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How do you produce a seedless watermelon?

Development and Determination of Breeding Characteristics:

A seedless watermelon is a hybrid that has three sets of chromosomes and is called a triploid. Producing a triploid plant requires a tetraploid(four sets of chromosomes) female parent to be crossed with a diploid (two sets of chromosomes) male parent. The resulting offspring is sterile. Different characteristics in seedless watermelons are produced by selecting a diploid or tetraploid parents expressing other desired traits.

Watermelon plants normally have a diploid compliment of chromosomes. To induce a nucleus to have more than a normal number of chromosomes requires the use of a chemical that alters mitosis so that more than the usual number of chromosomes can be obtained. By 1938 the chemical colchicine was discovered to double the number of chromosomes in somatic cells. This is called "induced polyploidism."

Colchicine is a white powder that readily dissolves in water and is obtained from any one of a number of species of plants. When colchicine comes into contact with dividing cells, it alters the mitotic spindle fibers. This is achieved by the application of a 0.2% aqueous solution of colchicine for a period of not less than 48 hours. The chemical acts specifically on the spindle fibers without seemingly to alter the individual chromosomes. When the cell recovers from being treated with an application of colchicine, a new spindle appears and the nucleus undergoes a regular mitosis with the increased number of chromosomes. If sufficient numbers of cells are have been changed from diploid to tetraploid, the new plant tissue is tetraploid.

Both tetraploid and diploid parent lines are bred separately for desirable characteristics; taste, internal color, size and shape, rind color, rind thickness, productivity, growing pattern, maturity time and many other traits. A plant breeder may require from five to ten generations before creating a parent line that breeds "true" - consistently for a set of traits.

Watermelon plant breeders do not currently have the option of using the genetic engineering tools of recombinant DNA techniques to alter specific traits such as flesh or rind color because knowledge of what genes regulate these types of characteristics is not currently well documented. Furthermore, vectors used to insert genetic information into plant cells are limited in number.




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