PHENOLOGICAL STUDIES OF THREE NATURAL STANDS OF JOJOBA (SIMMONDSIA CHINENSIS (LINK) SCHNEIDER) NEAR TUCSON, ARIZONA.

Abstract

Jojoba (Simmondsia chinensis (Link) Schneider) is a wild desert shrub known for the liquid wax extracted from its fruits. As the plant undergoes the first stages of domestication into a commercial crop, it is important to understand its response to environmental factors and to study its regularity of production. Phenological studies including vegetative growth, floral biology, seed production, and seed wax content were conducted from 1979 to 1982, complementing investigations in 1978 in three natural stands of jojoba, near Tucson, Arizona and air and soil precipitation, temperatures were continuously recorded at each study site. Periods of vegetative growth were identical for staminate and pistillate plants and were generally observed after the occurrence of measurable rainfall. In late winter vegetative growth occurred after monthly average minimum temperatures of 4-5°C, although local responses to small differences in temperature were observed. Anthesis was first observed in late February or early March. Fruits generally originated from flower buds produced in the previous summer. Incidence of fruit abortion was greatest in May and June. Variations from year to year in seed production from 1978 to 1982 suggested biennial bearing. Factors in addition to frost incidence were believed to be associated with the absence of seed production in 1979 and the low seed crop of 1981. Levels of foliar total nonstructural carbohydrates were not found to be appreciably different between a low production year and a high production one. Seed wax percent was found to be independent of annual variation in seed production. Plant growth and productivity was greatest on the site with the best developed soil profile, highest water holding capacity and highest exchangeable sodium percentage.