Rubber Clones Research Articles

Rubber Agroforestry Systems (RAS) in West Kalimantan, Indonesia: An historical perspective

In 1994 in the Sanggau/Sintang area in West Kalimantan province, most farmers relied mainly on jungle rubber, an old agroforestry system based on rubber seedling with low productivity, low establishment cost and low maintenance but high biomass and biodiversity. Most farmers at that period wanted to have access to clonal rubber planting material in order to improve their productivity (rubber clones do produce 3 times more than seedlings). The CIRAD/ICRAF/IRRI project called SRAP (Smallholder Rubber Agroforestry project) has set-up in 1994 on farm trials with 60 farmers in order to optimize clonal based new RAS according to local conditions and constraints. When SRAP started (1994/2007), the original objectives were multiple: i) to provide clone and high rubber productivity, ii) to maintain agroforestry practices to profit from positive externalities, and iii) to diversify income through timber, fruits, resins (Gaharu, Damar…) and other forest products (rattan, medicinal plants, forest vegetables etc). In 1997, came in the landscape oil palm estates though the very high and rapid development of private concessions. Oil palm became in the 2000’s the main priority for most smallholders. Today, all forest and most local jungle rubber have disappeared to the profit of roughly 2/3 of the area planted with oil palm (estates and smallholder) and 1/3 with clonal rubber for smallholder, either in monoculture or agroforestry. In 2019, CIFOR/FTA program funded a mission to CIRAD to obtain information about the evolution of RAS trials plots evolution in the province of West Kalimantan. The survey provide an idea of the historical and current trend in terms of local farming strategies concerning agroforestry. It raised also the question of clonal planting material availability for replanting and the poor tapping quality that lead to a reduction of the clonal rubber lifespan. Evolution of trials status over the period1994/2019 display the following results: i) Conversion to oil palm (20 %) or to clonal rubber monoculture (20 % mainly in Trimulia in Transdmigration area), ii) with agroforestry systems maintained in RAS 1 or 2 (50 %) and iii) evolution to tembawang at the end of rubber lifespan (10 %). We are back to the same problems faced in 1994: poor access to clonal planting material, no training on tapping frequency and practices but with some knowledge on clones and AF practices. The lessons learned are the following: i) Rubber agroforestry trials came right in time in 1994, with a strong demand from farmers, ii) but oil palm came in 1997 with a very strong pressure from concession companies providing a lucrative alternative to rubber cultivation with full credit (but loss of land) and better return to labor, iii) Interest in agroforestry practices remains high for old men but no interest is witnessed from younger generation, iv) It is now time for rubber replanting but the same old story remains: poor access to planting material), v) no good tapping practices, poor technical information available). These are essential to be able to maximize tree lifespan up to 35 years long.

Progress of Rubber Breeding Program to Support Agroforestry System in Indonesia

The use of superior rubber planting materials is one of the most important components of technology to support the cultivation and sustainability of the natural rubber industry. The effect of the genetic components of planting materials to the rubber productivity can reach 60%, and the rest is the influence of agro-climatic conditions. The aim of the rubber plant breeding program is to obtain the new superior rubber clones that have a high latex yielding potential and good agronomic characters. The fluctuations of natural rubber price and climate changes also influence the direction and objectives of the rubber plant breeding program. To deal with the conditions, it is important to provide the rubber agroforestry technology by through intercropping of rubber with various other crops. The article will provide the information about progress of rubber breeding program in Indonesia and it is role in supporting agroforestry system. Several of new superior rubber clones have been released by IRRI, and some of these clones such as IRR 112 and IRR 118 had been planting with rice, corn, and other crops by through rubber agroforestry system. The system was estimated be able to maintain latex yielding potential of clones as well as farmers’ income can be improved.

