Latex Yield Research Articles

Identification of the HbZAR1 Gene and Its Potential Role as a Minor Gene in Response to Powdery Mildew and Anthracnose of Hevea brasiliensis

Powdery mildew and anthracnose are the main diseases of rubber trees. In recent years, there have been large outbreaks in the rubber-planting areas of Asia, seriously affecting the yield and quality of rubber latex. ZAR1 is a conserved and distinctive coiled-coil nucleotide-binding leucine-rich (CNL) repeat in the plant kingdom, playing a crucial role in disease-resistance processes. To elucidate the function of the HbZAR1 gene in rubber trees (Hevea brasiliensis), three candidate HbZAR1 genes were identified using bioinformatics methods and comprehensively analyzed. The results indicate that the HbZAR1 protein is conserved in different plant species. Examination of cis-regulatory element sequences of HbZAR1genes reveals that the HbZAR1 gene promoter exhibits a remarkable enrichment of stress, light, and hormone elements. An expression analysis shows that the expression levels of the three HbZAR1 genes are highest in the bark and lowest in latex. Three HbZAR1 genes can respond to both rubber tree Erysiphe quercicola and Colletotrichum siamense infection; especially, HbZAR1.1 and HbZAR1.2 show significant upregulation in expression levels during the early stages of infection. These findings suggest that the three HbZAR1 genes may be involved in rubber tree susceptibility to E. quercicola and C. siamense through different immune mechanisms. Subcellular localization results indicate that the HbZAR1 genes are expressed in the nucleus and plasma membrane. This study also shows that the three HbZAR1 genes and activated mutant HbZAR1.1D481V do not induce stable ROS production and cell death, suggesting possible gene degradation, functional redundancy, or acting as minor genes in disease resistance. This research provides valuable insights for further studying the function of HbZAR1 genes in rubber trees and the mechanisms of immune molecules.

Transcriptomic and Proteomic Integration Reveals Key Tapping-Responsive Factors for Natural Rubber Biosynthesis in the Rubber Tree Hevea brasiliensis

Natural rubber is a crucial industrial material, and it is primarily harvested from the latex of the rubber tree Hevea brasiliensis by tapping the tree trunk. During the regular tapping process, mechanical damage seriously affects latex reproduction and rubber yield, but the molecular mechanisms on tapping stimulation remain unclear. In this study, we firstly determined the changed physiological markers on latex regeneration, overall latex yield, and latex flow time during the tapping process. Then, we combined proteomics and transcriptomics analyses of latex during tapping and identified 3940 differentially expressed genes (DEGs) and 193 differentially expressed proteins (DEPs). Among them, 773 DEGs and 120 DEPs displayed a persistent upregulation trend upon tapping. It is interesting that, in the detected transcription factors, basic helix-loop-helix (bHLH) family members occupied the highest proportion among all DEGs, and this trend was similarly observed in DEPs. Notably, 48 genes and 34 proteins related to natural rubber biosynthesis were identified, and most members of small rubber particle protein (SRPP) and rubber elongation factor (REF) showed a positive response to tapping stimulation. Among them, SRPP6 and REF5 showed significant and sustained upregulation at the gene and protein levels following tapping, indicating their pivotal roles for post-tapping rubber biosynthesis. Our results deepen the comprehension of the regulation mechanism underlying tapping and provide candidate genes and proteins for improving latex production in the Hevea rubber tree in future.

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.

Latex Yield and Tree Growth in Kanchannagar Rubber Estate of Bangladesh - a Preliminary Study

