Crop varieties carrying qualitative resistance to targeted pathogens lead to strong selection pressure on parasites, often resulting in resistance breakdown. It is well known that qualitative resistance breakdowns modify pathogen population structure but few studies have analyzed the consequences on their quantitative aggressiveness‐related traits. The aim of this study was to characterize the evolution of these traits following a resistance breakdown in the poplar rust fungus, Melampsora larici‐populina. We based our experiment on three temporal populations sampled just before the breakdown event, immediately after and four years later. First, we quantified phenotypic differences among populations for a set of aggressiveness traits on a universally susceptible cultivar (infection efficiency, latent period, lesion size, mycelium quantity, and sporulation rate) and one morphological trait (mean spore volume). Then, we estimated heritability to establish which traits could be subjected to adaptive evolution and tested for evidence of selection. Our results revealed significant changes in the morphological trait but no variation in aggressiveness traits. By contrast, recent works have demonstrated that quantitative resistance (initially assumed more durable) could be eroded and lead to increased aggressiveness. Hence, this study is one example suggesting that the use of qualitative resistance may be revealed to be less detrimental to long‐term sustainable crop production.

中文翻译：

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杨树锈菌Melampsora larici-populina的主要抗性分解后，形态上但非侵略性相关性状的演变

对目标病原体具有定性抗性的农作物品种会导致对寄生虫的强烈选择压力，从而经常导致抗性崩溃。众所周知，定性抗性分解会改变病原体的种群结构，但是很少有研究分析其对侵略性相关性状的影响。这项研究的目的是表征在杨树锈病真菌Melampsora larici-populina抗性分解后这些性状的进化。我们基于故障事件之前，之后和四年之后采样的三个时间总体进行了实验。首先，我们对普遍易感品种的一组侵略性特征（感染效率，潜伏期，病灶大小，菌丝体数量和孢子形成率）和一个形态特征（平均孢子体积）的种群之间的表型差异进行了量化。然后，我们估计了遗传力，以确定哪些性状可以进行适应性进化并测试选择的证据。我们的结果表明，形态特征发生了显着变化，但攻击性特征没有变化。相比之下，最近的研究表明，定量抗性（最初假定为更耐久）可能会被侵蚀并导致侵略性增强。因此，