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Biological activity of Phaeocryptopus gaeumannii in Christmas trees (Pseudotsuga menziesii var. glauca) in Mexico

María de Jesús Yáñez-Morales: Colegio de Postgraduados

<div>In some countries, the ascomycete <em>Phaeocryptopus gaeumannii</em> has reduced the quality and production of the Douglas fir (<em>Pseudotsuga menziesii</em>) ornamental Christmas trees because of severe foliar damage. Little is known about this disease in Mexico, so that appropriate control measures are difficult to develop. This study evaluated various aspects of <em>P. gaeumannii</em> biology (via cultured agar isolates, ascospores in pseudothecia and airborne ascospores) and trees quality (incidence, severity and defoliation) over a year. From Summer 2011 to Spring 2012, a 9-year-old ornamental Christmas tree plantation in Valle de Bravo, Mexico State was sampled. Seven needle samples from various branch positions and different needle ages were collected; naturally fallen needles were sampled too. The fungus was identified and sequenced. A pseudothecia opening mechanism was indirectly observed under the scanning electron microscope. Results showed fungal biological activity fluctuated and simultaneously occurred throughout the year. Fungal activity was scarcely shown in fallen needles. A different airborne ascospore peak was detected. The pseudothecia showed an equatorial and polar split, resembling an opening mechanism. In terms of tree quality, the most severe reduction and highest fungal activity were observed mainly in 1-year-old needles from the upper section of trees. Defoliation was severe and increased proportionally with increasing needle age. These results were similarly, with a few exceptions, to what is known in Douglas fir (a different variety of <em>Pseudotsuga menziesii</em>) worldwide. This new information on the study area will enable the design of sustainable disease control strategies in Christmas tree plantations.</div>