Host specificity testing and assessment of the pathogenicity of the rust, Puccinia abrupta var. partheniicola, as a biological control agent of Parthenium weed (Parthenium hysterophorus)

Abstract

Parthenium hysterophorus, a native of Central America, is a problem weed of Australian rangeland, particularly in Queensland. Following field surveys in Mexico, the rust fungus Puccinia abrupta var. partheniicola was selected as a potential biological control agent. One isolate was chosen for further investigation after infection studies with one Kenyan and five Mexican isolates. Assessment of inoculation conditions showed that temperatures of less than 20° C and dew periods of more than 6 hours were required for abundant pustule production. Infection with the rust hastened leaf senescence, significantly decreased the life span and dry weight of Parthenium plants, and reduced flower production 10‐fold. Subsequent host‐range studies against 120 species and varieties, with further screening against a limited number of species conducted under a range of environmental regimes, indicated the rust to be sufficiently host‐specific to be considered for introduction. Additional host‐range tests against sunflowers demonstrated that resistance to P. abrupta var. partheniicola was not modified by prior inoculation with P. helianthi.