The Importance of Cotton Identity: Differences Between Different Cotton Types

Traditionally, the task of fiber identification has been restricted to the distinction between fibers of different types (e.g. cotton vs. wool or synthetic fibers). This task has been relatively easy due to the distinguished differences between different fiber types in chemical composition, surface morphology, and physical attributes. These differences made it largely straightforward to identify fibers via common standard techniques such as optical microscopy, SEM, burning, chemical reaction, or basic physical testing. When the task is to identify different varieties of the same fiber type, particularly in natural fibers such as cotton, a great deal of challenge arises from the significant similarity between these varieties particularly in their polymeric structures, and physical characteristics. This challenge is partially overcome as one crosses the major categories of cotton varieties. For example, when fiber identity strictly aims at identifying whether the cotton belongs to U.S. medium staple upland cotton or U.S. extra long staple (ELS) Pima cotton, identification of genetic differences can be very useful in this regard. This type of identification is a direct result of the fact that ELS cotton is produced from the lint fibers of Gossypium Barbadense, a perennial plant originally domesticated in South America, while upland cotton is produced from the lint fibers of Gossypium Hirsutum, a separate species that was domesticated independently in the Tehuacan Valley of Mexico. Genetic differences are based on obtaining cotton DNA markers at the plant stage. In addition, the two categories of fibers are different in a number of physical properties such as fiber length, fiber fineness and fiber strength, which makes it possible to perform standard physical tests for establishing fiber identity. However, even at this level of genetic differences, identity is often blurred by dissimilar cotton classification techniques, particularly in ELS producing countries. In cases where different ELS cottons are being identified, say U.S. Supima, Egyptian Giza 45, or Giza 70, or China's Xiniang 149, it becomes nearly impossible to segregate these varieties using standard techniques, and DNA faces major obstacles imposed by methodologies, sampling, and surrounding conditions.  In this paper, we tackle the issue of fiber identity using fundamental comparative analysis in which both standard and non-standard measures of fiber characteristics are used.