Cybrid | Biology for Grade 12 PDF Download

CYBRID:

Cybrids posses a nuclear genome from only one parent but cytoplasmic genes from both parents. The process of protoplast fusion resulting in the development of cybrid is known as cybridisation / cytoplasmic hybrids. 

Formation of cybrids : - Two methods-

(i)   By fusion of nucleated protoplast of one parent to enucleated protoplast of another protoplast.

(ii)  By elimination of one nucleus form heterokaryon.

Use of Cybrids :   In plant cell, some genetic factors are also present in cytoplasm. During cybridisation these factors fused together and perform cytoplasmic inheritance.

eg. (i)  Streptomycin resistant gene is transfer from Nicotiana tabacum to N.silvestrise.

(ii)  Gene of male sterility is transferred in Nicotiana, Brassica and Petunia from one-another.

APPLICATION OF PLANTLETS PRODUCED BY PLANT TISSUE CULTURE

(I)  Rapid clonal propagation of superior lines ⇒ e.g. oil palm

Clone : Group of individuals or cells derived from a single individual or cell by asexual reproduction.

Multiplication of genetically identical copies of a cultivar by asexual reproduction is called clonal propagation or cloning or micro propagation.

All the cells in culture are derived from a single explant by mitotic division, so all plantlets regenerate from a culture generally, have the same genotype and constitute a clone. These plantlets can be used for rapid clonal propagation of superior lines like oil palm.

Two common types of micro propagation are :

(a) Multiple shootlet production 

(b)  Somatic embryogenesis 

(II) Somaclonal variation : Genetic variation presents among plants regenerated from tissue culture have been termed as somaclonal variation.

• These variations are originated by minor chromosomal aberration or by gene mutation.
• The variation which are stable and have agronomic characters like resistance to diseases and pests, stress tolerance, early maturation, better yields are used in agriculture.
• By somaclonal variations many useful varieties are developed.
• Rusts resistance in wheat.
• Resistance for tungro virus and leaf hopper in rice.
• Resistance for late blight in potato.
• High protein content in potato.
• Shortening of harvest duration in sugarcane.

(III) To produce transgenic plants : 

Transgene : A foreign gene that is transferred in to an organism by genetic engineering.

Transgenic plant/organism ⇒ plant/organism that contains and expresses a transgene. The cells containing and expressing transgenes can be easily selected in vitro and valuable plants can be regenerated from these cells. 

NEW AND UNDER UTILIZED CROPS

1. Out of 3,50,000 known plants at this time, a few i.e about 100 plants are being used for fulfilling man's daily requirement.

2. Less known and under-utilized crop plants, which can be used for food and other purposes in future are known as new crops.

(i)   Triticale (Muntzing) :- It is the first man made cereal crop, which has been produced by inter-generic hybridization between common wheat (Triticum aestivum) and European rye (Secale).

Triticale is hexaploid (When tetraploid wheat is used) or Octa ploid (when hexaploid wheat is used)

Triticale is not suitable for purpose of bread making because of low gluten content, but it is a good forage crop.

(ii)  Winged bean : (Psophocarpus tetragonoloba) :This is a herbaceous plant, which has capacity of nitrogen fixation. It produces long pods with four prominent wings (So named winged bean).

• The tuberous roots, leaves, pods and seeds are highly nutritious due to rich source of proteins.
• The ripened seeds contain about 34% proteins and 13% oils (similar to soyabean)
• This plant can be used as a green manure plant, fodder plant.

(iii) Jojoba = (Simmondsia chinensis) : This is a shrub, which is native of Mexican deserts. It is important desert plant and hence is being grown in deserts.

• The seeds of this plant contain about 50% liquid wax, which is similar to sperm whale oil (spermaceti)
• This liquid wax was originally used in cosmetic, but now is also being used in high-performance lubricants required to withstand extreme pressures.
• So growing of this plant, can reduce the pressure on sperm whales, which are killed for their oil.
• Jojoba can thrive under poor soil and low moisture conditions. Its cultivation in arid regions of the world help in economic development of the poor.

(iv) Guayule = (Parthenium argentatum) : It belongs to family Asteraceae.

• This is the native of America. 
• This plant commonly known as ''Congress grass''. It is a terrestrial weed in India.
• This plant is a shrub and can grown on poor desert soil.
• This plant is now days used in obtaining rubber, which is called ''Guayule rubber''. 
• Guayule rubber is similar to Para rubber or hevea rubber. 
• The plant contains 12-20% rubber on dry weight basis.
• This plant can be a natural source of rubber in future.

(v)  Leucaena or Subabul :- Leucaena leucocephala (fam. leguminosae) 

• This is a fast growing leguminous tree and native of Central America.
• This plant is nowadays being planted on a large scale under ''social forestry'' 
• This plant is used as wind breakers, fire breaker, shade plant for deforested tropical regions.
• It's leaves are used as fodder, wood as fuel and in charcoal formation, paper pulp, rayon and timber.

OTHER UNDER UTILIZED CROPS

(a)  Oil plants :- Some potential oil yielding plants are there, which provide edible and non edible oils after suitable treatments. Some potential oil crops are as follow :-

(i)   Margossa or neem :- Azadiracta indica (fam. meliaceae) 

It is native of Burma and is widely grown tree in India. Seeds are source of margossa or neem oil with bitter taste, used in soap making.

(ii)  Buffalo gourd (Cucurbita foetidissima) seeds of this plant provide oil.

