Evaluating mechanical wounding as a surrogate for aspen shoot blight caused by Pollaccia americana in the assessment of crop loss

Abstract

It is difficult to maintain, in trembling aspen (Populus tremuloides), controlled levels of aspen shoot blight (ASB) caused by Pollaccia americana, under field conditions. Thus, simulating the disease by mechanical wounding may be useful in crop-loss assessment. Three treatments were compared to evaluate the suitability of decapitation as a surrogate for ASB: (1) artificial inoculation with P. americana causing ASB and (2) cutting of the shoot between the fifth and sixth expanded leaves (decapitation), both these treatments being later referred to as injury treatments, and (3) no injury (control). The three treatments were applied to trees from four different seed lots, which subsequently grew under field conditions, and to two different clones held in a growth chamber at soil temperatures of 6, 12, or 20 °C. Leader length, frequency of axillary-shoot development, and lateral- and axillary-shoot lengths were evaluated. Trees infected with ASB and trees that were decapitated responded very similarly and had significantly longer leaders and more axillary shoots than did control trees. Although there were significant differences in branching patterns among seed lots, and significant clone and temperature effects on infection, the effects of treatments were typically consistent across all levels of clone, seed lot, and temperature. These results indicate that decapitation could be used to simulate ASB in assessing crop loss.