Widmer T L, Shishkoff N, Dodge S C
Foreign Disease and Weed Science Research Unit, United States Department of Agriculture-Agricultural Research Service, Fort Detrick, MD 21702.
Plant Dis. 2012 Nov;96(11):1675-1682. doi: 10.1094/PDIS-12-11-1024-RE.
Little is known about colonization of roots of trees by Phytophthora ramorum. We examined zoospore concentration and exposure time needed to infect six Quercus (oak) species and the inoculum produced from their roots. Sprouted acorns, exposed to zoospores (3,000/ml) for different times and transplanted to potting soil, were susceptible to infection within 1 h of exposure but root weights were not impacted after 4 weeks (P = 0.952). Roots of Quercus prinus seedlings, inoculated with sporangia, had 0.6 to 3.2% colonization of the total root mass after 5 months. Neither root lesions nor obvious root sloughing were observed. Inoculum threshold levels were tested by exposing radicles to varying zoospore concentrations for 24 h. Results showed that radicle infection occurred even at 1 zoospore/ml. To test inoculum production, roots were inoculated with sporangia and transplanted into pots. Periodically, samples of runoff were collected and plated on selective medium. Afterward, root segments were plated to calculate percent colonization. After 16 and 35 days, root colonization and inoculum production from oak was lower than that of Viburnum tinus, a positive control. This study shows that P. ramorum is able to infect sprouted oak acorns and produce secondary inoculum, which may be important epidemiologically.
关于恶疫霉对树木根系的定殖情况，人们了解甚少。我们研究了感染六种栎属（橡树）树种所需的游动孢子浓度和暴露时间，以及从它们根系产生的接种体。将发芽的橡子暴露于不同时间的游动孢子（3000个/毫升）中，然后移植到盆栽土壤中，在暴露1小时内就易受感染，但4周后根重未受影响（P = 0.952）。用孢子囊接种的栗栎幼苗根系，5个月后总根量的定殖率为0.6%至3.2%。未观察到根系损伤或明显的根系脱落。通过将胚根暴露于不同的游动孢子浓度24小时来测试接种体阈值水平。结果表明，即使游动孢子浓度为1个/毫升时，胚根也会发生感染。为了测试接种体的产生，将根系用孢子囊接种后移植到花盆中。定期收集径流样本并接种到选择性培养基上。之后，将根段接种以计算定殖百分比。16天和35天后，橡树的根系定殖和接种体产生低于阳性对照欧洲荚蒾。本研究表明，恶疫霉能够感染发芽的橡子并产生次生接种体，这在流行病学上可能很重要。
