Question

write notes on evolution of crop plants of varieties?​

Answer 1

Answer:

maize on evolution ofcrop plant of varieties

Answer 2

Answer:

The modern crop plants have developed in nature from the primitive forms as a result of evolution.  The genetic evolution of some important field crops such as wheat, cotton, tobacco, Brassica, potato, maize and rice is briefly described below:

1. Evolution of Bread Wheat:  Wheat is a cereal crop of global importance. It belongs to the genus Triticum of the family Poaceae (old Gramineae). There are three types of species in the genus Triticum, viz., diploid, tetraploid and hexaploid. The tetraploid species developed as an amphidiplod between two diploid species, and hexaploid species originated from a cross between tetraploid and diploid species. It is believed that tetraploid species Triticumturgidum evolved as an amphidiploid between Triticummonococcum (AA) and an unknown species (now probably extinct) with BB genome.

2. Evolution of Upland Cotton:  Cotton is one of the major fibre crops of global importance. It is grown in more than sixty countries in the world. Cotton belongs to the genus Gossypium of the family Malvaceae. There are about 50 species in the genus Gossypium. Some of them are diploid [2n = 26] and some tetraploid [2n = 52], Out of 50 species, only four species are cultivated, viz., G. arboreum, G. herbaceum, G. hirsutum and G. barbadense

3. Evolution of Tobacco:  Tobacco is a narcotic plant which belongs to the genus Nicotiana in the family Solanaceae. It is a native of America, but now it is grown in all the countries of South and South-East Asia. There are two cultivated species of tobacco, viz., Nicotiana tabacum and N. rustica. Both these species are tetraploid (2n = 48). The wild species are diploids.

4. Evolution of Tetraploid Brassica:  The genus Brassica belongs to the family Crucifereae and has several oil bearing species. There are three basic species of Brassica from which three different tetraploid species have originated (Table 39.4). The tetraploid species have originated through interspecific hybridization between diploid species and chromosome doubling of the F1 in nature.

5. Evolution of Potato:  Potato is an important vegetable crop of global importance. It belongs to the genus Solanum in the family Solanaceae. The commercially cultivated potato (Solanum tuberosum) is native of Central and South America from where it has spread to other parts of the world.

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