South American Leaf Blight Research Articles

Leaf spectral reflectance of Hevea brasiliensis in response to Pseudocercospora ulei

South American Leaf Blight (SALB) is a fungal disease caused by the pathogen Pseudocercospora ulei. It is the main disease affecting rubber trees in Latin America. This study was designed to investigate the changes in the spectral reflectance of rubber leaflets inoculated with P. ulei under controlled conditions. Young leaflets of two clones of Hevea brasiliensis with different degrees of resistance to SALB were tested. The results demonstrated that SALB severity affected the spectral properties of the rubber leaflets, increasing the spectral reflectance in the visible range, decreasing the near-infrared range, and causing variating in the spectral vegetation indices. The changes were more obvious in the most susceptible clone (FX 3864) than in the most resistant one (FX 4098). The SALB severity classes were correlated with the relative chlorophyll content, the leaflet phenology, and the appearance of disease symptoms after the pathogen inoculation. New mathematical models for predicting the SALB severity in the leaflets B (10–18 days old) and C (22–30 days old) in the two rubber tree clones were designed.

Dynamics of adaptive responses in growth and resistance of rubber tree clones under South American leaf blight non-escape conditions in the Colombian Amazon

Rubber trees (Hevea brasiliensis) in Latin America are strongly affected by a disease known as South American Leaf Blight (SALB), which is caused by the foliar fungus Microcyclus ulei, renamed Pseudocercospora ulei. This study analyzed the temporal dynamics (eight years) of growth and resistance to SALB in nine promising American clones and the IAN 873 clone (control) during the immature phase in large-scale clone trials, using models for longitudinal data and GGE biplot analyses as a measurement of their specific adaptation to climatic conditions in a SALB non-escape zone in the Colombian Amazon. High averages of monthly precipitation (>300 mm), temperature (>25.2 °C), relative humidity (>88%) and dew point (>23 °C) were recorded in the years with a high incidence of SALB. After 8 years, the better clones (FDR 5788, FDR 5597, FX 4098 and GU 198) blended the desirable characteristics pre-tapping vigour (CMT > 40 cm), foliar retention (FRL ≤ 1 or ≥79% of leaves retained) and partial resistance to SALB (low severity, AT1 and AT2 had scores <2 and low conidial and ascosporic sporulation, TR had scores <4, and ST had scores <2), which indicated an adaptive advantage over SALB’s high pressure agro-climatic conditions, contrary to that observed in clones IAN 873 (control), CDC 56 and FX 3899 P1. Finally, these clones need to be analyzed in terms of their productive performance before making a valid recommendation to producers.

Early assessing performance and resistance of Colombian rubber tree genotypes under high South American Leaf Blight pressure in Amazon

In Latin America, natural rubber production is limited by an endemic disease known as South American Leaf Blight (SALB), caused by a leaf plant pathogen fungus, Microcyclus ulei, recently renamed Pseudocercospora ulei. The main strategies for managing the disease are using genotypes with SALB resistance and identifying escape zones. The objetive of this study was to assess early performance (four growth parameters) and reaction to SALB (four variables of the disease) of nine Colombian rubber tree genotypes and clone IAN 873 (susceptible control) during the immature phase (an annual cycle analyzed by three climatic periods) in large-scale clone trials under SALB non-escape conditions in the Colombian Amazon. It was evident that most of the genotypes demonstrated optimal early growth, and severity and sporulation significantly increased in the genotypes most susceptible to SALB (ECC 35, ECC 83, ECC 60 and IAN 873), especially in the time between the transition into the dry period, and the consolidation of the dry period. The highest SALB scores were present in the latter. Genotypes with higher resistance to SALB generally demonstrated lower growth indices compared with more the susceptible genotypes. Genotypes ECC 29, ECC 64 and ECC 90 bring together optimal growth and partial SALB resistance characteristics and constitute a promising gene pool of evidence for expanding the genetic resource of rubber tree in the Colombian Amazon region.

