South American Leaf Blight Research Articles

Productivity evaluation of 10 Hevea brasiliensis clones in Ecuador under escape conditions for South American leaf blight

Productivity evaluation of 10 Hevea brasiliensis clones in Ecuador under escape conditions for South American leaf blight

Dynamic analysis of resistance in Colombian elite Hevea brasiliensis genotypes as a breeding strategy for enhancing South American leaf blight management under disease non-escape conditions in the Amazon region

South American Leaf Blight (SALB) is the primary limitation to the establishment of new rubber (Hevea brasiliensis) crops in Latin America. This study aimed to assess the temporal dynamics of resistance to SALB in 99 elite Colombian genotypes and the IAN 873 cultivar (control) of H. brasiliensis in small-scale clone trials conducted under conditions with a high disease prevalence in the northwestern Colombian Amazon. Resistance monitoring was carried out on a monthly basis and analyzed over five climatic periods. Three variables were recorded: attack severity (AT, ranging from 0 to 4), reaction type (TR, ranging from 1 to 6) and stromal density (ST, ranging from 0 to 4). The maximum scores for TR and ST were used to classify the level of resistance of the genotypes. Highly significant differences in the mean values of AT, TR and ST among the genotypes, across the periods, and in the interaction between genotype and period were found. Over time, an increase in symptoms (AT) and signs (TR and ST) of SALB was observed. During the rainy periods, SALB intensity was highest, resulting in a leaf area affected ranging from 16 to 30%. Eight genotypes showed partial resistance (PR) (TR < 5 and ST < 2), while 16 genotypes demonstrated complete resistance (CR) (TR < 3 and ST = 0), and 76 genotypes were highly susceptible (HS) (TR > 5 or ST > 2). The temporal analysis identified 23 Colombian superior genotypes with varying degrees of SALB resistance, which can be a valuable breeding resource for improving SALB management in the Colombian Amazon region.

Isu dan Impak Perkembangan Penanaman Getah di Perak, 1958-1984

This research is to see to what extent the development of commercial plantations, in particular rubber plants in Perak between 1958 and 1984 has had a positive impact on the socioeconomic progress of the population in this state. The elemental of this rubber plant development is seen through the development of this plant in the state of Perak, the challenges faced by the people in rubber cultivation activities, especially in facing the problem of South American Leaf Blight (SALB) disease and how they resolved it during the period studied. This research adopted historical qualitative method on sources and materials obtained from the National Archives of Malaysia Kuala Lumpur, National Archives of Malaysia Perak State Branch, Hamzah Sendut Library 1, Universiti Sains Malaysia in the Malaysiana and Archives section, Kuala Kangsar Public Library, Perak, and the library at the National Archives of Malaysia Perak State Branch.This study has found that the rapid development of rubber plantations in Perak has left a significant impact on socioeconomic aspects among residents in the state of Perak. For example, the rate for employment opportunities and generated income had increased especially for women, as well as there were improvements in infrastructure, education, and health. This matter shows that the progressiveness of the economic sector in Perak is not solely contributed by tin mining activities as widely discussed by previous studies. It turns out that economic activities based on rubber cultivation have also had a positive impact on the progress of the lives of residents in the state of Perak.

Isu dan Impak Perkembangan Penanaman Getah di Perak, 1958-1984

This research is to see to what extent the development of commercial plantations, in particular rubber plants in Perak between 1958 and 1984 has had a positive impact on the socioeconomic progress of the population in this state. The elemental of this rubber plant development is seen through the development of this plant in the state of Perak, the challenges faced by the people in rubber cultivation activities, especially in facing the problem of South American Leaf Blight (SALB) disease and how they resolved it during the period studied. This research adopted historical qualitative method on sources and materials obtained from the National Archives of Malaysia Kuala Lumpur, National Archives of Malaysia Perak State Branch, Hamzah Sendut Library 1, Universiti Sains Malaysia in the Malaysiana and Archives section, Kuala Kangsar Public Library, Perak, and the library at the National Archives of Malaysia Perak State Branch.This study has found that the rapid development of rubber plantations in Perak has left a significant impact on socioeconomic aspects among residents in the state of Perak. For example, the rate for employment opportunities and generated income had increased especially for women, as well as there were improvements in infrastructure, education, and health. This matter shows that the progressiveness of the economic sector in Perak is not solely contributed by tin mining activities as widely discussed by previous studies. It turns out that economic activities based on rubber cultivation have also had a positive impact on the progress of the lives of residents in the state of Perak.

