A) Triploids

• Triploids are produced by hybridization between tetraploid and diploid strains.
• They are generally highly sterile, except in a few cases.
• This feature is useful in the production of seedless watermelons.
• In certain species, they may be more vigorous than the normal diploids, e.g., in sugarbeets. These two examples are described in some detail.
• Seedless watermelons are produced by crossing tetraploid (4x, used as female) and diploid (2x, used as male) lines, since the reciprocal cross (2x x 4x) is not successful.
• The triploid plants do not produce true seeds; almost all the seeds are small, white rudimentary structures like cucumber (cucumis stivus) seeds. But few normal size seeds may occur which are generally empty. For good seed setting pollination is essential.
• For this purpose, diploid lines are planted in the ratio 1 diploid : 5 triploid plants.
• There are several problem viz. genetic instability of 4x lines, irregular fruit shape, a tendency towards hollowness of fruits, production of empty seeds and the labour involved in triploid seed production.

B) Allopolyploidy

• Allopolyploids have genomes from two or more species production of allopolyploids has attracted cons adorable attention; the aim almost always was creation of new species.
• Some success has been evident from the emergence of triticale. Raphano brassica and allopolyploids of forage grasses.