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Ethylene enhances latex flow and latex regeneration in rubber trees. The physiological regulation of ethylene-stimulated latex flow mainly involves processes such as alleviating laticifer plugging, prolonging latex flow duration, increasing laticifer turgor pressure, and enhancing latex stability. The molecular mechanisms underlying these physiological effects, particularly those related to the ethylene signaling transduction pathway, remain unclear. This study aims to establish the link between these physiological changes and specific genes in the ethylene signaling pathway. We identified four ethylene dose-dependent response factors, namely HbRAP2.3, HbERF110, HbERF3, and HbERF1B, and a cluster of ethylene dose-dependent genes, including those encoding enzymes involved in latex stability, such as HbPMCA4 and HbGCL , and those involved in latex coagulation, such as HbGLU14 and HbECH. These genes exhibit a similar expression pattern with these ethylene dose-dependent response factors, and the promoter region of some contains the "GCC-box", the core sequence for ERFs binding. This suggests that they may be directly regulated by these ethylene dose-dependent response factors. Additionally, we cloned HbRAP2.3 , which can activate the expression of latex flow-related genes HbGLU14 and HbECH. These findings provide novel insights into the intricate relationship between ethylene signaling and latex flow in rubber trees, laying the foundation for future research aimed at optimizing latex yield. • Ethylene enhances latex production in rubber trees with a dose-dependent effect observed. • Ethylene-responsive genes exhibit dose-dependent and tissue-specific expression patterns. • HbRAP2.3 plays a pivotal role in strengthen ethylene signaling and latex flow under high ethylene level. [ABSTRACT FROM AUTHOR]

Previously, we have realized CRISPR/Cas9-RNP and plasmid-mediated genome editing in the rubber tree protoplast by transient transformation, but it is a challenge to generate editing plants hindered by low stable genetic transformation efficiency. In the present study, we firstly reported genome-edited rubber trees with expected phenotype, related works including demonstrated that 10 mg/L hygromycin is suitable for embryo screening, based on this foundation, CRISPR vector targeting the Phytoene desaturase gene (HbPDS) was transformed into embryos, the results showed that more than 90 % of T0 edited embryos are chimeric, and the editing efficiency is 3.2 %. In order to improve the homozygous embryo ratio, a T0 embryo with 9.8 % edited cells was sliced into 33 small pieces for one more cycle embryogenesis to produce T1 generation embryos, it turns out the editing efficiency has been improved to nearly 90 %, and 50 % of T1 embryos were homozygous. At last, 8 plantlets were regenerated from the 29 T1 generation edited embryos, 4 chimeric and 4 homozygous albino plantlets, respectively. Next-generation sequencing demonstrated that, the threshold for the proportion of edited cells displaying expected albino phenotype is between 70 % and 85 %. Additionally, Tail-PCR' results, combined the different genotypes considered, the four homozygous plantlets can be confirmed as independently derived from different single transformed cells. Overall, this study presents a significant advancement in transgenic and gene editing for rubber trees, will be conducive to gene functional validation and accelerate the molecular breeding process of rubber tree. • We found the optimal antibiotic for rubber tree embryo transformation is hygromycin. • We demonstrated that a constant 10 mg/L hygromycin is the best selection strategy. • To our knowledge, this study produced the highest genetic transformation efficiency in rubber tree. • It has been proven that most of the transformed T0 embryos are chimeric, and we overcome this problem. • This is the first gene editing rubber tree with expected phenotype reported publicly. [ABSTRACT FROM AUTHOR]

• Developed a simulation model to study the air-fed spraying system by CFD-DEM. • Investigated the kinematic characteristics of mixed spherical and non spherical particles. • Designed simulation experiments Based on the Box-Behnken experimental method. • Established multiple linear regression models between each factor and response index. • Optimized structural parameters of the air-fed application device. In order to enhance the effectiveness of natural rubber disease control and achieve precise pesticide application, the air-fed spraying system has been optimized and designed to improve pesticide powder utilization rate without compromising spraying performance. On the basis of the research on the air-fed powder spraying device, the main factors affecting the spraying performance and powder deposition characteristics were obtained by combining the law of air jet motion and the analysis of the motion characteristics of sulfur powder particles. In the discrete element simulation, these particle shapes (round, oval, and elongated) were assigned a ratio of 1:3:1 based on their equivalent sizes. A CFD-DEM coupling simulation system for the air-fed spraying system was designed in this study. Therein, the kinematics of the internal airflow and the role of the sulfur powder equivalent in its action were investigated. Henceforth, the centrifugal fan speed, the tilt angle of the duct, and the diameter of the duster outlet were taken as the test factors, and the particle ejection speed and the mass of particles retained in the model were taken as the response indexes. A three-factor and three-level response surface simulation experiment was designed to evaluate the pesticide application process. Following that, the significance tests and the regression equations were established to optimize the parameters. The experiment findings indicate that the optimal operating parameter combination for the air-fed spraying system was as follows: the centrifugal fan speed of 2200r/min−1, the tilt angle of the duct of 65°, and the diameter of the duster outlet of 140 mm, at which time the particle ejection speed was increased to 81.074 m/s and the mass of particles retained in the model was decreased to 9.93g. When the prototype test of the rubber plantation was conducted on the basis of this group of parameters, the variation coefficient of canopy deposition per unit area was 3.8 %, and the effective deposition rate of the powder was 59.06 %. These research results provide a theoretical foundation for the design and optimization of air-fed powder spraying devices. [ABSTRACT FROM AUTHOR]

As a major industrial raw material, natural rubber (NR) is also an important strategic material. Commercial NR is almost exclusively produced from rubber tree latex at present. Given that polyamines (PAs), especially putrescine (Put), can accelerate NR biosynthesis by scavenging ROS in laticifers, arginine decarboxylase (ADC) is likely involved in ROS balance by regulating Put content. In the present study, HbADC2 , a novel ADC gene, was cloned and analyzed in detail. HbADC2 were expressed in different tissues and developmental stages of leaves, suggesting that HbADC2 was involved in rubber tree growth and development. As a multifunctional gene, HbADC2 was also modulated by several stresses and hormone treatments. Put contents were consistent with the expression levels of HbADC2 in latex between healthy rubber tree and tapping panel dryness (TPD)-affected one, implying that HbADC2 was likely associated with Put biosynthesis in rubber tree. In addition, tobacco plants overexpressing HbADC2 can enhance tolerance to methyl viologen (MV)-induced oxidative stress by increasing Put biosynthesis to decrease hydrogen peroxide (H 2 O 2) content. Taken together, our results suggest that HbADC2 not only is related to rubber tree growth, TPD, development, stress and hormone responses, but also enhances the tolerance to MV-induced oxidative stress by increasing Put biosynthesis in tobacco plants. • HbADC2 was expressed in different tissues and developmental stages of leaves • HbADC2 was related to tapping panel dryness, various stress, and hormone responses • Put and H 2 O 2 in tobacco expressing HbADC2 was separately higher and lower than the WT • HbADC2 enhanced tolerance to MV-induced oxidative stress by increasing Put content [ABSTRACT FROM AUTHOR]

