Exploring rubber tree foliage as biomass for natural rubber: Breeding strategies for high-content cultivars and water-based rubber extraction

Natural rubber (NR) production currently relies on labor-intensive bark tapping. This study investigates rubber production from both fallen and fresh leaves of rubber trees, by developing breeding strategies for cultivars optimized for leaf rubber content and establishing an economical and eco-friendly extraction process. For the first time, we demonstrate that rubber tree leaves contain NR with molecular weight and conformation comparable to that derived from bark. The estimated annual rubber yield from fallen leaves of four commercial clones ranges from 60.84 to 82.90 kg ha⁻¹—a potential that can be significantly expanded through targeted breeding. We found no correlation between bark and leaf rubber content, indicating that high bark rubber yield does not predict high leaf rubber potential in conventional cultivars. To address this, we developed a petiolule latex assay for high-throughput screening of leaf rubber in commercial clones and F1 populations. Preliminary screening identified a genotype with 79.3 % higher leaf rubber content than the control, demonstrating the feasibility of selecting high leaf-rubber cultivars. Furthermore, a scalable water-based extraction method was developed, achieving a crude rubber extraction yield of 2.5 % based on a fresh-to-dry conversion factor of 47.5 %. This process is expected to support periodic harvesting from trees bred specifically for leaf rubber production (e.g., coppiced trees), paving the way for an innovative and sustainable rubber production system. • Discovery: Leaves produce high-quality NR, with fallen leaves yielding 60.84–82.90 kg ha⁻¹. • Breeding Breakthrough: We found bark and leaf rubber uncorrelated, and developed a high-throughput leaf rubber screen. • Sustainable Process: We established a scalable, water-based extraction method.