Biofertilizers & Development of New Varieties | Biology for Grade 12 PDF Download

BIOFERTILIZERS

•  Fertilizers are used to increase soil fertility. Total consumption of chemical fertilizers in India is about 9.2 million tonnes.

• Nitrogen, phosphorus and potassium are primary nutrients or critical nutrients.

• Among the seventeen essential plant nutrients N, P, K are deficient in Indian soil.

• Fertilizers, which contain only one primary nutrient are called straight fertilizers or simple fertilizers.

• Fertilizers, which contain two or more primary nutrients are called compound or multi-nutrient fertilizers.

• Use of chemical fertilizers increase food production, but side by side there are many hazardous effect of these chemical substances on environment and organisms.

• Chemical fertilizers are highly expensive.

•  So 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) Bio-fertilizers

(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.
  Organic Manure

Three types of manures

(i) Farmyard manure :-

• This type of manure consists 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. Y Product of gobar gas plant.

(ii) Composited manure (Compost) :-

• This manure consists of rotten vegetable matter, sewage sludge and animal refuse. Some chemical fertilizers are added in small amount.

(iii) Green manure :-

• These are fast growing herbacious 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 follows:

Biofertilizers :- These are the organisms like bacteria, blue green algae and fungi (mycorrhiza) which enrich the soil in nutrients. Some important bio-fertilizers are :-

(1) Bacteria as bio-fertilizers :-(a) Symbiotic nitrogen fixing bacteria :-

•  "Rhizobium leguminosarum" 

•  Frenkia, a nitrogen fixing filamentous bacterium is associated symbiotically with the root nodules of non-legume plants like Casurina, Rubus, Alnus myrica.

(b) Free-living nitrogen fixing bacteria :-

•  Azotobacter, Clostridium, Beijerinckia, Bacillus polymixa.

(c) Loose association of nitrogen fixing bacteria :-

•  A bacterium "Azospirillum lipoferum" forms loose association with roots of maize and some Brazilian grasses, which increase crop yield(Dobriner).

(2) Blue green algae (Cyanobacteria) as bio-fertilizers :-

(a) Free living nitrogen fixing BGA :-

•  Blue green algae like Anabaena, Aulosira, Tolypothrix, Plectonema are most common nitrogen fixing organism.

•  "Aulosira fertilissima" is the most effective nitrogen fixer of rice fields.

(b) Symbiotic nitrogen fixing cyanobacteria :

•  "Azolla pinnata" is a small aquatic fern inoculated to rice fields of South-East Asian countries. It's leaf cavities contain symbiotic BGA-Anabaena azollae.

•  A. pinnata is best bio-fertilizer for rice. Farmers have reported upto 50% - higher yield of rice by using A.pinnata.

(3) Fungi as biofertilizer :-

(i) Mycorrhiza :- Symbiotic association between roots of higher plants and fungal hypae is called mycorrhiza.

GENETIC IMPROVEMENT

Trait : Trait or character is any morphological, anatomical, biochemical or behavioural feature of an organism.

Variety : A group of plant that has the almost same genotype, but it differs for one or more characters from other varieties of the same crop.

An improved variety is superior to the other existing varieties of the same crop in one or more characters.

DEVELOPMENT OF NEW VARIETIES:

The 4 main steps in variety development are –

(A) Creation of variation

(B) Selection

(C) Evaluation

(D) Seed multiplication & distribution.

(A) Creation of variation :- Difference among individuals of a population or species for a given character is known as variation.

Variations are of 2 types –

(i) Genetic variations :- Differences in genotype of individuals.

•  These are created by recombination of new alleles of different genes present in a crop.

•  These are heritable variations.

•  These are useful for selection.

(ii) Variation due to environment :-

•  Aries due to environment.

•  Not inheritable.

•  Not useful for selection.

A species can be improved only when genetic variations are present. For the species success of breeding programme depends on creation of desired variation.

