BBYET 143 Solved Guess Paper 2026 for IGNOU Economic Botany and Biotechnology (BSCG B.Sc. General)

Describe the concept of centres of origin according to Vavilov. What is meant by the top-down and bottom-up approach of the genetic basis of domestication?

The process in which wild plants get evolved into crop plants through artificial selection is known as domestication.

Alphonse de Candolle (1883) studied 247 cultivated species and wrote Origin of Cultivated Plants. Darwin (1868) said that changes in wild plants gave rise to crop plants. The centre of origin idea was first given by de Candolle (1890) and later described by Nikolai Vavilov (1926).

Vavilov's Work

1. Gene centres: Vavilov collected plants from all over the world. He saw that plants are not spread evenly. Some small areas hold a lot of variation.
2. Number of centres: he first suggested six geographic centres in 1926 and later recognised 11 centres.
3. Old and new world: about 85 per cent of the 640 species he listed came from the old world, that is Asia, Europe and Africa. The rest came from the new world.
4. Small area: all these centres together make only about 2 to 3 per cent of the land area of the earth.
5. Primary and secondary centres: domestication starts in the primary centre and is marked by dominant genes. A secondary centre forms later, is marked by recessive genes and has no wild relatives.
6. Agro-ecological groups: small areas rich in species inside a centre were called agro-ecological groups. Harlan (1951) later called such a region a microcentre.

Why the Idea Was Later Questioned

1. The area with the greatest diversity is not always the centre of origin. Maize has its diversity in Peru but was domesticated in Mexico.
2. Centres are not limited to hilly areas only. Maize shows high diversity in the plains too.
3. Some crops like bottle gourd have no centre of diversity at all.
4. Harlan (1971) gave the idea of centres and non-centres, Hawkes (1983) gave nuclear centres and Zhukovsky (1968) gave twelve megagene centres.

Top-down and Bottom-up Approaches

1. Top-down approach: it starts from the phenotype, that is the visible change. Traits of wild and domesticated plants, such as plant shape or seed size, are compared, and the gene behind that trait is then found. This approach is precise for one particular trait.
2. Bottom-up approach: it starts from the genetic variation inside the genome. Signals of selection are found first and then linked to important loci and domestication phenotypes. It covers a larger share of selected traits, morphological, developmental, physiological and biochemical.

Conclusion: Vavilov showed that crop plants came from a few restricted centres. Modern work shows the picture is more complex, and top-down and bottom-up studies now explain the genes behind domestication.

Give a general account of cereals. Describe the morphological characters of any two cereals.

The word cereal comes from cerealia munera, which means gift of Ceres, the Roman goddess of grain, harvest and agriculture. Cereals are members of the grass family Poaceae and are grown for their starchy seeds. Plants that are not grasses but are used in the same way are called pseudocereals, for example buckwheat, quinoa and amaranthus.

Why Cereals Were Chosen as Food Crops

1. Great adaptability to different environments, so they spread fast into many habitats.
2. Easy cultivation and high yield per unit area.
3. Compact grains that can be handled, stored and carried easily.
4. Good nutritive value, with a high share of carbohydrates, protein, fats, vitamins and minerals.

Common Features of Cereals

Most cereals are herbaceous annuals. The stem is erect, cylindrical and hollow except at the nodes. Leaves are alternate and distichous with parallel venation, and have a leaf sheath and a lamina. A thin membranous outgrowth called the ligule sits where the sheath meets the lamina.

The inflorescence is a spike of spikelets in wheat, barley and rye, or a panicle of spikelets in oats, rice and sorghum. The main axis is the rachis and that of the spikelet is the rachilla. The perianth is reduced to two scales called lodicules. The fruit is a one-seeded indehiscent caryopsis.

Morphology of Wheat, Triticum aestivum Linn.

1. Habit and roots: an annual grass with many tillers, bright green when young and golden brown at maturity. Roots are of two types, primary or seminal roots from the embryo which live only six to eight weeks, and secondary or coronal roots which are adventitious and form the permanent root system.
2. Stem and leaves: the main stem, called the culm, and the tillers are erect and cylindrical, with 5 to 7 nodes, 0.3 to 1.5 m tall and hollow internodes. A colourless membranous ligule and a pair of auricles sit at the junction.
3. Inflorescence: a terminal spike of many spikelets in two rows. Each spikelet is sessile with 2 to 5 florets, a pair of sterile glumes and fertile glumes made of an outer lemma and an inner palea. The lemma usually extends into an awn.
4. Flower and fruit: two lodicules, three stamens and a monocarpellary gynoecium with two feathery stigmas. The fruit is a caryopsis, and the fruit wall and seed coat fuse to form the bran. Endosperm makes 82 to 86 per cent of the grain and its outermost layer, the aleurone, holds vitamins, minerals and proteins but no gluten.

