South American Leaf Blight Research Articles

Comparison of growth, yield and related traits of resistant Hevea genotypes under high South American leaf blight pressure

Most natural rubber (NR) comes from the cultivation of Hevea brasiliensis in tropical areas. However, South American leaf blight (SALB), caused by Microcyclus ulei (P. Henn.) Arx, is the main factor limiting Hevea cultivation in the American humid tropics. Based on a preliminary selection from among more than 960 accessions, the aim of this work was to propose new SALB-resistant genotypes for South American plantations. Agronomic traits (SALB resistance, growth, production) and characters related to latex production, such as sucrose and inorganic phosphorus, along with structural traits of the bark of nine Hevea genotypes resistant to SALB (TP875, FDR5788, MDX608, PMB1, CDC429, CDC312, FDR4461, MDF180, SIAL893) were evaluated during the course of a 12-year trial located in the Michelin plantation (Bahia, Brazil). These genotypes presented a quantitative resistance to SALB characterized by partially sporulating lesions (anomorph stage). No sexual form of M. ulei (stromata, teleomorph stage) was found in FDR5788, MDF180, CDC312, PMB1. Only FDR5788 genotypes presented a higher NR yield than genotype TP875 used as a control. For FDR5788, MDX608, CDC312 and PMB1, the estimated yields of 12-year-old trees were, respectively 2.6, 2.0, 1.8 and 1.2tyear−1ha−1. In all genotypes, medium sucrose and inorganic phosphorus concentrations were related to intermediate metabolism for cis-polyisoprene synthesis. The low yield of genotypes SIAL893 and MDF180 is related to the limited number of vessel rings, limited translocation of sucrose in the latex, and a slow metabolism indicated by low average concentrations of inorganic phosphorus in the latex. For the south east of the Bahia state, FDR5788 and CDC312 are recommended for new planting areas because of their capacity to prevent teleomorph formation, combined with high NR yields.

Performance of different rubber tree clones against South American leaf blight (Microcyclus ulei)

SummaryThis study was aimed to evaluate the behaviour of eighteen clones of Hevea brasiliensis (rubber) against South American leaf blight and to study progress of the disease. The experiment was conducted in Cachoeiro de Itapemirim‐ES, where 18 clones were evaluated. The experimental design was a randomized block with four replicates; each experimental unit consisted of three plants. Evaluations were performed at 15‐day intervals on 30 leaflets per tree. Disease incidence was quantified and infection classified according to the stages of development and type of damage. Leaf blight occurred during the entire experimental period; however, disease intensity varied with the resistance level of the clones and the time of year. Clones FX 3864, RRIM 725, RRIM 711, IAC 300 and IAN 873 exhibited the highest resistance to leaf blight.

Role of ascospores and conidia in the initiation and spread of South American leaf blight in a rubber tree plantation

Microcyclus ulei, the fungus causing South American leaf blight (SALB) on rubber tree leaves, produces two main types of spores: ascospores and conidia. To assess their respective epidemiological role, a field experiment was conducted in French Guiana over 3 years. Tree phenology, disease severity and climate variables were recorded while airborne spores were trapped and quantified. Ascospores were shown to play an essential role in the perpetuation of the disease outside the host's growth periods, in the resumption of epidemics, and in the spread of the disease to disease‐free zones. Conidia were trapped in visibly infected plots only, during periods of host growth. Disseminated over short distances and present only temporarily on leaves, the conidia enabled the disease to spread stepwise when the climate was conducive. Segmentation analysis revealed that the duration of high relative humidity was the climatic variable most related to ascospore trapping. Ascospore release did not require low temperatures. Considering the essential role of the ascospores in the initiation and spread of disease, artificial defoliation as a means of reducing the inoculum pressure during tree refoliation is proposed to control SALB. To check the validity of this method, a survey over several years of natural defoliation–refoliation in relation to climate and other leaf diseases is needed.

