American Leaf Research Articles

First record of South American leaf miner, Tuta absoluta (Meyrick, 1917) from Jammu, India

First record of South American leaf miner, Tuta absoluta (Meyrick, 1917) from Jammu, India

Mycena citricolor isolates from diverse hosts in Costa Rica: Colony aspect, growth dynamics, reproduction in vitro and aggressiveness on Coffea arabica

AbstractThe basidiomycete fungus Mycena citricolor hosts on about 80 plant families. The asexual morph causes the disease known as American leaf spot of coffee (Coffea arabica). We isolated and characterized 15 isolates of M. citricolor collected from coffee plants, shade trees and weeds. Cultures on potato‐dextrose‐agar + yeast extract (PDAY) medium were kept for a week in complete darkness. The cultures were then exposed to light for 7 weeks and co‐cultivated with coffee foliar discs, to stimulate the production of gemmifers. We evaluated the speed of growth, appearance, colour of the mycelium and gemmifers production capacity. All isolates conformed to the typical cultural characteristics of M. citricolor, with beige/white thin and slightly aerial mycelium. The whitest isolate was from Persea americana, which had the slowest growth rate in vitro (6.4 mm/day), while the isolate from weed Kalanchoe pinnata was the fastest, with a speed of 9 mm/day. The most gemmifer‐producing isolates were those isolated from the coffee cultivar Catimor‐Costa Rica 95, Citharexylum donnell‐smithii and Cissus verticillata, with over 200 gemmifers per Petri dish. Isolates from Erythrina and Ipomoea nil produced <50 gemmifers on average. The Composite Aggressiveness Index (CAI) was determined on 2‐year‐old detached coffee branches of the Caturra variety foliage. The least aggressive isolate was from Erythrina poeppigiana (CAI = 0) and the most aggressive was from Kalanchoe pinnata (CAI = 18.87). The isolate from the coffee cultivar Catimor‐Costa Rica 95 was more aggressive than that from the cultivar Caturra (CAI = 9.94 vs. CAI = 3.66). Moreover, successful infection occurred only when the apex of gemmae made direct contact with the coffee leaf when using the inoculum derived from C. verticillata and Anredera cordifolia. These results show the variability in the population of the pathogen. This is the first study that characterizes the growth, morphology, reproduction and aggressiveness of M. citricolor obtained from hosts other than coffee. In addition, it is the first to report the use of coffee foliar discs to induce gemmifer production in vitro and to assess and quantify the effect of gemma position when inoculating coffee leaves.

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.

Control Strategies of American Leaf Miner (&lt;i&gt;Tuta absoluta&lt;/i&gt;) (Meyrick) Adopted by Farmers in Lalitpur District, Nepal

Control Strategies of American Leaf Miner (&lt;i&gt;Tuta absoluta&lt;/i&gt;) (Meyrick) Adopted by Farmers in Lalitpur District, Nepal

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.

Differential Volatile Organic Compound Expression in the Interaction of Daldinia eschscholtzii and Mycena citricolor.

Fungi exhibit a wide range of ecological guilds, but those that live within the inner tissues of plants (also known as endophytes) are particularly relevant due to the benefits they sometimes provide to their hosts, such as herbivory deterrence, disease protection, and growth promotion. Recently, endophytes have gained interest as potential biocontrol agents against crop pathogens, for example, coffee plants (Coffea arabica). Published results from research performed in our laboratory showed that endophytic fungi isolated from wild Rubiaceae plants were effective in reducing the effects of the American leaf spot of coffee (Mycena citricolor). One of these isolates (GU11N) from the plant Randia grandifolia was identified as Daldinia eschscholtzii (Xylariales). Its antagonism mechanisms, effects, and chemistry against M. citricolor were investigated by analyzing its volatile profile alone and in the presence of the pathogen in contactless and dual culture assays. The experimental design involved direct sampling of agar plugs in vials for headspace (HS) and headspace solid-phase microextraction (HS-SPME) gas chromatography-mass spectrometry (GC-MS) analysis. Additionally, we used ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS/MS) to identify nonvolatile compounds from organic extracts of the mycelia involved in the interaction. Results showed that more volatile compounds were identified using HS-SPME (39 components) than those by the HS technique (13 components), sharing only 12 compounds. Statistical tests suggest that D. eschscholtzii inhibited the growth of M. citricolor through the release of VOCs containing a combination of 1,8-dimethoxynapththalene and terpene compounds affecting M. citricolor pseudopilei. The damaging effects of 1,8-dimethoxynaphthalene were corroborated in an in vitro test against M. citricolor pseudopilei; scanning electron microscopy (SEM) photographs confirmed structural damage. After analyzing the UHPLC-HRMS/MS data, a predominance of fatty acid derivatives was found among the putatively identified compounds. However, a considerable proportion of features (37.3%) remained unannotated. In conclusion, our study suggests that D. eschscholtzii has potential as a biocontrol agent against M. citricolor and that 1,8-dimethoxynaphthalene contributes to the observed damage to the pathogen's reproductive structures.