Rubber (Hevea brasiliensis Muell. Arg.) is a perennial, hardy and moderately quick-growing tree of the tropical regions (Khisa 1991). An initiative of its cultivation was taken in Bangladesh during 1960-61 considering the multiple uses of the latex and its products including the utility of timber (Chowdhury 1974). In Bangladesh, experts recommended its cultivation in the hilly land, terrace mostly evaluating the land suitability class and within the limitation of climatic factors (Hasan 1983). Bangladesh Forest Industry Development Cooperation (BFIOC) sent a proposal to Bangladesh Forest Research Institute (BFRl), Chittagong to find out the causes of latex yield variation in the rubber station of Rangamatia and Doluchari of Kanchannagar Rubber Estate of Fatickchhari upazila of Chittagong District. Thus, a preliminary study was conducted on these rubber gardens during 2007-08. The clones in those estates are RRlM-600; PBIG/GG, GT-1 and PB-235, which were planted during different planting years (BFIDC 1993). Management of the Doluchari garden was comparatively better than Rangamatia. Total number of trees in Doluchari and Rangamatia is 29850 and .36149 respectively. Two (2004-06) years latex yield records showed that average productions were 3.16 kg/tre/yr for Doluchari and 1.86 kg/tree/yr in Rangamatia. The latex yield variation may be due to different factors viz: site quality, management efficiency, age group of clones, etc. (Anon,1989). The Chittagong Univ. J. B. Sci. 8(1&2): 33-36, 2013

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.

Evaluation of Four Yield Stimulants on Hevea brasiliensis Yield

Latex yield stimulants, such as ethephon (2-chloroethylphosphonic acid), are widely utilised in the rubber industry to extend latex flow, ultimately improving latex yield. In this study, which lasted 44 months, the efficacy of three promising liquid stimulants (referred to as Products A, B, and D) was compared with Product C which is the common stimulation product used currently. Overall, all tested latex stimulation products demonstrated the ability to increase latex yield per tapping by 75 to 89 grammes per tree per tapping (g/t/t) or 50 to 78 per cent during the months of stimulation. However, on a long-term basis, when the yields of stimulated and non-stimulated (wintering) months were taken into account, the yield per tapping of stimulated trees increased by 11 to 18 g/t/t or 32 to 51 per cent. Notably, Product A, when applied three times a month, showed the highest incidence of tapping panel dryness (TPD) compared to the Control and Product D treatments, where no TPD was observed. The cost-benefit analysis showed that Product C was the most economically viable option, costing only RM 0.10 per kilogramme of latex yield, in contrast to the other stimulants, which ranged from RM 0.19 to RM 2.15 per kilogramme of latex yield. Keywords: Natural rubber, panel dryness, rubber production, latex yield stimulants.

Testing intra-species variation in allocation to growth and defense in rubber tree (Hevea brasiliensis).

Plants allocate resources to growth, defense, and stress resistance, and resource availability can affect the balance between these allocations. Allocation patterns are well-known to differ among species, but what controls possible intra-specific trade-offs and if variation in growth vs. defense potentially evolves in adaptation to resource availability. We measured growth and defense in a provenance trial of rubber trees (Hevea brasiliensis) with clones originating from the Amazon basin. To test hypotheses on the allocation to growth vs. defense, we relate biomass growth and latex production to wood and leaf traits, to climate and soil variables from the location of origin, and to the genetic relatedness of the Hevea clones. Contrary to expectations, there was no trade-off between growth and defense, but latex yield and biomass growth were positively correlated, and both increased with tree size. The absence of a trade-off may be attributed to the high resource availability in a plantation, allowing trees to allocate resources to both growth and defense. Growth was weakly correlated with leaf traits, such as leaf mass per area, intrinsic water use efficiency, and leaf nitrogen content, but the relative investment in growth vs. defense was not associated with specific traits or environmental variables. Wood and leaf traits showed clinal correlations to the rainfall and soil variables of the places of origin. These traits exhibited strong phylogenetic signals, highlighting the role of genetic factors in trait variation and adaptation. The study provides insights into the interplay between resource allocation, environmental adaptations, and genetic factors in trees. However, the underlying drivers for the high variation of latex production in one of the commercially most important tree species remains unexplained.

