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Araucaria araucana root rot caused by Phytophthora multivora and P. citrophthora

Alejandra Larach: Pontificia Universidad Católica de Valparaíso

<div><em>Araucaria araucana</em> is an endemic conifer from central and southern Chile, associated with the culture of Mapuche people. It is also important as an ornamental species. During the last year, plants of <em>A. araucana</em> have been detected in commercial nurseries, with symptoms of decay, chlorosis, brown necrosis in the leaf apex and dark brown rot in roots. Necrotic tissues obtained from the margin of the root lesions were plated on P5ARP semiselective medium and incubated at 25°C for 7 days. From soil samples <em>Phytophthora</em> was recovered employing rhododendrum leaves bates. <em>Phytophthora </em>spp. was isolated from the advance zone of necrotic lesions and replicated to Corn meal agar (CMA), for oomycete purification and its subsequent taxonomic and molecular identification. Two isolates were identified as <em>P. multivora</em> and <em>P. citrophthora</em>. A pathogenicity test was carried out using these two isolates, inoculating asymptomatic <em>A. araucana</em> 2-year old plants (n = 3), with 100 ml of 1 x 10<sup>4</sup> propagules ml<sup>-1</sup>. Three plants were left as negative control adding only sterile distilled water. After 45 days from the inoculation, plants show chlorosis, brunch decay, leaf tip necrosis and severe root rot symptoms. Control plants were symptomless. <em>Phytophthora multivora</em> isolate was more aggressive than <em>P. citrophthora</em> isolate. Both species were re-isolated from inoculated plants, thus completing Koch's postulates. To our knowledge this is the first reference of these <em>Phytophthora </em>species causing <em>Araucaria</em> <em>araucana</em> root rot in Chile or worldwide.</div>