Rubber Hevea Research Articles

Transcriptomic and Proteomic Integration Reveals Key Tapping-Responsive Factors for Natural Rubber Biosynthesis in the Rubber Tree Hevea brasiliensis

Natural rubber is a crucial industrial material, and it is primarily harvested from the latex of the rubber tree Hevea brasiliensis by tapping the tree trunk. During the regular tapping process, mechanical damage seriously affects latex reproduction and rubber yield, but the molecular mechanisms on tapping stimulation remain unclear. In this study, we firstly determined the changed physiological markers on latex regeneration, overall latex yield, and latex flow time during the tapping process. Then, we combined proteomics and transcriptomics analyses of latex during tapping and identified 3940 differentially expressed genes (DEGs) and 193 differentially expressed proteins (DEPs). Among them, 773 DEGs and 120 DEPs displayed a persistent upregulation trend upon tapping. It is interesting that, in the detected transcription factors, basic helix-loop-helix (bHLH) family members occupied the highest proportion among all DEGs, and this trend was similarly observed in DEPs. Notably, 48 genes and 34 proteins related to natural rubber biosynthesis were identified, and most members of small rubber particle protein (SRPP) and rubber elongation factor (REF) showed a positive response to tapping stimulation. Among them, SRPP6 and REF5 showed significant and sustained upregulation at the gene and protein levels following tapping, indicating their pivotal roles for post-tapping rubber biosynthesis. Our results deepen the comprehension of the regulation mechanism underlying tapping and provide candidate genes and proteins for improving latex production in the Hevea rubber tree in future.

Isolation and in silico analysis of a transcript variant for a putative terpene synthase (HbTPS6L-X1) from the bark tissues of rubber Hevea brasiliensis RRIV 209

Hevea brasiliensis is the only tree species grown to produce natural rubber. The method of harvesting latex by slicing a groove into the bark of the tree mimics a mechanical wounding. In addition, rubber trees could be frequently exposed to pest and pathogen attacks through the scraped bark region. Terpenoids are a group of specialised compounds that play an important role in plant-environment interactions, especially in plant response to stress factors. The diversity of terpenoids is mainly determined by enzymes of the terpene synthase (TPS) family. Screening the RNA-seq data of H. brasiliensis revealed the presence of many putative TPS genes expressed in the bark tissues of rubber trees; however, their function has not been studied. This paper presents the identification of a TPS gene transcript variant (designated as HbTPS6L-X1) from the bark tissues of H. brasiliensis RRIV 209. Through the analysis of the phylogenetic tree, the presence of conserved motifs, and the signal peptide sequence region of the protein, as well as structural homology to known sesquiterpene synthases from other plants, HbTPS6L-X1 was predicted to belong to the TPS-a subfamily, be localised in the cytoplasm and catalyse the conversion of farnesyl diphosphate (FPP) to sesquiterpenes. These in silico functional characteristics are the basis for designing experiments to confirm the in planta biological function of HbTPS6L-X1 protein.

The Interplay of Protein Hydrolysis and Ammonia in the Stability of Hevea Rubber Latex during Storage.

Natural rubber (NR) latex derived from Hevea brasiliensis is a complex colloid comprising mainly rubber hydrocarbons (latex particles) and a multitude of minor non-rubber constituents such as non-rubber particles, proteins, lipids, carbohydrates, and soluble organic and inorganic substances. NR latex is susceptible to enzymatic attack after it leaves the trees. It is usually preserved with ammonia and, to a lesser extent, with other preservatives to enhance its colloidal stability during storage. Despite numerous studies in the literature on the influence of rubber proteins on NR latex stability, issues regarding the effect of protein hydrolysis in the presence of ammonia on latex stability during storage are still far from resolved. The present work aims to elucidate the interplay between protein hydrolysis and ammoniation in NR latex stability. Both high- and low-ammonia (with a secondary preservative) NR latexes were used to monitor the changes in their protein compositions during storage. High-ammonia (FNR-A) latex preserved with 0.6% (v/v) ammonia, a low 0.1% ammonia/TMTD/ZnO (FNR-TZ) latex, and a deproteinized NR (PDNR) latex were labeled with fluorescence agents and observed using confocal laser scanning microscopy to determine their protein composition. Protein hydrolysis was confirmed via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results revealed that protein hydrolysis increased with the storage duration. The change in protein composition accompanying hydrolysis also allows the spatial distribution of allergenic proteins to be estimated in the latex. Concurrently, the latex stability increased with the storage duration, as measured by the latex's mechanical stability time (MST) and the zeta potential of the latex particles. As monitored by AFM, the surface roughness of the NR latex film increased markedly during extended storage compared with that of the DPNR latex, which remained smooth. These results underscore the pivotal role of ammonia in bolstering NR latex stability brought on by protein hydrolysis, which greatly impacts latex film's formation behavior. NR latex stability underpins the quality of latex-dipped goods during manufacturing, particularly those for medical gloves.

