Exotic rust fungus Puccinia abrupta var. partheniicola on the invasive alien weed Parthenium hysterophorus in India: rediscovery and first report of an epiphytotic.

Puccinia abrupta var. partheniicola , the winter rust of the invasive alien weed Parthenium hysterophorus has been rediscovered in India for the first time on an epiphytotic scale in February 2023. Disease incidence was 80-90% in large tracts of P. hysterophorus stands along the roadsides in an area of 5 km 2 near Attibele-Sarjapura road (948A) in Anekal taluk of Bengaluru Urban district in Karnataka. Pycnial, aecial or telial stages of the rust were not found. The morphological parameters of uredinia and urediniospores completely matched those originally described by Parmelee (1967), thus confirming the fungal identity. The implications of this rust in P. hysterophorus biocontrol are discussed.