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Poster: Biology & Disease Mgmt: Cultural Control


Nutrients and in vitro growth of Phaeocryptopus gaeumannii, a fungus causing the Swiss needle cast disease on Pseudotsuga menziesii
M. Yáñez-Morales (1), O. Salgado-Feregrino (1), J. Velázquez-Mendoza (1), M. Jiménez-Casas (1) (1) Colegio de Postgraduados, Mexico

The hyphae intercellular development of Phaeocryptopus gaeumannii, a foliage pathogen in Douglas-fir trees, is affected by the nutritional composition of the needles. The objective was to examine the effect of different nutrients and silicon, Si, on the in vitro growth of the pathogen. Two experiments were established in a completely random design with a fungus isolate (JN204508). The first experiment was by plating the isolate aliquot (1 mm, 0.002 g) in 2% MEA amended with different nutrients, 10 treatments, and incubated at 21 °C in darkness for 42 days; diameter colony growth was measured and instantaneous relative rate growth was estimated. The second experiment was in liquid medium, potato extract-dextrose, and amended with nutrients, 21 treatments; incubation was under shaking conditions at 250 rpm at 23 °C for 35 days. Mycelium growth was measured by their weight in wet and dry stage. The macronutrients (N P K Ca Mg S) favored the growth of P. gaeumannii; in contrast the micronutrients (Fe Cu Zn Mn Mo B) severely inhibited the development of the fungus. The complete nutrient solution plus Si at 1000 ppm reduced colony growth in the agar medium, and at 250 ppm in the liquid medium. Thus, the addition of Si inhibited growth of the fungus and this was attributed to a possible toxic effect of the element. The results provide a basis for designing a fertilization formula for Douglas-fir and allowing to partially inhibit intercellular fungal growth in needles.