Selected Leaf Diseases of Rubber: Symptoms and Control – A Review

This paper is a review article with the objective of providing valuable, recent and solid information and critical understanding of symptoms and control of selected leaf diseases of rubber tree (Hevea brasiliensis Muell. Arg) using secondary information and data harvested from previously published studies found online. Data gathered showed that H. brasiliensis is subject to a plethora of economically important diseases mainly of fungal origin, classified as leaf, stem and branch, panel and root disease. Some fundamental causal organisms of leaf diseases in H. brasiliensis includes Pseudocercospora ulei, Oidium heveae, Colletotrichum gloeosporioides and Corynespora cassiicola. Corynespora leaf fall caused by Corynespora cassiicola is currently accepted as the leaf disease which causes about 45% of yield loss to rubber in mostly Asian and African continents. The symptoms of South American Leaf Blight (SALB) range from discoloration of lamina to death of tree when untreated. Leaf disease symptoms range from white powdery patches to shriveling and falling off of tender leaves and translucent brownish yellow spots in semi-matured leaves in Oidium leaf disease. Colletotrichum leaf disease symptoms range from necrosis of tender leaves of young plants to defoliation and death of entire plant. Disease control is achieved by the use of chemicals and planting of disease-resistant varieties. Some phylloplane fungi are prospective biological control agents. The best treatment to manage Corynespora leaf fall disease (CLFD) in nurseries is the introduction of overhead shading coupled with application of the fungicide mancozeb. Diseases affecting the leaves of H. brasiliensis can be devastating and can lead to loss of multiple rubber trees and reduction in the latex production of the trees. Therefore, adequate preventive, curative and control measures against the diseases should be taking to ensure maintenance of a healthy rubber tree plantation.

Performance- and Resistance-Related Early Responses of Colombian Elite Rubber Tree Genotypes under Low Pressure of South American Leaf Blight: Implications for Disease Management in the Amazon.

The cultivation of Hevea brasiliensis, the primary commercial source of natural rubber, is strongly impacted by South American leaf blight (SALB) disease, caused by the fungus Pseudocercospora ulei. Various management strategies have been implemented, including the selection of resistant genotypes and the identification of escape zones. This study evaluated the growth, early yield, and resistance to SALB of nine Colombian elite genotypes from the ECC-100 series and IAN 873 clone (control) in a large-scale clone trial in an area with low SALB pressure in the Colombian Amazon during 2017-2020. Favorable early performance was evident, although there was a significant increase in the severity and sporulation of P. ulei over time, especially in the ECC 35, ECC 60, and IAN 873 genotypes. However, these scores indicate low susceptibility. Genotypes with higher resistance to SALB demonstrated greater growth and early yield compared to more highly susceptible genotypes. The ECC 64, ECC 73, ECC 90, ECC 25, and ECC 29 genotypes were more desirable in low SALB pressure zones due to their higher resistance and early performance. It is important to highlight that this research contributes to the selection of new SALB-resistant Colombian genotypes of H. brasiliensis. However, it is also necessary to evaluate the productivity of these selections in the mature stage and long-term resistance to SALB before recommending and promoting their commercial adoption in the Colombian Amazon.

The Diseases and Pests of Rubber Tree and Their Natural Control Potential: A Bibliometric Analysis

In order to trace the research history of diseases and pests in rubber tree and explore the potential for their natural control, a bibliometric analysis was conducted based on relevant documents retrieved from the Clarivate Analytics Web of Science (WoS) core collection SCI-E database. VOSviewer software was utilized to analyze the research distribution, scientific collaboration, knowledge structure, and research frontiers. The results show that annual publications on the diseases and pests of rubber tree have increased rapidly after 2005 after a long period of emergence and fluctuation. A total of 624 relevant publications from 51 countries/regions were identified. China was the most productive country with 152 documents, most of which were related to Colletotrichum leaf disease, powdery mildew, and other emerging diseases of rubber tree. France and Brazil produced rich research to tackle South American leaf blight, and have established a close collaborative relationship. Based on the analysis of themes and trend topics, pathogenicity mechanisms of fungal pathogens and plant defense mechanisms are currently hot topics. By further looking into the research, the defense-related genes of rubber tree and antagonistic mechanisms behind candidate biocontrol agents reveal great potential in developing natural control strategies. This study provides a useful reference about the progress and evolution of research into diseases and pests in rubber tree.

