৪৯তম বিসিএস ⎯ কৃষিবিজ্ঞান [৮০১]

Totipotency মানে হলো, একটি মাত্র উদ্ভিদ কোষের ক্ষমতা থাকে পুরো একটি গাছ গড়ে তোলার।

Morphogenesis → কোষ থেকে অঙ্গ-প্রত্যঙ্গ বা গঠন তৈরি হওয়ার প্রক্রিয়া।
Differentiation → কোষ বিশেষায়িত হয়ে নির্দিষ্ট কাজ করার উপযোগী হওয়া।
Organogenesis → অঙ্গ (shoot, root) গঠনের প্রক্রিয়া।

Callus is an unorganized, proliferating mass of undifferentiated plant cells. It is typically induced to grow in a lab setting (in vitro) from a piece of plant tissue, known as an explant, placed on a solid nutrient medium. 
Meristem culture is a specific type of tissue culture that uses meristematic tissue (the actively dividing tips of shoots or roots) as the explant. This technique is often used to produce virus-free plants because the meristematic regions are generally free from viruses.
Suspension culture involves growing single plant cells or small groups of cells in a liquid nutrient medium. The medium is continuously agitated to keep the cells in suspension, allowing for rapid and uniform growth.
Organ culture is a technique for growing an entire plant organ (such as a root, stem, or embryo) in vitro. The goal is to maintain the organ's structure and function, rather than to produce an undifferentiated mass of cells.

Breeder seed → Foundation seed → Certified seed
Foundation seed হলো breeder seed থেকে উৎপাদিত, এবং এটি Certified seed উৎপাদনের মূল উৎস।
Certified seed হলো এমন বীজ যা কৃষকদের কাছে বিতরণের জন্য গুণগত মান ও বিশুদ্ধতা নিশ্চিত করে উৎপাদন করা হয়।
তাই Certified seeds কখনো farmer-saved বা market seeds থেকে হয় না, বরং সবসময় Foundation seeds থেকে হয়।

Transgenic plants = যেসব উদ্ভিদের DNA তে recombinant DNA technology ব্যবহার করে নতুন জিন (same species বা অন্য species থেকে) প্রবেশ করানো হয়।
এর মাধ্যমে উদ্ভিদের কাঙ্ক্ষিত বৈশিষ্ট্য যেমন → রোগ প্রতিরোধ ক্ষমতা, কীট প্রতিরোধ ক্ষমতা, পুষ্টিগুণ বৃদ্ধি ইত্যাদি অর্জন করা যায়।

Apomictic plants → বীজ তৈরি করে কিন্তু যৌন প্রজনন ছাড়াই (asexual seed formation)।
Hybrid plants → দুটি genetically ভিন্ন parent থেকে cross করে উৎপাদিত।
Wild plants → প্রাকৃতিকভাবে জন্মানো, জেনেটিকালি পরিবর্তিত নয়।

Auxin : Cytokinin ratio টিস্যু কালচারে কোষের অঙ্গ (shoot/root) গঠনে গুরুত্বপূর্ণ ভূমিকা রাখে।
High Auxin : Low Cytokinin → Root formation
 Low Auxin : High Cytokinin → Shoot formation
 Balanced Auxin & Cytokinin → Callus formation

Southern blotting হলো DNA বিশ্লেষণের একটি পদ্ধতি, যা একটি নির্দিষ্ট জিন/সিকোয়েন্স শনাক্ত করতে ব্যবহৃত হয়।
আবিষ্কারক: Edwin Southern (1975) → তাই নাম Southern blot।
এতে DNA fragment গুলোকে electrophoresis করে আলাদা করা হয়, তারপর একটি নির্দিষ্ট DNA probe ব্যবহার করে কাঙ্ক্ষিত জিন শনাক্ত করা হয়।

Cell suspension culture is a method used in plant tissue culture to grow plant cells, or small clumps of cells, in a liquid nutrient medium. The medium is continuously shaken, usually by an orbital shaker, to ensure several critical things:

Uniform distribution: Shaking keeps the cells from settling at the bottom of the flask, ensuring they are evenly distributed throughout the medium.
Nutrient and oxygen availability: Continuous agitation ensures that every cell has equal access to the nutrients in the medium and that oxygen is properly mixed in, which is crucial for cell respiration and growth

