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Rubber and resin are potentially important products of guayule (Parthenium argentatum A. Gray) that can assure the profitability of this crop as an agricultural alternative for the semi-arid areas of central and eastern Spain. This study analyzes, for the first time, the changes in rubber and resin production across 27 guayule accessions (traditional and modern) and along three cycles under the agroclimatic conditions of Castilla-La Mancha, simulating industrial management with a biannual harvest. The rubber content (% of dry mass) increased from 4.2% in one-year-old plants to 6.6% in two-year-old plants, but decreased after harvesting. Contrastingly, the rubber yield doubled in contiguous sampling, reaching a mean of 303.6 kg ha−1, with a maximum yield of 341.2 kg ha−1 after the first harvest. Three patterns of rubber production were established based on the production periods. A similar analysis was performed for resin production, which was heterogeneous across accessions belonging to the same rubber groups. In this case, three independent groups were established to classify the resin accumulation profiles following the same criteria of production periods. Here, we demonstrate that biannual harvesting has the potential to enhance rubber accumulation in summer, although more research is needed for its adaption to current harvesting techniques in this area. [ABSTRACT FROM AUTHOR]

The economic sustainability of guayule (Parthenium argentatum A. Gray) cultivation will largely depend on its profitability, which drives strategies for the integral utilization of its biomass. Because guayule resin has been proposed as a broad-spectrum biopesticide, the aim of the present study was to test and compare its bioactivity against the agricultural pest Labidostomis lusitanica (Coleoptera: Chrysomelidae) Germar, with essential oils (EOs) from thyme (Thymus vulgaris L.), savory (Satureja montana L.), and oregano (Origanum vulgare L.). Repellency, oviposition and feeding inhibition activity were measured using free choice assays under controlled conditions, and minimal inhibitory concentrations of guayule resin fractions and isolated compounds were determined. Finally, guayule resin was tested under simulated field conditions. Results showed that the solvent used to dissolve and apply the resin had a great impact on its performance. Guayule crude resin was more active than tested EOs, particularly as an antifeedant. However, its activity did not seem to be concentration dependent, and was effective within a narrow range. In contrast to low molecular-weight rubber (LMWR), which acted as attractant, the refined resin was repellent. Nevertheless, the two different enriched resin fractions, with sesquiterpene bioactive compounds acted as attractants and feeding stimulants, as well as the isolated compounds. In the semi-field trial, crude guayule resin again showed repellency and feeding deterrence, with no mortality, overall suggesting that while guayule resin is active against L. lusitanica , the compounds responsible for this activity are likely not the sesquiterpenes. • Guayule resin does not cause mortality on Labidostomis lusitanica. • Guayule resin shows antifeedant activity against Labidostomis lusitanica. • The activity is due to the synergistic effect between compounds. • The solvent used to dissolve the resin has a great impact on its bioactivity. [ABSTRACT FROM AUTHOR]

