BIOMASS, RUBBER, AND RESIN YIELD POTENTIALS OF NEW GUAYULE GERMPLASM

Substantial improvement in rubber yield must be made in order to establish guayule as a reliable source of natural rubber. Selection among heterogeneous apomictic polyploids was used to improve rubber yield in a relatively short period of time. In a replicated test, 24 new selections and four old varieties were planted to examine the yield potential of the new selections and to determine the optimum age at which guayule plants may be harvested. Plants were harvested at the age of 21, 33, and 45 months and were analyzed for rubber content, resin content, and dry matter. Rubber content ranged from 2.2 to 7.68%; resin content varied from 4.04 to 8.41%; and dry biomass yield ranged from 5623 to 15 860 kg ha-1 year-1. Annual yields averaged 325-908 kg of rubber, 310-1307 kg of resin, and 615-2135 kg in rubber plus resin. New selections produced 40-127% more rubber than the old check varieties, which suggests that selection among apomictic plants for increased rubber yield has been successful. The various total yields of all entries increased by age. The annual rubber yield, however, was found to be genotype dependent with some genotypes giving their highest annual rubber yield at the age of 21 months. Such genotypes may play a crucial role in guayule commercialization.