Currently, one of the most serious threats to rubber tree is the tapping panel dryness (TPD) that greatly restricts natural rubber production. Over-tapping or excessive ethephon stimulation is regarded as the main cause of TPD occurrence. Although extensive studies have been carried out, the molecular mechanism underlying TPD remains puzzled. An attempt was made to compare the levels of endogenous hormones and the profiles of transcriptome and proteome between healthy and TPD trees. Results showed that most of endogenous hormones such as jasmonic acid (JA), 1-aminocyclopropanecarboxylic acid (ACC), indole-3-acetic acid (IAA), trans-zeatin (tZ) and salicylic acid (SA) in the barks were significantly altered in TPD-affected rubber trees. Accordingly, multiple hormone-mediated signaling pathways were changed. In total, 731 differentially expressed genes (DEGs) and 671 differentially expressed proteins (DEPs) were identified, of which 80 DEGs were identified as putative transcription factors (TFs). Further analysis revealed that 12 DEGs and five DEPs regulated plant hormone synthesis, and that 16 DEGs and six DEPs were involved in plant hormone signal transduction pathway. Nine DEGs and four DEPs participated in rubber biosynthesis and most DEGs and all the four DEPs were repressed in TPD trees. All these results highlight the potential roles of endogenous hormones, signaling pathways mediated by these hormones and rubber biosynthesis pathway in the defense response of rubber trees to TPD. The present study extends our understanding of the nature and mechanism underlying TPD and provides some candidate genes and proteins related to TPD for further research in the future. • Levels of various endogenous hormones are significantly altered in TPD rubber trees. • Transcriptomic and proteomic analyses were combined to reveal the mechanism of TPD. • Genes and proteins involved in rubber tree TPD occurrence were identified. • Rubber biosynthesis pathway is significantly inhibited in TPD rubber trees. • Multiple hormone-mediated signaling pathways are involved in TPD occurrence. [ABSTRACT FROM AUTHOR]

Biochar is a potential tool to mitigate climate change by enhancing C sequestration in soils, but its use as a soil amendment to improve soil fertility and crop yields is still a contentious subject. In North East (NE) Thailand, biochar has been promoted to restore soil fertility in rubber tree plantations. Despite this, there is scarce information on the impact of biochar application on the soil biota, particularly on microbial communities associated with rubber trees. The effects of increasing doses of biochar on microbial communities were investigated in a rubber tree plantation in NE Thailand, 28 months after application. Biochar application resulted in increases of soil pH and nutrient contents and also had an impact on both bacterial and fungal communities. Changes in microbial composition and structure were observed although fungal communities were more markedly affected than bacterial communities. The nature and magnitude of the observed changes were strongly related to soil properties (pH, soil moisture and P content), while biochar dose (5, 10 or 20 tons/ha) effect was not significant. Our results highlight the need for additional research for a better understanding of the impact of biochar application on soil microbial communities and further cascading effects on ecosystem functions. Unlabelled Image • Biochar addition affected soil microbial communities associated with rubber trees. • Biochar application resulted in higher soil pH and nutrient content. • Both community composition and structure were affected by biochar application. • Fungal communities were more severely affected than bacterial communities. • The effect of soil type was stronger than that of biochar dose on all parameters. [ABSTRACT FROM AUTHOR]

Commercial binders based on formaldehyde are the main adhesive to produce particleboards, however, these binders are harmful to human health and the environment. In this scenario, alternative binders are a possibility to reduce the formaldehyde content in the particleboards. Therefore, the focus of this original scientific study is to explore the thermal, physical and mechanical properties of particleboards produced with natural rubber latex as a potential polymeric binder. Bagasse-latex particleboard (BLP) with nominal density of 800 kg/m 3 , with different latex content: 28% (BLP-28), 42% (BLP-42) and 56% (BLP-56) by mass were evaluated. The quality of the particleboards produced was assessed by determining their thermal, physical and mechanical properties. The formation process of interfacial structure between sugarcane bagasse and latex was observed, configuring the adhesion of the two phases. The thermal conductivity of all the particleboard formulations showed attractive performance as thermal insulating material, considering that these are medium to high nominal density particleboards. According to physical tests, higher latex contents in the particleboard did not affect the density, however, it created a binder protection against water absorption. Contrarily, an increase in the latex content (as in BLP-56 formulation) did not cause increase in the mechanical properties under flexural loading. The BLP-42 particleboards performed better mechanically based on modulus of rupture (MOR) and modulus of elasticity (MOE) with average values of 6.32 MPa and 1275 MPa, respectively. These results indicated the potential use of latex natural rubber as an alternative to produce insulation particleboards in civil construction. [ABSTRACT FROM AUTHOR]

Natural rubber (cis-1, 4-polyisoprene) is being produced from bark laticifer cells of Hevea brasiliensis and the popular high latex yielding Indian rubber clones are easily prone to onset of tapping panel dryness syndrome (TPD) which is considered as a physiological syndrome affecting latex production either partially or completely. This report describes an efficient protocol for development of transgenic rubber plants by over-expression of 3-hydroxy 3-methylglutaryl Co-enzyme A reductase 1 ( hmgr1 ) gene which is considered as rate limiting factor for latex biosynthesis via Agrobacterium -mediated transformation. The pBIB plasmid vector containing hmgr1 gene cloned under the control of a super-promoter was used for genetic transformation using embryogenic callus. Putatively transgenic cell lines were obtained on selection medium and produced plantlets with 44% regeneration efficiency. Transgene integration was confirmed by PCR amplification of 1.8 kb hmgr1 and 0.6 kb hpt genes from all putatively transformed callus lines as well as transgenic plants. Southern blot analysis showed the stable integration and presence of transgene in the transgenic plants. Over expression of hmgr1 transgene was determined by Northern blot hybridization, semi-quantitative PCR and real-time PCR (qRT-PCR) analysis. Accumulation of hmgr1 mRNA transcripts was more abundant in transgenic plants than control. Increased level of photosynthetic pigments, protein contents and HMGR enzyme activity was also noticed in transgenic plants over control. Interestingly, the latex yield was significantly enhanced in all transgenic plants compared to the control. The qRT-PCR results exhibit that the hmgr1 mRNA transcript levels was 160-fold more abundance in transgenic plants over untransformed control. These results altogether suggest that there is a positive correlation between latex yield and accumulation of mRNA transcripts level as well as HMGR enzyme activity in transgenic rubber plants. It is presumed that there is a possibility for enhanced level of latex biosynthesis in transgenic plants as the level of mRNA transcripts and HMGR enzyme activity is directly correlated with latex yield in rubber tree. Further, the present results clearly suggest that the quantification of HMGR enzyme activity in young seedlings will be highly beneficial for early selection of high latex yielding plants in rubber breeding programs. [ABSTRACT FROM AUTHOR]

Natural rubber ( Hevea brasiliensis ) is a high-valued industrial crop in tropical areas. Reasonable fertilization can improve the quality and production of the natural rubber. Hence, there is a great interest in developing an accurate and robust model to detecting the nitrogen content of rubber tree to improve the production. In this study, we propose a new method for detecting the nitrogen content using fractional calculus augmented NIR spectra. Fractional calculus is applied as a tool to extract additional information from the original spectra. Three different mathematical transforms ( R , 1/ R , log ( R )) are utilized before the fractional order derivative analysis. After derivative analysis with different orders (0–2), the PLS regression method is utilized to develop the estimation models with the wavelengths selected by significant test of correlation coefficient at 0.01 level. The optimal prediction result R P = 0.9245 is achieved by reciprocal spectrum with the order 0.6. Results show that fractional calculus with NIR can be utilized to build a more accurate nitrogen estimation model for rubber tree. The result presented here provides us a fast and non-destructive strategy to evaluate the nitrogen condition of rubber tree and provides a direct way to support the field management. [ABSTRACT FROM AUTHOR]

