Location: Plant Physiology and Genetics Research2010 Annual Report
1a. Objectives (from AD-416)
Objective 1: Develop enhanced germplasm and cultivars for low input, high yielding, cost-competitive oilseed, latex, and biomass crops as bio-fuels and bio-based products. Objective 2: Determine the physiological, biochemical, and molecular factors limiting the growth and yield of oilseed, latex, and biomass crops that could be targeted for improvement in a conventiional and/or molecular breeding program. Objective 3: Develop economical production systems for new/alternative industrial crops.
1b. Approach (from AD-416)
Germplasm that has been previously collected as well as new germplasm collections will be evaluated for important characteristics to meet the objectives. Evaluation data and seed will be sent to the appropriate curators for entry into the National Plant Germplasm System. Standard and molecular breeding procedures will be used in selecting and improving germplasm to develop enhanced germplasm with increased levels of desired traits such as oil content, specific fatty acid profiles, latex and resin contents, yield, resistance to biotic and abiotic stresses, and biomass. Production systems will be devised and evaluated utilizing traditional plus new/alternative crops to develop systems that provide farmers profitable and sustainable management practices. New and improved analytical procedures will be developed as needed to evaluate germplasm for desired traits and potential co-products.
3. Progress Report
Lesquerella: The research geneticist leading the lesquerella breeding and agronomic portion of the CRIS transferred to the NCGRP at Fort Collins. However, research to meet milestones 1 and 2 above was continued in-house to develop plant populations with lesquerolic acid contents above 65%, oil contents above 35%, and a harvest index above 35. Yield trials evaluating this germplasm were conducted at two locations for a second year. Oil and fatty acid analyses are underway. A growers’ handbook for Arizona has been developed in cooperation with extension personnel at the University of Arizona. Efforts to develop stable transformation methods for Lesquerella to further improve oil and agronomic traits are ongoing. Guayule: Genetically modified germplasm lines were evaluated in the field for morphological traits and in the laboratory for rubber and resin contents. Preliminary analyses of the results do not indicate any significant increases in rubber, resin or biomass yield compared to the non-transformed control plants. Samples from herbicide tests completed in 2008 were evaluated for rubber and resin contents to determine if herbicides used in plant establishment affected rubber and resin yields. A three year field study was completed at Halfway, Texas to screen for cold tolerance in guayule germplasm. Samples were taken for biomass yield and rubber and resin concentration determination. A new test is planned for FY11 at Lubbock, Texas based on preliminary analyses of these results which showed there are differences in the germplasm for cold tolerance in guayule germplasm at this location. A study to determine the effects of month of harvest on guayule rubber, resin, and biomass yields and the subsequent regrowth of plants following harvest was conducted. Results indicate harvesting during the summer months is not recommended if regrowth of plants for subsequent harvests is a priority. A study was completed to develop a rapid method for evaluating ploidy levels in guayule and to evaluate ploidy levels in guayule germplasm obtained from the collection at USDA-ARS, Parlier, CA. The method was successful and indicated that only two diploid lines were in the germplasm collection. Additional germplasm screenings are underway of genetically modified populations and traditional breeding populations. Additional diploid plants needed for developing new germplasm have been identified in the traditional breeding population. Methods developed for accelerated solvent extraction of resin and rubber from guayule tissues were used to evaluate samples from herbicide tests and other agronomic studies. Other oilseeds: Selection nurseries were conducted for camelina and improved germplasm was identified for further evaluation.
1. Using waste biomass materials to produce value-added products. Using biomass materials such as cotton gin byproducts (CGB) and guayule wastes in value-added products can help the economics of these crops, and additionally, aid in alleviating waste management and environmental problems. A study was conducted by ARS scientists at Lubbock, Texas and Maricopa, Arizona in cooperation with a scientist at the University of Illinois to assess important physical and mechanical properties of composition boards made from select CGB and guayule waste. Boards were made from five different ratios of cotton gin and guayule wastes: 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. Overall, the biobased CGB and guayule waste boards showed great potential and refinement is needed to further enhance the performance of these biomasses for composite board applications. Development of acceptable wood products from these waste materials will enhance the value of these crop for growers and industry.
2. Guayule biomass affects herbicide performance. Current recommendation for guayule production is to have multiple harvests from regrowth after an initial harvest. Weeds can be a major problem during the regrowth requiring the use of herbicides for weed control. Experiments were conducted by ARS scientists at Maricopa, Arizona to determine the extent to which soil organic matter derived from guayule residues can affect the sorption of the herbicide pendimethalin (Prowl). Pendimethalin sorption to the soil increased with increasing guayule organic deposition as measured by time under cultivation. Results show that the use of pendimethalin in a guayule–cotton rotation requires sufficient time and primary tillage before planting cotton. In addition, the use of pendimethalin during regrowth of guayule from the stump following harvest may require higher herbicide application rates to control weeds. Results from this experiment will be of value to growers in planning their herbicide practices in a rotation using guayule and may result in increased production costs.
