Notes-Part-1-Class-12-Biology-Chapter-11-Enhancement in Food Production-Maharashtra Board

Objectives of plant breeding:

Primary aim of plant breeding is to obtain a new crop variety superior to the existing type, in all characters.

Some Objectives of plant breeding are common (as given below) and some vary according to type and use of the plant.

• To increase crop yield.
• To improve quality of produce.
• To increase tolerance to environmental stresses.
• To develop varieties of plants resistant to pathogens and insect pest.
• To alter the lifespan.

The main steps of the plant breeding program (Hybridization) :

(1) Collection of variability :

• Germplasm collection is the entire collection of all the diverse alleles for all genes in a given crop.
• Wild species and relatives of the cultivated species having desired traits are collected and preserved.

Germplasm conservation can be done in following ways :

• In situ conservation : It can be done withthe help of forests and Natural Reserves.
• Ex situ conservation : It is done through botanical gardens, seed banks, etc.

(2) Evaluation and selection of parents :

• The collected germplasm is evaluated toidentify healthy and vigorous plants with desirable and complementary characters.
• Selected parents are selfed for three to four generations to increase homozygosity.
• Only pure lines are selected, multiplied and used in the hybridization.

(3) Hybridization :

• The variety showing maximum desirable features is selected as female (recurrent) parent and the other variety which lacks good characters found in recurrent parent is selected as male parent (donor).
• The pollen grains from anthers of male parent are artificially dusted over stigmas of emasculated flowers of female parent.
• Hybrid seeds are collected and sown to grow F₁ geneartion.

(4) Selection and Testing of Superior Recombinants :

• The F₁ hybrid plants which are superior to both the parents and having high hybrid vigour, are selected and selfed for few generations to make them homozygous for the said desirable characters.
• This ensures that there is no further segregation of the characters.

(5) Testing, release and commercialization of new cultivars :

• The newly selected lines are evaluated for the productivity and desirable features like disease resistance, pest resistance, quality, etc.
• They are initially grown under controlled conditions of water, fertilizers, etc. and their performance is recorded.
• The selected lines are then grown for at least three generations in natural field, in different agro climatic zones.
• Finally variety is released as new variety for use by the farmers.

Indian Hybrid Crops :

Wheat and Rice :

• Hybrid wheat varieties in India : Sonalika and Kalyan Sona
• Semi-dwarf rice varieties in India: Jaya, Padma and Ratna
• Semi-dwarf rice varieties were developed from IR—8 (International Rice Research
• Institute] and Taichung native—I (from Taiwan) and introduced in India.

Sugar cane :

• Saccharum barberi : Native of North India and it has poor yield and sugar content.
• S.officinarum : Grown in South India, has thicker stem and high sugar contents, but it does not grow Well in North India.
• Hybrid varieties developed by crossing these two species have desirable combinations of characters like high sugar content, thicker stem and the ability to grow in North India.
• Sugar cane varieties developed at Coimbatore, Tamil Nadu : CO-419, 421, 453

Millets : Hybrid maize (Ganga-3), Jowar (CO-12) and Bajra [Niphad) : These varieties are high yielding and resistant to water stress.

Some of the plant diseases are as follows :

Some disease resistant plants developed are :

Mutant varieties :

• Rice : Jagannath
• Wheat : NP 836 (rust resistant)
• Cotton : Indore-2 (resistant to bollworm)
• Cabbage : Regina-II (resistant to bacterial rot), etc.

Some pest resistant varieties :

Requirements of tissue culture :

(i) Maintenance of aseptic conditions :

• Sterilization of glassware : It is carried out using detergents, hot air oven.
• Sterilization of nutrient medium : It is done by using autoclave.
• Sterilization of explant : It is carried out by treatment of 20% ethyl alcohol and 0.1% HgCl₂.
• Sterilization of inoculation chamber (Laminar air flow) : It is carried out by using UV ray tube for 1 hour before performing actual inoculation of explant on the sterilized nutrient medium,

(ii) Temperature : 18 °C to 20 °C

(iii) pH of nutrient medium : 5 to 5.8

(iv) Aeration (particularly for suspension culture)

Callus culture :

• In callus culture, nutrient medium is solidified using agar-agar is used.
• Shaker or agitator is not required.
• Sterilized explant is placed on solid nutritive medium.
• The cells of explants absorb nutrients and start multiplying.
• This results in the formation of callus.
• Callus is a mass of undifferentiated cells, formed by division of the cells of explants.
• Growth hormones, auxins and cytokinins are provided to callus in specific proportion to induce formation of organs.
• If auxins are in more quantity, roots are formed (rhizogenesis) and if the cvtokinins are in more quantity, shoot formation takes place (caulogenesis).
• Thus new plantlets are formed.
• Callus culture required subculturing to ensure its continuous growth.

Suspension culture :

• In suspension culture, small groups of cells or a single cell are transferred to liquid nutritive medium as explants.
• The liquid medium is constantly agitated by using shakers (agitators).
• The agitation serves the purpose of aeration, mixing of medium and prevents the aggregation of cells.
• Generally the suspension culture shows a high proportion of single isolated cells and small clumps of cells.
• Suspension culture grows much faster than callus culture.
• Suspension culture is used for cell biomass production which can be utilized for biochemical isolation, regeneration of new plants etc.

Applications of micropropagatlon :

• Micropropagation involves in rapid multiplication of genetically similar plants (clones).
• A large number of plantlets are obtained within a short period and in a small space.
• Plants are obtained throughout the year, under controlled conditions, independent of seasons.
• As micropropagation results in the formation of clones, desirable characters (genotype and sex) of superior variety can be maintained for many generations.
• The rare plant and endangered species are multiplied and conserved using this technique.
• With the help of somatic hybrids (cybrids), new variety can be obtained in short time span.
• Micropropagation is involved in commercial production of ornamental plants like orchids, Chrysanthemum, Eucalyptus, etc. and fruit plants like banana, grapes, Citrus, etc.

Applications of tissue culture are as follows :

• Production of healthy plants from diseased plants using apical meristems as explants.
• Production of stress resistant plants.
• Production of haploid plantlets by pollen culture.
• Production of secondary metabolites such as alkaloids, enzymes, hormones, etc.
• Multiplication of rare and endangered plants.
• Production of somaclonal variants.
• Use of micropropagation techniques to produce large number of genetically identical plants.
• Protoplast culture
• Tissue culture has applications in forestry, agriculture, horticulture, genetic engineering and physiology.

Advantages of Single-Cell Protein :

• Microorganisms have a high rate of multiplication that means a large quantity of biomass can be produced in a comparatively short duration.
• The microbes can be easily genetically modified to vary the amino acid composition. They have high protein contents- 43% to 85% (W/W basis).
• A broad variety of raw materials, including waste materials, can be used as a substrate for SCP. This also helps in decreasing the number of pollutants.
• SCP serves as a good source of vitamins, amino acids, minerals, crude fibres, etc.
• SCPs can be used as fodder for achieving fattening of calves, pigs, in breeding fish poultry and cattle farming.

Some examples of biofortification :

• Fortified Maize having twice the amount of amino acids- lysine and tryptophan.
• Wheat -Atlas 66 has a high protein content and Iron-fortified rice has 5 times more iron, are developed.
• Vegetable crops like carrot and spinach have more vitamin A and minerals.
• Vitamin C enriched bitter gourd, tomato have been developed by IARI.