A newly identified locus controls complete resistance to Microcyclus ulei in the Fx2784 rubber clone

Using cultivars which are genetically resistant to South American leaf blight (SALB) caused by the fungus Microcyclus ulei is the only way to plant rubber trees in disease-affected areas. Numerous field observations led to the hypothesis that the resistance of the cultivar Fx2784 to SALB is likely to be monogenic. In this study, we investigated this hypothesis by examining the distribution of the trait in a cross between the resistant cultivar and a susceptible one. The individuals resulting from this cross were planted in field trials in French Guiana and Brazil. The resistance of all the trees was assessed by field observations. Bulk segregant analysis (BSA) using microsatellite markers was performed in French Guiana to determine which markers were genetically linked to resistance, and the results were validated by field observations in Brazil. In both locations, a 1:1 segregation of the resistance trait was observed, thus reinforcing the monogenic hypothesis. BSA showed tight linkage between resistance and the microsatellite markers located in linkage group 2 in the Hevea genome and enabled to pinpoint the resistance locus. The location was confirmed by observations on the trees planted in Brazil. This result should facilitate the use of Fx2784 resistance in future breeding programs for SALB resistance. This is the third major locus conferring resistance to SALB identified in rubber tree (Hevea spp.). These three loci are genetically independent, a favorable situation for genetic improvement of SALB resistance.

Clones de copa de seringueira resistentes ao mal-das-folhas para o cultivo na Amazônia tropical úmida

O objetivo deste trabalho foi avaliar o desempenho de 11 clones de copa de seringueira de Hevea pauciflora × H. guianensis, H. guianensis × H. pauciflora, H. pauciflora × H. rigidifolia e H. pauciflora resistentes ao fungo Microcyclus ulei, causador do mal-das-folhas, sobre o painel de CNS AM 7905 (seleção primária de H. brasiliensis), durante 14 anos nas condições edafoclimáticas da Amazônia tropical úmida. Foram avaliados: produtividade de borracha seca durante sete anos, aspectos anatômicos, características fisiológicas do látex, estado nutricional das plantas e métodos de sangria (oriental e amazônica). Os clones de copa CPAA C 01, 06 e 45 produziram, na média, mais de 1,4 t ha- 1 ano- 1 de borracha seca, seguido pelos clones CPAA C 13, 14, 15, 16 e 20, com produtividade acima de 1,0 t ha-1 ano- 1, enquanto os clones CPAA C 18, CPAA C 33 e CBA 2 registraram produtividade inferior a 0,9 t ha-1 ano- 1. A concentração de Pi e Mg no látex e os teores foliares de K e Cu estão relacionados com a produtividade dos clones CPAA C 01, 06 e 45, sendo esses fatores importantes no programa de seleção de clones de copa de seringueira. Em plantio comercial, o método da sangria oriental é mais eficiente que a amazônica.

The Potential of the South American Leaf Blight as a Biological Agent

When asked by the Department of Homeland Security to create potential terrorism scenarios, even “Out of the Box Thinkers” initially failed to come up with the following scenario. Oil tankers, refineries, nuclear plants, etc., are obvious potential terrorists’ targets, and adequate measures are being taken to protect them. However, what if the target were to be a non-food commodity product, such as natural rubber tree plantations located in places as remote as southeast Asian countries like Thailand or Indonesia? Would it be of concern? At first thought “maybe not”, but think again. What could the release of a deadly microorganism (fungus/virus/bacteria) in a rubber tree plantation in Indonesia, Malaysia or Thailand possibly mean to you or the world economy?

Understanding the recent colonization history of a plant pathogenic fungus using population genetic tools and Approximate Bayesian Computation.

Understanding the processes by which new diseases are introduced in previously healthy areas is of major interest in elaborating prevention and management policies, as well as in understanding the dynamics of pathogen diversity at large spatial scale. In this study, we aimed to decipher the dispersal processes that have led to the emergence of the plant pathogenic fungus Microcyclus ulei, which is responsible for the South American Leaf Blight (SALB). This fungus has devastated rubber tree plantations across Latin America since the beginning of the twentieth century. As only imprecise historical information is available, the study of population evolutionary history based on population genetics appeared most appropriate. The distribution of genetic diversity in a continental sampling of four countries (Brazil, Ecuador, Guatemala and French Guiana) was studied using a set of 16 microsatellite markers developed specifically for this purpose. A very strong genetic structure was found (F(st)=0.70), demonstrating that there has been no regular gene flow between Latin American M. ulei populations. Strong bottlenecks probably occurred at the foundation of each population. The most likely scenario of colonization identified by the Approximate Bayesian Computation (ABC) method implemented in DIYABC suggested two independent sources from the Amazonian endemic area. The Brazilian, Ecuadorian and Guatemalan populations might stem from serial introductions through human-mediated movement of infected plant material from an unsampled source population, whereas the French Guiana population seems to have arisen from an independent colonization event through spore dispersal.