Comparative phosphoproteome analyses provide new insight into ethephon stimulated latex yield in rubber tree

Comparative phosphoproteome analyses provide new insight into ethephon stimulated latex yield in rubber tree

Evaluating the latex yield of rubber tree (Hevea brasiliensis muel arg.) based on the ages of the plant and the time of tapping

Evaluating the latex yield of rubber tree <i>(Hevea brasiliensis muel arg.)</i> based on the ages of the plant and the time of tapping

EFFECTS OF MANAGEMENT PRACTICES AND TAPPING SYSTEM ON LATEX AND DRY RUBBER YIELDS OF RUBBER TREE CLONE RRIT 251

The cultivation of Hevea brasiliensis, as the main source of natural rubber, is facing the tapping labor shortage and low dry rubber yield problems. Management practices and tapping system could nevertheless remedy these constraints. Accordingly, the study aimed to assess the latex and dry rubber yields of rubber trees clone RRIT 251 under different irrigation with fertilizer management methods and rubber tapping systems. The experiment was laid out in a split-plot design, 4 replications with 3 rubber trees per replication. Two main plot treatments: 1) application of irrigation combined with chemical and organic fertilizers treatment (IF) and; 2)no-irrigation-fertilizer treatment (NIF). Four subplot treatments: 1) (10 cm)S.d/3+ET – tapping 10 cm long of trunk girth (at 45° angle) above an installed bag of ethylene, for 1 day with 2 days interval; 2) (1/2)S.d/2 – tapping half of trunk girth every other day; 3) (1/2)S.2d/3, tapping half of trunk girth for 2 days with 1 day interval (the practice of most para rubber farmers) and; 4) (1/2)S.3d/4, tapping half of trunk girth for 3 days with 1 day interval. The controlled treatment was a combination treatment of NIFx (1/2)S.2d/3. The results showed that both IFx (10 cm)S.d/3+ET and IFx (10 cm)S.d/3+ET combination treatments had significant effects (P≤0.01) in enhancing latex weight per tree, dry rubber weight per tree, latex yield, and dry rubber yield higher than the controlled treatment. IF treatment had a significant effect (P≤0.01) in enhancing latex weight per tree, dry rubber weight per tree, latex yield, and dry rubber yields higher than NIF treatment. Rubber tapping system under (1/2)S.3d/4 had a significant effect (P≤0.01) in enhancing latex weight per tree, dry rubber weight per tree, latex yield, and dry rubber yield while it was significantly (P≤0.01) low under (1/2)S.d/2 as compared with the practice used of most farmers—(1/2)S.2d/3. It is concluded that the application of ethylene under IFx (10 cm)S.d/3+ET management is a better innovation and technology attributable to having 45% less time and less bark area consumed for tapping but with increased dry rubber yield, while IFx (1/2)S.2d/3 spent more time to increase the dry rubber yield, as compared with the controlled treatment. Keywords: Ethylene, Fertilizer, Irrigation, Latex, Rubber

Construction and analysis of the tapping panel dryness-related lncRNA/circRNA-miRNA-mRNA ceRNA network in latex of Hevea brasiliensis

Tapping panel dryness (TPD) results in a severe reduction in latex yield in Hevea brasiliensis. However, the molecular regulatory mechanisms of TPD occurrence are still largely unclear. In this study, whole-transcriptome sequencing was carried out on latex from TPD and healthy trees. In total, 7078 long noncoding RNAs (lncRNAs), 3077 circular RNAs (circRNAs), 4956 miRNAs, and 25041 mRNAs were identified in latex, among which 435 lncRNAs, 68 circRNAs, 320 miRNAs, and 1574 mRNAs were differentially expressed in the latex of TPD trees. GO and KEGG analyses indicated that plant hormone signal transduction, MAPK signaling pathway, and ubiquitin-mediated proteolysis were the key pathways associated with TPD onset. Phytohormone profiling revealed significant changes in the contents of 28 hormonal compounds, among which ACC, ABA, IAA, GA, and JA contents were increased, while SA content was reduced in TPD latex, suggesting that hormone homeostasis is disrupted in TPD trees. Furthermore, we constructed a TPD-related competitive endogenous RNA (ceRNA) regulatory network of lncRNA/circRNA-miRNA-mRNA with 561 edges and 434 nodes (188 lncRNAs, 5 circRNAs, 191 miRNAs, and 50 mRNAs) and identified two hub lncRNAs (MSTRG.11908.1 and MSTRG.8791.1) and four hub miRNAs (hbr-miR156, miR156-x, miRf10477-y, and novel-m0452-3p). Notably, the lncRNA-miR156/157-SPL module containing three hubs probably plays a crucial role in TPD onset. The expression of network hubs and the lncRNA-miR156/157-SPL module were further validated by qRT-PCR. Our results reveal the TPD-associated ceRNA regulatory network of lncRNA/circRNA-miRNA-mRNA in latex and lay a foundation for further investigation of molecular regulatory mechanisms for TPD onset in H. brasiliensis.