Improved spatial transferability of ecological niche models is crucial for accurately predicting species preferred habitat; this is especially true for a planted tree species ( Hevea brasiliensis Muell. Arg.). Amazonian valley of South America (AZ) is known as native range of this species. To test the transferability of Maxent ecological niche model among two distinct bio-geographical regions of India, Western Ghats (WG) and North-East (NE) regions and AZ, the present study was designed. The present spatial distribution of H. brasiliensis was evaluated using the Maxent algorithm using bioclimatic variables and species occurrence data from respective regions. An alternate approach of calibrating the model with pooled occurrence points of various introduced ranges of the species was adapted for predicting the species' presence in unsampled region. Spatial distribution of Hevea species in two biogeographic regions of India modelled by Maxent was found to be quite accurate when the model was calibrated with the sampled occurrence points of the same region as evidenced from our previous studies. However, the present study addresses the issue related to transferability of niche based model to predict the probable distribution of Hevea species in an unsampled region based on either its native or introduced range of the species. The result indicates that transferability depends on the extent of similarity between the climatic spaces occupied by the species in sampled region and unsampled regions of the species' distribution. The spatial transferability of the model was improved by using pooled occurrence data of the species from both introduced regions. [ABSTRACT FROM AUTHOR]

The genus Erysiphe was an obligate parasite causing powdery mildew disease on a wide range of higher plants. However, the knowledge of their mitogenome architecture for lifestyle adaptability was scarce. Here, we assembled the first complete mitogenome (190,559 bp in size) for rubber tree powdery mildew pathogen Erysiphe quercicola. Comparable analysis of the Erysiphe mitogenomes exhibited conserved gene content, genome organization and codon usage bias, but extensive dynamic intron gain/loss events were presented between Erysiphe species. The phylogeny of the Ascomycota species constructed in the phylogenetic analysis showed genetic divergences of the Erysiphe species. Compared with other distant saprophytic and plant pathogenic fungi, Erysiphe had a flat distribution of evolutionary pressures on fungal standard protein-coding genes (PCGs). The Erysiphe PCGs had the highest mean selection pressure. In particular, Erysiphe's cox1, nad1, cob and rps3 genes had the most elevated selection pressures among corresponding PCGs across fungal genera. Altogether, the investigations provided a novel insight into the potential evolutionary pattern of the genus Erysiphe to adapt obligate biotrophic lifestyle and promoted the understanding of the high plasticity and population evolution of fungal mitogenomes. [ABSTRACT FROM AUTHOR]

Abst ract Rubber tree plantations ( Hevea brasiliensis ) are expanding into marginal areas with low soil fertility and long dry seasons with a high risk of soil erosion and drought damage to trees. Introducing an N 2 -fixing legume cover crop in rubber plantations may reduce runoff and soil erosion as well as increasing the availability of nutrients but may also increase competition for water. This study quantified the effect of the legume cover crop Pueraria phaseoloides on N, P and K nutrition, water status and growth of young rubber trees (three years old in 2007) over a four year period (2007–2010). The plantation was located on a toposequence with a range of soil depths and water storage capacities in northeast Thailand. The legume aboveground biomass production and its nutrient content and decomposition rate were measured and the N 2 fixation was estimated using the abundance of 15 N (δ 15 N) in the legume. Measurements were taken of the tree stem girth and height and tree leaf predawn water potential, nutrient content and greenness. The transfer of N 2 fixed by the cover crop to the trees was estimated using δ 15 N in the tree leaves. The annual biomass production of the legume was 8 Mg ha −1 year −1 and the N accumulation by the legume was 250 kg N ha −1 year −1 . The natural abundance method applied to the aboveground components of the legume gave N 2 fixation rates varying from 85 to 93% depending on the year. The leaf δ 15 N was similar in the three non-legumes ( H. brasiliensis , Vetiveria zizanioides and Praxelis clematidea ) used as reference plants for estimating the N 2 fixation. The higher level of N and the much lower leaf δ 15 N values for the rubber trees intercropped with P. phaseoloides , compared to rubber trees growing without a legume cover crop, showed that there was a relatively high transfer of fixed N from the legume to the trees, varying from 39% to 46% of tree leaf N depending on the year. Neither N 2 fixation nor N transfer varied significantly along the toposequence. At the bottom of the toposequence, both the nutrient (N, P and K) and water status of trees was significantly improved with the legume cover crop, doubling the tree girth at seven years of age (tree girth: 28 cm, tree height: 700 cm). However, at the top of the toposequence with low water storage capacity, the legume cover crop improved tree nutrition and growth but reduced the trees' ability to survive intense drought. These results raise concern about the resilience to drought of the rubber tree/ P. phaseoloides system, since the positive effect of the legume on rubber tree nutrition and growth may increase the risk of water stress and tree mortality. With future changes in climate, an increasing number of areas will be concerned by the question of optimizing the tradeoff between N inputs and water availability. [ABSTRACT FROM AUTHOR]

Many cultivated rubber trees ( Hevea brasiliensis ) are invaded by various Phytophthora species fungi , especially in tropical regions which result in crop yield losses. Comparative proteome analysis coupled with liquid chromatography electrospray/ionization (LC-ESI) mass spectrometry identification was employed to investigate the relative abundance of defense related proteins in Phytophthora sp. susceptible (RRIM600) and tolerant (BPM24) clones of rubber tree. Proteome maps of non-rubber constituent of these two model clones show similar protein counts, although some proteins show significant alterations in their abundance. Most of the differentially abundant proteins found in the serum of BPM24 illustrate the accumulation of defense related proteins that participate in plant defense mechanisms such as beta-1,3-glucanase, chitinase, and lectin. SDS-PAGE and 2-D Western blot analysis showed greater level of accumulation of beta-1,3-glucanase and chitinase in latex serum of BPM24 when compared to RRIM600. A functional study of these two enzymes showed that BPM24 serum had greater beta-1,3-glucanase and chitinase activities than that of RRIM600. These up-regulated proteins are constitutively expressed and would serve to protect the rubber tree BPM24 from any fungal invader. The information obtained from this work is valuable for understanding of defense mechanisms and plantation improvement of H. brasiliensis. Biological Significance Non-rubber constituents (latex serum) have almost no value and are treated as waste in the rubber agricultural industry. However, the serum of natural rubber latex contains biochemical substances. The comparative proteomics analysis of latex serum between tolerant and susceptible clones reveals that the tolerant BPM24 clone contained a high abundance of several classes of fungal pathogen-responsive proteins, such as glucanase and chitinase. Moreover, other proteins identified highlighted the accumulation of defensive-associated proteins participating in plant fungal immunity. The isolation of beta-1,3-glucanase, chitinase, and lectin from latex serum should be further investigated and may provide a therapeutic application. This investigation will lead to possible use of latex serum as a great biotechnological resource due to the large quantity of serum produced and the biochemicals contained therein. [ABSTRACT FROM AUTHOR]

Studying seed dispersal and the associated processes of germination, seedling establishment and survival are important for understanding plant regeneration dynamics and dispersal ability, especially for introduced plant species. Rubber trees ( Hevea brasiliensis ) have been introduced and cultivated in Xishuangbanna in southwest China for over 60 years. However, almost no adult rubber trees occur in natural forests in the region. In order to determine the factors preventing the expansion of rubber trees into natural forests, we investigated the seed dispersal, seed germination and seedling recruitment of rubber trees. Rubber seeds released in natural forests were frequently visited and largely handled by Rattus spp., but the rubber seeds released in rubber plantations were seldom visited or fetched by any animals, indicating that habitat type had a significant effect on the fate of rubber seeds ( P < 0.001). The majority of released rubber seeds were eaten (57.80% in 2012, N = 5795; 64.45% in 2013, N = 12,455) and only a very few seeds were cached under forest litter or soil surface (0.32% in 2012 and 0.16% in 2013). When missing seeds (about 30% of all released seeds) were omitted in the analysis, it was found that the majority of the seeds were removed within 10 m (60–90% in different years and different sites), and only few seeds were transported to more than 30 m (maximum distance was 55 m in 2012 and 67 m in 2013). Rubber seeds buried in natural forests had a lower germination rate (mean ± SE = 11.67 ± 2.11%, N = 300) compared to those in rubber plantations (mean ± SE = 44.33 ± 4.25%, N = 300) (one-way ANOVA, P < 0.01). Results from our seed germination experiment and natural regeneration survey showed that rubber seedlings had a very low survival rate, both in natural forests and in rubber plantations. Poor seed dispersal, seed germination and seedling survival may explain why rubber trees do not expand into the natural forests in Xishuangbanna. The findings of this study can help to better understand the natural dispersal ability and regeneration dynamics of rubber trees, providing insights important for forest conservation planning. [ABSTRACT FROM AUTHOR]