Global Assessment of Climate-Driven Susceptibility to South American Leaf Blight of Rubber Using Emerging Hot Spot Analysis and Gridded Historical Daily Data

South American leaf blight (SALB) of Para rubber trees (Hevea brasiliensis Muell. Arg.) is a serious fungal disease that hinders rubber production in the Americas and raises concerns over the future of rubber cultivation in Asia and Africa. The existing evidence of the influence of weather conditions on SALB outbreaks in Brazil has motivated a number of assessment studies seeking to produce risk maps that illustrate this relationship. Subjects with dynamic and cyclical spatiotemporal features need to embody sufficiently fine spatial resolution and temporal granulation for both input data and outputs in order to be able to reveal the desired patterns. Here, we apply emerging hot spot analysis to three decades of gridded daily precipitation and surface relative humidity data to depict their temporal and geographical patterns in relation to the occurrence of weather conditions that may lead to the emergence of SALB. Inferential improvements through improved handling of the uncertainties and fine-scaled temporal breakdown of the analysis have been achieved in this study. We have overlaid maps of the potential distribution of rubber plantations with the resulting dynamic and static maps of the SALB hot spot analysis to highlight regions of distinctly high and low climatic susceptibility for the emergence of SALB. Our findings highlight the extent of low-risk areas that exist within the rubber growing areas outside of the 10° equatorial belt.

Leaf gas exchange and chlorophyll a fluorescence in Hevea brasiliensis in response to Pseudocercospora ulei infection

South American leaf blight (SALB), the main disease found in the rubber tree crops of Latin America, is caused by the fungus Pseudocercospora ulei. This study aims to determine the photosynthetic response of two clones of H. brasiliensis with different resistances to SALB from P. ulei under controlled conditions, by means of a temporal analysis of gas exchange and chlorophyll a fluorescence. The results show that the effect on photosynthesis was proportional to the temporal progress and intensity of the disease symptoms to this effect, the maximum significant decrease (p < 0.05) in photosynthetic rates in the clone FX 3864 (susceptible) (88.3%) and in FX 4098 (moderately resistant) (45.2%) was observed 8 days after inoculation in B leaflets that were 18 days old. Meanwhile, a significant difference was found between the two clones' ability to capture, use, and dissipate light energy through photosystem II, which was evidenced by the minimum photosynthetic activity registered in the susceptible clone.

A Review of a Century of Studies on South American Leaf Blight of the Rubber Tree.

In the past, South American leaf blight (SALB) of the rubber tree has been responsible for very severe damage in rubber plantations in South America. It is still the main obstacle holding back the development of rubber cultivation on the American continent and is a major risk for Asia and Africa, which are still exempt from this scourge. However, knowledge about the disease and about rubber tree resistance factors has progressed over the last decade, suggesting some solutions, notably for varietal improvement. This article is an overview of knowledge on this subject, particularly the most recent achievements.

English

South American Leaf Blight (SALB) of the rubber tree, caused by Microcyclus ulei and foliar anthracnose caused by Colletotrichum gloeosporioides, are diseases that adversely affect rubber cultivation in America. Both diseases have a significant economic impact on this agricultural subsector. The aim of the present study was to evaluate the potential as biological control agents of three Streptomyces species strains, namely A20, 7.1 and 5.1, against M. ulei and C. gloeosporioides. The results of analysis of variance (ANOVA) and Tukey post-hoc test of the in vitro antifungal activity assays evidenced the potential of the three Streptomyces strains to inhibit C. gloeosporioides growth through the production of diffusible (A20 and 5.1) and volatile compounds (7.1). Furthermore, other results indicated that strain 5.1 had a high biocontrol activity against C. gloesporoides, and thus such strain was selected for further evaluations as a possible biocontrol agent against M. ulei. In vitro assays suggested that active compounds produced by 5.1 inhibited M. ulei growth by interfering with conidia germ tube and stroma formation. Bioassay-guided fractionation with organic solvents of 5.1 fermentation broths, suggested that antifungal compounds produced by this strain were nonionic compounds of medium-polarity. Currently, studies are ongoing to elucidate the chemical structure of these antifungal compounds. These approaches aim to generate a biological control agent to provide the Colombian rubber subsector with a preventive measure for controlling M. ulei and C. gloeosporioides. Key words: Biological control, foliar anthracnose, rubber tree, South American Leaf Blight (SALB), Streptomyces species.

