Micropropagation of Guayule (Parthenium argentatum)

Guayule is a member of the family Compositae, and belongs to the genus Parthenium (Fig. 1). It is a rubber-producing shrub, native to a semi-arid area in north-central Mexico and southwestern Texas, USA. The plant, with chromosome numbers of 2n = 36 to 108 or more, has narrow leaves, covered in a drought-protecting white wax, that alternate along the stems, and a canopy of small flowers borne on exceptionally long stems. Only about 60 cm high, it develops a taproot that may penetrate the soil more than 6 m, supplemented by extensive fibrous roots to absorb moisture from a considerable area of desert soil and thus withstand periodic drought. It may survive 30 or 40 years under desert conditions where annual rainfall may be less than 250 mm (Rollins et al. 1977).