Rubber Tree Growth Research Articles

Long term performance of certain ortets and hybrid clones of Hevea brasiliensis in a high altitude region in Kerala, India

Long term performance of four hybrid Hevea clones and ten ortet selections including nine from a high elevation site within the traditional rubber growing tract of Kerala was studied. Significant variability was observed among the hybrids and ortets for all major agronomic traits. Growth of rubber trees was invariably poor in the high altitude region and tappability by the tenth year of planting was less than 50 per cent. The hybrid clones RRII 203 and RRIC 100 showed highest growth vigour with 80 per cent tappability by the 13th year of planting. Among the ortets, P 270 and Iritty 1 recorded the highest tappability of 64 per cent. The ortet P 270 was the best performer with the highest girth at the opening (61 cm), girth increment during immaturity (5.5 cm) on tapping (3.4 cm) and bole volume (0.1 m3). RRII 203 was the highest yielding clone with 56 g tree-1 tap-1 over eight years of tapping. High annual yield (48 g tree-1 tap-1) and lean season yield of P 270 combined with high drc on par with the highest yielding clone RRII 203 indicated the specific adaptability of this ortet to high elevation areas. The ortets P 213 and Iritty 1 and hybrid clone RRIC 100 were the other promising clones exhibiting growth adaptation and high yield potential under high altitude conditions.

Pilot-scale production of Boletus colossus culture for promoting the growth of Para rubber trees

Boletus colossus is an Ectomycorrhiza fungi. It grows on roots of big trees such as Rubber tree, Mango tree and etc. This mushroom grows by using the organic materials released from the roots. The moisture adsorbed on the fungi makes the roots resist the drought better. The mushroom can also turn some insoluble inorganic materials into the form that plants can make use of. This research is to study the production of the starter culture by using low-cost media. The result shows that the fungi can grow best in whey to 9.2 g/L (dry weight) in 10 days. The liquid broth can inhibit the growth of pathogens (Alternaría brasicola, Alternaría pori, and Fusarium solani) on Potato-Dextrose agar. The starter culture can also be produced in a 50L fermenter to the dry weight of 8.1 g/L in 6 days. Loam is the best as solid carrier followed by peat moss. The result in one year shows that the Para rubber trees grow with the fungi that have significantly longer stems, leaves, and roots.

Genome-Wide Identification of Aluminum-Activated Malate Transporter (ALMT) Gene Family in Rubber Trees (Hevea brasiliensis) Highlights Their Involvement in Aluminum Detoxification

The rubber tree (Hevea brasiliensis) is a widely cultivated crop in tropical acidic soil that is tolerant to high concentration of aluminum and the aluminum-activated malate transporter (ALMT) plays an important role in plant aluminum detoxification. However, the effects of ALMT on rubber tree aluminum tolerance, growth performance, and latex production are unclear. In this study, 17 HbALMT genes were identified from the genome of rubber trees. The physiological and biochemical characteristics, phylogenetic relationships, gene structures, conserved motifs, cis-elements of promoter, and expression patterns of the identified HbALMT genes were studied. Phylogenetic relationships indicated that these genes were divided into four clusters and genes in the same cluster have similar gene structures and conserved motifs. The promoters of HbALMT genes contain many cis-elements associated with biotic stress and abiotic stress. Quantitative real-time PCR analysis revealed HbALMTs showed various expression patterns in different tissues, indicating the functional diversity of HbALMT genes in different tissues of rubber trees. Transcriptome analysis and qRT-PCR assay showed that most of the HbALMT genes responded to aluminum stress, and among the 17 HbALMTs, HbALMT1, HbALMT2, HbALMT13, and HbALMT15 displayed higher expression levels in roots after two or five days of Al treatments, indicating their potential involvement in aluminum detoxification. Taken together, this study laid a foundation for further understanding the molecular evolution of the ALMT genes and their involvement in rubber tree aluminum adaption.

