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Genome size variation in guayule and mariola: Fundamental descriptors for polyploid plant taxa

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... Wild quinine is a perennial herbaceous plant native to central and eastern United States (Mears, 1975;Rollins, 1950) and a potential source of cold resistance and non-arid adaptation (Thompson and Ray, 1989). However, with the exception of a recent ploidy and nuclear genome size evaluation of mariola accessions (Sanchez et al., 2014), minimal genomic information is available for these two Parthenium species, and the availability of this information is expected to greatly facilitate interspecific breeding programs. ...
... Building upon previously published data for 10 guayule, mariola, and Parthenium hybrid accessions (Gore et al., 2011;Sanchez et al., 2014), we used flow cytometry to expand ploidy and nuclear genome size characterization to four interspecific hybrids between guayule and other Parthenium species. Additionally, we estimated the nuclear genome size and ploidy level of a wild quinine accession, a first for this Parthenium species. ...
... The pedigrees for all accessions in this study are summarized in Fig. 1, and more extensive information is available in Table A.2 and references therein. Plants were grown as described in Sanchez et al. (2014). All experimental procedures that do not differ significantly from Sanchez et al. (2014) are described in Appendix C for reference (see Supplementary data). ...
Article
Guayule (Parthenium argentatum A. Gray) is a perennial woody shrub native to the North American Chi-huahuan Desert that holds promise as a sustainable source of natural rubber and hypoallergenic latex. The improvement of guayule for commercial-scale production could be accelerated through genomics-assisted breeding, but such a strategy is severely limited by the paucity of available genomic tools and well-characterized genetic resources. To that end, we used genotyping-by-sequencing (GBS) to simultaneously identify and genotype tens of thousands of single-nucleotide polymorphism (SNP) markers across 62 plant samples from seven wild and cultivated guayule, three Parthenium interspecific hybrid, four mariola (Parthenium incanum Kunth), and one wild quinine (Parthenium integrifolium L.) accession(s) that have been characterized for ploidy level and nuclear genome size in this and a prior study. Phyloge-netic analysis using the SNP data identified at least two distinct sources of guayule breeding material in the cultivated accessions, previously unknown multi-species hybrids within two Parthenium hybrid cul-tivars, and guayule/mariola hybrids within one guayule and one mariola wild collected accession. Similar to previously reported results for guayule and mariola, we observed aneuploidy and multiple ploidy levels among individual plants (mixed ploidy) within three Parthenium interspecific hybrid accessions newly characterized in this study. Nuclear genome size characterization of wild quinine, a first for this species, found an estimated haploid nuclear genome size (5757 Mb) for the tetraploid (2n = 4x = 72) accession that was more than 1.5-fold larger than that of tetraploid (2n = 4x = 72) guayule or mariola. Together, these results further underscore the need for a comprehensive characterization of available guayule germplasm and sister taxa with both SNP markers and flow cytometry, illustrate the novel utility of GBS for the genus Parthenium, and lay the foundation for genomics-assisted breeding in guayule.
... Thus, identification and development of alternative sources of natural rubber are important to the tire industry. The sequencing and annotation of the 1.6 Gb [5,6] nuclear genome of a diploid guayule was undertaken to facilitate the application of current molecular and breeding tools to guayule improvement. ...
... All genomic and transcriptome sequences were derived from a single diploid guayule plant, accession W6 429 developed from a selection obtained in a 1942 Durango, Mexico collection expedition [1,5,6]. ...