Interactions of REF1 and SRPP1 rubber particle proteins from Hevea brasiliensis with synthetic phospholipids: Effect of charge and size of lipid headgroup

According to the fatty acid and headgroup compositions of the phospholipids (PL) from Hevea brasiliensis latex, three synthetic PL were selected (i.e. POPA: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate POPC: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and POPG: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol) to investigate the effect of PL headgroup on the interactions with two major proteins of Hevea latex, i.e. Rubber Elongation Factor (REF1) and Small Rubber Particle Protein (SRPP1). Protein/lipid interactions were screened using two models (lipid vesicles in solution or lipid monolayers at air/liquid interface). Calcein leakage, surface pressure, ellipsometry, microscopy and spectroscopy revealed that both REF1 and SRPP1 displayed stronger interactions with anionic POPA and POPG, as compared to zwitterionic POPC. A particular behavior of REF1 was observed when interacting with POPA monolayers (i.e. aggregation + modification of secondary structure from α-helices to β-sheets, characteristic of its amyloid aggregated form), which might be involved in the irreversible coagulation mechanism of Hevea rubber particles.

Acclimatization of Tropical Palm Species Associated with Leaf Morpho-Physiological Traits to the Understorey Environment of Hevea Rubber Farms

Hevea rubber farm is viable for agroforestry systems since its canopy lessens extreme weather conditions and contributes to the adaptation of shade-tolerant plants. However, some limitations in the availability of soil water and shades vary with the age of rubber trees and affect the understorey plants’ acclimatization. Tropical palms are potentially associated plants for the rubber-based agroforestry systems because they are rainforest species adaptable to understorey environments. Two rubber farms, ages 12 and 25 years, intercropped with tropical palms were selected to investigate the acclimatization of the palms to the seasonal abiotic variations in the mature rubber farms. The studied palm species were Chrysalidocarpus lutescens and Rhapis excelsa in the 12-year-old rubber farm and Livistona speciosa and Licuala spinosa in the 25-year-old rubber farm, respectively. Leaf area, stomatal conductance, photosynthesis pigments, and leaf nitrogen content were identified as the palms’ morpho-physiological traits. The 12-year-old rubber farm had a marked soil water deficit in all soil depths at the beginning of the rainy season, reaching around 200 kPa at the 80 cm soil depth, while the 25-year-old rubber farm received greater light transmissions, ranging between 37 and 46% in the late dry season. All palms adjusted leaf area to balance the photosynthetic capacity. The Rhapis palm had greater acclimatization with significant responses of stomatal conductance. Other than the Licuala palm, all palms exhibited the allocation of chlorophyll pigments and nitrogen content significantly in their leaves in response to the different intensities of abiotic stresses in the understorey of the rubber farms.

First Report of Eucalyptus Wilt Caused by Chalaropsis thielavioides in China.