The guayulins are a family of sesquiterpene compounds that consist of an isoprenoid nucleus substituted either by trans-cinnamic or p-anisic acid, and are present only in the resinous fraction of the rubber plant guayule (Parthenium argentatum, Gray). While the natural role of the guayulins remains enigmatic, they may serve as a defense function against other plants or herbivores by virtue of the accumulation of cinnamic acid. Prior research has suggested seasonal variation in guayulin content, which has been shown to decrease as winter arrives in two different varieties. In the present study, the effect of guayulins has been evaluated in 13 different accessions cultivated under the same conditions during autumn. A general reduction in guayulin content was found in the stems from all varieties between the September and November harvest, which was accompanied by an increase in the resin content. With respect to individual guayulins, while guayulin A was the most prominent member during most of the year, guayulin C had more prominence when temperature started to decrease. In this seasonal period, the production of each member of the guayulin family in the leaves was very balanced. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum Gray) is a promising alternative source to Hevea brasiliensis for the production of natural rubber, which can reach levels of 8–9% under industrialized farming conditions. The most common method for determining rubber concentration is by accelerated solvent extraction (ASE), a technique developed by the Dionex Corporation and almost exclusively performed with the Dionex ASE-200 or 350 systems. Herein, it is sought to apply and adapt the most common methods used in the literature for the Dionex system to another extraction platform, the BÜCHI Speed Extractor E-914. Results showed that using a sand sandwich method to confine the sample in the center and exploiting a larger cell volume (80 mL) for extraction prevents the occurrence of overpressure and problems with clogging. Under optimized conditions, the coefficient of variation was <15% for both resin quantification for samples containing 5.0–15.8% of resin and for rubber quantification for samples with 1.7–10.3% rubber content. The extraction time for resin (2 cycles of 5 min each) was smaller than for rubber (2 cycles of 20 min each). It would be interesting to carry out interlaboratory comparisons to standardize the method at an international level. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum Gray) is an interesting alternative and renewable source of rubber/latex which has been used in the past. Guayule rubber and latex products are not available in the market largely because the raw material cost is higher than the current sources produced in South-East Asia and other tropical countries (Hevea brasiliensis). Guayule contains many other compounds whose joint exploitation could make guayule cultivation profitable, especially in semi-desert areas where cultivation of other crops is difficult or impossible. Guayulins A–D, sesquiterpene esters, appear to have some commercial promise. Despite being accumulated in relatively high concentrations (its majority representative, guayulin A, can account for up to 13.7% of the resin content of this plant, which itself ranges from 6%–12%), guayulins have received little direct attention from scientists. This review presents the current knowledge about the activity of these compounds and, based on known activities of similar compounds from other species, potential uses as fungicides, miticides and insecticides are suggested. [ABSTRACT FROM AUTHOR]

For guayule (Parthenium argentatum A. Gray) to become a viable market option, it will be necessary to exploit not only the rubber and resin components, but also other high-value plant products such as essential oils (EOs). A detailed EO profiling study was conducted on 16 guayule accessions for first time, which revealed significant differences in EO yield and profile among them. Accession AZ-2 had the highest yield up to 0.9% (dry weight), followed by CFS18–2005, CAL-7, and CFS17–2005. These yields were comparable with those of aromatic plants used in the industry, providing valuable economic insights. The volatile EO composition of the accessions was unique and discriminating. Volatile sesquiterpenes were the most abundant compounds at the beginning of the flowering stage (S1-June sampling), while monoterpenes became more abundant as flowering progressed (S2-July and S3-August sampling). At S1, it was possible to distinguish between hybrid (mariola and non-mariola) and other accessions by the EO profile. By the end of the summer season (S3, August 2023), the EO volatile profile could more easily distinguish the accessions according to their genetic origin, enabling the separation of pure guayule accessions. The extraction of guayule EOs on an industrial scale (1.2 Mg fresh biomass) demonstrated high yield and consistency in terms of volatile profile, underscoring its potential for commercial exploitation. • Essential oils from sixteen accessions were characterized for first time. • The yield of essential oils depended on the variety and sampling date. • Sesquiterpene volatiles were more abundant at the beginning of the flowering period. • Monoterpene volatiles were more abundant at the end of the flowering period. • Yield at industrial scale was similar to that of the laboratory-scale. [ABSTRACT FROM AUTHOR]

There is considerable interest in the exploitation of compounds belonging to the triterpenoid family from guayule (Parthenium argentatum , A. Gray), as they offer several beneficial effects to human health. The most abundant triterpenoids in guayule resin are the argentatins, which are currently analyzed by labor-intensive and time-consuming techniques. The purpose of the present study was to estimate argentatins and isoargentatins A and B in guayule using near-infrared spectroscopy (NIRS) and flow injection analysis (FIA). Results revealed that the best partial least squares regression model exhibited excellent correlation with the values estimated by NIRS calibration (r 2 c = 0.99–1.00) and cross-validation (r 2 cv = 0.94–0.99), and the residual predictive deviation was >3 in all cases. After optimization of the liquid chromatography–mass spectrometry and FIA parameters, the FIA mode could reliably collect data for argentatin A and B after applying a calculated coverage factor. In sum, NIRS and FIA appear to be a robust option for the estimation and routine analysis of argentatins in guayule stems and resin, respectively. [Display omitted] • Argentatin A and B quantification by NIRS in guayule stems for first time. • Residual predictive deviation higher than 3 for both argentatins by NIR. • LC-MS and FIA methods optimization for argentatin A and B. • Quantification of argentatins in the resins by FIA, after applying calculated coverage factor. [ABSTRACT FROM AUTHOR]

