Data from: Trait evolution in topical rubber (Hevea brasiliensis) trees is related to dry season intensity

1. Drought shapes the distribution and survival of trees even in tropical wet forests, and the wood and leaf trait spectra are used to understand drought adaptations. However, trait variation may result from ontogenetic adjustment or be related to tree size, and not reflect evolutionary adaptations. 2. Intraspecific variation in adaptations to drought can be an important factor in a species’ distribution and response to climate change, but excluding potentially confounding factors and proving adaptive evolution is challenging. Provenance trials can identify hereditary variability. 3. We analysed wood and leaf traits in rubber (Hevea brasiliensis) tree clones from 15 locations in the Amazon basin that were planted in northern Thailand, controlled for tree size, tested for genetic relatedness and the phylogenetic signal in traits, and compared trait variations with the climate at the location of origin. 4. Correlations between traits and tree size were low. Intra-specific trait variation was similar to relationships in published among-species comparisons and correlations among wood traits and correlations among leaf traits were stronger than between wood and leaf traits. Genotype explained 30 – 70% of the trait variation, and traits differed in how much of this variation was controlled by location or the relatedness among clones. 5. There was no correlation with mean temperature or total annual rainfall. However, rainfall in the driest quarter (19 – 199 mm) was strongly related to leaf mass per area, carbon isotopic composition and area-based nitrogen content(r2 = 0.54 - 0.70) and weaker to wood traits (vessel density and vessel lumen fraction). Trees from locations with a stronger dry season also had higher growth rates in Thailand. 6. All traits correlating with climate showed a significant phylogenetic signal. We found no evidence of increased drought tolerance, but the trait spectrum and higher growth in trees from drier locations suggests that deciduous rubber trees have adapted via drought avoidance rather than tolerance. Our study also underlines the importance of looking at a suite of traits rather than individual ones to understand adaptive strategies

Identification of Candidate Gene-Based Markers for Girth Growth in Rubber Trees

Girth growth is an important factor in both latex and timber production of the rubber tree. In this study, we performed candidate gene association mapping for girth growth in rubber trees using intron length polymorphism markers (ILP) in identifying the candidate genes responsible for girth growth. The COBL064_1 marker developed from the candidate gene (COBL4) regulating cellulose deposition and oriented cell expansion in the plant cell wall showed the strongest association with girth growth across two seasons in the Amazonian population and was validated in the breeding lines. We then applied single molecule real-time (SMRT) circular consensus sequencing (CCS) to analyze a wider gene region of the COBL4 to pinpoint the single nucleotide polymorphism (SNP) that best explains the association with the traits. A SNP in the 3’ UTR showing linkage disequilibrium with the COBL064_1 most associated with girth growth. This study showed that the cost-effective method of ILP gene-based markers can assist in identification of SNPs in the candidate gene associated with girth growth. The SNP markers identified in this study added useful markers for the improvement of girth growth in rubber tree breeding programs

Functional traits of Hevea brasiliensis clones

wood and leaf traits and tree size for Hevea brasiliensis clones from Brazil planted in a provenance trial in Thailan

Clonal variability for vulnerability to cavitation and other drought-related traits in Hevea brasiliensis Müll. Arg.

Selection for drought-tolerant clones has become a major challenge in rubber breeding programs undertaken to ensure the sustainability of natural rubber production, as rubber plantations are expanding in drought-prone areas. Xylem vulnerability to cavitation is a trait related to drought-induced mortality. It can be rapidly evaluated without subjecting plant materials to drought stress, making it useful in large-scale screening for drought tolerance in the near future. We first compared the most widely used techniques for measuring vulnerability to cavitation (air pressurization and Cavitron) on this species, and the effect of sample conditions (size, age and sunlight exposure), in order to ensure reliable analysis. Secondly, ten rubber clones were compared for their xylem vulnerability to cavitation in branches and petioles, and for other traits related to drought response, including stomatal response and leaf shedding occurring during a simulated drought. We also tested the plasticity of vulnerability to cavitation on two clones grown in three locations with contrasting precipitation regimes. We found no clonal variability and a small phenotypic plasticity for xylem vulnerability to cavitation in branches. However, clonal differences in xylem vulnerability to cavitation were found in petioles, and clones also showed differences in stomatal response and in leaf shedding behavior in response to a simulated drought. Our study suggests a genetic canalization for vulnerability to cavitation in organs critical for survival, such as branches, whereas there are clonal differences for traits related to drought avoidance: vulnerability to cavitation of petioles, leaf shedding behavior and stomatal response. The insights gained in this study for screening rubber tree clones for drought tolerance is also discussed