Direct seeding of guayule (Parthenium argentatum Gray) in west Texas has been successful. However, studies have involved only USDA and 'Mexican Bulk' lines. New selections developed by plant breeders must be screened for their adaptability to direct seeding. The objective of this study was to evaluate the standard establishment and production parameters (biomass, rubber and resin content, rubber and resin yield) of six direct seeded guayule selections (AZ-RI, AZ-R2, CAL-6, CAL-7, UC-101, and UC-104). An experiment was initiated on a Delnorte gravelly loam on 23 July 1993 at the Texas Agricultural Experiment Station near Fort Stockton, TX. Conditioned and raw seed of the six guayule selections were planted 10 mm deep on raised beds spaced 1 m apart. Laboratory seed germination ranged from 34-92%. Seedling density was greatest with conditioned seed (61 seedlings/m) versus raw seed (37 seedlings/m) when averaged across all lines 30 days after planting. Individually, seedling density in plots established by conditioned seed was greatest with CAL-6 (68 seedlings/m), UC-104 (66 seedlings;m), AZ-R1 (65 seedlings/m), UC-101 (64 seedlings/m), and CAL-7 (61 seedlings/m), and were significantly greater than the seedling density in plots established with raw seed. Both conditioned and raw seed produced adequate guayule stands. Nonetheless, conditioning improved germination, and in the field, conditioned seed was observed to germinate and emerge quicker resulting in more efficient irrigation management. The AZ-R1 seedlings were the most vigorous and were tolerant to flea beetles (Epitrix sp.). Plants were thinned to a 0.36 m spacing in April 1994. Six plants from each selection in the conditioned seed treatments were harvested on 23 February 1995 and 6 March 1996. Each plant was divided into branch (clipped 10 cm above the soil surface) and root sections. Biomass and rubber and resin yields were greatest in the branch versus root fractions. Total rubber yield (branches plus roots) at both harvests was greatest in selections AZ-R2 and UC-104. (C) 1999 Elsevier Science B.V. All rights reserved.
