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Thesis (M. Agr. St.)--University of Queensland, Gatton, 2002. / Includes bibliographical references.

Thesis (M. Agr. St.)--University of Queensland, Gatton, 2003. / Includes bibliographical references.

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.

Inoculation of Parthenium argentatum (guayule) with an endomycorrhizal fungus (Glomus intraradices) increased the growth of guayule in saline and non-saline soils low in available phosphorus. Addition of 100 ug/g of P as Ca(H2PO4)2 to soils low in available phosphorus was as efficient as G. intraradices in stimulating the growth of guayule. The concentrations and total plant accumulations of minerals within guayule shoots varied depending on growth of the plants and the minerals assayed. In most cases, the concentrations of Cu, Zn, Mn, Na and Cl increased in the shoot tissues of guayule grown in soils which contained added NaCl. Generally, addition of phosphorus to the soil resulted in decreased concentrations of Cu and Zn and increased concentrations of PO4 in guayule shoots. The total accumulations of minerals by guayule was directly influenced by the biomass of plants. Increased biomass of plants generally resulted in increased total accumulations of the minerals assayed. The influence of mycorrhizae on the accumulations of minerals by guayule grown in a saline soil was evaluated by comparing nonmycorrhizal plants with the same biomass and phosphorus nutrition as mycorrhizal plants. Mycorrhizae increased the concentrations and total plant accumulations of Zn and decreased the content of Cl within guayule shoots. Colonization of guayule roots by G. intraradices was not affected by addition of P to the soil. Addition of NaCl to the soil decreased the formation of arbuscules and vesicles within roots and increased the incidence in which no fungal structures were seen. The combination of P and NaCl added to soil had a synergistic effect on the mycorrhizae of guayule. Addition of both P and NaCl to soil reduced the occurrence of hyphae, arbuscules and vesicles within roots and decreased the overall infection of guayule roots by G. intraradices.

The metabolism of carbohydrates in guayule is a subject which has not been considered with respect to its role in cis-polyisoprene synthesis, It has been suggested that acetate or sucrose act as the distal, and isopentenylpyrophosphate as the immediate precursor of the isoprenoid biosynthetic pathway. Application of radioactive precursors to the leaves of guayule plants in Winter and Summer showed that the fate of the carbohydrate depends on the chemical structure of the carbohydrate and the time of application. [[14]C] Sucrose was incorporated into the acetone (resin) fraction during the Summer and petroleum ether (rubber) fraction during the Winter. The amount of radioactivity that was translocated in Winter and Summer was similar. The loss of leaves during Winter reduced the area for photosynthesis, while the loss of carbon from the leaves during Summer, probably due to photorespiration, decreased the amount of available photosynthates. These two phenomena did not disadvantage the plant as far as the allocation of carbon was concerned. No plant components were acting as sinks during the Winter. The pith of the crown area incorporated the most radioactivity in Summer. [[14]C] Fructose was more readily translocated than [[14]C] sucrose during a 12 hour experiment. When fructose was applied and plants were left for 48 hours, more radioactivity was translocated to the stems and roots during the Summer. The [[14]C] from fructose was incorporated into the acetone (resins) rather than the petroleum ether (rubber) fraction in Winter therefore apparently having a different fate to [[14]C] sucrose. The principal reserve carbohydrates in guayule are fructans. Two types of fructans were detected and are referred to as water-soluble or ethanol-soluble fructans. The ethanol-soluble fructan polymers apparently played an active role in metabolism of guayule and showed cyclic patterns of accumulation. The water-soluble fructans seem to be true reserve carbohydrates, depolymerizing when the carbon supply decreased at the end of Winter, and the demand for carbon increased at the inception of bud break. Fructans provide carbon for budbreak and exposure of plants to longer days and higher temperatures did not seem to alter this role. It is proposed that fructans are providing carbon for budbreak and renewed growth and are utilized for flowering when required. Starch production occurs during the warmer months in the leaves and young stems. Starch is synthesized from the immediate photosynthetic supply and it is this source of carbon which is utilized for the synthesis of cis-polyisoprene (rubber). Sucrose in the cytosol is sequestered for cis-polyisoprene synthesis while fructose, which can enter the plastid, is providing carbon for the synthesis of isoprenoids. Compartmentation of resin and rubber production ensures that the supply of carbon is adequate for both processes. As cis-polyisoprene synthesis occurs at a time when the plant is not disadvantaged by insufficient carbon , induction of rubber transferase enzymes would not depend on excess substrate, but would use a more reliable cue like temperature or daylength. Any attempt therefore to increase the carbon supply in guayule during the winter months would not necessarily lead to partitioning into cis-polyisoprene, but may be stored as fructan to ensure that, at bud break, the plant has an adequate and utilizable carbon supply. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Four species of the genus Parthenium were involved in a hybridization attempt. The species were: guayule (Parthenium argentatum Gray), Parthenium fruticosum Less, Parthenium bipinnatifidum (Ortega) Rollins, and Parthenium incanum H. B. K. Primary attention was given to the formation of hybrids between P. argentatum and P. fruticosum. Characteristics of the latter species such as size, growth rate, possible disease resistance, and wider geographical adaptation were desirable for transfer to P. argentatum. Reciprocal crosses were made between these two species and the production of hybrids was not difficult. However, in the case of selfing, backcross and sibcrosses, germination percent was 0.86 from a total of 3,471 achenes. Therefore, a search for the cause or causes of the negative results was initiated. The factors which were considered of primary interest were: incompatibility, genic and chromosomal sterility, pollination and planting techniques, and seed germination treatment. Incompatibility was considered the main limiting factor in the formation of a backcross population. Rubber analysis was performed in the interspecific hybrids. Mean rubber percent for hybrids between P. artentatum and P. fruticosum was 1.19; and for the reciprocal cross it was 0.39. Hybrids of the cross P. fruticosum x P. bipinnatifidum had a mean rubber percent of 0.19.

Guayule (Parthenium argentatum Gray) is a rubber producing plant native to the Chihuahuan Desert, which is currently being investigated as a source of hypoallergenic latex. Current efforts are focusing on increasing latex/rubber production in the plant by either manipulating the rubber biosynthetic pathway, altering agronomic practices to take advantage of environmental conditions that increase rubber synthesis, or both. Field and greenhouse studies were conducted to more fully understand the effect of genetic and environmental manipulation on rubber production in guayule. Three guayule breeding lines were transformed in order to increase the availability of the initiators of rubber synthesis. The tissue-culture-derived transgenic plants and their seed-generated progeny were grown in separate field experiments. Transformation with the genes for the initiators of rubber synthesis did not increase rubber concentration or yield. Height and width had high heritability estimates in the transgenic progeny and were the traits most correlated with rubber yield, while rubber concentration was poorly correlated with height and width. Greenhouse studies were conducted to understand why water stress and low night temperatures increase rubber concentration. Water stress increased the contribution of the stems to the total rubber in the plant and increased the bark to wood ratio of the stem. Most rubber is accumulated in the stems and these two effects of water stress contributed to the increased rubber concentration in water-stressed plants. Low night temperature reduced plant growth without a decrease in carbon exchange. Allocation of carbon fixation products to rubber synthesis rather than growth, contribute to the high rubber production under low night temperatures. Contributions from both breeders and agronomists are needed to further improve guayule rubber/latex yield.

Thesis (Ph. D. - Plant Sciences)--University of Arizona, 1984. / Includes bibliographical references (leaves 75-77).

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