Phenology and South American leaf blight of polyclonal seedlings population of natural rubber trees in Colombia

The phenological development of polyclonal rubber plantations has been little explored, although they present adaptive potential to specific biotic and abiotic conditions. Between 2016 and 2021, rubber tree seedlings were evaluated for leaf ontogeny, leaf area index (LAI), and reproductive phenology (flowers and fruits). The climatic conditions were correlated with the foliar and reproductive rubber phenology and the incidence and severity of the South American leaf blight (SALB). The tree phenology showed a relationship between defoliation-refoliation with the water deficit intensity and high temperatures. The development of the trees in a polyclonal plantation was heterogeneous, and the defoliation-refoliation phases were extended over time. A higher SALB severity was associated with higher relative humidity and radiation periods, reducing the leaf area (atypical defoliation) and changing flowering and fruiting seasonality. The intensity and duration of climatic factors, particularly water deficit, are important for determining phenological processes and fungal diseases such as SALB, which serves as a tool to build management strategies both in seed production and obtaining latex in scenarios of climate change.

Agroecological and South American leaf blight escape zones for rubber cultivation in Colombia

AbstractIn agriculture, agroclimatic zoning procedures through geographic information systems provide producers, technical assistants, decision‐makers, and investors with land‐use planning and decision‐making tools. This study aims at identifying and delimiting areas suitable for the cultivation of rubber [Hevea brasiliensis Willd. ex A. Juss.) Müll. Arg.] in Colombia, using the species requirements at a scale of 1:100,000, as well as identifying escape zones for the South American leaf blight (SALB) disease (caused by the fungus Pseudocercospora ulei). The study was carried out following the agroecological zoning methodology for the definition of land use proposed by the Food and Agriculture Organization of the United Nations. Spatial analysis tools were used to raster data with ArcGIS Desktop 10.7, incorporating and evaluating climatic and soil variables. The obtained results showed that there are 5,480,543 ha suitable for cultivating natural rubber in Colombia. However, these areas present favorable climatic conditions for the development of the SALB.

Recent insights on gene expression studies on Hevea Brasiliensis fatal leaf fall diseases.

Hevea brasiliensis is one of the most important agricultural commodities globally, heavily cultivated in Southeast Asia. Fatal leaf fall diseases cause aggressive leaf defoliation, linked to lower latex yield and death of crops before maturity. Due to the significant consequences of the disease to H. brasiliensis, the recent gene expression studies from four fall leaf diseases of H. brasiliensis were gathered; South American leaf blight, powdery mildew, Corynespora cassiicola and Phytophthora leaf fall disease. The differential analysis observed the pattern of commonly expressed genes upon fungi triggers using RT-PCR, DDRT-PCR, Real-time qRT-PCR and RNA-Seq. We have observed that RNA-Seq is the best tool to seek novel genes. Among the identified genes with defence-against fungi were pathogenesis-related genes such as β-1,3-glucanase and chitinase, the reactive oxygen species, and the phytoalexin biosynthesis. This manuscript also provided functional elaboration on the responsive genes and predicted possible biosynthetic pathways to identify and characterise novel genes in the future. At the end of the manuscript, the PCR methods and proteomic approaches were presented for future molecular and biochemical studies in the related diseases to H. brasiliensis.

Prediction of South American Leaf Blight and Disease-Induced Photosynthetic Changes in Rubber Tree, Using Machine Learning Techniques on Leaf Hyperspectral Reflectance.

The efficiency of visible and near-infrared (VIS/NIR) sensors and predictive modeling for detecting and classifying South American Leaf Blight (SALB) (Pseudocercospora ulei) in rubber trees (Hevea brasiliensis) has been poorly explored. Furthermore, the performance of VIS/NIR analysis combined with machine learning (ML) algorithms for predicting photosynthetic alterations caused by SALB is unknown. Therefore, this study aimed to detect and classify the SALB levels, as well as to predict, for the first time, disease-induced photosynthetic changes in rubber trees. Leaf hyperspectral reflectance combined with five ML techniques (random forest (RF), boosted regression tree (BRT), bagged classification and regression trees (BCART), artificial neural network (ANN), and support vector machine (SVM)) were used. The RF, ANN, and BCART models achieved the best performance for classifying the SALB levels on the training dataset (accuracies of 98.0 to 99.8%), with 10-fold cross-validation repeated five times, and test dataset (accuracies of 97.1 to 100%). The ANN and RF models were better at predicting leaf gas exchange-related traits such as net CO2 assimilation rate (A) and extrinsic water use efficiency (WUEe) in the training (R2 ranged from 0.97 to 0.99) and testing (R2 ranged from 0.96 to 0.99) phases. In comparison, lower performances (R2 ranged from 0.24 to 0.52) were evidenced for the photochemical traits. This research provides a basis for future designs of a remote monitoring system based on early detection and accurate diagnosis of biotic stress caused by SALB, which is fundamental for more effective rubber crop protection.

