Bellah Hadjer, Seiler Nicolas F, Croll Daniel
Laboratory of Evolutionary Genetics, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland.
Microbiol Spectr. 2023 Feb 7;11(2):e0444322. doi: 10.1128/spectrum.04443-22.
Plant diseases are often caused by co-infections of multiple pathogens with the potential to aggravate disease severity. In genetically diverse pathogen species, co-infections can also be caused by multiple strains of the same species. However, the outcome of such mixed infections by different conspecific genotypes is poorly understood. The interaction among pathogen strains with complex lifestyles outside and inside of the host are likely shaped by diverse traits, including metabolic capacity and the ability to overcome host immune responses. To disentangle competitive outcomes among pathogen strains, we investigated the fungal wheat pathogen Zymoseptoria tritici. The pathogen infects wheat leaves in complex strain assemblies, and highly diverse populations persist between growing seasons. We investigated a set of 14 genetically different strains collected from the same field to assess both competitive outcomes under culture conditions and on the host. Growth kinetics of cocultured strains (~100 pairs) significantly deviated from single strain expectations, indicating competitive exclusion depending on the strain genotype. We found similarly complex outcomes of lesion development on plant leaves following co-infections by the same pairs of strains. While some pairings suppressed overall damage to the host, other combinations exceeded expectations of lesion development based on single strain outcomes. Strain competition outcomes in the absence of the host were poor predictors of outcomes on the host, suggesting that the interaction with the plant immune system adds significant complexity. Intraspecific co-infection dynamics likely make important contributions to disease outcomes in the wild. Plants are often attacked by a multitude of pathogens simultaneously, and different species can facilitate or constrain the colonization by others. To what extent simultaneous colonization by different strains of the same species matters, remains unclear. We focused on intra-specific interactions between strains of the major fungal wheat pathogen Zymoseptoria tritici. The pathogen persists in the environment before infecting plant leaves early in the growing season. Leaves are typically colonized by a multitude of strains. Strains cultured in pairs without host were growing differently compared to strains cultured alone. Wheat leaves infected either with single or pairs of strains, we found also highly variable outcomes. Interactions between strains outside of the host were only poorly explaining how strains would interact when on the host, suggesting that pathogen strains engage in complex interactions dependent on the environment. Better understanding within-species interactions will improve our ability to manage crop infections.
植物病害通常是由多种病原体共同感染引起的，这有可能加剧病害的严重程度。在基因多样的病原体物种中，共同感染也可能由同一物种的多个菌株引起。然而，对于不同同种基因型的这种混合感染的结果，我们了解得还很少。病原体菌株在宿主内外具有复杂生活方式的相互作用，可能受到多种性状的影响，包括代谢能力和克服宿主免疫反应的能力。为了弄清楚病原体菌株之间的竞争结果，我们研究了真菌小麦病原体小麦黄斑叶枯病菌（Zymoseptoria tritici）。该病原体以复杂的菌株组合感染小麦叶片，并且在生长季节之间存在高度多样的种群。我们研究了从同一田地收集的一组14个基因不同的菌株，以评估培养条件下和宿主上的竞争结果。共培养菌株（约100对）的生长动力学明显偏离单菌株预期，表明竞争排斥取决于菌株基因型。我们发现，相同菌株对共同感染后，植物叶片上病斑发展的结果同样复杂。虽然有些组合抑制了对宿主的总体损害，但其他组合超过了基于单菌株结果的病斑发展预期。在没有宿主的情况下菌株竞争结果并不能很好地预测在宿主上的结果，这表明与植物免疫系统的相互作用增加了显著的复杂性。种内共同感染动态可能对野外病害结果有重要影响。植物经常同时受到多种病原体的攻击，不同物种可能促进或限制其他物种的定殖。同一物种的不同菌株同时定殖的重要程度尚不清楚。我们专注于主要真菌小麦病原体小麦黄斑叶枯病菌菌株之间的种内相互作用。该病原体在生长季节早期感染植物叶片之前在环境中存活。叶片通常被多种菌株定殖。与单独培养的菌株相比，在没有宿主的情况下成对培养的菌株生长情况不同。我们还发现，感染单菌株或菌株对的小麦叶片，结果差异很大。宿主外菌株之间的相互作用只能勉强解释菌株在宿主上的相互作用方式，这表明病原体菌株参与了依赖于环境的复杂相互作用。更好地理解种内相互作用将提高我们管理作物感染的能力。