Eucalyptus species are widely planted in the tropics and subtropics, and eucalyptus is among the most important cash crop in Southern China. One of the most important diseases on eucalyptus is Ceratocystis wilt, caused by the fungus Ceratocystis fimbriata Ellis & Halst., and the genus name Chalaropsis has been proposed for anamorphs of Ceratocystis species (de Beer et al. 2014). During April 2018, severely infected Eucalyptus robusta trees were observed in Kunming, Yunnan Province, China. Symptomatic trees initially exhibited yellowing and wilting of foliage on individual branches, then spread to the whole canopy, sometimes followed by death of the whole tree. Reddish-brown to dark-brown discoloration in the woody xylem of affected trees, sometimes a grayish white layer of fungal growth may be seen. The disease was observed on 16% of trees surveyed. The base of trunks with typical symptoms were collected, then the discolored xylem tissues were surface disinfected with 75% ethanol for 30 s and 0.1% mercuric chloride (HgCl2) solution for 2 min, rinsed three times with sterile distilled water, plated onto potato dextrose agar (PDA) medium, and incubated at 25°C. After 6 days, a fungus was consistently observed growing from the tissue. Three isolates were obtained. In culture, colonies reaching 54mm diam within 15 days, mycelium initially white, then becoming celadon. Endoconidia unicellular, smooth, cylindrical, straight, biguttulate, 11.21 - 32.26 × 4.12 - 5.25 μm. Phialides produced on short, septate, aerial hyphae, lageniform and chain of phialoconidia (3.62 - 5.89 × 31.39 - 65.76 μm) were also observed. Chlamydospores (11.45 - 14.26 × 10.06 - 12.22 μm) were single, dark, thick-walled. Morphological characteristics of the fungus were consistent with the description of Chalaropsis thielavioides (Paulin-Mahady et al. 2002). The two of three isolates were used for molecular identification and genomic DNA was extracted from isolates (EKY2-2-1, EKY2-2-2) using the chelex-100 method (Xu et al. 2020). The ITS region of rDNA was sequenced using the procedures of Thorpe et al. (2005). Analysis of ITS sequence data (GenBank accessions MW242701, MW242702) showed that the isolates were 99% - 100% homologous to isolates of C. thielavioides from Hevea rubber, Monstera deliciosa L. and ants in China and Rosa sp. in Australia (GenBank accessions KT963172, KJ511482, KT963173 and KX954598) by BLAST analysis. Neighbor-joining (NJ) phylogenetic analysis were performed using MEGA 6.06 based on ITS sequences (Fig 1), the evolutionary distances were computed using the Maximum Composite Likelihood method. Analyses showed that both isolates (EKY2-2-1, EKY2-2-2) located on the same clade with all C. thielavioides, and clustered with the C. thielavioides strains with high bootstrap support (97% - 100%). Therefore, the fungus was identified as C. thielavioides based on morphology and molecular evidences. Pathogenicity of C. thielavioides was tested by inoculation of six one-year-old pot grown Eucalyptus citriodora seedlings. The sterilized soil of six seedlings was inoculated by drenching with 20 ml spore suspension (2.0 × 106 spores / ml). Control plants were inoculated with 20 ml of sterile distilled water. The seedlings were kept in a controlled greenhouse at 25°C and watered weekly. After one month incubation, all the isolates produced wilt symptoms, whereas control trees showed no symptoms. The original fungus was successfully re-isolated from inoculated trees and identified as C. thielavioides according to the methods described above, and no fungal growth was observed in the controls, thus satisfying Koch's postulates. Although wilt and canker caused by Ceratocystis fimbriata on eucalyptus have been previously reported in Brazil, Uruguay, Uganda, China and Pakistan (Ferreira et al. 1999; Li et al. 2014; Alam et al. 2017), eucalyptus wilt caused by C. thielavioides has not been reported anywhere. Also, wilt of rubber tree and postharvest rot on carrot caused by C. thielavioides have been reported (Li et al. 2021; Xu et al. 2020). To our knowledge, this is the first report of eucalyptus wilt caused by C. thielavioides in China.