Bayesian random regression for genetic evaluation of South American leaf blight in rubber trees

O mal das folhas causado pelo fungo Microcyclus ulei e a doenca mais seria dos seringais da America Latina. Com o objetivo de identificar clones de seringueira mais resistentes em diferentes ambientes ao longo do tempo, compararam-se diferentes modelos de regressao aleatoria (MRA) ajustados via abordagem Bayesiana. Oito clones foram testados em campos clonais no delineamento em blocos completos casualizados com quatro repeticoes, utilizando-se 80 arvores por parcela. As duas fileiras centrais foram avaliadas a cada dois meses em relacao as variaveis severidade (SEV) e indice de estroma em folha adulta (EFA). Foram incluidas como covariaveis nos modelos a circunferencia do tronco e as variaveis climaticas de cada campo clonal. Os MRA foram comparados por meio do criterio DIC (Deviance Information Criterion). O modelo M2 (que assumiu os efeitos aleatorios quadratico para clone e linear para planta) foi o melhor (menor valor de DIC) para descrever SEV e EFA em todas as localidades consideradas. Tal modelo permitiu inferir que os clones FDR 5788, CDC312 e CDC56 apresentaram maior resistencia, enquanto o clone FX 3864 foi o que apresentou a maior suscetibilidade, em todas as localidades consideradas.

A climatic risk analysis of the threat posed by the South American leaf blight (SALB) pathogen Microcyclus ulei to major rubber producing countries

South American leaf blight (SALB) of the Para rubber tree, Hevea brasiliensis Muell. Arg., caused by the plant pathogenic fungus Microcyclus ulei (Henn.) Arx, is recognized as the most serious threat to the natural-rubber industry worldwide. While the pathogen is currently restricted to South America, the warm humid climatic conditions in Asia and Africa, which contribute to over 97 % of world’s natural rubber production are similar to the South American tropics, indicating a significant threat to global rubber production, should the pathogen be introduced to these regions. The present study aims to assess climate suitability for the occurrence of M. ulei in different parts of the world, based on the available literature for M. ulei pathogen establishment, including temperature, relative humidity and precipitation. The risk analysis study provides a preliminary indication of the likely threat of M. ulei in different rubber growing areas of the world and highlights the need for more information on pathogen biology, diversity and environmental tolerance.

Performance of 10 Hevea brasiliensis clones in Ecuador, under South American Leaf Blight escape conditions

Rubber (Hevea brasiliensis) growing in Latin America is severely limited by South American Leaf Blight, a disease caused by the Ascomycete fungus Microcyclus ulei, recently renamed Pseudocercospora ulei. Sustainable ways of controlling it may be genetic, using resistant cultivars, or may consist in seeking so-called “escape zones”, where disease incidence is low thanks to climatic conditions unsuitable for the fungus. After identifying one such zone on the Pacific coast of Ecuador, between 2006 and 2014 we used an 8.2ha trial to compare the agronomic performance of ten rubber clones originating from Asia and Africa. The study focused on tree growth, susceptibility to the disease and clone phenology. For most of the assessed clones, the results obtained over 8 months showed good adaptability and a good agronomic performance during the immature period, so that tapping could begin on the earliest trees at 6½ years. An examination of the monthly values for climatic factors such as rainfall, relative humidity, minimum temperature and dew point temperature, showed that conditions during the dry season, which lasted 5 months, were detrimental to P. ulei fungus development, even though the mean relative humidity of the driest months did not fall below 75%. In addition, between September and December, the minimum temperature remained above the dew point temperature, preventing dew formation on the leaf surface. These conditions enabled the trees to complete their natural refoliation without any risk of parasite pressure, and to conserve a foliar density over 90% up to natural defoliation the following year. The results obtained during the early growing phase, i.e. the immature phase, confirmed the suitability of this zone for rubber growing, especially for materials with a high yield potential, despite their known susceptibility to the disease. These escape zones consequently offer an undeniable alternative for developing rubber, due to a low phytosanitary risk arising from P. ulei.

