Potato susceptibility to aerial stem rot caused by Dickeya spp.

Dickeya dianthicola and ‘Dickeya solani’ are the most problematic bacteria in the Swiss seed-potato production. They are responsible for aerial stem rot symptoms in the field, usually named «blackleg». This study has two main objectives. On the one hand, to study the susceptibility of five cultivars, namely Agria, Victoria, Charlotte, Innovator, Arinda and Lady Claire, to Dickeya spp. On the other hand, to study the aggressiveness of three D. dianthicola and 3 ‘D. solani’ isolates on the cultivar Agria. Trials using plants in pots were managed in the greenhouse to achieve both objectives. Agria appears to be the most susceptible cultivar to Dickeya spp. The most virulent ‘D. solani’ are not more aggressive than the most virulent D. dianthicola isolates tested. The aggressiveness of the D. dianthicola isolates seems to be more variable compared to that of the ‘D. solani’ isolates. Finally, the risk of developing stem rots appears to be more closely correlated to the isolate used than to the cultivar tested. Indeed, the most susceptible cultivar presents a six-fold increase in symptoms, compared to the least susceptible one, while the most aggressive isolate causes a 40-fold increase in symptoms, compared to the least aggressive one.