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Background: Guayule (Parthenium argentatum A. Gray) is a rubber-producing desert shrub native to Mexico and the United States. Guayule represents an alternative to Hevea brasiliensis as a source for commercial natural rubber. The efficient application of modern molecular/genetic tools to guayule improvement requires characterization of its genome. Results: The 1.6 Gb guayule genome was sequenced, assembled and annotated. The final 1.5 Gb assembly, while fragmented (N50 = 22 kb), maps > 95% of the shotgun reads and is essentially complete. Approximately 40,000 transcribed, protein encoding genes were annotated on the assembly. Further characterization of this genome revealed 15 families of small, microsatellite-associated, transposable elements (TEs) with unexpected chromosomal distribution profiles. These SaTar (Satellite Targeted) elements, which are non-autonomous Mu-like elements (MULEs), were frequently observed in multimeric linear arrays of unrelated individual elements within which no individual element is interrupted by another. This uniformly non-nested TE multimer architecture has not been previously described in either eukaryotic or prokaryotic genomes. Five families of similarly distributed non-autonomous MULEs (microsatellite associated, modularly assembled) were characterized in the rice genome. Families of TEs with similar structures and distribution profiles were identified in sorghum and citrus. Conclusion: The sequencing and assembly of the guayule genome provides a foundation for application of current crop improvement technologies to this plant. In addition, characterization of this genome revealed SaTar elements with distribution profiles unique among TEs. Satar targeting appears based on an alternative MULE recombination mechanism with the potential to impact gene evolution.
... Plants were greenhouse grown and leaf tissue samples were collected and prepared for ploidy analysis as previously described (Ilut et al., 2015, sec. 2.3;Sanchez et al., 2014), with an average of two technical replicates for each plant. For each plant, we calculated its ploidy level as described in Sanchez et al. (2014), then assigned an integer-valued ploidy level if the nearest integer value was within two standard deviations of the mean across technical replicates, and a fractional value (denoting likely aneuploid samples) otherwise. ...
... 2.3;Sanchez et al., 2014), with an average of two technical replicates for each plant. For each plant, we calculated its ploidy level as described in Sanchez et al. (2014), then assigned an integer-valued ploidy level if the nearest integer value was within two standard deviations of the mean across technical replicates, and a fractional value (denoting likely aneuploid samples) otherwise. Supplementary Table A1 contains detailed source information for all the plants genotyped in this study, including NALPGRU seed inventory identifiers and detailed ploidy measurements. ...
... It is a perennial, small (10 cm high), aromatic, spreading, and very branched shrub with grayish bark below and tender and small leaves (Rollins 1950). It is a facultative apomictic plant with a natural ploidy series ranging from triploid to pentaploid (Sanchez et al. 2014). Mariola is considered the closest related taxon of guayule as it coexists with guayule in the wild (Rollins 1945). ...
Chapter
Jojoba (Simmondsia chinensis (Link) C. K. Schneid), lesquerella (Physaria fendleri (A. Gray) O’Kane & Al-Shehbaz), and guayule (Parthenium argentatum A. Gray) originate from semiarid climate zones of North America; meadowfoam (Limnanthes alba Hartw. ex Benth., Limnanthes bakeri J. T. Howell, Limnanthes douglasii R. Br.) is endemic to the western part of California, Oregon, and Southern Canada and grows around vernal pools and seasonally wet areas. This chapter discusses historic and current uses, domestication efforts, breeding, and cultivation challenges and describes the conservation status of the crops’ genetic resources. Meadowfoam and guayule are already cultivated on a limited industrial scale. Jojoba and lesquerella are not grown commercially in North America but are economically important in countries beyond the Americas and are of particular interest to nations with extensive areas of arid lands. North America is an important source of wild genetic resources for these crops, and further efforts are needed to ensure their conservation.
... Only one TkREF was found in the T. kok-saghyz genome and TkREF/TkSRPPs clustered into a clade that were different from the HbREFs/HbSRPPs clade, implying genetic divergence and different mechanisms were involved in rubber biosynthesis between the two species. So far, there has been no draft genome report about P. argentatum, due to its complex natural ploidy series [103,104]. ...