Molecular markers to devise predictive models for juvenile selection in Hevea rubber

AbstractNatural rubber is extracted from the Hevea tree, through shaving the bark. As a major raw material source for many industries especially the tyre sector, Hevea rubber clones are intensively cultivated in the tropics. The world production of Hevea rubber is almost 13.64 million metric tonnes, and the productivity is around 1200 kg ha−1. However, the field production achieved so far is still well below the theoretical yield estimated (7000–12,000 kg ha−1). Even though this is a calculated estimate, efforts can be kept live to achieve this target, because Hevea rubber is being increasingly cultivated under several suboptimal environments after the 1980s. In this era of climate change, newer biotic and abiotic stresses encounter Hevea rubber culture that demands new clones at definite intervals. Hence, like any other species, Hevea rubber breeding is a continuous process in quest of new clones achieved through exploiting new sources of genetic variation. Hevea rubber breeding is to produce high‐yielding clones with good timber value. First priority is to explore and exploit genetic variation in clones, half‐sib, full‐sib and illegitimate (open‐pollinated) seedlings, where dry rubber yield and wood volume are the target traits. Next is to maximize genetic gains per unit time, through understanding juvenile–mature correlations and to practice selection of high‐yielding genotypes at the juvenile stage. Hevea rubber had a long breeding cycle of 33 years but could be reduced to 17 years after culling non‐essential steps of deriving clones. However, this could be reduced to 10 years, if a DNA marker‐assisted selection system is applied to seedlings. This system must also ensure significant juvenile–mature correlations on yield. This is a formidable task because under given circumstances, such a correlation is almost absent. However, this can be turned into a reality through employing yield‐related DNA markers with genomic selection (GS). The impact of DNA markers linked with REF, SRPP, acetyl‐CoA acetyltransferase, HMGS, HMGR and JAZ need to be specifically evaluated. GS that aims to improve quantitative traits by using genome‐wide marker data without requiring identification of markers associated with quantitative trait loci (QTLs) of interest can be used in Hevea also. Subsequently, by a predictive model, genomic estimated breeding values (GEBVs) can be calculated for untested individuals from a ‘testing population’. GS captures the total additive genetic variance with genome‐wide marker coverage and effect estimates. Therefore, selection of an individual without phenotypic data can be performed based on the individual's predicted breeding value. This review makes an assessment of the molecular markers in Hevea rubber and aims to streamline an efficient selection system to be applied onto seedlings through GS that owes a significant correlation with the mature phase.

Near infrared spectroscopy to rapid assess the rubber tree clone and the influence of maturation and disease at the leaves

The rubber tree is a species of great economic importance due to its natural rubber, which is widely used in the tire industry due to its resistance and does not yet have a synthetic formula capable of completely replacing it. Near infrared spectroscopy (NIRS) is an emerging technique for soil and plant analysis. The aim of this study is to predict the Hevea rubber tree clones, detect and discriminate leaves at different stages of development (young or adult), as well as to discriminate healthy and affected adult leaves by South American Leaf Blight, through the spectroscopic technique of visible to infrared (Vis-NIR) combined with chemometrics. Using dried ground leaves samples, leaves from 14 rubber trees clones (H. brasiliensis) were evaluated, these leaves were collected in 3 tree stages young trees; adult or mature trees; and mature trees with symptoms of Microcyclus ulei (disease leaves). The near infrared (NIR) reflectance spectra were acquired using a spectrometer FOSS-NIRS (model DS2500). An average of 64 scans operating in a range between 400 and 2500 nm under spectral resolution of 0.5 nm were used for all the spectral acquisitions. With the use of reflectance spectroscopy in visible and near infrared, it was possible to efficiently discriminate the clones of the rubber tree, regardless of the use of spectra obtained from young leaves or from mature leaves. Which might enable studies with characterization of the genetic materials present in the germplasm banks and in situ. The technique also efficiently differentiated the young leaves from the mature leaves, as well as separating the healthy mature leaves from the diseased mature leaves. These results can contribute to the breeding and conservation programs of the species, obtaining fast results and without the use of chemical reagents.

