Rubber Clones Research Articles

Physiological Behavior of Rubber Plants (<i>Hevea Brasilliensis</i>) to Different Soil Moisture Conditions

Drought conditions can severely impact rubber (<i>Hevea brasiliensis</i>) plantations, leading to economic loss in Malaysia. The study aimed to assess the impact of varying soil moisture levels on the physiological characteristics of five latex timber clones (LTCs) of rubber, with the goal of identifying the most suitable clone for specific soil moisture conditions. These conditions include (1) field capacity, (2) 75% available water (AW), (3) 50% AW, (4) 25% AW, and (5) wilting point, with the ultimate objective of optimizing cultivation methods and fostering sustainable rubber production in Malaysia. The five clones under investigation include RRIM3001, RRIM2025, RRIM2001, RRIM928, and PB350. Leaf chlorophyll content, stomatal conductance, and net photosynthesis were measured 4 and 8 months after treatment (MAT). The findings indicated significant effects of moisture stress on various physiological attributes, including total chlorophyll content, relative chlorophyll content, stomatal conductance, and net photosynthesis rate. At 4 and 8 MATs, the clones subjected to field capacity exhibited the highest values for these physiological characteristics, followed by those exposed to 75% available water, with the lowest values observed at the wilting point. RRIM3001 consistently exhibited the highest total chlorophyll content, stomatal conductance, and net photosynthesis among the clones at both sampling dates. The highest net photosynthesis was observed in the RRIM3001 clone under field capacity conditions. Furthermore, a significant positive correlation was identified between total chlorophyll and relative chlorophyll contents, as well as between net photosynthesis and stomatal conductance. These findings carry practical implications for water management during the initial growth phase of rubber seedlings and for replanting initiatives in rubber plantations.

EVALUACIÓN DEL PRENDIMIENTO Y DESARROLLO DE CLONES DE CAUCHO (Hevea brasiliensis) PROPAGADOS POR INJERTO EN LA SELVA PERUANA

<p><strong>Background.</strong> The latex yield in <em>Hevea brasiliensis</em> trees is highly variable; Therefore, it is important to propagate commercial clones of this species by grafting in order to standardize or improve latex yields and therefore improve the economic income of producers in this part of the Amazon region. <strong>Objective.</strong> To evaluate the attachment and development of rubber clones propagated by grafting in the Peruvian jungle. <strong>Methodology.</strong> Nine-month-old patterns installed in the field were used. These were grafted with budding rods from the commercial clones TR-1, FX-3864, RRIM-600, IAN-873 and MDF-180. A completely randomized block design was used with five treatments and three blocks with 15 experimental units; each containing 30 repetitions. The data obtained were subjected to analysis of variance and Tukey's multiple range test (p<0.05) and the Kruskal Wallis test. <strong>Results.</strong> The best results in attachment and number of shoots were obtained in grafts with clone MDF-180 with values of 73.33 % and 7.83 shoots respectively; Regarding days to the appearance of the shoot and length, clone TR-1 presented it with 36.63 days and 27.47 cm; The largest leaf area was presented by the graft with clone IAN-873 with 55.46 cm<sup>2</sup>, while the highest chlorophyll content was obtained in grafts with clone RRIM-600 with 47.18 SPAD. <strong>Implications</strong>. More studies are required to establish the quality and adaptability of rubber clones propagated by grafting in different site conditions and establish patterns of tree productivity in a short time; Likewise, it is desired to evaluate the quality and quantity of latex produced by these clones. <strong>Conclusions.</strong> These results indicate the feasibility of propagating <em>Hevea brasiliensis</em> through shoot grafting in the field, which opens great possibilities for propagating rubber trees with better commercial characteristics, particularly with greater latex production.</p>

Genetic analysis of agronomic and physiological traits associated with latex yield revealed complex genetic bases in Hevea brasiliensis