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Natural rubber is a kind of indispensable biopolymers with great use and strategic importance in human society. However, its production relies almost exclusively on rubber-producing plants Hevea brasiliensis, which have high requirements for growth conditions, and the mechanism of natural rubber biosynthesis remains largely unknown. In the past two decades, details of the rubber chain polymerization and proteins involved in natural rubber biosynthesis have been investigated intensively. Meanwhile, omics and other advanced biotechnologies bring new insight into rubber production and development of new rubber-producing plants. This review summarizes the achievements of the past two decades in understanding the biosynthesis of natural rubber, especially the massive information obtained from the omics analyses. Possibilities of natural rubber biosynthesis in vitro or in genetically engineered microorganisms are also discussed.
Article
Phenotypic characterization on historical breeding lines and wild genetic resources from the 1950′s to 1990′s of the rubber-bearing plant guayule (Parthenium argentatum A. Gray) and hybrids was conducted. Variation among germplasm on seed weight and germination was determined along with leaf traits and trichomes using image analyses. Flow cytometry was performed to estimate diversity in ploidy levels. Tetraploid guayule was the predominant type in the germplasm collection (64%), followed by triploids (34%), pentaploids (1.5%), and hexaploid (1%). No plants with octaploid or higher ploidy level were observed. Guayule 100-seed weight averaged 57.5 mg and was determined to have significant positive correlation to 7 and 14-day seed germination and seed size for this seed lot. Phenotypic similarity among germplasm was determined from quantitative analysis of leaf traits and trichomes. Measurements of other traits on young leaves were highly correlated to those on mature leaves. Most leaf traits within each development stage were found to be positively correlated. Guayule leaves averaged 6.85 cm long and 2.06 cm wide, with 1–6 serrations. Leaf serration height ranged from 2.9 to 6.4 mm. Germplasm lines AZ-2, AZ-3, and N566 had the greatest number of serrations, while R1093 and W6–429 with the least number. Trichome density was consistent between young and mature leaves with average density of 17 trichomes per 0.04 mm². Accessions R1100, AZ-3, and CAL-4 had the highest trichome density (>21 trichomes per 0.04 mm²). The results from analyzing the relatively high number of plants for seed parameters, leaf traits and ploidy are useful for optimizing germplasm collection and to better aid agronomic management practices and utilization of guayule germplasm for crop improvement activities.
Chapter
Among the more than 2000 plant species known to synthesize rubber, guayule, Hevea and Taraxacum kok-saghyz produce commercial grade rubber and latex. Guayule (Parthenium argentatum A. Gray), originates from the Southern Texas and Northern Mexico deserts, and is receiving wide attention as a natural rubber crop that could successfully grow in arid and semiarid regions. Continued improvement of guayule for higher biomass, rubber production and resistance to biotic and abiotic stresses, as well as maximizing agronomic practices are necessary to meet the increasing demand of the guayule rubber industry. Early domestication and commercialization efforts have all centered on using natural guayule stands and unimproved germplasm as a source of natural rubber. However, limited and sporadic breeding efforts have slowed down guayule’s genetic gains compared to other crops. This chapter summarizes the most recent breeding progress, biotechnological advancements, and agronomic practices to increase guayule rubber and other industrial byproducts. This provides plant breeders an insight into the status of guayule improvement and possible directions to speed up the breeding progress.