Guayule, a plant native to the Mexican deserts of Chihuahua and southern USA, has attracted interest as a substitute source of natural rubber and other bioproducts, and is a promising alternative crop for the semi-arid regions of central and eastern Spain. The trials performed on guayule production in Spain in the 1960 s need to be updated following the emergence of climate change and the development of more productive guayule accessions. Accordingly, the objective of the present study was to search for those lines that best adapt to the agro-climatic conditions of Castilla-La Mancha with respect to biomass production when the crop is industrially managed. The adaptation of 27 guayule accessions was studied by comparing their vegetative development (height, width, volume, shape, branch number and diameter). Results revealed the contribution of genetic imprinting for growth in plants up to 24 months after transplanting, after which times environmental effects were dominant in the second and third cycle after harvesting every two years. Biomass production along the three cycles simulating industrial management with biannual harvest depended on the germplasm, the harvest management and the agro-climatic conditions. The accessions with higher biomass content in branches were CAL-7 and AZ-2. • Twenty-seven accessions adapted to Castilla-La Mancha agro-climatic conditions. • The genetic contribution is observed in plants up to 24 months after seeding. • Environmental effects were dominant after harvesting every two years. • Biomass production is dependent on many factors (germplasm, the harvest and clima). • The accessions with higher biomass content in branches were CAL-7 and AZ-2. [ABSTRACT FROM AUTHOR]

The argentatins are the most abundant compounds in guayule resin with promising potential for the biopharmaceutical industry. However, their accumulation along the vegetative cycle of the plant and their quantification in different guayule accessions has not been assessed. The present study established the profile of 16 known compounds of the argentatin family in 27 guayule and guayule interspecific accessions using UHPLC-Q-Orbitrap-HRMS. In addition, the structure of five unreported argentatins was tentatively identified. All compounds were present in all accessions (27) and samples (135) analyzed, although in varying amounts. Those compounds found in the highest proportion were argentatins A, B, C, G, isoargentatin A, 16-dehydroargentatin C and quisquagenin. The mass spectra of the compounds were more complex than expected, revealing the lability of the compounds and a high probability to partially degrade during analysis, even at the mildest ionization energies. Based on available standards, argentatins A and B and isoargentatins A and B were quantified in 27 accessions and five samplings along the growing season. The total abundance of the four compounds was 13.4–39.6% of the guayule resin in stems depending on the accession. The profiles of accumulation were related to the genetic origin, with the summer and spring periods producing the greatest yield of argentatins. Pure guayule accessions generally produced more argentatins than hybrids, although the most productive for argentatins and isoargentatins A and B was the non-mariola hybrid AZ-3. • Twenty-one argentatins and related compounds were found in 27 guayule accessions. • Major compounds were argentatins A, B, C, G, isoargentatin A and 16-dehydroargentatin C. • The argentatins profile of accumulation was related to the genetic origin. • Pure guayule accessions produced more argentatins than hybrids. • Four compounds' account for 13.4–39.6% of the resin depending on the accession. [ABSTRACT FROM AUTHOR]

