Epidemiology and management of fusarium basal rot in onions (VN20006)

To understand key drivers of disease development, crops were monitored in paddocks encompassing a range of rotation and production practices, soil moisture conditions and varieties. Incidence of bulb rot associated with Fusarium species ranged from nil to 55 per cent in monitored areas. Results from the first season of monitoring highlight the impact that high and prolonged soil moisture can have on increased incidence of bulb rots caused by Fusarium and bacterial infection. These findings are based on both monitoring soil moisture variation along the same planting lines within a crop, and measured differences in soil moisture between crops where inoculum of Fusarium oxysporum f. sp. cepae was known to be present.  Testing of samples at the 5-7 leaf stage indicated that infection can already have occurred, though may not be visually evident until late in the crop or storage.  Associations between reduced incidence of fusarium basal rot and nutrient levels have also been identified that will be further investigated.

Testing of mature bulbs with typical fusarium basal rot symptoms has confirmed they are primarily associated with the pathogen Fusarium oxysporum f. sp. cepae (FOC). The ability of the pathogen isolated from the onion bulbs to cause disease has been confirmed by controlled environment trials on onion seedlings.  Cultures of this pathogen are being maintained to assist in the controlled environment evaluation of chemical and biological treatments aimed at reducing fusarium basal rot.

A specific DNA test has been developed for FOC.  Testing of soil samples as part of the projects crop monitoring program covering high and low risk paddocks across two growing regions of South Australia has detected the pathogen in a small number of samples.  To understand key drivers of disease development crops are being monitored in paddocks encompassing a range of rotation and production practices, soil moisture conditions and varieties.