1Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Sydney, NSW 2006, Australia.
3Cotton Catchment Communities Cooperative Research Centre, Australian Cotton Research Institute, Locked Bag 1001, Narrabri, NSW 2390, Australia.
2E.H. Graham Centre for Agricultural Innovation (a collaborative alliance between NSW Department of Primary Industries and Charles Sturt University), Wagga Wagga, NSW 2678, Australia.
Lippia (Phyla canescens) is a perennial herb (Verbenaceae) of South American origin and is a serious weed of south eastern Australia. Allelochemicals are believed to be released by lippia that prevent seed germination and establishment of crop and pasture species. This work assessed the allelopathic potential of aqueous lippia extracts on seed germination of lettuce (Lactuca sativa), radish (Raphanus sativa), oats (Avena sativa), ryegrass (Lolium multiflorum), Namoi woolly pod vetch (Vicia villosa), subterranean clover (Trifolium subterraneum) and sorghum (Sorghum bicolor). Seeds of bioassay species were germinated at 20 ± 1 ◦C in petri dishes containing aqueous extracts of lippia leaves and/or stems at a range of concentrations [0, 4, 8, 12, 30, 40 and 50% fresh weight/volume (fw/v)]. Germination probability decreased exponentially with increasing rates of lippia extract in all species tested except sorghum. The lippia residue incorporation did not significantly reduce emergence in radish and oats. Bioassay species responded differentially to lippia extracts. Lippia extract concentrations≤12% fw/v reduced the germination probability of vetch and subterranean clover by more than 80% and 25%, respectively, which suggests that some legume species should not be sown immediately into soil previously infested by lippia. Germination probability of ryegrass, oats, radish and lettuce were only slightly reduced (<20%) by extract concentrations ≥ 12% fw/v.
Allelopathy, bioassay, lippia, Phyla canescens, phytotoxic effects, seed germination