Mapping rubber plantations in Xishuangbanna, southwest China based on the re-normalization of two Landsat-based vegetation–moisture indices and meteorological data

Information on where rubber plantations are located and when they were established is essential for understanding changes in the regional carbon cycle, biodiversity, hydrology and ecosystem services. Here, we proposed a simple and modified phenology-based method to map rubber plantations and evaluate the effectiveness of this method in Xishuangbanna in southwest China, the second largest area of natural rubber cultivation. Our phenological algorithm is supported by local meteorological data and involves the re-normalization of two Landsat-8 Operational Land Imager-derived vegetation moisture indices (i.e. the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Moisture Index (NDMI)). We then applied air temperature data (daily records from 1981 to 2015) and periodic in situ observations of rubber plantations (weekly records from 2017 to 2018) to determine the phenological stages of rubber tree growth with the goal of selecting the most effective Landsat images. The re-normalization algorithm was able to highlight the temporal differences in the vegetation canopy and moisture content of rubber plantations, because rubber trees in Xishuangbanna display unique defoliation-foliation signals during the dry season. The resultant map of rubber plantations showed a high overall accuracy of 92.3% and a Kappa coefficient of 0.846. The developed phenological re-normalization method with meteorological data greatly enriches remote sensing-based approaches for mapping rubber plantations.

Short-term effects of organic amendments on soil fertility and root growth of rubber trees on Hainan Island, China

Rubber [Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg.] plantations are the largest cultivated forest type in tropical China. Returning organic materials to the soil will help to maintain the quality and growth of rubber trees. Although many studies have demonstrated that organic waste materials can be used to improve soil fertility and structure to promote root growth, few studies have studied the effects of organic amendments on soil fertility and root growth in rubber tree plantations. Here, bagasse, coconut husk or biochar were applied with a chemical fertilizer to test their effects on soil properties after 6 months and compared with the effects of only the chemical fertilizer. Results showed that the soil organic matter content, total nitrogen, available phosphorus and available potassium after the chemical fertilizer (F) treatment were all significantly lower than after the chemical fertilizer + bagasse (Fba), chemical fertilizer + coconut husk (Fco) or chemical fertilizer + biochar (Fbi) (p < 0.05). Soil pH in all organic amendments was higher than in the F treatment, but was only significantly higher in the Fbi treatment. In contrast, soil bulk density in the F treatment was significantly higher than in treatments with the organic amendments (p < 0.05). When compared with the F treatment, soil root dry mass increased significantly by 190%, 176% and 33% in Fba, Fco and Fbi treatments, respectively (p < 0.05). Similar results were found for root activity, number of root tips, root length, root surface area and root volume. Conclusively, the application of bagasse, coconut husk and biochar increased soil fertility and promoted root growth of rubber trees in the short term. However, bagasse and coconut husk were more effective than biochar in improving root growth of rubber trees.

Integrated assessment of the natural conditions on suitability and adaptation of the project of conversion of dipterocarpaceae forest into rubber plantation in Dak Lak province

The results of surveys, investigation and assessment show that the climate conditions of dipterocarpaceae forests are relatively suitable for the growth and development of rubber trees. However, there are some rather severe indicators such as seasonal rainfall distribution, low humidity, inundation in rainy season and drought in the dry season; High and low temperatures reach the limit for the requirement of rubber trees. Most of dipterocarpaceae forest area consists of sandy or sandy soil, discrete soil texture, poor humus, poor water and nutrient retention, rapid heat absorption and transfer, at depths away from the surface of 20 - 40 cm is tombstone and gravel layer, under the clay, easily cause local inundation in the rainy season. The proportion of dipterocarpaceae forest land, which suitable for rubber trees is quite low, with the majority of adaptation levels S2 and S3, no suitable area at S1 level. In the first 2 years, the growth of rubber trees in dipterocarpaceae forest is less than that of rubber in upland fields, cleared land from evergreen forest, semi-evergreen forest. From the third year onwards, the difference in expression is clearer, in that the rubber tree’s diameter on the soil of the dipterocarpaceae forest is lower than that of the traditional rubber plantation at the same age.