Impact of non-rubber components on the branching structure and the accelerated storage hardening in Hevea rubber

Natural rubber (NR) contains cis-1,4-polyisoprene as well as a small quantity of non-rubber components, affecting the physical properties of NR, especially the storage hardening via gel formation. The free and/or linked non-rubber components were removed from NR by various treatments. The origin of gel formation in NR mainly resulted from proteins, which could be removed by enzymatic deproteinisation, surfactant washing or saponification treatment, and partly from phospholipids linked to NR molecule via H-bonding, which were decomposed by saponification or polar solvent treatment. The effect of the non-rubber components in NR on storage hardening was investigated by an accelerated storage hardening test (ASHT). The crude NR (CNR) containing proteins and lipids clearly showed the increase of gel content, suggesting the formation of crosslink structure during storage, resulting in the high plasticity number and Mooney viscosity after the ASHT. The gel content in protein-free NR did not change significantly only in washed NR (WSNR), but increased in the enzymatic deproteinised NR (DPNR). This resulted from the presence of residual proteins, such as oligopeptides. Interestingly, the gel content also reduced in the acetone extracted CNR (AE-CNR) and there was no significant effect on the storage hardening after ASHT, like WSNR. These were supposed to be due to the interaction or the participation of proteins and free fatty acids in the branching formation. Although the saponification could be decomposed branching at both terminal ends of the NR molecule, the protein and lipid residues occluded in the saponified NR (SPNR) affected the storage hardening. However, the flocculant remaining in the SPNR coagulated with acid and flocculant (AF-SPNR) would obstruct both gel formation and storage hardening.

Liquid guayule natural rubber, a renewable and crosslinkable processing aid in natural and synthetic rubber compounds

Liquid guayule natural rubber (LGNR) was produced by thermal degradation of guayule natural rubber and tested as a renewable alternative to naphthenic oil (NO) processing aid in natural rubber (Hevea and guayule rubber) and synthetic (styrene-butadiene) rubber composites filled with carbon black (CB). Processing oils are rubber additives commonly used to improve the processability of a compound. Most processing oils, like NO, are petroleum-based, and negatively impact the carbon footprint of the rubber industry. Moreover, these aids act as diluents that lower the mechanical performance of the resultant rubber products.The energy consumption of rubber compounding, mechanical properties and crosslinking networks of natural and synthetic rubber composites made with LGNR were characterized. LGNR effectively helped the compounds mix as demonstrated by 13–21% lower energy consumption compared to compounds mixed without processing aids. Moreover, unlike NO, LGNR acted as an active additive in the vulcanization reaction. Tensile strength, elongation at break, modulus at 100% strain and hardness increased when NO was replaced with LGNR in the compounds. The higher mechanical properties may be explained by additional crosslinking networks formed between LGNR and the rubber matrices and strong LGNR-CB interactions. LGNR, as a renewable processing aid, can address rising performance goals, and reduce carbon footprint for rubber products. In conclusion, LGNR provides the same benefits as conventional diluent processing aids, enhances the properties of the final material, and is produced from a renewable plant source.

Effect of Tackifier Addition on Cushion Compound Formulation for Tire Retreading Application

Tire retreading is a prospective industry. Old tires are repaired and retreaded with suitable tread compounds to fulfill the requirement as the new ones. One of the important components in tire retreading process is cushion compound. Cushion compound consists of unsaturated rubber, in this case natural rubber Hevea brasiliensis was used, less phr of filler compared to the retread compound, and additives such as peptizer, tackifier, processing oil, antioxidant, activator, accelerator and curatives. Tackifier is an important component in cushion compound since its role to make a bonding between different layer, the initial tire after buffing and new retread layer. Tackifier should has good resistance, good compatibility and does not affect the rheological and dynamical properties of bonded rubber. The general tackifier that used in industries are hexamethyl tetramine as methylene donor and resorcinol as methylene acceptor. There is certain reaction between those two additives that determine how good the performance of cushion compound and its effect to retreading process. To obtain optimum reaction, comparison between resorcinol and hexamethyl tetramine were varied as 1:1 (FRR1), 1:2 (FRR2) and 1:3 (FRR3). Hardness test, compression test, rebound resilience, tensile and tear strength, and FTIR were done to observe the optimum variation for retread application. Compared to the control with no tackifier at all, FRR2 showed the optimum result with 21.75 MPa (min. 19 Mpa) and 454,54% elongation at break (min. 450%). The most interesting result was observation by using FTIR, it was detected that the crosslink density was significantly higher than other formulation. It is a new breakthrough which is minimum tackifier with certain treatment could give better performance.

