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Major Evolutionary Patterns in Crop Plants: Implications for Breeding and Diversity, PATTERNS OF EVOLUTION IN CROP PLANTS Presentation by Satyam Sharma
Crop plants have evolved through a complex interplay of natural and human-driven processes that transformed wild species into the diverse and productive crops cultivated today. This presentation on Patterns of Evolution in Crop Plants explains how different evolutionary mechanisms—mutation, hybridization, polyploidy, diversification, and modern breeding—have shaped plant diversity and adaptation across time. The first pattern, Mendelian variation, involves mutations and recombination creating new genetic combinations, as seen in crops like cabbage, cauliflower, and broccoli derived from a single wild ancestor. The second, interspecific hybridization and introgression, introduces genes from related species, expanding genetic diversity and stress tolerance, such as in maize and wheat. The third, polyploidy, through genome doubling, results in increased vigour and adaptability, exemplified by hexaploid wheat and cotton. The fourth pattern, diversification after domestication, explains how crops spread from centres of origin, evolving into landraces and ecotypes adapted to varied agro-ecological zones. Finally, the fifth pattern, directed breeding and biotechnological enhancement, represents the modern phase of crop evolution, where plant breeders use genomic selection, CRISPR, and molecular breeding to accelerate improvement for yield, quality, and resilience. These five evolutionary patterns are interconnected, driving genetic diversity, adaptation, and sustainability in agriculture. Understanding them helps breeders design effective strategies for crop improvement, germplasm conservation, and climate-resilient farming systems. Integrating classical and modern breeding approaches ensures the continued evolution of crops suited for global food security. Keywords: crop evolution, plant breeding, domestication, mutation, Mendelian variation, hybridization, introgression, polyploidy, diversification, adaptation, biotechnology, CRISPR, genetic diversity, germplasm, landraces, genome evolution, Vavilov centres, artificial selection, crop improvement, sustainable agriculture PATTERNS OF EVOLUTION IN CROP PLANTS Genetic variability arisen by 3 major ways various crop species (1) Mendelian variation (generated mainly by gene mutation) (2) Interspecific hybridization (3) Polyploidy Patterns of evolution of various crops are therefore, considered here according to mode of origin of genetic variation crucial for evolution of that species Mendelian Variation Many crops evolved through variation generated by • Gene mutation • Hybridization b/w different genotypes within same species, followed by segregation & recombination. Ultimate source of variability present in any species: gene mutations. Most gene mutations: harmful & eventually eliminated. But some mutations: beneficial & retained in population. Mutations grouped into two broad categories • Macromutation and Micromutations
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Major Evolutionary Patterns in Crop Plants: Implications for Breeding and Diversity, PATTERNS OF EVOLUTION IN CROP PLANTS Presentation by Satyam Sharma
- 1. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं
- 2. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं PATTERNS OF EVOLUTION IN CROP PLANTS Selection by nature & humans: responsible for evolution of crop plants. Selection is effective in altering a species only when genetic variability exists in populations of that species.
- 3. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Genetic variability arisen by 3 major ways various crop species ❖(1) Mendelian variation (generated mainly by gene mutation) ❖(2) Interspecific hybridization ❖(3) Polyploidy ❖Patterns of evolution of various crops are therefore, considered here according to mode of origin of genetic variation crucial for evolution of that species
- 4. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Mendelian Variation ❖Many crops evolved through variation generated by 1. Gene mutation 2. Hybridization b/w different genotypes within same species, followed by segregation & recombination. ❖Ultimate source of variability present in any species: gene mutations. ❖Most gene mutations: harmful & eventually eliminated. ❖But some mutations: beneficial & retained in population.
- 5. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Mutations grouped into two broad categories 1. Macromutation: large & distinct morphological effect, & often affects several characters of plant
- 6. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Maize ❖A single macromutation affected positions of male & female inflorescences, habit of plant & several other characters led to differentiation of modern maize from grassy pod com ❖ 2 key genes 1. teosinte branched1 (tb1) 2. teosinte glume architecture1 (tga1)
- 7. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं
- 8. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं tb1 (teosinte branched1) ❖controls plant architecture. ❖In teosinte, low expression of tb1 results in a highly branched plant with many small, male inflorescences (tassels) at the top of each branch and small female inflorescences (ears) below. ❖In maize, high expression of tb1 in lateral branches suppresses their growth, leading to a single main stalk with a large male tassel at the top and a few large female ears on short lateral branches (shanks).
- 9. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं tga1 (teosinte glume architecture1) ❖tga1 gene controls fruitcase (glume) development around kernel. ❖In teosinte, a hard, protective glume encases each kernel. ❖A single amino acid substitution in tga1 gene during domestication led to soft, absent glumes of modern maize, making kernels naked & easily accessible on cob ❖tga1 mutation pleiotropic effects: kernel shape & prop root development.
- 10. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं ❖Cobbage, cauliflower, broccoli, & Brussel's sprouts all originated from a common wild species & they differ from each other with respect to a few major genes.
