Genetic diversity, Centers of origin of Cultivated plants

Genetic diversity:- Genetic diversity is the product of recombination of genetic material in the process of inheritance. It changes with time and space.

> Sexual reproduction is important in maintaining genetic diversity as it gives unique offspring by combining genes of parents.

> Mutation of genes, genetic drift and gene flow are also responsible for genetic diversity.

Importance of Genetic Diversity:-

i. Genetic diversity gives rise to different physical attributes to the individual and capacity to adapt to stress, diseases and unfavourable environmental conditions.

ii. Environmental changes that are natural or due to human intervention, lead to the natural selection and survival of the fittest. Hence, due to genetic diversity, the varieties that are susceptible, die and the ones who can adapt to changes will survive.

iii. Genetic diversity is important for a healthy population by maintaining different varieties of genes that might be resistant to pests, diseases or other conditions.

iv. New varieties of plants can be grown by cross-breeding different genetic variants and produce plants with desirable traits like disease resistance, increased tolerance to stress.

v. Genetic diversity reduces the recurrence of undesirable inherited traits.

vi. Genetic diversity ensures that at least there are some survivors of a species left.

Genetic Diversity Examples:-

i. Different varieties of rose flower, wheat, etc.

ii. There are more than 50,000 varieties of rice and more than a thousand varieties of mangoes found in India.

iii. Different varieties of medicinal plant Rauvolfia vomitoria present in different Himalayan ranges differ in the amount of chemical reserpine produced by them.

Centers of origin of Cultivated plants:-

•    According to De Candolle (1886)

i. Cultivated plants originate from wild plants.

ii. Cultivated plants originate in those geographical area in which their wild relatives are found.

iii. De Candolle published a book:- "Origin of Cultivated Plants"

•    N. I. Vavilov (1887 - 1943):-

i. He was a Russian Geneticist and Agronomist.

ii. He continued research on center of origin up to 10 years from 1920 to 1930.

iii. According to Vavilov, plant diversities are found in a geographical are isolated by hills, desert and rivers.

•    Definition:- A geographical area which has maximum diversity of a plant species, called as center of origin.

Types of centers of origin:-

•    Primary Center of Origin:- A geographical area which has maximum diversity as well as wild relatives of a plant species, called as primary center of origin.

•   Secondary Center of Origin:- A geographical area which has maximum diversity of a plant species, but do not have wild relatives, called as secondary center of origin.

•  Diversity centers are restricted between 20°N and 45°S on both side of equator.

8 Centers of Origin:- Vavilov made 8 centers of origin - 

i. China:- It is largest and oldest center of origin. 136 plants originate in China.

ii. Indian Center:- This center is further divided into 2 sub-centers-

•   Indo - Burma:- It includes India and Burma. 136 plants originate in this sub-center.

•   Indo - Malaya:- It includes Java, Sumatra, Malaya and Philippines. 55 plants originate in this sub-center.

iii. Central Asia:- It includes Punjab, Jammu - Kashmir, Afghanistan, Tajikistan and Uzbekistan. 43 plants originate in this center.

iv. Minor Asia (Near Eastern) (Persian Center):- It is also called as fertile crescent of Mesopotamia. It includes Iran, Iraq, Syria, Lebanon and Israel. 83 plants originate in this center.

v. Mediterranean Center:- It includes Portugal, Spain, France, Austria and Italy. 84 plants originate in this center.

vi. Ethiopian Center (Abyssinian Center):- It includes African country Ethiopia and hilly country Eritrea. 38 plants originate in this center.

Note:- Above 6 centers are collectively known as "Old World".

vii. Central America (Mesoamerican Center) (Mexican Center):- It includes south Mexico. 49 plants originate in this center.

viii. South America:- It includes Peru, Bolivia, Chile and Brazil . 62 plants originate in this center.

Note:- Last 2 centers are collectively known as "New World".