Background The rubber tree, Hevea brasiliensis , is a major commercial source of natural rubber. Increasing the rubber yield of rubber trees is a very serious problem since the demands for high quality rubber materials are great. Establishment of a tapping system is based on an estimate of tapping intensity from the rubber tree. Latex flowing time is one of the most critical factors that determine the rubber yield. Long-term flow is a type of phenomenon of the rubber tree latex with longer flowing time than normal latex flow, and is always caused by intensive tapping. Thus, transcriptome and expression profiling data for long-term flowing latex (LFL) are needed as an important resource to identify genes and to better understand the biological mechanisms of latex flow in rubber trees. Results The transcripts were sequenced using the Illumina sequencing platform. After cleaning, quality checks and sequencing, 98,697 transcripts and 38,584 unigenes were assembled with the mean size of 1437.31 bp and 923.86 bp, respectively. In BLAST searches of our database against public databases, 65.17% (25,147) of the unigenes were annotated with gene descriptions, conserved protein domains, or gene ontology terms. Functional categorization further revealed 853 individual unigenes related to long-term flow. According to KEGG classification, the clusters for “cysteine and methionine metabolism”, “energy”, “oxidative phosphorylation”, “terpenoid backbone biosynthesis”, “plant hormone signal transduction” and “copper, potassium transporter” were significantly enriched metabolic pathways. Conclusions We conducted high-resolution transcriptome profiling related to LFL in H. brasiliensis . The research facilitates further studies on gene discovery and on the molecular mechanisms related to the estimation of tapping intensity and prolonging latex flowing time. We concluded that it was necessary to improve energy supplies for intensive tapping and the copper ion content of rubber tree latex could be considered as a standard to estimate tapping intensity. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) plays an important role in soil fertility and C cycle. Detailed information about the spatial distribution of SOM is vital to effective management of soil fertility and better understanding of the process of C cycle. To date, however, few studies have been carried out to digitally map the spatial variation of SOM for rubber ( Hevea brasiliensis ) plantation at the regional scale in Hainan Island, China. In this study, a hybrid approach, random forest plus residuals kriging (RFRK), was proposed to predict and map the spatial pattern of SOM for the rubber plantation. A total of 2511 topsoil (0–20 cm) samples were extracted from a soil fertility survey data set of the Danzhou County. These soil samples were randomly divided into calibration dataset (1757 soil samples) and validation dataset (754 soil samples). In this study, stepwise linear regression (SLR), random forest (RF), and random forest plus residuals kriging (RFRK) were used to predict and map the spatial distribution of SOM for the rubber plantation, while generalized additive mixed model (GAMM) and classification and regression tree (CART) were employed to uncover relationships between SOM and environmental variables and further to identify the main factors influencing SOM variation. The RFRK model was developed to predict spatial variability of SOM on the basis of terrain attributes, geological units, climate factors, and vegetation index. Performance of RFRK was compared with SLR. Mean error (ME), mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R 2 ) were selected as comparison criteria. Results showed that RFRK performed much better than SLR in predicting and mapping the spatial distribution of SOM for the rubber plantation. The RFRK model had much lower prediction errors (ME, MAE, and RMSE) and higher R 2 than SLR. Values of ME, MAE, RMSE, and R 2 were 0.26 g/kg, 1.35 g/kg, 2.19 g/kg, and 0.86 for RFRK model, and were 0.65 g/kg, 2.99 g/kg, 4.37 g/kg, and 0.43 for SLR equation, respectively. Moreover, RFRK model yielded a more realistic spatial distribution of SOM than SLR equation. The good performance of RFRK model could be ascribed to its capabilities of dealing with non-linear and hierarchical relationships between SOM and environmental variables and of accounting for unexplained information in the random forest (RF) model residuals. These results suggested that RFRK was a promising approach in predicting spatial distribution of SOM for rubber plantation at regional scale. [ABSTRACT FROM AUTHOR]

The rubber tree is an economically important plant that produces natural rubber for various industrial uses. The application of ethylene contributes to increased latex production in rubber trees; however, the molecular biology behind the effects of ethylene on latex yield remains to be elucidated. Recently, the intersection between microRNA (miRNA) regulation and phytohormone responses has been revealed. Insight into the regulation of miRNAs and their target genes should help to determine the functional importance of miRNAs as well as the role of miRNAs in signaling under ethylene stimulation in the rubber tree. In this study, hbr-miR159 and hbr-miR166 were down-regulated in bark under ethylene treatment. The ethylene also down-regulated ATHB15-like (Class III Homeodomain Leucine Zipper, HD-ZIP III ) which have been extensively implicated in the regulation of primary and secondary vascular tissue pattern formation. The strong negative-regulation of ARF6/ARF8 caused by hbr-miR167 involved in an attenuation of vascular development and may gradually lead to bark dryness syndrome in the long term ethylene treatment. The negative correlation of hbr-miR172 and its target REF3 in the inner soft bark under ethylene treatment results in dramatic increases in latex yield in the ethylene-sensitive clone of the rubber tree. The overall results suggested that the differential expression of HD-ZIP III, miR167/ARF6, ARF8 , and miR172/REF3 and related genes may play possible roles in the response to ethylene treatment, resulting in longer latex flow and increased latex yield. [ABSTRACT FROM AUTHOR]

Trunk phloem necrosis (TPN), a physiological bark disorder of the rubber tree (Hevea brasiliensis), is a serious problem that affects the yield of natural rubber. The resultant bark dryness occurs in up to half of a plantation's trees in almost every rubber tree plantation region, causing a great annual loss of dry rubber for natural rubber production. Different types of injury and physical damage caused by mechanical activation as well as environmental stresses cause physiological bark disorder in tree. Due to the essential role of miR166, miR393 and miR167 in vascular development and abiotic stress response in diverse plant species, it was interesting to investigate the role of these miRNAs in rubber trees, particularly during development of a physiological bark disorder. In this study, the expression pattern of miR166, miR393 and miR167; and their target genes, HD-ZIP III; TIR1 and ARF8, respectively; was demonstrated in healthy tree and different TPN trees. Their existence and function in vivo was validated using RNA ligase-mediated 5′ rapid amplification of cDNA ends. Taken together, the results suggest a possible dual role of these three miRNAs in maintaining normal bark regeneration in healthy trees, coping with overtapping by affecting the wound healing system leading to abnormal bark regeneration in overtapped-TPN trees, and act as additional forces that enhance the attenuation of vascular development resulting in bark necrosis and cell death in the natural-TPN tree. This is the first study to address the molecular events of miRNAs involved in the physiological bark disorder TPN in rubber tree. Further study will open the possibility to better understanding of physiological and molecular perspectives during TPN development, and lead to improvement of monitoring the exploitation of rubber tree plantations. [ABSTRACT FROM AUTHOR]

