Thursday, February 19, 2015

The Color of Cotton

Ever since I first heard about it, I've been interested in naturally colored cotton (also known as "color grown cotton"). The cotton plants most people are familiar with produce a pure white fiber, which can then be dyed to match any desired color. Naturally colored cotton, on the other hand, is grown with color straight from the plant.

There is archaeological evidence for the existence of cotton in various shades of yellow, brown, green, and red. The pre-Columbian Peruvian textile at left is supposedly made from colored cotton without the processing of additional dyes. There are also reports of a naturally colored blue cotton, but the internet has provided minimal evidence for this.

The majority of commercially grown cotton belongs to the species Gossypium hirsutum. Varieties of this cotton species can be found in light brown and green, but the other colors are generally nowhere to be found.

2. Inheritance of different fiber colors in cotton.
During a recent web search, I came across an image of a very dark brown naturally colored cotton. The image also shows a nice orange cotton, in addition to the more typically seen tan and light brown colors. Seed for these varieties aren't generally available, however, but they can be accessed from different seed collections (such as GRIN) if you can show you have some worthwhile research, education, or other public good rationale for having them.

These more interesting colors are seen in relatively wild varieties of a second cotton species, G. barbadense. G. hirsutem and G. barbadense don't naturally cross in the wild due to different timing of pollen maturation and other mechanisms. These are all easily circumvented by directed hybridization efforts. The resulting F1 hybrids grow well and are fertile, though fertility issues do arise in some F2 generation plants. These issues wouldn't interfere greatly with the intentional recombination of pigment alleles from both species, which I think has interesting potential to create new interesting colored varieties.

After I've done some further experiments with growing the cotton lines I already have in Minnesota, I might request some of the interesting colored forms from the collections.

3. Cotton and I.
...wait, growing cotton in Minnesota (red star)? ...a thousand miles north of where cotton is grown in the USA (green regions)?

A few years ago, on a whim, I planted some cotton seeds I had come across in south Texas. Cotton is typically described as needing a long and hot growing season to mature. I don't know how the production of my plants compared to similar plants in the South, but their production was dramatically higher than I expected up here in the North. After the first hard freeze of winter, I broke the plants off at their base and hung them to dry in the garage. A few weeks later, the cotton fibers had completed drying and were easy to collect. This process might not be something that can be scaled up to a proper crop, but it might. Further research is needed.

  2. Dark brown cotton:
  3. GRIN:
  4. Crossing:$FILE/biologycotton08.pdf