Principles of Plant Breeding (2+1)

Significance of polyploids

Polyploids

1. Banana and some clones of mulberry, poplar, chrysanthemum and apple are natural triploids which are commercially grown.
2. Autopolyploid rye grass, sugarbeets, turnips, and fodder beets are commercially grown.
3. Triploids sugar beet are preferred over the tetrapolids.
4. Rye grass tetraploids give higher fodder yield as compared to dipoloids.
5. Pusa Gaint Berseem, tetraploid turnips, spinach pierce grapes, tetra petkus, steel rye, and tetraploid Brassica campestris var.toria are some other example of induced autotetraploidy.
6. Autopolyploidy plays an important role in bridging ploidy levels in the interspecific crosses where hybridizing species differ in ploidy levels.
7. Haploids can be used to produce completely homozygous lines in a short period as compared to 8-10 year required in in self pollinated crops.
Allopolyploids

1. Natural allopolyploids has played important role in the evolution of our major field crops such as wheat, cotton brassica species and sugarcane.
2. Raphanobrassica was developed but unfortunately it possessed radish like leaves and cabbage like roots.
3. Triticale a man made cereal is as an artificially synthesized allopolyploid.
Aneuploids

1. The aneuploids have not been much direct use in plant breeding. Used to incorporate alien addition of complete chromosomes or preferably segments of chromosomes.
2. Monosomics has been used in genemapping.
3. Aneuploids are used in the genetic studies to identify the chromosome or arm of the chromosome on which a particular gene is located.
4. Nullisomic lines have also been used to assign genes to a particular chromosome but the nullisomics are less vigorous and less fertile than monosomics.
5. Monosomics are also very useful for intervarietal chromosome substitution.