Tapping Panel Dryness Research Articles

Effect of different preceding crops and land preparation methods on the agrophysiological and health parameters of Hevea brasiliensis Muell. Arg clone GT 1 in southwestern Côte d'Ivoire

Land preparation method and preceding crops affect the evolution of rubber trees. Its ignorance and/or poor execution do not allow the efficient development of the agronomic and economic potentialities of plantations. In order to remove this constraint, a study was undertaken in southwestern Côte d'Ivoire. The rubber trees were planted at 510 trees/ha according to a Fisherblock experimental design, of six preceding crop treatments with three repetitions. Only one latex harvesting system was applied (S/2 d/4 6d/7 ET 2.5% Pa 1 (1) 6/y). The parameters measured were rubber yield, annual average girth increment, physiological profile, sensitivity to tapping panel dryness and sensitivity to root rot caused by the genus Fomes. The results showed that the rate of rubber trees found in the plots was good (90.73± 0.47 %) and had varied with land preparation method depending on the preceding crops. Vegetative growth at tapping (2.05±1.36 cm.year -1 ), and average rubber yield (2053±179 kg.ha-1 .year -1 ) and the rate of tree loss due to the genus Fomes (8.33±0.42%) were influenced by land preparation method. The good productivity, the good physiological state of the rubber trees were characterized by a well balanced physiological profile and a tapping panel dryness rate (3.60 ± 1.74%), independently of treatments. The Agroeconomic results showed that mechanically prepared fallow (813641 FCFA.ha-1 .year -1 ) was the best preceding crop and land preparation method. This technical result has two main interests for the national rubber-growing industry, since it actively participates in the national policy for fighting against deforestation but also contributes to the establishment of a secondary forest by the attributes of the rubber-growing plant cover.

Involvement of HbMC1-mediated cell death in tapping panel dryness of rubber tree (Hevea brasiliensis).

Tapping panel dryness (TPD) causes a significant reduction in the latex yield of rubber tree (Hevea brasiliensis Muell. Arg.). It is reported that TPD is a typical programmed cell death (PCD) process. Although PCD plays a vital role in TPD occurrence, there is a lack of detailed and systematic study. Metacaspases are key regulators of diverse PCD in plants. Based on our previous result that HbMC1 was associated with TPD, we further elucidate the roles of HbMC1 on rubber tree TPD in this study. HbMC1 was up-regulated by TPD-inducing factors including wounding, ethephon and H2O2. Moreover, the expression level of HbMC1 was increased along with TPD severity in rubber tree, suggesting a positive correlation between HbMC1 expression and TPD severity. To investigate its biological function, HbMC1 was overexpressed in yeast (Saccharomyces cerevisiae) and tobacco (Nicotiana benthamiana). Transgenic yeast and tobacco overexpressing HbMC1 showed growth retardation compared with controls under H2O2-induced oxidative stress. In addition, overexpression of HbMC1 in yeast and tobacco reduced cell survival after high-concentration H2O2 treatment and resulted in enhanced H2O2-induced leaf cell death, respectively. A total of 11 proteins, rbcL, TM9SF2-like, COX3, ATP9, DRP, HbREF/Hevb1, MSSP2-like, SRC2, GATL8, CIPK14-like and STK, were identified and confirmed to interact with HbMC1 by yeast two-hybrid screening and co-transformation in yeast. The 11 proteins mentioned above are associated with many biological processes, including rubber biosynthesis, stress response, autophagy, carbohydrate metabolism, signal transduction, etc. Taken together, our results suggest that HbMC1-mediated PCD plays an important role in rubber tree TPD, and the identified HbMC1-interacting proteins provide valuable information for further understanding the molecular mechanism of HbMC1-mediated TPD in rubber tree.

Insights into genes encoding respiratory burst oxidase homologs (RBOHs) in rubber tree (Hevea brasiliensis Muell. Arg.)

