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1. Evolution of Diploid and Hexaploid Wheat Done by: V SWATHIKA (2022002188) M SWETHA (2022002189)

2. EVOLUTION Evolution of a crop refers to the gradual process by which a wild plant species changes over time into a cultivated form through natural selection, mutation, and especially human selection (domestication). It involves genetic, morphological, and physiological changes that make the plant more useful and adaptable to human needs such as food, fiber, or industrial use.

3. Processes Involved in Crop Evolution: 1.Domestication: • The first step in evolution of a crop.Humans selected wild plants with desirable traits (like larger seeds, less shattering, or better taste) and began cultivating them. •Example: Wild wheat → cultivated wheat. 2.Selection: •Continuous selection of plants with better yield, resistance, or quality.Can be natural (adaptation to climate, pests, etc.) or artificial 3. Hybridization: •Crossing between different species or varieties to combine useful traits •Example: Modern wheat evolved through hybridization between Triticum and Aegilops species.

4. 4. Mutation: •Sudden genetic changes that create new varieties.
•Some mutations are beneficial and become fixed in populations. 5. Polyploidy :
•Increase in chromosome number (duplication of entire sets).
•Common in many crops and leads to larger cells, seeds, and adaptability.
•Example: Wheat evolved from diploid → tetraploid → hexaploid forms. 6. Adaptation :
•Over time, crops adapt to different climates, soils, and cultivation practices, forming local landraces.

5. WHEAT- Triticum sp. ( x =7 ) Wheat is the most important cereal in the world, giving about one-third of the total production, followed closely by rice. In temperate regions it is the major source of food. The chief use of wheat is, the flour for making bread. Wheat evolution is a classic example of allopolyploidy, where different species hybridize and their chromosome sets combine to form a new, fertile polyploid species.

6. EVOLUTION OF WHEAT A major milestone in the study of wheat evolution was the discovery of the chromosome number of the wheat species showing that the wheats comprise a polyploid series consisting of: PLOIDY CHROMOSOME NUMBER PLACE OF ORIGIN Diploid 2n=2x=14 Asia minor Tetraploid 2n=2x=28 Abyssinia, North Africa Hexaploid 2n=2x=42 Central Asia

7. CLASSIFICATION OF WHEAT

8. DIPLOID WHEAT Diploid wheats, like einkorn, were the first domesticated wheats, originating from the A-genome lineage and eventually developing into the cultivated form T. monococcum . Diploid species and donars: Species Common name Genome Triticum urartu Wild diploid wheat AA Triticum boeoticum Wild einkorn AA Triticum monococcum Cultivated einkorn AA

9. T. boeoticum is probably the ancester for all the cultivated wheats. T.boeoticum : forms with one to two seeded spikelets occur. The brittle ears shatter at maturity into individual spikelets armed with awns which provide an effective means of seed dispersal. T.monococcum : Primitive diploid form domesticated, evolved from T.boeoticum by mutation and selection.

10. Tetraploid wheat Tetraploid wheat ( Triticum turgidum) evolved through a natural hybridization and genome doubling event between a diploid species like Triticum boeoticum (giving the A genome) and a species related to Aegilops speltoides (giving the B genome). This tetraploid formed the basis for major domesticated wheat varieties like durum and emmer wheat and also served as one of the parents for the subsequent evolution of hexaploid bread wheat ( Triticum aestivum ).

11. Hybridization and Genome Doubling: These two diploid parents naturally hybridized, creating a sterile hybrid. A subsequent event of genome duplication, also known as amphiploidization, doubled the chromosome number, leading to a fertile tetraploid plant with AABB genomes Formation of Tetraploid Species: This process led to the creation of wild emmer wheat ( Triticum dicoccoides )and later cultivated emmer ( Triticum diccocum ) and durum wheats ( Triticum turgidum ).

12. T.dicoccum : The spikes are dense, bearded and laterally compressed, the spikelets are two grained and the grains are retained within the glumes after threshing (speltoid). It is the oldest of the cultivated wheat. Tetraploid wheats are more adaptable and resilient to various environments than their diploid ancestors, making them valuable crops and contributors to human civilization.

13. Hexaploid wheat The most important of all the hexaploid wheat is the common bread wheat , T.aestivum grown in all parts of the tropics and sub tropics. This hexaploid wheat from which most modern wheats have been developed. It exhibits an extremely wide range of morphological and physiological variation and ecological adaptation. Second Hybridization: The domesticated tetraploid (BBAA) hybridized with the wild diploid Aegilops tauschii (formerely called T. squarossa -DD genome).

14. Amphidiploidization: The result of this hybridization and a doubling of chromosomes (amphidiploidization) was hexaploid bread wheat (Triticum aestivum), possessing the BBAADD genome and 42 chromosomes. The D genome from Aegilops tauschii provided key traits for the milling and baking properties of bread wheat, leading to its broad adaptation and global importance.

15. Wheat Evolution

16. IMPORTANCE OF WHEAT EVOLUTION: 1.To Increase Genetic Variability • Diploid wheat (AA genome) had a limited gene pool.
•Through hybridization with other species (Aegilops), new genomes (B and D) were added.
•This increased genetic variability, providing a broader range of traits for:
Disease resistance
Environmental adaptation Grain and yield improvement 2. To Overcome Sterility in Interspecific Hybrids •When Triticum and Aegilops species hybridized, the hybrids were initially sterile because chromosomes from different species couldn’t pair during meiosis.
•Polyploidization (chromosome doubling) restored fertility by allowing homologous chromosomes to pair properly.

17. 3.To Improve Adaptability to Different Environments •Diploid einkorn wheat was suited only to specific regions (dry hills of the Fertile Crescent).
•Addition of B and D genomes improved tolerance to : Cold, Drought, Diseases, Soil variations 4. To Improve Grain and Yield Characteristics •Diploid wheat produced small, tightly hulled grains with low yield.
•Tetraploid and hexaploid wheats produced larger, free-threshing grains, and higher yields. 5. To Enhance Nutritional and Processing Quality •The D genome from Aegilops tauschii introduced genes for high-quality gluten proteins (gliadins and glutenins) •This led to better bread-making and dough elasticity in Triticum aestivum.