Effect of tapping rest during wintering months on latex yield and tapping panel dryness in three rubber (<em>Hevea brasiliensis</em>) clones

<em>Hevea brasiliensis</em> (Muell Arg.) undergoes annual leaf shedding commonly known as wintering. The wintering period in the traditional rubber growing areas in the Wet Zone of Sri Lanka is from December to February followed by flowering and flushing in March. Tapping rest during wintering is recommended in certain countries while in some other countries year round tapping is practiced. In Sri Lanka, until early1970s winter resting was practiced, but this is not being practiced at present. Incidence of tapping panel dryness appears to be high with currently recommended clones and hence the objective of the present study was to investigate on the effect of winter resting on the annual yield and tapping panel dryness in rubber clones. Experimental trials were conducted for two consecutive years (2018 and 2019) with three clones viz., RRIC 100, RRIC 121 and RRISL 203 at the Substation of RRISL at Kuruwita in Ratnapura district. Treatments tested were continued tapping with no winter rest (T1), resting during the wintering period (T2) and once in six days tapping during the wintering period (T3). Trees were tapped at S/2d3(once in three days) intensity. Data were collected on latex volume, bark consumption and TPD incidences. Results for two years showed higher g/t/t/ in all three clones when rested during the wintering period in both years as compared to those with no winter rest. Significantly higher annual total crop (kg) was recorded for T1 when compared to T2 in all three clones for both years. Though total number of partially and totally dry trees of winter rested trees of clones RRIC 100 and RRIC 121 were low, the differences were not significant. In terms of profits obtained as indicated by economic analysis, resting the trees during wintering resulted in the highest profits, followed by d6 tapping during the same period. Winter rest should be tested for a longer duration (4-5 years) for all the clones recommended at present that are vulnerable to tapping panel dryness.

Physiological and Productivity Impact of Mechanical Wounding and Mortex Stimulation on Rubber Clones RRIM 2025 and PB 350

The effects of mechanical wounding involving mechanical boring and tapping followed by the application of Mortex, an ethylene-based stimulant, on Hevea clones RRIM 2025 and PB 350 were investigated. Mortex at three different concentrations of 0.75%, 2.5% and 5% were applied at the tapping panel and the response of both clones in influencing wound-induced ethylene, latex yield, sugar, thiol and proline contents were determined. Data were analysed against control 1 (untapped and unstimulated), control 2 (tapped and unstimulated) and the application of nanosilver solution (Silversol), an ethylene inhibitor containing Ag+. Latex yield of both clones appeared to be induced and dependent on ethylene stimulation. Mortex at 2.5% was suggested to be optimum for high yield stimulation in both clones. Application of 5% Mortex gave the highest yield for both clones and induced highest wound-induced ethylene release in the shaved bark of RRIM 2025. Meanwhile, 2.5% Mortex gave the highest wound ethylene evolution in shaved bark of PB 350. Wounding by tapping alone produced wound ethylene at low levels in both clones. The very low levels of accumulated wound ethylene found in bored holes at 2 cm above tapping cut was likely due to tapping activity and not influenced by Mortex application. Silversol was found to successfully inhibit ethylene action by reducing wound ethylene release in shaved bark of both clones. Reduced sucrose content in the latex with 5% Mortex was observed. In contrast, unstimulated trees and an application of Silversol appeared to reduce latex yield in both clones with a concomitant increase in sucrose content. Suppression of ethylene action by Ag+ also reduced thiol and inorganic phosphorus content, suggesting that Silversol was effective in overcoming the stress effects related to ethylene regulation.

