This document summarizes the process of allopolyploidy in crop species evolution. It discusses how allopolyploids contain chromosomes from two or more different species and can occur naturally or be experimentally produced. A key example provided is the origin of Raphanobrassica, an allotetraploid produced by crossing Raphanus sativus (radish) and Brassica oleracea (cabbage). While the initial hybrid was sterile, chromosome doubling resulted in a fertile allotetraploid with 36 chromosomes that exhibited traits of both parent species. The document notes how allopolyploidization has contributed to the evolution of important crop species like wheat, cotton and tobacco.

1. Evolution Of Crop Species
Presented By-
Paritosh Mishra
Adm No-46C/15
2nd Yr. B.Sc.(Ag.)

2. Polyploidy
I. Types of polyploidy
A. Autopolyploidy: more than 2 genetically
identical genomes
B. Allopolyploidy: combines the genomes of more
than one species
C. Intermediate situations, e.g. segmental
allopolyploids
D. Ancient polyploidy followed by chromosomal
repatterning and restoration of diploid-like chromosome
behavior "diploidization"

3. Allopolyploids
There are times when organisms may contain two or more sets of
chromosomes that are from different species. When this occurs, we refer
to this as allopolyploidy. It may help to remember this if you think
about the prefix, 'allo-,' meaning 'other' or 'different,' and that 'poly-'
means 'many.‘

4. 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.
i. Production of F1 hybrids by crossing two distinct species and
ii. Chromosome doubling of such F 1 hybrids. The man made cereal
Triticale is an example of synthetic allopolyploid.

5. Amphidiploid
…double diploid,
2n1 + 2n2
…have balanced gametes of the type n1 + n2,
these gametes fuse to make fertile 2n1 + 2n2.

6. Origin of Raphanobrassica
 An allotetraploid has been produced by the Russian Geneticist G.D.
Karpechenko (1927) by crossing Raphanus sativus (2n = 18) and
Brassica oleracea (2n = 18).
 The hybrid formed by crossing these two species is itself a diploid (2n
= 18). It contains only one set of radish chromosome (n = 9) and one
set of cabbage (n = 9) chromosomes.
 The hybrid differs from both the parents and showed many characters
of both.

7. Genetics Of Raphanobrassica
 It is almost sterile, because radish and cabbage chromosome are so
different that they do not pair or fail to pair at meiosis I. But the
hybrid forms an occasional gamete which contains one complete set
of radish chromosomes and one complete set of cabbage
chromosomes.
 When such two gametes combine they produce a plant which contains
two sets of radish chromosome and two sets of cabbage chromosomes
(18+18 = 36). These F2 progenies were fertile and tetraploids. At
meiosis, pairing was regular and the plant was fertile. This plant
showed foliage like radish and root like cabbage. The fruit was
peculier.

8. Hybridisation

9. Rabbage Cross

10. Morphology Of Raphanobrassica
 It resembled the cabbage in its lower portion and the radish in its
apical portion.
 The allotetraploid bred true, hence of no practical value.
 As it combines characters of both radish and cabbage, therefore, has
been named Raphanobrassica.

11. Fig: Raphanobrassica

12. Raphanobrassica: A Profit from Loss
 However, the experiment was significant and it demonstrated a
method by which fertile interspecific hybrids can be obtained.
 Attempts to produce a fertile hybrid between potato and tomato,
with underground parts like potato and aerial parts like tomato, have
also been unsuccessful so far.
 Some of the synthetic allotetraploids resemble closely with the
existing species.
 Various species like wheat, cotton, tobacco etc. might have developed
by this method. During the recent years a new genus Triticale has
been synthesised by combining the chromosome of Triticum duram
and Secale cereale (rye).
 This new genus Triticale is a very useful allopolyploid (2n = 56).

13. Thank you