Superoxide-producing NADPH oxidases (NOXs), also known as respiratory burst oxidase homologs (RBOHs) in plants, are key players in the signaling network of reactive oxygen species (ROS) and involved in various plant processes. Despite the importance of RBOHs, little information is available in Hevea brasiliensis, a rubber-producing tree of the Euphorbiaceae family. This study presents the first genome-wide analysis of Rboh family genes in this special species. By using arabidopsis and rice RBOH proteins as queries, homology search of the rubber tree genome resulted in a relatively high number of ten Rboh genes. According to phylogenetic analysis, these genes were divided into seven groups named RBOHD, RBOHC, RBOHB, RBOHE, RBOHF, RBOHH, and RBOHN, which is consistent with best-reciprocal-hit-based sequence comparison with representative plant species. The former six groups are widely distributed in core eudicots, whereas RBOHN represents a novel but ancient group that has lost in many plants including poplar, grapevine, arabidopsis, and rice. Comparative genomics analysis showed that all rubber tree paralogs were derived from the recent whole-genome duplication (WGD) shared by cassava. Gene expression profiling revealed diverse patterns of different family members over various rubber tree tissues as observed in cassava, which also supports expression divergence between duplicates. Moreover, key members, which are related to tapping panel dryness, leaf senescence, hormone, and/or stress responses, were also identified in rubber tree. Results obtained from this study will facilitate further studies of Rboh genes in rubber tree as well as other species.

Semi-quantitative RT-PCR analysis of transcripts encoding protease inhibitor in Hevea brasiliensis Muell. Arg latex

In this paper, the semi-quantitative RT-PCR was carried out on four Hevea brasiliensis protease inhibitor transcripts (HbPI1-4) of rubber tree clone PB 260 under abiotic and biotic stresses. The research aimed to understand whether the expressions of HbPIs are induced by either biotic or abiotic stresses. The RNA isolation was performed under strict procedure to synthesize the best quality of cDNA. The accumulation of gene transcript was determined by RT-PCR (Reverse Transcriptase – Polymerase Chain Reaction) at the 30th cycle. Pre-PCR experiments were carried out on 20th, 25th, 30th, and 35th cycles for each gene. At the 30th cycle, PCR products were clearly visible on an agarose gel and could be quantified in comparison to the reference gene (HbActin). In general, the value of gene expression of HbPIs ranged from 0.222 to 0.531 in various conditions. However, the data were not statistically different under abiotic (tapping panel dryness, TPD) and biotic (white root disease, WRD) stresses. The semi-quantitative RT-PCR was able to confirm the relatively stable expression of HbPIs under five tree conditions (healthy trees, TPD-affected trees at <50% dry cut length (DCL), TPD-affected trees at >50% DCL, WRD-affected trees and both of symptoms).

Sucrose analysis in leaf tissue of two contrasted rubber tree clones under abiotic and biotic stresses

The sucrose content in rubber leaf is assumed to differ between genotypes and environmental conditions. We studied the relation of sucrose-content and -concentration between high- and low- latex metabolism clones, such as PB 260 and PR 300, respectively under biotic- and abiotic-stresses (white root disease and tapping panel dryness). The experimental design was a complete randomized design of two treatments (by genotypes and by stress conditions) with five replicates. Sucrose analysis was performed using the anthrone colourimetric modified method at 627 nm of spectrophotometry. Statistical analysis used the Student Newman-Keuls test of ANOVA at 5% significant level. The different types of latex metabolism clones had not affected the value of sucrose-content and -concentration in leaf tissue. By contrast, the results showed that WRD-affected trees of PB 260 clone (24.45 mg g−1) had significantly the highest sucrose content compared with healthy- (15.53 mg g−1) and TPD-affected trees (13.42 mg g−1). A similar trend was equally observed in TPD- (16.33 mg g−1), healthy- (14.51 mg g−1) and WRD-affected trees (14.52 mg g−1) of PR 300 clone. The sucrose-content and -concentration in PB 260 clone at WRD-affected trees were the highest than the others.