Perceived extension needs of rubber production among farmers in Delta State, Nigeria

The need to develop a sustainable exploitation system for the Nigerian rubber farmers requires that extension services should be available to assist the farmers in specific areas that can help them function effectively and improve productivity. The study investigated the perceived extension needs of rubber production farmers in Delta state Nigeria. The specific objectives of the study were to determine sources of information on rubber production, varieties of rubber clones cultivated by the respondents, perceived extension needs of rubber farmers, and constraints to rubber production. A multi stage sampling technique was used to select 120 rubber farmers as respondents for the study. Data were analysed using frequency, percentages, means and Pearson Product Moment correlation analysis. Results showed that majority of the respondents (85.5%) were male, married (83.3%) and had average farming experience of 14 years. The NIG801 and NIG800 varieties were the local clones majorly cultivated and the GT1 and PB217 varieties were the exotic clones majorly cultivated. Findings also showed that respondents need production information on use of formic acid for latex coagulation (66.7%), use of ammonia for latex preservation (73.3%) and marketing information (60.8%). The constraintsindicated by the respondents were problem of land tenure (81.7%), lack of adequate credit facilities (70%), fire outbreaks (72.5%) among others. The result of the hypothesis showed that age (r = 0.199) had a positive significant relationship with farmers’ extension needs. It was recommended that extension personnel should be trained on techniques of rubber production in order to deliver effectively to the farmers.&#x0D; Key words: extension needs, rubber, farmers, Delta, Nigeria

Effect of exploitation system using a tapping stimulant on the production of four rubber plant clones (Hevea brasiliensis Mull-Arg.) in Bulukumba Regency

This study aims to determine the effect of tapping stimulants on the performance of four rubber plant clones. The study was conducted at Palangisang Estate, PT. PP London Sumatera Indonesia Tbk in Tamatto Village, Ujungloe District, Bulukumba Regency, South Sulawesi Province located at an altitude of 0-25 meters above sea level. The study was carried out from September to October 2019 as an experimental research using Nested Design consisted of two factors, rubber clones and exploitation system. Four rubber clones, PB 260, PM 10, RRIM 901, and GT1, were treated with 2.5% ethrel tapping stimulant which repeated on six trees for each clone. Latex weight and dry rubber content were measured compared to the control treatment. The results showed that the application of the tapping stimulants had a very significant effect on latex weight and dry rubber content. Highest latex weight was obtained from the application of the stimulant to GT 1 clone with 226.33 grams. However, clone PB 260 in the control treatment resulted in the highest dry rubber content (34.50%).

Growth and physiological response of selected clones of rubber grown under different water frequencies

Effects of water frequencies on growth and physiological response of different clones of rubber were investigated. Different clones of rubber were screened with different watering frequencies as everyday watering (EW), every 2 days (E2D), every 3 days (E3D), every 5 days (E5D), and every 7 days (E7D). The treatments EW and E2D were found to be suitable for all the five clones for increasing as shown in plant height. A similar result was also found for plant biomass after 4 and 8 months of treatments. Noticeably, watering had a pronounced positive effect on clone RRIM 3001 and greatly increased vigorous growth as shown in its highest height, largest girth circumference and relative growth rate after 8 months of different watering frequencies. This clone equally showed superior performance with a significantly higher total plant biomass after 4 and 8 months of watering frequencies compared to the other four clones. The result could be used in water management and the clone RRIM 3001 could be suitable for rubber production at the nursery stage and replanting exercise in rubber plantations.

Phenological patterns of defoliation and refoliation processes of rubber tree clones in the Colombian northwest

The knowledge of the defoliation-refoliation process in rubber cultivation allows the development of management strategies in the production system to improve rubber yield. The objective of this study was to determine the intensity and duration of defoliation-refoliation of rubber clones FX 3864, IAN 710 and IAN 873 in the municipality of Tarazá and the FX 3864 and IAN 873 clones in the municipality of Nechí (northwestern Colombia). From October 2015 to June 2016, the measurements of the necromass were carried out in each location for each clone. The light environment was quantified, employing the hemispheric photographs technique to estimate canopy openness percentage (CO) and leaf area index. The assessed weeks were grouped by Principal Component Analysis (PCA) based on the original phenology and climatic variables. The defoliation-refoliation process was analyzed descriptively using graphical representations of the trend for the phenological variables that best described this process. The relationship between climatic and phenological variables in the period evaluated was evidenced; the rainfall was the most critical climatic characteristic in the induction of the defoliation process. The leaf area index was reduced to a minimum value in February, with values of 0.52 for IAN 710 clone in Tarazá, and 0.64 for the IAN 873 clone in Nechí, which corresponded to the highest defoliation stage in both locations. The refoliation period was short (4 to 6 weeks) and occurred during the dry season for all the clones in both places.