Climbing the mountain fast but smart: Modelling rubber tree growth and latex yield under climate change

Pará rubber (Hevea brasiliensis Müll. Arg) plantations have expanded into regions with sub-optimal growth conditions: distinct dry seasons and temperatures cooler than in humid tropics. The impact of these new marginal environments and future climate change on rubber tree development and latex yield is largely unknown. This hampers reliable prediction of farmers’ revenues and extent of carbon sequestration at landscape level. To improve our understanding of rubber trees response to planting at high altitudes and associated increase in planting densities, we applied the process-based Land Use Change Impact Assessment tool (LUCIA). It was calibrated with detailed ground survey data from Xishuangbanna, southwest China to model tree biomass development and latex yield in rubber plantations at the tree, plot and landscape level. Plantations were analyzed at <900 m above sea level (a.s.l., lowland rubber) and ≧900 m a.s.l. (highland rubber) in order to characterize the effect of elevation on rubber trees. Three planting densities: low (<495 trees ha−1), medium (495–600 trees ha−1) and high (>600 trees ha−1) were tested. Four greenhouse gas emission scenarios, with Representative Concentration Pathways (RCP) ranging from the lowest RCP 2.6 to the highest emission scenario RCP 8.5, were used to test rubber tree response to climate change. During a 40-year rotation under current climate, lowland rubber plantations grew faster and had larger latex yields than highland rubber. The average biomass of lowland rubber was 9% and 18% higher than those of highland rubber for aboveground and belowground biomass, respectively. High planting density rubber plantations showed 5% and 4% higher above ground biomass than those at low- and medium-planting density, but simulations suggest that the cumulative latex production decreased strongly by 26% and 14% respectively. The results of the RCP 8.5 climate change scenario suggested that during 40 years simulation mean total biomass and cumulative latex yield of highland rubber (per tree) increased by 28% and 48%, while lowland rubber increased by 8% and 10% respectively when compared to the baseline. Other rubber cultivation regions could also benefit from this modelling approach that helps in optimization of carbon stock and latex production in rubber-based system. The results could help in development of future climate change adaption and mitigation strategies.

Growth of churches submitted to different doses of hydrogel and containers

The cultivation of rubber trees in Brazil has been established as a sustainable and profitable activity, despite all the challenges, the production of rubber trees grows considerably each year. In order to optimize this production, it is necessary to develop techniques for the production of seedlings that present vigor and quality. Therefore, the objective of this work was to evaluate the growth of rubber tree seedlings submitted to different doses of hydrogel and containers. The work was carried out in the seedling nursery of the State University of Mato Grosso, Campus Nova Xavantina. The dosages used were 0, 1, 2, 3 and 4g and the containers were polyethylene bags in dimensions 20x30 and 25x35 cm. To evaluate the effect of the treatments on the growth of the rubber tree seedlings the following variables were measured at 90 days after sowing: Height (cm), stem diameter (mm), H / D ratio, number of triphophils, root length), Dry matter of the leaves (g), dry matter of the stem (g), dry matter root (g). The experimental design was a randomized complete block (DBC) in a 2x5 factorial scheme, two containers and five hydrogel doses, with six replicates for each treatment. From the results obtained in the present work it can be concluded that the dosage of 1g.L -1 of hydrogel and the container 25x35 cm were the most suitable treatments for the initial development of the rubber tree seedlings.

Seasonal Changes Impact on Growth of Rubber (&amp;lt;i&amp;gt;Hevea brasiliensis&amp;lt;/i&amp;gt;) Seedlings under Different Cultivation