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(Article in Russian). The history of acquaintance of Europeans to latex of some trees of the New World, and also questions of origin and development of the caoutchouc production are covered in the review since XVIII century up to now. The attention to the confusion taking place in the description of the first rubber-bearing plants is paid. The contribution of a number of scientists and inventors to studying of rubber and its advance as the major raw materials for many groups of industrial goods is noted. Briefly the chemical structure of rubber and a way of biosynthesis in plants are considered. The attention in this review is paid to the description of a big variety of rubber-bearing plants, from which, besides Hevea brasiliensis (Willd. ex A. Juss.) Muell.-Arg., as industrial rubber-bearing plants can be considered a guayule Parthenium argentatum Gray, the kok-saghyz Taraxacum kok-saghyz Rodin. Prospects for commercial use and the krym-saghyz or a autumn dandelion Taraxacum hybernum Steven are noted. It is raised the question of allergenicity of separate rubbers. In spite of the fact that production of synthetic rubber continues to increase, demand for natural rubber every year considerably grows. Synthetic rubber in general concedes on quality natural, and the last is irreplaceable by production of the tires experiencing the raised strain. Therefore modern rubber industry more and more needs natural rubber which is generally made from a Hevea. Almost world monopolists on production of natural rubber from a Hevea are some countries of Southeast Asia and Africa. In this regard there is a danger of increase of the world prices for natural rubber in view of the numerous reasons, for example mass death of Hevea plantations a which her natural pathogen can cause. This fungus-ascomycete Microcyclus ulei entered in the U.N. list of the biological weapon. In this connection the researches directed on possibility of cultivation of rubber-bearing plants in the territory of Russia in modern conditions taking into account the USSR and the USA experience which is saved up in the 1930-1940 years are presented very actual, and also relying on achievements of biotechnological science of the present time. Interest of Europe in cultivation in the countries of the European Union guayule and the kok-saghyz for what the special Consortium EU-PEARLS was created is noted. In general, the studied literature covers nearly 500 years period and includes the first scientific publication on caoutchouc of 1751 of writing, and also the modern works performed with use of molecular and biological methods. The most sign events connected with rubber in a chronological order, the list of the plants rubber-bearing plants which are characterized by rather high content of rubber, and also the main manufacturing countries of natural rubber are given in three Appendices to this article. For citation: Kuluev B.R., Garafutdinov R.R., Maksimov I.V., Sagitov A.M., Chemeris D.A., Knyazev A.V., Vershinina Z.R., Baymiev An.K., Muldashev A.A., Baymiev Al.K. Chemeris A.V. Natural rubber, its sources and components. Biomics (2017) 7(4) 224-283.
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Wheat is the most widely grown cereal in Pakistan. Abiotic and biotic stresses, especially rust diseases, are the main reasons for a low average national yield. Therefore, a dire need exists to develop genotypes with improved resistance to these diseases along with high yield potential. Synthetic hexaploid wheat (man-made wheat) is a novel source of wheat germplasm that may be used as a resource to break the yield barrier in the wheat crop. These synthetics (2n = 6x = 42; AABBDD) are a globally recognized, potent genetic stock and are used by several wheat-breeding programs (Mujeeb-Kazi et al. 2008, Trethowan and Mujeeb-Kazi 2008; Ogbonnaya et al. 2013). The Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan, is working on wheat improvement and has developed high-yielding recombinants; some promising ones contributing in multilocation microtrials. In addition, a large number of recombinants and synthetics were evaluated in different trials/generations. In the current studies, synthetic lines were evaluated in two different field experiments. The first experiment consisted of a set of 13 wheat-breeding introductions, advanced synthetic-derived lines, and two check cultivars (Punjab-2011 and Galaxy-2013) sown in six 6-m rows with a row-to-row distance of 30 cm and plot size of 10.8 m2. In the second experiment, 35 synthetic- derived lines were tested in the field along with the two check cultivars sown in a 4.95 m2 plot. The material was sown in November 2013. Data were recorded on days-to-heading, plant height (cm), tiller number, spike length (cm), number of grains/spike, 1,000-kernel weight (g), grain yield (kg/ha), harvest index (%), and reaction to leaf rust, yellow rust, and stem rust.
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Switchgrass (Panicum virgatum L.), a native perennial dominant of the prairies of North America, has been targeted as a model herbaceous species for biofeedstock development. A flow-cytometric survey of a core set of 11 primarily upland polyploid switchgrass accessions indicated that there was considerable variation in genome size within each accession, particularly at the octoploid (2n = 8X = 72 chromosome) ploidy level. Highly variable chromosome counts in mitotic cell preparations indicated that aneuploidy was more common in octoploids (86.3%) than tetraploids (23.2%). Furthermore, the incidence of hyper-versus hypoaneuploidy is equivalent in tetraploids. This is clearly not the case in octoploids, where close to 90% of the aneuploid counts are lower than the euploid number. Cytogenetic investigation using fluorescent in situ hybridization (FISH) revealed an unexpected degree of variation in chromosome structure underlying the apparent genomic instability of this species. These results indicate that rapid advances in the breeding of polyploid biofuel feedstocks, based on the molecular-genetic dissection of biomass characteristics and yield, will be predicated on the continual improvement of our understanding of the cytogenetics of these species.