Genetic diversity analysis of Corynespora cassiicola isolates on the rubber tree (Hevea brasiliensis) in Vietnam using ribosomal DNA internal transcribed spacer (rDNA-ITS) sequences and sequence-related amplified polymorphism (SRAP)

A total of 76 Corynespora cassiicola isolates collected from 16 rubber clones in several geographic regions of Vietnam, were studied for genetic diversity by ribosomal DNA internal transcribed spacer (rDNA-ITS) sequences and sequence-related amplified polymorphism (SRAP) techniques. Results of rDNA-ITS sequence analysis indicated 2 nucleotide polymorphisms at the 135th (cytosine/thymine) and 474th (guanine/adenine) base pair positions of rDNA-ITS region, which differentiated the 76 studied isolates into 3 clusters. All isolates could be uniquely distinguished by 208 polymorphism bands which generated 93.3% polymorphic ratio with SRAP markers. A dendrogram produced from UPGMA analysis based on Nei and Li’s coefficient divided the 76 C. cassiicola isolates into 2 main clusters. Cluster one included 54 fungal isolates of which 51 and 3 were observed in subgroup 1A and 1B, respectively. There were 22 C. cassiicola isolates belonging to cluster 2 with subgroups 2A and 2B consisted of 20 and 2 fungal isolates, respectively. Bootstrap values for groups one and two were 61% and 100%, respectively and the grouping was reliable, with similarity coefficient between the two main groups at 67%. rDNA-ITS sequence analysis revealed a new genetic group, signifying at least three C. cassiicola genetic groups that infect rubber trees in Vietnam. SRAP markers divided the studied isolates into two distinct groups, which correlated with geographical location rather than host source. To the best of our knowledge, this is the first demonstration using SRAP markers on the systematics of C. cassiicola isolates which cause the Corynespora leaf fall disease on various rubber (Hevea brasiliensis) clones in Vietnam.

Foliar and flowering phenology of three rubber (Hevea brasiliensis) clones in the eastern plains of Colombia

Annual defoliation and refoliation cycles that occur in rubber trees after 5 years of age have a strong interaction with foliar diseases attacks. The rubber phenology was studied in the eastern plains of Colombia, in the municipality of Puerto López, department of Meta, where variables such as foliar density, percentage of leaves in stages A, B, C and D and flowering density were evaluated in clones IAN 873, FX 3864 and RRIM 600, between August 2016 and September 2018. All three clones showed a foliar density higher than 80% with leaves in stage D, between March and December (weeks 12–50 of the year). The defoliation started in the last weeks of the year, with the beginning of the dry season. The refoliation extended until mid-March (week 11) in 2017, and until February (week 6) in 2018. The presence of leaves in stages A, B and C during 8–13 weeks was observed at the plantation level, according to the clone and the evaluation year. The duration of the refoliation per tree was on average 6.73 ± 0.22 weeks in 2017 and 4.42 ± 0.39 weeks in 2018. Flowering coincided with refoliation, during a period of negative water balance and high solar radiation. Expansion of inflorescences was observed in the first weeks of the year between January and March, with the absence of reproductive development when the crop was dominated by leaves in stage D.