Seed certification হলো এমন একটি প্রক্রিয়া যেখানে বীজের genetic purity, physical purity, germination, viability ইত্যাদি পরীক্ষা ও নিশ্চিত করা হয়।
এর ফলে কৃষকরা ভালো মানের বীজ পায় → যা ফসলের uniformity (এক রকম বৃদ্ধি ও বৈশিষ্ট্য) এবং productivity (উৎপাদন ক্ষমতা) বাড়ায়।
Objectives of Seed Certification
- Ensure genetic purity of seeds.
- Maintain high germination percentage.
- Control diseases and pests in seeds.
- Increase crop productivity and uniformity.
- Promote high-quality seed production in the seed industry.

DNA contains the bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
RNA contains the bases: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).

উদ্ভিদ explant-কে টিস্যু কালচারের জন্য জীবাণুমুক্ত করার সময় surface sterilization করা হয়।
সবচেয়ে সাধারণ এবং নিরাপদ sterilizing agent হলো Sodium hypochlorite (NaOCl)।
এটি বিভিন্ন ধরণের bacteria, fungi ধ্বংস করে।
Ethanol (70%) → সাধারণত quick dip বা short exposure-এ ব্যবহৃত হয়, প্রধান agent নয়।
Mercuric chloride (HgCl₂) → কার্যকর কিন্তু বিষাক্ত, তাই সচরাচর কম ব্যবহার হয়।
Formaldehyde → গ্যাস বা solution হিসেবে ব্যবহার হয়, কম ব্যবহৃত।

Plant Tissue Culture - Growing plant cells, tissues, organs in an artificial nutrient medium under sterile conditions.
Plant tissue culture enables the rapid production of many identical plants from a small amount of plant tissue. This is especially useful for plants that are difficult to propagate by seeds or cuttings, ensuring uniformity and faster multiplication. 

Meristem Culture – Produces virus-free plants.
Meristematic tissues remain virus-free mainly because:

Rapid cell division – viruses cannot keep up with the fast division of meristem cells.
Lack of vascular connections – viruses often move through phloem and xylem, but meristems lack these connections, preventing virus spread.

In plant tissue culture, a major risk is microbial contamination. Even a tiny presence of bacteria, fungi, or viruses can ruin the entire culture because the nutrient-rich media provide an ideal environment for microbial growth

pentose sugar + N base = Nucleoside
Nucleoside + Phosphate group = Neucleotide
Many Neucleotide = Nucleic Acid  

Somatic embryogenesis is the process in which somatic (non-reproductive) cells develop into embryos that can grow into complete plants. This is widely used in plant tissue culture for clonal propagation and genetic improvement.
 Organogenesis → formation of organs (shoots, roots) from cultured tissues
Differentiation → process where cells become specialized
Clonal propagation → producing genetically identical plants, but not necessarily via embryos

A callus is a mass of undifferentiated plant cells that forms when plant tissues (explants) are cultured on a suitable nutrient medium with the right balance of plant growth regulators (mainly auxins and cytokinins).

Uses:

Mass clonal propagation of plants.
Genetic engineering (e.g., producing transgenic plants).
Secondary metabolite production in biotechnology.

Clonal propagation is the process of producing genetically identical plants (clones) from a single parent plant. 

Genetic Uniformity: All plants produced are exact copies of the parent.
Methods of Clonal propagation:

Vegetative propagation – cuttings, grafting, layering, rhizomes, tubers.
Plant tissue culture – using techniques like organogenesis or somatic embryogenesis.

Acclimatization (also called hardening) is the process of gradually adapting in vitro-grown plantlets to external environmental conditions such as natural light, temperature, humidity, and soil. This is essential before transferring tissue-cultured plants to the field to ensure survival and normal growth.

Other options
 Tissue culture → the entire in vitro propagation process
Gene transfer → introduction of new genes into a plant
Callus induction → formation of undifferentiated cell mass in culture

The gene gun (also called biolistic method) is a technique used to deliver DNA-coated microscopic particles (usually gold or tungsten) directly into plant cells. This method is commonly used in plant genetic engineering, especially for plants that are difficult to transform using Agrobacterium.

