Johnston Steven F, Cohen Michael F, Torok Tamas, Meentemeyer Ross K, Rank Nathan E
First, second, and fifth authors: Department of Biology, Sonoma State University, Rohnert Park, CA 94928; third author: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA 94720; and fourth author: Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27606.
Phytopathology. 2016 Jan;106(1):47-55. doi: 10.1094/PHYTO-01-15-0016-R. Epub 2015 Dec 3.
Spread of the plant pathogen Phytophthora ramorum, causal agent of the forest disease sudden oak death, is driven by a few competent hosts that support spore production from foliar lesions. The relationship between traits of a principal foliar host, California bay laurel (Umbellularia californica), and susceptibility to P. ramorum infection were investigated with multiple P. ramorum isolates and leaves collected from multiple trees in leaf-droplet assays. We examined whether susceptibility varies with season, leaf age, or inoculum position. Bay laurel susceptibility was highest during spring and summer and lowest in winter. Older leaves (>1 year) were more susceptible than younger ones (8 to 11 months). Susceptibility was greater at leaf tips and edges than the middle of the leaf. Leaf surfaces wiped with 70% ethanol were more susceptible to P. ramorum infection than untreated leaf surfaces. Our results indicate that seasonal changes in susceptibility of U. californica significantly influence P. ramorum infection levels. Thus, in addition to environmental variables such as temperature and moisture, variability in host plant susceptibility contributes to disease establishment of P. ramorum.
植物病原体恶疫霉（Phytophthora ramorum）是森林病害橡树猝死病的致病因子，其传播是由少数能够支持从叶部病斑产生孢子的宿主推动的。利用多个恶疫霉分离株以及在叶滴试验中从多棵树上采集的叶片，研究了主要叶部宿主加州月桂树（Umbellularia californica）的性状与对恶疫霉感染的易感性之间的关系。我们研究了易感性是否随季节、叶龄或接种位置而变化。加州月桂树的易感性在春季和夏季最高，在冬季最低。老叶（>1年）比新叶（8至11个月）更易感。叶尖和叶缘的易感性高于叶片中部。用70%乙醇擦拭的叶片表面比未处理的叶片表面更易感染恶疫霉。我们的结果表明，加州月桂树易感性的季节性变化显著影响恶疫霉的感染水平。因此，除了温度和湿度等环境变量外，宿主植物易感性的变异性也有助于恶疫霉病害的发生。