Translocation of cyanogenic glycosides in rubber tree crown clones resistant to South American leaf blight

The objective of this work was to assess the possible transport of cyanogenic glycosides from leaves of rubber tree crown clones (Hevea spp.) resistant to South American leaf blight to the trunk of the panel clones in which they are grafted. The cyanogenic potential (HCNp) of the crown clones was determined in the trunk bark, at different distances from the cambium, and its gradient was evaluated along the trunk. The correlation between the HCNp of the crown leaves and that of the trunk bark was also evaluated. HCNp determined in leaves showed a wide range variation in the species studied as crown clones, with the lowest values registered in H. nitida clones, and the highest ones in H. rigidifolia. In the trunk bark, the tissue layer nearer the cambium showed higher HCNp values. A positive basipetal gradient was observed along the trunk, i.e., there was an increase in HCNp from the apex toward the base. Although the grafted crowns influence the cyanogenic potential of the trunk bark of panel clones, the absence of correlation between the HCNp of the leaves and trunk bark indicates that the crown is not the main source of the cyanogenic glycosides found in the trunk.

Development of microsatellite molecular markers and genetic diversity in Hevea Braziliensis

Background The rubber tree [Hevea Braziliensis (Willd. ex Adr. De Juss.) Muell-Arg.] is native from the Amazon region which has great economic importance for being the largest source of natural rubber in the world. Although Brazil is the center of origin and genetic diversity of this culture, the country is currently responsible for only 1% of the world production. Besides offering optimal weather conditions for crop development, the Amazon rainforest region is also favorable to the development of the fungus known as SALB (South American leaf blight), which causes the disease-of-leaves. Leaves fall sharply reducing the production of latex, limiting the production of rubber in this region. Thus breeding programs are seeking for clones which are resistant to this fungus and with high production in escape regions, which provide stress conditions such as low temperatures, high altitude, wind and other diseases [1]. The rubber tree is perennial and requires about 30 years to obtain an improved variety, starting from the controlled pollination of a clone to the final recommendation. Molecular markers such as microsatellites (Simple Sequence Repeats, SSRs) are an important tool for diversity studies and potentially to assist breeding programs. This study aimed to develop an enriched microsatellite library for H. Braziliensis, characterize these developed microsatellite markers and test the transferability of these markers to six other species of the genus Hevea. Material and methods For this study we used 36 accessions of H. Braziliensis donated by the Agronomy Institute of Campinas and one accession of each of six other species of genus Hevea (H. nitida, H.pauciflora (2), H.camargoana, H.guianensis, H. rigidifolia andH. benthamiana) provided by Embrapa. Genomic DNA samples were extracted from lyophilized leaf tissues using a modified CTAB method [2]. Trinucleotide and dinucleotide enriched genomic libraries for H. Braziliensis were constructed. The DNA samples were digested with AFAI and enriched using (CT)8 and (GT)8 biotinylated microsatellite probes for the dinucleotide library and (ATC)8 and (CCT)8 for the trinucleotide library. The clones obtained were sequenced and the sequences were evaluated with the Microsat program, which removes parts of the vector and the adapters and verifies the presence of restriction site within the sequence. After this step, the sequences were aligned and edited using the program SeqMan (DNAStar Inc.), which also allows analyzing the redundancy of the library. The identification of microsatellites was performed using a research tool SSRs SSRIT – “The Simple Sequence Repeat Identification Tool” avaiable at Gramene [http:// www.gramene.org]and primers complementary to sequences flaking the microsatellites were designed by Primer Select Program (DNAStar Inc) and Primer 3. Amplification tests were made from a temperature gradient to know the annealing temperature and the products were evaluated and resolved on 3% agarose gels stained with ethidium bromide and in denaturing 6% polyacrylamide and silver stained [3]. The loci were characterized on the number of alleles per locus, allele frequency and the Polymorph Information Content (PIC). It was also made analysis of ancestry for de accessions of H. Braziliensis using the program Structure v 2.3.3 [4]. * Correspondence: camila.mantello@gmail.com Molecular Genetic Analysis Laboratory Molecular Biology Center and Genetic Engineering (CBMEG), UNICAMP, Campinas, Sao Paulo, 13083-875, Brazil Full list of author information is available at the end of the article Mantello et al. BMC Proceedings 2011, 5(Suppl 7):P11 http://www.biomedcentral.com/1753-6561/5/S7/P11

Construction and analysis of a leaf cDNA library from cold stressed rubber tree clones

