Impact of Pseudomonas syringae on sweet cherry and plum trees in nurseries and in early-stage sweet cherry orchards

Bacterial canker caused by Pseudomonas syringae is an important disease on stone fruit trees. The development of infections after artificial inoculation of sweet cherry and plum trees in the nursery phase was examined. Furthermore, sweet cherry trees were observed in a nursery and for up to four years after planting in commercial sweet cherry orchards. If inoculated at the time of grafting, this caused near 100% death of the scions. Following inoculation of defeathering wounds, a mean of 52 and 61% of inoculation sites developed bacterial canker on sweet cherry and plum, respectively. Of non-inoculated nursery trees observed as healthy in the autumn, between 20 and 80% had developed visible bacterial cankers after a period of cold storage. In the planting year, a mean of 21% of the trees developed bacterial canker in seven commercial orchards included in the investigation, and by 2–4 years after planting 40% of the trees had symptoms of the disease. All sweet cherry cultivars and rootstocks developed bacterial canker in the commercial orchards. Cultivar Giorgia had the most severe symptoms. Up to 60% replacement of trees within two years after planting was experienced in the orchards.