Breeding of Fruit and Plantation Crops 2 + 1

Behaviour of polyploid crops

• Polyploid plants tend to be larger and better at thriving in early succession habitats such as farm fields. In the breeding of crops, the tallest and best thriving plants are selected for. Thus, many crops (and agricultural weeds) may have unintentionally been bred to a higher level of ploidy.
• The induction of polyploidy is a common technique to overcome sterility of a hybrid species in plant breeding. In some situations, polyploid crops are preferred because they are sterile. For example, many seedless fruit varieties are seedless as a result of polyploidy.
• Such crops are propagated using asexual techniques such as grafting. Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine.

Examples of polyploid crops

• Triploid crops : banana, apple, ginger, watermelon, citrus
• Tetraploid crops : potato, cabbage, leek, tobacco, peanut, kinnow, pelargonium
• Hexaploid crops : chrysanthemum, bread wheat, triticale, oat, kiwifruit
• Octaploid crops : strawberry, dahlia, pansies, sugar cane
• Some crops are found in a variety of ploidy. Apples, tulips and lilies are commonly found as both diploid and triploid. Bananas are available as diploid, triploid, tetraploid, and pentaploid. Daylilies (Hemerocallis spp) cultivars are available as either diploid or tetraploid. Kinnows can be tetraploid, diploid, or triploid.


• A survey of the chromosome numbers of the species in a genus or a family shows that these species generally fall into a polyploid series. The species are grouped together under a taxonomic head because of certain morphological resemblances and relationships.
  


• They may be crossable or may not hybridize at all with one another. However, the chromosome numbers of the species show a general relationship, i.e., they form multiples of a common basic number. The chromosome numbers of the family Solanaceae may be considered as an example.
Crops	Ploidy level
Capsicum annum nigrum	12
C. annuum	24
Datura fastuosa	24
D. metal	24
D. stramonium	24
Hyocyamus labus	36
H. canadensis	72
Nicotiana sylvestris	24
N. tabacum	48
N. digluta	72
Physalis philadelphica	24
P. peruviana	48
Solanum marginatum	24
S. muricatum	24
S. alatum	48
S. tuberosum	48
S. nigrum	72
S. nigrum var. gigas	144