Background Rubber tree [Hevea Braziliensis (Willd. ex Adr. de Juss.) Muell-Arg.], a native species of the Amazon Rainforest in South America, belonging to the Euphorbiaceae family, is world’s major source of natural latex. Brazil, despite being the center of origin and diversity of the species and latex main producer at the end of XIX century, nowadays imports around 70% of the rubber consumed in the country. Although the Amazonian basin provides optimal conditions for rubber plantation, the occurrence of South American leaf blight (SALB) disease, caused by the ascomycete Microcyclus ulei, limits the rubber production in this region. Therefore, rubber plantation has been extended to suboptimal areas that are prominently located in northeast India, Vietnam, southern China and southern plateau of Brazil. Besides the new conditions for crop development, these new areas present stress conditions like low temperatures, dry periods and wind. It was shown that low temperatures affect the development and latex production of rubber trees. Breeding programs have been searching for clones adapted to these suboptimal areas. A complete cycle of breeding and selection takes at least 20 years to succeed in obtaining a superior clone. As such, development of new methods for early evaluation is essential to reduce and optimize the breeding management. Aiming to help in the development of these methods, in this work, we have constructed a leaf cDNA library to study ESTs (Expressed Sequence Tags) from cold stressed rubber trees. The originated sequences from this library can be used to create an ESTs databank and will provide genetic knowledge about how rubber trees cope with chilling stress, being also a valuable source of polymorphic molecular markers, such as SSRs and SNPs. Some of these markers may be associated to chilling tolerance, and early evaluation would be possible in young rubber tree clones.

EST profiling of resistant and susceptible Hevea infected by Microcyclus ulei

In this report, we assess by suppression subtractive hybridization (SSH) the biological process of the South American leaf blight (SALB) that is an important disease of rubber tree caused by Microcyclus ulei (P. Hem.) v. Arx. Leaves from MDF180 (a partially resistant cultivar from Peruvian origin) and PB314 (a susceptible cultivar) were inoculated with M. ulei. Leaf fragments were collected from 6h post-infection (hpi) to 58 days post-infection (dpi) and five cDNA libraries enriched for genes induced by M. ulei in order to identify up-regulated genes at the different stages of the host-parasite interaction. We sequenced 8027 expressed sequence tags (EST). After control of their quality, trimming and assembling, we obtained 1165 singlets and 458 contigs. The EST redundancy within each SSH library varied from 23% to 87%. Based on sequence similarity 49% of the sequences could be assigned to functional categories, whereas 21% corresponded to unknown function and 30% did not show any significant similarity with other sequences. The profile of gene expression was different for each library and gave a comprehensive picture of the transcriptome dynamics of rubber tree in response to M. ulei throughout the infection process. Most of the ESTs described in this study (80%) are specific to leaf tissues since they did not show any homology with ESTs previously identified in latex transcriptome. The occurrence of ESTs whose functional annotation was related to “stress” or “defence” was compared between libraries and their specific function is discussed in relation to the corresponding stage of leaf lesions and to histological observations. As far as we known, this is the first report on ESTs from Hevea brasiliensis collected during a biotic stress. It provides a significant contribution to the understanding of the molecular mechanism of the resistance and the susceptibility to South American leaf blight and it represents a new molecular resource for the development of polymorphic markers and marker-assisted selection.

Assessment of rubber tree panels under crowns resistant to South American leaf blight

The objective of this work was to assess the performance of panel clones under crowns resistant to South American leaf blight (Microcyclus ulei). The experiment was carried out with 18 panel clones crown-budded with Hevea pauciflora x H. guianensis, in a Xanthic Ferralsol (Oxisol) in Manaus, AM, Brazil. The following parameters were evaluated: dry rubber yield, plant nutritional status, and anatomical and physiological characteristics of the latex vessels. In the first three years of evaluation, the panel clones IAN 2878, IAN 2903, CNS AM 7905, CNS AM 7905 P1, and PB 28/59 showed the highest dry rubber yield potential, while the clones IAN 6158, IAN 6590, and IAN 6515 should not be recommended for crown budding. Higher potassium and copper foliar content in panel clones were associated to an increase in dry rubber yield. The simultaneous evaluation of anatomical and physiological characteristics of latex is fundamental for the selection of panel clones in the Amazon region. Crown budding is an efficient technology for South American leaf blight management in endemic regions.