HbBIN2 Functions in Plant Cold Stress Resistance through Modulation of HbICE1 Transcriptional Activity and ROS Homeostasis in Hevea brasiliensis.

Cold stress poses significant limitations on the growth, latex yield, and ecological distribution of rubber trees (Hevea brasiliensis). The GSK3-like kinase plays a significant role in helping plants adapt to different biotic and abiotic stresses. However, the functions of GSK3-like kinase BR-INSENSITIVE 2 (BIN2) in Hevea brasiliensis remain elusive. Here, we identified HbBIN2s of Hevea brasiliensis and deciphered their roles in cold stress resistance. The transcript levels of HbBIN2s are upregulated by cold stress. In addition, HbBIN2s are present in both the nucleus and cytoplasm and have the ability to interact with the INDUCER OF CBF EXPRESSION1(HbICE1) transcription factor, a central component in cold signaling. HbBIN2 overexpression in Arabidopsis displays decreased tolerance to chilling stress with a lower survival rate and proline content but a higher level of electrolyte leakage (EL) and malondialdehyde (MDA) than wild type under cold stress. Meanwhile, HbBIN2 transgenic Arabidopsis treated with cold stress exhibits a significant increase in the accumulation of reactive oxygen species (ROS) and a decrease in the activity of antioxidant enzymes. Further investigation reveals that HbBIN2 inhibits the transcriptional activity of HbICE1, thereby attenuating the expression of C-REPEAT BINDING FACTOR (HbCBF1). Consistent with this, overexpression of HbBIN2 represses the expression of CBF pathway cold-regulated genes under cold stress. In conclusion, our findings indicate that HbBIN2 functions as a suppressor of cold stress resistance by modulating HbICE1 transcriptional activity and ROS homeostasis.

Extractable latex yield from Taraxacum kok-saghyz roots is enhanced by increasing rubber particle buoyancy

Taraxacum kok-saghyz (TK) is a leading alternative rubber-producing plant that produces natural rubber (NR) latex in laticifers within its roots. Unlike the tropical rubber tree, Hevea brasiliensis, TK can be grown in temperate regions, such as the northern United States, as the basis of a domestic rubber production industry. To support such an industry, efficient, scalable rubber extraction techniques are needed. In this study, aqueous extraction was used to recover TK natural rubber latex (TNRL) from four harvests of greenhouse-produced TK roots with a new technique that improves rubber particle buoyancy in root homogenate by chelation. The new method includes harvest, cleaning, and homogenization of freshly harvested roots, followed by centrifugation, vacuum collection of latex, and purification. Treatment of homogenate with ethylenediaminetetraacetic acid (EDTA), a divalent cation chelator, allowed more than twice as much latex to be extracted from fresh homogenate. EDTA-treated rubber particles contained lower concentrations of divalent cations than untreated ones in fresh homogenate and homogenate stored for two weeks. Long term (three months) storage of root homogenate similarly yielded more latex than fresh homogenate and had low divalent cation rubber particle concentrations, indicating that heavy cations had slowly leached from the particles into the aqueous medium during storage. Rubber particle size was larger in this treatment suggestive of rubber particle agglomeration but this was prevented and reversed by EDTA. Removal of divalent cations via chelation increased particle packing density of particles in concentrated latex and appeared to increase the gel content of dried latex samples. Molecular characterization of dried samples of purified TNRL established that the rubber was of the high molecular weight needed for product manufacturing.

