A center of diversity is an area that has a high degree of genetic variation for a particular plant taxon (e.g. family, genus or species) that can also be the center of origin for that group. The two areas often, but not always, coincide; the degree of coincidence remains the subject of debate in both areas, organisms have had the opportunity over many generations to evolve resistance, via mutation, to their pathogens.
The term was created by the Russian scientist Nikolai Vavilov and the U.S. scientist Jack Harlan. Vavilov published a study in 1926 (Studies on the Origin of Cultivated Plants) describing ten such centers:
The centers of crop diversity of three types viz:
1) Primary centers of diversity,
2) Secondary centers of diversity
3) Micro – Centers.
These are briefly discussed below:
1. Primary Centers of Diversity:
Primary centers are regions of vast genetic diversity of crop plants. These are original homes of the crop plants which are generally uncultivated areas like, mountains, hills, river valleys, forests, etc.
Main features of these centers are given below:
1. They have wide genetic diversity.
2. Have large number of dominant genes.
3. Mostly have wild characters.
4. Exhibit less crossing over.
5. Natural selection operates.
2. Secondary Centers of Diversity:
Vavilov suggested that values forms of crop plants are found for away from their primary area of origin, which he called secondary centers of origin or diversity.
These are generally the cultivated areas and have following main features.
1. Have lesser genetic diversity than primary centers.
2. Have large number of recessive genes.
3. Mostly have desirable characters.
4. Exhibit more crossing over
5. Both natural and artificial selections operate.
In some case, small areas within the centers of diversity exhibit tremendous genetic diversity of some crop plants. These areas are referred to as micro-centers. Microcenter is important sources for collecting valuable plant forms and also for the study of evolution of cultivated species.
The main features of micro centers are given below:
1. They represent small areas within the centers of diversity.
2. Exhibit tremendous genetic diversity.
3. The rate of natural evolution is faster than larger areas.
4. They are important sites for the study of crop evolution.