254 Stem Extension and Subsequent Flowering of Plugs Grown Under A Far-red-deficient Film

Abstract

Environments with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio (e.g., with high plant density) promote stem elongation, and a high R: FR suppresses it. While FR light promotes stem extension, it is also required for rapid, uniform flowering of many long-day plants. We investigated how a new FR filter [creating a FR-deficient (FRd) environment] influenced plug growth and subsequent flowering of pansy (Viola ×wittrockiana `Crystal Bowl Yellow'), petunia (Petunia ×hybrida `Carpet Pink'), impatiens (Impatiens wallerana `Accent Rose'), snapdragon (Antirrhinum majus `Liberty Scarlet'), and tomato (Solanum lycopersicon `Beefmaster'). One-week-old seedlings were placed under three filter treatments with 16-h photoperiods: the FRd filter, a neutral-density filter (N) that transmitted a similar PPF, and transferring plugs from the N to the FRd filter when leaves of each species began to touch (7 to 11 days later). The predicted phytochrome photoequilibria under the FRd and N filters was 0.80 and 0.72, respectively. After 25 to 35 days at 20 °C, node number and stem (or petiole for pansy) length were collected. Twenty plants of each species and filter treatment were then transferred to 4-inch pots and grown under natural photoperiods (14 to 15 h) at 20 °C until flowering. Compared to plants continually under the N filter, stem length under the FRd filter was significantly reduced in impatiens (by 11%), pansy (by 18%), petunia (by 34%), snapdragon (by 5%), and tomato (by 24%). Flowering of plants from plugs under the FRd filter was delayed by 2 to 3 days for snapdragon, petunia, and pansy. Filter treatment of plugs had no significant effect on flower number or plant height at flower.