Kover Paula X, Schaal Barbara A
Department of Ecology and Evolutionary Biology, University of Tennessee, 569 Dabney Hall, Knoxville, TN 37996, USA.
Proc Natl Acad Sci U S A. 2002 Aug 20;99(17):11270-4. doi: 10.1073/pnas.102288999. Epub 2002 Aug 9.
Pathogens can be an important selective agent in plant evolution because they can severely reduce plant fitness and growth. However, the role of pathogen selection on plant evolution depends on the extent of genetic variation for resistance traits and their covariance with host fitness. Although it is usually assumed that resistance traits will covary with plant fitness, this assumption has not been tested rigorously in plant-pathogen interactions. Many plant species are tolerant to herbivores, decoupling the relationship between resistance and fitness. Tolerance to pathogens can reduce selection for resistance and alter the effect of pathogens on plant evolution. In this study, we measured three components of Arabidopsis thaliana resistance (pathogen growth, disease symptoms, and host fitness) to the bacteria Pseudomonas syringae and investigated their covariation to determine the relative importance of resistance and tolerance. We observed extensive quantitative variation in the severity of disease symptoms, the bacterial population size, and the effect of infection on host fitness among 19 accessions of A. thaliana infected with P. syringae. The severity of disease symptoms was strongly and positively correlated with bacterial population size. Although the average fitness of infected plants was smaller than noninfected plants, we found no correlation between the bacterial growth or symptoms expressed by different accessions of A. thaliana and their relative fitness after infection. These results indicate that the accessions studied vary in tolerance to P. syringae, reducing the strength of selection on resistance traits, and that symptoms and bacterial growth are not good predictors of host fitness.
病原体可能是植物进化过程中的一种重要选择因子，因为它们会严重降低植物的适合度和生长。然而，病原体选择对植物进化的作用取决于抗性性状的遗传变异程度及其与宿主适合度的协方差。尽管通常认为抗性性状会与植物适合度相关，但这一假设在植物与病原体的相互作用中尚未得到严格验证。许多植物物种对食草动物具有耐受性，从而使抗性与适合度之间的关系脱钩。对病原体的耐受性可以减少对抗性的选择，并改变病原体对植物进化的影响。在本研究中，我们测量了拟南芥对丁香假单胞菌的三种抗性成分（病原体生长、疾病症状和宿主适合度），并研究了它们的协变关系，以确定抗性和耐受性的相对重要性。我们观察到，在感染丁香假单胞菌的19个拟南芥种质中，疾病症状的严重程度、细菌种群大小以及感染对宿主适合度的影响存在广泛的数量变异。疾病症状的严重程度与细菌种群大小呈强烈正相关。虽然感染植物的平均适合度低于未感染植物，但我们发现不同拟南芥种质所表现出的细菌生长或症状与其感染后的相对适合度之间没有相关性。这些结果表明，所研究的种质对丁香假单胞菌的耐受性存在差异，从而降低了对抗性性状的选择强度，并且症状和细菌生长并不是宿主适合度的良好预测指标。
