Sullivan M J, Melton T A, Shew H D
National Weed Management Laboratory, USDA APHIS PPQ CPHST, 2301 Research Blvd., Suite 108, Fort Collins, CO 80526.
Associate State Program Leader, AgNR/CRD, Cooperative Extension Service, North Carolina State University, Raleigh 27695-7602.
Plant Dis. 2005 Nov;89(11):1220-1228. doi: 10.1094/PD-89-1220.
Deployment of tobacco (Nicotiana tabacum) varieties with complete resistance to race 0 of Phytophthora parasitica var. nicotianae has led to a rapid increase in the field populations of race 1 in North Carolina. In a field study, population levels of race 1 decreased relative to race 0 when cultivars with partial resistance to both races were planted, suggesting that race 1 isolates were less fit than race 0 isolates. Experiments were conducted to quantify differences in aggressiveness and survivability of the two races. Tobacco varieties with low, moderate, or high levels of partial resistance were inoculated with 60 pathogen isolates, and symptom development was monitored for 3 weeks. Race 0 isolates were more aggressive than race 1 isolates on cultivars with moderate or high levels of partial resistance; incubation periods were shorter and root rot severity was greater with race 0 isolates. Isolates of race 1, however, caused greater stunting of plants with moderate and high levels of partial resistance than race 0 isolates. Field microplots were infested with either a single race or an equal mixture of each race. Soil samples were collected at the end of two growing seasons and again the following spring. Pathogen populations declined from 40 to 80% during winter months, but population declines for race 0 were lower than for race 1 in each treatment over each winter. Race shifts from race 1 to race 0 that were observed in the presence of cultivars with partial resistance appear to be primarily the result of differences in aggressiveness of the races, with a possible minor effect of enhanced overwintering survival of race 0 compared with race 1.
种植对烟草疫霉变种0号生理小种具有完全抗性的烟草（Nicotiana tabacum）品种，导致北卡罗来纳州田间1号生理小种的种群数量迅速增加。在一项田间研究中，当种植对两个生理小种均具有部分抗性的品种时，1号生理小种的种群数量相对于0号生理小种有所下降，这表明1号生理小种的分离株比0号生理小种的分离株适应性差。进行了实验以量化这两个生理小种在侵染力和生存能力方面的差异。用60个病原菌分离株接种具有低、中、高不同水平部分抗性的烟草品种，并监测症状发展3周。在具有中高水平部分抗性的品种上，0号生理小种的分离株比1号生理小种的分离株侵染力更强；0号生理小种分离株的潜伏期更短，根腐病严重程度更高。然而，对于具有中高水平部分抗性的植株，1号生理小种的分离株比0号生理小种的分离株导致的植株矮化更严重。田间小区接种单一生理小种或两个生理小种的等量混合物。在两个生长季节结束时以及次年春季再次采集土壤样本。在冬季，病原菌种群数量下降了40%至80%，但在每个处理的每个冬季，0号生理小种的种群数量下降幅度低于1号生理小种。在存在具有部分抗性品种的情况下观察到的从1号生理小种向0号生理小种的生理小种转变，似乎主要是由于两个生理小种在侵染力上的差异，与1号生理小种相比，0号生理小种越冬存活率提高可能有较小影响。
