Guayule (Parthenium argentatum Gray) is one of two major plants in the world grown for natural rubber and therefore, is of potential importance to the U.S. One area of research interest relates to methods of enhancing production of viable seeds. Therefore, studies were conducted in 1984, 1985, and 1986, in Tucson, Arizona to determine the effect of honey bee pollination on: seed set; seed weight; total seed yield; percentage of seed germination; yield and percentage of rubber and resin content. This experiment involved four guayule cultivars and four pollination treatments: plants caged with bees; plants caged without bees; plants open-pollinated; and plants individually covered with Delnet bags. All four cultivars responded positively to honey bee pollination. Plots with bees produced at least 195% more seeds than plots from which bees were excluded. However, there were no qualitative differences in the seed weights between the treatments. The percentage of seed germination from plots serviced by bees was significantly greater (65%) than from plots without bees (50%). Highest seed germination rates were obtained when seeds were collected in May (80%) and September (76%). June, July, and August seed collections resulted in lower seed germination rates (40%, 26%, and 63%, respectively). The plots in which bees were present gave a higher rubber yield (323 kg/ha) than plots without bees (255 kg/ha). However, there were no quantitative differences in the percentage of resin content between the treatments. These studies demonstrated that (1) honey bees can increase seed yield, seed germination, and rubber content in guayule, and (2) seeds produced during summer months had poorer germination rates and lower yields.

Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Guayule (Parthenium argentatum Gray) is a semi-desert plant with the potential to become an established crop on arid land in South Africa. The plant produces latex, which can be processed into rubber that is useful in application where disease transmission needs to be limited, such as for surgical gloves and condoms. The poor germination and natural dormancy characteristics of the embryo and the seed coats of guayule seed, motivated germination experiments. Germination of seed treated with solutions of gibberellic acid, smoke water and smoke watergibberellic acid was determined. Furthermore, combinations of gibberellic acid, smoke water and sodium hypochlorite treatment solutions were applied to seed to determine the germination responses. Vegetative propagation of guayule by means of cuttings was also investigated to determine the rooting responses of cuttings with treatment solutions of indole butyric acid, naphthalene acetamide and naphthalene acetic acid. Rooting percentage, root length and root weight was determined for each treatment. Dryland field trial plantings were established at different areas in South Africa to determine the growth potential and biomass production of guayule cultivars under different environmental conditions. Stand count, height, canopy diameter and stem diameter was determined for the different cultivars and areas. Lastly, latex production of guayule cultivars established in trial plots at Elsenburg, Oudtshoorn and Graaff- Reinet was determined after one year of growth. Treatment solutions of an aqueous smoke extract (commonly referred to as smoke water) and gibberellic acid were evaluated to determine their effectiveness in stimulating germination of four guayule seed lines (AZlOl, AZ-3, N565 and 11591). The split-plot analyses of variance showed no significant interaction between cultivar and treatment factors (P = 0.71), but when the day factor was included interaction was highly significant (P < 0.0001). The applied treatment thus had an effect on the time required for the germination response. Investigations into optimum germination responses indicated that smoke water-gibberellic acid required the shortest number of days (6.3 days) for optimum germination to occur with cultivar AZ-3. Furthermore, gibberellic acid treatment resulted in the greatest germination with the four cultivars 11591, AZ- 3, AZI0l and N565, at 93.78%, 93.35%, 94.41% and 99.42% respectively. These results show that guayule seed can be stimulated to germinate by treatment with gibberellic acid and smoke water solutions. Specific concentrations of treatment solutions of gibberellic acid, smoke water and sodium hypochlorite, and combinations thereof were used to evaluate the germination response of guayule seed cultivar AZ-2. Combinations of treatment solutions did not result in significantly increased seed germination responses. Single treatment solutions of gibberellic acid and smoke water did not significantly enhance germination, but sodium hypochlorite however, significantly (p <0.0001) suppressed germination at the 1% Cl and 2% Cl concentrations with about 5% and 10% respectively when compared to the control. Therefore, the applied seed treatments did not effectively increase the germination of guayule cultivar AZ-2 seed. Specific concentrations of indole butyric acid, naphthalene acetamide and naphthalene acetic acid treatment solutions were applied to guayule cuttings of cultivar AZ-3 and rooting response was determined for rooting percentage, root length and root weight. Naphthalene acetic acid treatment rooted the highest percentage of cuttings (52.38%) at a concentration of 60 mgll. Indole butyric acid treatment produced the longest roots (147.83 mm) at a concentration of 120 mg/l. Naphthalene acetamide obtained the heaviest roots (1.8 g) at a concentration of 120 mgll. Treatment solutions of indole butyric acid, naphthalene acetamide and naphthalene acetic acid indicated specific concentrations for optimum effect to improve root formation (by 30%), root length (by 50 mm) and root weight (by 1.5 g) when compared to the controls. Guayule trial plots of IOx10 m, rows 1 m apart and 30 cm between plants, and each cultivar (10 plants per unit) placed at random and replicated 6 times, were established in different areas under different environmental conditions in South Africa. Plantings were evaluated as a dryland practice, though irrigation was supplied only for establishment. Growth (stand count, height, canopy diameter, stem diameter) and biomass (wet and dry weight) were recorded for (1) oneyear old plantings established in April 2001 at Elsenburg, Graaff-Reinet and Oudtshoorn, and (2) six-month old plantings established in October 2001 at Bethulie, Glen and Upington. Analysis of variance was done to determine mean growth and biomass for the different areas and cultivars. (1) There were significant interactions between the factors area and cultivar for stand count and height, while canopy diameter and stem diameter differences were significant only within factors. The greatest growth potential was produced by cultivars AZ-2 and AZ-3, and Oudtshoorn was the best area for growth potential and biomass production. (2) Interaction between area and cultivar was significant for plant height, but were not significant for stand count, canopy diameter and stem diameter. Cultivars produced similar results for biomass production, but were significantly different in the different areas of Bethulie, Glen and Upington. Growth potential and biomass production of guayule was influenced by the availability of water during the growth of the plant. Latex production of guayule cultivars (AZ-2, AZ-3, N565, 11591) established in trial plots at different areas (Elsenburg, Oudtshoorn, Graaff-Reinet) in South Africa was investigated. Branch samples of one-year old plantings were harvested in April 2002, dipped in 1% ascorbate, sealed in plastic bags and chilled during airfreight to the United States Department of Agriculture (USDA) - Agricultural Research Service (ARS) in Albany CA. Latex extraction and quantification was done and mean latex production and comparisons of latex production for the cultivars in each area were determined. The evaluation of latex production show generally similar results in the different areas. Cultivars generally do not differ significantly from each other in the amount of latex produced in each area. Environmental stress factors on latex production occur in especially Oudtshoorn and Graaff-Reinet where the temperatures are above 25°C and below 1DoC. Since guayule is a slow growing shrub, latex accumulation is also slow and takes 4-6 years to reach economic harvesting potential. Production results are therefore preliminary and require further evaluation after each year of growth to present a complete view of guayule latex production over time. Propagation investigations were successful in identifying techniques to germinate guayule seed and promote rooting of cuttings with specialized treatment solutions. Field establishment of guayule under South African environmental conditions has identified suitable areas and indicated cultivar performances in these areas. Evaluation of the latex production of field plantings has demonstrated the potential of guayule in these areas. Currently the path to guayule development is paved with a network of research activities that is strengthened through cooperation between research institutions and private sector companies that bridge the gap between academic research and market exhibition. / AFRIKAANSE OPSOMMING: geen opsomming