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University of Arizona (1979)

ECOLOGICAL STUDIES OF NATIVE JOJOBA PLANTS — SIMMONDSIA CHINENSIS (LINK) SCHNEIDER — IN ARIZONA

Almeide, Francisco Aecio Guedes

Titre : ECOLOGICAL STUDIES OF NATIVE JOJOBA PLANTS — SIMMONDSIA CHINENSIS (LINK) SCHNEIDER — IN ARIZONA

Auteur : Almeide, Francisco Aecio Guedes

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1979

Résumé
The desert shrub jojoba — Simmondsia chinensls (Link) Schneider — was studied during an intensive one year investigation at three different sites in Arizona considering : (1) the vegetative and reproductive growth in relation to air and soil temperatures, precipitation, available water capacity, and potential evapotranspiration, (2) the monthly development of total nonstructural carbohydrates and proteins in the foliage and relating them to some of the ecological factors noted above, (3) the development of the seed oil and meal protein in relation to the maturity of the seed, and (4) the plant yield variables in relation to the environmental factors studied. Site 1 is located on the eastern slope of the Tucson Mountains, site 2 is on the west side of the Tucson Mountains, and site 3 is in the southern foothills of the Santa Catalina Mountains. Franseria dumosa, Cercidium microphyllum, Opuntia spinosior, and 0. Bigelovli were the only species common to all sites. The higher the density and coverage of Franseria dumosa, the lower was the jojoba fruit yield per plant. The higher the density of male jojoba plants in relation to females, the lower was the number of aborted and/or immature fruits. The ratio of male to female plants was less than 1.0 for all study sites. Male to female ratio coverage closer to 1.0 was more conducive to higher fruit yield per plant. When male plants were taller than females, plant fruit yield was significantly higher.
The extent of development of the soil, its available water capacity, and its pH influenced yield as well as the size and weight of the fruit. The higher the winter precipitation, the higher was the fruit yield. There was an inverse relationship between yield and the annual soil temperature.
Even though plants initiated new flowers two or three times during the year, fully developed flowers were present on most plants during the entire study. Although, anthesis was concentrated in the early spring at all sites, it was also observed in the middle of fall. Alternating temperatures of about 27°C during the day and 16°C during the night appeared to influence the opening of male flowers. Initiation of new fruits in the fall was observed only at site 2. These fruits were killed by frost during the following winter. Fruit maturation, occurring in a three to four week period at the end of spring, was accelerated by high temperatures at all sites. Vegetative growth of jojoba responded positively to precipitation.
The influence of temperature regimes was mostly found after the middle of fall and winter. The greater the fall vegetative growth, the more severe was the frost damage and less productive plants at a particular site. Total nonstructural carbohydrates in the foliage reached their highest level in early March and lowest in summer. Protein content in the foliage was highest at times of active growth.
Fruits at the beginning of maturation had the highest moisture content and the lowest dry seed weight. Dry fruits reached their highest weight at the full yellowing stage. Seed weight at full maturation averaged 0.54 g at site 1, 0.46 g at site 2, and 0.68 g at site 3. In addition to larger seeds, site 3 had fruits with less hull and more seed. Wax content increased with maturity of the seed. Wax content tended to relate to fruit size but not to seed weight. Using a dye method, protein content of the seed reached its highest value at the beginning of maturation. Using a method based on the total nitrogen determined, protein content was highest at full maturation of the seed.

Mots clés : Jojoba — Ecology — Arizona — Pima County.

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