MEDIA ROOT TRAINER MENGANDUNG COCOPEAT DAN GAMBUT MENDUKUNG PERTUMBUHAN DAN KUALITAS AKAR BATANG BAWAH KARET / Root Trainer Media Containing Cocopeat and Peat to Support Growth and Quality of Rubber Rootstock Roots

&lt;p&gt;The physical and chemical properties of the growing medium for &lt;em&gt;root trainer&lt;/em&gt; of rubber are critical to support plant growth. This study aimed to obtain the best medium for growing rootstock rubber seedlings in the &lt;em&gt;root trainer&lt;/em&gt;. Rubber clone PR 300 seeds were germinated for 21 days, then raised in &lt;em&gt;root trainer&lt;/em&gt; pots for five months. The treatments evaluated were a mixture of &lt;em&gt;cocopeat&lt;/em&gt;, Rawapening peat, and manure at different ratios. The experiment was designed in a Randomized Block Design, three replications, 30 plants per replicate, totaling 720 plants. The observed variables were N, P, K, Mg, C-organic content, pH, and cation exchange capacity of &lt;em&gt;cocopeat&lt;/em&gt;, peat, and manure, as well as plant growth (height, stem diameter, wet weight, and dry weight). ANOVA used for analyzing data, followed with the &lt;em&gt;Duncan Multiple Range Test&lt;/em&gt; at 5% level. The results showed that there were three best &lt;em&gt;root trainer&lt;/em&gt; media for PR 300 rubber rootstock seedlings were a mixture of &lt;em&gt;cocopeat&lt;/em&gt; + peat (1:1), &lt;em&gt;cocopeat&lt;/em&gt; + peat + manure (1:2:1), and &lt;em&gt;cocopeat&lt;/em&gt; + peat + manure (2:1:1). The growth and compactness of the roots are outstanding, so the seedlings are easily removed from the &lt;em&gt;root &lt;/em&gt;&lt;em&gt;trainer&lt;/em&gt; pots without significant damage. Based on the initiation and cost, the best &lt;em&gt;root trainer&lt;/em&gt; medium is a mixture of &lt;em&gt;cocopeat&lt;/em&gt; + peat + manure (1: 2:1). It is necessary to study the use of other types of peat soils apart from Rawapening. Also, it needs to be observed further plant growth after inoculation with the stem and after planting in the field.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords &lt;/strong&gt;: Planting medium, Rawapening peat, rubber clone PR 300.&lt;em&gt;&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt;&lt;br /&gt;&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Abstrak&lt;br /&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Sifat fisik dan kimia media tanam di dalam wadah &lt;em&gt;root trainer&lt;/em&gt; bibit karet sangat penting untuk mendukung pertumbuhan tanaman. Penelitian ini bertujuan mendapatkan media terbaik untuk pertumbuhan bibit batang bawah karet di dalam &lt;em&gt;root trainer&lt;/em&gt;. Benih klon karet PR 300 dikecambahkan selama 21 hari pada bedeng pengecambahan kemudian dipindah-tanam dan dibesarkan selama 5 bulan dalam pot &lt;em&gt;root trainer&lt;/em&gt;. Perlakuannya yaitu campuran &lt;em&gt;cocopeat&lt;/em&gt;, gambut Rawapening, dan pupuk kandang (pukan) pada berbagai ratio, dan kontrol. Penelitian dirancang secara Acak Kelompok, tiga ulangan, masing-masing 30 tanaman, sehingga totalnya 720 tanaman. Variabel yang diamati yaitu kandungan N, P, K, Mg, C-organik, pH, dan kapasitas tukar kation dari &lt;em&gt;cocopeat&lt;/em&gt;, gambut, dan pupuk kandang, serta pertumbuhan tanaman (tinggi, diameter batang, bobot segar, dan bobot kering). Data dianalisis dengan ANOVA, kemudian &lt;em&gt;Duncan Multiple Range Test&lt;/em&gt; pada taraf 5%. Hasil penelitian menunjukkan bahwa ada tiga macam media &lt;em&gt;root trainer&lt;/em&gt; terbaik untuk bibit batang bawah karet klon PR 300 yaitu campuran &lt;em&gt;cocopeat &lt;/em&gt;+ gambut (1:1), &lt;em&gt;cocopeat &lt;/em&gt;+ gambut + pukan (1:2:1), dan &lt;em&gt;cocopeat &lt;/em&gt;+ gambut + pukan (2:1:1). Pertumbuhan dan kekompakan akar sangat baik sehingga bibit mudah dilepas dari &lt;em&gt;root tainer&lt;/em&gt; tanpa kerusakan berarti. Berdasarkan kepraktisan dan biaya maka media &lt;em&gt;root trainer&lt;/em&gt; terbaik adalah campuran media &lt;em&gt;cocopeat &lt;/em&gt;+ gambut + pukan (1:2:1). Perlu dilakukan kajian mengenai pemanfaatan tanah gambut jenis lainnya selain dari Rawapening. Selain itu, juga perlu diamati lebih lanjut pertumbuhan tanaman setelah diokulasi dengan batang atas maupun setelah ditanam di lapangan.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Kata kunci &lt;/strong&gt;: Gambut Rawapening, klon karet PR 300, media tanam.&lt;/p&gt;

