Major Gene Pool Centres: Origin, Findings, and Limitations

Introduction

The concept of gene pool centers is fundamental to understanding the origin, evolution, and diversity of cultivated plants. A gene pool represents the total genetic diversity within a species. A large gene pool indicates increased genetic diversity, which often contributes to a robust population, while a smaller gene pool suggests reduced biological fitness. The study of gene pool centers helps identify regions where domesticated or wild plants first developed, providing valuable insights for plant breeding and conservation.

Centre of Origin

The center of origin is a geographic area where a group of organisms, whether domesticated or wild, first evolved. Understanding these centers is crucial for identifying the sources of genetic diversity, wild relatives, and related species. This knowledge helps avoid genetic erosion, which occurs when unique germplasm is lost due to the destruction of habitats or ecotypes.

Historical Background

• Alphonse de Candolle was the first to question the geographic origin of cultivated plants.
• Based on Charles Darwin’s Evolution Concept and Candolle’s observations, Nikolai Vavilov proposed the concept of gene pool centers in the 1920s.

Vavilov’s Assumptions

Vavilov’s hypothesis on gene pool centers was based on the following assumptions:

1. The main species could be traced back to a specific region, known as the center of origin.
2. These centers often supported a variety of crops.
3. The centers represented areas of genetic origin and diversification.

Vavilov’s Findings

1. Primary and Secondary Crops:
   • Primary crops were ancient cultivated plants, while secondary crops emerged as weeds in primary crop fields.
2. Maximum Variation:
   • Areas with the highest variation, often containing endemic species, were identified as centers of origin.
3. Foci of Type Formation:
   • Identified as “hearts of centers,” these were areas where unique types of species developed.
4. Dynamic Nature of Gene Pool Centers:
   • Vavilov found that the number and borders of these gene pool centers continuously changed over time.

Vavilov’s Centres of Origin of Cultivated Crop Plants

Vavilov proposed eight centers of origin for cultivated crop plants. These centers are not only where the species originated but also where they exhibit maximum genetic diversity. However, the centers of diversity and origin may differ for certain species.

Vavilov’s 8 Centers of Origin

1. Chinese Centre:
   • Location: Mountain regions of central and western China
   • Endemic Species: Soya bean, radish, turnip, pear, peach, plum, apricots, oranges, China tea, brinjal, opium poppy, buckwheat.
2. Himalayan Centre (Indian Centre):
   • Location: Regions of Assam, Burma, Indo-China, and Malayan Archipelago
   • Endemic Species: Rice, red gram, mung dal, chickpea, cowpea, brinjal, cucumber, sugarcane, black pepper, moth bean, cotton, turmeric, millets, indigo.
3. Mediterranean Centre:
   • Location: Borders of the Mediterranean Sea
   • Endemic Species: Durum wheat, emmer wheat, oat, barley, lentil, pea, grass pea, broad bean, cabbage, asparagus, peppermint.
4. Abyssinian Centre:
   • Location: Ethiopia and parts of Somalia
   • Endemic Species: Wheat, sorghum, bajra, safflower, castor, broad bean, okra, coffee.
5. Central Asian Centre:
   • Location: North-west India, Afghanistan, Uzbekistan, and western China
   • Endemic Species: Bread wheat, club wheat, sesame, linseed, muskmelon, carrot, onion, garlic, apricot, grape, hemp, cotton.
6. Asia Minor Centre:
   • Location: Near East Asian regions, including Iran and Turkmenistan
   • Endemic Species: Wheat, rye, pomegranate, almond, fig, cherry, walnut, alfalfa, Persian clover.
7. Central American Centre:
   • Location: Southern parts of Mexico, Costa Rica, Guatemala, and Honduras
   • Endemic Species: Maize, rajma, lima bean, melon, pumpkin, sweet potato, arrowroot, chili, cotton, papaya, guava, avocado.
8. South American Centre:
   • Location: Peruvian regions, southern Chile, Brazil, and Paraguay
   • Endemic Species: Potato, sweet potato, lima bean, tomato, papaya, tobacco, quinine, cassava, rubber, groundnut, cocoa, pineapple.

Importance of Vavilov’s Centres

• Plant Breeding: Helps locate wild relatives, related species, and new genes for crop improvement.
• Conservation: Knowledge of centers helps avoid genetic erosion and conserve germplasm diversity.

Limitations of Vavilov’s Views

The expansion of knowledge on cultivated plants has revealed some limitations in Vavilov’s concept, requiring modifications:

1. Diversity vs. Origin:
   • Vavilov considered the region with the greatest genetic diversity as the center of origin, but some species have different centers of genetic diversity and origin.
     • Example: Maize and tomato have distinct centers of diversity and origin.
2. Geographical Focus:
   • Vavilov’s centers were limited to mountainous and subtropical regions, but recent evidence suggests that many cultivated plants also originated in plains.
3. Multiple Centers of Origin:
   • Some crops have more than one center of origin, challenging Vavilov’s idea of single centers.
4. Genetic Dominance Assumption:
   • Vavilov assumed that primary centers exhibit dominant alleles, while the periphery had recessive alleles. This view is not supported by recent genetic studies.

Conclusion

Vavilov’s concept of gene pool centers was a groundbreaking contribution to understanding crop origins, providing a foundation for modern plant breeding and conservation. Although limitations exist, his work remains invaluable in guiding researchers toward preserving genetic diversity and safeguarding food security.

1. How has Vavilov’s concept of gene pool centers contributed to modern plant breeding and conservation practices? (250 words)
2. Discuss the limitations of Vavilov’s views on gene pool centers and how recent research has expanded our understanding of crop origins. (250 words)
3. Explain the significance of understanding centers of origin and diversity for the conservation of genetic resources and preventing genetic erosion. (250 words)