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Large quantities of cotton gin byproducts (CGB), also known as cotton gin trash or cotton gin waste, are being produced across the cotton belt of the United States annually. Similarly, guayule wastes after rubber latex production is expected to increase as this industry begins to expand. Use of these waste materials in value-added products can help the economics of the crops and aid in alleviating waste management issues and environmental problems. Conventional wood preservatives used to protect wood from insect and microbial damage are of concern to human health and the environment. Guayule bagasse (GB) has been shown to have termite control properties, and a combination of cotton gin and guayule wastes could also have such valuable properties. An initial study evaluating the physical and mechanical properties of boards produced from these two biomasses was published in 2009, this study is a continuation focusing on the termite resistance of boards produced. Thus, the objective of this research was to determine the termite resistance property of experimental composition boards made from CGB and GB. Composition boards were made from five different ratios of CGB to GB: 100:0, 75:25, 50:50, 25:75 and 0:100 (C100, C75–G25, C50–G50, C25–G75, and G100, respectively). Additionally, three-layered boards (3-layer) consisting of 25% GB (upper layer), 50% CGB (middle layer), and 25% GB (bottom layer) were made. For comparison, a commercial southern pine lumber board (SPB), a commercial oriented strandboard (OSB), and a commercial preservative treated medium density fiberboard (MDF) were included in the testing. This testing was an extension of a previous study where the mechanical properties of the CGB and GB composition boards were compared to select commercial standards. Five specimens were cut from each of the nine different board treatments and tested using Eastern subterranean termites. Weight loss, termite survival days, and visual grade of each specimen were determined according to testing standards. Results confirmed good termite control quality for boards made from GB alone. Boards containing CGB to GB ratios of 75–25 and 50–50 obtained similar termite resistance as the commercial OSB based on the total weight loss and one-week termite mortality rate. Visual grading of tested specimens revealed all six CGB and GB composition boards and the treated MDF showed better rating than the commercial OSB and pine lumber. No differences were noted among the total termite surviving days for the six CGB and GB composition boards. Overall, the biobased CGB and GB boards showed promise with the boards containing GB exhibiting improved termite resistance properties than SPB and OSB.
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Guayule (Parthenium argentatum A. Gray) is a potential source of natural rubber, but attempts to domesticate and cultivate this perennial crop for large-scale production in the southwestern United States have been intermittent over the past century. Genetic improvement through modern plant breeding is needed to increase its yield potential and suitability for commercialization. Natural variation for ploidy level is extensive among individuals in wild guayule populations, but less is known about the extent of ploidy level variation in guayule breeding germplasm. Because 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. To that end, we 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. Interestingly, 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.
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A rapid and simple protocol for estimation of nuclear DNA content of plants is described. Suspensions of intact nuclei are prepared either by chopping plant tissues or lysing protoplasts in a MgSO4 buffer, mixed with DNA standards, and stained with propidium iodide in a solution containing DNAase-free RNAase. Fluorescence intensities of the stained nuclei are measured by a flow cytometer. Values for nuclear DNA content are estimated by comparing fluorescence intensities of the nuclei of the test population with those of appropriate internal DNA standards. The same procedure can also be used for rapid determination of ploidy in plant tissues.