Hevea brasiliensis, a natural rubber producing species, is widely cultivated due to its high rubber yield potential. Natural rubber is synthesised in the rubber particles of laticifers. Latex diagnosis (LD) was established to characterise the physiological state of the laticiferous system by measuring its physiological parameters, i.e., sucrose, inorganic phosphorous (Pi), thiols and total solid content (TSC). Rubber clones are often classified in three groups i.e., quick starters, medium starters and slow starters. To better understand the genetic bases of latex yield, a biparental population was generated from a cross between the quick-starter clone PB 260 and the medium-starter clone SP 217. LD was performed during the peak latex production season and used to calculate sucrose loading. The agronomic and physiological parameters associated with latex yield led to the classification of genotypes according to the rubber clonal typology and to the identification of quantitative trait loci (QTL) using a high-density map. Inorganic phosphorous content was positively associated with yield during the first year of production thus enabling identification of quick-starter clones. In addition, the LD-based clonal typology led to determine the long-term yield potential and the use of appropriate ethephon stimulation. QTL analysis successfully identified several QTLs related to yield, sucrose, Pi and TSC. One QTL related to sucrose loading was identified in the same position as the QTL for sucrose on linkage group 1. To our knowledge, this is the first study to report QTL analysis for this trait. The use of a high-density map enables the identification of genes underlying QTLs. Several putative genes underlying QTLs related to yield, sucrose and TSC were identified.

Comparative growth response of three rubber (Hevea brasiliensis Muell. Arg) clones in somatic embryo propagation

Abstract Plants have the ability to grow with different responses depending on the clones and varieties of plants. In rubber plants, each clone has specific characteristics or traits that distinguish it from other clones, whether in terms of growth, latex production, or resistance to pests and diseases. The objective of this experiment was to assess the response of three rubber (Hevea brasiliensis Muell. Arg) clones to the same media conditions for the growth and development of somatic embryos (SE). Integuments from three rubber clones, namely PB 260, PB 330, and PB 340, were used as explants to induce embryonic callus on MH media. After four weeks post-induction, the callus was sub-cultured to expressed SE then SE was transferred to the RITA® bio-reactor for plantlets development in liquid MD media. Parameters for each steps, such as the percentage of contamination, percentage of callus response, color of callus, percentage of SE induction, number of stage of SE, and number of shoots were recorded. The results revealed that the highest percentage of viable callus was observed in the PB 260 clone at 23.20%. On SE expression, the highest being in clone PB 340 at 2.04%. On SE development the highest shoot growth was observed in the PB 260 clone, with a total of 5 shoots.

The Influence of Climate Change on Rainfall and Rainy Days for Rubber Production of Kusen Clone in Rambang District, Muara Enim Regency

Extreme rainfall impacts rubber production, reducing effective tapping days and cumulative annual output and having a wide-ranging effect on rubber crop cultivation. This study aimed to find out how rainfall and rainy days affected the rubber production of the Kusen clone in Muara Enim Regency’s Rambang District. The study was conducted on a rubber plantation of Kusen clone, which has an area of 1 ha. The initial stage in analyzing the impact of climate change on Kusen clone rubber production in Rambang District, Muara Enim Regency, was identifying the independent and dependent variables. The T-test was conducted to see whether each independent variable partially has a significant effect on the dependent variable. Rubber production has fallen year after year, with an average of 205.12 kg/ha in 2019 during the first year of tapping and 118.43 in 2023. The coefficient value (r) shows a 27.2% (sufficient correlation) magnitude association between the rainfall and rainy-day variables and the rubber productivity variable of the Kusen clone. In Correlation test results, rainfall and rainy days are strongly associated with producing Kusen clone rubber, as demonstrated by the correlation analysis value of 0.846. Regression research showed that rainfall and rainy days had a statistically insignificant effect on rubber production on the rubber clone Kusen in Rambang District, Muara Enim Regency.

Comparative transcriptomic analysis of rubber (Hevea brasiliensis) clones differing in disease tolerance provides novel insights into the disease response associated with abnormal leaf fall disease caused by Phytophthora meadii

Rubber is an important industrial commodity and Hevea brasiliensis is the commercial source of natural rubber (NR). Abnormal Leaf Fall (ALF) disease caused by Phytophthora meadii is one of the major diseases affecting yield of NR. Understanding Hevea-Phytophthora interaction mechanism is essential to manage this devastating disease. Transcriptome analysis was employed to gain an understanding on the molecular mechanisms that confer resistance to Phytophthora that would facilitate development of disease-tolerant Hevea clones. As our current understanding of Hevea-Phytophthora interaction is limited, an attempt was made to analyze and compare the transcriptomes of tolerant and susceptible clones of H. brasiliensis in response to P. meadii infection (in healthy and Phytophthora challenge-inoculated condition) during early, middle and late phases of infection by using the RNA-Seq technology. The transcriptome sequencing generated an average of 19,000 differentially expressed genes (DEGs) in both clones. When comparing the tolerant clone to the susceptible clone, there was an overall increase in the number of DEGs and a progression in the number of DEGs, indicating a more active engagement of transcriptional activity in the tolerant clone. Functional annotation, KEGG analysis and enrichment analysis revealed that the major pathways enriched for the DEGs were involved in plant hormone signal transduction and plant-pathogen interaction. An analysis of DEGs during each phase showed that the most active transcripts involved in defense mechanisms were activated during mid-phase and in the case of susceptible clone least transcripts were induced during mid-phase than in any other phase in both the clones. Many DEGs belonging to the MYB, NAC, WRKY and AP2/ERF transcription factor families were observed in both clones. Comparative studies revealed their differential involvement in tolerant and susceptible clones against Phytophthora infection. These findings may facilitate further exploration of Hevea-Phytophthora interaction and in cloning for defense related genes.