Pseudocercospora ulei (South American leaf blight of rubber (SALB))

Pseudocercospora ulei (South American leaf blight of rubber (SALB))

High-quality genome assembly of Pseudocercospora ulei the main threat to natural rubber trees.

Pseudocercospora ulei is the causal agent of South American Leaf Blight (SALB), the main disease affecting Hevea brasiliensis rubber tree, a native species to the Amazon. Rubber tree is a major crop in South American countries and SALB disease control strategies would benefit from the availability of genomic resources for the fungal pathogen. Here, we assembled and annotated the P. ulei genome. Shotgun sequencing was performed using second and third generation sequencing technologies. We present the first P. ulei high-quality genome assembly, the largest among Mycosphaerellaceae, with 93.8 Mbp, comprising 215 scaffolds, an N50 of 2.8 Mbp and a BUSCO gene completeness of 97.5%. We identified 12,745 protein-coding gene models in the P. ulei genome with 756 genes encoding secreted proteins and 113 genes encoding effector candidates. Most of the genome (80%) is composed of repetitive elements dominated by retrotransposons of the Gypsy superfamily. P. ulei has the largest genome size among Mycosphaerellaceae, with the highest TE content. In conclusion, we have established essential genomic resources for a wide range of studies on P. ulei and related species.

Photosynthetic performance of Hevea brasiliensis affected by South American Leaf Blight under field conditions

Photosynthetic performance of Hevea brasiliensis affected by South American Leaf Blight under field conditions

Long-term resistance in promising rubber tree genotypes as a breeding source for improving South American leaf blight management under high disease incidence in the Colombian Amazon

South American Leaf Blight (SALB), caused by Pseudocercospora ulei, is the most important disease in Hevea brasiliensis grown in South America. This study aimed to evaluate long-term resistance in the field for 11 years in 10 rubber tree genotypes (nine hybrid clones and one primary clone) in a large-scale clonal trial (LSCT) and under controlled and nursery conditions. Resistance was evaluated using two resistance components: type of reaction (TR, ranging from 1 to 6) related to asexual sporulation, and stroma density (ST, ranging from 0 to 4), which is linked to sexual sporulation. Resistance status ranking (RSR) based on the maximum scores of the variables was adapted to classify the genotypes (completely resistant, partially resistant or highly susceptible) over time, and against four indigenous isolates of P. ulei. Eight of the ten clones exhibited partial resistance in the field, and clones FDR 5597, GU 198 and FDR 5788 were more resistant with TR ≤ 4 and ST ≤ 2. These clones were completely resistant in the laboratory/nursery with TR < 3 and ST = 0. Only clone MDF 180 did not exhibit the sexual phase of the pathogen (i.e., ST = 0) in the field or in the nursery. Clones CDC 56 and IAN 873 (control) were highly susceptible, with TR > 5 and ST > 2. In this study, sources of partial resistance were evidenced for the effective management of SALB under conditions of high P. ulei incidence in the Amazon.

Ionic Liquids Separating Rubber Latex from Guayule.

Danger to rubber trees (Hevea brasiliensis) from South American leaf blight fungus imperils the world’s source of natural latex for essential rubber products. Avoiding latex allergies also requires a non-Hevea latex source. The present methods for removing latex entrapped in the individual cells of guayule plants require environmentally hazardous chemicals. This study proposes a new method for latex extraction from guayule using various ionic liquids (ILs) to dissolve cell walls and release latex, as substantiated by Fourier transform infrared spectroscopy (FTIR) data.

Near infrared spectroscopy to rapid assess the rubber tree clone and the influence of maturation and disease at the leaves

