Guayule production on the southern high plains

Guayule has long been known as a potential source of natural rubber. Native guayule populations are scattered throughout 300,000km² of rangeland in the Chihuahuan Desert of Texas and Mexico. The only native indigenous U.S. stands occur in the Trans Pecos region of southwest Texas, and represent the most northern extension of the plant's habitat. Maximum air temperatures of over 38°C are frequent and minimum temperatures of −23°C have been recorded. Guayule has been successfully cultivated across the arid and semi-arid Southwestern U.S., but new production areas need to be identified in order to meet the expected world-wide shortage of natural rubber by 2020. The objective of our study was to determine if guayule production could be successful farther north on the Southern High Plains near Halfway, TX. Guayule seedlings were transplanted May 18, 2006 at the Texas AgriLife Research Station at Halfway. Seed used included four released lines, AZ-1, AZ-2, AZ-3, and AZ-4; a released USDA cultivar (11591); and three unreleased breeding lines, N9-3, N6-5, and N13-1. Guayule cold damage was estimated in June of 2007 and 2008 using the following index: (1) no damage, (2) slight – injury of terminals to 6cm, (3) moderate – 2/3 of plant volume injured, (4) severe – all aerial portions killed but resprouting, and (5) complete – beyond recovery with no regrowth. Plant harvests were conducted in April 2008 and March 2009. Following the 2006/2007 winter the cold damage index ranged from 1.2 in 11591 to 3.8 in AZ-1. The minimum air temperature was −15°C. There was minimal cold damage during the 2007/2008 and 2008/2009 winters. Biomass of the 24 month-old shrubs harvested in 2008 varied from 9639kg/ha in 11591 to 13,393kg/ha in AZ-4. Shrub biomass in 2009 ranged from 26,721kg/ha in 11591 to 32,951kg/ha in N6-5. Rubber yield in 2008 was 222 and 639kg/ha in AZ-3 and N6-5, respectively. Line AZ-3 yielded 717kg/ha of rubber in 2009 while line AZ-4 yielded 2006kg/ha. The critical factor in winter survival appeared to be the temperature regime that existed in the late fall and early winter: a gradual and progressive onset of low temperatures that allowed the shrubs to be dormant when freezing temperatures occurred. Lines 11591 and N6-5 had the least cold damage and hold promise for establishment and rubber production on the Southern High Plains of Texas. Certain production criteria make this area an ideal guayule production site: the long-term annual rainfall averages 460mm, irrigation water salinity is less than 1 E.C. and is pumped from only 90m, and center pivot sprinklers are available for establishing guayule by direct-seeding.