100 Years of Breeding Guayule - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 346

guayule rubber by native populations to make balls for games was first reported by
the Spanish in the early 1500s [ 1 ]. Use of guayule rubber as a commercial source
began in the late 1800s, when it was “rediscovered” by a Mexican Boundary Survey
party.
In the last 100 years, breeding efforts for guayule have been sporadic and largely
correspond to four major commercialization efforts in North America [ 4 , 5 ]. These
efforts have all centered on the production of guayule as an alternative source of
natural rubber. The limited and sporadic nature of these breeding efforts has limited
the progress in guayule breeding compared to other crops.
The initial major commercialization attempt started in the early 1900s with
harvesting wild guayule stands in Mexico due to the high price of imported rubber
from the Amazon region [ 6 ]. Production during this effort accounted for up to 24 %
of the total rubber imported into the United States by 1910 [ 6 ] with 20 extraction
plants either operational or under construction in Mexico. Harvesting of wild stands
in Mexico came to a halt in 1912 because of the Mexican Revolution. The effort
was then moved across the border with plantings in Arizona and California in the
United States, [ 4 ]. This effort came to a halt in 1929 as a result of the Great
Depression [ 4 ]. Breeding efforts during this attempt involved mainly the collection
and selection of plants and their seed from wild stands.
The second major effort to utilize guayule as a source for natural rubber was the
Emergency Rubber Project of World War II. Natural rubber production had moved
almost exclusively to large plantations of the Brazilian rubber tree grown in
Southeast Asia, and these sources were cut off at the beginning of the war
[ 4 ]. This second effort was very successful, generating the bulk of our knowledge
about the basic biology of guayule, and developed the germplasm upon which the
current breeding programs are based [ 5 ]. The effort ended with the end of the war,
the return of availability of natural rubber from Southeast Asia, and the develop-
ment of synthetic rubber.
The third major effort to commercialize guayule started in the late 1970s because
of the quadrupling of crude oil prices [ 5 ]. The fear was if the oil supply could be
manipulated, then there might again be a shortage of natural rubber due to either
natural disaster or political unrest in Southeast Asia. Two laws were enacted by the
US Congress in response to this fear - the Native Latex Commercialization and
Economic Development Act of 1978 and the Critical Agricultural Materials Act of
1984 (Laws 95-592 & 98-284). Again, a tremendous amount of work was accom-
plished, resulting in significant yield increases and the refinement of cultural
practices to fit modern mechanized agriculture [ 4 , 5 , 7 , 8 ]. This third effort again
showed that guayule could be planted, cultivated, harvested, and processed as a
source of natural rubber. However, as the political climate changed, this effort was
also terminated.
The future for guayule appeared bleak until the report of latex allergy to Hevea
rubber products in the general population [ 9 ]. The development of Hevea latex
allergy made the development of an alternative, safe source of natural rubber
imperative. Guayule proved to be a source of non-allergenic latex for those with
latex allergy [ 10 ]. Guayule latex was found to contain many fewer proteins than