The vegetative growth of rubber tree is an important basis for rubber tree cultivation and economic management. Stem diameter and height growth patterns of rubber seedlings and the seasonal variability are still poorly understood. Studying the annual growth patterns and seasonal variation of rubber seedling will help understanding biological characteristics of rubber tree and provide a reference for field cultivation and management. Height growth and stem diameter of field-sown rubber seedlings cultivation and polybag-raised cultivation all displayed a distinct annual pattern of “slow-fast-slow”. Height growth and stem diameter growth response fitted the logistic equation preferably, supporting the observed pattern. Fast-growth of plant height for polybag-raised rubber seedlings cultivation and field-sown rubber seedlings cultivation occurred from June to November and May to November, respectively. This period saw the greatest accumulations of plant height growth for polybag-raised rubber seedlings cultivation and field-sown rubber seedlings cultivation accounting for 83.99% and 86.65% of total growth, respectively. Fast-growth of stem diameter for polybag-raised rubber seedlings cultivation and field-sown rubber seedlings cultivation occurred from June to November and May to November, respectively. This period saw the greatest accumulations of stem growth for polybag-raised rubber seedlings cultivation and field-sown rubber seedlings cultivation accounting for 86.71% and 84.60% of total growth, respectively. Polybag-raised rubber seedlings cultivation and field-sown rubber seedlings cultivation for the whole year had nine extension units and each month had one extension unit from May to November. Extension unit of for the whole year did not stop period and plant height growth rate has the seasonal difference. However, leaf phenophase of field-sown rubber seedlings cultivation was earlier than that of polybag-raised rubber seedlings cultivation and each extension unit of field-sown rubber seedlings cultivation was greater than that of poly-bag-raised rubber seedlings cultivation. The precipitation had the greatest impact on seedlings growth under different cultivation. There was no period annually in which height growth and stem diameter growth did not occur and the fastest growth occurred during the rainy season. Plant height and stem diameter of rubber seedlings under different cultivation showed isogony phenomenon. Extension unit and leaf phenophase of polybag-raised rubber seedlings and field-sown rubber seedlings showed consistency and synchronization characteristic. Different cultivation of rubber seedling should take corresponding measures tending management and operation.

Effects of aluminum toxicity on physiological and leaf chlorophyll fluorescent characteristics of rubber tree seedlings.

Aluminum toxicity is common in tropical acid soils. However, its effects on rubber tree growth and latex production are still unclear. Using potted sand culture seedlings of rubber tree, the effects of different aluminum ion concentrations on physiological and chlorophyll (Chl) fluorescence characteristics were investigated. The results showed that the cell membrane permeability, free proline content, and soluble sugar content were significantly increased, while the relative water content, catalase and peroxidase activities, Chl a content, Chl maximum fluorescence yield, maximum photosynthesis efficiency and potential activity of PSII, photochemical quenching coefficient, non-photochemical quenching coefficient and photosynthetic electron transport rate were significantly decreased when the saplings were subjected to AlCl3 treatments with concentration higher than 200 mmol·L-1. When the AlCl3 concentration was lower than 100 mmol·L-1, the aforementioned parameters did not show any significant variation among different treatments for the entire duration of the experiment. These results indicated that the rubber tree could tolerate some degree of aluminum toxicity. The threshold concentration of aluminum toxicity for rubber tree seedlings would be between 100 to 200 mmol·L-1. When this threshold was exceeded, aluminum toxicity would cause irreversible damage to rubber tree seedlings.

Peeling of small diameter rubber log using spindleless lathe technology: evaluation of veneer properties from outer to inner radial section of log at different veneer thicknesses

Rubber forest plantation (RFP) in Malaysia was currently governed by small holders who provided lower diameter logs as they managed plantation using higher planting density, higher frequency tapping practice and young-tapping systems to enhance latex harvesting yield and fulfil demand for rubber timber. Nevertheless, these new planting systems will affect the growth of rubber tree and result in the production of smaller diameter (< 20 cm) rubber logs compared to conventional planting systems. Hence, this raises the question of the small diameter log with respect to its impact on veneer quality. The aim of this study is to determine the properties of rubberwood veneers manufactured from outer to inner radial section of log at different veneer thicknesses. The rubber logs with diameter less than 20 cm were peeled up to 3 cm of peeler core to produce 1, 2 and 3 mm veneer thickness using spindleless lathe. Veneer properties such as thickness variation, lathe checks, surface roughness and contact angle were evaluated from outer to the inner radial section of log at three different veneer thicknesses. Results showed that rubber trees are suitable for peeling due to its consistent density ranging from 650 to 706 kg/m3. Better visual grades recovery can be obtained when peeling thinner rubberwood veneers. The thickness variation, lathe check depth, length and surface roughness of rubberwood veneers increased with increasing veneer thickness, whereas lathe check frequency decreased with increasing veneer thickness. In general, veneer thickness has more prominent effects on the properties of rubberwood veneer compared to the effect of log radial section.

