Origin of cultivated plants and centres of diversity
Selection is the science of creating new plant varieties, animal breeds and microbial strains useful to people and of improving existing ones. The gene pool (the sum of all genes in a population) of cultivated varieties and breeds is narrower than that of their wild ancestors, so it is important to look for new useful traits (resistance to disease and drought, yield) in wild relatives. In 1920–1940 N. I. Vavilov organised many expeditions, collected a world collection of crop varieties and created the teaching on centres of origin of cultivated plants: in these centres a crop shows the greatest genetic diversity. The textbook gives 7 centres: tropical South Asia (rice, sugarcane), East Asia (soybean, millet), South-West Asia, including Central Asia (wheat, legumes, flax, carrot), the Mediterranean (cabbage, sugar beet, olive), Abyssinia (barley, coffee), Central America (maize, beans, pumpkin, cotton) and South America (potato); later the number of centres was refined to 12. Today diversity is kept in seed banks, which help to create varieties against climate change and diseases.
“On the map”. Colour the 7 centres on a world outline and write 3 crops of each. Find from which centre three of the most-grown crops of Uzbekistan came.