3. Guayule is a new crop being grown for its hypoallergenic latex. Little research has been done on determining the optimum harvest time of guayule for latex concentration and yield. ARS researchers at Maricopa, Arizona harvested three guayule lines every other month for two years and analyzed for latex concentration, total biomass and latex yields. Results varied among lines and harvest dates. There is enough difference among lines that planting lines selected for different optimum harvest dates would allow growers to spread the optimum harvest time throughout most of the year. This would also benefit processors by allowing them to reduce their production costs by spreading the harvest over several months instead of only a few months. More research must be done to determine the specific environmental factors associated with optimal harvest time.
4. Producing high quality guayule seed. The commercialization of guayule for hypoallergenic latex has renewed interest in factors that affect seed quality. A two year study was conducted by ARS scientists at Maricopa, Arizona, and Fort Collins, Colorado in cooperation with scientists at Colorado State University to determine the effects of location, irrigation frequency, and initial nitrogen fertility level on seed quality of different guayule lines. All of the factors tested (lines, locations, irrigation frequency, and initial nitrogen fertility level) affected seed germination. The greatest influence was environmental effects. The results will be of value to guayule seed producers in identifying the environmental factors needed to produce higher quality guayule seed.
5. Descriptors developed for guayule germplasm. Commercialization of guayule as a source of rubber is receiving world-wide attention as an alternative to Hevea in order to meet increasing demand for natural rubber. As more breeders, agronomists, botanists, and other scientists become involved in evaluating and developing guayule germplasm, it is imperative that a uniform set of germplasm descriptors is available. These descriptors are also necessary for use in obtaining plant variety protection certificates. A set of descriptors was developed by an ARS scientist at Maricopa, Arizona in cooperation with a scientist at Yulex, Corporation and successfully used to evaluate breeding nurseries of both traditionally and transgenically developed guayule plants. The descriptors were easy to use and required a minimum amount of time per plant, so that a large number of lines could easily be evaluated. The descriptors adequately covered the range of diversity observed in the nurseries evaluated. A set of 14 minimum descriptors is proposed. For germplasm protection uses, the full set of 31 descriptors should be used. The descriptors will provide uniformity in comparing germplasm performance across experiments and environments. The descriptors will also be valuable to regulatory agencies in granting various plant protection certificates.
6. Optimum harvest height determined for guayule. The commercialization of guayule for hypoallergenic latex has renewed interest in production factors such as harvesting height and frequency. A four year study was conducted by an ARS researcher at Maricopa, Arizona in cooperation with a researcher at the University of Arizona on five guayule lines with variable plant height to determine the effects of harvesting at 50% of plant height compared to the recommended 100% at 2, 3, and 4 years of growth. Total yields of biomass, latex, rubber, and resin were determined for plants harvested annually and biannually after two years with a single harvest after three and four years. Harvesting at 100% of plant height gave higher yields than harvesting at 50% of plant height independent of harvest frequency. Harvesting at 100% after four years of growth gave the highest yields, but harvesting on a two year schedule may be better for harvesting and extraction equipment. Optimum harvesting schemes at 100% of plant height may need to be developed for each line and environment. These results will benefit guayule growers, processors, and researchers.
7. Rapid method for determining guayule ploidy levels developed. Genetic improvement through modern plant breeding is needed to increase guayule yield potential and suitability for commercialization. Ploidy variation is among the factors that slow the rate of genetic gain in guayule breeding programs. Determining the ploidy level of publicly available guayule accessions would help to accelerate the development of stable, high yielding cultivars. ARS scientists at Maricopa, Arizona in cooperation with a scientist at Kansas State University adapted flow cytometry to examine the ploidy of 34 guayule accessions available from the National Plant Germplasm System. The data revealed a natural polyploid series, ranging from diploid (2n=2x=36) to pentaploid (2n=5x=90), with 4x being the predominant ploidy. Not all plants sampled from an accession had the same ploidy level (mixed ploidy). Notably, the integration of ploidy and pedigree data uncovered complex ploidy variation in guayule breeding programs. The frequency and range of ploidy variation observed in this germplasm will help to direct future breeding efforts as well as linkage analysis and genome-wide association studies.
8. Cellular properties of lipid-producing enzymes identified. Lipids are vital components of plants that serve many important functions including the formation of the protective, waxy layer on the surface of leaves and the accumulation of oils in seeds. Lipids are produced by complex metabolic pathways in plant cells, and developing a better understanding of the specific enzymes involved in their production is important for improving the stress tolerance of plants and oil content and composition. In collaboration with scientists at the University of Guelph in Canada, ARS scientists at Maricopa, AZ characterized the properties of two enzymes called glycerol-3-phosphate acyltransferases (GPATs), including a description of exactly where in the plants cells these enzymes are located. These results will impact scientists interested in understanding how certain enzymes (and their associated enzyme activities) are organized in plant cells to produce specific types of plant lipids.Coffelt, T.A., Nakayama, F.S., Ray, D.T., Cornish, K., McMahan, C.M. 2009. Post-harvest storage effects on guayule latex and rubber yields. Industrial Crops and Products. 29(2-3):326-335.