A rubber tree’s durable resistance to Microcyclus ulei is conferred by a qualitative gene and a major quantitative resistance factor

The components of genetic resistance from the Hevea brasiliensis cultivar MDF 180 against South American Leaf Blight (SALB) caused by Microcyclus ulei were investigated by QTL mapping. MDF 180 has already been described as a cultivar with a high level of partial and long-lasting resistance. The resistance of progeny individuals from a cross between a susceptible cultivar and MDF 180 was assessed both under controlled conditions of inoculation by three M. ulei isolates and under natural infection in a field trial. Genetic maps of the two parents of this progeny were mainly established based on microsatellites and AFLP markers. No resistance QTL were found in the susceptible parent. In the resistant parent, we identified a qualitative gene responsible for the resistance against isolates from French Guiana and a major quantitative resistance factor determining the resistance against isolates from the state of Bahia (Brazil). The qualitative resistance gene was denominated M15md and was located in the linkage group g15. Four minor resistance QTLs were also identified, two of which showed an epistatic interaction with M15md. The durability of the resistance of MDF 180 is discussed in light of these data.

OBTAINING ISOLATES OF MICROCYCLUS ULEI, A FUNGUS PATHOGENIC TO RUBBER TREES, FROM ASCOSPORES

Microcyclus ulei, a fungus causing South American leaf blight of rubber tree, can only be isolated from asexual spores, which remain on a lesion just for a few days. This is a serious problem when wishing to study the diversity of the fungus on wild trees, which bear stromatic lesions almost exclusively on old leaves. The proposed technique can be used to isolate the fungus easily from sexual spores occurring in these stromata, even on leaves that are several months old.

Foliar endophytic fungi from Hevea brasiliensis and their antagonism on Microcyclus ulei

Endophytic fungi live inside plants as symbionts for at least one period of their life cycle. They play an important role in plant defence and could be promising sources of valuable natural bioactive products. The present study aimed to select endophytic fungi antagonistic to Microcyclus ulei, the agent of South American Leaf Blight (SALB) responsible for the weak development of rubber plantations in Latin America. Endophytic fungi were isolated from leaves of three cultivars (FX3864, CDC312, MDF180) of Hevea brasiliensis (the rubber tree) with distinct resistance levels to the attack by Microcyclus ulei. Leaf samples were collected from a 5,000 ha area of the Michelin plantations (Igrapiuna, Bahia, Brazil). A total of 435 colonies of endophytic fungi were isolated, purified, and preserved in sterilized distilled water. Lyophilized culture filtrates obtained from 88 fungal isolates, grown in liquid malt extract medium, were tested in vitro at concentrations of 50% and 12.5% for their inhibitory potential against the germination of M. ulei PMB26 conidia. Thirteen filtered cultures of endophytic fungi that presented inhibitory activity above 80% (at the concentration 12.5%) were characterized taxonomically by sequencing the ITS regions of rDNA, revealing the following taxa: Fusarium sp., Gibberella sp., Glomerella cingulata, Microsphaeropsis sp., Myrothecium sp., Pestalotiopsis sp. and Phomopsis sp. Three taxa were detected only in the resistant cultivars: Microsphaeropsis sp., and Pestalotiopsis sp. in MDF180, and Myrothecium sp. in CDC312. The present work constitutes the first study showing inhibitory activity of rubber tree endophytic fungi on Microcyclus ulei. These results provide an encouraging basis for the identification of new bioactive molecules for an effective control of South American leaf blight.

Assessing resistance of rubber tree clones to Microcyclus ulei in large-scale clone trials in Ecuador: a less time-consuming field method

Resistance of rubber tree clones to South American Leaf Blight (SALB) caused by the fungus Microcyclus ulei is normally assessed in specific large-scale clone trials, which in general entail a considerable amount of work. Four variables are observed monthly on each tree over many years: disease severity and conidial sporulation intensity on young leaves, and severity and stroma density on mature leaves. In order to simplify this field assessment method, we tested the resistance of eight rubber tree clones to M. ulei in Ecuador in a Fisher block design with four replicates per treatment. Three months after planting, monthly observations were made for a period of 12 months on the foliage focusing on the four variables, in order to quantify disease development. Given the correlations between the four variables, assessment of conidial sporulation intensity on young leaves and stroma density on mature leaves should be sufficient. The most suitable period to start the assessment was 6 months after planting, for a duration of six to nine months. As repeated observations on the same trees were autocorrelated, it was possible to reduce the assessment frequency to once every 2 months. To conclude, assessing the resistance of rubber tree clones to SALB in large-scale clone trials can be optimized to reduce the number of observation times by 50%.