• The present study indicates the potential of using the rubber tree seed as a raw material for the production of biodiesel. • In natura rubber tree seed oil has a high acidity content, which after treatment was reduced by up to 99.55% • The rubber tree seed biodiesel presented an ester content of up to 98.0%. • The method used in this manuscript is characterized by having few steps, low reagent consumption, low temperatures and reaction times. The Hevea Brasiliensis (HB) seed is a potential raw material for biodiesel production, having a high oil content. However, it is inappropriate for biodiesel production due to the free fatty acids (FFA) value, requiring an adjustment of this parameter. Thus, this work aimed to develop a treatment capable of reducing the acidity content and enabling the quality this biofuel. Firstly, the acid index was decreased by an esterification reaction using sulphuric acid and methanol. Under the best condition corresponding to 1.5% sulphuric acid and 1:2 oil:methanol (v:v), the acidity reduction achieved was a range of 99.55%, and after this, the basic transesterification method was employed to produce the Hevea Brasiliensis biodiesel. As a result, the condition mentioned before shows 98% of ester content and the main physicochemical characteristics required by the market as acidity index, specific gravity and corrosivity to copper. [ABSTRACT FROM AUTHOR]

Highlights: [•] The 12 years observation of a trial has allowed an accurate agronomic comparison of 9 Hevea genotypes. [•] Latex vessel rings, sucrose and inorganic phosphorus contents were correlated with yield. [•] In the susceptible genotype, SALB impacted not only the leaf crown, but also the structure of the bark. [•] FDR5788 and CDC312 cv. were selected for SALB resistance and yield and will be recommended in South-East of Bahia state. [ABSTRACT FROM AUTHOR]

Abstract: Corynespora cassiicola is an important plant pathogenic Ascomycete causing the damaging Corynespora Leaf Fall (CLF) disease in rubber tree (Hevea brasiliensis). A small secreted glycoprotein named cassiicolin was previously described as an important effector of C. cassiicola. In this study, the diversity of the cassiicolin-encoding gene was analysed in C. cassiicola isolates sampled from various hosts and geographical origins. A cassiicolin gene was detected in 47 % of the isolates, encoding up to six distinct protein isoforms. In three isolates, two gene variants encoding cassiicolin isoforms Cas2 and Cas6 were found in the same isolate. A phylogenetic tree based on four combined loci and elucidating the diversity of the whole collection was strongly structured by the toxin class, as defined by the cassiicolin isoform. The isolates carrying the Cas1 gene (toxin class Cas1), all grouped in the same highly supported clade, were found the most aggressive on two rubber tree cultivars. Some isolates in which no Cas gene was detected could nevertheless generate moderate symptoms, suggesting the existence of other yet uncharacterized effectors. This study provides a useful base for future studies of C. cassiicola population biology and epidemiological surveys in various host plants. [Copyright &y& Elsevier]

Highlights: [•] A novel ultrasound assisted rubber yield promotion technology. [•] Ultrasound treatment of 4min significantly increases latex and dry rubber yields. [•] Ultrasound enabled higher supply and uptakes of sucrose for more active rubber biosynthesis. [Copyright &y& Elsevier]

Abstract: Rubber trees provide a variety of raw materials to manufacturing industries. Evaluating the environmental impacts throughout the life cycle of the trees is therefore important. In this study, the carbon stock and greenhouse gas emission profile throughout the complete cropping cycle of rubber plantations was estimated. The amount of biomass carbon stocks per hectare were estimated using a logistic growth model, expressed as 142.47/(1 + 13.31e−0.19t ), where t is rubber age. Using this model, we found that carbon stocks in rubber tree plantations were continuously increasing until the rubber trees reached an age of 22–25 years. On average, the carbon stock in the 25 years of a rubber tree biomass was about 128.4 t C ha−1. Although the carbon stock in latex also increased in a similar way to that of rubber trees, it was much less than that in the biomass of the rubber trees. Based on calculations involving Thailand's total rubber planting area (with various ages of rubber trees), the yearly average carbon stock change was the net increase of 1.71 Mt C y−1. On the other hand the yearly average greenhouse gas emission from cultivation of rubber tree was 0.32 Mt C-e y−1. Compared to the increment of biomass carbon, the carbon emissions from rubber cultivation activities, mainly from fertilizer and herbicide application, were relatively small. [Copyright &y& Elsevier]

Abstract: Three types of roots (taproots, first order laterals and second order laterals) were functionally characterized on 7-month-old in vitro plantlets regenerated by somatic embryogenesis in Hevea brasiliensis. A histological analysis revealed different levels of differentiation depending on root diameter. A primary structure was found in first and second order lateral roots, while taproots displayed a secondary structure. The expression of 48 genes linked to some of the regulatory pathways acting in roots was compared in leaves, stems and the different types of roots by real-time RT-PCR. Thirteen genes were differentially expressed in the different organs studied in plants grown under control conditions. Nine additional other genes were differentially regulated between organs under water deficit conditions. In addition, 10 genes were significantly regulated in response to water deficit, including 8 regulated mainly in lateral roots types. Our results suggest that the regulation of gene expression in lateral roots is different than that in taproots, which have a main role in nutrient uptake and transport, respectively. [Copyright &y& Elsevier]

Abstract: Natural rubber is synthesized in laticifers in the inner liber of the rubber tree (Hevea brasiliensis). Upon bark tapping, the latex is expelled due to liber turgor pressure. The mature laticifers are devoid of plasmodesmata; therefore a corresponding decrease in the total latex solid content is likely to occur due to water influx inside the laticifers. Auxins and ethylene used as efficient yield stimulants in mature untapped rubber trees, but, bark treatments with abscisic acid (ABA) and salicylic acid (SA) could also induce a transient increase latex yield. We recently reported that there are three aquaporin genes, HbPIP2;1, HbTIP1;1 and HbPIP1;1, that are regulated differentially after ethylene bark treatment. HbPIP2;1 was up-regulated in both the laticifers and the inner liber tissues, whereas HbTIP1;1 was up-regulated in the latex cells, but very markedly down-regulated in the inner liber tissues. Conversely, HbPIP1;1 was down-regulated in both tissues. In the present study, HbPIP2;1 and HbTIP1;1 showed a similar expression in response to auxin, ABA and SA, as seen in ethylene stimulation, while HbPIP1;1 was slightly regulated by auxin, but neither by ABA nor SA. The analysis of the HbPIP1;1 promoter region indicated the presence of only ethylene and auxin responsive elements. In addition, the poor efficiency of this HbPIP1;1 in increasing plasmalemma water conductance was confirmed in Xenopus oocytes. Thus, an increase in latex yield in response to all of these hormones was proposed to be the major function of aquaporins, HbPIP2;1 and HbTIP1;1. This study emphasized that the circulation of water between the laticifers and their surrounding tissues that result in latex dilution, as well as the probable maintenance of the liber tissues turgor pressure, favor the prolongation of latex flow. [ABSTRACT FROM AUTHOR]

