Host specificity of the rust Phragmidium violaceurn, a potential biological control agent of European blackberry

The host specificity of the rust fungus Phragmidium violaceum, a potential biological control agent of European blackberry (Rubus fruticosus) was studied by inoculating a mixture of 15 isolates of the rust on 108 plants of importance to the Australasian region. A scale of infection types was developed based on the results of microscopic and macroscopic observations of the reaction of host and non-host plants to the rust. The results showed that P. violaceum has a limited host range in the genus Rubus. The rust was able to reproduce on 17 taxa of Rubus previously unrecorded as hosts, including Australasian species of Rubus subgenera Dalibarda and Lampobatus. All other taxa attacked were species of Rubus subgenus Eubatus and the majority were hybrid cultivars containing European blackberry species.