Phytophthora cinnamomi has been killing jarrah forests in Western Australia for generations. The pathogen, commonly called dieback disease, attacks tree roots and has proven nearly impossible to control once established in soil. For years, the only real hope has been breeding jarrah varieties with natural resistance.

The resistance breeding program at the Department of Biodiversity, Conservation and Attractions has been running since the 1980s. The basic approach is screening jarrah seedlings for resistance, selecting the most resistant individuals, and using them as parent stock for the next generation.

Progress has been real but slow. Resistance isn’t a simple genetic trait controlled by a single gene. It appears to be polygenic, involving multiple genes that each contribute partial resistance. This makes selective breeding more complex than it would be for a simple dominant trait.

The screening process itself is labor-intensive. Seedlings are grown in controlled conditions, inoculated with Phytophthora, and monitored for months to see which survive. Many die. Some show partial resistance. A small percentage demonstrates strong resistance. Those survivors become candidates for breeding.

Over successive generations, the program has increased the proportion of resistant seedlings. Early generations might have had 10-15% survival rates. Recent generations are achieving 40-50% resistance in some seed lots. That’s progress, but it’s still nowhere near the 90%+ resistance you’d want for confident replanting in dieback-affected areas.

Part of the challenge is that resistance in controlled conditions doesn’t always translate to resistance in the field. A seedling that survives inoculation in a pot might still succumb when planted in forest soil with multiple Phytophthora strains and varying environmental stresses.

Field trials of resistant jarrah have shown mixed results. Some plantings have survived and grown well in sites with known dieback presence. Others have experienced higher mortality than expected. Soil moisture, drainage, companion species, and local Phytophthora strain variations all seem to influence outcomes.

Genetic diversity is another consideration. Jarrah forests naturally have high genetic diversity, which is important for ecosystem resilience. Breeding programs that select too narrowly for resistance risk creating genetically uniform plantings that might be vulnerable to other threats.

The program tries to maintain diversity by using multiple parent trees and avoiding excessive inbreeding. But there’s inherent tension between selecting for resistance and maintaining broad genetic diversity. Every generation that focuses on resistance inevitably narrows the genetic base to some degree.

Seed production from resistant trees is limited. Not all resistant trees produce abundant viable seed, and the best resistance traits might not correlate with seed production traits. Growing enough resistant seedlings to supply forest rehabilitation projects at scale requires large numbers of parent trees, which takes decades to establish.

Clonal propagation has been explored as a way to scale up production of the most resistant individuals. Cuttings or tissue culture could theoretically produce unlimited copies of a single highly resistant tree. But jarrah doesn’t propagate easily through cuttings, and tissue culture techniques for jarrah are still being refined.

There’s also debate about whether clonal jarrah forests are ecologically desirable. Even if they survive Phytophthora, would they provide the same habitat value, ecosystem functions, and long-term resilience as genetically diverse forests? Probably not.

Climate change adds another layer of complexity. Resistance breeding has focused on current environmental conditions and current Phytophthora strains. If climate shifts significantly over coming decades, the traits that confer resistance today might be less effective in future conditions.

Warmer, wetter winters might favor Phytophthora and change disease pressure. Drier summers might stress trees in ways that reduce their ability to resist infection. The ideal resistant jarrah for 2026 climate might not be the ideal one for 2050 climate.

Some researchers are advocating for incorporating climate adaptability into the breeding program alongside disease resistance. Select for trees that show tolerance to water stress, heat events, and variable rainfall patterns, not just Phytophthora resistance. This makes the breeding goals even more complex.

The timeline for seeing breeding results in the landscape is extremely long. Jarrah can live for centuries, but it takes 10-15 years before a tree reaches sexual maturity and can produce seed for the next breeding generation. This means genetic improvement happens at a pace measured in decades.

Compare that to crop breeding programs where annuals can go through multiple generations per year, or even forestry programs with faster-growing species like eucalyptus where generation times might be 3-5 years. Jarrah breeding requires patience and long-term commitment that’s difficult to sustain through political and funding cycles.

Interim measures matter while waiting for breeding results. Hygiene protocols to prevent Phytophthora spread, phosphite injections to protect high-value trees, and careful site selection for plantings all help manage the disease even if they don’t solve it.

Some forest managers are taking a pragmatic approach: plant resistant seedlings where available, but don’t expect them to be a complete solution. Use them as part of a broader strategy that includes all available management tools.

The economics are challenging. Resistant seedlings cost more to produce than standard stock. Forest rehabilitation budgets often don’t account for these higher costs. The benefits accrue over decades, but budgets are annual.

Private landowners with jarrah on their properties generally can’t access resistant seedlings easily. The breeding program supplies government forest rehabilitation projects, but there’s no commercial pathway for resistant jarrah to reach private forestry or landcare groups at scale.

International collaboration has been limited because jarrah is endemic to a relatively small area of Western Australia. Other countries working on Phytophthora resistance are dealing with different tree species and different Phytophthora strains. The lessons don’t always transfer directly.

That said, genomic techniques being developed for tree breeding in other contexts could accelerate jarrah resistance breeding. Marker-assisted selection, where DNA markers linked to resistance are identified, could allow screening for resistance without having to grow and inoculate every seedling.

This would dramatically speed up the breeding cycle and reduce costs. But developing those markers requires sequencing and analyzing many resistant and susceptible trees to identify the genetic differences. That work is underway but still in relatively early stages.

CRISPR and other gene editing technologies are sometimes mentioned as potential tools, but they’re far from applicable to jarrah resistance breeding. The genetic basis of resistance isn’t well enough understood to know what edits would be beneficial, and the regulatory and social acceptance hurdles for genetically modified forest trees are enormous.

The research is important and worth continuing. But expectations need to be realistic. We’re not going to breed our way out of the jarrah dieback problem in the next decade. Resistant varieties will be part of the solution, but only part.

Forest managers need multiple strategies. Protecting uninfected areas from Phytophthora introduction remains the highest priority. Once disease is established in soil, it’s nearly impossible to eliminate. Prevention is vastly more effective than treatment or restoration.

For areas already affected, resistant jarrah offers hope for eventual recovery, but that recovery will be measured in generations of trees, not years. In the meantime, the forests continue to change, and species compositions shift as susceptible trees die and other plants fill the gaps.

The long arc of this research reminds us that ecological restoration works on timescales that don’t match political or even human lifespans well. The jarrah resistance breeding program started before many of the current researchers were born. It will continue long after they retire. That’s the nature of forestry research, particularly when dealing with long-lived species and complex genetic traits.

Progress is happening. It’s just slow, uncertain, and requires sustained commitment over decades. For anyone expecting quick solutions to jarrah dieback, the reality is disappointingly gradual. But for those willing to think in terms of forest generations rather than quarterly reports, the breeding program represents a legitimate path toward long-term landscape recovery.