Overexpression of HbGRF4 or HbGRF4-HbGIF1 Chimera Improves the Efficiency of Somatic Embryogenesis in Hevea brasiliensis.

Transgenic technology is a crucial tool for gene functional analysis and targeted genetic modification in the para rubber tree (Hevea brasiliensis). However, low efficiency of plant regeneration via somatic embryogenesis remains a bottleneck of successful genetic transformation in H. brasiliensis. Enhancing expression of GROWTH-REGULATING FACTOR 4 (GRF4)-GRF-INTERACTING FACTOR 1 (GIF1) has been reported to significantly improve shoot and embryo regeneration in multiple crops. Here, we identified endogenous HbGRF4 and HbGIF1 from the rubber clone Reyan7-33-97, the expressions of which dramatically increased along with somatic embryo (SE) production. Intriguingly, overexpression of HbGRF4 or HbGRF4-HbGIF1 markedly enhanced the efficiency of embryogenesis in two H. brasiliensis callus lines with contrasting rates of SE production. Transcriptional profiling revealed that the genes involved in jasmonic acid response were up-regulated, whereas those in ethylene biosynthesis and response as well as the S-adenosylmethionine-dependent methyltransferase activity were down-regulated in HbGRF4- and HbGRF4-HbGIF1-overexpressing H. brasiliensis embryos. These findings open up a new avenue for improving SE production in rubber tree, and help to unravel the underlying mechanisms of HbGRF4-enhanced somatic embryogenesis.

Climate Influences on Latex Yield in South Sumatra, Indonesia

This study addresses the impact of climate variability on latex yield. Field research was carried out in the Indonesian Rubber Research Institute Experimental Field, located in South Sumatra, Indonesia for 2020 to 2022. The study used mature IRR 118 clones of rubber (Hevea brasiliensis) planted in clay loam soil. Latex yields for dry and rainy seasons were compared to obtain the effects of climatic factors. A purposive sampling of latex clone IRR 118 was applied in the field. The results showed that declined rainfall and soil moisture content contributed to the low latex yield during dry season. A declined water availability acts as a limiting factor resulting in decreased latex yield. Latex yield consistently decreased when soil moisture content fell below 21.5%. Based on statistical analysis, the correlation between latex yield and climate factor was 0.36, 0.42, and 0.52 for rainfall, soil moisture content, and evapotranspiration, respectively. Our findings highlight the crucial influence of climatic factors, emphasizing the significance of optimal water availability for latex production.

Physiological characteristics of IRR 400 series rubber clones (Hevea brasiliensis Muell. Arg.) under drought stress

Background Drought stress is one of the main causes of plant death. Strategies for plants survival are morphological adaptations, specific signaling pathways, and tolerance mechanisms. Rubber plantations have many uses, such as foreign exchange sources, job sources, forest revitalization, and a source of alternative wood for building materials and furniture. The rubber plant’s response to drought stress is a complex biological process. A tolerant rubber clone in a dry area is the right approach. The present study aimed to identify drought tolerant traits in order to select or identify drought-tolerant clones at juvenile stage. Methods The first factor examined for this work was clones (IRR 425, IRR 428, IRR 429, IRR 434, IRR 440, RRIC 100, and BPM 24) and the second factor was water content (30%, 60%, and 90%). The study was arranged on a factorial randomized block design and repeated three times. Characteristics observed were total sugar (µM), proline (mg/L), chlorophyll a, b, total (µg/mL), hydrogen peroxidase (µmol/g), ascorbate peroxidase (unit/mg), superoxide dismutase (unit/mg), and peroxide dismutase (unit/mg). Results The tolerance ability of the IRR 400 series rubber clones to drought stress was determined by observing the characteristics of sugar total and proline. The concentration of total sugar and proline were higher when the plant was treated with a lower water content. The selected clones tolerant to drought stress are RR 425 and IR 434 with high total sugar content and proline. Other characteristics, namely chlorophyll a, b, and total, as well as hydrogen peroxidase, ascorbate peroxidase, super oxide dismutase, peroxide dismutase, cannot be used as selection characteristics for this study. Conclusions This drought study of IRR 400 clones with varying water content percentages illustrated that the total sugar and proline characteristics could be used to distinguish tolerance levels from other observed characteristics.