Genetic variation can be created by following methods –

(1) Domestication

(2) Germplasm collection & conservation

(3) Plant introduction

(4) Hybridisation

(5) Polyploidy

(6) Mutational breeding

(7) Genetic engineering

(1) Domestication :- All the present species of cultivated plants are of wild type species in origin and the process of cultivation of wild species in order to fulfill human need is called domestication of plant.

•  Genetic diversity is the occurrence of large number of varieties, biotypes, variations and alleles.

•  Greatest genetic diversity of plants is found in their natural home lands.

•  Germplasm collections are made mostly from an area, where agriculture is still primitive, and where relatives of crop plants still live in wild areas like Peru, Bolivia, Middle east etc.

•  Vavilov (1926) proposed that different crop plants originated in different areas, where their wild relatives are present and genetic diversity is maximum.

•  Vavilov proposed 11 centers of origin. Australia is the 12th center. He collected 26,000 varieties of wheat.

•  Cotton has developed in both old and new world.

•  New world was discovered by Christopher Columbus in 1492, when he landed on island of Bahmas in Caribbean sea.

The original homeland of some important  crops are listed below :-

• Natural home : It is the centre of origin of a crop, which often abounds in its wild relatives and has maximum genetic diversity.

• Secondary home :- It is the major centre of production of a crop plant, which is away from centre of origin and lacks wild relatives.

• Wild relatives :- Species related to cultivated plants that occur in the wild areas of their origin.

(2) Germplasm collection & conservation :-Germplasm is the sum total of all the alleles of the genes present in a cell of a crop and its related species.

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

It  consists of –

(i) Cultivated improved varieties.
(ii) Improved varieties that are no more cultivated.
(iii) Old local or desi varieties.
(iv) Varieties produced by plant breeders (undistributed).
(v) Wild species related to the crop species.

• The sum total of different types of all the genes and their alleles present in a population is called gene pool.

• The gene pool of a population is not static.

• Genetic erosion – The loss of genes from a gene pool is called genetic erosion.

• Genetic erosion occurs due to deforestation, urban expansion, damage to ecosystem and adoption of genetically uniform modern variety of crops.

• 11 million hectares of tropical forest disappear every year.

• There are four basic way to conserve plant germplasm.
  (i) Conservation of plant in wild state i.e. in natural habitat like forests.
  (ii) Conservation of plants in botanical gardens.
  (iii) Introduction of plants for cultivation in agriculture and horticulture.
  (iv) Preservation of plants in seed form or some other suitable form.

In–situ conservation – It means maintenance of biological diversity in natural habitats like forests and natural reserve like national parks, wildlife sanctuaries and bio–sphere reserves. In-situ conservation of wild plants help in protecting species threatened with extinction.

Ex–situ conservation – It is the conservation of selected or rare plant in a place outside the natural home.
In this conservation rare or selected plant material are grown in specific gardens. eg. Ginkgo biloba is so common in United states, because the cultivation of this plant is taken up by gardeners.

• Ex–situ conservation includes offsite collections and gene bank.
  (a) Offsite collection :- They are living collections of wild and domesticated species in botanical garden, zoo etc.
  (b) Gene bank :- For plant breeding purpose (i.e. for improvement to plants) a large number of varieties with different characters are needed. Hence number of plant germplasm (both wild and cultivated) are collected and stored at suitable place.

• The place or institution, where different plant material (genes) are kept or preserved, is called “Gene bank”.

• In gene bank, storage of germplasm is done either in the form of seed or vegetative material, but best and convenient way is storage of seed.

• Seed means, plant part that is used to grow a crop. Thus ‘seed’ would include grains of wheat, rice, tubers of potato, stem of sugarcane, which are used for producing new plants.

• Storage of dry seeds is done at low temperature (–10 to –20°C), because under these conditions the metabolic activities are minimum, prevent their germination.

Seeds are of two types –

(a) Orthodox seed :- The seeds which can not be killed or damaged as a result of decrease in moisture content & temperature. e.g seeds of wheat, rice, maize, oat, barley(Cereals) and also different pulses or legumes.

