Registration of Six Guayule Germplasms with High Yielding Ability

Six guayule (Parthenium argentatum A. Gray) germplasms, AZ-1 (Reg. no. GP-8, PI 599674), AZ-2 (Reg. no. GP-9, PI 599675), AZ-3 (Reg. no. GP-10, PI 599676), AZ-4 (Reg. no. GP-11, PI 599677), AZ-5 (Reg. no. GP-12, PI 599678), and AZ-6 (Reg. no. GP-13, PI 599679), were released jointly by the Agricultural Research Service, United States Department of Agriculture, and the Agricultural Experiment Station, The University of Arizona, in June 1997. These releases were selected for uniformity of plant appearance, fast growth, high resin content, and high rubber yielding ability. The original germplasm sources used in developing these germplasms were obtained from the National Seed Storage Laboratory, Fort Collins, CO. Individual plants were selected for rubber yield per plant and regrowth rate from within four original accessions. Single-plant families were grown from open-pollinated seed. Since guayule sets seed by facultative apomixis, the amount of crossing varies with environment and plant (1). Four cycles (seed to seed) of within-family selection were conducted at Maricopa, AZ, for uniformity, plant architecture, plant dry weight, rubber content, and resin content (short-chain isoprenoids that might become useful coproducts) (2). Traits used to determine plant architecture included canopy height, canopy width, plant volume, stem number, stem diameter, stem area, and stem circumference. The germplasms described herein represent bulked seed from the final cycle of this selection. These six germplasms were grown in a field trial at the Maricopa Agricultural Experiment Station and compared with the cultivars N565 (PI 478655) and 11591 (PI 478640) (3) in 1992 (two-year-old plants) and 1993 (three-year-old plants) (Table 1). AZ-1 was selected from PI 478660 and tested as C16-1. This germplasm was developed from a single-plant selected for its increased rubber production after 2 years of growth compared with N565 and 11591 (Table 1). AZ-1 has a higher resin content and a higher rubber yield than 11591 after 2 and 3 years of growth, AZ-2 was originally tested as G7-11 and AZ-3 was tested as G7-15. They were developed from individual plant selections from PI 478640. AZ-2 and AZ-3 were selected for very vigorous growth within the first two years. Plants of AZ-2 and AZ-3 produced more plant dry weight after 2 and 3 years of growth, and more resin and rubber yield after 2 years of growth than N565 or 11591 (Table 1). AZ-2 and AZ-3 produced more resin and rubber yield than 11591 after 3 years of growth. The higher rubber yields were in spite of a lower rubber content, indicating the influence of the higher plant dry weights on rubber yields. The exceptional attribute of these lines is their vigorous early growth that could decrease time to initial harvest from three to two years. AZ-4 is a mass selected line from one of the original accessions and was tested as N7-BULK. AZ-5 is a single-plant selection from the same source as AZ-4, and was tested as N7-11. AZ-5 is morphologically (height, width, leaf shape, branching habit) more uniform than AZ-4. AZ-4 and AZ-5 were selected for release based on their higher rubber content and yield after 2 years growth and higher resin content after 2 and 3 years growth compared with N565 and 11591 (Table 1). The most significant traits of AZ-4 and AZ-5 are their higher resin and rubber contents and rubber yield after two years growth. While AZ-2 and AZ-3 have higher rubber yields because of their higher plant dry weights, AZ-4 and AZ-5 have higher rubber yields because of their higher rubber content. AZ-6 is a very uniform line developed through mass selection from one of the original selections, and was tested as P2-BULK. Of the six releases, AZ-6 had the second highest rubber yield at both two and three years (Table 1). Plant dry weight and rubber content were higher than N565 and 11591 after two years growth and higher than 11591 after three years growth. Rubber yields were higher than N565 and 11591 both years. The most significant attribute of AZ-6 is that it incorporates higher plant dry weight and rubber content into one line as well as faster growth potential. Limited quantities of seed of these lines are available from the corresponding author. We ask that appropriate recognition be made if this germplasm contributes to the development of a new breeding line or cultivar. Requests from outside the USA should be accompanied by the appropriate customs control documents.