Testing intra-species variation in allocation to growth and defense in rubber tree (Hevea brasiliensis).

Background: Plants allocate resources to growth, defense, and stress resistance, and resource availability can affect the balance between these allocations. Allocation patterns are well-known to differ among species, but what controls possible intra-specific trade-offs and if variation in growth vs. defense potentially evolves in adaptation to resource availability. Methods: We measured growth and defense in a provenance trial of rubber trees (Hevea brasiliensis) with clones originating from the Amazon basin. To test hypotheses on the allocation to growth vs. defense, we relate biomass growth and latex production to wood and leaf traits, to climate and soil variables from the location of origin, and to the genetic relatedness of the Hevea clones. Results: Contrary to expectations, there was no trade-off between growth and defense, but latex yield and biomass growth were positively correlated, and both increased with tree size. The absence of a trade-off may be attributed to the high resource availability in a plantation, allowing trees to allocate resources to both growth and defense. Growth was weakly correlated with leaf traits, such as leaf mass per area, intrinsic water use efficiency, and leaf nitrogen content, but the relative investment in growth vs. defense was not associated with specific traits or environmental variables. Wood and leaf traits showed clinal correlations to the rainfall and soil variables of the places of origin. These traits exhibited strong phylogenetic signals, highlighting the role of genetic factors in trait variation and adaptation. The study provides insights into the interplay between resource allocation, environmental adaptations, and genetic factors in trees. However, the underlying drivers for the high variation of latex production in one of the commercially most important tree species remains unexplained.

Genome-wide association mapping of latex yield and girth in Amazonian accessions of Hevea brasiliensis grown in a suboptimal climate zone.

Latex yield and growth are the key complex traits in commercial rubber production. The present study is the first to report genome-wide association mapping of latex yield and girth, for 170 Amazonian accessions grown in a suboptimal area characterized by limited rainfall and a lengthy dry season. Targeted sequence enrichment to capture gene transcripts generated 14,155 high quality filtered single nucleotide polymorphisms (SNPs) of which 94.3% resided in coding regions. The rapid decay of linkage disequilibrium over physical and genetic distance found in the accessions was comparable to those previously reported for several outcrossing species. A mixed linear model detected three significant SNPs in three candidate genes involved in plant adaptation to drought stress, individually explaining 12.7-15.7% of the phenotypic variance. The SNPs identified in the study will help to extend understanding, and to support genetic improvement of rubber trees grown in drought-affected regions.