The guayulin content of guayule (Parthenium argentatum Gray) is subject to seasonal variation and follows specific patterns that are dependent on the accession and the organ (stems or leaves). However, little is known about guayulin in response to agronomic management such as irrigation or fertilization. A 24-month experiment was performed to investigate the accumulation of guayulin in one guayule accession (R-1040) and two hybrids (CAL-1 and AZ-2), in relation to crop system (irrigated or non-irrigated) and the nitrogen fertilizer units (NFU 0% or 100%). Irrigation increased biomass, which likely diluted guayulin concentration, but contributed to increase guayulins yield in both organs (stems and leaves). Fertilization had no effect on guayulin and resin production, but it increased the number of stems and total biomass. The pattern of accumulation of guayulins between stems and leaves was different. Differences were observed between the hybrids and the pure accession R1040, which was smaller in size but produced more guayulins. A strong relationship was found between guayulin yield and the production of rubber. • Hybrids accessions AZ-2 and CAL-1 behaved differently from pure guayule R1040. • Accession and harvest factors had the most significant effects on guayulin content. • Irrigation and fertilization interaction diluted drastically the concentration of guayulins. • Guayulins C and D seem to play a relevant role in the guayulins accumulation. • Strong correlation exists between guayulins and rubber content. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum A. Gray) exploitation has so far been focused on the production of rubber, but until now was unable to compete commercially, as other guayule co-products have not been equally considered for exploitation. However, to successfully exploit one of these co-products, the guayulins, it will be necessary to establish a robust resin extraction method that maximizes the yield of guayulin compounds for downstream purification. For this purpose, different resin extraction conditions (solvent, temperature, number and time of cycles, and plant material:solvent ratio) were evaluated to select those that produced a resin with a higher guayulins yield. First, accelerated solvent extraction (ASE) was performed using three solvents (ethanol, acetonitrile, and acetone) at three different temperatures (40, 56, and 80 °C) and two cycle times (5 and 20 min) to narrow down the conditions. Then, an industrial scale process was simulated with warm solvent extraction (WSE) using acetone and acetonitrile only at five different cycle times (30, 45, 60, 120, and 180 min). Finally, WSE performance was optimized using four different plant material:solvent ratios (1:20, 1:10, 1:5, and 1:3), and three consecutive extraction cycles. Results from the ASE studies revealed, as expected, that solvent choice had the greatest influence on resin and guayulins yield and allowed to discard ethanol as a suitable extraction solvent while acetonitrile performed best for guayulin extraction. No tangible differences in resin yield were observed in WSE studies between the different process parameters, but they were differences in guayulin extraction. Short cycle times worked best with both solvents, and again, acetonitrile was more selectively extracted guayulins, especially for the polar guayulins C and D. Finally, WSE optimization showed that a 1:5 plant material:solvent ratio and two extraction cycles were the best compromise in terms of guayulins yield and time/cost effectiveness. • Solvent followed by temperature had the greatest influence on resin and guayulins yield. • Acetonitrile and acetone performed better with two cycles and shorter times. • Acetonitrile at 30 min extracts the highest guayulins content, specially guayulins C and D. • Guayulin concentration assessment should be done in mg per extraction and in mg per g of resin. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum , A. Gray) is a promising alternative source to natural rubber from Hevea brasiliensis L. Recently, another important fraction of its composition, the resin, has been the focus of many studies due to its promising commercial applicability. In the resin extract there are guayulins (A, B, C and D), belonging to the sesquiterpene family, which are usually analyzed by HPLC-DAD and, lately, with other labor-intensive analytical techniques. Near infrared spectroscopy (NIR) has been successfully used in fresh guayule and dry biomass to assess moisture, and total rubber and resin content. The purpose of the present study is to estimate, for the first time ever, the detailed guayulin content in guayule dry stems using NIR spectroscopy. So, a set of 144 samples were analyzed by a Perkin Elmer Spectrum One FT-NIR equipment coupled with a near infrared reflectance accessory (NIRA). In addition, guayulins A and B standards, isolated in the lab, were scanned to generate the best partial least squares regression (PLSR) model. The best correlative PLSR models for resin, rubber and guayulins were developed within the range of 1100–2500 nm, showing an excellent calibration correlation (r 2 c = 0.92–1.00) and cross validation (r 2 cv = 0.87–0.92). The residual predicative deviation (RPD) was above 3 in the case of resin, rubber and guayulins A, B and D; while in guayulin C was 2.8. These high RPD values demonstrated a good prediction power of the model. In conclusion, the use of NIR spectroscopy for the estimation of resin and guayulin content in ground guayule stems is an excellent option for the routine analysis instead of time-consuming and labor-intensive traditional techniques. • Guayulin A, B, C, and D quantification by near infrared spectroscopy in guayule dry stems is achieved for first time. • Near infrared spectroscopy is an excellent technique for the analysis of rubber, resin and guayulins in guayule. • The best correlative partial least squares regression models were developed within the range of 1100–2500 nm. [ABSTRACT FROM AUTHOR]