In Vitro Propagation of Rubber Tree (Hevea Brasiliensis) Using Shoot-Tip and Nodal Cutting Explants

Hevea brasiliensis which belongs to the Euphorbiaceae family is the primary source of natural rubber. Propagation of rubber tree by grafting on to unselected seedlings sustains intraclonal heterogeneity for vigour and productivity which could be improved via in vitro techniques. Micropropagation from rubber nodal and shoot tip explants is possible. In vitro technique is needful to mass propagate disease-free and genetically similar rubber plantlets. In vitro results in increased growth and vigour of rubber tree, However, in vitro techniques of rubber tree have not been given much critical research attention in Ghana. Propagation of H. brasiliensis by in vitro techniques was used to study alternative procedures for mass production of rubber planting materials. Murashige and Skoog (MS) basal medium amended with 30.0g/L sucrose, 100.0mg/L myo-inositol, 2.0g/L activated charcoal, 1.0mg/L silver nitrate AgNO3, 2.0mg/L GA3 and control, 2.5, 5.0, 7.5 or 10.0mg/L kinetin was used to culture both H. brasiliensis shoottip and nodal explants. The MS medium with 5.0mg/L kinetin significantly (P<0.05) enhanced higher shoot development (84.00%), number of shoots (3.60) and leaves (23.40) of the shoot-tip explants compared to other treatments. In nodal explants, the control medium developed higher shoots (94.00%), the height of shoot (4.80cm), number of leaves (19.20), number of shoots (6.00) and number of roots (7.00) than those with kinetin treatments. Conversely, 7.5mg/L kinetin of the nodal culture also performed significantly after the controls. Successful in vitro regeneration of plantlets was achieved using Hevea brasiliensis shoot-tip and nodal cutting explants cultured on an MS medium supplemented with kinetin.

PENGARUH TANAMAN SELA SORGUM MANIS TERHADAP PERTUMBUHAN TANAMAN KARET BELUM MENGHASILKAN

The Land between row of immature rubber period has a potential to produce sweet sorghum. This sorghum is one of high value commodities for food and energy security due to its wide adaptation. The objective of this research were to study the effect of rubber+sorghum intercropping system on the growth of immature rubber trees and to study some agronomic parameters of sorghum and production of sweet sorghum as rubber intercrops. The experiment was conducted at the Sembawa Research Station from June to October 2013. The experiment was carried out as a single factori using Randomized Block Design with three replications. The treatment were 3 varieties of sorghum i.e: Pahat, Kawali and Mandau. Observation of rubber trees was conducted using simple random sampling method, comparing the rubber trees growth of sorghum intercropping system with the rubber trees growth of monoculture system. The results showed that sorghum had a positive effect on the growth of rubber tree IRR 118. Furthermore, fresh stem weight (37.11 t/ha), juice yield (1.80 t/ha), and grains yield (2.69 t/ha) of sweet sorghum Kawali higher than that of the varieties tested. The Kawali has a high potential to produce a biofuel because it had a highest fresh stem weight and juice content.

The plant defense and pathogen counterdefense mediated by Hevea brasiliensis serine protease HbSPA and Phytophthora palmivora extracellular protease inhibitor PpEPI10.

Rubber tree (Hevea brasiliensis Muell. Arg) is an important economic crop in Thailand. Leaf fall and black stripe diseases caused by the aggressive oomycete pathogen Phytophthora palmivora, cause deleterious damage on rubber tree growth leading to decrease of latex production. To gain insights into the molecular function of H. brasiliensis subtilisin-like serine proteases, the HbSPA, HbSPB, and HbSPC genes were transiently expressed in Nicotiana benthamiana via agroinfiltration. A functional protease encoded by HbSPA was successfully expressed in the apoplast of N. benthamiana leaves. Transient expression of HbSPA in N. benthamiana leaves enhanced resistance to P. palmivora, suggesting that HbSPA plays an important role in plant defense. P. palmivora Kazal-like extracellular protease inhibitor 10 (PpEPI10), an apoplastic effector, has been implicated in pathogenicity through the suppression of H. brasiliensis protease. Semi-quantitative RT-PCR revealed that the PpEPI10 gene was significantly up-regulated during colonization of rubber tree by P. palmivora. Concurrently, the HbSPA gene was highly expressed during infection. To investigate a possible interaction between HbSPA and PpEPI10, the recombinant PpEPI10 protein (rPpEPI10) was expressed in Escherichia coli and purified using affinity chromatography. In-gel zymogram and co-immunoprecipitation (co-IP) assays demonstrated that rPpEPI10 specifically inhibited and interacted with HbSPA. The targeting of HbSPA by PpEPI10 revealed a defense-counterdefense mechanism, which is mediated by plant protease and pathogen protease inhibitor, in H. brasiliensis-P. palmivora interactions.

