DiLeo M V, Bostock R M, Rizzo D M
Department of Plant Pathology, University of California, Davis 95616, USA.
Phytopathology. 2009 Nov;99(11):1307-11. doi: 10.1094/PHYTO-99-11-1307.
California bay laurel trees (Umbellularia californica) play a crucial role in the reproduction and survival of Phytophthora ramorum in coastal California forests by supporting sporulation during the rainy season and by providing a means for the pathogen to survive the dry, Mediterranean summer. While bay laurel is thus critical to the epidemiology of sudden oak death and other P. ramorum diseases in California, the relatively minor symptoms observed on this reservoir host suggest that it may not sustain ecologically significant injury itself. The long-term role that P. ramorum will play in California forests will depend in part on the extent to which this pathogen decreases the ecological fitness of bay laurel. Despite the importance of this question, no study has yet investigated in detail the physiological impact that ramorum blight imposes on bay laurel. This experimental study quantifies the impact that P. ramorum has on artificially inoculated bay laurel seedlings with measurements that integrate the full injury that infection with an oomycete may cause: photosynthetic efficiency, total photosynthetic area, and growth. Leaf area and leaf mass were not impacted significantly by infection of P. ramorum. Photosynthetic efficiency was mildly depressed in symptomatic, but not asymptomatic leaves, despite unnaturally high levels of necrosis that were imposed on the seedlings. These results demonstrate that bay laurel trees suffer only minor injury from ramorum blight beyond visible necrotic symptoms. Consequently, it is highly likely that bay laurel will continue to be widely available as a host for P. ramorum in California forests, which has long-term implications for the composition of these forests.
加利福尼亚月桂树（加州月桂，学名：Umbellularia californica）在加利福尼亚沿海森林中，对樟疫霉的繁殖和生存起着至关重要的作用。在雨季，它支持樟疫霉的孢子形成；在干燥的地中海气候夏季，它为病原体提供了生存途径。虽然月桂树对加利福尼亚突然橡树死亡病和其他樟疫霉病害的流行病学至关重要，但在这种贮藏寄主上观察到的相对较轻症状表明，它本身可能不会遭受具有生态意义的重大损害。樟疫霉在加利福尼亚森林中所起的长期作用，将部分取决于这种病原体降低月桂树生态适应性的程度。尽管这个问题很重要，但尚无研究详细调查樟疫霉叶枯病对月桂树的生理影响。这项实验研究通过整合卵菌感染可能造成的全面损害的测量指标，即光合效率、总光合面积和生长情况，来量化樟疫霉对人工接种的月桂树苗的影响。樟疫霉感染对叶面积和叶质量没有显著影响。尽管给幼苗施加了异常高水平的坏死，但光合效率在有症状的叶片中略有下降，而在无症状叶片中没有下降。这些结果表明，除了可见的坏死症状外，月桂树仅受到樟疫霉叶枯病的轻微损害。因此，月桂树很有可能在加利福尼亚森林中继续广泛作为樟疫霉的寄主，这对这些森林的组成具有长期影响。
