Vavilov’s Centres of Origin of cultivated crop plants

What is Centers of origin?

The concept of “centers of origin” refers to the geographical regions where specific groups of organisms, whether wild or domesticated, initially emerged on Earth. This term is often associated with the origins of crop plants and wild species, reflecting the places where these organisms first evolved. It is important to distinguish between centers of origin and centers of diversity. While a center of origin represents the primary locale of a species’ development, a center of diversity indicates regions where the species have diversified and adapted over time.

Typically, each species originated in a particular area before spreading to other regions. Therefore, the center of origin is usually a singular location, whereas centers of diversity may span multiple areas. The precise identification of a species’ original location often relies on indirect evidence and can be challenging to determine with absolute certainty.

Understanding the centers of origin is crucial for plant breeding and conservation efforts. Knowledge of where crop plants originally came from helps researchers identify wild relatives and related species, facilitating the acquisition of new genetic traits. Additionally, this knowledge is vital for preventing genetic erosion, which occurs when genetic diversity is lost due to the decline of specific ecotypes or habitats.

Nikolai Ivanovich Vavilov, a prominent Russian scientist, made significant contributions to this field by collecting extensive samples of crop plants and their wild relatives. Vavilov’s research utilized various scientific disciplines, including morphology, anatomy, cytology, genetics, and plant geography, to establish the locations of primary and secondary centers of origin. He posited that major centers of origin were often found in lower mountain and hill regions of tropical and subtropical climates. Vavilov also identified secondary centers of origin, where hybridization and selective pressures led to the development of new plant varieties. His work underscored that plant domestication was not a random event but a gradual and continuous process.

Concepts of Centre of Origin

The concept of the “centre of origin” was introduced by the Russian scientist Nikolai Ivanovich Vavilov. The key elements of this concept are outlined as follows:

• Origins of the Concept: Nikolai Ivanovich Vavilov (1887-1943) was instrumental in developing the concept of centres of origin. His research laid the groundwork for understanding the geographical origins of crop plants and their wild relatives.
• Fieldwork and Collections: Vavilov and his colleagues conducted extensive fieldwork, traveling to numerous countries to collect a diverse array of crop plants and their wild relatives. This collection was crucial for understanding the genetic diversity of plants.
• Purpose of Collection: One of Vavilov’s primary objectives was to gather crop-related germplasm to support national plant breeding programs. This collection aimed to improve crop varieties through breeding by utilizing genetic resources from their centres of origin.
• Observations on Crop Diversity: Vavilov noted that crop diversity is often concentrated in specific geographical regions. This observation suggested that the development of crop plants is not random but rather occurs in particular areas where species originally evolved.
• Contrary to Prevailing Views: Vavilov’s concept challenged the then-prevailing belief that plant cultivation began randomly across the globe. Instead, he proposed that crops originated in specific centres and later dispersed to other regions.

Vavilov’s original concepts

Nikolai Ivanovich Vavilov’s original concepts in plant science introduced groundbreaking ideas about the origins and distribution of cultivated plants. The following points summarize his key contributions:

• Differential Taxonomy and Dispersal: In 1940, Vavilov proposed that differential taxonomy—a method of classifying organisms based on their evolutionary differences—could trace the dispersal patterns of cultivated plants. This approach allowed the analysis of plants’ stages of evolution from their initial origins to their spread across various regions. It also highlighted how plants evolved under domestication and the influence of natural and artificial selection.
• Primary vs. Secondary Crops: Vavilov distinguished between primary (more ancient) and secondary crops. This classification helped him identify the original centres of agriculture and the pathways through which these crops spread. Primary crops were those domesticated earliest, while secondary crops arose later, often through further selection and cultivation.
• Geographical Distribution and Diversity: Vavilov’s studies revealed that cultivated plants exhibit enormous infraspecific diversity, which helped in pinpointing their geographical origins and the time frames of their domestication. His work suggested that human civilizations and agriculture date back much further than ancient historical records.
• Evolution of Centres of Origin: The number of centres of origin identified by Vavilov varied over time, reflecting the accumulation of new data. Initially, he identified three centres, but this number increased to eight by 1935, only to be reduced to seven in 1940. Each adjustment was based on new evidence and refined understanding.
• Regional Concentrations of Diversity: Vavilov emphasized the importance of regions with high concentrations of plant variation. He initially ranked the Chinese and Hindustani centres highly but later revised these rankings based on further data. His research indicated that the southern Asiatic tropical centre and eastern Asia were particularly rich in cultivated plant species.
• Division and Renaming of Centres: Vavilov’s work included refining the geographical boundaries and names of various centres. For example, the Southwestern Asian centre was divided into the Middle Asian and Asia Minor centres. The Middle Asian centre, later renamed Inner Asian, encompassed regions such as northwestern India and parts of Central Asia.
• Use of Terminology: Vavilov used terms like ‘centre’, ‘focus’, and ‘area’ of origin interchangeably to describe the primary geographical regions where crops originated. These terms helped delineate large territories as the sources of agricultural crops.
• Impact on Modern Agriculture: Vavilov’s concepts underscored the historical significance of crop domestication and its role in the development of human societies. His work revealed that the domestication of plants was a gradual process influenced by both environmental conditions and human intervention.