The rubber tree is a species of great economic importance due to its natural rubber, which is widely used in the tire industry due to its resistance and does not yet have a synthetic formula capable of completely replacing it. Near infrared spectroscopy (NIRS) is an emerging technique for soil and plant analysis. The aim of this study is to predict the Hevea rubber tree clones, detect and discriminate leaves at different stages of development (young or adult), as well as to discriminate healthy and affected adult leaves by South American Leaf Blight, through the spectroscopic technique of visible to infrared (Vis-NIR) combined with chemometrics. Using dried ground leaves samples, leaves from 14 rubber trees clones (H. brasiliensis) were evaluated, these leaves were collected in 3 tree stages young trees; adult or mature trees; and mature trees with symptoms of Microcyclus ulei (disease leaves). The near infrared (NIR) reflectance spectra were acquired using a spectrometer FOSS-NIRS (model DS2500). An average of 64 scans operating in a range between 400 and 2500 nm under spectral resolution of 0.5 nm were used for all the spectral acquisitions. With the use of reflectance spectroscopy in visible and near infrared, it was possible to efficiently discriminate the clones of the rubber tree, regardless of the use of spectra obtained from young leaves or from mature leaves. Which might enable studies with characterization of the genetic materials present in the germplasm banks and in situ. The technique also efficiently differentiated the young leaves from the mature leaves, as well as separating the healthy mature leaves from the diseased mature leaves. These results can contribute to the breeding and conservation programs of the species, obtaining fast results and without the use of chemical reagents.

Development parameters of the latent period as a response of rubber tree resistance to South American leaf blight

ABSTRACT The major phytosanitary problem for rubber tree cultivation in Brazil is the disease known as South American leaf blight, caused by the fungus Microcyclus ulei. Its symptoms manifest in young leaves and cause intense defoliation, resulting in reduced latex production and even the death of susceptible plants. Thus, this disease consists in a constant threat to East Asian plantations. As worldwide traditional breeding programs have evolved, interspecific hybrid clones have currently been used for planting. They are more productive and show better resistance to pathogens. However, traditional breeding programs have not led to significant progress in resistance to South American leaf blight since the selection is directed to clones with complete resistance. In this pathosystem, horizontal or partial resistance (HR) and vertical or complete resistance (VR) can act simultaneously, evidencing their complexity and difficult quantification. This study aimed to: characterize the foliar lesion type in Hevea sp. X M. ulei pathosystem; verify the clonal susceptibility to pathogens; analyze the infection frequency for resistance quantification in Hevea sp. x M. ulei pathosystem, and recommend differentiating rubber tree clones to quantify M. ulei races in Brazil. The monocyclic parameters (latent period and lesion diameter) are applicable for resistance quantification in Hevea sp. x M. ulei pathosystem. Latent period had slight variation among clones. Lesion diameter had wide variation among clones and was a discriminating parameter for horizontal resistance and vertical resistance.

Assessing growth, early yielding and resistance in rubber tree clones under low South American Leaf Blight pressure in the Amazon region, Colombia

In Latin America, there are areas that favor the cultivation of rubber (Hevea brasiliensis) and reduce the risk of South American Leaf Blight (SALB), produced by the pathogen Pseudocercospora ulei. This study aimed to analyze the growth, early yielding and SALB resistance of nine promising clones and IAN 873 (control) in the pre-tapping and early tapping phases in a large-scale clone trial in a low SALB pressure zone in the Colombian Amazon, 2010−2019. San Vicente del Caguán (Caquetá) has climatic characteristics that are not very favorable for SALB (mean precipitation < 2600 mm year−1 and average relative humidity < 82 %). After 10 years, the better clones (FX 3899 P1, FDR 4575, FDR 5578, GU 198 and FDR 5597) presented an acceptable average for the main trunk circumference (CMT < 52 cm) at the end of the pre-tapping phase (9th year), a favorable CMT (< 58 cm) in the early tapping phase (1 st year tapping or 10th year), a superior early dry rubber yield (EDRY) (< 43 g.tree−1.tap−1), a high partial resistance to SALB (low severity, with mean scores for AT1 and AT2 < 1 and low asexual and sexual sporulation, with mean scores for TR and ST < 1) and a high percentage of leaves retained in the canopy (80–100 %), as compared to clone IAN 873. This study provides the basis for final clonal selection once peak yield (5th year tapping) is identified for later development in the Amazon region, Colombia.

Differential expression and structural polymorphism in rubber tree genes related to South American leaf blight resistance

South American leaf blight (SALB) is the worst impairment for rubber tree cultivation in the Amazon. Hevea brasiliensis clones produce high latex yields but most are SALB-susceptible (SS). So, resistance has been searched in related species. We selected defense related genes among those differentially expressed while contrasting SALB-resistant (SR) and susceptible clones from three Hevea species. SS clones over-expressed pathways responsive to salicylic (SA) and also jasmonic acid, thus entering a self-harmful cycle. SR clones displayed tightly coordinated SA-responsive and stress-control pathways. Polymorphism in the selected gene sequences supported SS × SR clone divergence.