Transcriptome analysis in Hevea brasiliensis latex revealed changes in hormone signalling pathways during ethephon stimulation and consequent Tapping Panel Dryness

Tapping Panel Dryness (TPD) affects latex production in Hevea brasiliensis. This physiological syndrome involves the agglutination of rubber particles, which leads to partial or complete cessation of latex flow. Latex harvesting consists in tapping soft bark. Ethephon can be applied to stimulate latex flow and its regeneration in laticifers. Several studies have reported transcriptome changes in bark tissues. This study is the first report on deep RNA sequencing of latex to compare the effect of ethephon stimulation and TPD severity. Trees were carefully selected for paired-end sequencing using an Illumina HiSeq 2000. In all, 43 to 60 million reads were sequenced for each treatment in three biological replicates (slight TPD trees without ethephon stimulation, and slight and severe TPD trees with ethephon treatment). Differentially expressed genes were identified and annotated, giving 8,111 and 728 in response to ethephon in slight TPD trees and in ethephon-induced severe TPD trees, respectively. A biological network of responses to ethephon and TPD highlighted the major influence of metabolic processes and the response to stimulus, especially wounding and jasmonate depression in TPD-affected trees induced by ethephon stimulation.

Incidence Des Fortes Fréquences De Stimulation Hormonale Sur Deux Régimes de Saignée Descendante Du Clone PB 215 : Faible (d6) et Modéré (d4), Au Sud-Est De La Côte D’Ivoire

The clone PB 235 of Hevea brasiliensis is characterized by a rapid growth, homogeneity, and a virgin bark which is suitable for tapping. However, it is sensitive to the very intense latex systems harvesting technologies. This paper focuses on determining the incidence of strong frequencies of stimulation on two downward tapping systems of clone PB 215: low (d6) or moderate (d4). Rubber trees were planted with the density of 510 trees/ha (7 m x 2.8 m) in accordance with a randomized complete block design. Tapping at d6 frequency with 8 and 12 hormonal stimulations and the d4 stimulated 0 and 8 times per year were evaluated. The intensification of hormonal stimulation with the d6 did not have any worthy beneficial effect on the dry rubber yield of the rubber trees. In d4, the stimulation involved a reduction in the sucrose content which led to a significant increase of the dry rubber yield. However, it contributed to an increase in the tapping panel dryness. At moderate tapping, the application of hormonalstimulation allowed us to distinguish between the two latex harvesting technologies. At d6, the two treatments were similar regardless of the stimulation level. Tapping at d6 supports a reduction of tapping workforce and a longer economical durability of the trees, compared to tapping at d4. The intensification of hormonal stimulation applied to lower tapping frequencies (d6) did not have any negative incidence on the clone PB 235. However, it has promoted tapping panel dryness in tapping at d4 frequency.

STIMULATION OF LATEX PRODUCTION IN SERINGUEIRA (HEVEA BRASILIENSIS L.) WITH ETRHEL DOSES

ABSTRACT The use of the Ethrel® stimulant on rubber cultivation has become essential to ensure greater rubber production. When applied on the cut of the tree, this stimulant releases the ethylene gas that causes an increase of the exudation period of the latex flow. Dilutions and applications should be performed correctly so that they do not cause tapping panel dryness, which would leave the plant unproductive for a long time. Thus, the objective of this study was to evaluate the effects of increasing doses of ethrel on tapping panel dryness and rubber production of rubber tree clones. Three experiments were conducted using a randomized block design with four treatments (ethrel doses) and three replicates. The clones used were RRIM600, PR255 and PB217 submitted to doses of the stimulant Ethrel 0%, 2.5%, 3.3% and 5% with an interval of application of 30 days. The d/7 bleeding system was used. The productive performance was evaluated monthly and the total of plants with tapping panel dryness at the end of the work. All clones presented a linear positive response to increasing doses. The dose of ethrel 5% favors higher rubber yields in the three evaluated clones, but is associated with high percentage of drying. Thus, it was concluded that the production of rubber is affected positively with the increase of ethrel doses, but this increase causes a higher incidence of panel drying. Thus, it is recommended to use the ethrel 2.5% dose so the production is guaranteed without causing the tapping panel dryness.

