or physiological characteristics.

Characters that make the plant resistance to insect pest:

  • Hairy leaves in several plants make them resistant to insect pest.
  • Solid stem in wheat lead to non-preference by stem sawfly.
  • Smooth leaves and nectar-less cotton variety do not attract bollworms.
  • High aspartic acidlow nitrogen and sugar content in maize make them resistant to stem borers.
  • Steps for developing insect pest resistant variety of crop are same as others.
  • The resistant variety selected either form the wild variety of from other available cultivars.

Plant breeding for Improved Food quality:

  • Around three billion people suffer from micronutrient, protein and vitamin deficiencies called Hidden hunger.
  • Diets lacking essential micronutrients particularly iron, vitamin A, iodine or zinc- increase the risk of diseases; reduce life span, reduce mental ability.
  • Biofortification:-breeding crops with higher levels of vitamins and minerals or higher protein and healthier fats – is the most practical means to improve public health,
  • Objectives of biofortification: is to improve
    • Protein content and quality.
    • Oil content and quality
    • Vitamin content and
    • Micronutrient and mineral content.
  • Hybrid maize developed with twice the amount of amino acids lysine and tryptophan, compared with existing maize.
  • Wheat variety Atlas 66, having high protein content has been used as donor for improving cultivated wheat.
  • Iron fortified rice developed with five times more iron than existing variety.
  • IARI New Delhi developed:
    • Vitamin A enriched carrots, spinach pumpkin.
    • Vitamin C enriched bitter gourd, bathua mustard tomato.
    • Iron and Calcium enriched spinach and bathua
    • Protein enriched beans- broad, lablab, French and garden peas.

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