Evolution of Nicotiana

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.