Physiological and Proteomic Analyses of Molybdenum- and Ethylene-Responsive Mechanisms in Rubber Latex.

Molybdenum (Mo) is an essential micronutrient in many plants. In the rubber tree Hevea brasiliensis, Mo application can reduce the shrinkage of the tapping line, decrease tapping panel dryness, and finally increase rubber latex yield. After combined Mo with ethylene (Eth), these effects become more obvious. However, the molecular mechanism remains unclear. Here, we compared the changed patterns of physiological parameters and protein accumulation in rubber latex after treated with Mo and/or Eth. Our results demonstrated that both Eth and Mo can improve the contents of thiol, sucrose, and dry yield in rubber latex. However, lutoid bursting is significantly inhibited by Mo. Comparative proteomics identified 169 differentially expressed proteins, including 114 unique proteins, which are mainly involved in posttranslational modification, carbohydrate metabolism, and energy production. The abundances of several proteins involved in rubber particle aggregation are decreased upon Mo stimulation, while many enzymes related to natural rubber biosynthesis are increased. Comparison of the accumulation patterns of 25 proteins revealed that a large portion of proteins have different changed patterns with their gene expression levels. Activity assays of six enzymes revealed that Mo stimulation can increase latex yield by improving the activity of some Mo-responsive enzymes. These results not only deepen our understanding of the rubber latex proteome but also provide new insights into the molecular mechanism of Mo-stimulated rubber latex yield.

Curative Activity of Watery Fermented Compost Extract as a Bark Treatment against Tapping Panel Dryness

Background: Tapping panel dryness (TPD) is a stress-related disorder that afflicts rubber trees, contributing to yield losses in nearly every rubber-growing region. Method: We demonstrated the curative effects of biostimulants containing a fermented watery extract of shrimp waste-enriched compost (SWCE) on TPD in field trials. Undiluted SWCE was applied to lightly scraped bark in the first, third, and fourth trials, and applied directly without bark scraping in the second trial. Results: Bark treatment significantly (p &lt; 0.05) reduced tapping cut dryness and increased latex yield, suggesting recovery from the disorder. When SWCE was applied to pre-scraped bark, 80% and 30% of trees with partial and complete TPD, respectively, recovered from tapping dryness within 2 months. The latex dry weight of treated trees with partial and complete TPD was 77.5% and 21.1% that of healthy trees, respectively. We observed slight recovery from TPD in trees treated without bark scraping and in trees with a history of ethephon stimulation. No curative effect of SWCE was demonstrated in treated trees without a tapping rest period. These findings suggest that compost extract could be a useful treatment for partial TPD.

Over-expression of 3-hydroxy-3- methylglutaryl-coenzyme A reductase 1 (hmgr1) gene under super-promoter for enhanced latex biosynthesis in rubber tree (Hevea brasiliensis Muell. Arg.)

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

Study on the Secant Segmentation Algorithm of Rubber Tree

Natural rubber is one of the most important materials in the national defense and industry, and the tapping panel dryness (TPD) of the rubber tree is one of the most serious diseases that affect the production of rubber. Although considerable progress has been made in the more than 100 years of research on the TPD, there are still many areas to be improved. At present, the method of artificial observation is widely used to identify TPD, but the diversity of rubber tree secant symptoms leads to the inaccurate judgement of the level of TPD. In this paper, image processing technology is used to separate the secant and latex, so that we can get rid of the interference factors, get the exact secant and latex binary image. By calculating the area ratio of the corresponding binary images, the grade of TPD can be classified accurately. and can also provide an objective basis for the accurate identification of the tapping panel dryness (TPD) level.