• In this study, we proposed a rubber leaf nitrogen content detection model to provide guidance for the precise fertilization of rubber trees. • We proposed the KPCA-GMM method, which uses a clustering algorithm to extract spatial information. • For the accuracy of model detection, this study discussed the necessity of using nonlinear algorithms in the process of spectral data feature extraction. • After obtaining the spectral domain information and the spatial domain information at the same time, the research proposed three methods to combine them. Rapid and non-destructive detection of nitrogen concentration in rubber tree is of great significance for estimating rubber yield and precise fertilization of rubber trees. The characteristic spatial distribution of nitrogen is uneven. So the weighted average spectrum of NIR hyperspectral data obtained based on the proportion of different regions contains more spatial information than the average spectrum, which is related to the accuracy of the rubber leaf nitrogen content detection model. In this study, a hyperspectral data clustering method based on spatial-spectral information was proposed to establish the nitrogen model of rubber leaves. The KPCA-GMM method is used to cluster the hyperspectral data of each rubber leaf into C categories, and the area ratio of each category on the blade is obtained based on the clustering result, thereby calculating the weighted average spectrum of each blade. As the number of clustering centers increases, the weighted average spectrum will gradually approach the average spectrum, and the leaf spatial spectrum information will be lost. The experiment obtains different weighted average spectra by setting different numbers of cluster centers, and uses different weighted average spectrum data sets to establish models. The data with the clustering center parameter of 8 set up the best prediction model. The experimental results show that the average spectral data set obtained when the clustering center parameter is 8 is more suitable for estimating the nitrogen content in rubber leaves. The unsupervised and fast performance of KPCA-GMM provides guidance for the area division during the online sample spectrum acquisition process. [ABSTRACT FROM AUTHOR]

The rubber tree (Hevea brasiliensis) belongs to the evergreen broadleaved species in its native ranges, but it has a concentrated leaf senescence period after it was introduced to the Asian tropics. The mechanism behind the leaf senescence is still unclear. Models for predicting leaf senescence dates of this introduced tree have been rarely explored. This study proposed a series of models to identify the main abiotic drivers for the rubber leaf senescence which include temperature, daylength, and water stress. Model tests using data observed from the rubber plantations over the Xishuangbanna region in China show that: (1) Low temperature or cold stress played more critical roles than water stress and daylength in driving rubber leaf senescence. While models using air temperature and soil temperature showed similar performance, the former was recommended for leaf senescence modelling as it is easy to obtain. (2) The root mean square error of all the proposed models was significantly lower than that of the null model which used the mean date of leaf senescence over the study years, indicating the ability of our proposed models in predicting rubber leaf senescence dates. However, no significant differences were found among the proposed models. The thermal time senescence model was recommended for leaf senescence modelling as it is easy to implement. This study helps to better understand the driving mechanism of rubber leaf senescence. [Display omitted] • A family of models were developed to identify drivers of rubber leaf senescence. • Temperature is the most critical driving factor. • Cold stress has much stronger effects on rubber leaf senescence than drought stress. • Thermal time model best predicts rubber leaf senescence with RMSE< 11 days. [ABSTRACT FROM AUTHOR]

Abstract: Latex from the commercial Hevea brasiliensis contains 30–50% (w/w) of natural rubber (cis-1,4-polyisoprene), the raw material for the many products of the rubber industry. We have constructed a cDNA library from the latex of H. brasiliensis to investigate the expressed genes and molecular events in the latex. We have isolated two cDNAs from this library, Hb-PEL-1 and Hb-PEL-2 that could encode for pectate lyase enzymes (EC4.2.2.2). From their sequence analysis Hb-PEL-1 and Hb-PEL-2 encode for proteins of 393 and 323 amino acids, respectively. Comparison of these deduced amino acid sequences with other pectate lyase enzymes showed they contained the conserved NADPH, Ca2+ and substrate binding sites and had a 74% identity to Arabidopsis thaliana pectate lyase. Only the Hb-PEL-1 recombinant protein expressed from Escherichia coli had enzymic activity which was Ca2+ dependent. Interestingly, Hb-PEL-1 contained an extra internal peptide between amino acid residue 38-108 when compared to Hb-PEL-2 and this peptide was also present in other pectate lyase enzymes. The transcript of pectate lyase (Hb-PEL) in the latex of rubber tree at various times after the first tapping was quantified by real-time PCR using 18s genes as internal standard. Most transcripts were detected on the first day after tapping and then decreased with time. This indicates that the pectate lyase may be involved in either the release of latex by breaking down the laticifer wall or in the development of laticifers. [Copyright &y& Elsevier]

Abstract: The latex of Hevea brasiliensis, expelled upon bark tapping, is the cytoplasm of anastomosed latex cells in the inner bark of the rubber tree. Latex regeneration between two tappings is one of the major limiting factors of rubber yield. Hevea species contain high amounts of cyanogenic glucosides from which cyanide is released when the plant is damaged providing an efficient defense mechanism against herbivores. In H. brasiliensis, the cyanogenic glucosides mainly consist of the monoglucoside linamarin (synthesized in the leaves), and its diglucoside transport-form, linustatin. Variations in leaf cyanide potential (CNp) were studied using various parameters. Results showed that the younger the leaf, the higher the CNp. Leaf CNp greatly decreased when leaves were directly exposed to sunlight. These results allowed us to determine the best leaf sampling conditions for the comparison of leaf CNp. Under these conditions, leaf CNp was found to vary from less than 25mM to more than 60mM. The rubber clones containing the highest leaf CNp were those with the highest yield potential. In mature virgin trees, the CNp of the trunk inner bark was shown to be proportional to leaf CNp and to decrease on tapping. However, the latex itself exhibited very low (if any) CNp, while harboring all the enzymes (β-d-diglucosidase, linamarase and β-cyanoalanine synthase) necessary to metabolize cyanogenic glucosides to generate non-cyanogenic compounds, such as asparagine. This suggests that in the rubber tree bark, cyanogenic glucosides may be a source of buffering nitrogen and glucose, thereby contributing to latex regeneration/production. [Copyright &y& Elsevier]

Production of rubber smoked sheets of Thailand is carried out by over 700 small cooperative rubber sheet factories (CRSFs). A survey of CRSFs in southern Thailand revealed that most do not have adequate treatment for their wastewater. To investigate potential of this wastewater for agricultural use, a representative CRSF in southern Thailand was selected as a study site. Results showed that the waters in all the treatment ponds were in anaerobic state, and the final effluent from the system had never met the discharge standards. In the first experiment, pH of the final effluent was adjusted by the residual ash from fuel rubber wood, used in rubber smoking, before being mixed with tap water at ratios 1:0 (pure effluent), 1:1, 1:2, 1:4 and 0:1 (pure tap water as control). The experiment was carried out in a glasshouse where Chinese green mustard and cucumber were used as test plants. Results showed that the plants irrigated with effluent mixtures had higher yields than those plants in the control set, and the ratio of 1:2 with ash addition showed a prominent result. In the second set of experiments, impacts of effluent on economic crops, rice and rubber tree, were investigated. It was found that the latex production of rubber trees irrigated with effluent was significantly higher, at 112±49% on average. However, in the paddy field experiment, empty-grain occurred in the effluent irrigated plot more than the control plot. This might be due to the impact of effluent application at grain-filling period. On the other hand, effluent application at pre-flowering significantly increased seed yield as compared to the applications at other stages of plant development and the control. Knowing the potential and method for correct application is of interest to the farmers since it can increase crop yields and reduce spending and application of chemical fertilizer, and finally eliminating additional cost for wastewater treatment. [Copyright &y& Elsevier]

Abstract: The inoculum of some species of the genus Colletotrichum, responsible for the secondary leaf fall of rubber tree (SLF), is present as conidia on all the organs of the tree. On young lesions, the fungus produces acervuli, but on old lesions kept in prolonged wetness, conidia are produced without acervuli. Acervuli occur frequently on senescent tissues, especially on the epidermis of the fruits, which are infected in the early stages of their development. The fungus can spread from diseased organs to healthy organs and sporulate on them. Conidial production and pathogenicity differ greatly according to the organ of the rubber tree from which the fungus is isolated. The higher the leaf wetness duration and the inoculum concentration are, the greater are fungal sporulation and damage. Although heavy rains and high winds favour conidial dispersal, it can also occur in drizzle. Heavy dew is sufficient to ensure downward dispersal of the conidia. The epidemiological pattern of the disease in a rubber tree plot during 1.5 years agrees with all these observations. The results of these investigations will enable the control of the disease to be improved in the rubber estate of Mitzic (Gabon). [Copyright &y& Elsevier]