Physiological characteristics of IRR 400 series rubber clones (Hevea brasiliensis Muell. Arg.) under drought stress

Background: Drought stress is one of the main causes of plant death. Strategies for plants survival are morphological adaptations, specific signaling pathways, and tolerance mechanisms. Rubber plantations have many uses, such as foreign exchange sources, job sources, forest revitalization, and a source of alternative wood for building materials and furniture. The rubber plant’s response to drought stress is a complex biological process. A tolerant rubber clone in a dry area is the right approach. The present study aimed to determine the mechanism of drought-tolerant clones, based on physiological characteristics, to obtain character selection and drought-tolerant clones early. Methods: The first factor examined for this work was clones (IRR 425, IRR 428, IRR 429, IRR 434, IRR 440, RRIC 100, and BPM 24) and the second factor was water content (30%, 60%, and 90%). The study was arranged on a factorial randomized block design and repeated three times. Characteristics observed were total sugar (µM), proline (mg/L), chlorophyll a, b, total (µg/mL), hydrogen peroxidase (µmol/g), ascorbate peroxidase (unit/mg), superoxide dismutase (unit/mg), and peroxide dismutase (unit/mg). Results: The tolerance ability of the IRR 400 series rubber clones to drought stress was determined by observing the characteristics of sugar total and proline. The concentration of total sugar and proline were higher when the plant was treated with a lower water content. The selected clones tolerant to drought stress are RR 425 and IR 434 with high total sugar content and proline. Other characteristics, namely chlorophyll a, b, and total, as well as hydrogen peroxidase, ascorbate peroxidase, super oxide dismutase, peroxide dismutase, cannot be used as selection characteristics for this study. Conclusions: This drought study of IRR 400 clones with varying water content percentages illustrated that the total sugar and proline characteristics could be used to distinguish tolerance levels from other observed characteristics.

Combination of exploitation systems to optimize yield of GT1 clone in smallholder rubber (Hevea brasiliensis) plantation in Sumatera Utara, Indonesia

Clone GT1 is one of the low metabolism clones and is recommended for smallholder and large plantations. These clones are responsive to stimulants and reach production peak at the mid-economic cycle period. Its production can reach 2200-3000 kg-1ha-1year-1 and is relatively more resistant to high exploitation pressures if the agroecosystem conditions are suitable. This study aimed to determine the effect of the combined application of liquid stimulant concentration and tapping interval on the physiology and productivity of latex in rubber clone GT1. This research was conducted at Naga Rejo Village, Galang District, Regency of Deli Serdang, Province of Sumatera Utara, located at an altitude of 49 masl with Ultisol soil type. The research design is factorial randomized completed block design (RCBD) consisting of 9 levels, namely S2d4 without a stimulant, S2d4 ET 3.5%, S2d4 ET 4.5%, S2d5 without a stimulant, S2d5 ET 3.5%, S2d5 ET 4.5%, S2d6 without a stimulant, S2d6 ET 3.5%, S2d6 ET 4.5 % with three replicas of each treatment. The results showed that the tapping system on clone GT1 obtained the highest annual production with tapping system S2d4 ET 4.5% (DS3) of 214.51 g/t/y. The lowest production is obtained in January-March when the leaves fall. High sucrose levels in the non-stimulant treatment (8.54 -12.98 mM) indicated that at least sucrose was converted into latex. The pH of latex is directly proportional to the stimulant, so an increase in the concentration of the stimulant raises the pH and metabolism of latex formation.

Molecular Investigation on Expression Analysis of Tapping Panel Dryness (TPD) Syndrome Associated Genes in Rubber Tree (Hevea brasiliensis Muell.Arg.)