• Profile of guayulins has been established along the growth cycle (14 accessions). • Four behavior patterns were identified based on the accumulation of guayulins. • Guayulin A and B content increases between spring and autumn and decreases in winter. • Guayulins C and D content is much more stable throughout the vegetative cycle. • Accessions 11591 (CL-1) / AZ-6 were the highest guayulin producers. The commercial development of guayulins might help spur industrial-scale applications of guayule as an alternative source of natural rubber, making necessary to build knowledge on their seasonal response and accumulation in plants. In the present study, the seasonal content of the four known guayulins (A–D) was profiled in 14 different guayule accessions, including hybrids, from age 13 months to age 23 months. Analysis revealed that the accessions could be categorized into four groups based on guayulin content and potentially reflective of their genetic origin and hybridization: one rich in guayulin A, one rich in guayulin C, one rich in guayulin D, and one with intermediate values. Despite the evident differences in guayulin profiles, all four groups shared the same general response. The content of guayulins A and B increased between April and September, followed by a drastic fall in content in November likely triggered by low temperatures, and then a gradual recovery. By contrast, the content of guayulins C and D was much more stable, especially for those accessions showing the highest production. The relationship between the guayulins was useful to characterize their evolution during the growth cycle, with some groups halting production of guayulins during the summer (group rich in guayulin C) and others initiating production earlier, after the winter period (groups rich in guayulin A and those with intermediate values). The higher producers of guayulins were the accessions 11591(CL-1) and AZ-6, and the best harvest time was between September and November, depending on climatic conditions. [ABSTRACT FROM AUTHOR]

• Chromatographic guayulin analysis benefits from smaller, narrower columns. • Mass spectrometric analysis of guayulins should be extended. • There are more than four compounds within the guayulin family. • Guayulin content decreases when rubber biosynthesis is induced. • There may be a connection between guayulins and rubber metabolic processes. Guayule (Parthenium argentatum Gray) is a promising alternative and renewable source of natural rubber/latex. There is a general acceptance that to successfully industrialize the cultivation of guayule, it will be necessary to valorize all of its co-products, including resins, which can reach 16 % of weight of dry matter. Guayule resins have been reported to have antifungal, insect antifeedant and wood protector activities, although it remains to be clearly established which compounds are responsible for such actions. Here, we focus on a terpene family present in guayule resin that is a candidate for these activities, the sesquiterpenes, which are present in significant amounts (10–15 %). We studies the versatility of the most common analytical method used in their analysis, HPLC-UV, with mass spectrometry techniques including LC–MS, ESI-TOF and MALDI-TOF to address the following objectives: 1) to explore whether there are other members of the guayulins family, 2) to determine the applicability of new methods based on mass spectrometry, and 3) to establish the relationship between the four known major guayulins in the seasonal changes described by other authors. Our results have allowed us to: tentatively identify a new member of this family and to suggest the existence of others; propose changes to the chromatographic approaches currently used; extend the use of mass spectrometry (direct identification and monitoring of purification of guayulins); and finally, demonstrate that the content of guayulins A and B decreases at the start of winter when the most active period of natural rubber biosynthesis begins. [ABSTRACT FROM AUTHOR]