This document discusses the evolution of allopolyploids in Nicotiana plants, specifically tobacco. It defines allopolyploids as polyploids containing chromosome sets from two or more species, which most commonly originate from chromosome doubling of an F1 hybrid. Tobacco is an example of a natural allopolyploid crop, with Nicotiana tabacum arising from a cross between N. sylvestris and N. tomentosa, and N. rustica from a cross of N. paniculata and N. undulate. The document provides background on the center of origin and cultivation of different tobacco species.

1. EVOLUTION OF
Nicotiana

2. Allopolyploids:
• A polyploid containing genetically different chromosome sets from two or
more species is known as allopolyploid.
• The prefix ―allo‖ indicates the involvement of non-homologous sets of
chromosomes.

3. Origin of allopolyploids:
• Natural allopolyploids most likely originate through chromosome doubling of F1
hybrid produced by chance through natural hybridization between two distinct species
of the same genus or from different genera.
• Experimental production of allopolyploids is achieved through chromosome doubling
of F1 hybrid with the help of colchicine. Such allopolyploids are often called synthetic
allopolyploids.
• The synthesis of allopolyploids involves two steps.
1. Production of F1 hybrids by crossing two distinct species and
2. Chromosome doubling of such F 1 hybrids.
• The man made cereal Triticale is an example of synthetic allopolyploid.

4. • Amphidiploid: It is an allopolyploid (allotetraploid) which arises by
combining genomes of two different species. 62 The amphidiploids are
fertile due to the presence of homologous chromosomes and behave as a
diploid during meiosis. The term amphidiploid was proposed by Nawashin.
• Natural allopolyploids: Inter-specific crossing followed by chromosome
doubling in nature have resulted in origin of some natural allopolyploid
crops like cotton, tobacco, mustard, wheat, etc.

5. Nicotiana
• Centre of origin- may be from America
• Some believe it was brought as a medicine.
• It was introduced in india in 17th century only.
• India is the 2nd leading producer of nicotiana followed by china.
• A.P is the leading state in producing tobcco

6. Tobacco
• There are about 50 natural species of nicotiana.
• Most of them occur in temperate and sub tropical region of north and south
America and a rest of distinct group is found in Australia.
• Most of them belong to 12 chromosome category except for some9-10
chromosomes.
• The 2 cultivated species i.e. N.rustica & N. tabaccum are 24 chromosome
species and are amphidiploid to the 12 chromosome species.

7. Origin of natural allopolyploid crops(tobacco)
• There are two cultivated species of tobacco. i. e. Nicotiana tabacum and
Nicotiana rustica.
• Nicotiana tabacum is an allotetraploid and available evidence suggests that it
is derived from a cross between Nicotiana sylvestris x Nicotiana tomentosa.
• Nicotiana rustica is believed to be an amphidiploid obtained from a cross
between Nicotiana paniculata and Nicotiana undulate.