Hierarchical classification approach for mapping rubber tree growth using per-pixel and object-oriented classifiers with SPOT-5 imagery

There has been growing interest in Malaysia to increase the productivity of latex. This made accurate knowledge of rubber tree growth and age distribution a helpful decision making tool for the government, rubber plantation managers, and harvesters. Gathering this information using conventional methods is difficult, time consuming, and limited in spatial coverage. This paper presents hierarchical classification approach to obtain accurate map of rubber tree growth age distribution using SPOT-5 satellite imagery. The objective of the study is to evaluate the performance of pixel-based and object-oriented classifiers for rubber growth classification. At the first level, the general land cover was classified into eight land cover classes (soil, water body, rubber, mature oil palm, young oil palm, forest, urban area, and other vegetation) using Mahalanobis distance (MD), k-nearest neighbor (k-NN), and Support Vector Machine (SVM) classifiers. Thereafter, the best classification map, k-NN output, was used to select only pixels that belong to the rubber class from the SPOT-5 image. The extracted pixels served as input into the next classification hierarchy where four classifiers, MD, k-NN, SVM, and decision tree (DT), were implemented to map rubber trees into three intra-classes (mature, middle-aged, and young rubbers). The result produced overall accuracy of 97.48%, 96.90%, 96.25%, and 80.80% for k-NN, SVM, MD, and DT respectively. The result indicates that object-oriented classifiers are better than pixel-based methods mapping rubber tree growth.

PENDUGAAN POTENSI KEBUN KARET RAKYAT SEBAGAI CADANGAN KARBON DI KECAMATAN CEMPAKA KOTA BANJARBARU PROPINSI KALIMANTAN SELATAN

Calculation of carbon stocks using allometric equation system is done to get the value of carbon stocks in smallholder rubber plantations in Cempaka district, Banjarbaru City South Kalimantan needs to be done in order to know the carbon stocks contained in the smallholder rubber plantations. Based on the statistical report plantation Banjarbaru City first quarter of 2013, the people's rubber plantation area of 986 hectares. However, data obtained from field surveys note that the data are actually rubber plantation area of 1318.61 ha. This study aims to determine the amount of carbon stocks in jungle rubber at different age levels and determine other factors that affect carbon stocks in jungle rubber. The methods of this study includes data collection and determination of the point of the plot as well as the selection of a plot point. Primary data collection is done by taking the coordinates of the field (the survey) using a GPS (Global Positioning System), and the data analysis was conducted on the data collection for the measurement of carbon stocks above the surface of the carbon on the surface and below the surface measuring carbon stocks. The results showed that the highest carbon stocks contained in the 7-year age group with a score of 716.61 Mg carbon stocks / ha followed by 5-year age group was 685.21 Mg / ha, 3-year age group was 603.51 Mg / ha and the smallest to the carbon value of 585.62 Mg / ha. While based on the factors that influence the obtained results that the pH is tolerated for acid soil types, categorized as very low C Organic, Organic materials in the high category, total N and P were categorized very low, K can be categorized as high. All these factors are still can be considered good for the growth of rubber trees until they reach the age of 30 years. Concluded that the more composition and structure of rubber gardens stands then the greater carbon storage in stands in people rubber plantation area at the Cempaka district Banjarbaru City and soil conditions can be categorized as land that can still be used for the growth of rubber trees.