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.

The endophytobiome of wild Rubiaceae as a source of antagonistic fungi against the American Leaf Spot of coffee (Mycena citricolor).

The American leaf spot, caused by Mycena citricolor, is an important disease of coffee (Coffea arabica), mostly in Central America. Currently, there are limited pathogen control alternatives that are environment friendly and economically accessible. The use of fungi isolated from the plant endomycobiota in their native habitats is on the rise because studies show their great potential for biological control. To begin to generate a green alternative to control M. citricolor, the objectives of the present study were to (i) collect, identify, screen (in vitro and in planta), and select endophytic fungi from wild Rubiaceae collected in old-growth forests of Costa Rica; (ii) confirm endophytic colonization in coffee plantlets; (iii) evaluate the effects of the endophytes on plantlet development; and (iv) corroborate the antagonistic ability in planta. Through in vitro and in planta antagonism assays, we found that out of the selected isolates (i.e. Daldinia eschscholzii GU11N, Nectria pseudotrichia GUHN1, Purpureocillium aff. lilacinum CT24, Sarocladium aff. kiliense CT25, Trichoderma rifaii CT5, T. aff. crassum G1C, T. aff. atroviride G7T, T. aff. strigosellum GU12, and Xylaria multiplex GU14T), Trichoderma spp. produced the highest growth inhibition percentages in vitro. Trichoderma isolates CT5 and G1C were then tested in planta using Coffea arabica cv. caturra plantlets. Endophytic colonization was verified, followed by in planta growth promotion and antagonism assays. Results show that Trichoderma isolates CT5 and G1C have potential for plant growth promotion and antagonism against Mycena citricolor, reducing incidence and severity, and preventing plant mortality.

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.

Alternative plant protection strategies for tomorrow's coffee

AbstractContinuous pesticide usage has negative impacts on people and ecosystems associated with coffee farms. Alternative plant protection strategies can be implemented that are sustainable for both the environment and the coffee farmer. In this review, new genomic techniques (NGTs) such as RNAi (RNA interference, using spray‐induced gene silencing – SIGS) are presented as a possible novel strategy to manage Coffea arabica pests and diseases. Exploitation of the coffee agroforestry system (AFS) is presented as another strategy, offering both plant protection and ecosystem restoration functions. Interactions within a coffee‐AFS were found to both hinder and bolster the development of some coffee pests and diseases. Biological control represents a third strategy that has been examined to‐date to combat important coffee pests and diseases (i.e., American leaf spot, black coffee twig borer, coffee berry borer, coffee berry disease, coffee leaf miner, coffee leaf rust, coffee wilt disease and green coffee scale). The astute use of RNAi, AFS and/or biological control have the potential to provide alternatives to conventional pesticides for future sustainable coffee production. However, these approaches must be compatible with the coffee farmers' local needs and accessibility and bolstered through nationwide support by advisory services and coffee authorities.

Metabolomic and Genomic Approach to Study Defense Induction by Nesidiocoris tenuis against Tuta absoluta and Tetranychus urticae in Tomato Plants.

The phytophagy of the predator Nesidiocoris tenuis (Hemiptera: Miridae) can trigger defense responses in tomato plants against pests, such as two spotted spider mite Tetranychus urticae (Acari: Tetranychidae) and South American leaf miner Tuta absoluta (Lepidoptera: Gelechiidae). The expression of genes governing Jasmonic Acid (JA) biosynthesis pathway and fluctuations in the levels of underlying metabolites have been rarely studied in mirid-infested plants. In the present study, fifteen 3rd instar nymphs of N. tenuis were caged on each top and lower leaf of tomato plants for 4 d to induce plant defense; after this period the predators were removed. With regard to T. absoluta, oviposition preference; larval period; and pupal weight were significantly reduced in N. tenuis-punctured plants. T. urticae adults exhibited a significantly higher escape tendency and reduced survival on punctured plants. Metabolomics confirmed such observations revealing substantial differences between N. tenuis-punctured and unpunctured (control) plants. Metabolites directly associated with the activation of the JA defense pathway, such as the precursor α-linolenic acid, had increased concentrations. The expression of the defense-related genes PI-II, MYC2, VSP2, and HEL was increased in the top leaves and only VSP2 and MBP2 in the lower leaves; interestingly, in the middle (unpunctured) leaves VSP2, HEL, and MBP2 were also upregulated, indicating systemic signaling. Collectively, phytophagy of N. tenuis caused adverse effects on T. absoluta and T. urticae, whereas the multi-omics approach (phenomics, metabolomics, and genomics) offered valuable insights into the nature of the plant defense responses and provided useful evidence for future applications in integrated pest management, plausibly resulting in the reduction in the required pesticide volumes.

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.

Mycena citricolor (American leaf spot of coffee)

Mycena citricolor (American leaf spot of coffee)

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

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