Aktivitas Askorbat Peroksidase dan Tanin pada Tanaman Karet (Hevea brasiliensis Muell. Arg.) Klon PB 260 dan RRIM 921 Kas Parsial dengan Pemberian Antidepresan

The aim of the research was to determine the activity of ascorbic peroxide and tannin value on rubber plant clones PB 260 and RRIM 921 with partial Tapping Panel Dryness (TPD) which has been applied with a growth regulator. The results showed that RRIM 921 and PB 260 clones initiate significant value with productivity on 0 and 1 month observed also inactivity of ascorbic peroxide on 1 month observed. Plant condition with healthy and partial TPD showed significant value with tannin on 0 months observed. Positive correlation before the application was on APX and IP (0.060), APX and TSC (0.163), IP with productivity (0.154) and productivity with TSC (0.163). Positive correlation after the application was on APX and tannin (0.057), APX and TSC (0.051), tannin and IP (0.141), IP with productivity (0.316) and productivity with TSC (0.148.)

Contribution of Latex Micro Diagnosis to Modern Management of Rubber Plantations: Case of Clones With Low or Slow Metabolism PB 217 and PR 107

The cultivated rubber clones are sensitive to latex harvesting regimes according to their laticiferous metabolism. Thus, in order to determine the best latex harvesting systems of clones with low or slow metabolism, six latex harvesting technologies are applied to them in a bulk statistical device from Fisher to four rehearsals. The rubber is tapped in downward half spiral stimulated or not for nine years after the opening of the tapping panel. The agronomic parameters (production, vegetative growth), the tapping panel dryness and those of the latex micro diagnosis were evaluated. The results indicate that these clones independently of the latex harvesting system have good rubber productivity (2310 kg.ha -1 .y-1 ) with good radial vegetative growth (2.9 cm.y -1 ). Their trees show a well-balanced physiological profile and an acceptable sensitivity to the tapping panel dryness (4.9%). However, the physiological index, the bark consumption and the sensitivity to the tapping panel dryness lead to retain the latex harvesting technologies "S/2 d3 6d/7 Pa1(1) ET2.5% 4/y, S/2 d4 6d/7 Pa1(1) ET2.5% 4/y and S/2 d4 6d/7 Pa1(1) ET2.5% 8/y” for the best. This index, favorably influencing the choice of technologies adapted to clones with active metabolism, contributes to the modern and efficient management of a rubber plantation.

Latex micro diagnosis, modern management tool of rubber plantations of clones with moderate metabolism GT 1, RRIC 100 and BPM 24

Objective : The cultivated rubber clones are sensitive to latex harvesting regimes according to their laticiferous metabolism. This study was done to determine the best latex harvesting system (s) of clones with moderate metabolism (GT 1, RRIC 100 and BPM 24). Methodology and Results : Six latex harvesting technologies were applied to these clones in a bulk statistical device from Fisher to four rehearsals. The rubber trees were tapped in downward half spiral stimulated or not, for nine years after the opening of the tapping panel. The agronomic parameters (latex production, vegetative growth), the tapping panel dryness and those of the latex micro diagnosis were evaluated. The results indicate that these clones independently of the latex harvesting system have good rubber productivity (2234 kg.ha -1 .y -1 ) with good radial vegetative growth (2.4 cm.y -1 ). Their trees showed a well-balanced physiological profile and an acceptable sensitivity to the tapping panel dryness (3.2 %). However, the physiological index, the bark consumption and the sensitivity to the tapping panel dryness lead to retain the latex harvesting technology S/2 d4 6d/7 Pa1 (1) ET2.5% 4/y” for the best. Conclusion and application of results : This index, favourably influencing the choice of technologies adapted to clones with active metabolism, contributes to the modern and efficient management of a rubber plantation. Key words : latex-harvesting technology, rubber clones, moderate metabolism, tapping panel dryness, physiological parameters

Latex Micro Diagnosis, Modern Management Tool of Rubber Plantations of Clones With Active or Rapid Metabolism IRCA 18, IRCA 130, PB 235, PB 260 and PB 330