De novo Transcriptome Analysis Reveals Distinct Defense Mechanisms by Young and Mature Leaves of Hevea brasiliensis (Para Rubber Tree).

Along with changes in morphology in the course of maturation, leaves of Hevea brasiliensis become more resistant to leaf diseases, including the South American Leaf Blight (SALB), a devastating fungal disease of this economically important tree species. To understand the underlying mechanisms of this defense, and to identify the candidate genes involved, we sequenced the Hevea leaf transcriptome at four developmental stages (I to IV) by Illumina sequencing. A total of 62.6 million high-quality reads were generated, and assembled into 98,796 unique transcripts. We identified 3,905 differentially expressed genes implicated in leaf development, 67.8% (2,651) of which were during the transition to leaf maturation. The genes involved in cyanogenic metabolism, lignin and anthocyanin biosynthesis were noteworthy for their distinct patterns of expression between developing leaves (stages I to III) and mature leaves (stage IV), and the correlation with the change in resistance to SALB and the Oidium/Colletotrichum leaf fall. The results provide a first profile of the molecular events that relate to the dynamics of leaf morphology and defense strategies during Hevea leaf development. This dataset is beneficial to devising strategies to engineer resistance to leaf diseases as well as other in-depth studies in Hevea tree.

Expression analysis of ROS producing and scavenging enzyme-encoding genes in rubber tree infected by Pseudocercospora ulei

South American Leaf Blight (SALB), caused by the ascomycete Pseudocercospora ulei, is responsible for the low productivity of rubber trees in Latin America and is a serious threat to rubber plantations in Asia and Africa, where the rubber trees are derived from highly susceptible clones. Three contrasted genotypes were chosen for their levels of resistance to the pathogen: FX2784 (totally resistant), MDF180 (partially resistant) and PB314 (susceptible). Array analyses were previously performed to identify genes differentially expressed in resistant and susceptible genotypes. Twenty-one genes were selected for further gene expression analysis in non-inoculated and inoculated genotypes from 24 to 216 h post infection (hpi). These genes are involved in ROS production (HbRBOHA, HbRBOHB, HbRBOHC, HbRBOHD), ROS-scavenging systems (cytoplasmic and chloroplastic HbCuZnSOD, HbMnSOD, HbCAT, HbAPX1, HbAPX2, HbMDHAR, HbGCL1, HbGCL2, HbOASTL, HbGPX, HbDHAR), and leaf senescence (HbCASP, HbPCYST, HbWRKY2, HbPLY, HbKAT2). First, a genotype-dependent level of expression was observed. The genes HbRBOHA, HbCuZnSOD cyto, HbCAT, HbGCL and HbWRKY2 were constitutively expressed at lower levels in the MDF180 genotype than in the FX2784 and PB314 genotypes. Conversely, the levels of expression of HbDHAR, HbGPX and HbPCYST were higher in the older, non-inoculated leaves of MDF180. Lower production of ROS and efficient regeneration of reduced ascorbate ensure a balanced redox intracellular state in this genotype. Second, inoculation of the leaves induced few modifications in the expression level of the studied genes. In the MDF180 partially resistant genotype, an increase in the expression level of HbRBOHB, HbRBOHD 48 hpi and a decrease in the expression level of HbDHAR 216 hpi were observed. In the FX2784 totally resistant genotype, an increase in the expression level of HbRBOHD and HbCuZnSOD cyto and a decrease in HbCAT were observed 48 hpi. This transitory variation could be associated with the oxidative burst classically observed in hypersensitive response (HR). The increase in the synthesis of reduced glutathione in this genotype could ensure redox balance and consequently cell homeostasis. In the PB314 susceptible genotype, HbROHC, HbCuZnSOD chloro was up-regulated 216 hpi concomitantly with a decrease in the expression level of HbCAT, consequently causing an accumulation of H2O2 and programmed cell death. The level of expression of a transcription factor, HbWRKY2, was also modulated by the P. ulei infection with early transient up-regulation in the FX2784 totally resistant genotype and permanent up-regulation in the MDF180 partially resistant genotype. These results complement studies on genetic determinism of SALB resistance and a recent publication on Hevea glutathione reductase gene.