Base-dependent flocculant treatment improves the extraction of latex from guayule

The extraction of high-quality latex from guayule (Parthenium argentatum) is highly mechanized. Multiple purification steps are currently required to eliminate non-latex solids and soluble proteins from homogenized shrub to achieve medical-grade guayule latex purity. The present study evaluates flocculant systems to enhance filtration and reduce centrifugal clarification, hence making the extraction process simpler and more efficient. Five polyamine flocculants were tested at four concentrations in homogenates prepared in NH4OH buffer and filtered either through cheesecloth or a mechanical press. The efficiency of the highest latex-yielding flocculant, 1000 ppm Cysep 2707, was enhanced 12-fold by adding 0.1% alginate. Four additional cationic flocculants more effectively sedimented non-rubber solids in KOH-based homogenate and yielded more than double the amount of latex. Additionally, recycling of the bagasse waste enhanced latex yield when fed back into the extraction process. Use of ionic flocculants can enhance latex yield and facilitate commercialization of medical grade guayule latex.

Improved the growth and yield of rubber at mature period throught Iles-Iles (Amorphophallus muelleri Blume) intercropping

Rubber plants that have produced can be improved through iles-iles farming. This study aims to determine the effect of the iles-iles rubber intercropping system on soil fertility, rubber growth, and latex yield. The study used a completely randomized block design (CRBD) with three replications. The treatment compared the rubber monoculture system with iles-iles rubber intercropping. The results showed that the cultivation of iles-iles as a rubber intercropping during the mature period of two years of observation did not inhibit the growth of rubber because it was not significantly different (P = 0.255) compared to the monoculture system but had a significant (P = 0.0013) effect on the latex yield. The BEP (Break Event Point) value of this farming system was achieved at the price of wet tubers of IDR 7.139 kg-1 with a production of 2.368 kg ha-1, while the value of the LER (Land Equivalent Ratio) in this farming system was 1.84.

Brassinosteroids Regulate the Water Deficit and Latex Yield of Rubber Trees.

Brassinolide (BR) is an important plant hormone that regulates the growth and development of plants and the formation of yield. The yield and quality of latex from Hevea brasiliensis are regulated by phytohormones. The understanding of gene network regulation mechanism of latex formation in rubber trees is still very limited. In this research, the rubber tree variety CATAS73397 was selected to analyze the relationship between BR, water deficit resistance, and latex yield. The results showed that BR improves the vitality of rubber trees under water deficit by increasing the rate of photosynthesis, reducing the seepage of osmotic regulatory substances, increasing the synthesis of energy substances, and improving the antioxidant system. Furthermore, BR increased the yield and quality of latex by reducing the plugging index and elevating the lutoid bursting index without decreasing mercaptan, sucrose, and inorganic phosphorus. This was confirmed by an increased expression of genes related to latex flow. RNA-seq analysis further indicated that DEG encoded proteins were enriched in the MAPK signaling pathway, plant hormone signal transduction and sucrose metabolism. Phytohormone content displayed significant differences, in that trans-Zeatin, ethylene, salicylic acid, kinetin, and cytokinin were induced by BR, whereas auxin, abscisic acid, and gibberellin were not. In summary, the current research lays a foundation for comprehending the molecular mechanism of latex formation in rubber trees and explores the potential candidate genes involved in natural rubber biosynthesis to provide useful information for further research in relevant areas.

Rubber latex yield is affected by interactions between antecedent temperature, rubber phenology, and powdery mildew disease.