The cultivated rubber clones are sensitive to latex harvesting regimes according to their laticiferous metabolism. Thus, in order to determine the best latex harvesting systems of clones with active or rapid metabolism (IRCA 18, IRCA 130, PB 235, PB 260 and PB 330), six latex harvesting technologies are applied to them in a bulk statistical device from Fisher to four rehearsals. The rubber is tapped in downward half spiral stimulated or not for nine years after the opening of the tapping panel. The agronomic parameters (production, vegetative growth), the tapping panel dryness and those of the latex micro diagnosis were evaluated. The results indicate that these clones independently of the latex harvesting system have good rubber productivity (2310 kg.ha -1.y1) with good radial vegetative growth (2.9 cm.y-1). Their trees show a wellbalanced physiological profile and an acceptable sensitivity to the tapping panel dryness (4.9%). However, the physiological index, the bark consumption and the sensitivity to the tapping panel dryness lead to retain the latex harvesting technologies “ S/2 d3 6d/7 Pa1(1) ET2.5% 4/y and S/2 d4 6d/7 Pa1(1) ET2.5% 4/y ” for the best. This index, favorably influencing the choice of technologies adapted to clones with active metabolism, contributes to the modern and efficient management of a rubber plantation.

Incidence of latex harvesting technologies on agronomic and physiological parameters and profitability of some rapid metabolic class clones of rubber tree (&lt;i&gt;Hevea brasiliensis&lt;/i&gt;) in southwestern Côte d’Ivoire

Rubber tree rapid-metabolism clones generally have interesting agronomic and physiological characteristics. However, they are mostly sensitive to tapping panel dryness and breakage due to wind. This could be probably due to overexploitation caused by high tapping frequencies and/or high hormonal stimulation systems. To try solving this problem, a study was carried out over nine years using clones PB 260, PB 280 and PB 330 planted at a density of 510 plants/ha in southwestern Cote d’Ivoire. The experimental design was a randomized complete blocks with different latex harvesting technologies. The estimated parameters were rubber yield, radial vegetative growth, physiological profile and the profitability of applied latex harvesting technologies. Results indicated that non-stimulated combined with high tapping frequency latex harvesting system (d2 0/y) showed a level of rubber yield comparable to that of tapping frequencies d3 and d4 in all studied clones irrespective of the level of hormonal stimulation applied. Furthermore, the absence of hormonal stimulation had no negative influence on the vegetative growth and the physiological profile of rubber trees. Every two days (d2) tapping system without stimulation generated a profit margin statistically identical to that of low tapping frequencies (d4, d5 and d6) irrespective of the level of hormonal stimulation. © 2017 International Formulae Group. All rights reserved. Keywords: Rapid-metabolism clones, Cote d’Ivoire, tapping frequency, Hevea brasiliensis , rubber yield, physiological profile

Overexpression of EcGSH1 induces glutathione production and alters somatic embryogenesis and plant development in Hevea brasiliensis

Oxidative stress occurring during in-vitro culture is detrimental for clonal propagation by somatic embryogenesis in particular in Hevea brasiliensis. In previous work, overexpression of the gene encoding the cytosolic reactive oxygen species detoxification enzyme HbCuZnSOD led to reduce somatic embryo regeneration in Hevea. In this study, the role of antioxidant was tested by overexpression of the E.coli GSH1 gene involved in glutathione biosynthesis in rubber embryogenic callus lines. Transgenic lines were successfully established and some plants were regenerated. Overexpression of EcGSH1 gene led to glutathione over-accumulation, and affected dramatically the somatic embryogenesis process and plant development. Upon a water deficit treatment, these plants displayed the greatest drop in photosynthetic nitrogen use efficiency, higher proline content, and higher glutathione reductase activity. Changes induced in transgenic lines overexpressing HbCuZnSOD and EcGSH1 were discussed as well as possible applications on plant material propagation, overcoming loss of natural rubber production through Tapping Panel Dryness, and tropical soil remediation.

