Q.While studying the history of domestication of various cultivated plants _______ were recognized earlier.

Nikolai Vavilov (1887–1943) inventoried the diversity of the world's major cultivated plants using morphology, anatomy, cytology, genetics and plant geography, and showed that a crop's centre of greatest diversity is usually also its centre of origin. He first identified eight centres of origin in 1926 and expanded this to twelve by 1935 (splitting some centres and adding one in the USA), covering regions such as China, India, South East Asia, Central Asia, the Near East, the Mediterranean, Ethiopia, Mesoamerica, South America, the Chiloe region and the Brazilian-Paraguayan region — each linked to specific crops first domesticated there. Later scholars refined this idea: Zhukovsky (1968) proposed twelve 'mega gene centres', and Harlan (1971) argued a crop can have multiple independent centres of origin, distinguishing a true centre of agricultural origin from a 'non-centre' where a crop later spread.