Detecting spores of Pucciniastrum geopertianum, the fungus that causes blueberry witches’ broom rust

Description

Witches’ broom is a recurring problem in in all highbush blueberry fields. It was particularly widespread in 2016. However in Québec the disease has never been found on the witches’ brooms themselves. The brooms are just a symptom. According to the literature, the disease is probably caused by a rust fungus. Rusts are peculiar in that they complete their life cycle on two separate hosts.  In the case of witches’ broom rust, the hosts are highbush blueberry and balsam fir. In balsam fir, the disease causes needle rust. The spores are often observed in July, but the beginning and end of the sporulation period has not been determined in Québec. Witches’ broom rust causes economic loss in both these hosts. The aim of the project was to determine whether the witches’ broom symptom on blueberries is really caused by the rust Pucciniastrum geopertianum, which attacks balsam.

Objective(s)

• Using PCR tests and isolation on agar plates, study the symptom chronology of the rust caused by P. geopertianum, which grows on balsam fir and blueberries, by testing weekly samples of balsam needles and blueberry witches’ brooms throughout the season
• Determine sporulation start and end dates on each host
• Identify fungi in samples using PCR testing
• Determine whether the disease can be spread from one blueberry field to another