Development of Chrysanthemum Meristems Grown under Far-red Absorbing Filters and Long or Short Photoperiods

Abstract

Two chrysanthemum [Dendranthema ×grandiflorum (Ramat) Kitamura] cultivars, `Spears' and `Bright Golden Anne', were grown under artificial short or natural long photoperiod in benchtop chambers covered with clear double-walled acrylic panels (control) or under similar panels filled with CuSO4 (CuSO4*5H2O in solution at 6% w:v) that removed far-red (FR) (700 to 800 nm) light. Three times per week, a tip from one lateral branch from each of three plants per chamber was harvested and the stage of meristem development recorded. The experiment was conducted April through May and repeated May through June. For `Spears' all short photoperiod treatments developed floral primordia at the same time and the rate of development did not differ. All plants in natural photoperiod treatments initiated flower primordia simultaneously with plants in short photoperiod treatments, but development was delayed ≈3 d in the first experiment compared to plants receiving short photoperiods. During the longer photoperiods of the second experiment, plants under FR-absorbing filters and receiving natural photoperiods initiated and developed flowers ≈2 d after plants in short photoperiod treatments initiation and development. Plants under control filters and natural photoperiods had initiation delayed by ≈4 d and development was delayed by ≈11 d. Bud development was normal for all treatments. For `Bright Golden Anne' only short photoperiod treatments developed normal floral primordia. Plants under FR-absorbing filters and exposed to natural photoperiods eventually initiated floral primordia but development was abnormal. No floral primordia developed under natural photoperiod and control filter conditions. The results indicate that if FR-absorbing filters are used to regulate height of chrysanthemum and possibly other photoperiodic plants, the time of flowering may be affected. However, if artificial short photoperiods are imposed with the use of blackout cloth, FR-absorbing filters do not affect flowering response.