100 Years of Breeding Guayule - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 345

Chapter 16
100 Years of Breeding Guayule
Terry A. Coffelt, Dennis T. Ray, and David A. Dierig
Abstract Guayule has been known for 100 years as a potential source of natural
rubber. Breeding efforts have been sporadic limiting progress in guayule breeding
compared to other crops. Even though the genetic base appears to be rather narrow,
it has not hindered guayule breeding programs. The most extensively employed
breeding approach has been single-plant selections. The primary objective for
guayule breeding programs has been increased rubber yield. Limited studies utiliz-
ing biotechnology, chemical, molecular, or other new methods of improvement
have been conducted in guayule. Most have involved trying to understand the
rubber synthesis pathway or to modify the rubber biosynthesis pathway through
genetic engineering. While these previous attempts to increase rubber yields have
met with little or limited success, the studies have shown that guayule can be
successfully transformed. It might be more effective in the short term to use
biotechnology to insert genes for other potentially useful traits such as herbicide
tolerance and insect resistance. For future progress in guayule breeding to be made,
much work remains to be done.
Keywords Guayule ￿ Breeding ￿ Natural rubber ￿ Germplasm ￿ Genetic resources
Introduction
Guayule, Parthenium argentatum , (Gray) in the Compositae family has been
known for 100 years as a potential source of natural rubber, essentially identical
to that from the tropical rubber tree, Hevea brasiliensis [ 1 , 2 ]. The rubber in guayule
is located principally in the cortical parenchyma cells of the shrubs, with two-thirds
or more in the stem and branches and the remainder in the roots [ 3 ]. The use of