Segmentation applied to weather-disease relationships in South American leaf blight of the rubber tree

South American leaf blight (SALB) is a severe threat to world rubber production. One way of controlling it is to set up plantations in zones not conducive to the disease. Such zones are known once a plantation has been set up, but few data are available on how climate affects the disease, especially in the Amazon region. With better knowledge of conditions that are favourable to SALB epidemics it would be possible to more accurately identify risk zones in Asia and Africa, continents that are still SALB-free. Based on a trial design involving detailed and frequent observations, and with a method rarely used in plant epidemiology, the segmentation method, the results presented in this article make it possible to list, in order of importance, climatic factors that influence disease severity under conditions where the climate varies little over the year.

Avaliação do potencial de uso do hiperparasita<i> Dicyma pulvinata </i>(Berk. & M. A. Curtis) no controle biológico do mal-das-folhas [<i>Microcyclus ulei </i>(Henn.) Arx] de seringueira [<i>Hevea brasiliensis </i>(Wild. ex A. Juss.) Muell. Arg.] em São J

Mato Grosso foi o estado brasileiro de maior extensão em cultivo de seringueira (Hevea brasiliensis), com 45.727 ha de monocultivo em 2002. A ocorrência do "Mal-das-Folhas" causado pelo fungo Microcyclus ulei (Mycosphaerellaceae, Dothideomycetidae), considerado como a principal doença da seringueira, é um fator limitante à instalação de novos empreendimentos. Uma opção promissora, o controle biológico, poderá permitir o equacionamento desse problema fitossanitário. No presente trabalho, buscou-se avaliar o potencial de uso do hiperparasita Dicyma pulvinata (fungo anamorfo) no controle de Microcyclus ulei, em comparação ao controle químico. Foram conduzidos experimentos em campo e em casa de vegetação no município de São José do Rio Claro, MT. Foram realizadas aplicações em três concentrações diferentes de Dicyma pulvinata além dos princípios ativos Benomyl e Mancozeb. Em campo, as maiores porcentagens de controle foram obtidas com a pulverização de Benomyl e de 8,1 x 106 e 1,215 x 107 conídios/ml de Dicyma pulvinata. Em casa de vegetação, os melhores resultados foram obtidos com as pulverizações de 2,025 x 107 e 3,037 x 107 conídios/ml.

Long lasting rubber tree resistance to Microcyclus ulei characterized by reduced conidial emission and absence of teleomorph

The resistance of the MDF 180 Hevea brasiliensis cultivar to South American leaf blight caused by Microcyclus ulei has been studied under both controlled conditions of inoculation, and under natural infestation in the Brazilian state of Bahia. Inoculated isolates on this cultivar in most cases developed sporulating lesions and produced conidiospores, but at a moderate level, characteristic of a race non-specific, partial resistance. The teleomorph of M. ulei has never been reported on this cultivar, either in controlled conditions or in natural infestation, whereas it is commonly observed on other susceptible cultivars. This type of resistance has seldom been described for other pathosystems. MDF 180 resistance having also endured for more than 30 years in areas very conducive to the disease can, therefore, be described as a durable resistance. Rubber productivity of this cultivar is not sufficient to allow planting on industrial scale, but its resistance characteristics make it a good progenitor candidate for rubber tree resistance breeding programs.

Intensidade do mal das folhas em plantas jovens e adultas de seis clones de seringueira na região do Vale do Ribeira: South American leaf blight intensity evaluated in six clones of young and adult rubber trees in the Vale do Ribeira region, São Paulo state, Brazil

Clones de seringueira podem ter comportamento diferenciado, quanto a intensidade de sintomas causados por Microcyclus ulei, se estes sao avaliados na idade jovem ou adulta, pela presenca ou ausencia de folhas maduras e ascoporos, concomitantemente com fluxos de folhas novas suscetiveis. Foi objetivo do presente trabalho avaliar seis clones de seringueira com um e oito anos de idade, quanto a intensidade de sintomas do mal das folhas, na regiao do Vale do Ribeira, Estado de Sao Paulo. Os resultados permitiram observar que os clones mais atingidos pela doenca na fase jovem foram: FX 3864, RRIM 600, IAN 873 e IAN 717, na idade adulta os clones RRIM 600, IAN 717 e FX 3864. O clone IAN 873 teve uma das menores quantidades de doenca na fase adulta, que pode ser explicado pela troca uniforme das folhas e um re-enfolhamento compacto numa epoca desfavoravel ao patogeno, ocorrendo o fenomeno da evitacao ou evasao no tempo.