Confirmation molecular structure of the Hevea rubber molecule and its effects in storage hardening

Lipids are the one of major non-rubber components discovered in natural rubber (NR) latex, which reported to be the significant parameter affecting the properties of NR [1, 2]. Our previous work suggested that lipids are the major factor dominate branching formation in NR [3], which could bring about the change in physical properties of NR during long term storage as called storage hardening (SH) phenomenon. However, lipids found in NR consist of neutral and polar lipids, i.e., phospholipids and glycolipids [3]. The information on types of lipids affecting the storage hardening behaviour in NR have not yet been investigated. Therefore, the aim of this work was to study the relationship between types of lipids on the gel formation in NR under accelerated storage. In the present work, natural rubber was treated by deproteinization, acetone extraction, chloroform:methanol extraction and transesterification for eliminating proteins, neutral lipids, polar lipids and linked lipids, respectively. The molecular structure of the rubber samples and the remaining non-rubber components were analyzed using nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR). Moreover, the rubber samples were subjected to study the storage hardening behaviour under accelerated condition using phosphorus pentoxide (P2O5).

Design and Analysis of Moisture Content of Hevea Latex Rubber Using Microstrip Patch Antenna with DGS

A microstrip patch sensor is designed and analysis for determination of moisture content in Hevea Rubber Latex. The microstrip patch sensor was designed to operate at microwave frequency range 2.8GHz, 7.8GHz and 8.8GHz on FR4 substrate with 4.4 permittivity and 1.676mm thickness. The width and length of the rectangular patch antenna was 30mm and 35mm, respectively as well as defected ground structure in the ground and microstrip line feed used because of easy to feed and low spurious feed radiation with the simulated by using the CST software. The actual values of moisture content will be obtained by using standard oven drying method and measured by the vector network analyzer

Total Solid Content and Compound Properties from Different Collection Time of Hevea brasiliensis Latex

Abstract This study compared the total solid content and compound properties of Hevea rubber latex produced from material collected during different periods. Samples were collected from five trees, with the collection replicated three times with tapping task as replication. Observed parameters included total solid content, vulcanization characteristics, technical and physical properties. The results exhibited that the longer latex flowed, the more total solid content tended to decrease. Results indicate that compound of latex collected 20 minutes (C20), 60 minutes (C60), and 300 minutes (C300) after tapping qualified for SIR 20. Other parameters did not show a significant difference among the three tested compounds. Considering the products requiring high dry rubber content, it is suggested not to blend the late collection with main collected latex.

Possibility of artocarpus heterophyllus latex as an alternative source for natural rubber

Abstract Natural rubber (NR) has much application in rubber product manufacturing industries, which cannot be replaced by synthetic rubber. At present, Hevea rubber tree is the only economical and commercially viable source of NR. Therefore, the objective of the present research was to find alternative source of NR. NR mainly comprise of cis-1,4 polyisoprene. Artocarpus heterophyllus latex (jackfruit latex) was collected and analyzed to investigate if it can be considered as alternative source of NR. It was found from FTIR, 1H NMR and GC-MS study that jackfruit latex contains both cis-1,4 polyisoprene and trans- 1,4 polyisoprene along with few other chemical constituents. However, molecular weight of jackfruit latex is significantly lower than the NR. Because of low molecular weight polymer and presence of several other chemical constituents as impurity, jackfruit latex does not impart significant mechanical properties in vulcanized rubber compound, but it provides additional wet skid resistance (WSR) and aid in better dispersion of carbon black in rubber compound. Therefore, jackfruit latex cannot be used to replace NR, but can be used as low molecular weight natural resin, especially to improve dispersion of carbon black in rubber compound and to enhance WSR for tire.

