The economic impact of the bacterial blight of soybean under European agroclimatic conditions

The economic impact of the bacterial blight of soybean caused by Pseudomonas syringae pv. glycinea has been investigated in three countries belonging to the European Union: Italy, France and Spain. Weather and growing conditions have been monitored over three years of field experiments (1992-1994) and the data analysed in order to evaluate possible yield losses and in view of the production of pathogen free seed. In Italy and France, using different cultivars and seed with a contamination level of 0.5-20% no significant yield losses were found. In Italy the initial seed contamination level was positively correlated with the contamination of the harvested seed by the pathogen; both in Italy and in France on some cultivars, it was possible to correlate seed contamination level with the epiphytic population of the pathogen and the intensity of symptoms affecting plants in the field. No epiphytic contamination by the pathogen was observed in Spain, even at the highest seed contamination rate (20%), and there was no disease in the field and no yield reduction. The pathogen seemed not to become systemic since no contamination was observed on seed aseptically taken in the field just before harvest. The experiments highlighted the low impact of soybean bacterial blight under European climatic conditions, but suggested the choice of dry and warm regions for the production of quality seed to prevent the accumulation of effective inoculum on the seed year by year.