Studies to assess the suitability of Uromyces pencanus as a biological control agent for Nassella neesiana (Poaceae) in Australia and New Zealand

Nassella neesiana (Chilean needle grass), a South American species, is an intractable weed invading managed pastures and natural grasslands that has become a target for biological control in Australia and New Zealand. Studies have been carried out to assess the potential of three rusts naturally infecting this grass species in Argentina: Uromyces pencanus, Puccinia graminella and P. nassellae , as biocontrol agents. Of the three, U. pencanus was recognised as the most promising candidate. It causes significant damage to its host in the field and there is an isolate that can infect most Australian populations of the weed tested. Herein are described methods for: maintaining the rust in the glasshouse; storing urediniospores over 12 months; and, for inoculating urediniospores in order to test the host-specificity of selected isolates of the rust. Evidence from the literature, and a preliminary host range test indicates that U. pencanus is sufficiently host-specific for use as a classical biocontrol agent. Attempts at elucidating the life cycle of U. pencanus were unsuccessful as teliospores did not germinate. It appears that these have become redundant and the rust cycles as urediniospores on its grass host.