The Effect of Germination Stimulants on Kentucky Bluegrass (Poa pratensis) Seeds

Abstract

Kentucky bluegrass (Poa pratensis) is a consistently difficult to establish cool-season turfgrass species due to slow germination and low seedling vigor. The phytohormones abscisic acid and gibberellins are well known to be the key regulators of seed dormancy and germination stimulation, but to our knowledge there has been little research how well they stimulate Kentucky bluegrass germination. Germination stimulants have also been discovered in plant derived smoke, in which the primary stimulants are karrikins. Liquid smoke products, karrikins, and smoke enhanced biochar have been gaining interest as they may stimulate turfgrasses to establish faster. We performed a series of experiments to examine if liquid smoke, karrikin-1, gibberellin A1, gibberellin A3, gibberellin A4, and gibberellin A7 increased germination of Kentucky bluegrass cultivar 'Tirem' in a controlled environment. Results showed that liquid smoke decreased germination at increasing percentages relative to both water (control) and 0.20% potassium nitrate (a positive control). In our experiments, karrikins did not stimulate germination compared to our controls, and gibberellin A4 stimulated germination the fastest compared to the other gibberellins tested at 1 µM. A dose response experiment with gibberellin A4/A7 showed that concentrations greater than 100 µM stimulated germination more than 0.20% potassium nitrate, both in time to germinate and final germination. Overall, our results show that not all stimulants and phytohormones improve Kentucky bluegrass germination, but treatments with gibberellin A4/A7 could enhance establishment by speeding up and increasing overall germination.