Morphology of Rice, Oryza sativa Linn.

1. Roots and stem: the primary root comes out on germination, followed by two more. Adventitious roots then arise from the basal nodes and form a dense, highly branched surface mat. The culm is erect and smooth, 6 to 10 mm thick, with solid nodes and 10 to 20 internodes per stem.
2. Leaves: each leaf has a sheath, blade, ligule and auricles. The lamina of the uppermost leaf is wider and shorter and is called the boot or flag leaf.
3. Inflorescence and fruit: a loose terminal panicle, 14 to 42 cm long. Each spikelet has a single bisexual floret with a large boat-shaped five-nerved lemma, a narrow three-nerved palea, two broad lodicules, six stamens and two plumose stigmas. The fruit is a caryopsis closely covered by the husk, and this is called paddy.

Conclusion: cereals share the common grass plan of Poaceae. Wheat bears a spike and rice bears a panicle, and both give a caryopsis as fruit.

Describe the morphology, cultivation and processing of tea. What are the health benefits of the various types of tea?

Botanical name Camellia sinensis (L), synonym Thea sinensis (L), family Theaceae, vernacular name chai, chromosome number n = 15.

More than 50 per cent of the world's population drinks tea regularly. It is believed to be native to South Western China, North Eastern India (Assam) and nearby parts of upper Burma. China, India and Sri Lanka are the largest producers. The Chinese emperor Shen Nung is said to have found the stimulating property of tea leaf extract around 2700 BC.

Morphology

The tea plant is an evergreen tree or shrub that can grow 30 to 50 ft tall, but it is never allowed to grow beyond plucking height. The bushes are pruned back so that more leaves form. Leaves are alternate, elliptic to lanceolate with toothed margins and are glabrous.

The lower surface of young tender leaves is thickly covered with soft hairs that go away with age. Old leaves have many oil glands that give the leaf its fragrance. The flowers are yellow-centred, white or pinkish and fragrant, borne singly or in small clusters in the leaf axils. The fruit is a three-celled woody capsule and each chamber holds one brown seed about 1.25 cm across.

Cultivation

1. It grows in tropical and warm temperate climates with plenty of rainfall spread through the year.
2. An average monthly temperature of 21 to 32 degrees C is needed. Long dry spells damage the crop.
3. It needs deep, well drained, acidic soil of pH 4.0 to 6.0, with no lime and rich in humus.
4. It is a shade loving plant and grows better under the partial shade of leguminous trees such as Albizzia procera.
5. Tea is tolerant of high levels of aluminium, and aluminium is a diagnostic character for judging good tea soil.
6. Plucking starts when the plant is 4 to 5 years old. Picking the terminal bud with the first and second leaf gives the best quality tea.

Processing of Black Tea

Three kinds of tea are made commercially, black, green and oolong. Almost 80 per cent of tea is processed into black tea. Green tea does not go through withering and fermentation, and oolong tea is semi-fermented.

1. Withering: fresh leaves are dried in the sun or heated in shallow trays for about 24 hours. Water content falls and leaves become soft and flaccid.
2. Rolling: leaves are rolled by hand or machine. Leaf cells break so that juice and enzymes come out, which also helps fermentation.
3. Fermentation: rolled leaves are kept in high humidity at 24 to 27 degrees C. Tannins are partly oxidised and the leaves turn bright coppery red.
4. Drying or firing: leaves are passed through air chambers at 90 to 100 degrees C for 25 to 30 minutes. Moisture comes down to 3 to 5 per cent.
5. Grading: Indian tea is graded as leaf, broken waste and dusts. Leaf grades such as orange pekoe give better tea than broken grades.

Health Benefits by Type of Tea

• Green tea: prevents cardiovascular diseases, reduces neurological disorders like Alzheimer's and Parkinson's disease, reduces the risk of stroke.
• Black tea: protects the lungs from damage, reduces the risk of stroke, helps keep blood pressure normal.
• Oolong tea: protects the heart by reducing cholesterol, anticancerous, its fluoride keeps teeth strong, strengthens the immune system.
• White tea: lowers cholesterol level and keeps blood sugar under control.
• Chamomile tea: anticancerous, used in the treatment of bowel syndrome, stops gastrointestinal inflammation.

Conclusion: tea is the most popular non-alcoholic drink in the world. The way the leaf is processed decides whether it becomes black, green or oolong tea, and each type carries its own health benefits.

Define micro-propagation and explain the steps involved with the help of a flow chart. List the major applications of plant tissue culture.

