Guayule (Parthenium argentatum Gray) is a promising alternative to (Hevea brasiliensis Muell. Arg.) for rubber production in semiarid regions. Substantial improvement in yield is needed to establish guayule as a competitive source of natural rubber. A 4-year field study was conducted on a dryland site in southern Texas to evaluate productivity of selected guayule breeding lines from Arizona and California. Plants were harvested at the age of 22, 34, and 46 months and analyzed for dry weight, resin content, rubber content, resin yield, rubber yield, and percent mortality. While significant differences (P = 0.05) were found for dry weight, resin content, and rubber content within the harvest dates and among the guayule lines, no significant differences were found for rubber content between the harvest dates for each genotypes. Phytomass was highly correlated (r = 0.94) with rubber yield. Survivorship of all the guayule lines decreased progressively over the experimental period and mortality rates ranged from 38% to 67 %. Guayule lines `UC102' from California and `N6-5' and `P3-1' from Arizona were ranked highest for all traits measured.
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