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After the initial boom in the application of flow cytometry in plant sciences in the late 1980s and early 1990s, which was accompanied by development of many nuclear isolation buffers, only a few efforts were made to develop new buffer formulas. In this work, recent data on the performance of nuclear isolation buffers are utilized in order to develop new buffers, general purpose buffer (GPB) and woody plant buffer (WPB), for plant DNA flow cytometry. GPB and WPB were used to prepare samples for flow cytometric analysis of nuclear DNA content in a set of 37 plant species that included herbaceous and woody taxa with leaf tissues differing in structure and chemical composition. The following parameters of isolated nuclei were assessed: forward and side light scatter, propidium iodide fluorescence, coefficient of variation of DNA peaks, quantity of debris background, and the number of particles released from sample tissue. The nuclear genome size of 30 selected species was also estimated using the buffer that performed better for a given species. In unproblematic species, the use of both buffers resulted in high quality samples. The analysis of samples obtained with GPB usually resulted in histograms of DNA content with higher or similar resolution than those prepared with the WPB. In more recalcitrant tissues, such as those from woody plants, WPB performed better and GPB failed to provide acceptable results in some cases. Improved resolution of DNA content histograms in comparison with previously published buffers was achieved in most of the species analysed. WPB is a reliable buffer which is also suitable for the analysis of problematic tissues/species. Although GPB failed with some plant species, it provided high-quality DNA histograms in species from which nuclear suspensions are easy to prepare. The results indicate that even with a broad range of species, either GPB or WPB is suitable for preparation of high-quality suspensions of intact nuclei suitable for DNA flow cytometry.
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Flow cytometry (FCM) using DNA-selective fluorochromes is now the prevailing method for the measurement of nuclear DNA content in plants. Ease of sample preparation and high sample throughput make it generally better suited than other methods such as Feulgen densitometry to estimate genome size, level of generative polyploidy, nuclear replication state and endopolyploidy (polysomaty). Here we present four protocols for sample preparation (suspensions of intact cell nuclei) and describe the analysis of nuclear DNA amounts using FCM. We consider the chemicals and equipment necessary, the measurement process, data analysis, and describe the most frequent problems encountered with plant material such as the interference of secondary metabolites. The purpose and requirement of internal and external standardization are discussed. The importance of using a correct terminology for DNA amounts and genome size is underlined, and its basic principles are explained.
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This book gives an overview of industrial crops, various issues related to industrial crops, crops and processes involved in generating energy in the form of heat and electricity as well as liquid fuel, ethanol production from sugar crops, grain crops and lignocellulosic crops and processes and byproducts produced, biodiesel production from oilseed crops, industrial oil types and their uses separate from biofuel, improvement of oilseed crops for industrial uses, characteristics of different crop starches and their appropriate uses for various applications other than ethanol production, research towards improving the quantity and quality of starch composition in plants, fibre and dye crops (cotton, bast fibres and dye crops), production and processing of cotton as well as research accomplishments in improving cotton fibre quality, important feedstock crops, manufacturing process from plant to products and various end uses for these fibres, plants that supply natural fibre dyes and process of fibre dyeing, crops that are the sources of rubber, gums, resins and waxes, important rubber crops (rubber tree and guayule) and their culture, breeding and quantitative and qualitative aspects of their latex, gums, resins and waxes and their sources as well as their trade, botanical insecticides and important insecticidal crops and their active ingredients as well as the prospects for using natural insecticides in pest control. The utilization of industrial crops for the generation of products to their deployment for such applications as the remediation of contaminated soils, the principles of plant-based remediation, the traits that make certain crops suited for such use and a description of these remedial crops are also highlighted.
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Natural populations of guayule contain plants with different levels of ploidy. This ploidy level has a profound influence on reproductive behavior such as sexual and apomictic modes of reproduction, self-incompatibility and expression of different agronomic traits like biomass, rubber and resin content. A collection of 195 accessions of guayule germplasm was made from 28 locations in the Coahuila province to determine ploidy levels and to locate their origin within the province. Cytological examinations revealed 4 diploids (2n = 2x = 36), 25 triploids (2n = 3x = 54), 153 tetraploids (2n = 4x = 72), 6 pentaploids (2n = 5x = 90) and 7 aneuploids. Aneuploidy plants possess an irregular number of chromosomes. The natural population had 2.1% diploids, 12.8% triploids, 78.5%, tetraploids, 3.1% pentaploids and 3.6% aneuploids. Tetraploids were present in all 28 sites sampled, whereas diploids were found in three locations. The triploids and pentaploids were widely scatter among the different sites.