Clonal propagation under in vitro conditions is called micropropagation.

Clonal propagation means the multiplication of genetically identical copies of a plant species by asexual reproduction. In nature it happens by apomixis and vegetative propagation. Micropropagation starts with the selection of plant tissue, that is an explant such as a leaf, apical meristem, bud or root, taken from a healthy and vigorous parent plant. It is the only commercially viable method of clonal propagation for many horticultural crops such as orchids.

The Five Stages

1. Stage 0, preparation of donor plant: a suitable plant tissue or explant is taken from a plant growing under natural conditions and is then cultured in vitro.
2. Stage I, initiation stage: the culture is started and established in a suitable medium. The explant is surface sterilised and put on the nutrient medium. Common disinfectants are sodium hypochlorite, calcium hypochlorite, ethanol and mercuric chloride.
3. Stage II, multiplication stage: shoots multiply or an embryo forms from the explant. Cultures are kept at 20 to 24 degrees C with a light intensity of 2000 to 4000 lux, and subcultures are repeated until the wanted number of plantlets is reached.
4. Stage III, rooting stage: the shoots are moved to a medium that helps roots form. Rooting is induced by adding auxins to the medium.
5. Stage IV, acclimatization stage: plants raised in vitro are weaned and hardened. Hardening means moving the plant from high to low humidity and from low to high light intensity, after which the plantlets go into soil or to the greenhouse.

Advantages and Limitations

Advantages: more than 1,000,000 plants a year can be obtained from one explant, against 10,000 by ordinary vegetative propagation. From about 1 square metre of culture room, 20,000 to 100,000 plantlets can be made in a year. Disease-free plantlets are obtained, slow growing plants such as bulbous crops and Narcissus multiply faster, and sterile hybrids such as cabbage can be propagated.

Limitations: expensive laboratory equipment is needed. Plants are not autotrophic in culture, are poorly adapted to field conditions and must be acclimatized. There is a risk of genetic change. Mass propagation is not possible for all crops, for example cowpea is highly recalcitrant, and adult woody plants cannot be regenerated easily.

Major Applications of Plant Tissue Culture

1. Clonal propagation: the most widely used application. Apple, pears, strawberry, cardamom and orchids have been propagated this way.
2. Production of virus-free plants: meristem-tip culture gives virus-free plants. Potato virus X has been removed from potato and mosaic virus from cassava.
3. Production of synthetic seeds: somatic embryos are encapsulated in a matrix such as sodium alginate along with mycorrhizae, insecticides, fungicides and herbicides.
4. Breaking dormancy: zygotic embryo culture shortens seed dormancy and the breeding cycle. The life cycle of Iris was cut from 2 to 3 years to less than one year.
5. Haploid plants: obtained through anther or pollen culture, that is androgenesis, and ovary or ovule culture, that is gynogenesis.
6. Embryo rescue: embryos that would not germinate are rescued and grown into plants.
7. Secondary metabolites and germplasm conservation: large-scale production of useful chemicals and long-term storage of genetic resources.

Conclusion: micropropagation runs through five clear stages from donor plant to hardened plantlet. Along with virus-free plants, synthetic seeds and haploids, it is the most useful tool of plant tissue culture.

Short notes: shuttle vectors and genetic erosion.

Shuttle Vectors

Vectors designed to replicate in cells of two species, because they contain two origins of replication, are known as shuttle vectors.

1. Each origin of replication is specific to one species and carries the genes needed for its own replication.
2. Shuttle vectors multiply in two different unrelated species.
3. They allow efficient transfer of recombinant DNA into yeast cells, and most eukaryotic vectors belong to this group.
4. A yeast shuttle vector has an E. coli part with an origin of replication and a selectable marker such as beta-lactamase, and a yeast part with an autonomously replicating sequence (ARS), a yeast centromere (CEN) and a selectable yeast marker.

Genetic Erosion

Genetic erosion refers to the loss of genetic diversity, or the loss of genes or alleles.

1. Broadly it means the loss of varieties and crop species.
2. The causes are the replacement of traditional varieties by modern commercial or non-food crops, the cultivation of high-yielding varieties, natural catastrophes, and the destruction and modification of the natural habitats holding wild species.
3. Growing genetically uniform, high-yielding modern cultivars causes the loss of about three-quarters of the genetic diversity of agricultural crops.
4. Climate change, intensive development, habitat destruction by modern agriculture and poor knowledge of germplasm are other causes.
5. In India the area under six small millets dropped from 5.34 million ha in 1955-1956 to 0.80 million ha in 2011-2012.

Conclusion: keep every short note to a definition, the key worker or year, and three or four points. That is exactly what 2 and a half marks asks for.