Genomic technologies for Hevea breeding.

The commercial production of high quality natural rubber (NR) solely depends on Hevea brasiliensis Muell. Arg, (Para rubber tree) and accounts for >98% of total production worldwide. NR with its unique properties is an essential commodity for the automobile industry and its synthetic counterparts are in no way substitute to it. The rubber tree genome is very complex and plays an important role in delivering the unique properties of Hevea. But a lack of knowledge on the molecular mechanisms of rubber biosynthesis, disease resistance, etc., in elite clones of rubber still persists. Marker-assisted selection and transgenic techniques were proved to be advantageous in improving the breeding efficiency for latex yield, disease resistance, etc. The suppression subtractive hybridization (SSH), in the form of subtracted cDNA libraries and microarrays, can assist in searching the functions of expressed genes (candidate gene approach). Expressed sequence tags (ESTs) related to various metabolic aspects are well utilized to create EST banks that broadly represent the genes expressed in one tissue, such as latex cells, that assists in the study of gene function and regulation. Transcriptome analysis and gene mapping have been accomplished in Hevea at various stages. However, a selection criterion to delineate high yielding genotypes at the juvenile stage has not been accomplished so far. This is the main pit fall for rubber breeding apart from stock-scion interactions leading to yield differences among a clonally multiplied population. At least four draft genome sequences have been published on Hevea rubber, and all give different genome size and contig lengths-a comprehensive and acceptable genomic map remains unfulfilled. The progress made in molecular markers, latex biosynthesis genes, transcriptome analysis, chloroplast and mitochondrial DNA diversity, paternity identification through Breeding without Breeding (BwB), stimulated latex production and its molecular intricacies, molecular biology of tapping panel dryness, genomics for changed climates and genome mapping are discussed in this review. These information can be utilized to improvise the molecular breeding programs of Hevea in future.

Direction, Panel Height, and Tapping Frequency Affect The Daily Bark Consumption in Hevea Rubber Tapping

Bark consumption is defined as the thickness of sliced bark per time unit. This research, aiming to identify the effects of direction, panel height, and tapping frequency on daily bark consumption, was carried out at Sungei Putih Research Center, North Sumatera and several estates in Lampung (Kedaton, Bergen, and Way Lima) from January to March 2018. The observations involved 15 tapping tasks consisting of GT 1, PB 260, and mixed clones. Bark samples were collected from 10 randomized trees in each task. Tapping direction was distinguished as downward tapping and upward tapping, while panel height was classified into 170 cm in upward tapping. Tapping frequency effect was investigated in a trial plot using frequency of once in three days (d3), once in four days (d4), once in five days (d5), once in six days (d6), and once in eight days (d8) on the basal panel (B0-2). Bark consumption was measured directly using a digital caliper. The observation result indicated that upward tapping had higher bark consumption than downward tapping. In downward tapping, the lower tapping position, the higher bark consumption would be, whilst in upward tapping, bark consumption increased along with the panel height. Low tapping frequency (d4, d5, d6, and d8) showed higher bark consumption per tapping than d3, yet they had lower cumulative bark consumption per year.

Pathway to domestic natural rubber production: a cradle-to-grave life cycle assessment of the first guayule automobile tire manufactured in the United States

