01926nas a2200145   4500008004100000022001400041245006200055210006200117300001400179490000800193520147300201100001901674700001601693856007101709       2004                        eng d  a0953-756200aProduction of gametangia by Phytophthora ramorum in vitro0 aProduction of gametangia by Phytophthora ramorum in vitro  a823 - 8270 v1083 a<p>Until now gametangia have not been obtained between paired European A1 and American A2 isolates of <em>Phytopthora ramorum in vitro.</em> Their production in artificial culture relies on interspecific pairings. Using <em>P. drechsleri</em> and <em>P. cambivora</em> testers, 51 of 110 <em>P. ramorum</em> isolates from across Europe were all shown to be A1s; while 32 of 38 American isolates from across California and southwest Oregon were shown to be A2s. However, these interspecific pairings are complex, unusually slow and unpredictable. A range of culture media and conditions are described that were tested, unsuccessfully, with a view to enhancing the efficiency of the interspecific pairings. In further tests, gametangia were obtained between A1 and A2 isolates of <em>P. ramorum</em> when juvenile, pre-chlamydospore producing mycelia were mixed together on carrot agar. The gametangia formed in 3–10 d, sparsely to frequently, initially only within the boundaries of the mixed inocula but subsequently in the extended mycelial growth. Chlamydospores were also produced. This inoculum-mixing method, though again sometimes unpredictable, should enhance efficiency of testing for compatibility types and facilitate further studies on whether the sexual outcrossing system of <em>P. ramorum</em> is functional. Differences between sexual reproduction of <em>P. ramorum</em> and that of other heterothallic <em>Phytophthora</em> species are discussed.</p>1 aBrasier, Clive1 aKirk, Susan  uhttp://www.sciencedirect.com/science/article/pii/S0953756208603949