GA/ABA Ratio Affects Breaking Dormancy of Uncooled Herbaceous Peony

Herbaceous peonies are common perennials that have been used as garden or medicinal plants throughout temperate regions of the world and have been grown commercially as cut flowers for many years. Because of its short flowering period from May to June, off-season culture is needed. In our previous research, peonies were forced under greenhouse conditions to hasten flowering after long exposure to low temperatures. The effects of gibberellins (GA) were also investigated to break the dormancy of peonies. All uncooled peonies that were treated with GA₃ sprouted, but failed to flower due to shoot blind and flower bud abortion. The objective of the present study was therefore to examine the effect of ABA biosynthesis inhibitor or additional GA treatments on uncooled peonies, so that in the future we will be able to force peony without causing blind or abortion. Uncooled plants received 0 (control), 100, or 500 mg·L^-1 (250 mL/plant) GA₃ as a soil drench, were drenched 100 mg·L^-1 GA₃ + 100 mg·L^-1 fluridone (FLU: ABA synthesis inhibitor), or sprayed with 10 mL of 100 mg·L^-1 GA₃ every two weeks following the drenching with 100 mg·L^-1 GA₃ in the glasshouse for forcing. Control plants failed to emerge for 5 months, so there was no shoot or flower. However, plants emerged almost 100% following the GA or FLU application. When uncooled plants were treated with GA or FLU, shoots emerged within 10 days. However, shoot blind appeared in 85% or 90% of those treated with 100 or 500 mg·L^-1 GA₃, respectively. The drench application of GA showed shoot blind and flower bud abortion as in previous research. Shoot blind percentage decreased to 0% or 20% by GA₃+FLU or additional GA₃ spray treatments, respectively. Moreover, plants reached 80% or 50% anthesis without flower bud abortion with GA₃+FLU or additional GA₃ spray treatments, respectively. We assumed that treatments maintaining a high GA/ABA ratio decreased shoot blind or flower bud abortion in uncooled peony. However, chlorosis appeared on the leaves when treated with GA+FLU because FLU additionally blocks production of carotenoids.