A COMPARISON OF THREE FIELD LAYOUT SYSTEMS FOR MECHANISATION DURING EARLY PHASE OF RUBBER CULTIVATION

Mechanisation is needed to alleviate the shortage of labour in plantation agriculture. The first step towards a successful implementation of many mechanised operations in plantation agriculture is the need to have a field layout system which will facilitate bringing mechanised operations into the interior of the field. In fact, the implementation of such a field layout system must be done as early as possible after land clearing. This will allow more field operations to be mechanised. The design of such a layout system for rubber growing areas poses challenges since the crop is often planted on sloping to hilly terrain. A comparison was made for three field layout systems which comprised of an inter-connecting network of terraces which were: (a) 3.7 m wide, (b) 5.5 m wide and (c) double terraces of 2.7 m width for each terrace. It was seen that the 5.5 m wide terrace was the best in terms of speed to complete field operations coupled with good growth of rubber. However, this broad terrace can be difficult to construct on very steep areas especially when the soils are also shallow. Observations carried out at a very much later stage of 70 months after planting, showed that this area had a very large number of vacant points which would result in a lesser number of trees available for tapping later on. Thus, on the practical side, balancing performance in mechanisation, ease of terrace construction and anticipated number of trees available for tapping, a field layout system made up of terraces of 3.7 m width, would be the most suitable design for mechanisation in rubber cultivation. Keywords: Mechanisation, field layout system, terrace design, rubber tree growth.

Dinitrogen fixation by the legume cover crop Pueraria phaseoloides and transfer of fixed N to Hevea brasiliensis—Impact on tree growth and vulnerability to drought

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 N2-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 N2 fixation was estimated using the abundance of 15N (δ15N) 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 N2 fixed by the cover crop to the trees was estimated using δ15N in the tree leaves.The annual biomass production of the legume was 8Mgha−1 year−1 and the N accumulation by the legume was 250kg N ha−1 year−1. The natural abundance method applied to the aboveground components of the legume gave N2 fixation rates varying from 85 to 93% depending on the year. The leaf δ15N was similar in the three non-legumes (H. brasiliensis, Vetiveria zizanioides and Praxelis clematidea) used as reference plants for estimating the N2 fixation. The higher level of N and the much lower leaf δ15N 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 N2 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: 28cm, tree height: 700cm). 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.

Molecular identification and characterization of the pyruvate decarboxylase gene family associated with latex regeneration and stress response in rubber tree

In plants, ethanolic fermentation occurs not only under anaerobic conditions but also under aerobic conditions, and involves carbohydrate and energy metabolism. Pyruvate decarboxylase (PDC) is the first and the key enzyme of ethanolic fermentation, which branches off the main glycolytic pathway at pyruvate. Here, four PDC genes were isolated and identified in a rubber tree, and the protein sequences they encode are very similar. The expression patterns of HbPDC4 correlated well with tapping-simulated rubber productivity in virgin rubber trees, indicating it plays an important role in regulating glycometabolism during latex regeneration. HbPDC1, HbPDC2 and HbPDC3 had striking expressional responses in leaves and bark to drought, low temperature and high temperature stresses, indicating that the HbPDC genes are involve in self-protection and defense in response to various abiotic and biotic stresses during rubber tree growth and development. To understand ethanolic fermentation in rubber trees, it will be necessary to perform an in-depth study of the regulatory pathways controlling the HbPDCs in the future.

Weed Control Strips Influences on the Rubber Tree Growth

Hevea brasiliensis (rubber tree) is the most widely cultivated tree species for producing natural rubber latex whose productivity can be reduced by weeds. Field experiment was carried out during two years to evaluate the growth of rubber tree plants submitted to different weed control strips (0-weed-free, 50, 100, 150, 200, 250, 300, 350, and 400-(weedy cm) and to determine the critical width of weed control strip during the establishment of rubber tree plantation. Weed community was composed mainly by Urochloa decumbens (90%). The width of the weed control strip influenced on the initial plant growth of rubber trees, reducing the plant height, stem diameter, leaf area, and aboveground dry mass accumulation. In consequence, crop plantation was affected by the width of weed control. The critical width of the weed control strip for establishment of a rubber tree plantation was within 100 cm.