C. McMahan, H. Colvin, D. Dierig, W. Goldner, G. Lester, K. Ogden, W. Orts
USDA Agricultural Research Service, Western Regional Research Laboratory,
Keywords: natural rubber, bioproducts, biofuel, guayule
Summary:Natural rubber is a critical agricultural material (PL 95-592 & 98-284) required for U.S. industry, medicine, and defense, yet the current world’s supply is derived from one plant species, Hevea brasiliensis (rubber tree), grown in the tropics. Since all commercial rubber trees are derived from highly inbred clonal varieties, the global rubber supply is highly susceptible to disease such as leaf blight, which destroyed Brazil’s rubber production 100 years ago. Demand for natural (and synthetic) rubber is outpacing supply, due to economic expansion in developing nations. The creation of a domestic natural rubber production system will address national supply and defense security issues for this critical material, as well as offer opportunities for rural development, and provide alternatives for petroleum-based energy and materials. Guayule (Parthenium argentatum), a woody desert shrub indigenous to the Chihuahuan desert of North America, is under development in the semi-arid southwestern U.S. as a renewable agricultural crop. Development of guayule is driven by the need for low water use crops in this region and by world market demand for biobased products, including the natural rubber, resin, and bioenergy feedstock produced by the plant. In the past ten years, remarkable progress has taken place in creating a domestic natural rubber production system from guayule. Public sector and public/private partnerships have significantly contributed to these advancements. These include the USDA/DOE-BRDI consortium project: Securing the Future of Natural Rubber- an American Tire and Bioenergy Platform from Guayule, and the USDA-NIFA AFRI Coordinated Agricultural Program: Sustainable Bioeconomy for Arid Regions. Milestones achieved include sequencing of a guayule genome, expansion of available germplasm and genomic tools, the first irrigation scheduling app for guayule, and advancements in rubber and resin extraction technology. In 2017, a 100% guayule rubber-based passenger tire successfully passed DOT requirements, creating a modern-day benchmark validating both design and safety. A parallel guayule rubber sustainability model quantified the tire’s improved environmental impacts from cultivation through road use. Today, the questions of whether guayule natural rubber is of sufficient quality to meet industrial specifications, can be successfully used to build a modern passenger tire, can provide environmental benefits vs. petroleum-based tires, and can be genetically improved toward profitable yields have been answered (yes!). Mechanistic studies have offered new insight on how the crop responds to stresses such as cold and drought, known to increase rubber yield. Application of this knowledge in crop management will lead to higher yields with even less water use. Research and development strategies have now pivoted toward utilization of co-products, identified in ongoing techno-economic analyses to be the key to economic sustainability. Agronomic practices are being translated into Extension tools for guayule cultivation in Arizona and New Mexico. Importantly, sustainability and economic models have expanded in breadth and depth, providing strategic input to commercial scale-up planning. An historic combination of public and private investments and partnerships has moved the United States closer than ever to realizing domestic natural rubber production; key partnerships have moved an industry toward a more secure and sustainable future.