• The latex has high gene expression specificity comparing with other tissues. • Natural rubber biosynthesis is a principal metabolic activity in latex. • Ubiquitin-proteasome system is a primary regulation system in latex. • Ethylene and jasmonate signaling pathways perform different functions in latex. Natural rubber, produced in the laticifers of the para rubber tree (Hevea brasiliensis), is a valuable biopolymer of commercial and strategic importance. While the basic pathway of rubber biosynthesis has been established, further understanding of its regulatory mechanisms might be obtained by studying laticifer-specific gene expression. Here, gene expression patterns was investigated in five different tissues of the rubber tree to explore differentially expressed genes (DEGs). The expression of 4122 high expression genes and 6485 low expression genes in the laticifer was enriched in various metabolic pathways related to rubber biosynthesis. The study results suggest that isopentenyl pyrophosphate (IPP), a principal precursor of natural rubber, is supplied mainly via the mevalonate (MVA) pathway in rubber biosynthesis, rather than the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. The ubiquitin-proteasome system (UBS) that is surprisingly active in the laticifer might serve as an important metabolic control mechanism in rubber biosynthesis. The involvement of latex specific transcription factors (TFs) was identified in seven plant hormone signal transductions, suggesting that jasmonate (JA) signaling is active in the positive regulation of rubber biosynthesis. [ABSTRACT FROM AUTHOR]

Plant male sterility (MS) is an important agronomic trait that provides an efficient tool for hybridization and heterosis utilization of crops. Based on phenotypic and cytological observations, our study performed a multi-comparison transcriptome analysis strategy on multiple sterile and fertile rubber tree varieties using RNA-seq. Compared with the male-fertile varieties, a total of 1590 differentially expressed genes (DEGs) were detected in male-sterile varieties, including 970 up-regulated and 620 down-regulated transcripts in sterile varieties. Key DEGs were further assessed focusing on anther development, microsporogenesis and plant hormone metabolism. Twenty DEGs were selected randomly to validate transcriptome data using quantitative real-time PCR (qRT-PCR). Eleven key genes were subjected to expression pattern analysis using qRT-PCR and fluorescence in situ hybridization. Among them, nine genes, i.e., A6 , GAI1 , ACA7 , TKPR1 , CYP704B1 , XTH26 , MS1 , MS35 and MYB33 , that regulate callose metabolism, pollen wall formation, tapetum and microspores development were identified as candidate male-sterile genes. These findings provide insights into the molecular mechanism of male sterility in rubber tree. • Provide an alternative strategy to reduce the interference caused by genetic background in transcriptome analysis. • Atrophic protoplasts, decomposed organelles, and defective exine are common features in aborted microspores. • DEGs are involved in pathways related to callose metabolism, pollen wall formation, tapetum and microspores development. • A6 , GAI1 , ACA7 , TKPR1 , CYP704B1 , XTH26 , MS1 , MS35 and MYB33 are candidate genes related to male sterility in rubber trees. [ABSTRACT FROM AUTHOR]

• We estimated rubber tree biomass and nutrient stocks over a plantation cycle. • Nutrient accumulation rate in trees peaked between 2 and 5 years after planting. • 25–36 % of the stocks of N, P and K at the clear-cut stage were accumulated at 5 years old. • Logging residues could account for 120–1126 % of the nutrient input through fertilizers over the entire rotation. Rubber trees are the main source of natural rubber (NR). The area occupied by rubber plantations rose from 3.9 million ha in 1961 to 12.5 million ha in 2018. Both the expansion of rubber plantations in marginal zones (prone to biotic and abiotic stress), and long-term rubber tree cultivation in traditional areas, raise questions about the sustainability of NR production in a context of climate change. Our study set out to gain insights into the biogeochemical cycles in rubber plantations, for a better matching of fertilizer inputs to the dynamics of nutrient demand throughout rubber tree growth. Nutrient accumulation in tree biomass is a major component of the biological cycle in tree plantations. We studied the dynamics of biomass and nutrient accumulation in two chronosequences covering the whole lifespan of a plantation in Ivory Coast managed on a sandy soil at the SAPH site, and one on a clayey soil at the SOGB site. In total, 56 trees were destructively sampled in 2-, 5-, 20- and roughly 40-year-old stands. While the use of allometric relationships is common for estimating nutrient stocks in planted forests, this study was the first to provide allometric equations predicting nutrient stocks in rubber tree components. Allometric models were applied to the inventory of 4 commercial stands, for each age at each site, to estimate stand biomass and nutrient stocks. The current annual increments of nutrient stocks in tree biomass peaked between 2 and 5 years after planting. They reached 80 kg ha-1 yr-1 for N, 14 kg ha-1 yr-1 for P and 34 kg ha-1 yr-1 for K at SAPH (53, 7, and 39 kg ha-1 yr-1 respectively at SOGB), which highlighted the importance of an appropriate fertilization schedule for young rubber trees. At the clear-cut age (38–40 years), the amounts of nutrients accumulated in tree biomass were 970 kg N ha-1, 188 kg P ha-1, 366 kg K ha-1, 941 kg Ca ha-1 and 255 kg Mg ha-1 on the sandy soil at SAPH (907,118, 629 1499, and 375 kg ha-1 respectively on the clayey soil at SOGB). Contrasting soil properties and management practices at the two sites had a much greater effect on the amounts of P, K, Ca and Mg accumulated in the trees than on N accumulation. Logging practices in rubber plantations can lead to considerable nutrient exports on poor tropical soils. Harvest residues should be distributed uniformly in the plots so that the roots of young trees can quickly gain access to the nutrients released during decomposition. [ABSTRACT FROM AUTHOR]

Tree crop growers are particularly sensitive to commodity price fluctuations. Since 2012, rubber prices have been decreasing. This article provides a comprehensive analysis of how Thai family farms responded to that continuous decrease in rubber prices. The originality of this work was to combine a farming system approach for decision making with the sustainable rural livelihoods' framework for resource endowment and strategies to benefit from the complementarities of these two theoretical approaches. An existing database was used characterizing the rubber farms and farmers' practices in 2011 when the rubber price was at its maximum. A subsample of farmers was interviewed again in 2017 after six years of price decreases to characterize the new situation and to identify and explain the changes. Fifteen flexibility mechanisms to face the crisis were implemented at three different levels: rubber cropping system, farming system and activity system. Combinations of these mechanisms identified eight strategies of adaptation to the crisis, classified on the reversibility of the changes. Three major types of strategies were identified: (i) reversible adjustments at the level of activity system variables, (ii) mobilization of available production factors to be invested in an activity that allows, over a longer time perspective, compensation for the disturbances caused by the crisis. This type of adaptation was reversible, but its implementation expressed motivation in the medium and long terms; (iii) reallocation of the production factors already mobilized at the level of the rubber cropping system toward other activities, to compensate the disturbances caused by the crisis. This last type induced a deeper transformation in the distribution of the production factors in the activity system and was anchored in a long-term vision. The first type corresponded to a dynamics of disturbances absorption to maintain the smallholders' systems and overcome the crisis; the two other types corresponded to dynamics of compensation with more or less reversible changes. Overall, this study confirmed the capacity of adaptation of family agriculture when facing shocks. It also showed that the flexibility of these households relied greatly on rubber cropping systems through possible technical change and through the adaptation of the share-tapping labor contract. This highlighted the importance of considering farmers' practices (and changes of practices) to understand their strategies. • Family rubber farms were resilient to market shocks. • Flexibility mechanisms were adopted from cropping system to activity system levels. • Adaptation of the rubber cropping system offered high flexibility to the households. • The strategies of adaptation included different degrees of reversibility. • Both dynamics of absorption and compensation for the crisis were observed. [ABSTRACT FROM AUTHOR]

