| Summary: | From 2018 to 2020, surveys of oomycetes associated with root and crown rot of almond (<i>Prunus</i> <i>dulcis</i>) were conducted on diseased young almond trees in commercial orchards and nurseries in six provinces of Spain. A total of 104 oomycete isolates were obtained from plant and soil samples, which h were identified by sequencing the internal transcribed spacer (ITS) region of the ribosomal DNA. Diverse species belonging to the genera <i>Globisporangium</i>, <i>Phytophthora</i>, <i>Phytopythium</i> and <i>Pythium</i> were found, <i>Phytopythium</i> <i>vexans</i> and <i>Phytophthora</i> <i>niederhauserii</i> being the most frequent. The pathogenicity of these two species to one-year-old almond seedlings of ‘Garnem’ (<i>P. dulcis</i> × <i>P. persica</i>) rootstock was studied. All seedlings inoculated with <i>Pp. vexans</i> and <i>Ph. niederhauserii</i> isolates showed severe symptoms at the late stage of the pathogenicity test (defoliation, wilting and dieback) and several plants died. Some isolates of <i>Ph. niederhauserii</i> significantly reduced the dry weight of the roots compared with the control, but this effect was not observed in seedlings inoculated with <i>Pp. vexans</i>. These results provide new information about the oomycete species present in almond crops in Spain and highlight the importance of carrying out frequent phytosanitary surveys for a better knowledge of potential risks posed by these soil-borne pathogens.
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