Ocorrência de epidemia do mal das folhas em regiões de "escape" do Brasil

RESUMO: Entre janeiro e fevereiro de 2013 ocorreu uma epidemia de mal das folhas em regiões consideradas como de "escape" à doença, causando preocupações e indagações nos produtores de borracha e ao setor heveícola como um todo. Uma possível adaptação do fungo a essas zonas foi levantada e a consistência do controle da doença pela utilização do binômio plantas com troca uniforme das folhas + período seco, típicos de regiões de "escape", foi questionada. O objetivo deste trabalho foi trazer informações importantes aos heveicultores sobre a interação clima-patógeno-hospedeiro e comparar variáveis de normais climatológicas (média histórica) e dados climáticos deste período de ocorrência da epidemia (janeiro e fevereiro de 2013). Concluiu-se que não foi o patógeno que se adaptou às plantas de seringueira em clima mais seco, nas regiões de "escape", mas que o clima mais úmido ocorreu nessas regiões mais secas, nesse período.

Suitable climate for rubber trees affected by the South American Leaf Blight (SALB): Example for identification of escape zones in the Colombian middle Magdalena

South American Leaf Blight (SALB), caused by the fungus Pseudocercospora ulei, is the major constraint for rubber tree cultivation in Latin America, continent of origin of the rubber tree. The use of resistant tree cultivars and the identification of escape zones seem to be the best disease control measures. In order to characterize the climate and the pedological parameters in the region of Middle Magdalena, Colombia, we used temperature, relative humidity and annual rainfall records for a 20-year period (1990–2010) from 19 weather stations distributed across the region, together with definitions of the soil units for the area. With the recorded data, we calculated annual and monthly averages of temperature and relative humidity, annual rainfall, annual water balance, annual potential evapotranspiration, number of months with rainfall lower than 50 mm and 100 mm, and number of months with relative humidity lower than 75%. To determine the suitable climate for the rubber crop facing SALB, these results were interpolated through Inverse Distance Weighting with the software ArcGis 9.3 for each variable and their combinations, having as references the plant requirements and the disease escape areas. Regarding the annual rubber tree evapotranspiration requirement, the map showed that the region of Middle Magdalena is suitable for the rubber cultivation. However, La Gloria (Cesar), Regidor (Bolívar) and Gamarra (Cesar) are not suitable for rubber cultivation owing to the high soil hydric deficit (>500 mm). When we considered the rubber tree's requirements, the region was divided into the following types of areas: two unsuitable, two marginal and one suitable. However, considering the disease escape requirements, this region was divided into one unrestricted area and six preferential areas with different restrictions to the SALB control. The most important area of the Middle Magdalena Region is not an escape zone, hence in these areas, the use of highly productive clones resistant to P. ulei is suggested.

Assembly and Analysis of Differential Transcriptome Responses of Hevea brasiliensis on Interaction with Microcyclus ulei.

