Allelopathic Potential of Fruits and Seeds of Five Common Woody Landscape Plants Assessed by Lettuce Germination Bioassays

The effects of fruit and seed extracts of five species (Pyrus calleryana, Cornus florida, Cratageus phaenopyrum ‘Vaughn’,  Malus ‘Donald Wyman’ , Ilex x attenuata ‘Fosteri #2’) were investigated for their allelopathic potential on lettuce seed germination.  Collected fruits and seeds were dried, and five grams were triturated prior to a 24 hour soak in dH₂O, 15% EtOH, or 30% EtOH.  The supernatants were filtered, resulting in one aqueous, and two ethanolic solutions for each species.  The solutions were mixed with Captan fungicide at 0.9g/L and added to 47mm petri dishes with filter pads containing 30 ‘Black Seeded Simpson’ lettuce seeds.  Each of the 15 treatments was replicated 5 times, and germination was recorded daily over 16 days.  Lettuce seeds in both the aqueous and ethanolic extracts of Malus ‘Donald Wyman’ and Pyrus calleryana demonstrated significantly lower overall germination percentages compared to the other species.  Furthermore, T₅₀ and T_10-90 values were significantly greater in these two species germinated in the aqueous and 15% ethanol solutions.  All species germinated at lower rates in the 30% EtOH solutions, with C. florida failing to germinate a single seed.  Due to the apparent inhibitory effects of the Malus ‘Donald Wyman’ and Pyrus calleryana extracts, another experiment was conducted subjecting lettuce seeds to decreasing concentrations of the extracts.  Germination inhibition was again observed in these experiments, most clearly with the Malus extracts exhibiting increasing germination rates with decreasing concentrations of the solution.  Our results suggest possible allelopathic properties inherent in the fruits and/or seeds of Malus ‘Donald Wyman’ and Pyrus calleryana.  Further studies of this allelopathic potential could be beneficial in considering proximal plantings of these species in the landscape, or the use of plant material from these species in composting, and the possible future development of bio-herbicides.