Biosecurity versus Biocontrol: The Impact of Uromycladium falcatarium on Pacific Mimosaceae

Abstract

Uromycladium falcatarium is a gall-forming rust fungus that causes highly damaging disease on Falcataria moluccana in commercial plantations in Indonesia, Malaysia, and the Philippines. Falcataria moluccana is also an invasive weed that threatens infrastructure and native ecosystems in many Pacific Islands, including Hawaii, and is currently a target for biological control using host-specific natural enemies. Some Uromycladium species have been successfully used as biological controls for certain Acacia weeds. We conducted artificial inoculations to determine the ability of U. falcatarium from Indonesia to control F. moluccana in Hawaii, and to assess its impact on non-target Mimosaceae. Inoculations were applied in the laboratory and under net house conditions to three-month-old seedlings of F. moluccana, Acacia koaia, Acacia confusa, Albizia chinensis, Albizia lebbeck, and Leucaena leucocephala from Hawaii, and F. moluccana from Moluccas, Indonesia, as a control.  Inoculations in the laboratory, monitored by freehand sections at 1, 24, and 48 hours, showed that all species except A. confusa supported the early stages of infection by U. falcatarium. In the net house, 4 randomized complete blocks with 5 seedlings per unit sample for each species were monitored for 5 months after treatment with sprayed inoculum, as well as continuous exposure to mature teliospore-producing galls placed overhead on shade cloth. All species showed early symptoms of infection after the first month, but only F. mollucana, from both Hawaii and the Moluccas, supported full disease development and gall formation over 5 months, ultimately leading to seedling death. The results suggest that U. falcatarium may be a suitable candidate for biological control of invasive F. moluccana. However, since several non-target species from Hawaii have shown susceptibility to the early stages of infection by the rust fungus, biosecurity precautions should be taken to prevent its introduction until further tests demonstrate safety.

Keywords: biosecurity, Falcataria moluccana, rust fungus, Uromycladium falcatarium