Host-specificity testing of Puccinia xanthii var. parthenii-hysterophorae, a potential biocontrol agent for Parthenium hysterophorus in South Africa

Abstract

Following its introduction into Australia, the rust fungus Puccinia xanthii var. parthenii-hysterophorae has played an important role in the integrated approach to manage Parthenium hysterophorus. The rust was imported from Australia and established within quarantine facilities in South Africa. Supplementary host-specificity testing of the rust on indigenous members from the tribe Heliantheae and 13 commercial sunflower cultivars was conducted. The rust was shown to be highly specific to parthenium, with only a single incident of symptom development on leaves of the native Spilanthes mauritiana. The symptoms on S. mauritiana were considered to be a laboratory artifact as no further symptoms were observed on this species during subsequent inoculations. Microscopic evaluations revealed that although basidiospores germinate on the surface of S. mauritiana leaves, they do not penetrate the epidermis. Spilanthes mauritiana is host to Puccinia africana, but cross-inoculation greenhouse studies showed that although P. africana is assumed to belong to the P. xanthii complex, it can be separated as a morphospecies from P. xanthii var. parthenii-hysterophorae as it is highly specific to its host. Based on these results it was concluded that P. xanthii var. parthenii-hysterophorae was suitable for release as a biological control agent on Pa. hysterophorus in South Africa.