Genome Wide Identification of the MLO Gene Family Associated with Powdery Mildew Resistance in Rubber Trees (Hevea brasiliensis)

Powdery mildew (PM) is one of the most destructive diseases affecting rubber trees (Hevea brasiliensis), leading to severe yield losses. Sulfur dusting is used to control the propagation of the disease, and no specific fungicides have been developed yet. Therefore, identification of genetic level disease resistance in the rubber trees is very crucial. In this study, we describe the whole-genome sequencing of a PM resistant rubber clone, RRIC 52, as well as a PM susceptible clone, PB 235, using massively parallel paired-end sequencing. The MLO (mildew resistance locus O) genes were identified and analyzed for their structural features, and the variations were compared in the MLO gene family between the two clones. Sequencing results showed that RRIC 52 contained 4,280,477 SNPs and 400,667 InDels, while PB 235 contained 3,651,524 SNPs and 318,899 InDels. We identified 34 MLO genes (HbMLO 1 to 34) in the rubber genome. Multiple sequence alignment identified the conserved MLO domain and its TM domain in all HbMLO proteins. Sequence analysis identified non-synonymous variations (NSVs) in 12 HbMLO proteins. Phylogenetic analysis of the HBMLO genes revealed seven different clades. Six HbMLO genes in Clade V were orthologous to Arabidopsis genes where PM interaction was previously identified. The outcomes of this study widen the understanding of the MLO gene family, which can be used in breeding disease resistant rubber varieties in the future.

Yield Variation during the Period (April to July) 2017 in RRIC 121 and BPM 24 Rubber Clones (Hevea brasiliensis) Grown in WL3 Agro Ecological Zone of Sri Lanka

Monthly yield variation in rubber cultivations is common and it affects the livelihood of rubber smallholders and also the cash flows of plantation companies. The effect is more pronounced in rubber harvesters, workers, and other stakeholders as their income levels are partly governed by the monthly financial performance of the cultivation. This uncertain income levels results in the out migration of work force, causing the declining of rubber harvesters and other workers in WL3, Agro Ecological zone. This has become a major problem faced by the entire plantation industry in Sri Lanka. Thus a thorough knowledge on the variability of yield is essential for accurate estimation of monthly yields and income levels and thereby planning marketing and related activities. Therefore, the main objective of this study was to establish variation pattern in the yield components of two Hevea Brasiliensis clones grown in WL3 agro ecological zone in the country and to find possible reasons for such variation. Further, ways of enhancing yield and income levels were also looked at using the Ellakanda and Katuhenadivisons of Sorana Estate managed by Kotagala Plantation PLC as the study site. Based on the previous literature, relevant theories were formulated; independent and dependent factors that would result in the monthly yield variation and the required information to be collected were identified. Primary data were collected using tapping blocks of the selected divisions along with relevant meteorological data. The raw data were classified to purposeful and usable categories and were tabulated for statistical inferences. Results revealed that the physiological ability of the tree to produce latex, number of tapping days and the rainfall pattern as the main factors which affect the monthly yield variation of RRIC 121 & BPM 24 rubber clones cultivated in WL3 Agro Ecological zone of the country.