Rubber clones especially high yielding clones (RRII 105, PCK2, PB 217, and GT 1) are considered to be susceptible to Tapping Panel Dryness (TPD) syndrome. The main objective of this study was to find the significance of TPD associated genes in rubber tree and their expression of mRNA transcript level by Real Time PCR and Semi-Quantitative RT-PCR. A total of 15 TPD associated candidate genes were screened by RT-real time PCR. Among these, 8 candidate genes were analysed by Semi-Quantitative RT-PCR. RT-real time PCR result revealed that among 15 genes screened, mRNA transcript level of 3 genes (TOM 20, TCTP, and Myb 1) was down-regulated significantly in various TPD affected clones of rubber tree compared to healthy and their expression pattern was altered in different rubber clones due to various degrees of TPD tolerance. Semi-Quantitative RT-PCR results proved a down-regulation of five genes (TOM 20, TCTP, Myb 1, ABC, and PT2) in the TPD tree in comparison to the healthy tree. The findings of this study confirmed that the mRNA transcript levels of the TOM 20, TCTP, and Myb 1 genes were significantly lower in various rubber clones that had been affected by TPD and also suggested that these genes may be crucial for the development of TPD, which results in impaired latex biosynthesis in rubber trees.

Physiological characteristics of IRR 400 series rubber clones (Hevea brasiliensis Muell. Arg.) under drought stress

Background: Drought stress is one of the main causes of plant death. Strategies for plant survival include triggering of specific signaling pathways and tolerance mechanisms. Rubber plantations have many uses, including in forest revitalization and as foreign exchange sources, job sources, and as an alternative source for building materials and furniture. The rubber plant’s response to drought stress is a complex biological process. Planting tolerant rubber clone in drought prone areas would be more appropriate. The present study is aimed to identify drought tolerant traits in order to select drought-tolerant clones at juvenile stage itself. Methods: The first factor examined for this research was the clones (IRR 425, IRR 428, IRR 429, IRR 434, IRR 440, RRIC 100, and BPM 24), with water content (30%, 60%, and 90%) as the second factor studied. The study was arranged on a factorial randomized block design and repeated three times. Characteristics observed included total sugar (µM), proline (mg/L), chlorophyll a, b, total (µg/mL), hydrogen peroxidase (µmol/g), ascorbate peroxidase (unit/mg), superoxide dismutase (unit/mg), and peroxide dismutase (unit/mg). Results: The tolerance ability of the IRR 400 series rubber clones to drought stress was determined by observing the concentrations of total sugar and proline, which were higher when the plant was treated with a lower water content. The selected clones tolerant to drought stress were RR 425 and IR 434 with high total sugar and proline. Other characteristics, namely chlorophyll a, b, and total, as well as hydrogen peroxidase, ascorbate peroxidase, superoxide dismutase, and peroxide dismutase, cannot be used as selection characteristics for this study. Conclusions: This drought study of IRR 400 clones with varying water content percentages illustrated that the total sugar and proline characteristics could be used to distinguish tolerance levels.

Pengaruh Penambahan Ekstrak Jeruk Purut (Cytrus hitrix D.C) Sebagai Koagulan Alami Terhadap Karakteristik Karet

Natural rubber is a plantation commodity that has a significant role in the country's economy. This study aims to determine the effect of the natural coagulant extract of kaffir lime with centrifugation and non-centrifugation treatment on the coagulation process, pH and coagulation time, characteristics of rubber clone IRR 118 and comparison of the quality of rubber with 2% formic acid chemical coagulant. The volume of coagulant used was 75 mL mixed with 150 mL of latex, so that coagulation occurred and produced coagulum. Then the resulting coagulum is analyzed for the characteristics of the rubber to determine the quality of the rubber. Characteristic analysis carried out was Dry Rubber Content (DRC), Initial Plasticity (Po), Plasticity Retention Index (PRI), Mooney Viscosity, ash content, impurities content, volatile matter content, and nitrogen content. The results showed that the natural coagulant extract of kaffir lime could coagulate latex, lowering the pH of latex thereby speeding up coagulation time. From the rubber characteristic test using kaffir lime natural coagulant it complies with SNI 06-1903-2017 SIR 20. The quality of rubber produced from using kaffir lime natural coagulant extract as a coagulant can equate the quality of rubber produced by using 2% formic acid chemical coagulant, but coagulant The natural ingredients used have drawbacks, namely the availability of seasonal fruit, and the need for treatment before being used as a coagulant.

Study of Five Clones with Combinations of Growth Regulators Based on Growth and Anatomical Characteristics of Rubber Plant (Hevea brasiliensis L.)

