Potato susceptibility to blackleg disease caused by Dickeya spp

Pectin lytic bacteria belonging to the genera Pectobacterium and Dickeya can cause several diseases on potato, such as stem rots, commonly named blacklegs, and tuber rots, which are referred to as soft rots. The blackleg symptom is the primary cause for the rejection of potato seed lots in Switzerland. The field trials conducted in this study had two main objectives. On the one hand, to identify potential differences in the susceptibility of the cultivars Agria, Victoria, Charlotte and Innovator to Dickeya spp. and, on the other hand, to study the aggressiveness of three isolates of D. solani and two isolates of D. dianthicola on cv. Agria. For these purposes, the development of blackleg symptoms was followed in the fields, on plants whose mother tubers had been previously inoculated with the bacteria. Differences in susceptibility were recorded between cultivars, Agria being the most susceptible and producing twice as many blackleg symptoms as Charlotte. Of the two D. dianthicola isolates tested, one was the most aggressive of all isolates tested, while the other was the least aggressive: the latter being twenty six times less aggressive than the former. D. solani isolates presented intermediate aggressiveness. The risk of developing symptoms in the field seems therefore more closely related to the isolates than to the cultivars. Furthermore, a linear relationship was found between plant wilting and blackleg symptoms in the fields.