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Breeding a new domestic crop, such as guayule, is not appreciably different from enhancement and breeding of conventional crops. In both instances, plant breeders take the available germplasm and search for genetic variability in the desired traits. The major differences are that in new crops plant breeders are often working with an unfamiliar species that is not yet fully domesticated and the available germplasm is often limited.The main objective of the guayule breeding program is to facilitate successful commercialization by developing higher yielding cultivars. Improvement has been accomplished, with newer lines yielding up to 250% more rubber than lines developed in the 1940s and 1950s. This is surprising because the genetic base from which improvements have been made appears to be very narrow, and because guayule reproduces predominately by apomixis (asexual reproduction by seed). Improvements through breeding are dependent upon genetic diversity within the available germplasm, and being able to identify different genotypes. The available germplasm exhibits extreme variability both within and between lines for morphological traits such as height, width, and biomass; chemical constituents such as rubber, resin, and latex contents; and genetic and chromosomal markers. The measured variation is due partly to the facultative (asexual reproduction and sexuality coexisting) nature of apomixis in guayule, which periodically releases genetic variation among progeny. A great amount of this measured variation is due to environment, and selections, to take advantage of genetic differences, must be made within the first 2 years of growth. There have been relatively few individuals involved in guayule breeding. Thus, with limited resources and time, most of the improvements have been made through single-plant selections from within populations. Although this method has the potential for only modest long-term gains, improvements occur relatively quickly. Indirect measures have been developed to increase breeding efficiency. For instance, most selections are made for plant height, width and biomass because they are highly correlated with rubber yield. As guayule approaches commercialization, breeding will become a priority and other breeding schemes will be tested and utilized such as: mass selection; recurrent selection among sexually reproducing diploids, followed by chromosome doubling; family selection; crossing high yielding apomictic plants; and crossing high yielding apomictic plants to sexual diploid plants to release new genetic combinations.
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Guayule is a perennial shrub grown in the southwestern United States that is used to produce high quality, natural rubber latex. However, only about 10% of the plant material is used for latex production; the remaining biomass, called bagasse, can be used for renewable fuel production. Fast pyrolysis of guayule, both whole shrub and bagasse was performed. From both feedstocks a very viscous, high energy content (∼30 MJ/kg) pyrolysis liquid (bio-oil) was produced in yields averaging over 60% without any catalyst. The properties and compositions of the bio-oils were found to be similar in the two feedstocks. Co-products, charcoal (20–30 wt%) and non-condensable gas (5–15%), were also dense and had a high energy content. Of the two feedstocks, the whole shrub yielded higher quantities of charcoal that also had a higher energy content than the charcoal produced from bagasse. As a result, the energy recovery, estimated as the percentage of the energy products, to energy input into the reactor was lower (60%) for guayule bagasse than for the whole shrub (73%). This notwithstanding, the bagasse is a more attractive feedstock for thermochemical conversion, not only because it is a residue from a primary process (latex extraction) that is on-site, but also because it has a high energy content. Moreover, it produces high quality pyrolysis products. Co-production of latex rubber from the whole shrub and renewable fuels from the residual bagasse by pyrolysis should improve the already positive economics of the guayule latex rubber industry.
Estimation of nuclear DNA content in plants using flow cytometry
  • J Doležel
  • J Greilhuber
  • J Suda
Doležel, J., Greilhuber, J., Suda, J., 2007. Estimation of nuclear DNA content in plants using flow cytometry. Nat. Protoc. 2, 2233–2244.
Reproduction and pollination studies on guayule
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