Rubber (Hevea brasiliensis) latex production is crucial to the local economy, yet Xishuangbanna's climate is considered sub-optimal for rubber cultivation. The prevalence of the powdery mildew disease (Oidium heveae) in this region has decreased the annual latex yield by 20%. Rubber latex yield is influenced by several factors, including temperature, disease, other biotic conditions, and plantation management. However, the interrelationships and potential influencing networks between rubber latex yield and these factors are rarely quantitatively assessed, and understanding their impacts on latex yield could inform better management practices. To address this gap, we investigated the effects of temperature, phenology, and powdery mildew disease on rubber latex yield in March using observational data on daily rubber latex yield combined with detailed phenology, powdery mildew, and temperature data from 2004 to 2010 in a state farm in the Xishuangbanna, Yunnan, China. We found that the critical influencing periods of daily temperature difference (or diurnal temperature difference) on the rubber latex yield were during Nov 27-Jan 19 and Jan 21-Mar 17. Partial least square regression analysis and variance partitioning analysis were conducted on the 35 phenological variables, eight powdery mildew-related variables, and two climatic variables. The most influential factors were identified as the factors of the daily temperature differences during Jan-Mar, the duration of leaf flushing phenology, and mean and maximum percentage of leaves infected by powdery mildew. Subsequent canonical correlation analysis and linear regression found that temperature difference directly affected the rubber latex yield and indirectly affected the yield through phenology and powdery mildew disease. Raised daily temperature differences from Jan to Mar had the greatest impact, leading to a higher rubber latex yield. Our comprehensive quantitative assessment revealed the relative importance of antecedent daily temperature differences, phenology, and powdery mildew disease as well as their complex interconnections in influencing rubber latex yield. Our findings are essential tofuture studies on both powdery mildew disease and rubber latex yield, and alsodevelop rubber latex models.

Soil macrofauna diversity and weed dynamics in response to different methods of weed control in smallholder rubber farming

Abstract. Chaniago I, Yulistriani, Umami IM, Bukhari ZZ. 2023. Soil macrofauna diversity and weed dynamics in response to different methods of weed control in smallholder rubber farming. Biodiversitas 24: 3106-3113. Weeds interference in rubber farmland may reduce latex yield. Farmers apply herbicides to control weeds. However, the herbicide not only controls weed but also affects the presence of soil macrofauna. A study has been conducted to determine the effect of different method of weed control on soil macrofauna and weeds at smallholder rubber farming at Pulau Punjung, Dharmasraya District, West Sumatra, Indonesia. The experiment was conducted in a completely randomized block design with 6 treatments and 4 pseudo-replications. Treatment was mechanical control, without weed control, and 4 doses of herbicide glyphosate+metsulfuron-methyl (1.5 L ha-1 + 15 g ha-1, 2 L ha-1 + 15 g ha-1, 2.5 L ha-1 + 15 g ha-1, 3 L ha-1 + 15 g ha-1) with 400 L ha-1 of volume. Pitfall traps were used to collect the soil macrofauna. Data were analysis with ANOVA for weed and soil macrofauna in response to different methods of weed control. Results demonstrated that the application of glyphosate+metsulfuron-methyl herbicide significantly suppressed weeds higher than that of other methods of weed control (p&lt;0.05). Para grass (Brachiaria mutica (Forssk.) Stapf) was the most dominant weed but has been affected most by 3 L ha-1 + 15 g ha-1 herbicide mixture. Soil macrofauna of the order Hemiptera was affected most by the application of herbicide with a total reduction of 71.58% of number of individuals at 12 weeks after application of herbicide. In general, different weed control methods resulted in varied numbers of orders and individuals of the soil macrofauna.

Chromosome-level wild Hevea brasiliensis genome provides new tools for genomic-assisted breeding and valuable loci to elevate rubber yield.

The rubber tree (Hevea brasiliensis) is grown in tropical regions and is the major source of natural rubber. Using traditional breeding approaches, the latex yield has increased by sixfold in the last century. However, the underlying genetic basis of rubber yield improvement is largely unknown. Here, we present a high-quality, chromosome-level genome sequence of the wild rubber tree, the first report on selection signatures and a genome-wide association study (GWAS) of its yield traits. Population genomic analysis revealed a moderate population divergence between the Wickham clones and wild accessions. Interestingly, it is suggestive that H. brasiliensis and six relatives of the Hevea genus might belong to the same species. The selective sweep analysis found 361 obvious signatures in the domesticated clones associated with 245 genes. In a 15-year field trial, GWAS identified 155 marker-trait associations with latex yield, in which 326 candidate genes were found. Notably, six genes related to sugar transport and metabolism, and four genes related to ethylene biosynthesis and signalling are associated with latex yield. The homozygote frequencies of the causal nonsynonymous SNPs have been greatly increased under selection, which may have contributed to the fast latex yield improvement during the short domestication history. Our study provides insights into the genetic basis of the latex yield trait and has implications for genomic-assisted breeding by offering valuable resources in this new domesticated crop.