Methods used by Vavilov for determining the centers of type-formation (centers of origin) of cultivated plants

Nikolai Ivanovich Vavilov employed several methodological approaches to determine the centers of type-formation, or centres of origin, for cultivated plants. The methods he used are outlined as follows:

1. Differentiation of Plant Species:
   • Description: Vavilov initiated his research by meticulously differentiating plant species into Linnaean categories, as well as into various intraspecific groups.
   • Approach: This differentiation was achieved through a combination of morphological studies, agrobotanical research, phytopathological analysis, cytological examination, and, later, molecular techniques.
   • Function: This step ensured that the classification of plants was precise and comprehensive, laying the groundwork for further analysis.
2. Delimitation of Distribution Areas:
   • Description: The next step involved mapping out the current distribution areas of these plant species and, where possible, their historical distribution.
   • Approach: This involved examining past geographical distributions, particularly focusing on times when communication and seed exchange were less prevalent.
   • Function: Understanding both present and historical distributions helped in identifying regions where plant species might have originated or diversified.
3. Determination of Varietal Composition:
   • Description: Vavilov then focused on identifying the varieties and races within each species, as well as developing a general system to describe the genetic variability within species.
   • Approach: This involved detailed analysis of the composition of different varieties and races, including their genetic characteristics.
   • Function: This step was crucial for understanding the scope of genetic diversity within species and how it is distributed across different regions.
4. Establishment of Genetic Variability Distribution:
   • Description: Vavilov aimed to determine the distribution of genetic variability among forms of a given species, focusing on identifying geographical centers where these varieties were most concentrated.
   • Approach: This involved mapping regions with maximum diversity and identifying endemic types and characteristics.
   • Function: Regions with high concentrations of genetic diversity often indicated areas where the species had evolved or diversified significantly.
5. Identification of Closely Related Species:
   • Description: For a more precise identification of the centres of origin, Vavilov sought to establish geographical centers where species botanically related to the studied plants were concentrated.
   • Approach: This involved examining the distribution of species closely related to the cultivated plants under study.
   • Function: By including closely related species, Vavilov refined the understanding of where plant types originated and diversified.
6. Assessment of Wild Relatives:
   • Description: Finally, Vavilov considered the distribution areas of wild subspecies and species that were closely related to the cultivated plants.
   • Approach: This involved using the differential method to study these wild relatives and adjust the defined areas of origin.
   • Function: Incorporating data on wild relatives provided a more complete picture of the origins and evolutionary history of cultivated species.

Vavilov’s centers of origin

Nikolai Vavilov, a pioneering botanist and geneticist, identified several key centers of origin for cultivated plants based on his extensive studies of global plant diversity. His work laid the foundation for understanding the geographic origins and centers of genetic diversity of many crops. These centers are categorized into main centers and subsidiary centers. Here is a detailed examination of Vavilov’s proposed centers:

Main Centres of Crop Diversity

1. South Mexican and Central American Center:
   • Geographic Scope: Encompasses southern Mexico, Guatemala, Honduras, and Costa Rica.
   • Plant Species:
     • Grains and Legumes: Maize, common bean, lima bean, tepary bean, jack bean, grain amaranth.
     • Melon Plants: Malabar gourd, winter pumpkin, chayote.
     • Fibre Plants: Upland cotton, bourbon cotton, henequen (sisal).
     • Miscellaneous: Sweet potato, arrowroot, pepper, papaya, guava, cashew, wild black cherry, cochineal, cherry tomato, cacao.
2. South American Center:
   • Sub-centers:
     • Peruvian, Ecuadorian, Bolivian Center:
       • Root Tubers: Andean potato, other endemic potato species.
       • Grains and Legumes: Starchy maize, lima bean, common bean.
       • Vegetable Crops: Pepino, tomato, ground cherry, pumpkin, pepper.
       • Fibre Plants: Egyptian cotton.
       • Fruit and Miscellaneous: Cocoa, passionflower, guava, quinine tree, tobacco, cherimoya, coca.
     • Chiloe Center: (Island near southern Chile)
       • Key Plants: Common potato (48 chromosomes), Chilean strawberry.
     • Brazilian-Paraguayan Center:
       • Plants: Manioc, peanut, rubber tree, pineapple, Brazil nut, cashew, Erva-mate, purple granadilla.
3. Mediterranean Center:
   • Geographic Scope: Includes regions bordering the Mediterranean Sea.
   • Plant Species:
     • Cereals and Legumes: Durum wheat, emmer, spelt, Mediterranean oats, grass pea, pea, lupine.
     • Forage Plants: Egyptian clover, white clover, crimson clover, serradella.
     • Oil and Fibre Plants: Flax, rape, black mustard, olive.
     • Vegetables: Garden beet, cabbage, turnip, lettuce, asparagus, celery, chicory, parsnip, rhubarb.
     • Ethereal Oil and Spice Plants: Caraway, anise, thyme, peppermint, sage, hop.
4. Middle East:
   • Geographic Scope: Includes Asia Minor, Transcaucasia, Iran, and Turkmenistan.
   • Plant Species:
     • Grains and Legumes: Einkorn wheat, common wheat, barley, rye, lentil, lupine.
     • Forage Plants: Alfalfa, Persian clover, fenugreek, vetch.
     • Fruits: Fig, pomegranate, apple, pear, quince, cherry, hawthorn.
5. Abyssinian Center:
   • Geographic Scope: Covers Ethiopia, Eritrea, and parts of Somalia.
   • Plant Species:
     • Grains and Legumes: Abyssinian wheat, barley, grain sorghum, pearl millet, cowpea, flax, teff.
     • Miscellaneous: Sesame, castor bean, coffee, okra, myrrh, indigo, enset.
6. Central Asiatic Center:
   • Geographic Scope: Includes Northwest India, Afghanistan, Tajikistan, Uzbekistan, and western Tian-Shan.
   • Plant Species:
     • Grains and Legumes: Common wheat, peas, lentil, chickpea, mung bean, mustard.
     • Fiber Plants: Hemp, cotton.
     • Vegetables: Onion, garlic, spinach, carrot.
     • Fruits: Pistachio, pear, almond, grape, apple.
7. Indian Center:
   • Sub-centers:
     • Indo-Burma (Main Center): Includes Assam, Bangladesh, Burma.
       • Plant Species: Chickpea, pigeon pea, urd bean, rice bean, cowpea, eggplant, cucumber, mango, tangerine, coconut palm, sesame, safflower, jute, black pepper.
     • Siam-Malaya-Java: Includes Indo-China and the Malay Archipelago.
       • Plant Species: Job’s tears, velvet bean, pummelo, banana, clove, nutmeg, black pepper.
8. Chinese Center:
   • Geographic Scope: Covers a broad area in China.
   • Plant Species:
     • Cereals and Legumes: Rice, broomcorn millet, buckwheat, soybean, adzuki bean.
     • Roots, Tubers, and Vegetables: Chinese yam, radish, Chinese cabbage, onion.
     • Fruits and Nuts: Pear, peach, apricot, cherry, walnut, litchi, orange.
     • Fibre Plants: Sugar cane, opium poppy, ginseng, camphor, hemp.

Subsidiary Centres of Crop Diversity

1. Indo-Malaya:
   • Geographic Scope: Includes the region of Indo-China and the Malay Archipelago.
   • Significance: Known for its diverse plant species and agricultural importance.
2. Chile:
   • Geographic Scope: Covers regions in Chile, particularly in the southern part of the country.
   • Significance: Recognized for specific plant varieties endemic to this region.
3. Brazil and Paraguay:
   • Geographic Scope: Includes areas in Brazil and Paraguay.
   • Significance: Noted for its unique plant species and contributions to crop diversity in South America.

