Cotton is a very diverse crop
Cotton is a very interesting crop. It has a lot of diversity. If you look at the botany of the species, you will see that it is a warm season plant. It is a perennial grown as an annual. It is classified as a woody shrub and as a C3 plant. Background information will show that this refers to the type of photosynthesis that the plant uses. Cotton is in good company since 85 percent of the plant species have this classification. C3 plants use only the C3 photosynthesis.
Corn and sugarcane are two examples of the C4 type of photosynthesis. The CAM system is made up primarily of plants known as succulents. Regardless of which pathway is used, all plants take inorganic carbon dioxide and use it to make organic molecules through photosynthesis.
Its growth is also classified as indeterminate. In biology and botany, indeterminate growth refers to growth that is not terminated in contrast to determinate growth that stops once a genetically pre-determined structure has completely formed. Cotton is a member of the Malvaceae family.
Other family members are the mallows, okra, hibiscus, hollyhock, and Rose of Sharon. The genus of cotton is Gossypium has about 50 species. The two most important species are G. hirsutum, upland cotton, and G. barbadense, Egyptian or Sea Island cotton. Most of the cotton grown in the United States is the upland type. However, the G. barbadense is better suited for a number of uses because it has a finer fiber that is stronger than the upland varieties.
According to an article in the journal, Crop Science, there are eight major collections that are maintained around the world. In the United States, there are nearly 10,000 accessions covering 45 Gossypium species maintained in the National Collection of Gossypium. This collection is located at an USDA-ARS facility located in college Station, Texas.
Cotton can be found on all continents except Antarctica. In nature, the greatest diversity is found in Mexico, Australia, and Africa. While I was visiting in Costa Rico, I saw cotton growing as a tall woody shrub often referred to as tree cotton.
I have worked in two cotton breeding programs. One was at LSU and the other was a USDA ARS program located at Mississippi State, Mississippi. At both programs, we worked with the USDA collections and at Mississippi State we maintained a collection often referred to as racestocks. The reason for the interest in these primitive cottons is that they often had resistance to disease and insects.
At Mississippi State, we would plant seeds of these primitive cottons. Most of them were not adapted to our location since they were not day neutral. For the most part, they were very late in maturity.
In order to test these cottons to determine if they had useful properties, we would make crosses with an adapted cotton variety. If seed were produced, they would be sent to a winter nursery so they could be backcrossed to the original primitive cotton.
These seed were returned and the process was repeated until after six backcrosses, we had the original primitive cotton type that was day neutral. It could then be tested anywhere in the cotton belt. However, some of the seed planted, did not produce seed. The growing season was not long enough; in that case, we would dig up plants in the fall and transfer to a greenhouse.
Again, the purpose of these primitive cottons was so that they could be screened for nematode, disease, and insect resistance or other traits.
At both LSU and USDA we worked with natural mutations. Some of these were the nectariless trait, smooth leaves vs. hairy leaves, and glandless. One of the more interesting traits that we worked with was frego bract. Seed of this trait were sent to the U.S. Cotton Field Station at Stoneville, Mississippi by Mr. Keith Bilbrey from Blytheville, Arkansas in 1945.
Frego bracts were twisted away from the square, bloom and subsequent bolls. These twisted bracts were evaluated for several uses. This trait was non-preferred by boll weevils. It also allowed more insecticide to protect the square. It was found useful for reducing boll rot because it allowed more air movement around the bolls. It was being studied by many researchers. However, this trait had one fatal flaw. Due to the openness, this trait was much more vulnerable to tarnished plant bugs.
Part of my dissertation was to look at fast fruiting varieties and the other traits to see if we could make frego bract more resistant to the tarnished plant bug.
We were able to show that we could use these traits to improve tolerance to tarnished plant bugs. However, some of the Eastern European varieties that we used in the breeding project had such poor agronomic characteristics such as poor fiber quality, low yield, and low lint percentage that it was not feasible for use in a commercial variety. In addition, the Boll Weevil Eradication Program was successful which eliminated the need for boll weevil non-preference traits.
Cotton has so much diversity that these different species and primitive cottons have many uses to improve the genetic base of all our current varieties. It is hard to imagine all of the diversity found in the cotton genetic system.
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