Cytospora Canker Development on Aspen in Response to Nitrogen Fertilization

Abstract

The effect of nitrogen fertilization on Cytospora canker development in aspen (Populus tremuloides) was examined in a greenhouse hydroponic system. Aspen trees grown in rock wool or sand were watered with 1 of 5 nitrogen treatments: 0, 55, 111, 185, or 333 mg/L nitrogen as (NH4)2NO3. After 6 wk, trees were inoculated with 2 isolates of Cytospora chrysosperma in separate wounds. Canker length and width were measured every 2 wk for 6 wk, beginning the 2nd week after inoculation. To assess the effect of prolonged nutrient treatment on canker development, a subset of the original trees was selected to receive treatments for 2 growing seasons, with inoculations at 6 wk after treatments were begun in the 2nd season. Nitrogen deficiency (0 mg/L) contributed to significantly larger cankers in 1 of 4 trials run for 1 growing season and in the 2 trials carried out for 2 growing seasons (P = 0.00-0.006). Canker sizes on trees treated with the other nitrogen rates were not significantly different from each other. Large cankers formed on trees treated with the abnormally high rate (333 ppm), but the differences were not significant from the other nitrogen treatments. Thus, nitrogen deficiencies increase the likelihood of canker expansion, while proper nutrient management allows aspen to defend against canker expansion induced by Cytospora fungi.