• Model on preferential and non-preferential flow domains (PFD and NPFD) was developed. • Soil properties in the PFD led to a quick water response to rainfall. • PFD was of low storage and high flow capacities while NPFD has opposite features. • The two domains interrelated each other and that was helpful for rubber tree growth. • The findings have great implication to hydrological modeling and soil water supply. Preferential flow has always been hotspot of research regarding soil water flow, biological activity, and carbon and nitrogen dynamics. However, the mechanism of water flow exchange between two adjacent zones (with and without root system) and the pattern of soil water supply for rubber are still unclear. In the present study, we considered two plots experiencing similar farming history: in the first plot we measured soil physical properties and soil volumetric water content (VWC) during rainfall, and the second plot was used to visualise water flow path and to measure root biomass. Besides, a model was developed on preferential flow domain (PFD, matching the root zone) and on non-preferential flow domain (NPFD, matching the remote root zone) to compute differences in soil properties between the PFD and NPFD. The results revealed that the dominant flow type in the PFD was preferential flow and the one in the NPFD was capillary flow. Dye stained area and wetting front rate negatively correlated with bulk density, while they positively correlated to non-capillary porosity and root biomass. Accordingly, PFD showed a quick response to rainfall. Indeed, during the rain, a lateral flow (driven by water gravity and pressure head gradient) predominantly carried water (0.95, 0.27, and 0.44 cm3 cm−3 for various rainfall events 1, 2, and 3, respectively) from PFD to NPFD. During the soil drainage stage, the lateral flow direction changed, and water (about 0.63, 0.30, and 0.39 cm3 cm−3 for rainfall events 1, 2, and 3, respectively) flowed from NPFD to PFD. As a result, PFD presented low storage and high flow characteristics compared with NPFD, suggesting this complementary relationship for water interaction between the two domains could be beneficial for rubber plants growth and development. [ABSTRACT FROM AUTHOR]

• Melatonin improve rubber tree seedlings tolerance to salt stress. • Melatonin enhance salt stress tolerance directly or indirectly by counteracting H 2 O 2 accumulation in rubber tree. • Melatonin enhances salt tolerance by regulating the genes involved in photosynthesis, ROS metabolism, flavonoids and melatonin biosynthesis to counteract the cellular accumulation of H 2 O 2 in rubber tree. As a well-known agent, melatonin plays very important roles in animals. However, its possible function is less clear in plants, especially in rubber tree. In this study, we demonstrate that melatonin acts as a potential agent to enhance salt stress tolerance in rubber tree seedlings. Chlorophyll degradation and H 2 O 2 accumulation in leaves of seedlings under salinity stress were significantly relieved by melatonin treatment. Transcriptome analyses suggested that melatonin was a potential antioxidant, and its exogenous application resulted in enhanced antioxidant protection mainly by regulating the genes involved in photosynthesis, ROS metabolism, flavonoids and melatonin biosynthesis. These results demonstrate that melatonin can enhance salt stress tolerance directly or indirectly by counteracting the cellular accumulation of H 2 O 2 in rubber tree. Our findings are helpful for not only understanding melatonin's roles in salinity stress, but also providing new insights into potential utilization of melatonin against abiotic stresses in rubber tree. [ABSTRACT FROM AUTHOR]

• Tolerance to drought were investigated in four rubber tree clones. • Clone PR255 was the most susceptible to drought. • The clones GT1, IAC40, and RRIM600 were superior in their stability and efficiency of energy use. • Ecophysiological characteristics to identify tolerant clones were selected. Rubber tree cultivation distributed over a wide geographic area. Plant cultivation in these areas, however, generally imposes some type of abiotic stress such as drought. In order to identify the mechanisms responsible for rubber tree tolerance to, and recuperation from, drought conditions, we investigated some physiological characteristics associated with photosynthesis in five-month old plants of four different clones (RRIM 600, IAC 40, PR 255, and GT 1) exposed to progressive soil water deficits and the subsequent reestablishment of irrigation. The plants were submitted to 32 d of imposed drought (32 DIS) followed by soil rehydration for 15 d (15 DSR), totaling 47 d of experimental procedures. Gas exchange, chlorophyll fluorescence, relative water content, water potential (Ψw), cell viability, and photosynthetic pigments, proline, and hydrogen peroxide concentrations were evaluated. Decreasing Ψw resulted in diminishing photosynthetic and transpiration rates, as well as stomatal conductance in the clones. With the exception of the seedlings of clone PR 255, limitations of intracellular CO 2 concentrations under water deficit conditions were related to reductions in stomatal conductance. Photochemical processes as well as concentrations of hydrogen peroxide and proline were altered by water deficits in all of the clones, although all of the physiological processes recovered after 15 DSR in all of the clones. Clone PR 255 was the most susceptible to drought, showing photosynthetic electron transport inefficiency and the lowest cell viability. The clones GT 1, IAC 40, and RRIM 600 were found to be superior to clone PR 255 in terms of their growth and oxidative metabolism under water stress conditions, suggesting their greater adequacy for rubber tree cultivation in nontraditional areas experiencing hot, strongly sunny periods with low humidity during the rainy season or winter, and/or irregular rainfall. [ABSTRACT FROM AUTHOR]

The location of organic matter within the aggregate is a key factor for stabilizing and storing soil organic carbon (SOC). In this context, the purpose of this study was to answer the following question: How much is the contribution of aggregate associated-C in total SOC accumulation up to 1 m under different land uses in the Atlantic rainforest zone of Brazil? The experimental areas were: a secondary-forest; 3 and 5-year-old eucalyptus plantation; 35-year-old rubber tree plantation; and 50-year-old unfertilized pasture. Soil samples were collected at six different depths (0–10, 10–20, 20–40, 40–60, 60–80 and 80–100 cm), air dried and separated by wet-sieving into three fraction-size classes (2000–250 μm; 250–53 μm and <53 μm) – corresponding to macroaggregate, microaggregate and silt-and-clay size fraction, respectively. The ultrasonic method was used to quantify the C physically-protected in macro and microaggregates. Macroaggregates accumulated higher amounts of C (C Ma) than microaggregates (C Mi). The amount of C Ma stock in all land-use systems ranged from 33 to 8 Mg ha−1, and the C Mi ranged from 11 to 7 Mg ha−1. This represents around 22 to 4% and 7 to 4%, respectively, of physically protected C in the SOC storage up to 100 cm. The amount of C Ma + C Mi up to 1 m was 43 Mg ha−1 and 36 Mg ha−1 under 3- and 5-year-old eucalyptus plantations; 30 Mg ha−1 in the in secondary forest; and 19 Mg ha−1 in the rubber plantation and pasture. The C stabilization within aggregates represents a significant mechanism of C protection in these soils. • The aggregate associated-C storage was averaged 29 Mg ha−1 up to 100 cm. • The amount of aggregate associated-C was high in macroaggregate over the soil profile. • 3 and 5-year old pasture-eucalyptus conversion enhanced the C physically protected. [ABSTRACT FROM AUTHOR]