SPAD-502 and atLEAF CHL PLUS values provide good estimation of the chlorophyll content for Hevea brasiliensis Müll. Arg. Leaves

Measurement of chlorophyll content using destructive methods is not efficient due to a large number of samples, cost, and time needed. Estimationof chlorophyll content by nondestructive methods using handheld chlorophyll meter may be considered to improve efficiency. This research aimed to determine the formula to convert SPAD-502 and atLEAF CHL PLUS values (relative indicator of chlorophyll content) to estimated (absolute) rubber leaves chlorophyll content. Twenty leaves of rubber plant were measured using SPAD-502 and atLEAF CHL PLUS at the same time to determine SPAD-502 and atLEAF CHL PLUS values. The measured leaves were then collected to determine the chlorophyll content using a standard laboratory procedure. Regression and correlation analyses (among 3 methods) were conducted using SAS v.9 software. The results showed that between SPAD-502 and atLEAF CHL PLUS values were closely correlated, hence both of the devices can substitute each other to estimate rubber leaf chlorophyll content. In addition, the relationship between atLEAF CHL PLUS and SPAD-502 values with actual chlorophyll content of rubber clone SP 217, PB 260, GT1, and all clones (general) were significant with high coefficient of determination (R2) as well as low Root Mean Square Error (RMSE) and Coefficient of Variation (CV). Therefore, by using formula determined in this study, both atLEAF CHL PLUS and SPAD-502 can be suggested for accurate, fast, and non-destructive estimation of chlorophyll content of rubber plant leaf.

Assessing Yield and Yield Stability of Hevea Clones in the Southern and Central Regions of Malaysia

Increased volatility in global rubber prices has led to declining Malaysian rubber production and smallholder income. Identifying rubber clones that can produce a consistently high yield in various environments is one of the potential measures to alleviate the impact of price fluctuations and improve smallholder livelihoods. In this study, we assessed rubber yields and yield stability of 37 rubber tree clones at two major production regions in Malaysia: Kota Tinggi (Southern region) and Sungai Buloh (Central region). In addition, we assessed relationships between climate data with rubber yields. Rubber yield and stability differed widely by clone, but showed relatively consistent trends across regions. Clones RRIM 2007, PB 260, and RRIM 2012 were high yielding in both regions and had high stability. Conversely, clone RRII 308 had the lowest mean yield across both regions and low stability. Mean annual yields showed a negative relationship with rising minimum temperatures, declining by ~3 g per tapping per tree (g t−1 t−1) per 1 °C rise in minimum temperature. Our findings highlight clones capable of achieving stable high yields. This information may be useful for breeders and agronomists in identifying germplasm and traits for further development. Further, this information can be used to assist clone recommendations to smallholders in these regions to mitigate the dual impacts of climate change and market volatility.

Immature growth performance of three important rubber tree (Hevae brasiliensis) clones in a drought-prone area

Adaptation of rubber tree clones to water-limited areas and maintenance of trunk radial growth are important keys for performance of genetic material. The rubber farmers need to shorten the interim phases to produce latex, which is considered “immature” phase, i.e. the time without income. The objective of this study was to compare the performance of three important rubber tree clones: GT1, the elder clone as control, which is still widely used in Cambodia and West Africa; RRIM600, the “all-round” clone, the most planted clone in Thailand, the first world producer; and RRIT251, the expanding clone, recommended by the Rubber Authority of Thailand, all in the field condition. The investigation was conducted in a drought-prone area of Northeast Thailand, where the dry season lasts 5 to 6 months. The cumulated growth and the annual growth were analyzed 4.5 years after planting. The trunk girth and height were measured monthly. Main climatic variables were hourly recorded. The year was separated in three periods: the leaves-shed season from January to April, the wet season from May to September, and the dry season with canopy maintenance from October to December. The results showed significant clonal effect on both trunk girth and height; however, with relatively low differences. The trunk girth of clone RRIT251 was about 29 cm and 10% higher than GT1. The difference was not significant in RRIM600. The annual girth increment was mainly located in wet season (63%) without clonal effect. The clonal difference was occurred in the dry season, where RRIT251 was better performed particularly in the leave-shed period preceding wet season. On a monthly basis, the relative trunk girth increment rate was highly negatively related to the vapor pressure deficit. We hypothesized that rubber clones shared a common strategy of dehydration avoidance, while RRIT251 expressed a little less degree of avoidance.

