Use of Low Temperature to Improve Storage of in vitro Broccoli Seedlings Under Various Light Qualities

Abstract

ABSTRACT Broccoli (Brassica oleracea L. Botrytis Group ‘Green Duke’) seeds were germinated in vitro photoautotrophically (without sugar in medium) or photomixotrophically (with sugar in medium) for 3 weeks at 23 ° C and 150 μmol · m−2 · s−1 photosynthetic photon flux (PPF). Vessels were then stored at 1 ± 0.35°C under 1.6 ± 0.20,4.1 ± 0.35, or 8.6 ± 0.50 μmol · m−2 · s−1 constant PPF each of white (400–800 nm), red (600–700 nm), or blue (400–500 nm) light. Concentrations of CO2 inside the vessels were monitored until equilibrium was reached. Light compensation point was reached at $2.0 μmol · m−2 · s−1 for photoautotrophic seedlings and at $4.0 μmol · m−2 · s−1 for photomixotrophic seedlings. Therefore, in the long-term storage experiment, seedlings were stored for 4, 8, or 12 weeks at 1 ± 0.35°C in darkness or under 3 μmol · m−2 · s−1 constant PPF (average light compensation point) of white, red, or blue light. Variable to maximal chlorophyll fluorescence (Fv/Fm) of leaves decreased as storage time increased, regardless of media composition. Illumination during storage was necessary to maintain dry weight and regrowth potentials of in vitro seedlings. All photo-autotrophic seedlings stored in darkness were of poor quality and died when transferred to the greenhouse. Seventy-five percent of dark-stored photomixotrophic seedlings survived storage for 12 weeks but declined in appearance, dry weight, total soluble sugars (TSS), and chlorophyll fluorescence. Red light during storage increased seedling dry weight, TSS, and regrowth potential. Supplying 2% sucrose in the culture medium increased dry weight and maintained overall seedling quality during irradiated storage.