(iii) Bitter colocynth (Citrullus colocynthis) seeds give oil.

(iv) Mahua (Madhuca indica) :- seeds give oil, used in soap making and also cooking purposes.

(v)  Pilu (Salvadora persica), Brihath pilu (S. oleoides) sal (Shorea robusta), karanj (Pongamia pinnata) seeds of all these plants give oil.

(b)  Some non-alcoholic beverages (less known) :- 

(i)   Mate or Paraguay tea :- Leaves of Ilex paraguariensis 

(ii)  Cola :- Powdered seed of Cola nitida 

(iii) Khat or Arabian tea-From leaves of Catha edulis 

(c)  Fodder trees :- 

(i)   Acacia nilotica (kikar or Babul)

(ii) Albizzia lebbec (siris)

(iii) Ficus religiosa (Peepal)

(iv) Morus alba (white mulberry)

(v) Sesbania grandiflora (Basna)

PESTICIDES

Pesticides are those substances, which are used to kill, control or repel pest.

Pests : Pests are the organisms (viz-disease causing microbes, insects, mites, nematodes and weeds) those cause harm to human interests by destroying the agricultural crop, storage of plant products as well as bring about diseases in domestic animal and beings.

Pests cause loss in agricultural productivity up to about 30%.

Type of Pesticide :

Classification of Pesticides [On the basis of chemical structure]:

Mode of action of pesticides:  

1. Most of the herbicides have affected on photosystem II^nd of photosynthesis (disturbing the photolysis of water and oxygen evolution). Some herbicides block sieve tube i.e. disturb translocation of organic food.

2. Most of the insecticides kill insects by affecting their nervous system. Some insecticide arrest the respiratory system and kill the insects.

Advantages of pesticides

1. Increase in yield of food and other crop plants.

2. Pesticides control vectors or carriers of different disease causing organism.

HARMFUL EFFECTS OF PESTICIDES

(1)  Environmental pollution : As pesticides are non selective in their mode of action, so these also kill useful organisms along with harmful organisms thus equilibrium state of ecosystem is disturb.

Excessive use of insecticide in crop, some time leads to decrease in productivity. Because pollinator insects are also killed.

(2)  As pesticides are poisonous or toxic, so cause serious health hazards.

(3)  Excessive and prolonged use of pesticides leads to resistance in pest. Hence high concentration of pesticides is to be used in controlling to these resistant pests; this effect is called ''Pesticide trademill''. Pesticide trademill leads to increase in LD₅₀ concentration of pesticides.

LD 50 (Lethal Dose 50) : It is the minimum concentration of pesticide which can kill 50% of total pest population.

(4)  Due to their non biodegradable nature, their concentration increases in the body of organism of successive trophic level, with the rise in trophic level is called biomagnification or bioconcentration. 

Most organochlorines are fat soluble and undergo biomagnification.

In India as a result of prolonged use of DDT, 13-31 ppm of DDT can be detected in the body fat of people. (highest in world).

Development of resistance to pesticides

When pesticides are sprayed, some pest individuals having :

(i)   Less permeable cuticle

(ii)  Capability of faster storage of toxin in fat.

(iii)  Better enzyme equipment for metabolising the toxin.

So due to above reason pest individuals develop resistance to pesticide.

INTEGRATED PEST MANAGEMENT (IPM)

It is technique of pest control, which involves natural methods to a greater extent.

IPM involves use of different pest control method, which are ecologically sound i.e. do not cause hazards to environment. A complex system of check and balances and use of different methods to kept the pest population at manageable level and loss by pest at minimum level known as IPM.

eg. Biological control method. better agricultural practices like-crop rotation, sanitation, use of resistant varieties, etc.

BIO-FERTILIZER

• Fertilizers are used to increase soil fertility.
• Among the sixteen essential plant nutrients, N,P,K are deficient in Indian soil.
• Fertilizers, which contain only one primary nutrient are called straight fertilizer or  simple fertilizer.  eg. Urea, Mono ortho pottash (Mop). 
• Fertilizers, which contain two or more primary nutrient are called compound or multinutrient fertilizers. eg. Di-ammonium phosphate, N:P:K etc. 
• Use of chemical fertilizers increase food production, but side by side there are many hazardous effect of these chemical substance on environment and organisms. Chemical fertilizers are highly expensive.
• Excessive use of chemical fertilizer requires more number of irrigation which leads to increase in salinity of soil.
• Use of fertilizers of biological origin is an alternative for overcoming the harmful effects of these chemical fertilizers-

Fertilizers of biological origin.

They are two types :-

(A) Manures   
(B) Biofertilizers.

(A) Manures :- 

Manure is semi-decayed organic matter, which is added to the soil in order to increase soil fertility, aeration and water holding capacity.

Three types of manures 

(i) Farmyard manure : This type of manure consisting of cattle dung, farm refuse, fallen leaves and twigs. These materials are placed in heaps and allowed to decompose till they form a dark amorphous substance. e.g.  Product of gobar gas plant.

(ii) Composited manure (Compost) : This manure consist of rotten vegetable matter, sewage sludge and animal refuse. Some chemical fertilizers added in small amount.

(iii) Green manure : These are fast growing herbaceous crops, which are ploughed down and mixed with the soil, while still green. These provide both organic matter and nitrogen to the soil.

The green manure check ''soil erosion'' by forming protective soil cover and also prevent leaching of minerals.

Green manures increase crop yield by 30-50%

Some important green manure crops, which are mostly members of family leguminosae are as follow-