• Key message

Ash dieback decreases individual reproductive success of ash trees leaving healthy ash overrepresented as seed and pollen parents for next-generation seedlings. Substantial gene flow over hundreds of meters combined with superior fertility of healthy trees creates optimism for the species’ future in European forests.

• Context

Hymenoscyphus fraxineus is causing high mortality in European ash (Fraxinus excelsior L.). Due to inheritable resistance to the pathogen, natural selection is likely to act in favour of improved resistance in ash forests following natural regeneration. Still, the frequency of healthy trees is low, and the effect of natural selection will depend on survival, reproductive success and the dispersal capacity of healthy trees under natural conditions.

• Aims

We aim to test whether healthy trees contribute more to the next generation and to infer their potential for dispersing progenies across the forested landscape.

• Methods

Using parentage modelling, we estimate mating parameters and dispersal distances of seeds and pollen and compare realised reproductive success of healthy trees to that of unhealthy ones.

• Results

Healthy trees are overrepresented as the parents of randomly sampled seeds and seedlings in the forest, although that is more pronounced on the female side. We observe long dispersal events and estimate the mean seed and pollen dispersal distances as 67 m and 347 m, respectively.

• Conclusion

Variation in reproductive success results in selection in favour of lowered susceptibility to ash dieback. The large dispersal capacity decreases the risk of genetic bottlenecks and inbreeding and allows resistant trees to disperse their genes into the neighbourhoods of substantial sizes.

中文翻译：

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面对灰分枯萎的灰烬中的基因流动和生殖成功：恢复和保存

• 关键信息

灰分枯死降低了灰树的单株繁殖成功率，使健康的灰过分地代表了下一代幼苗的种子和花粉亲本。数百米的大量基因流动加上健康树木的出色育性，为欧洲森林中该物种的未来带来了乐观。

•上下文

油菜菌（Hymenoscyphus fraxineus）导致欧洲烟灰（Fraxinus excelsior L.）的高死亡率。由于对病原体具有可遗传的抗性，自然选择可能会促进自然再生后灰烬森林中抗性的提高。但是，健康树木的频率较低，自然选择的效果将取决于自然条件下健康树木的存活率，繁殖成功率和扩散能力。

•目的

我们的目标是测试健康树木是否对下一代有更多贡献，并推断其在森林景观中传播后代的潜力。

• 方法

使用亲子关系模型，我们估计种子和花粉的交配参数和传播距离，并比较健康树和不健康树的已实现生殖成功。

•结果

健康的树木作为森林中随机抽取的种子和幼苗的亲本的比例过高，尽管在女性方面更为明显。我们观察到长时间的散布事件，估计种子和花粉的平均散布距离分别为67 m和347 m。

•结论

繁殖成功率的差异导致选择对灰分回生的敏感性降低。较大的扩散能力降低了遗传瓶颈和近交的风险，并使抗性树将其基因分散到相当大的邻域中。