Description of the elongation of fire blight canker, caused by Erwinia amylovora, in trunks of pear trees

Fire blight is the most destructive pathogen of pears and other pome fruit. The developing fire blight cankers can cause significant damage to a tree. The models described in this study are devoted to the quantitative evaluation of scale of canker and fitted to the situation of artificial inoculations in the beginning of the summer growth phase (season), in 1-year newly developed shoots of perennial trunks. We evaluated the length of the canker at the end of the summer phase based on data collected in the beginning and in the middle of the season. The models based on logistic, Gompertz and Richards functions were applied. The upper asymptotes of the models served for description of the end-of-season fire blight canker length. These asymptotes were estimated for incomplete data of the middle of the season using the suggested computational method. Results suggested that the elongation of the fire blight canker in trunks of pear trees could be described by logistic and Richards models with better precision than by the Gompertz one. The smallest AIC values were observed with the logistic model.