Types of evidence that Vavilov used

• Archaeological Evidence:
  • Function: Provides historical context for the domestication and cultivation of plants.
  • Details: Vavilov examined ancient artifacts, tools, and remains to trace the origins of agriculture and the early use of plant species.
• Plant Remains:
  • Function: Offers direct physical evidence of ancient plant species and their uses.
  • Details: Vavilov analyzed preserved plant remains such as seeds, fruits, and grains found in archaeological sites to determine the historical distribution and domestication of plants.
• Living Plants:
  • Function: Serves as a primary source of current genetic and morphological data.
  • Details: Vavilov studied living plants from various regions to assess their genetic diversity and compare them with ancient and historical specimens.
• DNA, Proteins, Morphology, and Biochemistry:
  • Function: Provides detailed insights into the genetic makeup and biochemical properties of plants.
  • Details: Through molecular techniques and biochemical analyses, Vavilov investigated the genetic variations and protein profiles of plants to trace their origins and evolutionary relationships.
• Ecology and Distributions:
  • Function: Helps in understanding the environmental and geographical factors influencing plant diversity.
  • Details: Vavilov studied the ecological conditions and geographical distribution of plants to identify patterns of diversity and centers of origin.
• Plant Breeding Relevance:
  • Function: Supports the identification of genetic resources crucial for crop improvement.
  • Details: By locating the origins of crop plants, Vavilov’s work facilitated the identification of wild relatives and related species, providing a basis for plant breeding. This includes discovering new genes, particularly dominant genes, which can offer resistance to diseases and other beneficial traits.

Limitations of Vavilov’s views

Nikolai Vavilov’s theories on the centers of origin for cultivated plants represent a significant advancement in the study of plant genetics and biodiversity. However, as scientific research has progressed, several limitations of Vavilov’s views have become evident. These limitations highlight the need for a more nuanced understanding of plant domestication and genetic diversity.

• Discrepancy Between Genetic Diversity and Center of Origin:
  • Vavilov’s Perspective: Vavilov posited that the region with the highest genetic diversity of a species should be considered its center of origin.
  • Current Understanding: Contemporary research indicates that this is not always the case. For instance, maize (Zea mays) and tomato (Solanum lycopersicum) exhibit centers of origin that do not necessarily align with the regions of greatest genetic diversity. This discrepancy suggests that genetic diversity alone may not accurately pinpoint a species’ center of origin.
• Geographic Limitations:
  • Vavilov’s Perspective: Vavilov’s model primarily identified centers of origin in mountainous and hilly regions within tropical and subtropical zones.
  • Current Understanding: Recent evidence reveals that plains and lowland areas also serve as significant centers of origin for numerous cultivated plants. This broader geographic scope indicates that Vavilov’s model may be overly restrictive and fails to account for the full range of environmental contexts where plant domestication can occur.
• Multiple and Ambiguous Centers of Origin:
  • Vavilov’s Perspective: According to Vavilov, each cultivated plant species originated from a single primary center characterized by a predominance of dominant alleles.
  • Current Understanding: Modern research has identified multiple centers of origin for several crops, contrary to Vavilov’s singular-center hypothesis. Additionally, the origins of many species remain ambiguous due to insufficient evidence. This multiplicity and the challenge of tracing precise origins underscore the complexity of plant domestication.
• Genetic Allele Distribution:
  • Vavilov’s Perspective: Vavilov suggested that primary centers of origin are marked by a high frequency of dominant alleles in the center, with recessive alleles becoming more common towards the periphery.
  • Current Understanding: This allele distribution model is now considered inadequate. Advances in genetics and plant breeding have demonstrated that allele frequencies can vary independently of geographic origin, challenging the validity of Vavilov’s original hypothesis.

Importance of Centres of Origin

These centers are the geographic regions where specific crops first evolved and from which they spread. Knowledge of these origins has significant implications for plant breeding, genetic preservation, and overall crop management.

• Facilitating Plant Breeding:
  • Locating Wild Relatives: Identifying the centers of origin helps breeders locate wild relatives of cultivated plants. These wild relatives often possess unique genetic traits that can be valuable for enhancing crop resilience, disease resistance, and yield.
  • Discovering Related Species: The centers of origin provide insights into related species that may offer additional genetic resources for breeding programs. This can lead to the development of new varieties with improved characteristics.
• Preventing Genetic Erosion:
  • Avoiding Loss of Germplasm: Knowledge of crop plant origins is essential for preventing genetic erosion, which refers to the loss of genetic diversity within crop species. This loss can occur due to habitat destruction, such as deforestation and urbanization, which reduces the availability of ecotypes.
  • Mitigating Habitat Loss: Centers of origin often include critical habitats that are essential for maintaining diverse plant genetic resources. Protecting these areas helps preserve the natural genetic diversity of crops and their wild relatives.
• Germplasm Preservation:
  • Utilizing Gene Banks: Gene banks play a vital role in preserving genetic material from crop plants and their wild relatives. These banks primarily store seeds but increasingly include frozen stem sections and other plant tissues to maintain genetic diversity over time.
  • Preserving Natural Habitats: In addition to ex situ conservation methods like gene banks, preserving natural habitats within the centers of origin is crucial. These habitats serve as reservoirs for diverse genetic materials and are important for ongoing research and breeding efforts.