01898nas a2200157   4500008004100000245011000041210006900151260001200220300001400232490000700246520139000253100001601643700001701659700001501676856004901691       2012                        eng d00aInfectivity and inoculum production of Phytophthora ramorum on roots of eastern United States oak species0 aInfectivity and inoculum production of Phytophthora ramorum on r  c11/2012  a1675-16820 v963 a<p>Little is known about colonization of roots of trees by <em>Phytophthora ramorum</em>. We examined zoospore concentration and exposure time needed to infect six <em>Quercus</em> (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 (<em>P</em> = 0.952). Roots of <em>Quercus prinus</em> 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 <em>Viburnum tinus</em>, a positive control. This study shows that <em>P. ramorum</em> is able to infect sprouted oak acorns and produce secondary inoculum, which may be important epidemiologically.</p>1 aWidmer, T L1 aShishkoff, N1 aDodge, S C  uhttp://dx.doi.org/10.1094/PDIS-12-11-1024-RE