Natural rubber (Hevea brasiliensis) is a tropical tree used commercially for the production of latex, from which 40,000 products are generated. The fungus Microcyclus ulei infects this tree, causing South American leaf blight (SALB) disease. This disease causes developmental delays and significant crop losses, thereby decreasing the production of latex. Currently several groups are working on obtaining clones of rubber tree with durable resistance to SALB through the use of extensive molecular biology techniques. In this study, we used a secondary clone that was resistant to M. ulei isolate GCL012. This clone, FX 3864 was obtained by crossing between clones PB 86 and B 38 (H. brasiliensis x H. brasiliensis). RNA-Seq high-throughput sequencing technology was used to analyze the differential expression of the FX 3864 clone transcriptome at 0 and 48 h post infection (hpi) with the M. ulei isolate GCL012. A total of 158,134,220 reads were assembled using the de novo assembly strategy to generate 90,775 contigs with an N50 of 1672. Using a reference-based assembly, 76,278 contigs were generated with an N50 of 1324. We identified 86 differentially expressed genes associated with the defense response of FX 3864 to GCL012. Seven putative genes members of the AP2/ERF ethylene (ET)-dependent superfamily were found to be down-regulated. An increase in salicylic acid (SA) was associated with the up-regulation of three genes involved in cell wall synthesis and remodeling, as well as in the down-regulation of the putative gene CPR5. The defense response of FX 3864 against the GCL012 isolate was associated with the antagonistic SA, ET and jasmonic acid (JA) pathways. These responses are characteristic of plant resistance to biotrophic pathogens.

Maturation of perithecia and ascospores discharge in South American leaf blight of rubber tree

The Ascomycota fungus Microcyclus ulei is a major threat for natural rubber production. The ascospores play a major role in the survival and dissemination of the fungus. The present study indicates that the ascospores are present on the leaves shortly after infection. Although their abundance is higher on leaflets 50–70 days after they reach maturity, ascospores are still found on 6 months-old leaves, ensuring the survival of the fungus during the dry season in the case of no defoliation of the rubber trees. Indeed, their viability does not depend on the age of the leaf. The pycnidiospores, whose role in the lifecycle of the fungus is not established, are also present on the leaves several months after their maturity. The ascospores are disseminated only if the leaves are wetted and exposed to an airflow. The discharge of ascospores starts a few minutes after a single wetting event but the number of ascospores discharged decreases rapidly and stops 90 min after the wetting event. However, the perithecia are rapidly able to discharge ascospores if wetted again but at a lower level. Compared to other Ascomycota, the discharge of ascospores is quick but brief.

Suitable rubber growing in Ecuador: An approach to South American leaf blight

Rubber growing (Hevea brasiliensis) is showing real development in Latin America, where the production of natural rubber is still held back by the incidence of the South American leaf disease caused by a fungus, Microcyclus ulei, recently renamed Pseudocercospora ulei, which causes repeated defoliation of trees. The solutions are genetic in order to grow varieties resistant to the disease, or developing new plantations in areas where disease incidence is less severe and does not present a serious risk due to adverse climatic conditions for the fungus. The aim of this study was to identify areas in Ecuador for their climatic characteristics suitable for rubber growing, and also the zones that are unsuited to the fungus P. ulei, in order to allow the establishment of rubber plantations with less phytosanitary risk. A geographic study was thus carried out at national level based on the biophysical basis of existing data, by selecting the most relevant parameters with their appropriate ranges for rubber cultivation. Different maps were obtained, displaying 749,824ha suitable for cultivation, of which 80,174ha are in escape areas.

Erasing the Past: A New Identity for the Damoclean Pathogen Causing South American Leaf Blight of Rubber

