Parasitic plant as a native biocontrol for major invasive weeds
Robert M. Cirocco
Co-authors Jennifer R. Watling & José M. Facelli Parasitic plants Taxonomically and functionally diverse
The root parasite Nuytsia in brilliant flower which attaches to host roots and is only found in Western Australia. Photo by José M. Facelli Stem parasite, Mistletoe, Photo by Joseph Fourier United by the haustorium
Haustoria of Cassytha pubescens: Photo by David Hollingworth & microscopy work/pictures by Noriko Wynn General effects
• Some tap the host xylem • Remove water and nutrients (e.g. nitrogen) • Leads to lower host photosynthesis • Less photosynthesis, less carbohydrate • Less growth Cassytha pubescens (Lauraceae)
• Native, perennial
• Stem parasite
• Taps host xylem
• Multiple hosts Cassytha’s hosts
• Generalist • Native hosts: Leptospermum myrsinoides, Acacia paradoxa, Banksia marginata, Daviesia leptophylla
• Invasive hosts: Cytisus scoparius (Scotch broom), Ulex europaeus (Gorse), Rubus fruticosus (Blackberry) Cassytha on broom
Cassytha’s differential impact
• Much greater effect on weeds, such as scotch broom • Potential as native bio-control • Annual control costs: approx. > $7 million (Gorse, WoNS) • Agricultural/grazing land, cover for pests • Biodiversity, including threatened species
Cassytha’s effect
• Looks like Cassytha kills gorse in the field • Not sure how? What are the mechanisms? • By removing large amounts water & nitrogen? • Leads to decreased photosynthesis? • Less carbohydrate, less growth, death! Mt. Lofty Ranges
• North-South
• 500,000 ha
• Mediterranean
• 1100-700 mm
• Acidic soils
www.ga.gov.au Experimental design
Three field sites Experimental design
Three field sites: following measured on uninfected and Cassytha infected Gorse
• Water potential (water-status) • Nitrogen (needed for pigments/enzymes) • Photosynthesis • Long-term breakdown of photosynthesis Gorse long-term water-status
Uninfected = open bars; Infected = shaded bars Gorse nitrogen-status
Uninfected = open bars; Infected = shaded bars Gorse photosynthesis
Uninfected = open bars; Infected = shaded bars Gorse long-term breakdown
Uninfected = open bars; Infected = shaded bars Conclusions
Cassytha removes host resources
Gorse becomes water and nitrogen stressed
Gorse photosynthesis declines
Long-term breakdown of photosynthesis Conclusions
• Impacts mostly consistent across sites • Differences in strength of effect may be due to differences in duration of infection • Engelbrook < Bradbury < Crafers • Cassytha continues to show promise as an effective native bio-control against major invasive weeds such as Gorse Future research questions • How does Cassytha affect other major invasive weeds and native species in the field • Compare the effects of Cassytha on its hosts in areas that differ in water availability • How do abiotic/biotic factors (not yet studied) influence the effect of Cassytha on its hosts • How does a combination of abiotic factors influence the effect of Cassytha on its hosts Thank You! • Matthew Pearson, Sonia Croft • Maria Johns (Bradbury) • Dr. Russell Sinclair & National Trust (Engelbrook Reserve) • Prof. Milton Hearn (Crafers) • The University of Adelaide • Nature Foundation