(b) Recalcitrant seeds :- The seeds which can be killed or damaged as a result of drying and decrease in temperature.
These can be stored for a short span. e.g seeds of rubber, tea, coconut, Jack fruit(Artocarpus) litchi, oil palm(elaies) etc.

• Conservation of crop with recalcitrant seed, can be made by in-situ conservation method and also by tissue culture method.

• Plants with recalcitrant seed are grown in orchard, where all possible strains and varieties are maintained.

• Storage of germplasm by tissue culture :- The tissue culture technique for storage of germplasm is used in case where :-
  (a) No seeds are produced (banana, sugarcane)
  (b) Nonviable seeds
  (c) Crop with recalcitrant seeds
  (d) Specific clone is to be maintained

• Best method of tissue culture for germplasm storage is "Shoot tip culture".

• Shoot tip culture rapidly becoming preferred material for international exchange of germplasm as they are more stable, easier to regenerate in to, whole plants and produce virus free clonal plants.

• Now a days germplasm of potato, Cassava and banana are exchanged by this methods.

• The main advantage of tissue culture storage of germplasm are :-
  (a) Economical
  (b) Requires small area for storage of many genotype
  (c) Can be used for multiplication of rare and endangered species.

Significance of germplasm of wild species –

• It is very important to conserve wild species of plant as these are highly resistant to insects, pests, disease and unfavourable growth conditions, which are necessary for survival of plants.

• The loss of wild plants, will reduce the genetic variability and will be a great loss to gene pool.

• Potato and sugarcane has been improved by use of germplasm of wild species having many defensive characters like disease resistance and resistance to environmental stress.

• In potato (Solanum tuberosum), gene for resistance to potato virus–X and potato leaf roll virus have been obtained from a wild species “Solanum acaule”.

• Resistance to wilt fungus (Fusarium) and cyst nematode (Globodera) has been introduced from "Solanum spegazzini".

• Potato got resistant gene to potato virus - Y from a wild relatives "Solanum stoloniferum".

• Resistance to late blight of potato (Caused by fungus Phytophthora infestans) has been derieved from "S.demissum".

• Similarly, sugarcane(Saccharum officinarum) got resistance to red rot of sugarcane and adverse environment from a wild species "Saccharum spontaneum".

Cryopreservation :- Preservation of germplasm at ultra low temperature about –196° C(liquid nitrogen) is called cryopreservation.
International efforts for utilization of crop-germplasm :-

• Cereals (rice, wheat, maize, rye, sorghum, bajra etc) are the main sources of food for human population in the world and rice alone constitutes staple food of more than 50% world's population.

Improvement in rice :-

• Dwarfing gene "dee-geo-woo-gen" was noticed in Taiwan.

• This gene produced many improved varieties in rice

• This gene was picked up by IRRI (International Rice Research Institute) Manila (Philipines) and incorporated to produce high yielding early maturing IR-8 and IR-24 varieties.

• Gurdev S. Khush and his team crossed 13 varieties of rice from six countries and wild rice Oryza nivara (from India) to develop IR-36 variety of rice.

• IR-36 variety of rice is resistant of grassy stunt virus.

• IR-36 is the high yielding variety of rice and has solved major food problem in Asia.

• Prior to green revolution a dwarfing gene of wheat named norin-10 , was noted in Japan and picked up by American plant breeder.

• Dr.N.Borlaug(Mexican wheat breeder) develop many dwarf wheat varieties like Sonora-64 and Lerma rojo-64

• N.Borlaug got Nobel prize for peace in 1970

• In 1963 two Mexican wheat varieties viz. Sonora-64 &  Lerma rojo-64 and a Japanese variety Norin-10 were introduced in India, but these varieties could not adopt to Indian conditions, they were subjected to mutations and selections at Indian Agricultural Research Institute at New Delhi under the direction of Dr. M.S Swaminathan.