ABSTRACT
The objective of this work was to evaluate the development of Davidiella sp. and its asexual form, Cladosporium sp., under different environmental conditions in the rubber tree (Hevea brasiliensis). Rubber tree leaves were inoculated with a spore suspension and kept in a humid chamber under different temperatures and wetness periods. The behavior of the fungi was evaluated using a scanning electron microscope (SEM) and an ultraviolet light microscope (UV). In the images obtained in SEM, four hours after inoculation of the fungus, it was possible to verify the germination and penetration of conidia at temperatures of 10 to 20 °C. The formation of conidiophores was verified from six hours after inoculation, indicating that it is in the reproductive period. In the sexual phase, in SEM, from four hours after inoculation, it was possible to verify the formation of small protuberances at temperatures between 10 and 20 °C. These black dots evolve into circular, protruding black spots, like the symptoms of black crust, with apparent spore formation on them. The data obtained from the UV analyses corroborate those from SEM, showing that the fungus has good development in its two phases between temperatures of 20 and 25 °C and that the period of wetness on the leaf can contribute to the initial development of the pathogen.
ABSTRACT
The aim of the present study was to evaluate structural and biochemical aspects related to the interaction of resistant (RRIM 937, IAC 502 and 507) and susceptible (RRIM 600) rubber tree clones with C. tamarillo. For such analysis, ultrathin sections of the leaf limb were embedded in historesin and differently stained to verify structural alterations and presence of starch grains, arginine, lipids, tannins and lignins. The total proteins and activity of the enzymes peroxidase and (PAL) were quantified. Stomatal density was also analyzed under a scanning electron microscope. Data indicated alterations in the cell content of resistant clones inoculated with the pathogen, as well as greater lignin and lipid accumulation in these samples. For tannins, there was no difference between inoculated and non-inoculated clones. Arginine was found at greater quantities in IAC 502 and 507. Starch grains were not detected in any of the analyzed samples. Protein level and stomatal density were lower in resistant clones. Peroxidase activity was more expressive in resistant clones. PAL activity, there was no significant difference between clones. The lignin and lipids, total protein, peroxidase activity and stomatal density may be related to the resistance of rubber tree clones to anthracnose.
ABSTRACT
The objective of this study was to evaluate the genetic variability of natural rubber latex traits among 44 elite genotypes of the rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Müell. Arg.]. Multivariate analysis and machine learning techniques were used, targeting the selection of parents that demonstrate superior characters. We analyzed traits related to technological or physicochemical properties of natural rubber latex, such as Wallace plasticity (P0), the plasticity retention index [PRI (%)], Mooney viscosity (VR), ash percentage (Ash), acetone extract percentage (AE), and nitrogen percentage (N), to study genetic diversity. Multivariate [unweighted pair group method with arithmetic means (UPGMA) and Tocher)] and machine learning techniques [K-means and Kohonen's self-organizing maps (SOMs)] were employed. The genotypes showed high genetic variability for some of the evaluated traits. The traits PRI, Ash, and PO contributed the most to genetic diversity. The genotypes were classified into six clusters by the UPGMA method, and the results were consistent with the Tocher, K-means and SOM results. PRI can be used to improve the industrial potential of clones. The clones IAC 418 and PB 326 were the most divergent, followed by IAC 404 and IAC 56. These genotypes and others from the IAC 500 and 400 series could be used to start a breeding program. These combinations offer greater heterotic potential than the others, which can be used to improve components of rubber latex quality. Thus, it is important to consider the quality of rubber latex in the early stage of breeding programs.
Subject(s)
Hevea/genetics , Genetic Variation , Genome, Plant , Plant Breeding , Plant Proteins/geneticsABSTRACT
The rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell. Arg.] is the only plant species worldwide that is cultivated for the commercial production of natural rubber. This study describes the genetic diversity of the Hevea spp. complex that is available in the main ex situ collections of South America, including Amazonian populations that have never been previously described. Genetic data were analyzed to determine the genetic structure of the wild populations, quantify the allelic diversity and suggest the composition of a core collection to capture the maximum genetic diversity within a minimal sample size. A total of 1,117 accessions were genotyped with 13 microsatellite markers. We identified a total of 408 alleles, 319 of which were shared between groups and 89 that were private in different groups of accessions. In a population structure and principal component analysis, the level of clustering reflected a primary division into the following two subgroups: cluster 1, which consisted of varieties from the advanced breeding germplasm that originated from the Wickham and Mato Grosso accessions; and cluster 2, which consisted of the wild germplasm from the Acre, Amazonas, Pará and Rondônia populations and Hevea spp. The analyses revealed a high frequency of gene flow between the groups, with the genetic differentiation coefficient (GST) estimated to be 0.018. Additionally, no distinct separation among the H. brasiliensis accessions and the other species from Amazonas was observed. A core collection of 99 accessions was identified that captured the maximum genetic diversity. Rubber tree breeders can effectively utilize this core collection for cultivar improvement. Furthermore, such a core collection could provide resources for forming an association panel to evaluate traits with agronomic and commercial importance. Our study generated a molecular database that should facilitate the management of the Hevea germplasm and its use for subsequent genetic and genomic breeding.
Subject(s)
Genetic Variation , Hevea/genetics , Genes, Plant , GenotypeABSTRACT
Hevea brasiliensis (Willd. Ex Adr. Juss.) Muell.-Arg. is the primary source of natural rubber that is native to the Amazon rainforest. The singular properties of natural rubber make it superior to and competitive with synthetic rubber for use in several applications. Here, we performed RNA sequencing (RNA-seq) of H. brasiliensis bark on the Illumina GAIIx platform, which generated 179,326,804 raw reads on the Illumina GAIIx platform. A total of 50,384 contigs that were over 400 bp in size were obtained and subjected to further analyses. A similarity search against the non-redundant (nr) protein database returned 32,018 (63%) positive BLASTx hits. The transcriptome analysis was annotated using the clusters of orthologous groups (COG), gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Pfam databases. A search for putative molecular marker was performed to identify simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs). In total, 17,927 SSRs and 404,114 SNPs were detected. Finally, we selected sequences that were identified as belonging to the mevalonate (MVA) and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathways, which are involved in rubber biosynthesis, to validate the SNP markers. A total of 78 SNPs were validated in 36 genotypes of H. brasiliensis. This new dataset represents a powerful information source for rubber tree bark genes and will be an important tool for the development of microsatellites and SNP markers for use in future genetic analyses such as genetic linkage mapping, quantitative trait loci identification, investigations of linkage disequilibrium and marker-assisted selection.