BackgroundSouth American leaf blight (SALB) of rubber has been the main constraint to production in its neotropical centre of origin since commercial plantations were first established. The fungal causal agent was identified and described more than a century ago but its precise placement within the Ascomycota still remains uncertain. Indeed, such is the ambiguity surrounding the pathogen that each of the spore morphs would, according to their present classification, be placed in different ascomycete families: the Microcyclus sexual morph in the Planistromellaceae and the two purported asexual morphs - Fusicladium and Aposphaeria – in the Venturiaceae and Lophiostomataceae, respectively. Given the historical importance of the fungus and the ever-menacing threat that it poses to rubber production in the Palaeotropics – and, thus to the rubber industry and to the global economy – its phylogeny, as well as its biology, should be resolved as a matter of urgency.Methods and ResultsHere, six genomic regions (LSU rRNA, mtSSU, MCM7, EF-1α, Act and ITS) were used for reconstructing the molecular phylogeny of the SALB fungus based on material collected throughout Brazil. The analyses support the classification of the fungus in the family Mycosphaerellaceae s. str. (Capnodiales, Dothideomycetes) and place it firmly within the clade Pseudocercospora s. str., now accepted as one of the distinct genera within Mycosphaerellaceae. The new combination Pseudocercospora ulei is proposed and the life cycle of the fungus is confirmed, based on both experimental and phylogenetic evidence, with the Aposphaeria morph shown to have a spermatial rather than an infective-dispersal function.ConclusionsBecause the phylogeny of the SALB fungus has now been clarified, new insights of its epidemiology and genomics can be gained following comparison with closely-related, better-researched crop pathogens.

Evaluation of Rubber Tree Crown Clones for Yield and Magnesium Use Efficiency in a Xanthic Ferralsol

The cultivation of rubber trees in the humid tropical Amazon region is only possible with the use of crown grafts with species of Hevea sp. that are resistant to South American leaf blight – (SALB) [Microcyclus ulei (P. Henn.) v. Arx.]. However, it has been observed that plants with grafted crowns are not efficient in remobilizing magnesium from the crown to the latex. The experimental design was a randomized block, with three replicates. Five crown clones were studied (CPAA C 01, CPAA C 06, CPAA C 18, CPAA C 45, and CBA 2) with two magnesium (Mg) levels [source: magnesium sulfate(MgSO4): low-Mg (150 g plant−1 of MgSO4 × 7H2O] and high-Mg (450 g plant−1 of MgSO4 × 7H2O). The panel clone used for tapping was CNS AM 7905 (Hevea brasiliensis). The results showed that the Mg levels influenced the crown clones differently in relation to yield, efficiency index and leaf and soil Mg concentration. Clone CPAA C 01 with a high-Mg produced over 2.0 t ha−1 of dry rubber. Clones CPAA C 01 and CPAA C 45 were the most efficient, while clone CPAA C 06 showed moderate efficiency and clones CPAA C 18 and CBA 2 were inefficient in using Mg. The Mg concentration in the latex was not influenced by the two Mg levels, with the only differences being between the crown clones.

Leaf-, panel- and latex-expressed sequenced tags from the rubber tree (Hevea brasiliensis) under cold-stressed and suboptimal growing conditions: the development of gene-targeted functional markers for stress response.

Hevea brasiliensis is a native species of the Amazon Basin of South America and the primary source of natural rubber worldwide. Due to the occurrence of South American Leaf Blight disease in this area, rubber plantations have been extended to suboptimal regions. Rubber tree breeding is time-consuming and expensive, but molecular markers can serve as a tool for early evaluation, thus reducing time and costs. In this work, we constructed six different cDNA libraries with the aim of developing gene-targeted molecular markers for the rubber tree. A total of 8,263 reads were assembled, generating 5,025 unigenes that were analyzed; 912 expressed sequence tags (ESTs) represented new transcripts, and two sequences were highly up-regulated by cold stress. These unigenes were scanned for microsatellite (SSR) regions and single nucleotide polymorphisms (SNPs). In total, 169 novel EST-SSR markers were developed; 138 loci were polymorphic in the rubber tree, and 98 % presented transferability to six other Hevea species. Locus duplication was observed in H. brasiliensis and other species. Additionally, 43 SNP markers in 13 sequences that showed similarity to proteins involved in stress response, latex biosynthesis and developmental processes were characterized. cDNA libraries are a rich source of SSR and SNP markers and enable the identification of new transcripts. The new markers developed here will be a valuable resource for linkage mapping, QTL identification and other studies in the rubber tree and can also be used to evaluate the genetic variability of other Hevea species, which are valuable assets in rubber tree breeding.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-014-0095-2) contains supplementary material, which is available to authorized users.