- 11. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं
- 12. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Micromutations ❖Small & less drastic effects: accumulated in a population by natural selection ❖Greater part of genetic variation resulted from micromutations. ❖Humans selected for desirable plant types leading to differentiation of domesticated species from wild ones ❖Several important crops evolved differentiation of domesticated species from wild ❖Several important crops evolved through Mendelian variation: barley, Phaseolus, peas (Pisum sativum), tomatoes, linseed (Lınum usitatissimum), jowar (Sorghum bicolor), bajra (Pennisetum glaucum ssp. monodi) etc
- 13. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Interspecific Hybridization ❖Crossing of two different species of plants. ❖F1: generally more vigorous than parents, & ❖F2 & later generations: segregation & recombination produce a vast range of genotypes since parental species are likely to differ from each other for a large number of genes ❖Most of recombinants in segregating generations likely to be weak & undesirable ❖Often interspecific hybrids highly sterile & do not set seed.
- 14. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Introgressive hybridization ❖Little evidence to suggest that interspecific hybridization contributed to any great extent in evolution of crop species. ❖In some cases, interspecific F1 repeatedly backcrossed to one of parental species. ❖As a result, most of genotype of that parental species, to which hybrid had repeatedly back crossed would ha recovered along with few or several genes from other parental species. ❖This process is known as introgressive hybridization it leads to transfer of some genes from one species into another.
- 15. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Contribution of introgressive hybridization 1. Primitive maize × Tripsacum wild grass (contribute some genes)= Modem maize 2. Development of several varieties 3. Fragaria virginiana × F. chiloensis = F1 × backcrossed to two parental species to produce many strawberry varieties of commercial value 4. many varieties are interspecific hybrids (F1) of Pears, plums, cherries & grapes, & ornamentals (irises (Iris sp.), roses (Rosa sp.), lilies (Lilium sp.) vegetative propagation commonly used
- 16. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं
- 17. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Polyploidy ❖Autopolyploidy: increased vigour, larger flowers & fruits over diploid forms ❖Autopolyploidy played a limited role in crop evolution ❖Ipomoea batatas (sweet potato): autohexaploid species (2n = 6x = 90) ❖Avena abyssinica (Abyssinian oat) Auto-tetraploid (2n = 4x = 28) ❖Medicago sativa (alfalfa): autotetraploid (2n = 4x = 32), with its polyploid nature posing challenges for traditional breeding due to polysomic inheritance.
- 18. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं ❖Banana (most commercial varieties (Cavendish), are naturally occurring sterile triploids). ❖Musa sapientum (grouped under Musa × paradisiaca) is a triploid hybrid. Autotriploid (3n = 33) causes irregular meiosis, leading to sterility and seedlessness. Triploid bananas are thus preferred for commercial cultivation because of their better taste, texture, large, seedless fruits and lack of seeds. ❖Citrus (many seedless varieties of oranges, lemons, and limes are triploid). ❖Grapes (some seedless grape varieties are triploid). ❖Mulberry (leaves feed silkworms; triploid leaves higher protein content & biomass). ❖Saffron crocus (a sterile triploid). ❖Cassava (triploid varieties have higher yields and starch content). ❖Ornamental plants (Tulips, lilies & certain cannabis): bred for larger flowers/leaves or sterility ❖Apple: Malus domestica (formerly Pyrus malus) ❖Watermelon: Citrullus lanatus (formerly Citrullus vulgaris) ❖Sugar beet: Beta vulgaris
- 19. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं
- 20. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं commonly grown potato (S. tuberosum): autotetraploid ❖Interspecific hybridization may also be involved, S. tuberosum has 2x & 4x types. ❖Some of 2x progeny obtained from 4x potato are fully fertile & as vigorous as 4x types, indicating that it is largely an autotetraploid ❖S. tuberosum: most widely grown species, tetraploid, 48 chromosomes. 2 subspecies: 1. S. tuberosum subsp. andigena: Adapted to short-day conditions in the equatorial Andes. 2. S. tuberosum subsp. tuberosum: Adapted to long-day conditions in higher latitudes & commonly cultivated in North America & Europe. ❖S. ajanhuiri: A diploid species native to Andes. ❖S. juzepczukii: A triploid species found in Andes ❖S. curtilobum: A pentaploid species.
- 21. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं Allopolyploidy ❖Results from chromosome doubling of interspecific F1 hybrids ❖Allopolyploidy more important in crop evolution than autopolyploidy. ❖About 50% crop plants: allopolyploids ❖Allopolyploid crop: wheat, tobacco, cotton, sugarcane, oats (Avena sp.), rai (Brassica juncea), rapeseed (B. napus), etc. ❖Allohexaploid: Common bread wheat (T. aestivum) is an ❖Allotetraploids: Cotton (G. hirsutum & G. barbadense) & tobacco (N. tabacum & N. rustica) ❖Triticale: man made 6X allopolyploid developed by chromosome doubling of F1, b/w rye (Secale cereale) & tetraploid wheats (Triticum turgidum). ❖Triticale much promise particularly in areas of moisture or temperature stress.
- 22. Agriculture by SatyamSharma: क ृ षि ज्ञानं, समृद्धि यानं