As an export commodity, rubber is a major contributor to Indonesia's foreign exchange. Regarding the increase in rubber production, a study on combinations of growth regulators and rubber clones has been carried out based on plant growth and anatomical characteristics during the immature plant period. This research is conducted for eighteen months at the KSO Karang Inong plantations, PTPN-I, and PTPN-III, East Aceh District, using five clones. This study adopts a nested design with three factors: clones, Growth Regulators (GRs), and paclobutrazol. The clones used are PB 260, IRR 104, IRR 112, IRR 39, and 105. The GRs combination factor between IAA and Kinetin consists of seven levels and three levels of paclobutrazol. The results show that the rubber clones PB260 and IRR105 give higher stem girth and plant height than the other clones when applied with GRs at six different levels. The most expansive leaf area is found in clone IRR 104 compared to other clones. In addition, paclobutrazol affects plant height. Applying paclobutrazol can reduce plant height for all clones but increases stem girth, skin thickness, number and diameter of latex vessels, and total chlorophyll at 46 months after treatment.

Somatic Embryo (SE) Formation from Culturing Floral Explants of Rubber Tree (Hevea brasiliensis Muell. Arg.) and Assessment of Genetic Stability by RAPD and SSR Markers

Rubber tree is economically important rubber producing plant of Thailand. At present, a rubber tree plantation is susceptible to white root disease. Therefore, the use of rootstock from early introduce clone that proved to be resistant to white root disease could help sustain growing of rubber tree. Thus, the objectives of this research were to study the effects of plant growth regulators and different explants on somatic embryo (SE) induction of this rubber clone and assessment genetic stability. The results revealed that mix flower explant cultured on MS medium supplemented with 2.0 mg/L 6-benzyladenine (BA) and 1.5 mg/L 2,4-Dichlorophenoxyacetic acid (2,4-D) provided callus subsequent somatic embryo (SE) formation at the highest frequency of 39.84 % and number of cotyledonary embryos (CEs) at 3.25 embryos /callus after 3 passages of subculture in the same culture medium (4 weeks/passage). SEs germinated into embryonic axis at 50 % and further development into shoot at 25 % after transfer to 0.25 mg/L GA3 containing MS medium with the best concentrations of BA and 2,4-D for 4 weeks. The assessment gene stability by RAPD and SSR markers showed no variation between mother plant and in vitro plantlets. In this work, a novel explant source - the floral section of the rubber tree - was used for the first time in order to design an effective technique for in vitro somatic embryogenesis. HIGHLIGHTS The first report on plantlets regeneration using floral explant of rubber tree This mother plant is proved to be resistance to Phytopthora leaf fall and white root diseases Assessment genetic stability of regenerated plantlets by SSR and RAPD markers GRAPHICAL ABSTRACT

Canopy reflectance spectra’s variability, physical traits’ uniqueness and the prediction of rubber clones (Hevea brasiliensis)

Before implementing any further precision agriculture applications, the crucial task is to determine the rubber (Hevea brasiliensis) clones. This paper addresses the potential of using canopy spectral indices (CSIs) to delineate mature rubber clones. Each rubber clone responds differently to its local environment. Unfortunately, checking a sizeable mature rubber plantation and determining each rubber tree’s clone is tedious and time-consuming. It is, therefore, of interest and objective to classify and predict rubber clones via CSIs. This study highlighted statistically significant differences in the physical and spectral functional traits’ variability among nine mature rubber clones in a micro-agroclimatic environment with uniform management practices. We analysed the trunk girth, leaf physical properties and multispectral remote sensing data collected by a low-cost unmanned aerial vehicle (UAV) to explore the mature rubber canopy’s spectral indices, which are a crucial unique trait of rubber clones. We found that rubber leaf area increases with leaf mass. There is a positive relationship between trunk girth and leaf mass per area (LMA). Furthermore, leaf density and NDVI have a strong relationship that potentially links both traits. The additional assessment indicates that none of the 89 CSIs independently could discriminate between all nine rubber clones. However, several CSIs could distinguish several individual rubber clones or two or more groups of rubber clones. The classification results selected B1, NDVI, NDRE, RB3B2B4, GARI and BWDRVI as the most important CSIs. The generated models estimated that individual rubber clone prediction by CSIs provided low to moderate overall accuracy between 41.8 ± 5.3% and 82.3 ± 3.9%. Despite the variability, our findings highlighted a promising approach using CSI traits as a practical way to achieve accurate rubber clone predictions because of their uniqueness for specific clones or groups of clones.

