Plant Breeding- strategies of Enhancement in Food Production

Plant Breeding: Green revolution was dependent to a large extent on plant breeding techniques for development of high – yielding and disease resistant varieties 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, giver better yields and are disease resistant.

The main steps in breeding a new genetic variant of a crop are –

a)  Collection of variability – Collection and preservation of all the different wild varieties, species and relatives of the cultivated species.

b)  Evaluation and selection of parents – Evaluation is done to identify plants with desirable characters.  The selected plants are multiplied and used in the process of hybridization.

c)  Cross-hybridization among the selected parents – By cross-hybridizing the two parents to produce hybrids that genetically combine the desired characters in one plant.

d) Selection and testing of superior recombinants – The selection process is crucial to the success of the breeding objective and requires a careful scientific evaluation of the progeny.  These are self-pollinated for several generations till they reach a state of uniformity so that the characters will not segregate in the progeny.

e) Testing, release, and commercialization of new cultivars – This evaluation is done by growing these plants in the research fields and recording their performance under ideal fertilizer application irrigation, and other crop management practices.  It will be followed by testing the materials in farmers’ fields, for at least three growing at several locations in the country.

Wheat and Rice:

• In 1963, several varieties such as Sonalika and Kalyan Sona, which were high yielding and disease resistant, were introduced all over the wheat-growing belt of India.
• Semi-dwarf rice varieties were derived from IR-8, and Taichung Native-1 were introduced in 1966.  Later better-yielding semi-dwarf varieties Jaya and Ratna were developed in India.

Sugarcane: Saccharum Barberi and Saccharum officinarum were crossed to get the desirable qualities of high yield, thick stems, high sugar and ability to grow in the sugar cane areas of north India.

Millets: Hybrid maize, jowar, and bajra have been developed in India, which is high yielding and resistant to water stress.

1. a) Plant Breeding for Disease Resistance:
   
   Methods of Breeding for disease resistance: The various sequential steps are;
   Screening germplasm for resistance, hybridization of selected parents, selection and evaluation of the hybrids and testing and release of new varieties.CROP                 VARIETY                                            RESISTANCE TO DISEASES
   Wheat                        Himgiri                                                Leaf and stripe rust, hill bunt
   Brassica                      Pusa swarnim                                      White rust                                            Cauliflower                  Pusa Shubhra, Pusa Snowball K – 1       Black rot and Curl blight black rot
   Cowpea                       Pusa Komal                                         Bacterial Blight
   Chilli                            Pusa Sadabahar                                  Chilly mosaic virus, Tobacco mosaic virus and Leaf curl
   
   Mutation Breeding:

• It is the process by which genetic variations are created through changes in the base sequence within genes resulting in the creation of a new character or trait not found in the parental type.
• It is possible to induce mutations artificially through use of chemicals or radiations, and selecting and using the plants that have the desired character as a source inbreeding.
• For example, in mung bean, resistance to yellow mosaic virus and powdery mildew were induced by mutations.
• Resistance to the yellow mosaic virus in bhindi (Abelmoschus esculentus) was transferred from a wild species and resulted in a new variety of A. esculentus called Parbhani Kranti.

1. 
   b) Plant Breeding for Developing Resistance to Insect Pests:

• Insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics.
• Hairy leaves in several plants are associated with resistance to insect pests, e.g., resistance to jassids in cotton and cereal leaf beetle in wheat.
• High aspartic acid, low nitrogen and sugar content in maize lead to resistance to maize stem borers.
• Smooth-leaved and nectar-less cotton varieties do not attract bollworms.

CROP                     VARIETY                                          INSECT PESTS
Brassica                  Pusa Gaurav                                      Aphids
Flat bean                 Pusa Sem 2, Pusa Sem 3                   Jassids, aphids and fruit borer
Okra (bhindi)            Pusa Sawani, Pusa A – 4                   Shoot and Fruit borer

c) Plant Breeding for Improved Food Quality:

• Diets lacking essential micronutrients – particularly iron, vitamin A, iodine, and zinc – increase the risk for disease, reduce lifespan and reduce mental abilities.

Biofortification:- It is the process of breeding crops with higher levels of vitamins and minerals, or higher protein and healthier fats.

Breeding for improved nutritional quality is undertaken with the objectives of improving;

• Protein content and quality
• Oil content and quality
• Vitamin content ; and
• Micronutrient and mineral content

Examples;- Vitamin A enriched carrots, spinach, pumpkin; Vitamin C enriched bitter gourd, mustard, tomato; Iron and Calcium enriched spinach and Protein enriched Beans.

d) Single Cell Protein (SCP):

• Single cell proteins can be produced from algae, fungi, yeasts, and bacteria.
• Some low-cost substrates are used to produce microbial biomass to produce single cell proteins.
• SCP is rich in high-quality protein and is low in fat content, hence it is a desirable human food.
• SCP should also reduce the pressure on agricultural production systems for the supply of proteins and it can reduce environmental pollution.
• For example, microbes like Spirulina can be grown easily on materials like waste water from potato processing plants, straw, molasses, animal manure and even sewage, to produce large quantities and can serve as food rich in protein, minerals, fats, carbohydrate, and vitamins.

1. d) Tissue Culture: Plant tissue culture refers to the maintenance and growth of plant cells, tissues and organs on a suitable synthetic medium in vitro and the whole plants could be regenerated from explants.Explant: An explant is the plant part excised from a specific location in a plant, to be used for initiating a culture.In this tissue culture process, explant, i.e., any part of a plant is taken out and grown in a test tube, under sterile conditions in special nutrient media.  This capacity to generate a whole plant from any cell/explant is called Totipotency. This method of producing thousands of plants through tissue culture is called Micropropagation. Each of these plants will be genetically identical to the original plant from which they were grown i.e., they are somaclones.Somatic Hybridisation/ Somatic Hybrids: The first step in somatic hybridization is to remove the cell wall by digesting it with enzymes like pectinase and cellulase.

   Isolated protoplasts from two different varieties of plants – each having a desirable character – can be fused to get hybrid protoplasts, which can be further grown to form a new plant. These hybrids are called somatic hybrids while the process is called somatic hybridization.  For example, a protoplast of tomato is fused with that of potato to form new hybrid plants combining tomato and potato characteristics.