Seed Germination and Seedling Survival of Invasive Callery Pear (Pyrus calleryana Decne.) 11 Years After Fruit Collection

Background/Question/Methods - Recently, Callery Pear has gained a reputation within the ecological community for its aggressive ability to invade open fields as it forms dense monocultures. This occurs following bird dispersal of seed formed by cross-pollination among genetically different ornamental cultivars and rootstock. Perhaps even more alarming is evidence that Callery pear has started to invade forested areas, with the potential of causing ecological damage to forested ecosystems within the Midwest United States. To understand the extent of damage and the associated implications for removal and control, we began by studying the long-term seed viability of Callery pear, a characteristic shared by many invasive plants that often leads to the formation of seed banks in invaded sites. To test this species’ long-term seed viability, we compared the rate of seed germination and seedling survival collected fresh in 2006 with those kept in cold storage for 11 years. To accomplish this, seeds were extracted by cracking open the hard endocarp with vise grips both in 2006 and in 2017, placed under refrigerated conditions to mimic cold stratification, and placed in soil once radicals emerged. We also measured the viability of stored seeds that failed to germinate in our tests by tetrazolium testing.

Results/Conclusions - Although rates of seed germination and seedling survival declined over time, germination rates continued to be substantial after 11 years (52%, 45%, and 87% for ‘Aristocrat,’ ‘Cleveland Select,’ and ‘Bradford’, respectively). Seeds that did not germinate were viable in some cases, but it depended on the maternal cultivar type (27%, 14%, and 0% for ‘Aristocrat,’ ‘Cleveland Select,’ and ‘Bradford’, respectively). These results suggest that a prominent seed bank may exist in invaded sites, posing a challenge to management programs of the Callery Pear. Once such a seed bank is formed, Callery Pear has the potential to persist in a disturbed area despite surface-level eradication efforts, meaning that further effort needs to be made on removing such seed banks as well for complete eradication of Callery pear.