| A research collaboration between Clemson University and Mitsui Chemicals, Inc., Japan has been established to develop and test photoselective greenhouse films that can remove far-red (FR) light as an alternative to chemical growth regulators for reducing stem elongation of greenhouse grown plants. Initial research focused on selecting a dye, an optimum concentration and establishing light transmission characteristics for photoselective filters. Two FR light absorbing dyes that can be incorporated into plastic light filters were identified. With both dyes, transmission of photosynthetic photon flux (PPF) was reduced and removal of FR light increased with increasing dye concentration in the filters. The phytochrome photoequilibrium (Pfr:Ptotal) estimates of transmitted light increased from 0.72 to 0.83 as the dye concentration increased in both materials. Both filters reduced the stem elongation of selected crops and the effect was greater at higher dye concentrations. Plant response varied with species. A dye concentration that gives a PPF reduction of 25% and establishes a Pfr:Ptotal of 0.80 was selected for further testing because filters with higher dye concentrations reduced PPF but did not result in a significant height reduction.;Flowering of photoperiodic species was investigated during inductive and non-inductive photoperiods under the R and FR light absorbing films. Flowering of selected short day and day neutral plants was not influenced by the films. Flowering of selected long day plants was not affected during inductive photoperiods but was delayed up to 12 days by FR light absorbing films during non-inductive photoperiods. Examination of the floral meristem showed that the floral primordia initiation and floral development of a long day plant, petunia, were delayed during non-inductive photoperiods.;Methods to promote flowering without increasing stem elongation of petunia under FR absorbing films were evaluated using anti-gibberellins known to promote flowering. Petunia did not respond to exo-C-16,17-dihydro GA5. Increasing concentrations of the GA biosynthesis inhibitor, Prohexadione-Ca, inhibited stem elongation but delayed flowering. Combinations of dihydro GA5 and GA4 promoted both flowering and stem elongation. |