Field screening of RRISL recommended rubber clones against Corynespora Leaf Fall Disease

Identification of resistant clones is of vital importance in the management of Corynespora leaf fall disease (CLFD) of rubber. The recommended and potential clones were screened in a bud wood nursery which was especially designed for screening purposes at Ratnapura, Kalutara, Moneragala and Padiyatalawa. The lesion types agreed with the symptoms observed in the field plants and new symptoms have been identified from Padiyatalawa, in non-traditional rubber growing areas. Analysis of results from test methods showed that 81% of the recommended clones by the Rubber Research Institute of Sri Lanka (RRISL) can be ranked as resistant. Among the clones screened, no clones were found to be severely susceptible, yet moderately or mildly susceptible clones have been identified. This information should be used in future breeding programmes and also should be considered by the growers while selecting clones for their own plantations. The cultivation of resistant clones with a wide genetic base is considered as the most reliable long-term solution in the management of CLFD.

Physiological mechanisms responsible for tolerance to, and recuperation from, drought conditions in four different rubber clones

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 CO2 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.

The bioinformatics method of protein dehydration induced drought stress in Hevea brasiliensis Muell. Arg

Hevea brasiliensis Muell. Arg. (rubber plant) is one of the most significant sources natural rubber in the world. Planting material used is vegetative propagation that called a clone. Each rubber clone has specific adaptability. Adaptation of rubber in drought area is a complex trait. The current study assesses of the bioinformatics on the NCBI database as well as expected the physicochemical of protein dehydration. Several parameters of physicochemical protein dehydration in H. brasiliensis were varied among the genes observed. There is twenty (20) protein dehydration induced from H. brasiliensis deposited in NCBI. The length of the genes was alternated with the genes ascertained. Several lines of coded amino acids were 370 to 1490 bp. The mitochondria target peptide value diversified from 0.020 to 0.342, signifying that it is expected to be a presence. The present resulted indicated the prominence of the variation and role of a physical and chemical characteristic of the distinct amino acids in protein dehydration genes as drought stress in rubber.

Production and Physiology Characteristics of Some Rubber Clones in Early Tapping with Growth Regulator

The study was aimed to study latex production and physiology character of some rubber clones in early tapping with the use of Plant Growth Regulators (PGR) and the relationship between production and latex yield characters. The research was conducted in KarangInong Farm, PTP-N I Kso PTP-N III, East Aceh. The research was prepared using two factors Nested Design, namely 5 clone factors and 7 hormone factors. The treatment was repeated twice, but nested in the clone factor, so the number of experimental units was 7 x 5 x 2 = 70. Each experimental unit consists of 4 plants with the total is 280 plants. The results showed that response of each clone and hormone was different for production parameters and latex yield character. Treatment of clone PB 340 and hormone H6 (600 ppm IAA + Kinetin 60 ppm) yield the highest production (g/p/s). The best Interaction of clone and hormone treatment is K4H4 (IRR 107 clone with IAA 500 ppm + Kinetin 60 ppm) as indicated by production parameters (38.04 g/p/s), sucrose content (9.14 mM, phosphoric acid (6.84 mM), Thiol (0.50 mM) and plugging index (16.34%)