Assessing the determinant factors of risk strategy adoption to mitigate various risks: An experience from smallholder rubber farmers in West Kalimantan Province, Indonesia

Abstract Over the past decade, smallholder rubber farming experienced significant issues related to risks of rainy season, rubber diseases, and price decreases. The risk exposure will reduce agricultural productivity, income, and sustainability. Farmers are expected to mitigate various risks by adopting the appropriate risk strategy. Efforts to support the risk strategy adoption are constrained by the lack of scientific research in rubber farming, especially for simultaneous risk strategy adoption. This study aims to identify the risk strategy adoption in rubber farming and analyse the determinant factors by considering farmers’ socioeconomic, rubber farm characteristics, and risk perception. The data were collected from 200 rubber farmers in West Kalimantan, Indonesia, and analysed using a multinomial logit model. The study results show that the most selected strategy was income diversification. The multinomial logit model indicates that farmers’ age, family members, rubber age, rubber clones, and rainy season risk perception positively affect the adoption of risk strategy. In contrast, experience, farm area, and farm distance have a negative effect. The results also indicate that family members, farm area, and farm distance variables significantly affect all choices of risk strategy adoption. The results of this study suggest several implications for government and policymakers in providing assistance and counselling, capital assistance, input access, and improving transportation, road access, and communication.

New leaf fall disease in rubber-pathogen characterization and rubber clone resistance evaluation using detached leaf assay

Abstract. Darojat MR, Ardhie SW, Oktavia F, Sudarsono. 2023. New leaf fall disease in rubber-pathogen characterization and rubber clone resistance evaluation using detached leaf assay. Biodiversitas 24: 1935-1945. Leaf fall disease (LFD) has become a significant issue for rubber plantations worldwide. Over the last four years, a newly emerging LFD has posed an alarming problem in natural rubber production. The most efficient way to control LFD is to use resistance rubber clones. Therefore, this study aims to characterize the pathogen causing the newly emerging LFD and evaluate rubber clone resistance to the pathogen using detached-leaf assay. The fungal pathogens were isolated from 32 F1 progenies of PB 260 x SP 217 crosses, and the fungi were characterized and identified based on their morphological and molecular characteristics. The results showed that the isolated pathogen causing LFD was Neopestalotiopsis sp. Although they were all pathogenic, the arrays of isolated fungi exhibited various degrees of virulence, and P-212 was the most virulent fungal isolate. The resistance evaluation showed that rubber clones, isolates, and rubber clones by isolate interactions had a significant (p<0.05) effect on the lesion-symptom diameters. Based on the lesion diameter responses, the IRR 112 and RRIC 100 rubber clones were resistant to Pestalotiopsis sp. since they only showed less than 10 mm lesion diameters. The IRR 39 and PB 260 rubber clones were susceptible and showed more than 20 mm lesion diameters. The detached-leaf assay can easily screen rubber clones' responses to the fungi causing LFD. The resistance evaluation results can assist future rubber breeding strategies for the newly emerged LFD-resistant characters.

Prediction of Rubber Yield Based on Soil Water Content

Fluctuation of monthly rainfall resulted in fluctuation of monthly rubber yield. This study was aimed to determine a model to predict rubber yield based on soil water content. This study was conducted at Indonesian Rubber Research Institute, South Sumatera in May 2022. The plant materials used in this study were rubber clones PB 260 that were planted in 2001 in two blocks of rubber field. The soil texture in these two blocks was clay loam with good drainage conditions. The average of monthly soil water content and rubber yield data for 11 years from the first block was used to determine the model. Whereas the average of monthly soil water content and rubber yield data for 12 years from the second block was used to validate the model. The soil water content was generated by field water balance calculation. The regression and correlation analysis showed that the highest correlation and the most suitable model to predict rubber yield based on soil water content was the power model with formula Y = 0.0668X2.1423 (coefficient of determination (R2) = 0.80). Where, Y = rubber yield (kg/month) and X = soil water content (%). Furthermore, the validation of the model showed that the goodness of match (GOM), Pearson correlation coefficient (R), coefficient of determination (R2), and root mean square error (RMSE) were 0.94, 0.95, 0.90. and 10.3 respectively. These values showed that the model was accurate and strong enough to predict rubber yield based on soil water content.