Gene gun or Agrobacterium-mediated transfer (for monocot and Dicot plants)

Recombinant DNA: DNA that is formed by combining genetic material from two or more different sources using laboratory techniques, to produce new genetic combinations. Example: Human insulin gene inserted into E. coli bacteria.

Plasmid is a small, circular, double-stranded DNA molecule found mainly in bacteria Types of Plasmids
- F plasmid → helps in conjugation (gene transfer between bacteria).
- R plasmid → provides resistance to antibiotics. 
-  Col plasmid → produces bacteriocins (toxic proteins that kill other bacteria).
- Ti plasmid (Agrobacterium tumefaciens) → causes tumors in plants, used in plant genetic engineering.

Golden Rice is a genetically modified (GM) rice developed to combat vitamin A deficiency in populations that rely heavily on rice as a staple food.
Rich in beta-carotene, a precursor of vitamin A.
Helps prevent night blindness, immune deficiencies, and other health issues caused by vitamin A deficiency.
The rice grains have a yellow-orange color due to beta-carotene, which gives it the name "Golden Rice

- In bacterial transformation, treatment with calcium ions (Ca²⁺) and heat shock is used to make bacterial cells competent, meaning their cell membrane temporarily becomes permeable to foreign DNA, such as a plasmid. This allows the bacteria to take up the DNA and express new genes.

Somaclonal variation refers to genetic variation observed in plants regenerated from tissue culture. It arises due to stress and changes in in vitro culture conditions, such as the type and concentration of growth regulators, culture duration, and physical conditions.
Somaclonal variation বলতে সেই জেনেটিক ও এপিজেনেটিক পরিবর্তনকে বোঝায় যা উদ্ভিদ টিস্যু কালচার থেকে পুনরায় উদ্ভিদ তৈরি করার সময় ঘটে। যদিও টিস্যু কালচারের প্রধান উদ্দেশ্য হলো জেনেটিকভাবে একরকম ক্লোন তৈরি করা, এই প্রক্রিয়ায় উদ্ভিদের কোষগুলোতে বিভিন্ন চাপ সৃষ্টি হয়, যা মিউটেশন এবং DNA-তে অন্যান্য পরিবর্তন ঘটাতে পারে।

Genome Mapping is like creating a high-level street map of a city. It pinpoints the location of genes and other important DNA landmarks on chromosomes and shows the relative distances between them. This is done without reading the exact DNA sequence.

Genome Sequencing is like writing out the exact address of every single house on that street map. It determines the precise order of the four nucleotide bases (A, T, C, and G) that make up a DNA molecule. A complete genome sequence is the ultimate physical map.

(জিনোম ম্যাপিং হলো এমন একটি প্রক্রিয়া যা শহরের একটি উচ্চ-স্তরের রাস্তার মানচিত্র তৈরির মতো। এটি ক্রোমোসোমে জিন এবং অন্যান্য গুরুত্বপূর্ণ DNA ল্যান্ডমার্কের অবস্থান নির্ধারণ করে এবং তাদের আপেক্ষিক দূরত্ব দেখায়। এটি করা হয় সঠিক DNA ক্রম পড়া ছাড়াই।

জিনোম সিকোয়েন্সিং হলো সেই রাস্তার মানচিত্রে প্রতিটি বাড়ির সঠিক ঠিকানা লেখা। এটি নির্ধারণ করে চারটি নিউক্লিওটাইড বেসের (A, T, C, এবং G) সঠিক ক্রম, যা DNA অণুকে তৈরি করে। একটি সম্পূর্ণ জিনোম সিকোয়েন্স হলো চূড়ান্ত শারীরিক মানচিত্র।)

Explant sterilized using:
- Ethanol (70%),
- Sodium hypochlorite / Mercuric chloride,
- Sterile distilled water (final wash).
- All operations done in a Laminar Air Flow (LAF) cabinet. 

The Ti plasmid (Tumor-inducing plasmid) is found in Agrobacterium tumefaciens, a soil bacterium. It is responsible for transferring a part of its DNA (T-DNA) into plant cells, causing crown gall disease. This natural gene transfer ability is widely used in plant genetic engineering to introduce new genes into plants.