Guayule (Parthenium argentatum) is a perennial shrub that can be cultivated in the Southwestern US. It produces natural rubber that could be a viable substitute for Hevea natural rubber and synthetic rubbers currently used in tires. Drivers for producing domestic guayule rubber include fluctuations in price and availability of imported Hevea rubber. A tire was manufactured in 2017 where guayule rubber was substituted for all of the Hevea and synthetic rubber in the conventional tire. Life cycle assessment (LCA) from cradle to grave was used to evaluate the environmental and energy sustainability of the guayule tire, and these metrics were benchmarked against those of the conventional tire (CT). Functional units of 1 kg natural rubber for agricultural processes, as well as 1 tire for the cradle-to-grave study were considered. Life cycle inventory (LCI) data were collected directly from primary sources, including guayule field experiments, a rubber-processing company, and a major tire manufacturer. Scenario analysis was used to evaluate alternative processes, such as irrigation options in guayule cultivation, processing scale in rubber extraction, and selection of allocation methodology in LCAs. Model uncertainty was characterized using Monte Carlo analysis. The LC energy consumption of the guayule tire (GT) was 13.7 GJ/tire (including co-product credits, excluding C sequestration during agriculture), compared to 16.4 GJ/tire for the CT. The GT had 6–30% lower emissions than CT in ten different environmental impact categories. Bagasse co-product in energy applications showed benefits of reducing energy consumption by 10% and decreasing environmental impacts by up to 11%. GT’s use-phase resulted in the highest energy consumption (95%) and environmental impacts ranging between 81 and 99%. Variables in use phase, i.e., rolling resistance coefficient, vehicle efficiency, and tire lifetime, and those in guayule cultivation i.e., rubber and biomass yields, were key model parameters. The effect of excluded but potentially important model parameters, i.e., guayule carbon sequestration and resin co-product were tested via sensitivity analyses. Based on these results that factored in the lower rolling resistance coefficient of a guayule tire—a significant element that improves the fuel economy of an automobile—the guayule rubber tire shows promise in its ability to replace current conventional tires. The first commercially manufactured guayule rubber passenger tire will most likely substitute components, which are either partially or fully guayule, instead of guayule replacing 100% of the existing rubbers as shown in this study.

Investigating the Mechanistic and Structural Role of Lipid Hydrolysis in the Stabilization of Ammonia-Preserved Hevea Rubber Latex.

The stabilization mechanism of natural rubber (NR) latex from Hevea brasiliensis was studied to investigate the components involved in base-catalyzed ester hydrolysis, namely, hydrolyzable lipids, ammonia, and the products responsible for the desired phenomenon observed in ammonia-preserved NR latex. Latex stability is generally thought to come from a rubber particle (RP) dispersion in the serum, which is encouraged by negatively charged species distributed on the RP surface. The mechanical stability time (MST) and zeta potential were measured to monitor field latices preserved in high (FNR-HA) and low ammonia (FNR-LA) contents as well as that with the ester-containing components removed (saponified NR) at different storage times. Amounts of carboxylates of free fatty acids (FFAs), which were released by the transformation and also hypothesized to be responsible for the like-charge repulsion of RPs, were measured as the higher fatty acid (HFA) number and corroborated by confocal laser scanning microscopy (CLSM) both qualitatively and quantitatively. The lipids and their FFA products interact differently with Nile red, which is a lipid-selective and polarity-sensitive fluorophore, and consequently re-emit characteristically. The results were confirmed by conventional ester content determination utilizing different solvent extraction systems to reveal that the lipids hydrolyzed to provide negatively charged fatty acid species were mainly the polar lipids (glycolipids and phospholipids) at the RP membrane but not those directly linked to the rubber molecule and, to a certain extent, those suspended in the serum. From new findings disclosed herein together with those already reported, a new model for the Hevea rubber particle in the latex form is proposed.

English

Hevea brasiliensis is the major source of natural rubber. Natural rubber being a unique biopolymer of strategic importance needs to be continuously well managed and protected against biotic damages. Many rubber producing countries include South East Asia, Africa and Latin America among others. Corynespora leaf fall caused by Corynespora cassiicola is currently considered as the most destructive leaf disease of Hevea rubber in Asian and African continents causing about 45% of yield loss. It had caused great loss to the rubber industry in various countries, thus the need for prompt action against the disease. The rubber breeding over the years have been on the development of clones with high yield combined with the desirable secondary traits. The resistance of rubber clones to C. cassiicolla depends on its ability to neutralize the toxin or its use of the hypersensitive response of the clone. The major objective of this review was to awaken the consciousness to C. cassiicolla, having in mind that rubber clones once tolerant to the disease had later become susceptible. Key words: Bio polymer, Corynespora cassiicolla, Hevea brasiliensis, natural rubber, tolerant.