Ethephon, an ethylene releaser, is used to stimulate latex production in Hevea brasiliensis. Ethylene induces many functions in latex cells including the production of reactive oxygen species (ROS). The accumulation of ROS is responsible for the coagulation of rubber particles in latex cells, resulting in the partial or complete stoppage of latex flow. This study set out to assess biochemical and histological changes as well as changes in gene expression in latex and phloem tissues from trees grown under various harvesting systems. The Tapping Panel Dryness (TPD) susceptibility of Hevea clones was found to be related to some biochemical parameters, such as low sucrose and high inorganic phosphorus contents. A high tapping frequency and ethephon stimulation induced early TPD occurrence in a high latex metabolism clone and late occurrence in a low latex metabolism clone. TPD-affected trees had smaller number of laticifer vessels compared to healthy trees, suggesting a modification of cambial activity. The differential transcript abundance was observed for twenty-seven candidate genes related to TPD occurrence in latex and phloem tissues for ROS-scavenging, ethylene biosynthesis and signalling genes. The predicted function for some Ethylene Response Factor genes suggested that these candidate genes should play an important role in regulating susceptibility to TPD.

The natural rubber biosynthetic pathway is well described in Hevea, although the final stages of rubber elongation are still poorly understood. Small Rubber Particle Proteins and Rubber Elongation Factors (SRPPs and REFs) are proteins with major function in rubber particle formation and stabilization. Their corresponding genes are clustered on a scaffold1222 of the reference genomic sequence of the Hevea brasiliensis genome. Apart from gene expression by transcriptomic analyses, to date, no deep analyses have been carried out for the genomic environment of SRPPs and REFs loci. By integrative analyses on transposable element annotation, small RNAs production and gene expression, we analysed their role in the control of the transcription of rubber biosynthetic genes. The first in-depth annotation of TEs (Transposable Elements) and their capacity to produce TE-derived siRNAs (small interfering RNAs) is presented, only possible in the Hevea brasiliensis clone PB 260 for which all data are available. We observed that 11% of genes are located near TEs and their presence may interfere in their transcription at both genetic and epigenetic level. We hypothesized that the genomic environment of rubber biosynthesis genes has been shaped by TE and TE-derived siRNAs with possible transcriptional interference on their gene expression. We discussed possible functionalization of TEs as enhancers and as donors of alternative transcription start sites in promoter sequences, possibly through the modelling of genetic and epigenetic landscapes.

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Corynespora cassiicola is an important pathogen causing Corynespora leaf fall disease on the rubber tree. Analysis of virulence, rDNA-ITS sequence and identification of cas gene were undertaken to investigate the effect of agro-climatic conditions and host rubber clones to virulence of 23 C. cassiicola isolates on six clones (RRIC 100, BPM 24, BPM 1, PB 260, GT 1 and RRIM 600) and to observed the evolution pattern of C. cassiicola isolates. Virulence analysis showed that there is an interaction between isolates and clones, indicating the differences of each isolates virulence to six clones. Agro-climatic conditions and host clones influenced the virulence of isolates and rDNA-ITS sequence variation. Analysis of rDNA-ITS showed that there were three of Single Nucleotide Polymorphism (SNP) that separated of isolates into 5 haplotypes. Most of the isolates belonging to the haplotype 1. Phylogenetic analysis indicated that C. cassiicola have a high diversity, however the clustering did not indicate country and host species of isolates. This information will be very useful on developing strategies of disease management and rubber plant breeding towards resistance to CLF disease.

The accession of the IRDB 1981 (PN'81) population is a newly introduced and an important rubber tree germplasm while the Wickham clone is a commercial variety one. The objectives of this study were to assess the genetic diversity and the population structure of PN'81 populations and the Wickham clones using 15 EST-SSR loci. Results of the analysis showed that the evaluated SSR primers yielded polymorphic markers. The gSSR 268 primer pairs yielded the most informative markers while HBE 280 primers generated the lowest ones. Results of the genetic diversity analysis supported that the PN'81 population belonged to a single large natural population of rubber trees while the Wickham clones belonged to a different group than that of PN'81. The population structure analysis of the rubber accessions was also in agreement with the results of the genetic diversity analysis. The experiment also indicated that PN'81 populations would be useful for future rubber breeding in Indonesia, especially as the sources of parent clones for rubber tree hybridization programs and rubber tree genetic resource conservation.