Glyphosate-resistant soybean is a genetically modified (GM) crop that can tolerate the herbicide glyphosate (commercially known as Roundup). This allows farmers to spray glyphosate to kill weeds without harming the soybean plants.

Pest resistance: Bt cotton, Bt brinjal
- Herbicide resistance: Glyphosate-resistant soybean
- Improved nutrition: Golden Rice (rich in vitamin A)
- Disease resistance: Papaya resistant to Papaya Ringspot Virus

- Restriction endonucleases (restriction enzymes) are called molecular scissors because they cut DNA at specific sequences (recognition sites). This property makes them essential tools in genetic engineering and recombinant DNA technology.

Other options-
DNA ligase → joins (ligates) DNA fragments together
DNA polymerase → synthesizes new DNA strands
Reverse transcriptase → converts RNA into complementary DNA (cDNA)

In plant tissue culture, sucrose is the most commonly used carbon source because:

It is readily metabolized by plant cells.
It provides energy for growth and development.
It acts as an osmotic agent, maintaining proper medium balance.
It acts as Energy Source:, Transport Sugar, Stability:, Osmotic Regulation:

When a bacterium successfully takes up a plasmid (foreign DNA) through the process of transformation, it is called a transformed bacterium.
Transformation is the process by which a bacterium takes up foreign genetic material (like a plasmid) from its surroundings. This is a key step in genetic engineering and molecular cloning.

Bt crops get their name from the bacterium Bacillus thuringiensis (Bt), a soil-dwelling microbe that naturally produces crystal proteins, also known as Cry proteins. These proteins are toxic to specific types of insects, particularly the larvae of moths and butterflies (Lepidoptera), beetles (Coleoptera), and flies (Diptera).
When a susceptible insect pest, like the corn borer or cotton bollworm, eats a part of the Bt plant, it ingests the inactive Cry protein.
The alkaline conditions in the insect's gut activate the protein, which then binds to receptors on the gut lining, causing it to rupture. This leads to the insect's death.

Plasmids are commonly used in genetic engineering because they are ideal vectors (carriers of foreign DNA).

Plasmids are commonly used in genetic engineering because:
Small and easy to manipulate → Plasmids are much smaller than chromosomal DNA, making them easier to isolate and modify.
Self-replicating → They contain an origin of replication (Ori), so they can replicate independently inside host cells.
Multiple Cloning Sites (MCS) → Contain recognition sites for restriction enzymes, allowing easy insertion of foreign DNA.
Selectable markers → Usually carry genes for antibiotic resistance, which helps in identifying transformed cells.
Stable inheritance → Once inside a bacterium, plasmids are stably maintained and passed on to daughter cells.
Versatility → Can be engineered to carry large DNA fragments, reporter genes, or expression systems for producing proteins.

Restriction enzyme → cuts DNA at specific points. (EcoRI, HindIII, BamHI, PstI, TaqI, EcoRV, Hpa II, Mob I)
Start codon (AUG) → signals beginning of protein synthesis.
Stop codons (UAA, UAG, UGA) → signal end of protein synthesis.

Sterilization
- To prevent microbial contamination.
- Autoclave - High temperature (121°C) and pressure (15 psi) maintained for 15–20 minutes kills all microbes and spores.
Explant sterilized using:
- Ethanol (70%),
- Sodium hypochlorite / Mercuric chloride,
- Sterile distilled water (final wash).
- All operations done in a Laminar Air Flow (LAF) cabinet

Multi-Location Trials (MLT) are conducted to test adaptability and performance across regions. 

MLTs are a crucial step in the plant breeding and variety development process. A plant variety that performs well in one location (due to specific soil, climate, and pest conditions) may not perform as well in another.

Multi-Location Trials (MLT) are conducted to evaluate a new crop variety in different agro-climatic regions. The aim is to check:

Adaptability → how well the variety performs under varied environments.
Stability → consistent yield and quality across regions.
Performance → resistance to local stresses like pests, diseases, and climate.

PCR (Polymerase Chain Reaction) is a technique used to amplify (make millions of copies of) a specific DNA sequence in vitro.
It uses:

DNA template (the sequence to be copied)
Primers (short DNA sequences to start replication)
DNA polymerase (Taq polymerase)
Nucleotides (dNTPs)