Genome assembly of Eucalyptus recurva provides insights into inbreeding and conservation priorities in Australia's rarest Eucalyptus

Abstract

Eucalyptus recurva (Mongarlowe Mallee) is Critically Endangered, with only six known adult individuals persisting across two sites in the Southern Tablelands of New South Wales, Australia. Its extreme rarity, uniquely long lifespan, and limited reproductive output make it a priority for conservation genomics. Here we report the first genome assembly of E. recurva: a haplotype-resolved, gapless, telomere-to-telomere (T2T) assembly produced from Oxford Nanopore Technologies (ONT) long-read sequencing. Both haplotypes span 11 chromosomes (consistent with the conserved Eucalyptus karyotype of 2n = 22), with assembly sizes of 521.1 Mb (Hap 1) and 501.5 Mb (Hap 2), BUSCO completeness >99.6%, and quality values of >QV 62. Comparative analyses place E. recurva within section Maidenaria as sister to Eucalyptus viminalis and reveal high synteny between the two species. Inter-haplotype comparison identified 3.6 million SNPs and modest structural variation, suggesting that, despite extreme demographic bottlenecking, E. recurva retains meaningful genomic heterozygosity. We also characterise the chloroplast genome, which exhibits heteroplasmy, and report an apparently bipartite mitochondrial genome. This reference genome provides an essential resource for conservation management, population genetics, and the study of eucalypt genome evolution.