Genomic evidence reframes the risks of genetic rescue for Australia's rarest Eucalyptus

Conservation of extremely small populations requires decisions about whether intervention risks outweigh those of continued genetic decline, an assessment that genomic data can directly inform. Eucalyptus recurva , Australia's rarest eucalypt, has only six known wild adult individuals and exhibits ongoing reproductive failure. To inform conservation management we genotyped 65 individuals (six wild adults, seven ex situ adults and 52 ex situ seedlings) together with 19 sympatric Eucalyptus species and subspecies using genome-wide SNPs (DArTseq). All wild E. recurva adults were genetically distinct but showed variable kinship, and higher multilocus heterozygosity than ex situ seedlings, indicating ongoing inbreeding in the managed cohort. Parentage analyses showed that most ex situ progeny resulted from intended crosses among wild adults, while a minority arose through self-fertilisation or hybridisation with E. rubida and E. mannifera . Selfed seedlings retained unexpectedly high MLH (≈55–70% of parental MLH), consistent with selection favouring heterozygous offspring, a mechanism that may paradoxically suppress recruitment in small, inbred populations. Hybrid individuals have also persisted in cultivation for over two decades, demonstrating long-term viability of admixed lineages. Collectively, these results reveal a species whose reproductive failure and narrowing ex situ gene pool present an urgent genomic case for rescue through hybridisation with related taxa. Genomic evidence suggests the expected costs of inaction exceed those of carefully managed genetic rescue through introgression, illustrating how conservation genomics can reframe decision-making for species facing extreme demographic bottlenecks.