Fast track evaluation and selection of Hevea brasiliensis clones from a clonal nursery

Ten female parents of natural rubber (Hevea brasiliensis), introduced from two Southeast Asian countries were allowed to natural cross breeding. After a primary culling of seedlings based on growth and test tap yield in juvenile stage, 20 half-sib (HS) progenies were cloned and evaluated in a clonal nursery trial (CNT) laid out (RCBD, plot size 6 with 3 replication) in a close spacing of 2.5m×2.5m. Four established precocious high yielding clones (RRII 430, RRII 414, RRII 105 and PB 235) were included as control. Superior clones were identified based on the important agronomic traits viz., growth, juvenile yield, tolerance to pink disease and bark thickness within a short span of five years, instead of fifteen years in conventional small scale trials (SST) with a wide spacing (4.9m×4.9m). The results indicated that one of the half-sib progeny of mother clone PB 86 (HS PB 86/57) registered significantly (P<0.05) superior dry rubber yield of 18g per tree per tapping (g/t/t), and vigorous trunk girth (43cm) at breast height in the 5th year after planting when compared to that of RRII 105 (11.9g/t/t; 34.1cm girth) and on par with RRII 430 (14.9g/t/t; 31cm girth) and RRII 414 (14g/t/t; 38cm girth), the best among the checks. The second best clone HS LCB 1320/30 also recorded comparable yield and growth with RRII 430 and was better than RRII 414. Three clones (HS PB 86/57, HS BD 5/27 and HS LCB 1320/30) could be selected based on the growth, yield and other secondary traits. None of the trees of HS PB 86/57showed incidence of pink disease and Tapping Panel Dryness (TPD) during field evaluation which deserves attention. The results support superior performance of new genotypes in CNT, saving time and space required to complete the breeding-evaluation cycle. Besides, these clones could be used as improved genetic stocks for initiating new breeding programmes to enrich the genetic base of natural rubber.

Molecular cloning and expression analysis of the mevalonate diphosphate decarboxylase gene from the latexof Hevea brasiliensis

Mevalonate diphosphate decarboxylase (MVD) catalyzes the conversion of mevalonate diphosphate to isopentenyl diphosphate (IPP), a monomer of a large family of plant isoprenoids and cis-1,4-polyisoprene (natural rubber), which is present in most rubber-producing plants including Hevea brasiliensis (Para rubber tree). Here, we isolated the gene encoding MVD from the latex transcriptome of an elite rubber tree clone, Chinese Academy of Tropical Agriculture Sciences (CATAS) 7-33-97. The full-length cDNA of this gene, designated HbMVD, is 2032 bp long with a 1248-bp open reading frame (ORF) encoding a putative MVD of 415 amino acid residues with a theoretical molecular mass of 45.83 kDa and an isoelectric point (pI) of 6.52. Sequence alignment demonstrated that HbMVD cDNA shares 91 % identity with MVD genes from both Ricinus communis and Jatropha curcas. The genomic sequence of HbMVD is 11,749 bp long, comprising 10 exons and nine introns. The HbMVD promoter contains numerous cis-regulatory elements that are responsive to light, hormones, stress, and so on. Reverse-transcription quantitative PCR (qRT-PCR) revealed that HbMVD was most highly expressed in female flowers, followed by the bark, latex, male flowers, and leaves of untapped, mature rubber trees. The expression level of HbMVD in latex decreased progressively from the first, second, fourth, and third leaf stories of young shoots. Bark tapping (mechanical wounding), as well as exogenous ethephon and methyl jasmonate treatment, significantly upregulated HbMVD expression in the latex. This gene was upregulated in the bark and latex of tapping panel dryness (TPD)-affected trees but downregulated in latex from healthy, renewed bark. Further characterization of HbMVD would provide valuable insights into the involvement of HbMVD in regulating the biosynthesis of natural rubber and other IPP-derived isoprenoids in rubber tree.