Crop Improvement PDF

UNIT-1 Crop Improvement Crop improvement program includes various method to develop a new crop variety or to modify the existing crop variety in order to achieve higher production, higher nutritional value and wider adaptability against various environmental stress such as abiotic and biotic stress....

UNIT-1 Crop Improvement Crop improvement program includes various method to develop a new crop variety or to modify the existing crop variety in order to achieve higher production, higher nutritional value and wider adaptability against various environmental stress such as abiotic and biotic stress. Some of the methods are described below: ❖ Plant Introduction: → Plant introduction usually means the introduction of the plants from places outside the county, may be of same or another continent. It can be defined as the “process of introducing plants from their growing locality to a new locality.” → Plant introduction is an oldest method of crop improvement. → Plant introduction is usually done from one country to other. But sometimes it may take place between two climatic regions of the same country. → Earlier, the introduction of plants from one place to another used to be done by travellers, traders, invaders and merchants. Now specific organizations have been established for this work. → In India, plant Introduction work is undertaken by National Bureau of Plant Genetic Resources (NBPGR), New Delhi. NBPGR deals with the introduction of Agricultural and Horticultural crops. → In India, two more organizations, viz.: (1) Forest Research Institute (FRI), Dehradun, and (2) Botanical Survey of India (BSI), Kolkata, are also concerned with plant introduction work. Reasons for plant introduction: To improve the plant wealth of the country by introduction of economical important new sources of food, To increase the germplasm diversity of introduced plant. Plants can be introduced to new abiotic stress-free areas to protect them from damage Introduction of new plant is a way to build up new industries (palm oil factories). Mung mustard, pear, apple and walnut were introduced from the Central Asian Center of origin into various parts of India. Similarly, sesame, Jowar, arhar, Asian Cotton and finger millet originated in Africa and traveled to India in the prehistoric period. ❖ Tissue Culture: → Plant-tissue culture: Plant-tissue culture is in-vitro cultivation of plant cell or tissue under aseptic and controlled environment conditions, in liquid or on semisolid well defined nutrient medium for the production of primary and secondary metabolites or to regenerate plant. → Explant: An excised piece of differentiated tissue or organ is regarded as an explant. The explant may be taken from any part of plant body e.g. leaf, stem, root. → Callus: The unorganized and undifferentiated mass of plant cells is referred to as callus. Generally, when plant cells or explant are cultured in a suitable medium, they divide to form callus. It is parenchyma cells. → Totipotency: The inherent potentiality of a plant cell to give rise to a whole plant is described as cellular totipotency → Application: It has several useful applications in crop improvement for e.g., development of haploids, embryo rescue generation of variability, selection of disease resistance, selection for salinity and metal toxicity resistance, selection for drought resistance, micro propagation, preservation of germplasm, somatic hybridization etc. ❖ Conventional breeding → Conventional plant breeding method, known as cross breeding, is used to improve plant traits, e.g. disease resistance since long time via crossing an elite recipient parent line with a donor line with desirable trait. → Finally, an outstanding progeny with the desired trait/s is selected after many successive backcrossing. Recipient plant/ elite plant/recurrent plant: used to have a large number of desirable traits (good agronomic traits) but may be deficient in a few traits. Recipient plant also known as recurrent plant because this parent is repeatedly back cross to create new line. Donor plant/non-recurrent plant: donor plants are the plant that have specific traits that is lacking in the elite variety, but with poor agronomic traits  → This technique is time-consuming (10-12 years), laborious, less efficient and contains many other limitations as well. ❖ Mutation Breeding: → A sudden heritable change in a characteristic of an organism is called mutation; function of mutations with the aid of mutagens is called mutagenesis. → Breeding method utilizing variation created through mutagenesis is called mutation breeding. In this method, gamma rays and X-rays are the most commonly used physical mutagens, while EMS (ethyl methane sulphonate), EI (ethylene imine) and sodium azide are the most commonly used chemical mutagens. → 6–7 years to get desirable results, which is time-consuming and tedious process. → One of the major limitations and disadvantages of this technique is the random mutations in genome, which sometimes become hard to detect and predict.  → More than 300 varieties have been developed through mutagenesis in various countries. In India, a number of varieties have been developed by mutation breeding e.g., BGM 408 (Chick pea), Hans (pea), JRO 3690 (Jute), Sharbati Sonora, (Wheat), Jagannath (Rice), Co8152 (sugarcane) etc. ❖ Ploidy → The somatic cells have two complete sets of chromosomes. This is referred to as diploid (2n). The gametes have only one set of chromosomes. This is referred to as haploid (n). → An organism having more than two sets of chromosomes is called polyploid. Such a condition is called polyploidy. → Polyploidy occurs in nature due to the failure of the separation of chromosomes at anaphase. It can be artificially induced by: 1. Physical agents - heat, cold treatment and X-rays. 2. Chemical agents - colchicine. → Depending on the number of sets of chromosomes present in a polyploid, it is called triploid (3n), tetraploid (4n), pentaploid (5n), hexaploidy (6n) etc. The polyploids with an odd number of chromosome sets are sexually sterile and thus, must be vegetatively propagated. The types of polyploidy: a. Autopolyploid  b. Allopolyploid → Some of the achievements of polyploidy breeding include: i. Seedless watermelons (3n) and bananas (3n). ii. Triticale (6n) is a wheat-rye hybrid. Polyploidy is used to make this plant fertile. It has more dietary fibre and protein. Among artificially produced polyploidy, ❖ Transgenic plants through genetic Engineering: → Isolation, introduction and expression of foreign/transgene DNA in plants and animals is called genetic engineering. → DNA insert: short segment of DNA with desired trait. → Plasmid: work as vehicle that carry desired DNA segment. → Restriction enzyme: molecular scissors which cut the DNA at its specific restriction sites. → DNA ligase: enzyme that paste/join the two DNA segments. → Following steps are involved in transgenic plant development: 1. First step is to identify desired gene of interest in tolerant plant variety. 2. Isolation and amplification of gene of interest from cell/tissue of tolerant plant variety. 3. Restriction digestion of gene of interest with the help of restriction enzymes. 4. Transfer of gene of interest into plant cell/ tissue of susceptible plant variety 5. Transformed cell analysis. 6. Acclimatize in green house conditions.  This process allows for the development of crops with improved traits, such as: → Resistance to pests, herbicides, and viruses: For example, genes from Bacillus thuringiensis (Bt) have been introduced to make crops like cotton, corn, and potatoes resistant to pests. → Tolerance to abiotic and biotic stresses: Genetic engineering can help develop crops that are resistant to multiple types of stresses. → Removal of heavy metals from soil: GM crops can be used to remediate waste land for agricultural use. Genome Editing → Genome editing allows plant breeders to make very precise changes to DNA. Genome editing can be used to make changes to a plant or other organism by targeting at a specific location in a gene within the DNA. Genome editing can be used to add, remove, or alter DNA in the plant genome. Tools for Genome Editing → There are several genome editing tools that scientists can use such as CRISPR Cas 9, TALEN, Zinc finger. → CRISPR" stands for Clustered Regularly Interspaced Short Palindromic Repeats. Cas 9 is an enzyme. → TALENs, was used to develop the first genome-edited plant to be commercially grown in the United States and sold as a food product: soybeans that produce high oleic, low linolenic oil that is a healthier alternative to partially hydrogenated oils.  → CRISPR gene editing is generally to modify particular portion of DNA. CRISPR, on the other hand, has also been designed to do other things, such as turning genes on or off without affecting their sequence. → The CRISPR technique relies on CRISPR-associated enzymes also known as CAS 9 enzymes. The CRISPR-Cas 9 system is comprised of two major components: → The Cas-9 enzyme functions as a pair of "molecular scissors" that can cut the two strands of DNA at a specified spot in the genome, allowing for the addition or removal of bits of DNA. → A gRNA (guide ribose nucleic acid) is a fragment of RNA. The RNA protein is related to DNA. The guide RNA is intended to locate and attach to a specific sequence in the DNA. The gRNA contains RNA bases (A, U, G, and C) that are complementary to the target DNA bases (A, T, G, and C) in the genome. → ❖ Other methods to improve crop performance include: Improving farm practices Improving irrigation and drainage Improving herbicide, pesticide, and fertilizer use